钛硅分子筛的合成及其催化氧化反应研究进展

综述了近几年关于钛硅分子筛的合成方法及催化氧化反应方面的研究进展。钛硅分子筛是一类由四配位钛原子取代分子筛骨架中的硅或铝所形成的杂原子分子筛。孤立的四配位钛原子使分子筛具有优异的催化氧化特性,尤其是与H₂O₂组成的氧化体系,对烃类的低温选择氧化反应具有良好的应用前景。不同孔道结构的钛硅分子筛对于反应物及产物的分子尺寸具有不同的选择性,TS-1、TS-2等微孔分子筛更适合小分子反应(如丙烯环氧化反应),而Ti-SBA-15、Ti-MCM-48等介孔分子筛则对较大分子的反应更有利(如苯乙烯环氧化反应)。     

矽酸盐型镍矿石矿物加工技术研究

针对矽酸盐型镍矿石采用目前成熟的浮选方法回收其中的镍,在产出合格镍精矿的前提下,通过强化矿浆分散、脱泥的小型试验和工业试验,镍回收率提高有限.为进一步提高镍回收率,对工艺条件、流程结构和选矿设备进行分析,提出建议,以期充分利用有限的镍资源.     

灰砂材料水化产物与其若干性能的关系

本文总结了灰砂材料的水化硅酸钙单体的物理力学性能以及水化产物与性能关系方面的研究进展,论述了研究水化产物与性能关系应注意的问题。     

Long-chain polyamines (LCPAs) from marine sponge: possible implication in spicule formation

Two distinct marine organisms, diatoms and sponges, deposit dissolved silicates to construct highly architectural and species-specific body supports. Several factors such as proteins, long-chain polyamines (LCPAs), or polypeptides modified with LCPAs are known to be involved in this process. The LCPAs contained in the silica walls of diatoms are thought to play pivotal roles in the silica deposition. In sponges, however, a protein called silicatein and several other proteins have been reported to be the factors involved in the silica deposition. However, no other factors involved in this process have been reported. We have identified the LCPAs from the marine sponge Axinyssa aculeata and present here some evidence that sponge-derived LCPAs can deposit silica and that the LCPA derivatives are associated with spicules. The results indicate a common chemistry between sponges and diatoms, the two major players in the biological circulation of silicon in the marine environment. A wide variety of organisms are known to utilize silica in their biological processes. Polyamines or other functional molecules might be involved, in combination with proteins, in their biosilicification process.     

Crystallinity and crystallization mechanism of lithium aluminosilicate glass by X-ray diffractometry

1 Introduction Lithium aluminosilicate(LAS) glass-ceramics has been one of the most intensively studied systems because of its great creep resistance, very low thermal expansion characteristics and excellent thermal shock resistance [1?3]. It has been co…     

Some speculations on the mechanisms of abrasive grinding and polishing

The mechanisms of grinding, a predominantly fracture mechanism in brittle material, and polishing, a predominantly plastic shearing mechanism, appear quite different. However, in a number of cases, it can be shown that the difference between the two mechanisms can be triggered by differences in depth of cut and abrasive size. Results are presented from recent polishing research that tend to support a physico-chemical interaction model involving aqueous diffusion, internal hydrolysis and ion exchange mechanisms that may explain the plastic to brittle transition in silicate materials. The model would seem to have clear implications for both low-scatter polishing and fine machining of silicate materials.     

Non-hydrothermal synthesis of copper-, zinc- and copper-zinc hydrosilicates

Cu/SiO₂, Zn/SiO₂ and Cu-Zn/SiO₂ samples have been prepared by the homogeneous deposition-precipitation method. The samples were analyzed by thermal analysis, X-ray diffraction and infrared spectroscopy after various heat treatments and compared with data obtained for several minerals. It has been shown that interaction between the components occurs through formation of hydrosilicates. Copper-silica system at a Cu:Si ratio ≤ 1, gives rise to a hydrosilicate stable up to a calcination temperature of 930 K resembling the mineral Chrisocolla; at higher ratios a hydroxonitrate (gerhardite type) is also formed. Zinc-silica interaction produces two hydrosilicates such as a well crystallized Hemimorphite at Zn:Si = 2 and highly dispersed Zincsilite at Zn:Si ≤ 0.75, both stable up to 1073 K. The Zincsilite structure consists of three layered sheets (an octahedral layer sandwiched by two tetrahedral ones) like the Stevensite mineral group. For the copper-zinc-silica system no copper hydrosilicate is formed. Copper merely enters the Zincsilite structure independenly of the applied (Cu + Zn):Si ratio. Resulting layered copper-zinc hydrosilicate may be described by formula Zn_x-yCu_y(Zn_3-x–zCu_z–y▪_x)[Si₄O₁₀](OH)₂.nH₂O, where Zn_3-x-zCu_z-y– ions are located in octahedral sites, Zn_x-yCu_y–ions in the interlayer; ▪_x are vacancies in the layers. Copper and zinc in excess of the Zincsilite ratio of Me:Si = 0.75, gives rise to copper and copper-zinc hydroxonitrates. Received: 7 November 2000 / Reviewed: 23 January 20001 / Accepted: 23 January 2001