动态水热法合成超轻硬硅钙石的研究

硬硅钙石质隔热材料具有体积密度小,隔热效果好的优点,是优良的保温隔热材料。本研究采用动态水热合成工艺制备硬硅酸钙粒子,研究硅质原料粒径、水固比、添加剂等因素对水热合成产物成份和晶体形貌的影响。在此基础上对制备工艺进行优化,制备出具有中空结构的超轻硬硅钙石二次球团粒子。     

石灰活性对中空硬硅钙石二次粒子球形貌的影响

研究了石灰CaO晶粒尺寸和消解速度对合成中空硬硅钙石二次粒子球的影响。CaO对晶粒尺寸小，石灰消解速度快。CaO晶粒对合成硬硅钙石晶体没有影响，但影响硬硅钙石二次粒子球的形貌。CaO晶粒尺寸小能形成中空二次粒子球，球尺寸随CaO晶粒尺寸增大有所增大。CaO晶粒一旦烧结变粗则形成的是硬硅钙石堆积团。     

利用电石渣制备硬硅钙石

利用动态水热合成工艺,首次采用电石渣作钙质原料合成了硬硅钙石。探讨了原料、电石渣处理方法和水热合成工艺参数等因素对合成硬硅钙石晶体结构和微观形貌的影响,并采用XRD和SEM对其结构和形貌进行了分析及表征。结果表明,煅烧后的电石渣可以制备出纯度较高且结晶良好的硬硅钙石;电石渣处理方法对合成硬硅钙石晶体及其二次粒子形貌有很大的影响;煅烧后的电石渣与分析纯CaO作钙质原料制备硬硅钙石的水热合成工艺参数基本一致。     

用稻壳灰水热合成硬硅钙石的研究

研究了用稻壳灰作硅质材料水热合成硬硅钙石。结果表明，在合理选择钙硅比、水固比、搅拌时间，反应时间、反应温度等水热合成条件的情况下，稻壳灰中的ＳｉＯ２能够与Ｃａ（ＯＨ）２反应生成硬硅钙石晶体，并且这种纤维状的晶体还能相互交织成二次球形粒子。     

超声改性电石渣水热合成硬硅钙石晶体的初步研究

利用动态水热合成工艺,用超声技术改性电石渣作钙质原料合成了硬硅钙石晶体。采用XRD和SEM对合成产物的矿物组成和微观形貌进行了分析与表征。结果表明,超声改性后的电石渣可以制备出纯度较高的,具有球形结构的硬硅钙石。研究表明,超声改性电石渣使得电石渣预处理工艺简单,且为电石渣二次回收利用提供了一条有效的途径。     

不同硅质材料对水热合成硬硅钙石的影响

采用晶体与非晶态硅质原料,与氧化钙在高压釜中进行动态水热反应,合成晶须状硬硅钙石晶体,研究合成温度,保温时间等工艺参数对最终结晶产物的影响,并使用XRD、SEM对水热合成的产物进行分析.     

硬硅钙石水热合成的形成历程及硝酸锶对它的影响

利用XRD，SEM，TEM等方法对动态水热法合成硬硅钙石的形成历程进行了研究，由C-S-H凝胶不能在高于200℃温度下稳定存在，使硬硅钙石在180℃和220℃时的形成历程不同，配料中加入硝酸锶，提高料浆的离子强度，产生原盐效应，降低了C-S-H凝胶的生成速率，延缓了硬硅钙石的形成，硬硅钙石合成过程中的料浆中固体粒子的ζ电位是不断变化的，加入硝酸锶，可以降低料浆固体粒子ζ电位的绝对值，有利于硬硅钙石纤维状晶体以及团聚体的长大。     

不同硅源对硅钙材料中硬硅钙石物相生成及力学性能的影响

以熔融石英粉、白炭黑、硅溶胶为硅源,氢氧化钙为钙源,研究了硅源对水热法制备硅钙材料性能的影响.结果表明:以熔融石英为硅源时,材料中没有合成硬硅钙石相,以白炭黑和硅溶胶为硅源时合成了硬硅钙石纤维.硅溶胶具有更高的活性,形成硬硅钙石相含量较多,且呈针状结构.硬硅钙石的形成决定了硅钙材料的常温及高温性能,以硅溶胶为硅源的试样...     

较粗石英微粉制备超轻硬硅钙石隔热材料

用中位粒径20μm的粗石英和石灰石为原料，配制成Cao／SiO2摩尔比1．0，水固比20的料浆，倒入3000L的反应釜内进行水热反应，反应温度197℃，时间3h，合成的晶体料浆经XRD、SEM和TEM检测确认为由针状硬硅钙石缠绕组成的中空二次粒子球。球直径为30～100μm，球壁厚2～4μm。在料浆中加入纤维等辅助材料压制成型干燥后．即为容重小于130kg·m－3的超轻硬硅钙石隔热材料。     

不同硅质原料水热合成水化硅酸钙物相及其反应效率的研究

为探究不同硅质原料对水热合成水化硅酸钙物相的影响，研究了温度和硅钙比对产物的影响。采用X射线衍射(XRD)分析了水化硅酸钙物相，并探究了不同硅质原料与Ca(OH)₂的反应效率。结果表明，不同硅质原料与Ca(OH)₂的反应效率由高到低依次为硅藻土、石英、珍珠岩；在硅藻土-石灰体系中，硅藻土中非晶态二氧化硅的Si—O更易被破坏，具有不稳定性，致使硅藻土反应效率更高。在石英-石灰体系中，随着钙硅比的提高，空气中的CO₂参与反应，生成碳硅钙石与片柱钙石，且托贝莫来石与硬硅钙石会逐渐消失，通过合理调控硅钙比和水热温度可有效地控制反应产物，这对于不同硅质原料的选择、水热合成水化硅酸钙中产物的控制及水热合成水化硅酸钙应用领域具有重大意义。     

Calcium silicate based high efficiency thermal insulation

Abstract

The preparation by hydrothermal synthesis of a high efficiency, calcium silicate based thermal insulation is described using raw material mixes of silica, bentonite, and magnesium acetate or acetic acid. The materials were reacted in a high pressure autoclave at 200–250°C resulting in a product consisting of cenospheres of needle-like xonotlite crystals and some tobermorite. Properties including density, strength, microstructure, thermal stability, and water absorption and water repellence are presented.     

