The role of alkali content in the devitrification mechanisms of SiO2–Fe2O3–Na2O–PbO SYSTEM

Three batch compositions of pure oxides (SiO₂, Fe₂O₃, PbO, Na₂O) with equivalent SiO₂, Fe₂O₃ and PbO contents and a gradually increased Na₂O content were vitrified through heating in a high temperature electric furnace and subsequent quenching. The resulting vitreous products were thermally treated in order to study the devitrification behaviour, under conditions designated from differential thermal analysis experiments. Depending on the Na₂O content, crystal phase separation gave rise to the growth of acmite and hematite or maghemite. A uniformly phase separated glass-ceramic material, with crystallites of similar size and population density, was produced from devitrification of the vitreous product with the higher Na₂O content.     

Mechanism of lamellar spacing adjustment in directionally frozen agar gels

A theory is presented for predicting the size of ice crystals which result from steady-state, unidirectional growth within aqueous agar gels. Cellular arrays of adjacent ice crystals were separated by an amorphous water-agar membrane at a composition near the vitrification point. Using this vitrification composition and both a steady-state condition and a minimum free energy criterion, the size of ice crystals was predicted for a given solidification velocity and diffusion condition. It was found, however, that this simple model could not predict the trend towards larger crystal sizes that was observed when the initial agar concentration in the gels increased from 3% to 10% by weight agar.     

Scaling considerations for modelling the in situ vitrification process

Thermal-electric field interactions occur in many areas of engineering. An example is the in situ vitrification process, a relatively new technology for remediating hazardous wastes. Mathematical and physical modelling of this process requires knowledge of the similarity constraints involving thermal- electric fields. This paper addresses this issue and derives the scaling relationships for modelling the remediation process from fundamental principles. Requirements for maintaining temperature and electric potential field similarity between the model and the prototype are determined as well as requirements for maintaining similarity in off-gas generation rates. A scaling rationale for designing reduced scale experiments is presented, and the results are assessed numerically.     

VITRIFICATION OF LIGNITE FLY ASH AND METAL SLAGS FOR THE PRODUCTION OF GLASS AND GLASS CERAMICS

This work focuses on the production of glass and glass-ceramics by using industrial wastes or by-products, e.g., two fly ashes from the combustion of lignite, a slag from the production of Fe-Ni and a slag from the making of steel. Vitrification took place at 1 350°-1450℃ and crystallization was achieved by heat treatment at 900, 950 and 1 000℃. The capability of the waste to be vitrified and subsequently devitrified was determined by XRD techniques. The crystalline phase depends greatly on the structure of the by-product and the heat treatment. The final products showed low leachability and good hardness.     

胡萝卜悬浮培养细胞和原生质体的玻璃化法超低温保存

采用玻璃化法成功地超低温保存了胡萝卡悬浮培养细胞及其原生质体，存活率分别为83．3％（TTC法检测）和47％（RDA法检测）。冻后细胞能恢复生长并再生植株。分析了玻璃化法超低温保存植物悬培养浮细胞和原生质体的主要影响因素。     

Effect of the segmental mobility restriction on the thermoset chemical kinetics

The cure kinetics of an epoxy–amine commercial thermoset system have been investigated with the isothermal differential scanning calorimetry technique. In particular, a kinetic study has been performed in the glass–transition zone, in which diffusion phenomena compete with the chemical transformations and the overall reaction rate is partially slowed by the reduced segmental chain mobility. A generalized form of the Vogel equation has been formulated to account for the effect of the increasing glass–transition temperature on the chain mobility and, therefore, on the overall reaction rate. The kinetic model has been expressed with two factors representing the chemical reaction rate and the segmental mobility reduction. As the main result, the activation energy relative to the diffusion phenomena has been found to be very low, having a value of 42.5 K ≈ 0.356 kJ/mol, which is compatible only with the small‐angle rotation of the reactive unit. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3757–3770, 2002     

Vitrification during the isothermal cure of thermosets

The process of vitrification that occurs during the isothermal cure of a cross-linking system at temperatures below T _g∞, the glass transition temperature of the fully cured resin, has been studied by TOPEM, a new temperature modulated DSC (TMDSC) technique based upon the use of stochastic temperature pulses. A comparison is made between TOPEM and another TMDSC technique, and some advantages of TOPEM are considered. The TOPEM technique is used to show that the mobility factor is not always a reliable approach to predicting the cure rate during vitrification, in view of its frequency dependence. Also, the dependence of the apparent vitrification time on frequency is examined. There appears to be a non-linear relationship between the apparent vitrification time and log(frequency), which is further discussed in the second part of this series.     

低温生物医学与热物理

本文阐述了低温生物学、低温医学与热物理的关系；着重讨论生物体低温保存的问题，细胞和组织的低温损伤是溶液冻结相变过程所引起的冰晶损伤和高浓度溶液的损伤；这个过程和传热传质密切相关；而低温保存的机理则是溶液的非晶态化（玻璃化）。本文还讨论了低温生物医学当前的研究热点，以及其中的热物理问题。