Question

Answer all the following questions: -

I- Choose the best correct answer:

  

1- The …………… defect is a ……………… defect which refers to the presence of a pair of vacant sites.

A) Schottky, stoichiometric B) Schottky, non-stoichiometric   

C) Frenkel, non-stoichiometric D) Frenkel, stoichiometric

2- ……………….. is a powerful method for the determination of phase diagrams, especially in conjunction with other techniques, such as ……………………. for phase identification.

A) in order; DTA/DSC, XRD B) in order; DTA/DSC, TGA

C) in order; TGA, XRD D) no correct order

3- ……… defects arise on doping pure crystals with aliovalent impurities.

A) Schottky B) Frenkel C) Extrinsic D) intrinsic

4- In some …………………… cells, the sample and reference are maintained at the same temperature during heating and the extra heat input to the sample required in order to maintain this balance is measured.

A) thermogravimetry (TG) B) differential thermal analysis (DTA)   

C) differential scanning calorimetry (DSC) D) thermal titration

5- For …………………. defect in ceramics, to maintain the charge neutrality, a cation vacancy-cation interstitial pair occur together.

A) Schottky B) Frenkel C) Extrinsic D) non-stoichiometric

6- ……………. records the mass of a sample as a function of temperature or time.

A) Thermogravimetry (TG) B) differential thermal analysis (DTA)   

C) differential scanning calorimetry (DSC) D) thermal titration

7- In ……………. , the equipment is designed to allow a quantitative measure of the enthalpy changes that occur.

A) thermogravimetry (TG) B) differential thermal analysis (DTA)   

C) differential scanning calorimetry (DSC) D) thermal titration

8- For …………….. defect in ceramics, to maintain the charge neutrality, remove 1 cation and 1 anion; this creates 2 vacancies.

A) Schottky B) Frenkel C) Extrinsic D) non-stoichiometric

9- DTA cells are designed for maximum sensitivity to …………………… changes.

A) voltage B) current C) thermal D) both A and B

10- Polymorphic phase transitions may be studied easily and accurately by ………. technique.

A) DTA B) DSC C) TGA D) DTA or DSC (A & B are correct)

II- Put a sign (√) in front of correct sentence or a sign (X) in front of wrong sentence, then correct the mistake.

1- Many material properties are improved by the presence of imperfections (defects). ( )

………………………………………………………………………………………………….

2- Alloying is done to improve only the strength of a material. ( )

………………………………………………………………………………………………….

3- In solid solutions, the impurity atoms are randomly and uniformly dispersed within the solid. ( )

………………………………………………………………………………………………….

4- The types of dislocations (linear defects) in solids are edge, screw or mixed. ( )

………………………………………………………………………………………………….

5- The strength of a material with no dislocations is 20-100 times smaller than the strength of a material with a high dislocation density. ( )

………………………………………………………………………………………………….

………………………………………………………………………………………………….

6- The atmosphere (above the sample) has not any effect on the thermal decomposition (TG curve) of different solids. ( )

………………………………………………………………………………………………….

………………………………………………………………………………………………….

7- During arrangement used in DTA, sample and reference are placed in different heating blocks. ( )

………………………………………………………………………………………………….

………………………………………………………………………………………………….

8- It is possible to calibrate DSC equipment so that quantitative enthalpy values can be obtained, but it is better to use DTA for quantitative measurements. ( )

………………………………………………………………………………………………….

………………………………………………………………………………………………….

9- It is advantageous to use both DTA/DSC and TG together. ( )

………………………………………………………………………………………………….

10- An important application of DTA and DSC in glass science is to measure the glass transition temperature, Tg. ( )

………………………………………………………………………………………………….

………………………………………………………………………………………………….

Answer 1

Ans 1

Option A is the correct answer

Evaluate the given options

Option A

Schottky, stoichiometric defect is a point defect. It consists those sites where anion and cation doesn't occupy. For example if an ionic crystal AB in which A+ is cation and B- is anion. In Schottky, stoichiometric defect one cation vacancy and one anion vacancy occurs.

Option A is the correct

Option B

Schottky, non-stoichiometric defect is a point defect. It consists those sites where only one either anion or cation doesn't occupy. For example if an ionic crystal AB in which A+ is cation and B- is anion. In Schottky, non stoichiometric defect either one cation vacancy or one anion vacancy occurs.

Option B is incorrect

Option C

Frenkel, non-stoichiometric defect is a point defect. It occurs when a small cation leaves the place and vacates the place and creates the interstitial vacancy.

For example if an ionic crystal AxBy in which Ay+ cations and Bx- anions. In Frenkel, non stoichiometric defect only one A cation leaves and forms an interstitial vacancy.

Option C is incorrect

Option D

Frenkel, stoichiometric defect is a point defect. It occurs when a small cation leaves the place and vacates the place and creates the interstitial vacancy in the stoichiometric amount.

For example if an ionic crystal AxBy in which Ay+ cations and Bx- anions. In Frenkel, stoichiometric defect all Ay+ cation leaves and forms interstitial vacancy.

Option D is incorrect