Solid Glass Defects Identification

Using

SEM-EDX Microanalysis

Martina Jezikova

martina.jezikova@gsl.cz

GLASS SERVICE, a.s.

June 22, 2017

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Solid glass defects analyses

Field of interest

cords clear knots

metallic inclusions surface defects knots with crystals

secondary stones

cords with crystals

stones

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Field of interest

- foreign solid inclusions in glass products with different optical, chemical, mechanical, thermo-physical, color and structural properties

Goal

- identification of the defect source in order to avoid production loss

- understanding why the defect appeared

Approach

- correct sampling (representative set of marked samples, statistical evaluation)

- piece of the suspected material to compare with the defects

- considering all the information about the production process, furnace design, its corrosion state and repair history

- chemical and phase composition of the defects provided by the laboratory

Motivation

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Observation by naked eye, using magnifying glass or polariscope

- location in the product (on the surface, in the mass), shape (sharp or

rounded edges), dimensions, color, transparency/opacity, stress,

presence of accompanying bubbles, crystals or cords, other phenomena

Identification methods

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Observation under the polarizing microscope

- transmitted polarized light without analyzer – microstructure and

morphological properties; optical properties

- transmitted polarized light with analyzer (nicols crossed) – microstructure

and morphological properties; optical properties

- incident light – surface structure of the opaque samples

- thin sections of the stones (approx. 30 microns thick) – stone

microstructure

Identification methods

polarizing

microscope

polarized light polarized light,

crossed nicols

crossed nicols

lambda plate

incident light

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Sample preparation for the SEM-EDX microanalysis

- cutting the defect out of the glass product

- grinding the defect to expose the core (EDX is surface sensitive method)

- preparing a cross-section of the sample containing cords

- polishing the section of the sample

- coating of electrically conducting material – carbon coater

- preparing thin section of the stone for the final microscopic observation

Identification methods

stone

before cutting

stone

in a section

knot

in a cross-section

stone in

thin section

knot

before cutting

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Scanning electron microscope (SEM) coupled with an

Energy-Dispersive X-ray Detector (EDX)

Identification methods

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Identification methods

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Point analysis

- points or other differently shaped areas of the sample surface can be

defined as areas for the analysis

- cumulated intensities of X-ray spectra are then quantified and

recalculated to mass percent composition

SEM-EDX microanalysis

Zone A

Knot

Zone 1

Knot

Glass

/Float

Ox% Ox% Ox%

Na2O 14.56 14.75 13.90

MgO 0.93 0.60 4.00

Al2O3 14.81 16.02 0.42

SiO2 66.78 65.67 72.93

CaO 2.92 2.35 8.75

ZrO2 – 0.61 –

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Line scan analysis

- primary electron beam is scanning the sample along a selected straight

line of individual measuring points

- the resulting concentration profiles for selected elements are plotted in a

diagram

SEM-EDX microanalysis

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X-Ray mapping

- creating element X-ray compositional maps over a broader area by

means of rastering the beam

- two-dimensional concentration distribution of elements in the sample

- higher brightness of the single color displays higher concentration of the

corresponding element

SEM-EDX microanalysis

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Defect: Partially translucent white stones

- surface is composed of granular particles with almost spherical shapes

and reflects light well; low stress

Case sudy No. 1

in float glass in green container glass

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Source: Imperfectly melted sand

- stones with lower degree of transformation

- remnants of the silica sand grains – dense aggregates of lath-shaped

Tridymite (SiO2)

- obvious recrystalization in the grain boundaries

Case study No. 1

Zone A

SiO2 grain

Zone 1

Tridymite

Zone 2

Vitreous

Glass

/Container

Ox% Ox% Ox% Ox%

Na2O 0.30 – 13.67 14.15

MgO – – – 0.34

Al2O3 0.53 – 1.61 1.76

SiO2 98.89 100.00 77.56 73.72

CaO 0.29 – 7.16 9.82

FeO 0.25 – – 0.21

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Stones from the silica crown

- free cluster of Tridymite crystals (SiO2)

- increased content of Al2O3 in the glassy phase

- liquid corrosive products of the silica crown run

down over a zone where some Al2O3

containing material is used

Case study No. 2

Zone 1

Tridymite

Zone 2

Vitreous

Glass

/Float

Ox% Ox% Ox%

Na2O – 13.24 14.55

MgO – 2.38 4.45

Al2O3 – 2.05 0.78

SiO2 100 74.7 71.5

CaO – 7.62 8.72

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Defect: Large clear knots in float glass

- considerable stress – cracks appeared during the grinding of the knots

- no crystalline phase

Case study No. 3

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Analysis results:

- ZrO2 and high content of Al2O3 → AZS?

