Dilatometric Softening Temperature Research Articles

Transformation Range Behavior of Lithium Galliosilicate Glasses

The transformation range viscosity and thermal expansion behavior of lithium galliosilicate glasses were studied. The glass transformation and dilatometric softening temperatures exhibit maxima at gallium to lithium ratios of somewhat greater than one. Similar behavior was observed for the transformation range viscosity. The effect of phase separation on the dilatometric softening temperature is discussed in detail. These results are compared with those obtained for lithium alumino‐silicate glasses in other studies. The results are discussed in terms of the structural role of aluminum and gallium in the glass network.

Formation and Properties of Calcium Aluminosilicate Glasses

The glass‐forming region for calcium aluminosilicate glasses has been determined. A number of properties of these glasses (thermal expansion coefficient, glass transformation and dilatometric softening temperature, and refractive index) have been studied. The results of these measurements suggeq that the structures of these glasses may not as closely resemble those of alkali aluminosilicate glasses as is commonly assumed. Evidence is presented which suggests that the binary calcium aluminate glasses may be phase separated.

Properties and Structure of Lanthanum Borate Glasses

Glass formation limits were determined for the lanthanum borate glasses. Stable immiscibility prevents the formation of clear glasses over the range 0 to 20 mol% La2O3, but excellent quality glasses could be formed between 20 and 28 mol% La2O3. Data are reported for the density, refractive index, thermal expansion coefficient, glass transformation and dilatometric softening temperatures, transformation range viscosity, helium permeability, and chemical durability of these glasses. A limited Raman and infrared spectroscopy study suggests that lanthanum plays a similar structural role in these glasses and in the related crystals.

Thermal expansion characteristics of some iron-containing glasses and their corresponding crystalline materials

The thermal expansion of some lithium silicate glasses containing varying proportions of Fe 2O 3 (replacing silica) has been investigated before and after thermal treatment. The coefficient of thermal expansion of the glasses at different temperatures, the transformation and dilatometric softening temperatures were determined to detect local structural changes that might be induced by the Fe 2O 3/SiO 2 replacement. The experimental results and anomalies observed were related to different views concerning the change in the valency and state of coordination of iron with its concentration in the glass, and to the phase separation that might develop in lithium silicate glasses. In the crystalline state, the expansion coefficient was measured from room temperature up to 700°C for various iron-containing samples, and the data obtained were correlated to the type and content of the mineral phases formed as indicated by the X-ray technique.

Thermal expansion of high lead borate glasses and the boric oxide anomaly

The thermal expansion of some binary high lead oxide-boric oxide glasses and glasses derived from them by replacements were measured. The thermal expansion coefficient, α, was calculated at successive temperatures up to the dilatometric softening temperature. The experimental results and the anomalies observed were discussed on the basis of the different views concerning the changes in the boron coordination with composition. The differing effects of the introduced oxides were related to the ionic sizes of the cations and the ease of movement or fluidity of the internal structural units.

Thermal Expansion of Alkali Borate Glasses

The thermal expansion behavior of lithium, sodium, potassium, and rubidium borate glasses was measured. The results indicate that the “borate anomaly” in the thermal expansion coefficient occurs at ∼20 mol% alkali oxide. A maximum in the glass transformation and dilatometric softening temperatures also occurs at ∼27 mol% alkali oxide. No evidence for phase separation was observed in this study. These effects are related to the structural changes reported for these glasses by Bray and coworkers.

Effect of crystal content on the properties of willemite glass-ceramics

Helium permeability, thermal expansion properties, and density have been measured for a series of glass-ceramics based on willemite as a lone crystalline phase. These glass-ceramics were prepared such that the compositions of both the glassy and crystalline phases were fixed, and only the relative concentrations of glass and crystal varied. Results of this study demonstrate that the helium permeability and glass transformation temperature of glass-ceramics are controlled by the glassy phase composition, whereas the density, thermal expansion coefficient, and dilatometric softening temperature are a function of both phases. All of these conclusions can be explained readily by simple continuity and mixing arguments.

Viscosity and thermal expansion of lithium aluminosilicate glasses

Viscosity and thermal expansion have been measured for 12 series of lithium aluminosilicate glasses. The compositional dependency of the viscosity, glass-transformation temperature, dilatometric-softening temperature, and refractive index all exhibit an abrupt change in slope at an aluminum-to-lithium ratio between 1.05 and 1.10. The thermal-expansion coefficients of these glasses were found to depend only on the lithium oxide content, i.e., to be independent of the aluminum-to-silicon ratio. These results suggest that the traditional structural model for these glasses must be modified slightly. A new model is proposed which allows some aluminum to act as a modifier in all alkali aluminosilicate glasses.

1310. Surface analysis with heavy ion induced Auger electrons; basic properties of a new method for materials sciences: K O Groeneveld et al, Vacuum, 25 (1), 1975, 9–12

Viscosity of soda-lime-silicate glass doped with rare earth oxides (Pr6O11, Eu2O3, Yb2O3) was investigated by the rotating crucible viscometer, the melting temperature and activation energy for viscous flow of the studied melt were derived on the basis of the Arrhenius Equation, the coefficient of thermal expansion, glass transition temperature and dilatometric softening temperature were also determined with dilatometry, in order to reveal the effects of rare earth elements on the behavior of soda-lime-silicate glass. The results showed that introduction of rare earth oxides decreased the viscosity of soda-lime-silicate glass and melting temperature of corresponding melt, increased coefficient of thermal expansion of soda-lime-silicate glass. The glass transition temperature, dilatometric softening temperature, and melting temperature of soda-lime-silicate glass doped with rare earth oxides increased with increasing cationic field strength of corresponding rare earth ions.