Property-composition Curves Research Articles

Sm2S3-Sm2O3 phase diagram

The Sm2S3-Sm2O3 phase diagram was studied by physicochemical methods of analysis from 800 K up to melting. Two oxysulfides are formed in the system: Sm10S14O with tetragonal crystal structure (space group I41/acd; unit cell parameters: a = 1.4860 nm, c = 1.9740 nm; microhardness: H = 4700 MPa; solid decomposition temperature: 1500 K) and Sm2O2S with hexagonal structure (space group P-3m1; a = 0.3893 nm, c = 0.6717 nm; H = 4500 MPa; congruent melting temperature: 2370 K). Within the extent of the Sm2O2S-based solid solution (61–70 mol % Sm2O3) at 1070 K, a singular point appears at the compound composition on property-composition curves. The eutectic coordinates: 23 mol % Sm2O3 and 1850 K; 80 mol % Sm2O3 and 2290 K.

Medium range order in glass and the `germanate anomaly' effect

The origin of extrema in the property-composition curves of germanate glasses has been a much debated issue. Using density and structural data for K- and Rb-germanate glasses we find that the short-range order structure alone cannot reproduce the maximum in density. By combining short- and medium-range order structures we calculate the dependence of density on composition in remarkably good agreement with experiment. The results show that the maximum in density can be traced to the coexistence of germanate octahedral units with compact three-membered rings of tetrahedral units.

Further studies on the IR spectra of silicate glasses

Infrared spectra of the PbOSiO 2 glass system were studied by the KBr method. The absorption peaks show some different features as compared with the author's previous work on infrared spectra of alkali silicate glasses. It was found that with increasing PbO content the main absorption peak at a wave number larger than 1000 cm −1 originally shifts to less than 1000 cm −1 as the PbO content reaches 40 mol%; at the same composition occurs the abrupt change in property-composition curves of the PbOSiO 2 glass system. It is interesting that the absorption peak of non-bridging SiO links near 950 cm −1, being typical in the IR spectra of Na 2O·2SiO 2 glass, is rather weak in the spectra of Li 2O·2SiO 2 glass and almost disappears in that of PbO·2SiO 2 glass; this agrees with the different stability of the crystalline phase of corresponding bisilicate compounds. Infrared spectra of a series of Na 2OCaOSiO 2 glasses have also been studied. A new peak appears when the SiO 2 content is below 74 mol% and the glass composition enters the narrow region of commercial soda-lime glasses. As to K 2OPbOSiO 2 glasses, the shifting of the main absorption peak becomes obvious when the glass composition is near those of commercial glasses. Discussions have been given on different structural groups of SiO links adjacent with different metal ions. An attempt has been made to give some structural interpretations of the reason why the chemical compositions of commercial soda-lime and potash-lead silicate glasses are concentrated in a narrow region.

Rheological properties of the homogeneous and inhomogeneous blends of polyvinylidene fluoride and polymethyl methacrylate

PVDF-PMMA blends are used to illustrate how the viscous properties and the high elasticity of blends of mutually soluble (intersoluble) polymers differ qualitatively in different thermokinetic states. A considerable number of property-composition curves may accordingly be plotted depending on conditions of the experiments. In the case of blends of fractions of thermodynamically compatible polymers the relations between viscosity and composition should be nonadditive in character. On the basis of the viscosity anomaly index n and the degree of expansion B of the extrudate jet in the compositionally homogeneous and inhomogeneous PVDF-PMMA blends, different conclusions may be reached about the high elasticity of the system.

Coordination number of aluminum ions in alkali-free alumino-silicate glasses

The oxygen coordination number of aluminum ions in alkali-free alumino-silicate glasses has been investigated by means of Alkα fluorescence spectra. The glasses studied were XCaO·(100- X- Y)Al 2O 3· YSiO 2 wt% (with 50 ⩾ X ⩾ 20, 70 ⩾ Y ⩾ 0) and, 20MgO·(80− Y′)Al 2 O 3· Y′SiO 2 wt% (65 ⩾ Y′ ⩾ 45). The density, thermal expansion coefficient and elastic moduli of the glasses were also measured. In glasses with an Al/(Al+Si) ratio larger than 0.5, the chemical shifts of the Alkα lines for the glasses relative to aluminum metal were equal to that for Na-feldspar, indicating that Al 3+ ions are four-fold coordinated in the glasses. In glasses with an Al/(Al + Si) ratio less than 0.5, the chemical shifts depended on SiO 2 content and increased from the value nearly equal to that for Na-feldspar towards those for α-Al 2O 3, dickite and kaolinite as the Al/(Al+Si) ratio decreased, indicating that the average coordination number of Al 3+ ions in these glasses increases with SiO 2 content. The minimum, maximum oor an abrupt change in the slope of property-composition curves of alkali-free alumino-silicate glasses could be understood by assuming the presence of six-fold coordinated Al 3+ ions.

Helium migration in alkali germanate glasses

Helium permeability, diffusivity, and solubility have been measured for sodium, potassium, rubidium, and cesium germanate glasses, and for one series of sodium-potassium germanate glasses. In each case, the helium permeability and diffusivity exhibit minima in the property-composition curves. These minima shift to greater alkali oxide content and increase in magnitude in the order Cs, Rb, K, Na-K, Na. These minima result from corresponding maxima in activation energy for helium migration. Helium solubilities do not exhibit similar minima, but rather decrease monotonically with increasing alkali oxide content. These results appear to be related to free-volume changes in the glasses as a function of composition. The inability of the current structural model for these glasses to explain the results of the present study raises questions regarding the validity of that model.

Refractive index of chalcogenide glasses over a wide range of compositions

The refractive index frequency dependence in the 1–11 μm range for AsSe, GeSe and AsGeSe glassforming systems and for three- and four-component systems obtained by substitution of antimony, bismuth, tin, lead, sulphur and tellurium for arsenic, germanium and selenium, being their periodic system counterparts, is investigated. A comparison of optical constants of chalcogenide glasses with those for other optical materials by means of constructing of an Abbe-type diagram in n 2.0 − v 2.0 coordinates is considered. The possibility of chalcogenide glass refraction calculation by means of additive formulas is discussed. It is shown that critical points on the property-composition curves coincide with structural region boundaries in all of the investigated systems. These data are considered as further experimental support for the polymer nature of chalcogenide glasses.

A dielectric investigation on water-pyridine system

The property-composition curves in water-pyridine mixtures in the full concentration range at 283 to 333 K for volume and « free volume » contraction, viscosity, relaxation lime, and dielectric constant and refractive index diverge from the additive law : they were all found to heve a maximum in the vicinity of 30 mole percent of pyridine. The evidence for the existence of the hydrogen-bonded complex C5H5X, 2H2O in solution to which this maximum is due, was subsequently justified by molecular beam experiments.

The Electric Conduction in mixed Cation Glasses of the Ag<sub>2</sub>O-Na<sub>2</sub>O-B<sub>2</sub>O<sub>3</sub> System

The electrical conductivities of glasses in the Ag2O-B2O3, Na2O-B2O3 and Ag2O-Na2O-B2O3 (Ag2O+Na2O=27.4mol% in average) systems have been determined over the temperature range from room temperature to about 400°C using both d. c. and a. c. measurements. The temperature dependence of the electrical conductivities of the glasses could be described by the Rasch-Hinrichsen equation:σ=σ0exp(-ΔH/RT)The Ag2O-B2O3 glasses showed higher conductivity and lower activation energy for conduction than the Na2O-B2O3 glasses did. The mixed cation effect was observed in the Ag2O-Na2O-B2O3 system; a minimum in the electrical conductivity and a maximum in the activation energy were found around the Ag/(Ag+Na) ratio of 1/5 on the property-composition curves. A minimum in the dielectric constant was also found. The magnitude of the mixed cation effect in the silver-containing system was, however, considerably smaller than that found in mixed-alkali glasses involving Li, Na, K or Cs ions.The electrical conductivity was much greater and the activation energy was smaller for the Ag2O-Na2O-B2O3 glasses of the composition range of Ag/(Ag+Na)>1/5, in which Ag+ ions are dominant current carriers, than for the single cation Ag2O-B2O3 glasses of the same Ag2O content. This indicates that the mobility of Ag+ ions is increased on addition of Na+ ions in contrast with that of the alkali ions in mixed-alkali glasses which remains the same or is decreased on addition of alkali ions of the other type. Such behavior of the mobility of Ag+ ions was discussed by assuming the formation of Ag+ ion clusters which results in the shortening of the jump distances required for the migration of Ag+ ions.

Structure of Borate Glasses

Anomalous thermal expansion and other properties of borate glasses have previously been given a structural explanation by Abe. This explanation is here reinterpreted and revised in terms of the structon theory of Huggins. In agreement with Warren, it is postulated that, in glasses containing, in addition to boric oxide, small relative amounts of an alkali or alkaline‐earth oxide, some of the boron atoms are surrounded by four oxygen atoms and all the oxygen atoms bridge between two boron atoms. At concentrations beyond that of the thermal expansion minimum, some oxygens are assumed to have only one boron neighbor. These ideas are formulated quantitatively and are used to interpret pertinent experimental data. From the concentrations where the property‐composition curves show breaks, conclusions may be drawn as to the average number of oxygens surrounding each metal atom.

Diamagnetism of Liquid Mixtures

MR. S. P. RANGANADHAM states, in NATURE of June 27, that he has obtained values for the specific susceptibility of mixtures of organic liquids which differ markedly from those obtained by us.1 It is impossible to answer Mr. Ranganadham's assertion without a full knowledge of his data, consequently we must await the publication of his results before we can reach an opinion as to the comparative value and accuracy of the two sets of values. In the meantime, however, we must justify our continued belief in the accuracy of our work. In the first place, as pointed out in our paper, the specific susceptibilities of the pure liquids used in our experiments were found, with a single exception, to be closer to Pascal's calculated values than any values hitherto published. We attribute this fact to the carefully checked purity of the material used. The susceptibility values used in plotting our curves were, in every case, obtained several times with fresh portions of the mixtures; the symmetry of the curves and the fact that they exhibit maxima in the same positions as other property-composition curves is confirmatory of the accuracy of our results.

Contributions to the knowledge of liquid mixtures—I. Property-composition curves and the molecular changes which take place on forming binary liquid mixtures

Contributions to the knowledge of liquid mixtures—I. Property-composition curves and the molecular changes which take place on forming binary liquid mixtures

Contributions to the knowledge of liquid mixtures—II. Chemical combination in liquid binary mixtures as determined by a study of property-composition curves

Contributions to the knowledge of liquid mixtures—II. Chemical combination in liquid binary mixtures as determined by a study of property-composition curves