Solubility of Si3N4 in Liquid SiO2

The nitrogen solubility in the SiO₂-rich liquid in the metastable binary SiO₂-Si₃N₄ system has been determined by analytical TEM to be 1%–4% of N/(O + N) at 1973–2223 K. Analysis of the near edge structure of the electron energy loss peak indicates that nitrogen is incorporated into the silicate network rather than being present as molecular N₂. A regular solution model with a positive enthalpy of mixing for the liquid was used to match the data for the metastable solubility of N in the presence of crystalline Si₃N₄ and to adjust the computed phase diagram. The solubility of Si₃N₄ in fused SiO₂ is far less than reported in liquid silicates also containing Al, Mg, and/or Y. Apparently, these cations act as modifiers that break anion bridges in the silicate network and, thereby, allow further incorporation of Si₃N₄ without prohibitive amounts of network cross-linking. Finally, indications emerged regarding the diffuse nature of the Si₃N₄-SiO₂ interface that leads to amorphous regions of higher N content.     

Composite sheets with biodegradable polymers and paper,the effect of paper strengthening agents on strength enhancement,and an evaluation of biodegradability

Composite sheets composed of biodegradable polymers (BP) and paper were prepared, and their physical and biodegradable properties were investigated. The paper sheets were soaked in BP emulsions and cured at 100°C for 20 min. The wet strength of composite sheets with the same basis weight increased significantly with increasing BP content, although dry strength increased only moderately. A 0.5% addition of a common wet paper‐strengthening agent, poly(amidoamine‐epichlorohydrin) (PAE) resin, enhanced the wet strength, which reached 9.3 MPa, of composite sheets consisting of a BP : paper ratio of 20 : 80. Further enhancement was achieved by the addition of polyvinylamines (PVAm). The wet tensile strength of composite sheets consisting of BP and paper (20 : 80) increased by 27% with the addition of 0.2% PVAm and 0.5% PAE, whereas it was enhanced by only 3–4% with the addition of 0.7% PAE. The biodegradability of the composite sheets was somewhat retarded by the addition of PAE and PVAm. However, a 90% weight loss was observed 60 days after placing composite sheet samples in soil. A similar weight loss was observed after 45 days for composites without additives and after 30 days for base paper alone. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 861–866, 2005     

High-Temperature Fracture Mechanism of Low-Ca-Doped Silicon Nitride

High-purity Si₃N₄ (with 2.5 wt% glassy SiO₂) doped with 0 to 450 at.ppm of Ca was prepared as a model system to investigate the effects of grain-boundary segregants on fracture phenomenology at 1400°C. Subcritical crack-growth (SCG) resistance as well as creep resistance was degraded significantly by the presence of a small amount of Ca. The internal friction of the doped materials exhibited the superposition of a grain-boundary relaxation peak and a high-temperature background, and the apparent viscosity of the grain-boundary film was determined from the peak. Based on these experimental data, the fracture mechanism at 1400°C was divided into three regions: "brittle," SCG, and creep failure as a function of both external strain rate and Ca concentration, C _Ca. From the investigation of the C _Ca dependence of the critical strain rate for the transition from "brittle" to SCG fractures, the SCG phenomenon is suggested to be triggered by small-scale, grain-boundary sliding. The C _Ca dependence of "steady-state" creep rate was far from the theoretical dependence of diffusional creep via a solution-precipitation mechanism. The discrepancy was interpreted to be due to the presence of an impurity-insensitive creep component. This component may correspond to the lowest limit of the tensile creep rate in Si₃N₄ polycrystalline materials containing intergranular glassy-SiO₂ film.     

Activation of a Au/TiO2 Catalyst by Loading a Large Amount of Fe–Oxide: Oxidation of CO Enhanced by H2 and H2O

Catalytic activity of a 1 wt% Au/TiO₂ catalyst is markedly improved by loading a large amount of FeO_x, on which the oxidation of CO in excess H₂ is selectively promoted at temperature lower than 60 °C. Oxidation of CO with O₂ on the FeO_x/Au/TiO₂ catalyst is markedly enhanced by H₂, and H₂O moisture also enhances the oxidation of CO but its effect is not so large as the promotion by H₂. We deduced that activation of Au/TiO₂ catalyst by loading FeO_x is not caused by the size effect of Au particles but a new reaction path via hydroxyl carbonyl intermediate is responsible for the superior activity of the FeO_x/Au/TiO₂ catalyst.     

