chapter 2 analysis of clay minerals using xrd.ppt [...

Clay Sedimentology, Prof. Zhifei Liu 2017-10-17

School of Ocean and Earth Science, Tongji University 1

Chapter 2 Analysis of clay minerals using X-ray diffraction (XRD)

2.1 X-ray diffractometer2.2 Sample preparation2.3 XRD analysis2.4 Data processing

X-ray diffractometer

X-ray generator

goniometer

X-ray detector

Reference:Holtzapffel, T., 1985. Les minéraux argileux: Préparation, analyse diffractométrique et determination. Soc. Géol. Nord Publ, 12. 136 pp.

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2.1 X-ray diffractometer

X-ray generator: produce X-rays under high output power Goniometer: rotate the sample (or X-ray detector arm) and

measure diffraction angles X-ray detector: count circuits to detect, amplify and measure the

diffracted radiation. 2



X-ray generator tube

High voltage

Tungsten filamentX rays

Electron

Target (Cu)

X rays

Cooling water

λmin λIntensity

Continuous spectrum

Characteristic spectrum

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Characteristic X-rays

N

M

K

L

Kγ

Kα

Kβ

Lα

Lβ

K series excitation

L series excitation λmin λ

Intensity

Continuous spectrum

Characteristic spectrum

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X-rays filtering

Kα

Kβ

Kα

Kβ

I

λ λ

A crystal monochromator is used to absorb other spectrum and produce monochromatic radiation, mostly as K characteristic spectrum.

filter filter

K X-ray (Cu target)

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X-ray diffraction

K X-ray (Cu target)

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Bragg’s Law:

n 2d sin

n = an integer (1, 2, 3, …)= wavelength (Cu 1.54Å)d = interplanar spacingincidence angle(”)

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2.2 Sample preparation Significance of oriented mounts of clay particles: to identify clay minerals, it

is essential to record their diagnostic basal reflections, the intensities of which are enhanced if the platy clay minerals of the sample lie generally parallel to the plane surface of the diffractometer.

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Separation of fine-grained fraction, i.e. <2 m

Stokes equation:t = 190 x/d2

t = time of sedimentation (minutes)d = diameter of targeted particles (m)x = distance of particles descend

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Oriented mounts making method 1: filtration

Advantage: thick clay film.

Disadvantage: differential setting, difficult operation (to remove filter); not good quality on oriented mounts surface; relative large amount of sample request.

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Oriented mounts making method 2: dropping

Advantage: very quick and easy operation, small amount of sample request.

Disadvantage: differential setting, too thin clay film.

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Oriented mounts making method 3: smearing

Advantage: thick clay film, relative easy operation, excellent quality of oriented amounts surface.

Disadvantage: relative large amount of sample request.

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Power (non-oriented) mounts making method

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Ethylene-glycol solvation (24 hours)

Heating (490ºC, 2 hours)

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PANalytical X’Pert PRO Multi-Purpose Diffractometer

2.3 XRD analysis

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Receiving slit + detector

Polycrystalline sample

Line focus

Divergence slitScan directionScan direction

Classical geometry (Bragg-Brentano)

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X’Celerator

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X’Celerator

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X’Celerator

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2.4 Data processing

Identification

Calculation

Multiple X-ray diffractograms of a typical sample from the South China Sea. Liu et al. (2010, Mar. Geol.) 23

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Semi-quantitative calculation of clay minerals

1. Selection of peakssmectite (001), illite (001), kaolinite (001), chlorite (002)

2. Calculation methods(1) Ratio of peak areas: Biscaye (1965, GSA Bull.)(2) Ratio of integrated peak areas:

Petschick et al. (1996, Mar. Geol.)

(3) Ratio of peak heights: Fagel and Boës (2008, Palaeo-3)(4) Weighting factors:

Biscaye (1965)smectite × 1, illite × 4, kaolinite × 2, chlorite × 2

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(1) Ratio of peak areas and weighting factors: Biscaye (1965, GSA Bull.)

(2) Ratio of integrated peak areas: Petschick et al. (1996, Mar. Geol.)

(3) Ratio of peak heights: Fagel and Boës (2008, Palaeo-3)

(4) Ratio of peak areas (without weighting factors): Liu et al. (2010, Mar. Geol.)

Homework:Semi-quantitative calculation of clay minerals

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chapter 2 analysis of clay minerals using xrd.ppt [...

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