x-ray spectroscopyfiles.alfresco.mjh.group/alfresco_images/pharma/... · ubm americas () is a...

November 2017 Volume 32 Number s11 www.spectroscopyonline.com

X-RAY

SPECTROSCOPY METHODS & APPLICATIONS

®®

A Supplement To

Learn more about Shimadzu’s EDX-7000/8000. Call (800) 477-1227 or visit us online at

www.ssi.shimadzu.com/xray5JKOCF\W�5EKGPVKƂ�E�+PUVTWOGPVU�+PE��4KXGTYQQF�&T��%QNWODKC��/&��7�5�#�

+PEQTRQTCVKPI�C�PGY�JKIJ�RGTHQTOCPEG�UGOKEQPFWEVQT�FGVGEVQT��Shimadzu’s EDX-7000/8000 spectrometers�QHHGT�GZEGNNGPV�UGPUKVKXKV[��TGUQNWVKQP��CPF�VJTQWIJRWV�HQT�CP�CTTC[�QH�CRRNKECVKQPU��HTQO�IGPGTCN�UETGGPKPI�CPCN[UKU�VQ�CFXCPEGF�OCVGTKCNU�TGUGCTEJ�

� No Liquid Nitrogen Required�HQT�TGFWEGF�QRGTCVKPI�EQUVU�CPF� maintenance requirements� Five Primary Filters� Large Sample Chamber with Small Footprint� High Speed Detector�RGTOKVU�JKIJN[�RTGEKUG�CPCN[UKU�KP�C� shorter time� Sample Observation Camera�GPCDNGU�RTGEKUG�UCORNG��RQUKVKQPKPI

'CU[�VQ�WUG�QRGTCVKPI�UQHVYCTG�QHHGTU�CP�KPVWKVKXG�WUGT�KPVGTHCEG�CPF�KU�RTG�NQCFGF�YKVJ�ECNKDTCVKQP�EWTXGU�CPF�OGVJQFU��OCMKPI�QRGTCVKQP�GCU[�HQT�CNN�QRGTCVQTU�

A New Level of XRF Excellence

Scan the QR code

to learn more about

the Mixer/Mill.

GRIND YOUR SAMPLE WITH THE MIXER/MILL®

Our 8000 Series Mixer/Mills are renowned for their high energy milling capabilities.

They have been redesigned to be quieter and more robust to accommodate the

most demanding applications. The dual clamp Mixer/Mill allows users to grind two

samples at a time.

The 3636 X-Press® is an automatic,

programmable hydraulic pellet press that

applies 35 tons of pressure to samples.

Ideal for repetitive pressing of sample

pellets.

Our range of Katanax X-Fluxers®

are the next generation in electric fusion

X[HUV�b7KH\�DUH�LGHDO�IRU�KLJK�WKURXJKSXW�

ODEV�ZLWK�FRPSOH[�VDPSOHV�b�7KH\�DUH�

available as a one, two, three or six

position unit that can produce up to

��IXVHG�EHDGV�SHU�KRXU�IRU�;5)�DQDO\VLV�b

PREPARE PRESSED PELLETS & FUSED BEADS FOR XRF ANALYSIS

3636 X-Press®

X-300 X-Fluxer®

THE COMPLETE

SOLUTION FOR XRF

SAMPLE PREPARATIONSPEX SamplePrep has the tools you need to

prepare your samples for XRF analysis. Our

innovative products can grind samples to

micron level particle sizes, press pellets for

quick turn-around or prepare fused beads

for the ultimate sample homogeneity.

www.spexsampleprep.com • [email protected] • 1-855-GET-SPEX

4 X-ray Spectroscopy Methods & Applications November 2017

485F US Highway One South, Suite 210, Iselin, NJ 08830(732) 596-0276,

Fax: (732) 647-1235

Michael J. Tessalone Vice President/Group [email protected]

Stephanie Shaffer Publisher,

[email protected](774) 249-1890

Edward Fantuzzi Associate Publisher,

[email protected]

Michael KushnerSenior Director, Digital [email protected]

Laura Bush Editorial Director,

[email protected]

Megan L’Heureux Managing Editor,

Meg.L’[email protected]

Stephen A. Brown Group Technical Editor,

[email protected]

Cindy Delonas Associate Editor,

[email protected]

Kristen MooreWebcast Operations Manager

[email protected]

Vania OliveiraProject Manager

[email protected]

Sabina AdvaniDigital Production Manager [email protected]

Kaylynn Chiarello-EbnerManaging Editor, Special Projects

[email protected]

Dan Ward Art Director,

[email protected]

Anne Lavigne Marketing Manager,

[email protected]

Melissa Stillwell C.A.S.T. Data and List Information,

[email protected]

Wright’s Media Reprints,

[email protected]

Maureen Cannon Permissions,

[email protected]

Jesse Singer Production Manager,

[email protected]

Wendy Bong Audience Development Manager,

[email protected]

Ross Burns Audience Development Assistant Manager,

[email protected]

MANUSCRIPTS: To discuss possible article topics or obtain manuscript preparation guidelines, contact the editorial director at: (732) 346-3020, e-mail: [email protected]. Publishers assume no responsibility for safety of artwork, photographs, or manuscripts. Every caution is taken to ensure accuracy, but publishers cannot accept responsibility for the information supplied herein or for any opinion expressed.

SUBSCRIPTIONS: For subscription information: Spectroscopy, P.O. Box 6196, Duluth, MN 55806-6196; (888) 527-7008, 7:00 a.m. to 6:00 p.m. CST. Outside the U.S., +1-218-740-6477. Delivery of Spectroscopy outside the U.S. is 3–14 days after printing. Single-copy price: U.S., $10.00 + $7.00 postage and handling ($17.00 total); Canada and Mexico, $12.00 + $7.00 postage and handling ($19.00 total); Other international, $15.00 + $7.00 postage and handling ($22.00 total).

CHANGE OF ADDRESS: Send change of address to Spectroscopy, P.O. Box 6196, Duluth, MN 55806-6196; provide old mailing label as well as new address; include ZIP or postal code. Allow 4–6 weeks for change. Alternately, go to the following URL for address changes or subscription renewal: http://ubmsubs.ubm.com/?pubid=SPEC

RETURN ALL UNDELIVERABLE CANADIAN ADDRESSES TO: IMEX Global Solutions, P.O. Box 25542, London, ON N6C 6B2, CANADA. PUBLICATIONS MAIL AGREEMENT No.40612608.

REPRINT SERVICES: Reprints of all articles in this issue and past issues are available (500 minimum). Call 877-652-5295 ext. 121 or e-mail [email protected]. Outside US, UK, direct dial: 281-419-5725. Ext. 121

C.A.S.T. DATA AND LIST INFORMATION: Contact Melissa Stillwell, (218) 740-6831; e-mail: [email protected]

INTERNATIONAL LICENSING: Maureen Cannon, (440) 891-2742, fax: (440) 891-2650; e-mail: [email protected]

© 2017 UBM. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical including by photocopy, recording, or information storage and retrieval without permission in writing from the publisher. Authorization to photocopy items for internal/educational or personal use, or the internal/educational or personal use of specific clients is granted by UBM for libraries and other users registered with the Copyright Clearance Center, 222 Rosewood Dr. Danvers, MA 01923, 978-750-8400 fax 978-646-8700 or visit http://www.copyright.com online. For uses beyond those listed above, please direct your written request to Permission Dept. fax 440-756-5255 or email: [email protected].

UBM Americas provides certain customer contact data (such as custom-ers’ names, addresses, phone numbers, and e-mail addresses) to third parties who wish to promote relevant products, services, and other op-portunities that may be of interest to you. If you do not want UBM Americas to make your contact information available to third parties for marketing purposes, simply call toll-free 866-529-2922 between the hours of 7:30 a.m. and 5 p.m. CST and a customer service representative will assist you in removing your name from UBM Americas lists. Outside the U.S., please phone 218-740-6477.

Spectroscopy does not verify any claims or other information appearing in any of the advertisements contained in the publication, and cannot take responsibility for any losses or other damages incurred by readers in reli-ance of such content.

Spectroscopy welcomes unsolicited articles, manuscripts, photographs, illustrations and other materials but cannot be held responsible for their safekeeping or return.

To subscribe, call toll-free 888-527-7008. Outside the U.S. call 218-740-6477.

UBM Americas (www.ubmamericas.com) is a leading worldwide media company providing integrated marketing solutions for the Fashion, Life Sci-ences and Powersports industries. UBM Americas serves business profes-sionals and consumers in these industries with its portfolio of 91 events, 67 publications and directories, 150 electronic publications and Web sites, as well as educational and direct marketing products and services. Market leading brands and a commitment to delivering innovative, quality prod-ucts and services enables UBM Americas to “Connect Our Customers With Theirs. UBM Americas has approximately 1000 employees and currently operates from multiple offices in North America and Europe.

