硝酸锶对水热合成硬硅钙石球形团聚体的影响

硬硅钙石是一种用途广泛的保温材料，本工作以硝酸锶作为矿化剂，研究了在动态水热合成硬硅钙合成中，硝酸锶对硬硅钙石球形团聚体的影响。研究表明：在合成时添加硝酸锶，可以使水化硅酸钙（C－S－H）凝胶的ξ电位的绝对值减小，从而C－S－H胶团的凝聚长大，C－S－H凝胶粒度的增大是硬硅钙石球形团聚体增大的基础，Sr^2 进入到硬硅钙石晶体内引起其晶胞常数a和c的增大，促进硬硅钙石的纤维状晶体以及球形团聚体的长大，从而有利于得到轻质硬硅钙石材料。     

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。     

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。     

微孔硅酸钙绝热材料的密度和导热系数的关系

由动态水热合成得到的硬硅钙打球状团聚体料浆，通过压滤成型可制成微孔硅酸钙绝热材料。压滤成型工艺对最终材料的密度和显微结构有很大的影响，从而影响材料的导热系数。整个压滤过程可分为4个阶段，加压到第2与第3阶段边界附近，结束成型可获得低密度的材料，而在第4阶段内结束压滤成型则得到高密度的材料。对不同密度微孔材料的显微结构和孔径分布进行研究，并测定了不同密度材料的导热系数。结果表明：在100℃附近，材料的密度越小其导热系数也越小．而在200℃以上，则随着密度的增大，材料的导热系数降低。     

水热合成硅酸钙微孔球形颗粒

动态水热合成生成的硅酸钙微孔球形颗粒的空隙率可高达90%以上,颗粒由无数纤维状硬硅钙石晶体构成.讨论了合成工艺参数对形成球形颗粒的影响.反应物中SiO2 和CaO的比例需保持1∶1,否则反应最终产物中可能出现其它硅酸钙矿物.搅拌对形成球形颗粒起着决定性作用,在搅拌作用下C-S-H凝胶表面受到切向剪切力矩的作用,片状的凝胶被卷成为球形颗粒.在水热合成过程中加入矿化剂能够降低凝胶粒子ζ的绝对值,促进C-S-H凝胶形成大的团聚体,矿化剂的存在提高了由C-S-H凝胶团聚生成硬硅钙石的温度,从而保证C-S-H凝胶团聚有充足的时间形成大的球形团聚体.     

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...     

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。     

硅酸钾碱液水热合成针状硅灰石反应历程

利用钾长石–KOH–H_2O体系分解反应所得硅酸钾碱液合成针状硬硅钙石,用作合成硅灰石的前驱体。采用OLI Analyzer 9.2软件模拟K2O–CaO–SiO_2–H_2O体系化学平衡,预测了合成硬硅钙石的初始CaO/SiO_2摩尔比、反应温度和液固比范围。在此基础上通过单因素实验,确定了合成硬硅钙石的优化条件。反应历程为:水合硅酸钙→雪硅钙石→雪硅钙石+硬硅钙石→硬硅钙石。合成的硅灰石保持了硬硅钙石的针状形貌,分散较均匀,长约10~15μm,直径约300 nm,长径比约40,符合建材行业一级品标准。     

不同硅质原料对硬硅钙石二次粒子形貌的影响

几种硅质原料被用于硬硅钙石二次粒子制备中。实验表明。在单纯使用非品质硅质原料时，所生成硬硅钙石结晶发育差，由此形成的硬硅钙石二次粒子具有高密度和低的中空度。此实验结果与前人研究结果不一致。本实验结果同样表明使用天然粉石英作为硅质原料，加入氧氯化锆添加剂可以形成直径100nm左右结晶良好的硬硅钙石纤维，这些硬硅钙石纤维可以形成具有中空结构的低密度硬硅钙石二次粒子。它提供了一种低成本制备超轻硬硅钙石产品方法的可能。     

悬浮体中团聚体的产生机理及其对材料结构与性能的影响(英文)

