Chapter 8

what is static fatigue?

when subject to static tensile load over time these materials suddenly fail. this occurs when water vapor is present

describe the differences between the properties of glasses and those of ceramics.

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what is the significance of al2o3 in this chapter?

Alumina is the most widely used oxide ceramic, it is mixed with other oxides. it has high hardness and moderate strength.

what is a buckyball?

Buckyball, also known as Fullerenes are ball shaped carbon molecules produced from soot and are much like solid lubricants. They become superconductors when mixed with metals.

how are ceramics made tougher?

Ceramics are hard and brittle which make their toughness to impact low. What adds even more to its low toughness is the amount of porosity in the ceramics. these two properties, toughness and porosity are directly related. Starting at the raw materials, the processing method must be altered to reduce porosity. Blending ceramics with other compounds would also make it tougher.

Compare the major differences between the properties of ceramics and those of metals and plastics

Ceramics are hard and brittle, they have low thermal expansion but bad thermal and electrical conductivity, good corrosion resistance strong in compression but not in tension. they have low toughness and density Ceramics are brittle, except at elevated temperatures, high strength and hardness, high modulus of elasticity. low toughness and density when compared to metals. smaller conductor of heat and electricity.

list the major types of glasses and their application?

Soda- lime glass formed using soda carbonate and glass used for window panes, glass bottles, and bakeware lead-alkali Glass formed using lead oxide which has a higher refractive index. which is why it is used in decorative glass application,such as lead crystal ware. borosilicate glass made of boron oxide and silica. has a very low coefficient of thermal expansion. used in labs and cooking glass. Aluminosilicates contains aluminum and silicon used in high impact applications. Silica glass (96% silica) used in high temperature applications.

what is the difference between a carbide and a nitride

carbides are formed wit carbon in their molecular structure while nitrides are formed with nitrogen as their molecular structure

what do the following materials consist of ?a) carbides b) cermets c) sialon

carbides consist of tungsten and titanium nitrides combine with boron, titanium, silicone sailon consist of silicone nitride aluminum oxide, titanium carbide, and yttrium oxide

Explain why ceramics are weaker in tension than in compression

ceramics are very sensitive to cracks, impurities and porosity making them weaker in tension than in compression

explain why the mechanical properties of ceramics are generally better than those of metals

ceramics have very high strength and hardness at elevated temperatures, a high elastic modulus, and low density. they have very high compressible strength. in comparison to metals these properties are better because ceramics have a higher strength to weight ratio that some metals

ceramics are hard and strong in compression and shear. why, then, are they not used as nails or other fasteners?

ceramics have very low impact resistance, the are also brittle and susceptible to cracks, ceramics do not keep their strength after deformation,

what properties are important in making heat resistant ceramics for use on oven tops? why?

ceramics used for oven tops must be chemically resistant to cleaners, acids, and food. the must have a low thermal expansion coefficient. they must also be resistant to abrasives in order to maintain their appearance. of course the must also have a high melting point, high impact resistance

what is glass? why is it called supercooled materials?

glass is an amorphous solid with the structure of a liquid that was cooled to fast to create a crystalline structure.

what is the difference between the structure of graphite and that of diamond? is it important? Explain.

graphite has a dense layered crystalline structure, these layers are stacked on top of each other making them easy to slide across each other. this gives graphite the ability to be a great lubricant diamond on the other had has a very unique crystalline structure that is very tightly bonded, making it a very good abrasive

describe the major use of graphite

graphite is used as a solid lubricant due to is low frictional properties. these properties are only low when air and moisture is present. it is also chemical resistant so it is used to filter corrosive materials

list the major types of ceramics that are useful in engineering applications

industrial ceramics are known as engineering ceramics they are used as turbines,automotive, and aerospace components, heat exchangers, semi-conductors, seals, prosthetics; cutting tools

what is porcelain?

it is a white ceramic made of kaolin, quartz, and feldspar; largest use is in appliances and sanitary ware

how are alumina ceramics produced?

it is obtained by the fusion of molten al2o3 ore, iron fillings and coke in a electric furnace. it is then crushed

is diamond a ceramic? why or why not

no. a diamond is a form of carbon that has very unique properties.

how does porosity affect the mechanical properties of ceramics, and why does it do so?

porosity has detrimental effects on ceramics it can cause a decrease in strength, thermal and electrical conductivity, it increases the risk of cracks causing stress in unwanted areas. these instances occur because of porosity's effect on the bonds in the ceramics causing air to and gas to collect in pockets inside the ceramic. this is also the reason for the decrease in thermal and electrical conductivity

Explain why the electrical and thermal conductivity of ceramics decreases with increasing porosity.

porosity is the formation of pockets of air or gas in the ceramic. gasses are know insulators, meaning that as the porosity increases the electrical and thermal conductivity will decrease equally

what features of partially stabilized zirconia differentiate it from other ceramics?

psz has only a third of the thermal conductivity that ceramics have Partially stabilized Zirconia has high strength and toughness, better reliability in performance than does zirconia.

what material are suitable for use as a coffee cup? explain.

the ideal coffee cup will have a low thermal conductivity that will insulate the temperature of the liquid inside the cup, keeping it warm on the inside but cool to the touch on the outside. the material used for the coffee cup must also be light. Other ideal properties include impact, thermal shock, chemical and abrasive resistance. Possible materials include plastic, polymers, metals with insulated layers, ceramics and porcelain.

what are the major uses of diamonds?

the use of diamonds in engineering applications is mostly cutting tools or abrasive grinders, coating for cutting tools

what is devitrification?

this is re-crystallization in terms of ceramics. a process that occurs when glass ceramics are created. these products are are first shaped then heat treated