硬硅钙石晶须的水热合成

采用动态水热法,以硅酸钠钙为原料合成硬硅钙石晶须,通过搅拌使晶须形成高孔隙率的球形颗粒. 考察了温度、时间和原料CaO/SiO2摩尔比等反应条件对硬硅钙石晶须及其球形颗粒孔隙率的影响. 结果表明,将CaO和SiO2按摩尔比0.90~1.15溶于Na2O浓度为20 g/L的NaOH溶液中,控制液固比为30 mL/g,以300 r/min的转速在220℃下水热反应7 h以上,可制备出直径约200 nm、长径比大于20的硬硅钙石晶须,晶须相互缠绕形成的球形颗粒孔隙率最高可达93%.     

SiC/C纤维热力学生长机理研究

使用乙二醇作为稀释剂将硅溶胶稀释,得到不同浓度的硅溶胶溶液,用作涂覆商用碳纤维的原料。碳纤维表面改性后涂覆硅溶胶溶液,取出后在Ar气氛中于1 600 ℃保温30 min,硅溶胶涂层与碳纤维发生碳热还原反应形成SiC覆盖层。对制得的产物进行形貌和结构表征,并根据热力学数据对SiC包覆层的生长动力学和高温扩散机制进行研究。计算结果表明,反应过程为扩散控制。SiC/C纤维比碳纤维有更优异的耐高温氧化性能,为低成本制备新型陶瓷纤维提供可借鉴的思路和热力学依据。     

硬硅钙石中空二次粒子球形成机理的探讨

利用X射线衍射、扫描电镜等手段,对SiO     

A novel way to fabricate fibrous mullite ceramic using sol-gel vacuum impregnation

Inspired by bird's nest structure, fibrous mullite ceramic was fabricated by vacuum impregnation with mullite fibers as raw material and zirconia sol-gel as inorganic binder. The effect of impregnation times on the properties of the fibrous mullite ceramic, such as porosity, microstructure, compressive strength and room-temperature thermal conductivity were investigated. The results showed that low density (0.45–0.66?g/cm³), relative high compressive strength (0.62–3.34?MPa) and low thermal conductivity (0.037–0.125?W/mk) were exhibited for the sample. The toughness of fibrous mullite ceramic was enhanced due to the micro-creaks caused by transformation of zirconia. From the experimental results, it is suggested that it was an optimal method which have the potential use in high-temperature thermal insulation materials to produce fibrous mullite ceramics.     

Andalusite: An amazing refractory raw material with excellent corrosion resistance to sodium vapours

The chemical attack of alumina refractories by sodium vapours is far from been completely understood. In order to contribute to a better knowledge of this attack, a laboratory test was developed to simulate the sodium gaseous corrosion of different raw materials and refractories.Corrosion of alumina raw materials by sodium vapours is due to a dissolution–precipitation process by a Na₂O rich liquid phase. The gaseous corrosion strongly depends on the microstructures and the assemblage of phases in alumina raw materials. Fire clay and andalusite raw materials exhibit very high corrosion by Na vapours. In spite of an initial high silica glass content, and as a result of trapping of the main part of the glass in the capillary network of the mullite composite crystal, mullitised andalusite leads to excellent corrosion resistance which is close to monocrystalline fused mullite.Consequently, The use of mullitised andalusite particles in the matrix of alumina refractories limits the liquid phase formation during corrosion by sodium gas. These experimental results are in agreement with thermodynamic calculations.     

Wet-chemical coating of silicon carbide fibers with hexagonal boron nitride layers

Hexagonal BN fiber coatings and BN powders were prepared by pyrolysis of the raw materials boric acid and urea in an atmosphere consisting of hydrogen and nitrogen. The powders were used to determine the appropriate mixing ratio of the raw materials to produce BN with the desired composition and crystal structure. The pyrolysis of boric acid and urea in a molar mixing ratio of 1:2 resulted in a BN that was hexagonal and had a near-stoichiometric composition.To prepare a solution for the coating of fibers, boric acid and urea were dissolved in an ethanol-water mixture. The coating was then applied to SiC filaments using a continuous roll-to-roll dip-coating process. It could be shown by SEM/EDS that BN layers were applied to the fibers. No significant bridging in the fiber bundle was found. Furthermore, it could be demonstrated by grazing incidence x-ray diffraction that the layers were crystalline.     

利用煤矸石生产优质G级油井水泥的试验研究

油井水泥属专用水泥，生产中原材料往往选择优质天然硅石，随着天然材料的日益紧缺，急需寻找一种成本低性能优的材料替代硅石生产优质油井水泥，本文通过利用工业废渣煤矸石替代硅石生产优质G级油井水泥开展了试验研究，最终确定了高饱和比高硅酸率配料方案，调整了一系列生产工艺和粉磨工艺，获得各大油田配伍性能良好的高质量低成本的油井水泥。