Physical hardness density

So, the physical hardness density, = B. (In Parr s notation, the indentation hardness, H (kg/mm2) = (M/p)B, where (p/M) is the number density of the atoms, but this does not agree very well with measured values, most solids being anisotropic.)... 

Wood is prized for its physical properties, such as strength, compressibility, hardness, density, color, or grain pattern. Chemists classify physical and chemical properties as either intensive or extensive. All chemical properties are intensive, but physical properties can be either. Density is an important physical property of matter that is often used for identifying substances. By determining the density of a piece of wood, you can identify the specific sample. 

Physical hardness can be defined to be proportional, and sometimes equal, to the chemical hardness (Parr and Yang, 1989). The relationship between the two types of hardness depends on the type of chemical bonding. For simple metals, where the bonding is nonlocal, the bulk modulus is proportional to the chemical hardness density. The same is true for non-local ionic bonding. However, for covalent crystals, where the bonding is local, the bulk moduli may be less appropriate measures of stability than the octahedral shear moduli. In this case, it is also found that the indentation hardness—and therefore the Mohs scratch hardness—are monotonic functions of the chemical hardness density. 

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). 

It is shown that the stabilities of solids can be related to Parr s physical hardness parameter for solids, and that this is proportional to Pearson s chemical hardness parameter for molecules. For sp-bonded metals, the bulk moduli correlate with the chemical hardness density (CffD), and for covalently bonded crystals, the octahedral shear moduli correlate with CHD. By analogy with molecules, the chemical hardness is related to the gap in the spectrum of bonding energies. This is verified for the Group IV elements and the isoelec-tronic III-V compounds. Since polarization requires excitation of the valence electrons, polarizability is related to band-gaps, and thence to chemical hardness and elastic moduli. Another measure of stability is indentation hardness, and it is shown that this correlates linearly with reciprocal polarizability. Finally, it is shown that theoretical values of critical transformation pressures correlate linearly with indentation hardness numbers, so the latter are a good measure of phase stability. 

The Physical Properties are listed next. Under this loose term a wide range of properties, including mechanical, electrical and magnetic properties of elements are presented. Such properties include color, odor, taste, refractive index, crystal structure, allotropic forms (if any), hardness, density, melting point, boiling point, vapor pressure, critical constants (temperature, pressure and vol-ume/density), electrical resistivity, viscosity, surface tension. Young s modulus, shear modulus, Poisson s ratio, magnetic susceptibility and the thermal neutron cross section data for many elements. Also, solubilities in water, acids, alkalies, and salt solutions (in certain cases) are presented in this section. 

Properties that describe the look or feel of a substance, such as color, hardness, density, texture, and phase, are called physical properties. Every substance has its own set of characteristic physical properties that we can use to identify that substance (Figure 2.1). 

Although many polymer properties are greatly influenced by molecular weight, some other important properties are not. For example, chain length does not affect a polymer s resistance to chemical attack. Physical properties such as color, refractive index, hardness, density, and electrical conductivity are also not greatly influenced by molecular weight. 

It is customary to say that under the same external conditions all specimens of a particular substance have the same specific physical properties (density, hardness, color melting point, crystalline form, etc.). Sometimes, however, the word substance is used in referring to a material without regard to its state of aggregation for example, ice, liquid water, and water vapor may be referred to as the same substance. Moreover, a specimen containing crystals of rock salt and crystals of table salt may be called a mixture, even though the specimen may consist entirely of the one chemical substance sodium chloride. This lack of definiteness in usage seems to cause no confusion in practice. 

Botanical Origin. Wood is a natural material familiar in at least some way to everyone. Wood is obtained from two broad categories of plants known commercially as softwoods and hardwoods. These general names cannot be used universally to refer to the actual physical hardness or density of all woods because some softwoods are quite hard (e.g., Douglas-fir and southern yellow pines) and some hardwoods are soft (e.g., yellow buckeye, aspen, and cottonwood). Nevertheless, the names do accurately apply to many woods within these two categories and thus can be used as practical designations for the two general classes of commercial timbers. 

A second reason to consider solids here is that for this state the concept of physical hardness is important. Physical hardness is the resistance to a change in volume or shape of a solid object, produced by mechanical forces. Remembering that chemical hardness is subject to a restriction of constant nuclear positions, we see that physical hardness has the effect of removing this restriction. Nuclear positions must change, and this must be accompanied by a change in the electron density. 

Skill 12.1e-Discuss the physical properties of matter including structure, melting point, boiling point, hardness, density, and conductivity... 

All crystals of one given substance, which may exhibit different habits, have identical physical properties. On the other hand, the different polymorphs of a given substance, which may also differ in habit, will exhibit different physical properties density, hardness, melting point, solubility, reactivity, thermal properties, optical and electrical behaviour, etc. Each polymorph constitutes a separate phase of the given substance, in the Gibbs phase rule sense, whereas crystals of different habit constitute the same phase. Polymorphs may transform in the solid state, but crystals of different habit cannot. 

In the last decades of evaluation of the physical network density of SPU was done on samples swollen to equilibrium in two solvents. Swelling of SPU in toluene practically does not affect hard domains. Swelling of SPU (based on oligoethers diol) in a tributyl phosphate (a strong acceptor of protons) results in full destruction of the physical network with hard domains. The effective network density was evaluated for samples swollen to equilibrium in toluene according to the Cluff-Gladding method. Samples were swollen to equilibrium in TBP and the density of the physical network was determined from equar tion ... 

To understand the restrictions to swelling of SPU caused by the physical network containing hard domains, the following experiments were carried out. Segmented polybutadiene urethane urea (PBUU) on the base of oligobutadiene diol urethane prepolymer with functional NCO-groups (M 2400), cured with MOCA, and SPU-10 based on prepolymer cured with the mixture of MOCA and oligopropylene triol (M 5000) were used. The chemical network densities of PBUU and SPU were 0.05 and 0.08 kmol/m, respectively. The physical network density of initial sample, (VeA o)d> of PBUU was 0.99 kmol/m and of SPU-10 was 0.43 kmol/m. ... 

Methacrylic ester polymers display the same change from hard, brittle, glasslike materials below the Tg value to relatively soft, flexible, rubbery materials above the Tg. Movement to even higher temperatures can result in a change to a flowable, tacky material. Table 1 contains basic physical data (density, solubility parameters, and refractive index values) for the most common methacrylic ester polymers. 

Properties of materials Defined as those attributes, largely physical, (hat are intrinsic to the class of material. They would, for instance, include melting point, electrical and thermal conductivities, hardness, density, reflectivity, elasticity, etc. 

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