®

www.amptek.com

New in-house manufacturing = The highest performing detectors available

®

State-of-the-Art X-Ray Solutions

The best detector for optimal results

t'"45�4%%¥� ��t4%%� ��t4J�1*/

Confi gurations to meet your needs

For XRF

OEM Confi gurations

XR-100 and

PX5 Digital Pulse Processor

X-123 Complete X-Ray Spectrometer

XRF Experimenters Kit

A sample of detectors with

preamplifi ers and heat sinks

Digital Pulse Processors and

Power Supplies

240

Ty

pic

al R

eso

luti

on

(e

V F

WH

M @

5.9

ke

V)

Peaking Time (μs)0 5 10 15 20 25 30

FAST SDD®

25 mm2 and 70 mm2

120

140

160

180

200

220

SDD

25 mm2

Si-PIN

6 mm2

Si-PIN

13 mm2

Si-PIN

25 mm2

®


Articles 8 Advances in Stress Measurement with Portable

X-Ray Diffraction: Uncertainties in Normal and Shear Stress Determination on Mild Steel PipeSeung-Yub Lee, Jingjing Ling, and Adrian ChituTo test the accuracy of residual stress measurements made with portable X-ray devices, measured normal and shear stresses were compared with the applied (true) values for accuracy assessment. From those results, practical measurement and analysis protocols for precise and accurate stress measurements are proposed.

18 Recent Developments in Small-Angle X-Ray ScatteringN. Sanjeeva MurthyThere has been a resurgence in the application of small-angle X-ray scattering for a large range of problems in materials science. This article highlights experimental requirements and applications, with examples drawn from protein solutions, porous structures, and polymers.

25 EDXRF Analysis of Sulfur and Trace Element Content in FAMEsDirk WissmannThe EDXRF method described here is a quick and economical procedure to check samples for their oxygen content to ensure that the material used for diesel fuel blending is really FAME-based and not mineral-oil based.

31 In Vivo XRF Analysis of Toxic ElementsInterview with David R. ChettleDavid R. Chettle, a professor at McMaster University in Hamilton, Ontario, Canada, uses X-ray fluorescence spectroscopy for the in vivo measurement of toxic elements in human subjects, with the goal of developing devices that can be used to investigate the possible health effects of toxin exposure. He recently spoke to us about his research.

Cover image courtesy of Centurion Studio/Shutterstock.

x-�� s�� m�� & a��n�� 2017 v�� 32 i�� s11

New XRF Metrology Tool for Composition and Thickness

Measurement

The SMX benchtop analyzer is a complete non-

destructive XRF tool for total process control

from R&D and process development to

manufacturing.

• Optimized process control and yield

management

• Non-destructive bulk sample and thin

coating analysis

• Comprehensive failure analysis and quality

control

• Applications include photovoltaic

manufacturing, protective coatings, layer

measurements, corrosion/wear and thermal

barrier analysis

edax.com


X-ray diffraction (XRD) tech-niques have been used to measure the residual stress of

polycrystalline materials since the

1920s (1), and continuous advances have been made in both hardware development and analysis methods to determine the stress profile with

Advances in Stress Measurement with Portable X-Ray Diffraction: Uncertainties in Normal and Shear Stress Determination on Mild Steel PipeResidual stress measurements with portable X-ray devices using diffrac-tion techniques were first demonstrated in the 1960s. Since then, the measurement precision and portability of these devices have improved significantly because of advances in high-resolution detectors and analy-sis methods. However, questions regarding accuracy have persisted because of the intrinsic limitations of such small devices and the unknown true stress states in materials of interest. Previous studies of precision and accuracy have suggested that precision is mainly a function of the instrument and measurement environments and that accuracy depends not only on instrumental parameters, but also involves sample condi-tions such as anisotropy, heterogeneity, and processing history. Even though sample-dependent accuracy characterization is not trivial, it is worthwhile to quantify measurement errors from a nonideal sample when general assumptions (isotropic and homogeneous ensembles under a biaxial stress state) are not satisfied. Therefore, we carried out in situ uniaxial tension and torsion experiments with a round 1010 carbon steel tube, and then compared the measured normal and shear stresses with the applied (true) values for accuracy assessment. Based on the obtained uncertainties, we propose practical measurement and analysis protocols for precise and accurate stress measurements.

Seung-Yub Lee, Jingjing Ling, and Adrian M. Chitu

Think Outside the Lab

Thermal AnalysisX-ray FluorescenceSpectroscopy

Hitachi provides

comprehensive

laboratory solutions,

serving your needs

inside AND outside

the lab. Contact us

about our

specials!

Hitachi High-Technologies Science America, Inc.

www.hitachi-hightech.com /us Tel. 1-800-548-9001


increased accuracy and precision (2). However, measurement speed and portability have also become important criteria for industrial applications. In the 1960s, Boeing and Northrop Grumman led the development of portable X-ray sys-tems to survey their aircraft parts, using the Laue back-ref lect ion technique on photographic f i lm (3,4). After the 1970s, most portable X-ray devices were equipped with a position-sensitive detector (PSD)—that is, a linear detector instead of a point detector or film—to avoid sample rotation or nondigitized film reading, which causes consid-erable errors because of the short sample-to-detector distance (SD) of such small devices (5).

The advent of two dimensional (2D) detectors such as the mul-t iwire PSD, the charge coupled device (CCD, in the 1970s), and the image plate (IP, in the 1980s) greatly improved the performance of stress measurements because these detectors collect signals from more grains. To utilize the partial or full Debye ring contour from a 2D detector, relevant analysis meth-ods such as cosα (6), XRD2 (7), or the ful l-ring f it t ing method (8) had to be incorporated. Regardless of detector types, the traditional sin2ψ method was dominant until the 1980s; since the 1990s, the 2D method has become more avai l-able along with the development of high-resolution 2D detectors.

The X-ray stress analyzer in our study was based on an IP detector and used a cosα analysis method, and we performed a series of tests to answer the following questions:

• What is the intrinsic precision limit (smallest error) that an in-strument can provide (9)?

• How is the 2D analysis (cosα or full-ring fitting) different from the sin2ψ method (10)?

• What are the necessary condi-tions for an accurate stress mea-surement (11)? We have answered those ques-

tions by using stress-free ferrite powders and 1018 mild steel bar samples through in situ uniaxial tensi le loading tests in the past. Ba sed on ou r prev ious u nder-standing, we introduced two more complications to extend the use of this technique to more practical applications: Is there any sample dependency in terms of shape or chemical composition, even with the same elastic properties? And, can we measure shear stress as well as normal stress? In this article, we answer those questions by uniaxial tension and torsion tests with 1010 mild steel tube samples.

Data AnalysisThe basic principle of the stress measurement is to determine the interplanar spacing d

hkl from the

diffraction peak position in a lab coordinate system (ϕ0, ψ0), as a built-in strain gauge, followed by the transformation to the sample coordinate system (ϕ, ψ), and to re-late this strain to the stress via the stiffness (or compliance) tensor. If the isotropic assumption is satisfied, strain or stress can be expressed in a simple form as equation 1:

[1]

November 2017 X-ray Spectroscopy Methods & Applications 11

Sin2ψ Method

The standard sin2ψ method with a point detector requires a set of measurements at different sample tilt angles (ψ0) for a given rotation (ϕ0). Then, the interplanar spacing d

hkl measured at angles (ϕ, ψ) can

be written as shown in equation 2 if the material’s elastic behavior is isotropic and homogeneous:

[2]

where σϕ

=σ11cos2ϕ + σ12sin2ϕ + σ22sin2ϕ.

If the in-plane stress is not de-pendent on the angle ϕ, the equa-tion can be further simplif ied as shown in equation 3, which is the well-known sin2 ψ equation. The biaxial in-plane stress can then be determined from the slope of a d versus sin2 ψ plot.

[3]

Cosα Method

The cosα method was f irst pro-posed in the late 1970s using pho-tographic film (6), and was applied to the image plate in the early 1990s (12). Since each point on the Debye ring comes from a different orien-tation of the scattering vector (not only from ϕ, but also ψ in the sin2ψ geometry), one can utilize such in-formation with a single measure-ment without any sample rotation. A strain transformation for a given geometry, leads to the final stress, as shown in equations 4 and 5:

σ11

(ϕ0=0) =−

E

(1+ν)

1

sin2η

1

sin2ψ0

∂a1

∂cosα [4]

σ12

(ϕ0=0) =

E

2(1+ν)

1

sin2η

1

sinψ0

∂a2

∂sinα [5]

where

a1(ϕ

0)= {[ε

α−ε

π+α] + [ε

−α−ε

π−α]},

1

2

a2(ϕ

0)= {[ε

α−ε

π+α] − [ε

−α−ε

π−α]}

1

2

and a1 and a2 are the α dependent strain components and angles η

Figure 1: (a) Experimental setup with a portable X-ray device next to the tube sample in the electromechanical testing machine. Insets display strain gauges and the beam spot on the sample surface. (b) Measured back-diffracted Fe (211) peak. The black dashed lines show the region that the cosα method uses, and black circles indicate data used for the two-tilt sin2ψ method. 2η = π - 2ϴB, ψ = ψ0 ± η. 2ϴB = 156.4°.


and α are defined in Figure 1b. It should be emphasized that the stress equations 3–5 above are valid for isotropic, homogeneous, and biaxial-stress conditions. If not, or if a steep stress gradient exists near the surface, the equations must be modified as reported for the sin2ψ (2,13) and cosα (14,15) methods.

