Physical hardness, Table

Equation 16.12 expresses a relation between q and B.This is not a universal relation, but it does apply to the sp-bonded elements of the first four columns of the Periodic Table. Using chemical hardness values given by Parr and Yang (1989), and atomic volumes from Kittel (1996), it has been shown that the bulk moduli of the Group I, II, III, and IV elements are proportional to the chemical hardness density (CH/atomic volume) (Gilman, 1997). The correlation lines pass nearly through the coordinate origins with correlation coefficients, r = 0.999. Thus physical hardness is proportional to chemical hardness (Pearson, 2004). 

The values of H listed in Table 6.1 for the physical hardness of solids raise an interesting question. Should there not be a corresponding number, H for the physical hardness of molecules After all, there are force constants in molecules as well as in solids. Equation (6.13) might serve for a diatomic molecule, if n were simply set equal to one. 

This is true in all the examples in Table 6.7, and appears to be true in general. However, it should be borne in mind that there is no direct proof for the assumption of maximum physical hardness for molecules. 

Silicon carbide is noted for its extreme hardness [182-184], its high abrasive power, high modulus of elasticity (450 GPa), high temperature resistance up to above 1500°C, as well as high resistance to abrasion. The industrial importance of silicon carbide is mainly due to its extreme hardness of 9.5-9.75 on the Mohs scale. Only diamond, cubic boron nitride, and boron carbide are harder. The Knoop microhardness number HK-0.1, that is the hardness measured with a load of 0.1 kp (w0.98N), is 2600 (2000 for aAl203, 3000 for B4C, 4700 for cubic BN, and 7000-8000 for diamond). Silicon carbide is very brittle, and can therefore be crushed comparatively easily in spite of its great hardness. Table 8 summarizes some typical physical properties of the SiC ceramics. 

Kaolin s physical properties (Table 4.4) depend on the calcining temperature as well as on contamination by minerals. Calcination increases the oil absorption and improves the optical brightness, opacity and dielectric properties, together with the water absorption and hardness, but decreases the reinforcing capacity. 

Hundreds of test methods referring to polyolefin properties are actually employed. They consist of both physical (hardness, stiffness, tensile properties, solubility, viscosity, etc.) and chemical (acetone extractable, carbonyl content, etc.) tests, representing the objects of international, national, or industrial standards and specifications. Some of them, elaborated by ASTM Committee D-20, Subcommittee XII, Polyolefin Plastics, are indicated in Table 1. 

These elements form two groups, often called the alkali (Group I) and alkaline earth (Group II) metals. Some of the physical properties usually associated with metals—hardness, high m.p. and b.p.—are noticeably lacking in these metals, but they all have a metallic appearance and are good electrical conductors. Table 6.1 gives some of the physical properties. 

The physical characteristics of current commercial mbber and spandex fibers are summarized ia Table 1. Typical stress—straia curves for elastomeric fibers, hard fibers, and hard fibers with mechanical stretch properties ate compared ia Eigute 1. 

Despite variatioas ia hardness test procedures and the variations ia physical properties of the materials tested, hardness conversions from one test to another are possible (see ASTM E140 and Table 2). This approximate relationship is only consistent within a single-material system, eg, iron, steel, or aluminum. 

Thin films (qv) of lithium metal are opaque to visible light but are transparent to uv radiation. Lithium is the hardest of all the alkaH metals and has a Mohs scale hardness of 0.6. Its ductiHty is about the same as that of lead. Lithium has a bcc crystalline stmcture which is stable from about —195 to — 180°C. Two allotropic transformations exist at low temperatures bcc to fee at — 133°C and bcc to hexagonal close-packed at — 199°C (36). Physical properties of lithium are Hsted ia Table 3. 

Properties. Strontium is a hard white metal having physical properties shown in Table 1. It has four stable isotopes, atomic weights 84, 86, 87, and 88 and one radioactive isotope, strontium-90 [10098-97-2] which is a product of nuclear fission. The most abundant isotope is strontium-88. 

Zirconium is a hard, shiny, ductile metal, similar to stainless steel in appearance. It can be hot-worked to form slabs, rods, and rounds from arc-melted ingot. Further cold-working of zirconium with intermediate annealings produces sheet, foil, bar wire, and tubing. Physical properties are given in Table 3. 

Amino resins are lighter in color and have better tensile strength and hardness than phenoHc resins their impact strength and heat and water resistance are less than those of phenoHcs. The melamine—formaldehyde resins are harder and have better heat and moisture resistance than the urea resins, but they are also more expensive. The physical properties of the melamine—formaldehyde laminates are Hsted in Table 1. 

Table 3. Physical Properties of Diamondlike Carbides and Nonmetallic Hard Materials...

The physical properties of low melting point (60—105°C) syndiotactic polybutadienes commercially available from JSR are shown in Table 1. The modulus, tensile strength, hardness, and impact strength all increase with melting point. These properties are typical of the polymer made with a cobalt catalyst modified with triphenylphosphine ligand. 

Table 17 provides a list of various polysiloxane-poly(aryl ether) copolymers investigated. Depending on the type, nature and the level of the hard blocks incorporated, physical, thermal and mechanical properties of these materials can be varied over a very wide range from that of thermoplastic elastomers to rubber modified engineering thermoplastics. Resultant copolymers are processable by solution techniques and in some cases by melt processing 22,244). 

The physical properties of substances do not involve chemical changes. Color (see Textbox 17) and crystal structure (see Textbox 21), for example, are physical properties that are characteristic of a substance that serve to identify most substances. Other physical properties, such as density, hardness (see Table 3), refractive index (see Table 19), and heat capacity (see Table 101), are also useful for characterizing and identifying substances as well as distinguishing between different substances. 

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