X-ray diffraction identifies a material by measuring
Answer: A
Each crystalline phase has its own set of spacings and therefore its own pattern of peaks, which serves as a fingerprint. It identifies phases rather than elements, which is exactly what distinguishes it from a chemical analysis. Two samples of identical composition can give quite different patterns.
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Assertion (A): X-ray diffraction can distinguish quartz from cristobalite although the two have identical chemical compositions.
Reason (R): Diffraction responds to the arrangement of the atoms rather than to which elements are present.
Answer: B
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the principle. Diffraction measures the spacings between planes of atoms, and quartz and cristobalite arrange the same silica units differently, so they give quite different patterns. An elemental technique such as X-ray fluorescence would report both as pure silica and could not tell them apart - which is why phase and composition are separate questions needing separate instruments.
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Match each technique with the property it measures.
List I
A. X-ray diffraction
B. X-ray fluorescence
C. Thermogravimetry
D. Dilatometry
List II
1. Mass change on heating
2. Crystalline phases present
3. Dimensional change on heating
4. Elemental composition
Answer: C
Each technique answers one question and is blind to the others, which is why a raw material is characterised by several in combination. Diffraction sees structure, fluorescence sees elements, and the thermal methods follow what happens as the temperature rises.
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State whether the following is true or false.
X-ray fluorescence tells you which crystalline phases are present in a sample.
Answer: D
It reports the elements and their proportions but says nothing about how they are arranged. A sample of kaolinite and one of a mechanical mixture of the same oxides would give the same fluorescence result and quite different diffraction patterns.
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All of the following are established uses of X-ray diffraction on a ceramic raw material EXCEPT
Answer: A
Plasticity is a mechanical property of the wetted mass and has nothing to do with diffraction, which is carried out on a dry powder. The other three are all routine applications of the technique in a ceramic laboratory.
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An amorphous material such as a glass gives a diffraction pattern that is
Answer: B
Without long-range order there are no planes to satisfy the diffraction condition at any particular angle. The broad hump is itself informative and is how the glassy content of a fired body is estimated. Amorphous content is measured against an added internal standard.
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Assertion (A): The glassy phase in a fired ceramic can be estimated from a diffraction pattern.
Reason (R): An amorphous phase contributes a broad hump whose area is proportional to its quantity.
Answer: C
Both are true and the reason gives the method: the hump is measured against the crystalline peaks, usually with an added internal standard, which turns what looks like background into a measurement. The method needs care but is well established.
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Differential thermal analysis detects a reaction in a sample by measuring
Answer: D
A reaction absorbing or releasing heat makes the sample lag or lead the reference, and the difference is plotted against temperature. Thermogravimetry is the companion technique that follows mass rather than temperature.
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Match each thermal event in a clay with the technique that shows it most directly.
List I
A. Loss of adsorbed water
B. Dehydroxylation
C. Mullite formation
D. Quartz inversion
List II
1. Exotherm near 1,000 degrees
2. Mass loss near 100 degrees
3. Sharp expansion step at 573 degrees
4. Endotherm near 550 degrees
Answer: A
Thermogravimetry follows the mass losses, differential thermal analysis the heat effects and dilatometry the dimensional ones. Running them together gives a far fuller account of a clay's firing behaviour than any one alone.
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State whether the following is true or false.
An exothermic peak near a thousand degrees in a clay is generally attributed to mullite formation.
Answer: B
The crystallisation releases heat and produces a characteristic sharp exotherm well above the dehydroxylation endotherm. Its presence and size are used to judge how much mullite a clay will form. The peak is absent from a clay that forms no mullite at all.
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