This set of Powder Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Powder Manufacture – Electrochemical Method”.
1. In electrodeposition, the final product may be obtained in ____ different forms.
a) 4
b) 3
c) 2
d) 5
View Answer
Explanation: In electrodeposition, depending on the processing conditions, the final product may be obtained in 3 different forms. The deposit may be: (1) a hard-brittle layer which is later milled to obtain powder; (2) a soft, spongy substance which is loosely adherent and easily removed by scrubbing; (3) a direct powder deposit from the electrolyte which collects at the bottom of the cell.
2. Ta powder is produced commercially by electrolysis of ______ dissolved in a bath of K2TaF7, KCl, and KF.
a) Tantalum oxide
b) Tantalum sulphate
c) Tantalum chloride
d) Tantalum fluoride
View Answer
Explanation: Ta powder is produced commercially by electrolysis of tantalum oxide dissolved in a bath of K2TaF7, KCl, and KF. The addition of tantalum oxide is made continuous during the reaction. Leaching of Ta removes trapped electrolyte but the evolution of H2 at this stage causes embrittlement of the metal thus allowing it to crushed to the required size and finally softened by heat treatment under vacuum.
3. Which of the following factors does not promote powdery deposits?
a) Low temperature
b) High-current-density
c) High-metal concentration
d) High viscosity
View Answer
Explanation: The factors which promote powdery deposits are: low temperature, high-current density, high-metal concentration, high viscosity, pH of the bath (high acidity), and circulation of electrolyte to avoid or suppress convection.
4. Which of the following metal powder is generally not prepared by fused salt electrolysis?
a) Copper
b) Tantalum
c) Vanadium
d) Thorium
View Answer
Explanation: Copper is produced by electro-deposition from the aqueous solution where metals of high purity are precipitated from the aqueous solutions on the cathode of the electrolytic cell. Fused salt electrolysis has been used for the production of tantalum, vanadium and thorium powders.
5. Which of the following is not a characteristic of the electrolytic powder deposit?
a) Low apparent density
b) High apparent density
c) Crystalline
d) Dendritic shape
View Answer
Explanation: The electrolytic powders deposited are generally crystalline and are characterized by their dendritic or fern-like shape of low apparent density and flow rate, favorable for pressing due to the tendency of the individual particles to readily interlock.
6. _______ particle shape is obtained for powders produced from hard, brittle deposits.
a) Dendritic
b) Acicular
c) Angular
d) Irregular
View Answer
Explanation: Angular or needle-like shape is obtained in the case of powders produced from hard, brittle deposits, and the particle size is the function of mechanical methods employed for subsequent comminution.
7. _____ is generally added to the iron sulphate or chloride bath to favor high yield of iron powder.
a) NH4Cl
b) KCl
c) K2SO4
d) NH3
View Answer
Explanation: Iron powder id produced commercially by the electrolysis of sulphate or chloride bath. Addition of NH4Cl increases the conductivity and reduces oxidation of the product. Chloride bath has been preferred over the sulphate bath because the latter results in the precipitation of Sulphur in the deposit and tend to cause anode passivity.
8. _____ is used to calculate theoretical weight deposited on the electrode.
a) Faraday’s law
b) Hess law
c) De-Braggs law
d) Stoke’s law
View Answer
Explanation: Faraday’s law is used to calculate the theoretical weight of powder deposited on the electrode. Faraday’s law is given by Wth=I t A/F Nc where, I is current in amperes, t is time in seconds, A is atomic weight of metal in grams/mole, F is Faradays constant=96500 C and Nc is the valency.
9. Time and current are the two important variables which affect the amount of powder deposited on the electrode during electrodeposition of copper.
a) True
b) False
View Answer
Explanation: Time and current are the two important variables which affect the amount of powder deposited on the electrode during electrodeposition of copper. As time increases the amount of copper powder deposited on the cathode increases. Similarly, as the current increases, bath conductivity increase and thus the amount of powder deposited also increases.
10. What is the current density when current of 1.5A flows through the electrolytic cell with the cathode plate having an effective length of 46mm, breadth 38mm and negligible thickness?
a) 413.7 A/m2
b) 377.9 A/m2
c) 519.3 A/m2
d) 403.6 A/m2
View Answer
Explanation: Current density = current/ effective area of plate ——–(1)
Here, current=1.5A and effective area of plate=2lw+2lt+wt
Given, l=46mm, b=38mm and t=1mm; effective area of plate=36.26x 10-4 m2
Substituting the values in equation (1), we get Current density=1.5 A/36.26 x 10-4 m2=413.7 A/m2.
11. What is the current efficiency when actual weight deposited is 0.036g and theoretical weight deposited is 0.049g?
a) 73.46%
b) 136.11%
c) 73.12%
d) 88.88%
View Answer
Explanation: Current efficiency = (actual weight deposited / theoretical weight deposited) x 100——–(1)
Substituting the values in equation (1), we get
Current efficiency=\(\frac{0.036}{0.049}\) x 100=73.46%.
12. What is the theoretical amount of copper powder deposited on the cathode plate when a current of 1A passes through the electrolytic tank for 5 minutes?
a) 0.098g
b) 0.0016g
c) 0.190g
d) 0.980g
View Answer
Explanation: Faraday’s law is used to calculate the theoretical weight of powder deposited on the electrode.
Faraday’s law is given by:
Wth=I t A/F Nc————(1)
where, I the current in amperes, t is time in seconds, A is atomic weight of metal in grams/mole, F is Faradays constant=96500 C and Nc is the valency.
Substituting the values in equation (1), we get,
Wth=\(\frac{1 \times (5 \times 60) \times 63.5}{96500 \times 2}\)=0.098g.
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