Powder Processing Shape Forming

Question 1

Binder

Answer 1

added to help keep powder together

Question 2

Plasticizer

Answer 2

added to make powder pliable, improves the rheological properties

Question 3

Green or Green Body

Answer 3

a prefired ceramic compact

Question 4

Slip

Answer 4

ceramic powders suspended in liquid, thinner than slurry

Question 5

A _____________ partice size distribution is best to achieve high density.

Answer 5

multimodal

Question 6

You need some titanium carbide powders and come accross the powder below in the Sigma Aldrich website.

307807 Sigma-Aldrich

Titanium(IV) carbide
-325 mesh, 98%

What size of particles would you expect to receive?

Answer 6

particle size less than 45 microns

Question 7

Suppose you need to filter out all particles that are between 75 - 150 microns. Which two sieves (Tyler) would you use?

Answer 7

100

200

Question 8

What are the shape forming techniques applicable to ceramics

Answer 8

casting
pressing
injection molding

Question 9

Casting in ceramics has to be performed at extremely high temperatures to allow ceramic material to melt and properly flow into the molds

Answer 9

False

Question 10

Slurry

Answer 10

Suspension of ceramic particles in liquid

Question 11

Raw materials selection criteria

Answer 11

Depend on desired properties for final product including:

• Purity
• Particle size
• Reactivity
• Polymorphic form

Question 12

Purity

Answer 12

• Higher-temperature properties (strength, stress rupture life, oxidation
resistance).

• Effect of the impurity is dependent on the chemistry of both the matrix
and the impurity, distribution of the impurity, and service conditions of
the component (time, stress, temperature, environment).

• Inclusions act as flaws (concentrated stresses and decrease of tensile
strength).

Question 13

Particle Size

Answer 13

• Goal is to achieve maximum packing and uniformity.
• In some ceramics porosity usually > than 35%, or even > 50%.
• Low porosity and fine grain size results in high strength.

• High porosity results in low thermal conductivity and high
thermal shock.

Question 14

Reactivity

Answer 14

• Driving force for densification is the change in surface free
energy.

• Very small particles with high surface area have high surface
free energy and bond together.

• Particle size distribution and reactivity are also important to
determine time and temperature to achieve sintering.

Question 15

Screening/Sieving

Answer 15

• To separate particles into size ranges.

• Screen sizes are classified according to
number of openings per linear inch into mesh
sizes.

• Can be done in air (dry powder); Limited to 325 or 400 mesh; anything finer will agglomerate and lead to clogging of sieve.
• Can be done in suspension or dilute slurries “wet screening”; Limited to 500 mesh (25 𝜇𝑚)

Question 16

Air Classification

Answer 16

• Used to separate coarse and fine fractions from dry ceramics.

• Separation of horizontal
centrifugal force and vertical air currents.

• Can separate between 40 and
400 mesh at rates exceeding 400
tons/hour

Question 17

What are the two main goals of chemical sizing?

Answer 17

Reduce contamination

More control of the particle size distribution

Question 18

What are is the role of binder additives?

Answer 18

provide strength to the “green” body to survive

processes between shaping and sintering (polymers).

Question 19

What are is the role of lubricant additives?

Answer 19

decrease particle-particle and particle-tool

friction.

Question 20

What are is the role of sintering aides additives?

Answer 20

activate densification.

Question 21

What are is the role of deflocculates, wetting agents and plasticizer additives?

Answer 21

yield rheological (flow) properties necessary by promoting dispersion
of fine particles in a liquid.

Question 22

What is the goal of Spray-drying?

Answer 22

Goal is to achieve uniform, free-flowing

powder

Question 23

What is the goal of Granulation?

Answer 23

Goal is to achieve better flow properties.