Manu Final Exam (CH 8)

8.5 What is glass? Why is it called a supercooled material?

5. Glass is amorphous solid whose molecules are in a structure similar to that of a liquid. It has a wide variety of industrial and domestic uses ranging from protective coating to lenses and other uses requiring its transparency, such as is windows and frames. Most glass contains silicate; however, this is not a requirement in many modern applications. o Super cooling indicates that a material has been cooled at a rate fast enough to prevent crystals from forming. Glass is formed using a super cooling process.

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

1. Cermaics, for instance, represent compounds that are a combination of both metallic and nonmetallic elements. o Ceramics have characteristics different from those of most metals. They are brittle, except at elevated temperature, where their strength and hardness are relatively high. Additionally, they have a high elastic modulus. Also when compared to metals, ceramics have low toughness and density characteristics, expand much less when exposed to high temperatures and conduct smaller amounts of heat and electricity.

8.10 How are alumina ceramics produced?

10. Although Aluminum Oxide can be found naturally, it is now much more common for it to be engineered, or produced synthetically. This process allows for quality assurance and control in the formation of the aluminum oxide and greatly reduces possibility of manufactured flaw, defect, and catarophic failure once applied. o In order to manufacture aluminum oxide, molten bauxite, the principal sound of aluminum, iron filing, and coke are fused in electric furnace. Once the aluminum oxide is synthesized, it can be molded into parts via cold pressing and sintering.

8.11 What features of PSZ differentiate it from other ceramics?

11. Partially stabilized zirconia has different features compared to other ceramics. It has higher strength, toughness and better reliability in performance. Some other features are good resistance to thermal shock, wear, corrosion and have low thermal conductivity.

8.12 What are buckyballs?

12. Buckyball is a common name for the shape of a Buckminster-fullerene molecule, similar in shape to that of the geodesic domes described by Buckminster fuller. o These Buckminsterfullerene molecules are part of the group of molecules called fullerenes, a molecule comprised entirely of carbon atoms. They are produced from soot and exhibit properties similar to solid lubricant. In addition, Fullerenes will become superconductive when mixed with appropriate metals.

8.13 List the major use of diamond.

13. The properties diamond exhibit have made them excellent in the production of various tools and materials. As either a single crystal or as part of a polycrystalline structure, diamonds can be used as a cutting surface, being applied to many industrial cutting tools. o In addition, due to its hardness, diamonds can be used as either the abrasive or a dressing for grind wheels. The former application allows for the grinding of hard materials. While the latter allows for the sharpening of the grinding material.

8.2 List the major types of ceramics that are useful in engineering applications. o

2. The first is called industrial, engineering, high tech, or fine ceramics. This type of ceramics is often used in the development of turbines, automotive parts, or aerospace components. o The second major type of ceramics using in engineering applications is heat exchangers. These ceramics are also used in a variety of applications, from semi conductors and seals to prosthetics and cutting tools.

8.3 What do the following materials typically consist of (a) carbides, (b) cermets, and (c) sialon?

3. Typical members of the carbide family combine carbon with tungsten, titanium, and silicon, forming tungsten carbide, Titanium carbide, and silicon carbide, respectively. o Cermet family include oxides, containing oxygen, carbides, as described abive, and nitrides, which contains nitrogen. These cermets are often used in high temperature application. o Materials combine silicon nitride with various other compounds. Members include aluminum oxide, yttrium oxide, and titanium carbide.

What is porcelain?

4. Is a particular group of ceramics normally comprised of kaolin, a form of clay, quartz and feldspar. o Used primarily in consumer goods, including appliances and other household good such as tableware and baking dishes. Porcelain is also widely used for artistic applications as in porcelain figurines and dolls.

8.6 What is Devitrification?

6. Vitrification is the process of super cooling a liquid into a glass like state, preventing the formation of crystals in the structure. Devitrification is the opposite of this process, introducing crystallization into an otherwise crystal-free material. Devitrification is used in the formation of glass ceramics. The process of Crystallization within the glass creates a material stronger than normal, amorphous glass.