ExperimentalAn Instron 5984 electromechani-cal testing machine and an Instron 1321 axial torsional test frame were used to apply uniaxial tension and torsion to the tube sample, con-forming to ASTM International 179 and SAE International J524 standards. The tube material was very low carbon steel meeting the American Iron and Steel Institute (AISI) 1010 specif ications, which was cold drawn and annealed at 650 °C. The microstructure shows a pr imar y ferr ite phase (gra in size 12 μm) with small islands of pearlite. In addition, no significant texture was detected from the mi-croscopes (scanning electron mi-croscope and electron backscatter diffraction) and a laboratory dif-fractometer. The tube outer diam-eter, inner diameter, wall thickness, and length were 1 in. (25.4 mm), 0 .902 i n . (22 .9 m m), 0 .049 i n .

(1.24 mm), and 12 in. (305 mm), respectively.

The miniature portable X-ray device selected for this study was equ ipped w it h a n i mage plate 2D detector (spat ia l resolut ion: 50 μm) and analysis software (cosα method) for instantaneous results. In addition to portability, stress measurements are fast (less than 2 min) and convenient (single expo-sure) compared to the sin2ψ method. The specifications of the instrument are as follows: tube: 20 keV, 1.0 mA; target: chromium; beam energy: λ = 2.2909 Å, 5.4 keV; collimator size: 1 mm diameter; spot size: 2 mm diameter; sample-to-detector dis-tance: approximately 35–40 mm; data acquisition time: 40 s; data read or analysis time: 50 s.

X-ray diffraction profiles of the Fe (211) peak were measured at each loading point under load con-trol with various ti lt angles (ψ0) and sample-to-detector distances (SDs) for the uniaxial tensile tests and with ψ0 = 35°, SD = 35 mm for the torsional tests. The goal of the in situ loading tests is to quantify accuracy by comparing stresses measured by diffraction with the electromechanical testing machine values since an operator knows ex-actly how much stress is applied to

Table I: Property comparison between the old 1018 (11) and new 1010 mild steel. They have the same elastic modulus, but yield strength, carbon content, and sample geometry are different. Elastic modulus and yield stress were measured in-house using the electromechanical testing machine.

SamplesElastic

Modulus (GPa)

Yield Stress

σy (MPa)

Carbon

(wt%)

Sample

Geometry

Applied

Loading

1018 steel 203 370 0.14–0.20 Flat bar Tension

1010 steel 203 250 0.08–0.13 Round tubeTension and

torsion


the sample. Recently, we demon-strated such uncertainties using the 1018 steel bar with the X-ray beam on a f lat surface via uniaxial tensile loading (11). However, engineering components are not necessarily f lat, and also are not likely to have only normal stress components. There-fore, we chose a round 1010 mild carbon steel tube (McMaster, Inc.) for the torsion test. A tubular sam-ple is ideal for this study because it is more representative of actual ap-plications with alignment difficulty and is convenient to use in twisting experiments. The differences be-tween the old (1018) and new (1010) steel are shown in the Table I.

Results and DiscussionIn our previous study, we showed that the intrinsic precision limit of this device is 9 με, correspond-ing to 2 MPa for steel (9), and that cosα and sin2ψ are equivalent and generate the same results within t he error (10). In addit ion, we showed that the sample (machine) t i lt angle, ψ0, is one of the most

sensitive parameters for measure-ment accuracy of the cosα method analyzing the back-ref lected Debye ring (11) by stress-free reference powders and a solid bar with f lat geometry.

I n t h i s s t udy, we have c on-f i rmed t hese phenomena w it h some differences. Figure 2a shows t he measured st ress versus ap-plied stress using three different analysis methods from four inde-pendent measurements. Loading was applied up to 275 MPa with an interval of 25 MPa. Because a ψ0 angle of 45° was known to be the most accurate condition from the 1018 steel bar measurements, the same conditions were applied to the 1010 steel tube. First of all, this plot shows that the accuracy does not depend on the analysis method in the elastic regime even though each method is sensitive to different parameters (11). However, the measured stress values were around 75% of the correct ones (25% off ) for all cases. Figure 2b displays measured shear stress ver-

(a)

Line of equality

Line of equality

Loading (twist)

Unloading (release)

Full ring fitting

0

0 –10 0 10 20 30 40 50 60 7050 100 150 200 250 300

50

100

150

200

250

300 60

50

40

30

20

10

0

–10

–20

–30Measu

red

no

rmal st

ress

(M

Pa)

Measu

red

sh

ear

stre

ss (

MPa)

Applied normal stress (MPa) Applied shear stress (MPa)

(b)

Figure 2: (a) Measured stress versus applied stress at ψ0 = 45° under uniaxial tensile load with three different analysis methods and (b) under torsional loading at ψ0 = 35°. Error bars in (a) are the standard deviation from four measurements, that is, precision, and the error bar in (b) comes from the fitting error of the single dataset from equation 5.


sus applied shear stress. Because of the capacity limit of the axial torsional test frame, shear loading was only applied up to 50 MPa. It demonstrates that shear stress can be traced with reasonable accuracy. However, note that shear stress (σ12) error bars (±10–20 MPa) in Figure 2b are the f it t ing errors for the slope of a2 versus sin α as shown in equation 5 from a single measurement while the error bars (±10 MPa) in Figure 2a are the pre-cision determined from multiple measurements. Therefore, shear stress measurements seem margin-ally acceptable at this point with greater errors than normal stress, and need to be tested with higher loading a nd mu lt iple measure-ments.

To better understand the inaccu-rate normal stress measurements of the 1010 tube sample and discrep-

ancy from the previous 1018 bar sample, a tilt angle (ψ0)-dependent accuracy plot (Figure 3) was gen-erated from the five measurements at each value of ψ0 with a reduced number of tensi le loading steps. In other words, the cosα slope of Figure 2a is marked as a blue circle at ψ0 = 45° in Figure 3. Note that the manufacturer recommends that measurements be made at ψ0 = 35° because it provides the most precise and accurate results from the steel reference powders. How-ever, for solid steel samples, both 1018 and 1010 do not show the best results at or near 35°. Measure-ments with stress-free powders show reasonable accuracy at 25° < ψ0 < 45° (9), while our steel sample measurements were the most inac-curate in that range. The error at low tilt angles (ψ0 < 15°) is an inevi-table problem regardless of analysis

Measu

red

/ap

plied

str

ess

rati

o

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.40 10 20 30 40 50

1018 Steel rectangular bar (11)

1010 Steel hollow tube

Figure 3: Measured/applied stress ratio (slope in Figure 2a) versus sample (or machine) tilt angle (ψ0) with 1018 (11) and 1010 carbon steel from five independent measurements. Accuracy depends not only on the instrumental parameters (ψ0), but also on the sample itself. The green dashed line indicates 100% accurate results.


methods (cosα or sin2ψ) because of the narrow range of the scattering vectors.

Two problems in Figure 3 need to be addressed: inaccurate results from both the 1018 and 1010 sam-ples, and the discrepancy between them. It was known that X-ray mea-surements do not give macro-stress values because of residual pseudo-macro-stress formation if the spec-imens have been stretched, com-pressed, bent, rolled, or drawn (16). This f ictitious stress depends not only on the magnitude of deforma-tion, but also the crystallographic orientation. For example, the Fe (211) peak generates a lower mag-nitude of stress than the (310) peaks, even when X-ray elastic constants are applied, presumably because of plastic anisotropy (17,18). Despite the unknown processing history, these long bar and tube samples are suspected to have been subjected to rolling or drawing processes. Since this hkl dependency is well-known behavior in plain carbon steel, lower stresses from a proper instrumen-tal setting can be ascribed to the pseudo-macro-stress from the prior plastic deformation.

In addition to the hkl dependency of pseudo-macro-stress, Taira and colleagues reported that the mag-nitude of the measured stress in-creases with the amount of carbon content up to 0.5% (18). This stress increase with increased carbon con-tent can be one possible explanation of why 1010 steel with lower carbon content (C: 0.08–0.13%) shows a lower stress level than 1018 steel (C: 0.14–0.20%). Secondly, texture can be another reason. The discrepancy

between steel samples becomes larger at higher tilt angles. Based on the electron backscatter diffraction and full range diffraction profile, the 1018 steel bar shows some tex-ture along the vertical (axial) direc-tion whereas the 1010 steel does not. Since dif fraction measurements with higher tilt angles probe grains more aligned in the axial direction, texture developed from previous plastic deformation may cause this discrepancy.

