Net-Shape Manufacture of Low-Cost Ceramic Shapes by Freeze-Gelation

The use of freeze-gelation (or freeze-casting) overcomes many of the familiar limitations of sol-gel processing and permits the formation of low-cost, crack-free, essentially zero-shrinkage ceramic bodies of complex shape. There are many potential industrial applications for the manufacture of complex shapes by the freeze-gelation process. This paper presents the results of an investigation into the effects of materials and processing parameters on the performance, properties and microstructures of the ceramics produced. In particular, the effects on porosity and flexural strength of the type and composition of sol, filler particle size ranges, and variable freezing conditions, have been investigated.     

Differential barothermal analysis in the course of reactive powder barothermal processing of RuAl alloys

Summary Thermostable high-temperature structural alloys based on the refractory (melting temperature T_m=2060°C) RuAl intermetallic (IM) with an ordered B2 crystal structure (CsCl type) are developed. This IM surpass other aluminides (NiAl, TiAl and Ni₃Al) used as the base for the development of high-temperature alloys and matrices of high-temperature composites (CM) intended for hot parts of supersonic engines, which serve at the temperatures exceeding operation temperatures of modern nickel-base superalloys. The differential barothermal analysis was used to develop the basic technological process of barothermal reaction sintering to produce near-net shape billets from RuAl-based structural materials.     

Correlation Between the Surface Acid-base Nature of Solid Metal Oxides and Temperature of CaSO4 Decomposition

By means of the combined use of scanning electron microscopy+energy dispersive spectrometry(SEM+EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetry (TG), the thermal decomposition of gypsum and gypsum bonded investment used for casting jewellery products has been studied in order to gain a further insight into the origin of the gas porosity in gold-based alloys produced via lost wax casting. The occurrence of the defect is related to the thermal decomposition of CaSO₄ that constitutes with silica the investment material and the decomposition of which takes place at a temperature very close to the casting temperature of some typical gold alloys. The decrease of the thermal decomposition temperature of gypsum is induced by the presence of silica and is related to the surface acid-base interaction between SiO₂ and CaSO₄. On the base of these results, the solid state thermal decomposition of calcium sulphate in the presence of other metal oxides characterised by different acid-base nature has been investigated and a correlation between the surface acid-base properties measured as isoelectric point of the solid surface (IEPS) and via XPS analysis and the temperature of CaSO₄ thermal decomposition is observed. This revised version was published online in July 2006 with corrections to the Cover Date.     

激基激光对铜膜印刷板表面微细蚀刻的初期化过程

用KrF激基激光,在稀释的Cl₂气体中对镀有铜膜的印刷板进行微细蚀刻的初期化过程.     

Three-Dimensional Porous Network Structure Developed in Hydroxyapatite-Based Nanocomposites Containing Enzyme Pretreated Silk Fibroin

Chemically modified silk fibroin (SF) with an enzyme, Proteinase K, has been incorporated into hydroxyapatite (HAp)-based nanocomposite attempting to strengthen the interfacial bonding between the mineral phase and the organic matrix. Particular emphasis is laid on the microstructure and microhardness of the composite along with the crystallographic properties of HAp. The whisker-like HAp crystallites of nanometer size show the preferential self-assembly and anisotropic crystal growth along c-axis. There appears porous microstructure with 70% of open porosity and pore size distribution of 10–115 um in the composite. Attributed to the enzyme modification, the crosslinkage between HAp clusters and SF matrix is improved to form an enhanced three-dimensional network extending throughout the composites and an increase of 35% in microhardness of the composite is achieved as well.     

核磁共振弛豫方法测定砂岩有效渗透率

在对储油岩芯液体吸附特性研究的基础上，提出了用核磁共振弛豫方法测定岩芯“有效渗透率”的方法，并对实际样品进行了测定分析，获得了较满意的结果. 此方法测定的有效渗透率较传统方法测定的渗透率更接近于实际的储油岩层的渗透率. 有效渗透率的值可以用来进行油藏注水开发效果分析，研究油层剩余油分布. 相信此方法将获得更广泛的应用.     

Study of Structural Surface Modified Tin Oxide Membrane Prepared by Sol-Gel Route Sintered at 400°C

This work describes the chemical modification by Tiron® molecules of the surface of SnO₂ nanoparticles used to prepare nanoporous membranes. Samples prepared with Tiron® content between 1 and 20 wt% and fired at 400°C were characterised by X-Ray Powder Diffraction (XRPD), Extended X-ray Absorption Fine Structure (EXAFS), N₂ adsorption isotherms analysis and permeation experiments. XRPD and EXAFS results show a continuous reduction of crystallite size by increasing the Tiron® contents until 7.5 wt%. The control exercised by Tiron® modifying agent in crystallite growth allows the fine tuning of the average pore size that can be screened from 0.4 to 4 nm as the amount of grafted molecules decreases from 10 to 0 wt%. In consequence, the membrane cut-off can be screened from 1500 to 3500 g · mol^–1.     

Study of NMR porosity for terrestrial formation in China

NMR logging is an effective method for porosity measurement. NMR-derived porosity only comes from the pore fluid and is, in principle, not affected by rock matrix. However, it is found that the difference between NMR-derived and conventional log-derived porosities is often between 2 to 6 pu, which is unacceptable, in terrestrial formation in China. In the paper, the theory of NMR porosity was reviewed. The influence factors on NMR porosity error were analyzed based on NMR core measurements. More than 30 core samples with a wide range of porosities including sandstone, limestone and artificial ceramic were chosen for the conventional and NMR porosity measurements. The current NMR data acquisition method was studied based on laboratory NMR core measurements and found to be not good for terrestrial formation. A new NMR data acquisition method suiting for terrestrial formation in China was proposed and much improved the accuracy of NMR porosity measurement. It is suggested that the analysis of core samples from different regions should be carried out before logging in order to obtain accurate NMR porosity.     

Averaged model of a cross hydrodynamic–mechanic process in a double porosity mediumModèle homogénéisé d'un processus hydrodynamique–mécanique couplé en milieu de double porosité

For the single-phase flow of a compressible liquid in a deformable double porosity medium, the closed homogenized model is obtained with a total splitting between various cross mechanic–hydrodynamic effects. The transfer between matrix and fractures is completed by the peristaltic effect and the effect of flow arising due to shearing strain. In the equation of deformations, a new stress appears being generated by the cross effects and matrix relaxation. To cite this article: M. Panfilov et al., C. R. Mecanique 334 (2006).