8.7 List the major types of glasses and their applications.

7. Most common glass is Soda-Lime Glass, Formed from soda carbonate, line, and other materials. Most common application are in window panes, glass bottles, and bakeware. o Lead alkali Glass, formed using lead oxide. It is normally regarded as more attractive than common, sodalime glass due to its higher refractive index. Mostly used in decorative glass applications, Such as lead crystal ware. o Borosilicate glass is formed using silica and boron oxide. Properties include a very low coefficient of thermal expansion, enhancing its use in applications susceptible to high level of thermal shock. Found in glass cookware. o Alumino-Silicate Glass contains aluminum and silicon. It is commonly used in glass requiring high impact resistance, such as the windshields of helicopters and high speed trains. Most recently, in has been used as a screen protective layer in smart phones, such as Apple's iPhones.

8.8 What is static fatigue? What is its significance?

8. Ceramic undergoe fatigue failure while under cyclic loading. Unlike in a vacuum or in a dry air, in environments containing water vapor, ceramics also undergoes static fatigue. o Static fatigue is a process wherein ceramic subjected to static tensile loads over period of time will suddenly fail. This type of fatigue has been linked to a similar process as stress-corosion crackling in metals.

8.14 what is a carbon nanotube? Explain why they are not as prevalent as other forms of carbon?

8.14 A carbon nanotube is an allotrope of carbon. It is named because of its cylindrical configuration, the shape of tube like structure while maintaining a diameter on the order of magnitude of a few nanometers. o Except in a few potential natural locations, such as within detected astronomical nebulae, carbon nanotube have been found to exist naturally. This means that any carbon nanotubes used in manufacturing or within a particular design specification must be synthesized.

8.15 Explain why ceramics are weaker in tension than in compression.

8.15 Ceramic materials are hard and brittle, which makes their toughness low. When the bonds between particles are placed in tension, they are weak and yield easily. The natural porosity of ceramic also reduces the number of bonds available between particles and creates stress concentration at the voids. o In compression, the particles bonds do not have to work to hold the material together, and the particles are not subjected to the same type of crack propagation or stress risers as they are in tension. Ceramics behave very similarly to concrete in this regard.

8.31 Perhaps an internet search and determine the chemistry of glass used for (a) fiber-optics (b) communication lines, (b) crystal glass used for (c) high strength glass fibers. o

8.31 Glass used in fiber optic communications is made from ultra pure silica o Crystal glassware is primarily silica, but also incorporates major constituents of boron, magnesium, and lead, with minor constituents of zircon and aluminum. o High strength glass fiber is composed of magnesium alumino- silicate.

8.32 Investigate and list the ceramics used for high temperature superconductor applications.

8.32 Most of the recent development in superconductive ceramics has been centered around two oxides of bismuth, label as Bi- 2212 and Bi- 2223. These two ceramics are being used widely in the defense and aerospace industries. o Scientists are discovering that by making the ceramics as multifilament strips, their electrical conductivity and consistency is improved.

8.9 Describe the major uses of graphite.

9. Graphite is an allotrope of carbon. Along with carbon nano tubes, graphite fibers are used to create fiber-reinforced plastics. These plastics are often found in high stress automotive applications, such as those found in racing. It's significantly higher tensile-strength also finds its use strengthening other materials, such as concrete, masonry, and steel. o Graphite also often used in other composite materials, such as materials used in radar-absorption applications.

8.27 Aluminum oxide and PSZ are described as white in appearance. Can they be colored? If so how would you accomplish this?

Both aluminum oxide and partially- stabilized zirconia can be made in a wide range of color by introducing impurities into the ceramic mix which develop into color (chromium, sodium, and selenium are some examples). Also, since the materials are porous, they will accept surface strains, paints, enameling, and pigments.

8.30 Ceramics are hard and strong in both compression and shear. Why, then, and are they not used as nails or other fasteners? Explain. o

Ceramic has very low resistance to impact, which means it could not withstand the driving force to set it as a nail or staples. o For other fasteners, like bolts, screws, and pins, the proof strength of the material is an important factor to appropriately size and design the joint. Ceramics have how tensile strength with a wide range as well, making them unreliable and unpredictable as tension elements.

8.28 Why does the strength of a ceramic part depend on its size?

Ceramic strength is a function of probabilities. The strength of a ceramic is determined by how well it resists cracking. Cracks require imperfections or flaws to exist in the material to start the propagation. Since smaller parts have smaller volumes, there is a smaller possibility of a crack or a flaw existing within that volume.

