Dissolution processes,hydrolysis and condensation reactions during geopolymer synthesis: Part I—Low Si/Al ratio systems

Initial geopolymeric reaction processes governing dissolution of solid aluminosilicate particles in alkali solutions have been investigated using conventional experimental techniques, and the data analysed by speciation predictions of the partial charge model (PCM). For metakaolin powders activated with 5.0 M NaOH, solid-state nuclear magnetic resonance (NMR) spectra disclose the existence of monomeric [Al(OH)₄]⁻ species after two hours of dissolution, consistent with PCM predictions. However, no equivalent monomeric silicate species were observed for 5.0–10.0 M NaOH activator solutions characteristic of systems with nominal Si/Al ≤ 1. The apparent absence of monomeric silicate species suggest rapid condensation of silicate units with [Al(OH)₄]⁻ to generate aluminosilicate species, as indicated by the evolution of the shoulder at around −87 ppm in the ²⁹Si NMR spectra. Of the two possible stable silicate species [SiO₂(OH)₂]²⁻ and [SiO(OH)₃]⁻, the latter appears most likely to condense with [Al(OH)₄]⁻ to produce aluminosilicate oligomers, from which larger oligomers subsequently form through further condensation with [Al(OH)₄]⁻ leading to a gradual build up of aluminosilicate networks and a lowering of system alkalinity. This dissolution and hydrolysis sequence at the early stages of synthesis suggests a reaction path wholly consistent with predictions of the partial charge model.     

广州中信商城地下连续墙施工工艺

本文介绍了广州中信商城地下连续墙的施工工艺。该工艺采用膨润土制浆配制方式，施工质量高，效果好。     

辽河减压渣油中金属铁的赋存与分布特征

考察了辽河减渣在吸附分离、酸性溶液萃取和沥青质轻度降解过程中金属铁的分布和转移情况。结果表明，辽河减渣中有近90％的铁富集在胶质和沥青质中，部分铁以侧链较短的环烷酸盐或酚盐形式存在，部分铁连接在沥青质分子的侧链上，或是被包裹在沥青质大分子中。     

储罐中缓蚀剂的应用方法

缓蚀技术是减轻石油化学工业中各类油、气、水储罐内腐蚀的有效方法,但国内目前应用尚不普遍,原因之一是尚未找到较适宜的加入方法,使缓蚀剂的应用可以经济地和长时间地起作用,本文综述了储罐内缓蚀剂的各种应用技术,重点介绍在涂层中加缓蚀剂的技术,基于其溶解性或离子置换特性,在实际使用时缓蚀剂可持久、稳定地释放出来。这后一类技术可能是在储罐内应用缓蚀剂的最好方式之一。     

Pressure control for complete denture impressions

Pressures produced during a final impression have been discussed from the standpoint of where they should be applied and where they should be reduced. Areas of the edentulous mouth requiring little pressure are: the palate, residual ridges, and areas of easily displaced gingiva. More pressure is needed in the border seal, on the buccal shelf, and against the retromylohyoid fossa. A clear processed acrylic resin tray with escape holes has been shown to meet the requirements for selective pressure application. Zinc oxide paste is the final impression material of choice in most instances.     

Modeling low-frequency electrode-type resistivity tools in invadedthin beds

The authors formulate and implement a numerical mode-matching (NMM) method to model electrode-type resistivity tools in invaded thin beds. The authors derive the low-frequency approximation of the Maxwell's equations to obtain the partial differential equation for the potential field. The new NMM program is validated by comparing the numerical results with those obtained from other dc programs. It is found that this new program is much faster than the program using the finite-element method (FEM), and hence is useful for routine interpretation of resistivity logs and for inversion     

Morphology control of titanium oxides by tetramethylammonium cations in hydrothermal conditions

The effect of tetramethylammonium cations (TMA⁺) on TiO₂ crystal morphology in hydrothermal conditions has been studied. The as-synthesized samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) methods. The morphologies including besom-like particle, nanosheet and nanotube have been observed. The different ways TMA⁺ cations in the hydrothermal bases affect the crystal growth manner are suggested to be responsible for the different morphologies of the as-synthesized samples.