Therefore, the measurement ac-curacy is highly dependent on crys-tallographic plane, chemical com-position, texture, and processing history of the sample. Even though it is not possible to know all the sources of error, one can calibrate the sample and instrument together with a single parameter, such as ψ0 in this case. After the calibration chart is made, stress measurements with diffraction techniques can be quite useful in terms of speed, con-venience, and accuracy.

The effect of sample geometry and measurement environment also should not be neglected. The aver-age precision error bars (±16 MPa at 200 MPa, 8%) for 1010 steel are larger than those for 1018 (±6 MPa at 200 MPa, 3%) between 25° and 45° in Figure 3. This is likely be-cause of the round geometry caus-ing more problems of beam focus-ing and alignment, although some error may have come from sample heterogeneity since measurements took place at f ive dif ferent loca-t ions. Note that the best stress precision achievable from stress-free steel powders is 2 MPa; it was observed that the usual environ-


ment in New York City where sub-ways pass nearby easily increased the error up to 10% (±20 MPa at 200 MPa applied load) on the 1010 tube sample.

ConclusionWe can reach the following conclu-sions from this work:• Precision error by the instrument

has been reduced significantly from the past because of improvements in technology.

• The cosα method is fast, precise, and convenient, but accuracy is not guaranteed.

• The sin2ψ and other 2D analysis methods (cosα or full-ring fitting) yield statistically indistinguish-able results in the elastic regime, but they may deviate after yielding because of the information volume difference and heterogeneous plas-tic flow.

• Precision depends on the instru-ment parameters, measurement environment, and sample geometry.

• Accuracy depends not only on the measurement parameters but also on sample conditions such as elas-tic anisotropy, processing history, chemical compositions, and texture.

• Shear stress can be measured, but the error is much larger than for normal stress.

SuggestionsThe above conclusions allow some recommendations for stress measure-ments with a portable X-ray device. This general idea can be applied to any portable system, regardless of de-tector type (IP, CCD, semiconductor) or detection geometry (point detector, one-dimensional, linear PSD, 2D).

• Be aware that most commercial devices use the stress equation for isotropic and homogeneous materi-als under biaxial stress. The biaxial stress condition can be justified if the beam penetration depth is shal-low using a low X-ray energy. Try to measure different spots to check sample heterogeneity and use the X-ray elastic constant (XEC) to reduce the error arising from the elastic anisotropy.

• If XEC is not available and only a single reflection is used, the (211) for body-centered cubic (BCC) and (311) for face-centered cubic (FCC) mate-rials are good choices because XEC, S2/2, for each reflection is close to the (1+υ)/E that the stress equation uses. However, this is not valid if the speci-men has undergone plastic deforma-tion as demonstrated in this study.

• If a 2D detector is used, be sure to have a continuous Debye ring with sufficient intensity. Also check the lin-earity of strain against sin2ψ or cosα. If strain is not linear, the standard equations for sin2ψ or cosα cannot be used, and a more advanced treat-ment is required.

• Both sin2ψ and cosα methods can be used with the 2D data. For the sin2ψ method, make sure to place the specimen at the exact center of rota-tion. The cosα method is insensitive to the sample location and sample-to-detector distance, but beam center calibration is normally not adjustable by users.

• Repeat the measurement at the same and different spots to separate instrument precision and sample heterogeneity.

• If only relative measurements are important, use the instrumental


conditions that provide the best precision. For this specific device, ψ0 = 35°, SD = 35–40 mm.

• If the absolute values are important, create a calibration chart for the sample of interest by applying the known stresses, using one single adjustable instrumental parameter. For example, the tile angle, ψ0, is the calibration parameter, and the ψ0 of 45° gives the most accurate re-sults for the 1018 carbon steel.

AcknowledgmentDiscussions with Professor I.C. Noyan, Professor Pat Mooney, and Mr. Hazar Seren at Columbia University are gratefully appreciated. The authors acknowledge Dr. Adrian Brügger for providing the Instron 5984 at the Robert W. Carleton Strength of Ma-terials Laboratory. We also thank Mr. Toshikazu Suzuki for providing the portable X-ray machine and software.

References(1) H.H. Lester and R.M. Aborn, Army

Ordnance 120, 200 (1925).

(2) I.C. Noyan and J.B. Cohen, Residual

Stress (Springer-Verlag, New York, 1987).

(3) D.A. Bolstad, “Application of Portable

X-Ray Stress Techniques at the

Commercial Airplane Division

of the Boeing Co,” Automotive

Engineering Congress, Detroit,

Michigan (1967), pp. 1–4.

(4) R. Homicz, “Fundamentals and

Basic Techniques of Residual Stress

Measurements with a Portable

X-Ray Diffraction Unit,” Technical

Report No. 0148-7191, SAE

Technical Paper, 670151 (1967).

(5) M.R. James and J.B. Cohen, J. Test.

Eval. 6(2), 91–97 (1978).

(6) S. Taira, K. Tanaka, and T.

Yamazaki, J. Soc. Mater. Sci., Jpn.

27(294), 251–256 (1978).

(7) B.B. He, Two-Dimensional X-Ray

Diffraction (John Wiley & Sons,

Hoboken, New Jersey, 2011).

(8) A. Kampfe, B. Kampfe, S. Goldenbogen, B.

Eigenmann, E. Macherauch, and D. Lohe,

Adv. X-Ray Anal. 43, 54–65 (2000)..

(9) J. Ling and S.-Y. Lee, Adv. X-Ray

Anal. 59, 153–161 (2015)..

(10) J. Ramirez-Rico, S.-Y. Lee, J. Ling,

and I.C. Noyan, J. Mater. Sci.

51(11), 5343–5355 (2016).

(11) S.-Y.Lee, J. Ling, S. Wang, and J.

Ramirez-Rico, J. Appl. Crystallogr.

50, 131–144 (2017).

(12) Y. Yoshioka and S. Ohya, Adv. X-Ray

Anal. 35, 537–543 (1992)..

(13) H. Dolle, J. Appl. Crystallogr.

12(6), 489–501 (1979).

(14) T. Sasaki and Y. Kobayashi, Adv. X-Ray

Anal. 52, 248–255 (2009).

(15) T. Sasaki, Y. Maruyama, H. Ohba, and S.

Ejiri, J. Instrum. 9(07), C07006 (2014)..

(16) B.D. Cullity, Adv. X-Ray Anal.

20, 259–271 (1976).

(17) M.R. James and J.B. Cohen, Treatise

Mater. Sci. Technol. 19, 1–118 (1978).

(18) S. Taira, K. Hayashi, and S. Ozawa,

Mechanical Behavior of Materials,

Society of Materials Science, Japan

1974, 287–295 (1974).

Seung-Yub Lee, Jingjing Ling, and Adrian M. Chitu are with Applied Physics and Applied Mathematics at Columbia University in New York, New York. Direct correspondence to: [email protected] ◾

For more information on this topic, please visit our homepage at: www.spectroscopyonline.com


W ith the availability of syn-chrotron X-ray sources, f a s t t wo - d i m e n s i on a l

(2D) electronic detectors, and en-hanced computational capabilities, there has been a resurgence in the use of small-angle X-ray scatter-ing (SAXS) in biology and materi-als science. The technique is now more accessible and has become an indispensable analy tical tool for studying statistically represen-tative microstructures of hetero-geneous materials at 10–1000 nm length scales (1).

The ability of X-rays to be ab-sorbed, f luoresce, and diffract is used to examine materials by imag-ing, spectroscopy, and crystallogra-phy, respectively. SAXS, on the other

hand, measures the coherent scat-tering of X-rays at small angles to the primary beam (<2° with copper Kα radiation; 1.54 Å wavelength) to probe the structure at the meso-length scales that commonly occur in biology and materials science. This capability includes measuring the shapes and sizes of nanoparti-cles and large molecules, domains and voids, organized structures at large length scales, and, in general, electron density f luctuations and inhomogeneities with character-istic dimensions between 10 and a few hundred nanometers (2). SAXS complements other techniques such as microtomography, electron mi-croscopy, and atomic force micros-copy (AFM). When neutrons are

Recent Developments in Small-Angle X-Ray Scattering

With the availability of high intensity synchrotron sources, fast electronic detectors, and computational resources, there has been a resurgence in the application of small-angle X-ray scattering for a large range of prob-lems in materials science. Some of these developments are discussed using examples drawn from porous structures, protein solution, and polymers and fibers. New analytical techniques such as Monte Carlo simulations of solution scattering data and full pattern analysis of the diffraction data from lamellar structures are also described. Finally, some of the online resources available for such analysis are provided.

