摘要:

This two‐part paper develops a basis for discussing glass properties which has features in common with standard “actual vs. ideal” treatments of physicochemical behavior, by defining thermodynamically an ideal state for the glass and discussing the states of the actual glasses in terms of their “departures from ideality.” The glass transition, which freezes the state of the actual glass, is seen as the consequence of the progress of the liquid toward the ideal state, which, for kinetic reasons, is unattainable. The single complexion limit of the Gibbs‐DiMarzio treatment for chain polymers and a minimum volume zero excess entropy condition related to random close packing for simple liquids are seen as complimentary descriptions of the ideal state, which also sets the thermo‐dynamic low‐temperature limit to the liquid state. Glasses formed from simpler molten salt and concentrated aqueous solution systems appear to approach the ideal state and thus provide a behavior pattern against which departures from ideality in the more complex silicate and borate glasses of practical interest may be assessed. In part I general aspects of the problem posed by the glass transition phenomenon are discussed, a dynamic interpretation for simple glasses in terms of the state of phonon excitation of the glassy solid is conjectured, and the concepts of ideal and nonideal (practical) glasses and glass transitions are elucidated from consideration of thermodynamic and kinetic factors involved in the volume relaxation of liquids toward the glassy state. Attention is given to units for describing departures from ideality to permit comparisons among different systems. The limited data for inorganic glasses are examined. Departures from ideality, as usually found in the physicochemical comparison of “actual” with “ideal” behavior, are attributable to specific interactions among the particles of the system, but magnitudes also depend on heat capacity changes. The former factor reaches a maximum in vitreous SiO2which thus may be one of the

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11854.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The conclusions from Part I of this paper, that glasses formed from certain fused salt mixtures and aqueous electrolyte solutions closely approach a thermodynamically ideal state, is the basis for a discussion of various properties of molten oxide mixtures and the glasses that may be formed from them. The relevant properties of the simple ionic liquids are summarized, and the electrical conductance behavior of a halide analog of the silica‐alkali oxide systems is analyzed to provide a bridge for relating the nonideal behavior of the complex glasses to the near‐ideal behavior of the simple ion systems. Specific cases of silicate and borate glass behavior discussed are the compactibility of high‐silica glasses, the transport behavior in the region of the “boron anomaly,” the relation between viscosity and electrical conductance, and certain structural problems concerning the coordination of multivalent cations in melts and glasses. Finally, some points from the development pertaining to glass‐crystal relations and the nucleation problem are

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11855.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Liquid silicates, in common with phosphates and probably other oxygen‐containing inorganic polymers which are stable at high temperatures, contain in general a multitude of anionic species ranging in size and complexity from simple “monomeric” groupings such as SiO44−and P043−to continuous, cross‐linked networks of infinite molecular weight. The average size and distribution of these species in binary systems may be inferred, at least approximately, from thermodynamic data in combination with polymer theory on the assumption that the activity coefficients of the constituents are arrayed in geometric series. This is equivalent to assuming ideal mixing of polymeric segments. As anticipated, deviations from the theory become significant at the gel point, which varies with the nature of the cation. The significance of these concepts in relation to the constitution of glasses is discussed. In particular, it is indicated that a glass may consist of sol and gel portions, the complexity and relative proportions of which vary with the nature of the cation and the silica content. In theory, the ion SiO44−is the most abundant single species of discrete silicate ion at all si

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11856.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

It is suggested that the large expansion coefficient increase that occurs nearTg, for mixed oxide glasses is related to cooperative thermal displacements involving polyanionic clusters in the liquid state. This is illustrated by the striking relation between melt isoexpansion coefficient contours and structure for these ternary oxide systems. It is also shown that the molar volume dependence on composition for a series of oxide glasses can be quite similar to that observed for their liquid state analogs. The adjusted melt partial molar volume models can be used to develop realistic glass models, suggesting structural similarities between an oxide glass and its corresponding high‐temperature melt. Recently acquired evidence for alkali borogermanate compositions indicates a shift toward the right for the GeO6⇄GeO4equilibrium in GeO2−rich melts at relatively high temperatures. Thus, anexactstructural correlation between an oxide melt and its corresponding glass may, in some cases, be limited to temperatures belowTg+ΔT(where ΔT ~300° t

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11857.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The logarithm of measured high‐temperature fluidities is related to the square of the calculated probability of finding a nonbridging oxygen in a randomly chosen SO4 group. This is interpreted in terms of a flow mechanism (gliding) dependent on juxtaposition of two such oxygens. A theory of the glass transformation is developed. On cooling, the coordination number of nonbridging oxygens increases until, ideally, atT, each touches three oxygens of an external Si04 group (stabilization). Below this temperature, thermal expansion/contraction contains no coordination change component. These changes constitute a second‐order transition. Observed volume data are in agreement with hypothesis. On this view, stabilization creates vacant tetrahedral environments adjacent to existing ones. Migration of glass‐forming ions to these empty sites can unlock the structure and permit the operation of a new set of flow processes. The coordination requirements for stabilization severely restrict the types of local arrangement possible at high silica contents, and therefore reduce the configurational entropy and induce unmixing. The overall transformation is composite in character. Rather extensive bond rearrangement and unmixing (when present) are features of first‐ord

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11858.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Ultrasonic shear and longitudinal measurements were made in Bz03 from 650° to 1000° C. From these data both the shear and volume relaxation time spectra were determined. The spectra had the same temperature dependence, although the volume spectrum was always broader than the shear spectrum. The shear relaxation process can be represented by a single relaxation time above 800° C in the region where the shear viscosity is Arrhenius. Both processes exhibit an increasingly broad distribution of relaxation times in the non‐Arrhenius region. The temperature dependence of the shear spectrum was analyzed in terms of a distribution of activation energies. A surprising conclusion of this study is that activation energies at low temperatures are smaller than the activation energy in the Arrhenius re

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11859.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Glass compositions are correlated with published data for refractive index, specific volume, and fluidity, which indicate the presence of different structural types in silicate glasses. These structural types are shown to be uniquely related to the composition areas of primary crystallization phase fields. It is suggested that these different structural types are to be understood as silicate framework structures or “substructures” in which other appropriate cations may be accommodated. The described data relations definitely establish the presence of different recognizable substructures in silicate glasses but do not permit judgments on their detailed characterist

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11860.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

When a small amount of Ba or Sr is substituted for Pb in Pb(Mg1/3Nb2/3)O3‐PbTiO3‐Pb2rO3, the morphotropic boundary and the compositions which show the highest planar coupling coefficient and dielectric constant shift slightly toward the decreasing PbTiO3content. The tetragonality of Pb(Mg1/3Nb2/3)O3‐PbTiO3and Pb(Mg1/2Nb2/3)‐O3‐PbTiO3‐PbZrO3ceramics decreased with increasing Ba or Sr content. The lattice parameter (α axis) in the rhombohedral or pseudocubic phase increased with the increase of Ba but decreased with the increase of Sr substitution. Although the Curie temperature was lowered with the increase of Ba or Sr, the dielectric constants of the ceramics were increased. The dielectric and piezoelectric properties of the ternary compositions near the morphotropic boundary were improved through selection of sub‐stituent and base composition. A planar coupling coefficient of 0.66 and a low Young's modulus were obtained with substitution of 5 mole % Ba. A dielectric constant greater than 3500 and a planar coupling of 0.63 can be obtained by substituti

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11861.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11862.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1968.tb11864.x-i1

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY