Ceramics and Glasses Flashcards
What are general mechanical properties of ceramics?
Despite having a low toughness, ceramics have high hardness and excellent high temperature and corrosion resistance and are thermal and electrical insulators.
Why is the stress-strain behavior of brittle ceramics not usually ascertained by a tensile test?
- It is difficult to prepare and test specimens having the required geometry
- It is difficult to grip brittle materials without fracturing them
- Ceramics fail after only about 0.1% strain, which necessitates that tensile specimens be perfectly aligned to avoid the presence of bending stresses, which are not easily calculated
What is a suitable transverse bending test for ceramics?
A three or four point loading technique.
What does the three point bending point measure?
The stress at fracture is known as Flexural Strength (Modulus of rupture, fracture strength, bend strength)
Why does flexural strength depend on specimen size?
With increasing specimen volume there is an increase in the probability of the existence of a crack producing flaw.
What are the six types of ceramic?
Glasses Clay Products Refractories Abrasives Cements Advanced Ceramics
What is crystallization?
The process of transforming non-crystalline inorganic glasses to a crystalline state by a high temperature treatment. These are known as glass ceramics.
What are characteristics of glass ceramics
Glass-ceramic materials have been designed to have the following characteristics: relatively high mechanical strengths; low coefficients of thermal expansion (to avoid thermal shock); relatively high temperature capabilities; good dielectric properties (for electronic packaging applications); and good biological compatibility.
What are the two main types of clay products, give examples.
Structural Clay Products, bricks and tiles
Whitewares, porcelain and china
What are the desirable properties of refractories?
Capacity to withstand high temperatures and the capacity to remain unreactive and inert when exposed to severe environments. In addition, the ability to provide thermal insulation is often an important consideration
Name the four main categories of refractories
Fire Clay
Silica
Basic
Special
What are typical applications for refractories?
Furnace linings for metal refining, glass manufacturing, metallurgical heat treatment, and power generation
What are mechanical properties of abrasives?
They are very hard particles that do not easily fracture
What are common uses of abrasives.
Abrasives are used in several forms-bonded to grinding wheels, as coated abrasives, and as loose grains. Sandpaper or grind wheels are used for grounding and polishing.
Give an overview of cement.
The most common type is Portland Cement, it is produced by mixing clay and lime bearing materials and heating to up to 1400C in a process called Calcination. The resulting Clinker is ground to a powder which is a hydraulic cement. When mixed with water and left to set it goes solid.