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

Ceramic surface tops for kitchen ranges must be able to withstand chemical attack from cleaners, and weak acids on foods. Ceramic surfaces for stoves must be abrasion resistant to maintain their appearance. o Also, ceramic tops for stoves must be impact resistant to remain intact if a pot or lid is dropped on the surface. Ceramic tops for overs must have good heat transfer coefficient and low coefficient of thermal expansion.

8.21 explain how ceramics can be made tougher.

Ceramics toughness can be improved by starting with high purity raw materials. Altering the processing techniques to reduce porosity, and by adding internal reinforcement to the ceramic structure. o The addition of blending of several compounds can produce ceramics with tougher second phase. o Also introducing micro-cracks into the crystalline structure of the ceramics can prevent crack propagation when it begins, this making the ceramic tougher.

8.16 What are the advantages of cermets? Suggest applications in addition to those given in this chapter.

Cermets have already found a home in the audio industry as new, cooler amplifier designs. Their formulation makes them great candidates for use as travelling grates in power boilers, for internal combustion engine parts like intake manifolds, pistons, and cylinder sleeves, and as insulation lining in fluidized bed boilers and high temperature gas cyclone particle separators.

8.24 A large variety of glasses is now available. Why is this so?

Glass is available in such a large variety because of the many different applications for glass. High purity glass for fiber data transmission is essential. o Impact resistant glass is necessary in a variety military vehicle, armored cars and trucks, and VIP transportation like the president and the pope. Likewise, bulletproof or impact resistant glass is become increasing in urban shopping centers, jewelry stores, convenience stores, and banks.

8.25 What is the difference between the structure of graphite and that of diamond? Is it important? Explain.

Graphite exists as many crystalline layers of carbon atoms closely packed together. These layers easily slide across each other, making graphite an excellent lubricant. o Diamond had a crystalline structure of covalently bonded carbon atoms, which resists slipping. This makes diamond an excellent abrasive.

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

Porosity appears as voids and spaces between the particles in a ceramic. These pockets are normally filled with air or other gas. Since air is a very good insulator, and the void volume, i.e. the air trapped within the part increases, its ability to transmit heat and electricity decrease.

8.22 list and describe situations in which static fatigue can be important.

Static fatigue can exist anywhere there is a component subject to a load and water vapor is present. o Large vortex cooling towers, siliar to those used in the power generation industry, can see the lower layers of blocks crumble under the weight of over head layers and the high humidity atmosphere. o Underground piping for water or sewage can fatigue statically because of the overhead force of earth and structures combined with the moisture in the ground. o Demisting towers, used in chemical plains to separate particles from gasses, can see their tray, baffles, and supports fail by static fatigue

8.19 Describe the reasons that have encouraged the development of synthetic diamond.

Synthetic diamonds are not subjected to the production quotas and pricing whims of the few diamond owners in the world, which means they can be produced in large quantities economically. o Synthetic diamond is not susceptible to the same impurities present in natural diamond, which makes it an overall more reliable products. o The widespread possible uses for diamond as a cutting material in the energy, petro-chemical, mining and manufacturing industries in grinders, drill bits, cutter heads, and band cutters means that there are plenty of available opportunities for diamond to be used if it is available. The existing use can also be expanded if large, industrial- grade natural diamonds are not accessible.

8.20 Explain why the mechanical properties of ceramics generally differ from those of metals.

The crystalline structure of metal is fairly simple, and the bonding characteristics between atoms in those matrices are fairly simple. Ceramics on the other hand has very complex crystalline geometries, which makes it less susceptible to slip. o Metal rely on metallic bonding for strength, ceramics rely on ionic bonding for strength. o The thermal and electrical conductivity in metal is high. While in ceramics it is very low due to the porosity present in the part. This porosity also makes ceramic very attractive as a high temperature and high voltage insulator.

8.26 List and explain materials that are suitable for use as a coffee cup.

The ideal coffee cup will have a low thermal conductivity to insulate the coffee and keep it warm while being cooled to the touch on the outside. It must also be made of a material that can be repeatedly picked, which means it must be light. It must be impact, chemical, abrasion, and thermal shock resistant. o Possible materials include polymers, plastic, metal with insulated layers between, ceramics and porcelains.

8.29 in old castles and churches in Europe, the glass windows display pronounced ripples and are thicker at the bottom than the top. Explain.

o Silica glass does not exist as a solid merely as a super cooled liquid. Thus, like any flowable material, it is subjected to creep due to gravity. Glass made centuries ago have been subjected to this gravity-induced creep since it was installed.