N. Sanjeeva Murthy

MOXTEK X-RAY TUBES

AND TURNING DOWN THE

powerful with smaller spot size options than ever before. Demo Units are currently available for evaluation. Contact us to learn more .

MOXTEK®

Scan the QR code to request more information, or visit www.moxtek.com

[email protected] | 801-225-0930

4W 350W

X-ray Tube Power

50µm 800µm

X-ray Tube Spot Size

30W, 60kV, 50µm

WE’RE CRANKING UP THE POWER

SPOT SIZE

350W, 75kV, 600µm

Moxtek is developing new compact X-ray tubes that are more


substituted for X-rays, the result-ing small-angle neutron scattering (SANS) data can extend the utility of small-angle scattering (SAS) by being able to adjust the contrast based on the nuclear structure rather than the electron density dif-ferences as in X-rays (3).

The areas in biology and materi-als science that can benefit by using SAXS fall into two broad categories: par t iculate systems (di lute and crowded particles) and nonparticu-late systems (random two-phase and ordered structures). Systems with dilute particles include proteins and polymers in solution, colloids, defects in crystals, and inclusions in solids and voids (porous materials). Examples of dense particulate sys-tems with long-range organization are colloidal aggregates, clusters of nanoparticles, microemulsions, a nd f rac ta l objec ts . Sol id t wo-phase systems include polymers, catalysts, nanocomposites, porous media, metallic alloys, and other microphase separated systems. Fi-nally, examples of ordered struc-tures (self-assembled systems) can be found in biological structures, semicrysta l l ine polymers, block copolymers, f ibers, liquid crystal-line materials, and nanostructures. This article highlights experimen-tal requirements and applications, with examples drawn from protein solutions, porous structures, and polymers.

The SAXS MethodThe SAXS experiment is conceptu-ally simple. The sample is il lumi-nated by X-rays, and the scattered radiation is registered by a detector.

Because the SAXS measurements are done very close to the primary beam, at small angles, collimation of the beam is stringent and the in-strument requires long f light paths (on the order of meters). Conse-quently, essential elements of the instrument are proper alignment of the numerous slits to define the beam, containment of the sample in a cell with minimum scatter, the smallest possible beam stop that does not contribute to stray scat-tering, and an evaluated beam path.

Unti l the 1980s, SAXS experi-ments were carried out using in-st ruments equipped w it h labo-rator y X-ray tubes . But h igher intensity sources are required to compensate for the loss in inten-sity resulting from fine collimation and the long f light path. Synchro-tron sources reduce the t ime of SAXS data collection from as long as 24 h to seconds, or even shorter. Additionally, these sources make it possible to develop hyphenated techniques by combining X-ray scattering with differential scan-ning calorimetry (DSC) (4), infra-red (IR) or Raman spectroscopy, electrochemistr y, f luorescence, X-ray spectroscopy (5), dynamic mechanical analysis, and, more re-cently, computed tomography (6). It is now possible to routinely carry out time-resolved experiments to study the inf luence of temperature and deformation to understand the physical mechanisms behind mac-roscopic phenomena such as ther-mal expansion and physical defor-mation by monitoring the motion of the molecular chains. Micro-diffraction with beams of ~0.5 μm


(7,8) can be used to characterize spatial distribution of defects at polymer interfaces, nanostructures in fiber-reinforced composites and high-performance f ibers , inter-faces, and skin-core morphologies.

Applications of SAXSScattering from unoriented struc-tures are analyzed by reducing the obser ved data into one-dimen-sional (1D) scans such as the one shown in Figure 1. The various regions in the patterns are indi-cated in the f igure. Such 1D data are typically analyzed by using ap-proximations (such as Guinier and Porod) that are valid over a l im-ited angular range, correlation, or pair-wise distribution functions, and by modeling (2). Scattering

from oriented structures needs to be analyzed using 2D data of the type shown in Figure 2. Such pat-terns can be used to gain valuable insight into the relation between structure and deformation. These 2D patterns can be analyzed by ful l pattern f it t ing. In many in-stances, such 2D patterns fall on an elliptical grid, and therefore are best analyzed in elliptical coordi-nates (9,10).

The central dif fuse scattering that arises f rom di lute systems (Figure 1) is analyzed to obtain particle parameters such as the ra-dius of gyration (Rg) from Guinier plots, molecular weight from I(0), compactness of the molecule from Krat ky plots , sur face area , vol-ume, and surface-to-volume ratio

Sca

tte

rin

g i

nte

nsi

ty l(q

)

Guinier region

Radius of

gyration

l(q) ~ exp(-q2Rg2/3)

l(q) ~ q-4

l(q) ~ q-(6-ds)

Porod region

Fractal dimensions

q-4 sphere

q-2 plate

q-1 rod

Scattering vector q

Larger structure Smaller structure

Inter-particle

interference

Inter-atomic

structure

(WAXD)

Size Shape Interface Structure

Figure 1: Schematic of 1D SAXS scan from a particulate system. The intensity is plotted as a function of scattering vector q, which is related to the scattering angle 2ϴ by the relation q = (4π sinϴ/λ), where λ is the wavelength of the X-rays. The three commonly recognized regions of the SAXS regions are indicated in the figure.


and fractal dimensions (ds) from Porod plots (2 ,12). Immense ac-t iv it y to probe the behav ior of proteins in solution has led to the advent of robot-controlled, stream-lined data col lection at the syn-chrotron sources and automated high-throughput analysis (13,14). More recently, biomolecule struc-tures are being modeled with one-bead-per-residue representation (course-grain model), as a set of spherical structures, or composed of several candidate structures that are aligned and subsequently clus-tered to reproduce the observed data. In these modeling ef forts, SAXS data is used to choose a sub-set of conformations from a large pool of candidate structures gener-ated from prior knowledge of the interactions between the various domains or residues within the molecule. Alternatively, the scat-tering body is expressed as a series of spherical harmonics, and the

scattered intensity is calculated as the sum of the contributions from these substructures (15). Note that f itting high-resolution structural models to low-resolution data is susceptible to overfitting.

Central diffuse scattering is also present in catalysts and ceramics, where it is used to obtain void vol-ume fraction, pore size distribu-tions, internal surface areas, and pore morphologies (16). Examples include zeolites, solution-mediated colloids, gels and suspensions, and for nanoparticle assemblies of soot or si lica particles in f lames (17). Ultra-SAXS (USAXS) is used to examine sinter ing, microcrack-ing, cavitation, or creep damage on the micrometer scale. At syn-chrotron sources, it is possible to carry out anomalous SAXS studies by varying the energy close to an X-ray absorption edge of a specific element and thus vary the scatter-

250

200

ϕϕ

150

100

50

50 100 150 200 250

Figure 2: SAXS data in the form of contour plots from an ordered condensed phase. The data were fitted in elliptical coordinates to two functions corresponding to the lamellar peak and the equatorial streak (11). A schematic of the tilted lamellae that could give rise to such a pattern is shown on the right.


ing contrast of one microstructure component against another.

Mesosca le ordered structures give r ise to discrete ref lect ions rat her t ha n d i f f use scat ter ing. These Bragg-like features form a 2D scattering pattern such as the one shown in Figure 2. Many bio-logica l structures such as mem-branes and col lagen have been ex tensively i nvest igated usi ng SA XS, and continue to provide new insights into these structures (18). Ordered structures in syn-thetic polymers include lamellae and micelles from many polymers that crystallize, and a large number of very interesting ordered nano-structures, such as spherical mi-celles and cylindrical (worm-like) micelles, bilayers and vesicles, and bicontinuous structures in block copolymers. The 2D patterns of the type shown Figure 2 that arise from lamellar structures are ana-lyzed to obtain characteristics of the lamellae such as height, width, spacing, and the orientation, which are used to study the crystalliza-tion and deformation (11,19). The resu lts obta ined using a na no-calorimeter have been especially revealing about the nature of the thermal transitions and polymer. Similarly, nanobeam diffraction has been used to study interfaces and spherulitic morphology. In ad-dition to the lamellar ref lections, there is a streak along the equator and the central diffuse scattering that contains information about the larger length scale structures such as fibrils and lamellar stacks. Both the lamellar structure and the equatorial streak are best analyzed

by full-pattern fitting of the image in elliptical coordinates (9,10,20).

Software ResourcesMany software packages are avail-able online for processing, ana-lyzing, and modeling SAXS data. Some commonly used sof tware includes ATSAS from the Euro-pean Molecular Biology Labora-tory (EMBL), FIT2D and BIOSYS from the European Synchrotron Radiat ion Faci l it y (ESR F), and IRENA from the Advanced Photon Source (APS). Additional informa-tion about the software and other small-angle scattering resources is available at smallangle.org.

