Microstructure of hardened gypsum pastes

Specific surface areas and pore size distribution analysis were taken as essential parameters to explore the microstructure of hardened gypsum pastes. The hydration of gypsum plaster is essentially affected by the water/plaster ratio of the mix, and by the presence of additives which might act as retarders or accelerators to the hydration process. Affecting the microstructure would mutually lead to variations of the compressive strength of the hardened pastes, and these variations are also discussed. Results are mainly expressed in terms of the solid (measured by the extent of its specific area) to the space (pore) ratios. Dual distribution of pore sizes was observed and the two groups of pores are designed as S (small) and L (large) pores. Similarities to the microstructure of hardened Portland cement pastes are indicated. Accelerators appear to function differently from retarders, and the effects of water/plaster ratios were investigated in both cases. The results obtained may carry many significant practical implications to the future use of hardened gypsum pastes.     

Stabilizing quartz slip in the production of immersion sheaths

Conclusions A technology was developed for stabilizing quartz slip for making immersion sheaths at the Podolsk refractories factory using electrolytes, enabling us to reduce the slip preparation time by 19–22 h, reducing its viscosity with a reduction in the water content from 22 to 17–20%, reducing the loss of greenware. In the conditions of KTs-2 of the Novolipetsk plant, the experimental nozzles showed a resistance similar to that of nozzles obtained by the traditional method used at Podolsk.Translated from Ogneupory, No. 7, pp. 5–6, July, 1980.     

Selection of Polyacrylonitrile Fibre Modification Parameters

The studies conducted show that: the efficiency of modification of as-spun PAN fibre is higher than with modification of the conditioned fibre; the fibres obtained can be recommended for fabrication of fire-resistant fabrics for work clothing.     

Synthesis of an ultradispersed diamond phase during detonation of composites

Conclusion We have attempted to analyze the synthesis of the diamond phase during, the detonation of secondary explosives by comparing the results of an explosion experiment with data obtained by studying preserved UDD powders.These data show that during detonation the growth in the UDD particles is a strongly limited process that is essentially independent of the size of the explosive charge or the external cooling conditions. The size distributions of diamond particles formed during direct synthesis from the carbon contained in the molecular structure of the explosive and during dissociation of inert organic substances are in satisfactory agreement with a lognormal distribution. The thermodynamic conditions during synthesis determine the dispersivity of the product UDD particles and this must be taken into account in thermodynamic detonation calculations. The effect of the different constituents of the, explosive on UDD synthesis (heat and mass transfer) is strongly limited.These data may support the concept of detonation in secondary explosives as a set of relatively fast and much slower reactions [25, 26] where, in the case of composites, the coagulation of carbon released during decomposition of each component separately and diffusion processes among the components may both act as slow exothermic reactions.Novosibirsk. Translated from Fizika Goreniya i. Vzryva, Vol. 29, No. 1, pp. 120–128, January–February, 1993.     

The use of direct osmosis tests as complementary experiments to determine the water and salt permeabilities of reinforced cellulose acetate membranes

In this article the use of the direct osmosis test as a complementary experiment to the reverse osmosis test is described. The membranes investigated are cellulose acetate membranes reinforced with mineral fillers. In both tests the same influence of the type of fillers on the water permeability coefficients is found. The salt permeability coefficients indicate the presence of pressure sensitive defects in the reinforced membranes. The direct osmosis test is found to be a suitable test to confirm and predict the membrane properties under reverse osmosis conditions.     

Technological parameters of corundum chamotte

Conclusions It has been established that to obtain densely sintered macrocrystalline corundum chamotte it is most expedient to obtain the briquet in the form of granules 20–25 mm in diameter from finely ground GK alumina (or special alumina brands of high purity) followed by annealing at 1900–1950°C.Translated from Ogneupory, No. 3, pp. 31–36, March, 1980.     

Grafting of nylon 66 with methyl methacrylate using dimethylaniline–benzyl chloride–acetic acid initiating system

Grafting of nylon 66 with methyl methacrylate (MMA) under the initiating influence of dimethylaniline (DMA)–benzyl chloride (BC)–acetic acid (AC) mixture was studied to discover optimal conditions for grafting. Results of this investigation showed that a mixture of water/ethanol at a ratio of 90:10 constitutes the most favorable medium for the grafting reaction. Optimal grafting occurred when a concentration of 0.16 mole/l. DMA plus 0.17 mole/l. BC plus 0.2 mole/l. AC was used. Using lower or higher concentrations of this initiator led to lower grafting. On the other hand, increasing MMA concentration brings about a significant increase in the graft yield. The same holds true for reaction time and temperature, though an induction period was observed at a lower temperature (65°C) and when lower monomer concentration (2%) was used.     

H2S/Halogen promoted oxidative dehydrogenation of butene-1

An experimental program was carried out to determine the effectiveness of H₂S/mixed halogen promoters in the oxidative dehydrogenation reaction. Using the butene-1 to butadiene reaction as an example it was found that while H₂S or any of the hydrogen halides alone could be used as the promoter, superior conversions and selectivities (80–85%) were obtained when H₂S was used in admixture with the halogens, preferably HCl and/or HBr. The effect of different catalysts and some processing variables (temperature, space velocity) on the desired reaction will be presented.     

Application of Porous Glasses as Matrices for Nanocomposites

The use of matrices of different types makes it possible to prepare nanocomposites differing in the degree of ordering, the size and shape of structural units, their spatial distribution, and the type of contact between them. Porous glasses with controlled characteristics of pores can be used as matrices for nanocomposites. This provides a means for determining the basic parameters and the main properties of nanoclusters as a function of the size of their structural units. It is shown that the structural parameters of porous glasses can be controlled by varying the conditions of thermal and chemical treatments of the initial glasses.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Aleksashkina, Venzel, Svatovskaya.