Review Questions 7.1 What is a ceramic is.
Answer. A ceramic is an inorganic, nonmetallic compound, usually formed into useful products by a heating process.
7.2 What are the four most common elements in the earth's crust?
Answer. Oxygen, silicon, aluminum, and iron.
7.3 What is the difference between the traditional ceramics and the new ceramics?
Answer. Traditional ceramics are based primarily on clay products (e.g., pottery, bricks) while new ceramics are more recently developed ceramics which are generally simpler in chemical
composition (e.g., oxides, carbides).
7.4 What is the feature that distinguishes glass from the traditional and new ceramics?
Answer. Glass is noncrystalline (amorphous), while most other ceramics assume a crystalline structure.
7.5 Why are graphite and diamond not classified as ceramics?
Answer. Because they are not compounds; they are alternative forms of the element carbon.
7.6 What are the general mechanical properties of ceramic materials?
Answer. Usually high hardness, brittle, no ductility.
7.7 What are the general physical properties of ceramic materials?
Answer. Usually electrical and thermal insulators, medium density (typically below the density of metals), high melting temperatures, thermal expansion usually less than metals.
7.8 What type of atomic bonding characterizes the ceramics?
Answer. Covalent and ionic bonding.
7.9 What do bauxite and corundum have in common?
Answer. They are both minerals of alumina.
7.10 What is clay, used in making ceramic products?
Answer. Clay most commonly consists of hydrous aluminum silicate, the usually kaolinite (Al2(Si2O5)(OH)4).
7.11 What is glazing, as applied to ceramics?
Answer. Glazing involves the application of a surface coating of oxides such as alumina and silica, usually to a porous ceramic product such as earthenware, to make the product more impervious to moisture and more attractive.
7.12 What does the term refractory mean?
Answer. Refractories are heat resistant ceramic materials. The term is sometimes also applied to metals that are heat resistant.
7.13 What are some of the principal applications of the cemented carbides, such as WC-Co?
Answer. Important applications of WC-Co include: cutting tool inserts, drawing dies, rock drilling bits, dies for powder metallurgy, and other applications where hardness is a critical factor.
7.14 What is one of the important applications of titanium nitride, as mentioned in the text?
Answer. As a thin coating on cutting tools to prolong tool life.
7.15 What elements comprise the ceramic material Sialon?
Answer. Silicon, aluminum, oxygen, and nitrogen.
7.16 Define glass.
Answer. Glass is an inorganic, nonmetallic material which cools to a rigid solid without crystallization.
7.17 What is the primary mineral in glass products?
Answer. Silica, or silicon dioxide (SiO2).
7.18 What are some of the functions of the ingredients that are added to glass in addition to silica.
Answer. The functions of the additional ingredients include: (1) acting as flux (promoting fusion) during heating; (2) increasing fluidity in the molten glass during processing; (3) retarding
devitrification - the tendency to crystallize from the glassy state; (4) reducing thermal expansion in the final product; (5) increasing the chemical resistance against attack by acids, basic substances, or water; (6) adding color to the glass; and (7) altering the index of refraction for optics applications (e.g., lenses).
7.19 What does the term devitrification mean?
Answer. Devitrification is the transformation from the glassy state into a polycrystalline state.
7.20 What is graphite?
Answer. Graphite is carbon in the form of hexagonal crystalline layers, in which covalent bonding exists between atoms in the layers, and the (parallel) layers are bonded by van der Waals forces, thus leading to highly anisotropic properties.
Multiple Choice Quiz
There are a total of 18 correct answers in the following multiple choice questions (some questions have multiple answers that are correct). To attain a perfect score on the quiz, all correct answers must be given, since each correct answer is worth 1 point. For each question, each omitted answer or wrong answer reduces the score by 1 point, and each additional answer beyond the number of answers required reduces the score by 1 point. Percentage score on the quiz is based on the total number of correct answers.
7.1 Which one of the following is the most common element in the earth's crust? (a) aluminum, (b) calcium, (c) iron, (d) oxygen, or (e) silicon.
Answer. (d)
7.2 Glass products are based primarily on which one of the following minerals? (a) alumina, (b) corundum, (c) feldspar, (d) kaolinite, or (e) silica.
Answer. (e)
7.3 Which of the following contains significant amounts of aluminum oxide (more than one)? (a) alumina, (b) bauxite, (c) corundum, (d) quartz, or (e) sandstone.
Answer. (a), (b), and (c).
7.4 Which of the following ceramics are commonly used as abrasives in grinding wheels (two best answers)? (a) aluminum oxide, (b) calcium oxide, (c) carbon monoxide, (d) silicon carbide, or (e) silicon dioxide.
Answer. (a) and (d)
7.5 Which one of the following is generally the most porous of the clay-based pottery ware? (a) china, (b) earthenware, (c) porcelain, or (d) stoneware.
Answer. (b)
7.6 Which of the following is fired at the highest temperatures? (a) china, (b) earthenware, (c) porcelain, or (d) stoneware.
Answer. (c)
7.7 Which one of the following comes closest to expressing the chemical composition of clay? (a) Al2O3, (b) Al2(Si2O5)(OH)4, (c) 3AL2O3-2SiO2, (d) MgO, or (e) SiO2.
Answer. (b)
7.8 Glass ceramics are polycrystalline ceramic structures that have been transformed into the glassy state: (a) true, or (b) false.
Answer. (b) It's reversed in the statement. Glass ceramics are glasses that have been transformed into a mostly crystalline form through heat treatment.
7.9 Which one of the following materials is closest to diamond in hardness? (a) aluminum oxide, (b) carbon dioxide, (c) cubic boron nitride, (d) silicon dioxide, or (e) tungsten carbide.
Answer. (c)
7.10 Which of the following best characterizes the structure of glass-ceramics? (a) 95% polycrystalline, (b) 95% vitreous, or (b) 50% polycrystalline.
Answer. (a)
7.11 Properties and characteristics of the glass-ceramics include which of the following (may be more than one)? (a) efficiency in processing, (b) electrical conductor, (c) high thermal expansion, or (d) strong, relative to other ceramics.
Answer. (a) and (d).
7.12 Diamond is the hardest material known: (a) true, or (b) false.
Answer. (a)
7.13 The specific gravity of graphite is closest to which one of the following: (a) 1.0 (b) 2.0, (c) 4.0, (d) 8.0, or (e) 16.0.
Answer. (b)
7.14 Synthetic diamonds date to: (a) ancient times, (b) 1800s, (c) 1950s, or (d) 1980.
Answer. (c)