ConclusionSAXS, in contrast to the more com-mon imaging techniques such as tomography and microscopy, can provide a view of the structure that is statistically averaged over a large sampling area . However, SA XS data , un l i ke t he imag ing tech-niques, appears in reciprocal-space and thus cannot provide a direct view of the structure in real-space. To address this problem, computa-tional tools that model the struc-ture are being developed to make the technique accessible to nonex-perts. Because of these advances, coupled with remarkable develop-ments in instrumentation, SAXS has a great potential to be widely used for investigating mesoscopic structures in diverse fields includ-ing biology, soft materials, colloids, catalysts, glasses, ceramics, and metallurgy.


NoteThis article was adapted from the material that was presented at the Poly mer Di f f rac t ion workshop held as a part of the 2017 Denver X-ray conference (July 31–August 4, 2017).

References(1) A. Guinier and G. Fournet, Small-

angle Scattering of X-Rays (Wiley,

New York, New York, 1955).

(2) O. Glatter and O. Kratky, Small

angle X-Ray Scattering (Academic

Press, London, UK, 1982).

(3) J.E. Mark, Physical Properties

of Polymers Handbook, Vol.

1076 (Springer-Verlag New

York, New York, 2007).

(4) F. Bedoui, N. Murthy, and

J. Kohn, Macromolecules

50, 2257–2266 (2017).

(5) W. Bras, S. Nikitenko, G. Portale,

A. Beale, A. van der Eerden,

and D. Detollenaere, J. Phys.:

Conf. Ser. 247, 1742–6596

(2010). doi:10.1088/1742-

6596/247/1/012047.

(6) F. Schaff, M. Bech, P. Zaslansky,

C. Jud, M. Liebi, M. Guizar-

Sicairos, and F. Pfeif fer, Nature

527, 353–357 (2015).

(7) C. Riekel, M. Burghammer, and

M. Muller, J. Appl. Crystallogr.

33, 421–423 (2000).

(8) D.T. Grubb and N.S.

Murthy, Macromolecules

43, 1016–1027 (2009).

(9) N.S. Murthy, K. Zero, and

D.T. Grubb, Polymer 38, 1021–1028 (1997).

(10) N.S. Murthy, D.T. Grubb, and

K. Zero, Macromolecules

33, 1012–1021 (2000).

(11) N.S. Murthy and D.T. Grubb,

J. Polym. Sci. Polym. Phys.

40, 691–705 (2002).

(12) J.E. Martin and A. Hurd, J. Appl.

Crystallogr. 20, 61–78 (1987).

(13) M.V. Petoukhov and D.I. Svergun,

Biophys. J. 89, 1237–1250 (2005).

(14) H. Liu, A. Hexemer, and P.H.

Zwart, J. Appl. Crystallogr.

45, 587–593 (2012).

(15) M.H. Koch, P. Vachette, and

D.I. Svergun, Q. Rev. Biophys.

36, 147–227 (2003).

(16) H. Peterlik and P. Fratzl,

Monatshefte für Chemie/Chemical

Monthly 137, 529–543 (2006).

(17) J. Hyeon-Lee, G. Beaucage,

S.E. Pratsinis, and S. Vemury,

Langmuir 14, 5751–5756 (1998).

(18) A. Angelova, B. Angelov, V.M.

Garamus, P. Couvreur, and

S. Lesieur, J. Phys. Chem.

Lett. 3, 445–457 (2012).

(19) N.S. Murthy and D.T. Grubb,

J. Polym. Sci. Polym. Phys.

41, 1538–1553 (2003).

(20) W. Wang, N.S. Murthy, and D.T.

Grubb, J. Polym. Sci., Part B:

Polym. Phys. 50, 797–804 (2012).

N. Sanjeeva Murthy is an Associate Research Professor with the Center for Biomaterials at Rutgers, the State University of New Jersey, in New Brunswick, New Jersey. Direct corre-spondence to: [email protected] ◾



T hese days, renewable fuels a nd ot her biof uels play a growing role in the offer of

automotive fuels. Currently, fatty acid methyl esters (FAMEs), mostly derived from vegetable oil, are typ-ically blended with regular diesel fuel in the 5–10% or 20% range. An alternative for the fairly expensive fresh vegetable oil is recycled veg-etable oi l derived from the food industry. An elemental analysis of

the pure FAMEs, the used vegeta-ble oil, the reprocessed vegetable oi l, and the biofuel blends is re-quired to show compliance with actual specifications.

Typically, this type of analysis is done using inductively coupled plasma–optical emission spectrom-etry (ICP-OES) using the following test methods:• EN14538-2006 (1) describes the

analysis of Ca, K, Mg, and Na in

EDXRF Analysis of Sulfur and Trace Element Content in FAMEsFatty acid methyl esters (FAMEs) are usually derived from vegetable oil and are typically blended with regular diesel fuel in the 5–20% range. An elemental analysis of pure FAMEs, used vegetable oil, or the reprocessed vegetable oil as well as biofuel blends is required to show compliance with the relevant specifications. Several test methods are available that describe the use of energy-dispersive X-ray fluorescence (EDXRF) for the analysis of sulfur in fuel, such as International Organization for Standardization (ISO) 13032 and ASTM International D7220. The current test methods, using EDXRF, are limited to fuels with a discrete maximum amount of FAME or oxygen. This article describes a quick and economical procedure to check samples for their oxygen content to ensure that the material used for diesel fuel blending is really FAME-based and not mineral-oil based. The oxygen content determined by this approach is used to apply the required matrix correction without a priori knowledge (which is typically required using other approaches), improving sulfur content determination accuracy. In addition to the analysis of the sulfur content, this article describes EDXRF as a technique to monitor other elements, including P, Cl, Na, K, Mg, and Ca, among others, that can have detrimental effects on combustion engines.

Dirk Wissmann


FAME, samples require a 1:1 dilu-tion (50%) in kerosene (to reduce matrix effects) and no internal standard is used.

• EN16294-2012 (2) describes the analysis of P in FAME, samples require a 1:3 dilution (25%) in kerosene and the use of an inter-nal standard is mandatory.Sulfur is not part of these meth-

ods and is determined using dif-ferent technologies. The analysis requires some sample preparation and investment in purchase and operating cost of the analyzer.

This report describes a quick and economic alternative to quan-tify the sulfur content in FAMEs using energy-dispersive X-ray f luo-rescence (EDXRF).

Besides the analysis of the sulfur content, EDXRF equipment (de-pending on the analyzer perfor-mance), is capable of monitoring additional elements such as P, Cl, Na, K, Mg, Ca, and many more that can be harmful to car engines.

Recycled vegetable oils can be added into diesel fuel and used as secondary burner fuel. An elemen-tal analysis to show the absence of toxic elements is part of the quality control. This can also be done with the XRF equipment.

In addition, it would be of interest to at least check the samples for their oxygen content to make sure that the material used for blending in the die-sel fuel is really based on FAMEs and not based on mineral oil.

Test MethodsSeveral test methods are available that describe the use of EDXRF for the analysis of sulfur in fuel.

The International Organizat ion for Standardization (ISO) method 13032 (3) and ASTM International method D7220 (4) are two of them.

T he c u r rent ly ava i lable te s t methods using EDXRF are limited to fuels with a discrete maximum amount of FAME or oxygen. In the example of ISO 13032, the maxi-mum content of FAME is 10% or 3.7% of oxygen. The reason is that the oxygen has a matrix effect on the sulfur signal measured by XRF. To be able to use XRF for this type of analysis, various approaches are possible:• Correct ion using def ined cor-

rection values depending on the known oxygen content, which re-quires a priori knowledge of the oxygen content.

• Correction using fundamental parameters based on t he ma-trix, which has to be predefined, and which also requires a priori knowledge of the oxygen content.

• Correction using backscatter in-formation from the sample. This approach does not require any a priori knowledge of the sample matrix, but the backscatter cor-rection must be based on a signal, which should be close to the ana-lyte’s X-ray f luorescence energy because otherwise additional ef-fects occur.

• Addit iona l references to test methods are also available (5–7).For other elements of interest,

the same effect is visible. The in-f luence on the results varies de-pending on the element.


InstrumentationOur procedure used a Spect ro Xepos analyzer in which samples were excited by a forced-air-cooled 50 W end-window X-ray tube com-bined with a doubly curved HAPG crysta l for monochromatization

and polarization of the primary tube spectrum. In addition, direct excitation using Pd-K and Co-K ra-diation can be used to optimize the excitation conditions for groups of elements. A high-resolution si l i-con drift detector (SDD) was used

Table I: Measurement conditions

Element Range kV or mA Excitation Measurement Time (s)*

Ag, Cd, Sn, Sb 49.5 kV High energy 180

Fe, Co, Ni, Cu, Zn, Mo, Pb 0.72 mA Pd 180

K, Ca, V, Cr, Mn 40 kV Co 180

Mg, Al, Si, P, S, Cl 22.5 kV, 2.0 mA HAPG 180

* Measurement time = clock time, live time is about 50% shorter than given

measurement time

250

200

150

100

50

0

0 20 40 60

S concentration (mg/kg)

S in mineral oil

S in biofuel with 12.5% oxygen

Linear (S in mineral oil)

Linear (S in biofuel with 12.5% oxygen)

No

rmalized

S in

ten

sity

Figure 1: Calibration for S in mineral oil and biofuel with 12.5% oxygen.


to collect f luorescence radiation from the sample. The highly stable spectral resolution of the SDD was <130 eV for Mn Kα.