- content of TiO2, ZnO, As2O3 as well

- absence or very low content of CaO

Case study No. 3

Zone A

Knot

Glass

/Float

Ox% Ox%

Na2O 10.89 13.58

MgO 0.24 4.13

Al2O3 19.64 1.12

SiO2 63.96 72.26

K2O 0.45 0.14

CaO – 8.76

TiO2 1.94 –

ZnO 0.39 –

As2O3 1.37 –

ZrO2 1.12 –

BaO – –

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Source: Contamination of the batch by glass ceramics

- piece of a suspicious material to compare with

- most glass ceramic materials contain 20–25 mass% of Al2O3

- note: Lithium (Li) cannot be detected using SEM-EDX microanalysis

Case study No. 3

Zone A

Knot

Zone B

Knot

Glass

/Float

Glass

Ceramics

Ox% Ox% Ox% Ox%

Na2O 10.89 12.01 13.58 0.44

MgO 0.24 0.28 4.13 1.55

Al2O3 19.64 19.33 1.12 24.32

SiO2 63.96 62.95 72.26 68.08

K2O 0.45 0.44 0.14 0.26

CaO – 0.24 8.76 –

TiO2 1.94 2.16 – 2.20

ZnO 0.39 0.46 – –

As2O3 1.37 1.10 – 24.32

ZrO2 1.12 1.03 – 2.68

BaO – – – 0.47

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Defect: Milky white opaque glassy inclusions in container glass

- the defect appears non-crystalline

- contain clusters of rounded particles composed of glassy phase

Case study No. 4

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Analysis results:

- alumino-silicate-zirconia core of the glassy particle

- colloidal Zirconia particles (ZrO2) in the border part of each glassy particle

Case study No. 4

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Source: Ceramic fibre insulation

- alumino-silicate-zirconia insulation

- boards, blankets and papers commonly used

as glass tank exterior wall insulation, glass tank

linings and back up insulation

Case study No. 4

Zone A

Defect

Zone B

Defect

Zone C

Defect

Glass

/Container

Fibrous

insulation

Ox% Ox% Ox% Ox% Ox%

Na2O – 10.16 10.85 12.80 –

MgO – – 1.04 3.18 1.04

Al2O3 33.66 29.82 16.02 2.66 32.14

SiO2 54.30 48.05 55.43 70.38 55.22

K2O – 1.55 1.23 0.96 –

CaO – – 2.17 10.02 –

FeO – – – – 0.47

ZrO2 12.04 10.42 13.27 – 11.14

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Defect: White opaque stone with granular surface in container glass

- translucent rounded grains similar in shape to quartz grains, but with high

relief and birefringence – usually 2–6 μm

Case study No. 5

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Analysis results:

- Zircon grains in the core (ZrO2.SiO2)

- rims of fine grained Zirconia crystals (ZrO2)

Case study No. 5

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Source: Zirconia-silicate (Zircon) refractories or cements

- in alkali glasses in the low temperature region Zircon only dissolves –

only melted-off grains are released from the refractory

- at higher temperatures above 1 250 °C Zircon decomposes to Zirconia

(ZrO2) and glass melt

- Zirconia clusters resembling the original particles of Zircon particles

Case study No. 5

Zone A

Zircon

Zone 1

Zirconia

Glass

/Container

Ox% Ox% Ox%

Na2O – – 14.36

MgO – – 1.44

Al2O3 – – 1.94

SiO2 39.16 – 72.99

K2O – – 0.90

CaO – – 8.37

ZrO2 60.84 97.99 –

HfO2 – 2.01 –

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Defect: Recrystallized Zirconia grains (ZrO2)

- stone composed of unusually shaped small white grains

Case study No. 6

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Defect: Magnesia Spinel (MgO.Al2O3)

- grain with no birefringence

- crystals of the Magnesia Spinel were accompanied by Zirconia (ZrO2)

grains

Case study No. 6

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Analysis results:

- Spinel is generated by the reaction of the

following solid phases: MgO originating from

the raw materials and Al2O3 coming from the

refractory

Case study No. 6

Zone A

Spinel

Zone B

Zirconia

Zone B

Zirconia

Glass

/Float

Ox% Ox% Ox% Ox%

Na2O – – – 13.49

MgO 26.66 – – 4.10

Al2O3 73.34 – – 0.24

SiO2 – – – 73.35

CaO – – – 8.83

ZrO2 – 99.02 99.05 –

HfO2 – 0.98 0.95 –

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Source: Fused-cast AZS from the zone of the burner ports

- changes in the AZS microstructure in the highly corrosive environment of

the port mouths (high temperature, alkali vapors, batch carryover,

combustion gases flow)

Case study No. 6

piece of AZS applied at the

burner port area

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Defect: Rounded dark stones with laths on the surface – float glass

- greenish light-reflecting Escolaite (Cr2O3) laths

- no solution sac

Case study No. 7

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Source: Chromite – accessory mineral present in the silica sand

- Chromite core [(Fe2+, Mg2+) (Cr3+, Fe3+, Al3+)2O4]

- high density – these stones usually sink at the bottom of the furnace

Case study No. 7

Zone A

Chromite

Zone 1

Escolaite

Glass

/Float

Ox% Ox% Ox%

Na2O – – 14.28

MgO 22.03 – 3.26

Al2O3 17.45 – 0.81

SiO2 – – 75.08

K2O – – 0.20

CaO – – 6.37

TiO2 0.39 – –

Cr2O3 50.61 99.09 –

FeO 9.51 0.91 –

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Thank you for your attention

GLASS SERVICE, Inc.

Rokytnice 60 755 01 Vsetin Czech Republic

+420 571 498 511 info@gsl.cz www.gsl.cz