Ceramics, glasses, and glass ceramics: Basic Principles

Question 1

Bioceramics defintion

Answer 1

Broad range of materials that are inorganic, non-metallic compounds between METALLIC and NON-METALLIC ELEMENTS

Question 2

Interatomic bonds

Answer 2

• Between elements
• either totally ionic
• or predominantly ionic with covalent

Question 3

Element arrangement

Answer 3

• Crystal structures
• Ionic interactions between cations and anions
• dependant on size and ionic radii of cations and anions

Question 4

Sintering

Answer 4

• The process of densification closes those pores in a process commonly known as sintering.
• A thermal process of converting loose fine particles into a solid coherent mass by heat and/or pressure without fully melting the particles to the point of melting.

Question 5

Solid-state sintering

Answer 5

• Atoms move to fill up the pores and channels between the grains of the powder compact, causing the grains of crystals to bond together more tightly, thereby leading to greatly improved density, strength, and fatigue resistance for the sintered ceramic object.
• The rate of densification for solid-state sintering is typically slower than that for liquid-phase sintering, because material transport is slower in a solid state than in a liquid state.
• However, a higher degree of purity and uniformity in fine-grained microstructures can be obtained via the solid-state sintering process, making it a common process for forming many bioceramics.

Question 6

Liquid-phase sintering

Answer 6

• Liquid penetrates between the grains and fills the pores, it will draw the grains together by capillary attraction, thereby decreasing the volume of the powdered compact (densification).
• The microstructure resulting from this “liquid-phase sintering” will consist of small grains from the original powder compact surrounded by a liquid phase.
• As the compact is cooled, the liquid phase will crystallize into a fine-grained matrix surrounding the original grains.

Question 7

Alumina

Answer 7

• Aluminium Oxide
• Used in the articulating surfaces of total joint prostheses because of its excellent corrosion resistance, high wear resistance, and high strength.
• The strength, fatigue resistance, and fracture toughness of polycrystalline α-Al2O3 ceramics are functions of grain size and percentage of sintering aid.
• The use of polished alumina as part of the articulating joint was motivated mainly by its exceptionally low coefficient of friction and low wear rates.

Question 8

Bioactive ceramics and glasses

Answer 8

• Designed to elicit a bio- logical response that supports tissue repair, specifically bone formation and integration.
• Not simply dictated by material type, instead physical form including dense or porous, low or high surface area, among others.

Question 9

Calcium Phosphate

Answer 9

• Most widely used bioactive bioceramics
• Used to coat metallic and polymeric implants to provide a bioactive surface on a bulk material that is biologically inert.

Question 10

Why a 3-point bending test can replace a tensile test for ceramics to gauge stress-strain behaviour.

Answer 10

• As the sample bends, the top surface is placed under compression and the bottom surface under tension.
• Compressive strength (for ceramics) is approximately an order of magnitude greater than tensile.