The measurement parameters are given in Table I.

Sample PreparationThe sample preparat ion for the analysis is straightforward: 4 g of sample material is poured into a disposable XRF sample cup with an outer diameter of 32 mm. The analytical side of the sample cup is closed with a 4-μm-thick polypro-

21,000

R2 = 0.994220,000

19,000

18,000

17,000

16,000

15,000

14,000

13,000

12,000

0 5 10 15 20 25

No

rmalized

Co

mp

ton

in

ten

sity

Oxygen concentration (%)

Figure 2: Calibration for O in fuels.

Table II: Analysis results of S in fuel samples with different oxygen content

Sample Oxygen Content S Nominal (mg/kg) S Analyzed (mg/kg)

Diesel 0% 4.8 5.0 ± 0.1

Sample A 10.5% 11.7 12.5 ± 0.1

Sample B 11.0% 16.3 17.1± 0.1

Sample C 11.5% 19.8 20.1± 0.1

Sample D 11.5% 6.6 7.5± 0.1

Sample E 12.0% 7.8 7.7± 0.1


pylene film. For additional safety, the sample cups are placed into a sample holder, which is closed with a second polypropylene film of the same thickness.

ApplicationsAs explained above, biodiesel blends according to specification EN 590 typically can be analyzed with a calibration prepared for diesel fuel. Using the same calibration for the analysis of a biofuel sample with 12.5% oxygen would lead to a sig-nificant bias in the analysis result as can be seen in Figure 1.

In many cases the oxygen content of the sample being analyzed is not known, and therefore the best op-tion for an appropriate matrix cor-rection is to determine the oxygen content of the sample. Using XRF, the direct determination of the oxy-gen content in fuel is not possible because the f luorescence energy of oxygen is very low and is not de-tectable.

The second approach is to use the backscatter information of the sample to indirectly determine the content of oxygen. The so-called Compton scatter signal wi l l de-crease with increasing O-content. To be able to achieve this accurately, the energy of the Compton scatter signal should be at relatively low energy because otherwise volume effects will affect the determination.

Since the EDXRF system used in our procedure is equipped with an X-ray tube with a thick binary Pd-Co al loy anode, in principle, there are two options to use back-scatter information: one from the excitation using the characteris-

tic radiation of Pd and the second using the characteristic radiation of Co.

Because of the reasons l isted above, the cobalt excitation of the EDXRF system can be used for this determination with good accuracy. Figure 2 shows the calibration of

Table III: LODs in fuel using the EDXRF approach

Element LOD (mg/kg)

Mg 23*

Al 5

Si 1

P 0.3

S 0.2

Cl 0.2

K 0.5

Ca 0.2

V 0.2

Cr 0.2

Mn 0.3

Fe 0.5

Ni 0.5

Cu 0.5

Zn 0.1

Mo 0.5

Ag 0.5

Cd 0.5

Sn 1.0

Sb 1.2

Ba 1.0

Pb 0.2

* Can be signifi cantly improved if the

samples are analyzed without the

additional protection fi lm


the measurements of samples with known oxygen concentration.

The figure demonstrates the sen-sitivity and accuracy of this indirect determination of the oxygen con-tent. Based on this determination, the differentiation between materi-als based on FAMEs or on mineral oil is easily possible.

For the accurate determination of the trace element content, the oxy-gen content determined with this procedure is used within a funda-mental parameters program. Table II shows some examples.

As previously listed, other trace elements can be determined simul-taneously using EDXRF. Table III gives detection limits for additional trace elements.

Although there is currently no specif ied test method using XRF for the determination of these ele-ments in biofuels, the listed limits of detection (LODs) clearly dem-onstrate that at least a screening for the content of these elements is possible using the EDXRF, even at low levels.

SummaryEDXRF clearly can be used for the analysis of S and other trace ele-ments in biofuel. The determina-tion of the oxygen content helps to compensate for matrix effects effi-ciently, and a priori knowledge of the oxygen content is not required.

References(1) EN14538-2006: Fat and oil derivatives.

Fatty acid methyl ester (FAME).

Determination of Ca, K, Mg and

Na content by optical emission

spectral analysis with inductively

coupled plasma (ICP-OES).

(2) EN16294-2012: Petroleum

products and fat and oil derivatives.

Determination of phosphorus content

in fatty acid methyl esters (FAME).

Optical emission spectral analysis with

inductively coupled plasma (ICP-OES).

(3) International Organization for

Standardization, ISO 13032, “Petroleum

products – Determination of low

concentration of sulfur in automotive

fuels – Energy-dispersive X-ray

fluorescence spectrometric method”

(ISO, Geneva, Switzerland, 2012).

(4) ASTM International, D7220,

“Standard Test Method for Sulfur in

Automotive, Heating, and Jet Fuels

by Monochromatic Energy Dispersive

X-Ray Fluorescence Spectrometry”

(ASTM International, West

Conshohocken, Pennsylvania, 2017).

(5) European Committee for

Standardization (CEN, French:

Comité Européen de Normalisation)

http://www.cen.eu/cenorm/.

(6) http://www.iso.org/.

(7) http://www.astm.org or contact ASTM

Customer Service at [email protected].

Dirk Wissmann is the senior product manager and product manager for XRF at Spectro Analytical Instruments GmbH in Kleve, Germany. Direct correspon-dence to: [email protected] ◾



TO

M F

ULLU

M/G

ET

TY

IM

AG

ES

SPECTROSCOPY SPOTLIGHT

Your research has focused on the use of

XRF for noninvasive in vivo measure-

ments of several elements in human

subjects (1–4). In vivo bone lead mea-

surements were first performed in the

mid-1970s. What has been the main

motivation for developing in vivo bone

lead measurement techniques with XRF?

Lead (Pb) is toxic to humans. Nearly all Pb in the adult human body is stored in bone, and Pb stays in bone a long time, with biological half lives ranging between 5 years and 30 years. Taken together, these facts mean that bone Pb reflects long-term Pb exposure and measurements of bone Pb provide in-sight into the long-term human me-tabolism of Pb. Several research groups have therefore used in vivo XRF bone Pb measurements to study the metabolism

of Pb and to investigate the relationship between health effects in chronic Pb ex-posure, both in the workplace and in the general environment.

Can you briefly describe the major ad-

vances in the technique since the 1970s

with respect to instrumentation, method,

and minimum detectable level?

The first in vivo bone Pb measure-ments, carried out by Ahlgren and Mattsson in the early 1970s (5), used the 122-keV γ-rays from 57Co to excite Pb K-shell X-rays. They used a 90° scat-tering geometry and a Ge(Li) detector. Later Somervaille and colleagues (6) used the 88-keV γ-rays from 109Cd in place of 57Co, together with a near 180° scattering geometry and, by that time, a HpGe detector. There were two main

In Vivo XRF Analysis

of Toxic Elements

In recent years, researchers have been making important

developments to advance the effectiveness of spectroscopic

techniques for biomedical uses ranging from the identifica-

tion of infectious agents to measuring the edges of cancer-

ous tumors. X-ray fluorescence (XRF) spectroscopy is among

the techniques that can have useful medical applications.

David R. Chettle, a professor in the Department of Physics

and Astronomy at McMaster University in Hamilton, Ontario,

Canada, uses XRF for the in vivo measurement of toxic ele-

ments in human subjects, with the goal of developing devices

that can be used to investigate the possible health effects of

toxin exposure. He recently spoke to us about his research.


advantages: The energy was very close to the K-shell absorption edge (88 keV) in Pb, so the photoelectric cross section was larger than for 57Co. Secondly, the dominant Compton scattering feature was lower in energy than the Pb K X-rays for the 109Cd system, whereas the Compton scatter feature was higher in energy than the Pb K X-rays for the 57Co system. This meant that the continuum underlying the Pb X-ray signal was much smaller for 109Cd than for 57Co.

There have been subsequent develop-ments of the 109Cd bone Pb system. The first-generation system used an annular 109Cd source with an inner diameter of 22 mm, with a 16-mm-diameter HpGe detector, so the source surrounded the detector. The second-generation system, dating from the early 1990s, inverted this geometry; a small spot source of 109Cd was mounted centrally in front of a larger (51-mm-diameter, 20-mm-thick) HpGe detector. This configura-tion has been most widely adopted in different research laboratories. The limi-tation on the second-generation system was the maximum pulse throughput rate. So the third-generation system re-placed the single detector with an array of four smaller detectors in a “clover leaf” configuration. So, the total throughput could be four times larger and the de-tector resolution was also improved, resulting in a significant improvement in minimum detectable level. These suc-

cessive improvements are summarized in Table I.