Carbonization and liquid-crystal (mesophase) development. 12. Mechanisms of the co-carbonization of coals with organic additives

In industrial situations, coals interact with solvents or additives to produce liquid fuels, solvent-refined coal, coal extract and metallurgical coke. In these processes there occurs a wide variation in effects or modifications of the coal by these additives. This paper describes the modifications which can occur, using a wide range of rank of coal, when these coals interact and are co-carbonized with a wide range of additives of different chemical properties. The optical texture of the resultant cokes is given special attention. The objective of the paper is to summarize the current state of knowledge of the mechanisms of these interactions. Possible mechanisms of interactions are summarized, kinetic and chemical structural aspects of reactions are outlined, the importance is mentioned of the formation of liquid phases enabling anisotropic optical textures in modified cokes to be created, and the industrial relevance of its possible development is discussed.     

Carbonization and liquid-crystal (mesophase) development. 8. The co-carbonization of coals with acenaphthylene and decacyclene

Several coals of different rank have been carbonized singly and also co-carbonized with acenaphthylene and decacyclene. The resultant cokes were mounted in resin and polished surfaces were examined for optical texture using a polarized-light optical microscope fitted with a half-wave retarder plate. The optical texture can be assessed qualitatively (visually) or quantitatively by a point-counting technique in terms of size and shape of constituent isochromatic anisotropic units. Some cokes from coals were Isotropic. Acenaphthylene was only able to exert a smaller influence than decacyclene on the optical texture of the resultant cokes from co-carbonizations. Decacyclene was able to modify the optical texture for both the low-rank non-fusible and the caking coals. The effects of changing the proportions of coal to additive were examined. Results are interpreted in terms of ‘depolymerization’ of the coal by the action of the additive (as solvent) and also by the action of the additive in modifying the processes of formation of semi-coke via nematic liquid crystals.     

Rapid Quenching Technique Using Thermal-Image Furnace for Glass Preparation

A new technique combining a thermal-image furnace and a twin roller is described for quenching the melt to form glass. The technique was applied to the simple system Li₂O-SiO₂, since its fundamental parameters in the estimation of critical cooling rate are available. Glass flakes were obtained in the composition Li₄SiO₄, for which a very large critical cooling rate (∼10⁹ K·s⁻¹) was needed for glass formation.     

Impregnation of silk sericin into polyester fibers using supercritical carbon dioxide

Silk sericin was impregnated into polyester fabric using supercritical carbon dioxide (SCCO₂) to overcome polyester hydrophobicity. The effects of sericin molecular weight, pH of sericin, solution and cosolvent types on sericin impregnation were investigated. Enzyme‐hydrolyzed, acid‐, based‐hydrolyzed sericin in SCCO₂, and a 30 kDa sericin in SCCO₂ modified with cosolvents such as water, methanol, 1‐propanol, and acetone; and a modifier: sodium hydroxide solution were used in this work. Impregnation of sericin in polyester was indicated by Fourier transform infrared spectrophotometry (FTIR) and dyeing with acid dye. Degradation of polyester fibers during SCCO₂ process was indicated by scanning electron microscopy (SEM). Methylene blue dyeing was used to realize carboxyl group in polyester. The results showed no impregnation of sericin into polyester by using SCCO₂ modified with cosolvents. However, sericin was impregnated into modified surface polyester since hydrophilic groups such as carboxyl and hydroxyl groups were regenerated by alkaline hydrolysis. Samples impregnated with hydrolyzed sericin showed high color strength of Supranolechtbordeaux B acid dye. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Aspects of gasification and structure in cokes from coals

Cokes were prepared from nine coals of different rank and characterized by surface area measurement, reactivity to carbon dioxide at 1473K and Raman-laser spectroscopy. Rates of gasification of cokes on a unit surlface area basis (K¹ = g m^?2 min^?1) decreased with increasing rank of parent coal based on maximum oil reflectances. However rates of gasification could not be related to coke structure as measured by Raman-laser spectroscopy.     

Effect of perchloric acid on the molecular weight and yield of poly-THF

Polytetramethylene glycol (molecular weight range 1000–8000) was prepared by the polymerization of tetrahydrofuran (THF) using a binary catalyst system of fuming sulfuric acid and perchloric acid. When 28% fuming sulfuric acid alone was used as the catalyst, the average molecular weight of polymer was low, the maximum value being 1000–1100. By the combination of fuming sulfuric acid with a small amount of perchloric acid, the average molecular weight of the polymer was increased to about 8000. Furthermore, the molecular weight was readily controlled in the range of 1000 to 8000 by varying the amount of the binary catalyst.