# Powder Metallurgy Questions and Answers – Particle Characterisation, Particle Shape and Specific Area

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This set of Powder Metallurgy online quiz focuses on “Particle Characterisation, Particle Shape and Specific Area”.

1. Which of the following concepts are used to differentiate and describe particle shapes?
a) Dimensionality of particle
b) Dimensionality and Surface contour
c) Surface contour of particle
d) Dimensionality and atomic mass

Explanation: Two different concepts used to differentiate and describe particle shapes are based on, (1) the dimensionality of the particle (1D, 2D, 3D), and (2) the surface contour of the particle.

2. Particle shape can be defined as, “the recognized pattern of relationship between points that form the internal surface of the particle.”
a) True
b) False

Explanation: Particle shape can be defined as, “the recognized pattern of relationship between points that form the external surface of the particle.” Particle shape analysis is a fundamental characteristic of powder particles, which influences other parameters like flow rate, apparent density, compressibility, and sinterability.

3. Which of the following criteria can be used for shape characterization?
a) Verbal expression and evaluation of bulk properties
b) Shape factor
c) Verbal expression, shape factor, and evaluation of bulk properties
d) Shape factor, shape generation, verbal expression, and bulk property evaluation

Explanation: Shape characterization falls under 4 different classes. They are, (1) Verbal expression (spherical, elongated, irregular); (2) Use of dimensionless number (shape factor); (3) Shape generation using Fourier analysis, polynomial fitting, matrix mapping; (4) Evaluation of bulk properties.

4. Which method cannot be used to determine the particle shape?
a) Sieve analysis
b) Optical microscopy
c) SEM
d) TEM

Explanation: Particle shape can be determined through various methods like optical microscopy, scanning electron microscope (SEM), transmission electron microscope (TEM), image analyzer. Sieve analysis is used to evaluate particle size distribution.

5. Which of the following particle shape is not produced by the chemical decomposition process of powder manufacture?
a) Acicular
b) Flaky (large and thin plate-like)
c) Rod-like (irregular)
d) Rounded

Explanation: Acicular (needle-like: 1D), rod-like (irregular: 1D), rounded (3D) particle shapes are produced on chemical decomposition process to manufacture powder. Flaky (large and thin plate-like) is possessed by ball-milled aluminum.

6. ______ determines the surface area of powder by measuring the amount of gas adsorbed by a monomolecular layer of the powder.
a) Centrifugal method
b) Gas absorption method
d) Permeability method

Explanation: The gas adsorption method determines the surface area of powder by measuring the amount of gas adsorbed by a monomolecular layer of the powder. Nitrogen is the most commonly used gas. This method can also be used to determine the pore volume and size distribution, for pore diameters ranging from 600Ȧ down to 14Ȧ.

7. _____ measures the resistance to fluid flow through a compacted powder bed to calculate the specific surface of the powder.
a) Permeametry
c) Elutriation Method
d) Sedimentation method

Explanation: Permeametry or permeability method measures the resistance to fluid flow through a compacted powder bed to calculate the specific surface of the powder. The principle involves measuring the pressure drop across the bed of packed powder particles contained in a chamber in relation to the fluid flow. This information is used to determine related properties of the powder such as specific surface area and average particle size.

8. The unit for measuring the specific surface of the powder is _____
a) cm2/gm
b) cm/sec
c) cm3/gm
d) cm/gm2

Explanation: The specific surface of the powder is defined as the total surface area per unit weight (cm2/gm). It depends on the size, shape, density and surface conditions of the particle.

9. Carman’s equation is given by S0= _____
a) $$\frac{\sqrt{(g/k)K\gamma \epsilon^3}}{\sqrt{(1-\epsilon)^2}}$$
b) $$\frac{\sqrt{(g/k)K\gamma \epsilon^2}}{\sqrt{(1-\epsilon)^2}}$$
c) $$\frac{\sqrt{(g/k)K\gamma \epsilon^3}}{\sqrt{(1+\epsilon)^2}}$$
d) $$\frac{\sqrt{(k/g)K\gamma \epsilon^3}}{\sqrt{(1-\epsilon)^2}}$$

Explanation: The relation between surface area and permeability for gases and liquid is given by the Carman’s equation which is as follows: S0=$$\frac{\sqrt{(g/k)K\gamma \epsilon^3}}{\sqrt{(1-\epsilon)^2}}$$ where S0 is the specific surface (cm2/gm), k a proportionality constant with a value of 5, K the permeability constant (cm/sec), γ the kinematic viscosity of the fluid (stokes), ε is the fractional free volume and g the gravitational constant (cm/sec2).

10. The adsorption method used for determining the specific surface makes use of which instrument?
a) Fisher Sub-siever
b) BET apparatus
c) Hall Flowmeter
d) Scott Volumeter

Explanation: The adsorption method used for determining the specific surface makes use of the BET apparatus, named after Brunauer, Emmett, and Teller, who developed this method. The permeability method used for determining the specific surface makes use of the Fisher Sub-siever apparatus and for measuring apparent density we may use either Hall Flowmeter or Scott Volumeter.

11. The shape factor is given by the ratio of surface area to particle size.
a) True
b) False

Explanation: The shape factor is given by the ratio of surface area to particle size or as the ratio of the length of the particle to its breadth. The presence of cracks, fissures, or grain boundaries in the individual particles increases considerably the shape factor.

12. Which of the following characteristics does irregular shaped particles do not possess?
a) Reduced apparent density
b) Good pressing properties
c) Good sintering properties
d) Maximum flow rate