What other techniques have been used

to perform these measurements? What

are the advantages of the in vivo XRF

approach compared with those methods?

The main technique, apart from X-ray fluorescence, that is used for in vivo el-emental analysis is neutron activation analysis. This technique either counts γ-rays emitted following the decay of a radioisotope induced by the neutron irradiation, or γ-rays emitted promptly (~10-12 s) after neutron absorption. For most elements either X-ray fluorescence or neutron activation analysis is clearly preferable, so the two techniques should be seen as largely complementary. For example, for Pb, X-ray fluorescence is preferred. The Pb nuclei are unusually stable, because of their nuclear structure, so cross sections for neutron absorption are small compared to the photoelectric cross section in Pb. On the other hand, for aluminum, X-ray energies are so low that they are very unlikely to escape from the body, whereas the radioisotope 28Al, formed by neutron absorption in natural 27Al, emits a γ-ray of energy of 1.79 MeV, so neutron activation is to be preferred for Al. For some elements, ei-ther technique is viable. For cadmium, the photoelectric cross section at 60 keV is 49.0 cm-1. The cross section for neu-tron absorption in the isotope 113Cd

Table I: Improvements in XRF bone analysis since the 1970s

Date SystemMinimum Detectable Level

(g Pb/g Bone Mineral)

1970s 57Co, 90° 50–60

1980s 109Cd, 180°, fi rst generation 12–20

1990s 109Cd, 180°, second generation 6–10

2000s 109Cd, 180°, third generation 2–3


is 20,000 barn, which is equivalent to 931 cm-1, but 113Cd is only 0.1222 abun-dant, so across the element Cd, the neu-tron absorption cross section is 114 cm-1. There are other factors to be taken into account, but effectively the two tech-niques are comparable in the ability to detect Cd in the human body.

You used the in vivo XRF technique in

a four-year study of the levels of bone

strontium in individuals suffering from

osteoporosis or osteopenia who have

self-administered with strontium citrate

supplements (2). Can you briefly describe

the method used for collecting the data in

this study?

The radioisotope source 125I was used to excite the Sr K X-rays. 125I emits γ-rays at a little over 35 keV, but the predomi-nant emission is of tellurium X-rays. In addition, the 125I was in the form of seeds used for brachytherapy, in which the iodine is adsorbed onto silver beads, so the source emits silver X-rays, as well as the direct emissions from 125I. The detector was a Si(Li) (16 mm diameter, 10 mm thick) and a backscatter (~180°) geometry was used. The Sr was mea-sured in a finger and at the ankle, and each measurement took 30 min.

You and your group have also studied

the bone lead concentration of a cross

section of the population of Toronto, On-

tario, Canada (3). What basic approach

was used for those measurements? What

was the age range of your test subjects,

and what general results did you obtain?

The bone Pb study was conducted in close collaboration with Health Canada and colleagues at other institutions. A third-generation system (four HpGe detectors, each 16 mm diameter, 10 mm thick) was used for bone Pb measurements at the

tibia (shin) and at the calcaneus (heel). A questionnaire was administered and blood samples were also collected. One of the objectives for Health Canada was to test how much information could be col-lected in a 1-h visit by each participant; so each bone Pb measurement lasted 22 min. The youngest participant was one year old and the oldest 82. The participants were roughly equally distributed between the sexes and across the age range. The lowest bone Pb levels were in people in their 20s or early 30s, and there was little difference between women and men. The bone Pb levels were about a factor of two lower than they had been in the nearby city of Hamilton in studies conducted in the 1990s.

Gadolinium, which is used in magnetic

resonance imaging (MRI) contrast re-

agents, was the focus of another of your

in vivo XRF bone studies (4). Why was

gadolinium an important element for

monitoring by XRF in this study? How

did your experimental setup and method

for this study differ from that used in the

bone lead research?

Gadolinium is a very valuable contrast agent for MRI. It is administered in a bound form, and it is generally pre-sumed that virtually all the Gd is elimi-nated from the body over a short period of time. However, evidence is growing that a small proportion of the Gd can be retained and the question is being raised as to whether this minor amount of re-sidual Gd could in any way be harmful. This is the context in which the in vivo measurement of this residual Gd was de-veloped. The system used is very nearly the same as that used for bone Pb, using the four-detector array. The spectral analysis obviously focuses on the Gd X-rays, rather than the Pb X-rays; we have



also attempted to minimize the amount of tungsten associated with the source and the source collimator, because W K X-rays Compton scattered through about 180° raise the continuum level under the Gd X-rays and so worsen the detection limit.

What are the next steps in your research?

In terms of improving detection limit for Pb or Gd, we are exploring the ul-trahigh-throughput pulse processing electronics that have been successfully used with silicon drift detectors, primar-ily at synchrotrons. There are challenges with using these electronics with the relatively large HpGe detectors needed for the 40–100 keV energy range, so we are actively working with the companies concerned to improve detector resolu-tion while still being able to take advan-tage of the dramatically large count rate throughput that can be achieved.

In terms of applications, there is evi-dence that parameters that have been treated as fixed—such as the relation-ship between cumulative blood Pb and uptake of Pb into bone, or the half life governing the release of Pb from bone back into blood—may not be constant, but may depend on intensity of expo-sure or cumulative past exposure, or they may vary with a person’s age. This theory is controversial and does have potential public health consequences, so we wish to explore it further.

There is some evidence that levels of Sr in western people may be less than is best for their bone health, but there is also evidence that supplementing with Sr may have harmful side effects. Our data showed that bone Sr levels increased by at least 10 times, and as much as 100 times in people who were self supplementing, and this increase oc-

curred during a relatively short period of up to four years. It is possible that this is too much, in too short a time, and too late—that is, the supplementation was done after the damage to bone had already been sustained. We would like to investigate the hypothesis that much more modest supplementation, admin-istered very gradually and earlier in life, could help to diminish the prevalence of osteoporosis. This would be a multistep, multidisciplinary, and highly collabora-tive program of research.

We have only just begun to make Gd measurements. As well as trying to improve the detection limit, we need to find out how Gd retention varies with the type of contrast agent used, number of times administered, time since ad-ministration, and the varieties of health or disease of the people concerned.

References(1) D.R. Chettle, Pramana–J. Phys.

76(2), 249–259 (2011).

(2) H. Moise, D.R. Chettle, and A. Pejovi c-

Mili c, Physiol. Meas. 37, 429–441 (2016).

(3) M.L. Lord, F.E. McNeill, J.L. Gräfe, A.L.

Galusha, P.J. Parsons, M.D. Noseworthy, L.

Howard, and D.R. Chettle, Applied Radia-

tion and Isotopes 120, 111–118 (2017).

(4) S. Behinaein, D.R. Chettle, M. Fisher,

W.I. Manton, L. Marro, D.E.B. Flem-

ing, N. Healey, M. Inskip, T.E. Ar-

buckle, and F.E. McNeill, Physio.

Meas. 38, 431–451 (2017).

(5) L. Ahlgren, K. Lidén, S. Mattsson,

and S. Tejning, Scand. J. Work, En-

viron. & Health 2, 82 (1976).

(6) L.J. Somervaille, D.R. Chettle, and M.C.

Scott, Phys. Med. Biol. 30, 929 (1985).

Introducing the 2018 Powder Diffraction File™

Diffraction Data You Can TrustICDD databases are the only crystallographic databases in the world with quality marks and quality review processes that are ISO certifi ed.

PowderDiffraction File™

871,758Entries

Standardized Data

More Coverage

All Data Sets Evaluated For Quality

Reviewed, Edited and Corrected Prior To Publication

Targeted For Material Identifi cation and Characterization

PDF-4+Identify and Quanitate

398,726 Entries295,309 Atomic Coordinates

PDF-2Quality + Value298,258 Entries

PDF-4/OrganicsSolve Diffi cult Problems,

Get Better Results526,126 Entries

106,369 Atomic Coordinates

PDF-4/Minerals Identify and Quanitate

45,497 Entries37,210 Atomic Coordinates

WebPDF-4+ Data on the Go398,726 Entries295,309 Atomic

Coordinates

I N T E R N A T I O N A L C E N T R E F O R D I F F R A C T I O N D A T A

www.icdd.com

www.icdd.com | [email protected], the ICDD logo and PDF are registered in the U.S. Patent and Trademark Offi ce.

Powder Diffraction File is a trademark of JCPDS – International Centre for Diffraction Data©2017 JCPDS–International Centre for Diffraction Data – 10/17

Applied Rigaku Technologies, Inc.

website: www.RigakuEDXRF.com | email: [email protected]

x-ray spectroscopyfiles.alfresco.mjh.group/alfresco_images/pharma/... · ubm americas () is a...

Documents