研究了陶瓷胶态成型过程悬浮体中产生团聚体的微观机理,根据液体介质中陶瓷粉体颗粒之间的作用势,建立了团聚体产生的微观结构模型.利用环境扫描电子显微镜对悬浮体中粉体团聚的显微结构进行"准"直接观察,发现悬浮体中存在2种团聚体形态:Ⅰ型团聚体(硬团聚)和Ⅱ型团聚体(软团聚),揭示了团聚体的产生是由于浆料的固相含量偏离了稳定固相含量.研究发现:悬浮体中的团聚体会遗传到陶瓷体中,并对陶瓷构件的力学性能有显著影响.探讨了团聚体对烧结体的结构及力学性能影响的原因.当悬浮体中固相含量低于稳定固相体积分数ψ0时,悬浮体中会形成松散团聚即软团聚;当固相含量超过ψ0时,悬浮体中会形成紧密团聚即硬团聚:当固相含量等于ψ0时,悬浮体具有均匀分散的稳定结构.由于悬浮体固相含量偏离稳定周相含量ψ0而在悬浮体中产生的团聚体,会由于原位周化而遗传到坯体之中,影响烧结体结构的均匀性.     

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.     

硅钙基固废原料配比及蒸养条件对硅酸钙板力学性能的影响

研究协同利用硅钙渣、粉煤灰、水泥和脱硫石膏制备硅酸钙板时,原料配比、蒸养条件对硅酸钙板力学性能、水化产物的影响,并利用XRD、IR和SEM表征了原料的协同水化历程和水化产物的微观结构和表面形貌.试验结果表明:最佳原料配比为硅钙渣60%、粉煤灰24%、水泥10%和脱硫石膏6%;最佳蒸压养护条件为蒸养温度180℃,恒温蒸养时间8 h,硅酸钙板抗折强度满足国家标准强度的D1.3的Ⅱ级要求;随着蒸养温度升高,原料水化依次生成C-S-H凝胶、托贝莫来石和针状硬硅钙石,大量托贝莫来石和硬硅钙石的生成使得硅酸钙板的强度得以提升.     

Effects and mechanism research of the crystalline state for the semi-crystalline calcium silicate

Semi-crystalline silicates have wide varieties and are used in a wide range of fields for their unstable crystalline degrees. The crystalline state largely depends on the synthesis time, temperature and nucleation promoter. In this paper, the above three parameters have been researched. With different synthesis temperatures, the active calcium silicate, xonotlite and the intermediate products have been simulated. After that, the crystalline process has been tracked from 1 h to 8 h. A model of calcium silicate formation process has been set up based on the time and temperature experiments. Finally, a nucleation promoter, aluminum, has been added into the synthesis process. The crystalline degree is greatly increased with the aluminum addition. When the aluminum and silicate rate is 0.1, the crystalline degree is above 70% after 1 h.     

Reactivity of SiO2 fume from ferrosilicon production with Ca(OH)2 under hydrothermal conditions

Reactivity has been studied of SiO₂ fume from ferrosilicon production with Ca(OH)₂ in suspension, with stirring, under hydrothermal conditions at 190°C and 200°C from 1 to 12 hours. Reaction product after a 4-hour synthesis at 200°C is calcium silicate hydrate xonotlite C₆S₆H, with some C-S-H(I) phase. When glass fibers were added to the slurry, which was subsequently filtered, pressed, and dried, the product thus obtained was lightweight thermal insulation material, temperature-resistant up to 800°C and usable up to 1000°C. The product has excellent insulation properties with thermal conductivity 0.042–0.081 W/mK at bulk densities 150–500 kg/m³.     

硬硅钙石隔热水性乳胶涂料的制备及性能测试

研究硬硅钙石型硅酸钙作为隔热填料制备隔热涂料的配方及工艺,并对涂料进行常规性能和隔热性能的测试,测试结果表明,所制备的隔热涂料具有较好的隔热性能,各种常规性能指标符合GB／T9755—2001。     

钙硅比对水热合成水化硅酸钙实验的影响研究

针对钙硅比对水化硅酸钙产品成分与结构影响较大的现象,为了分析这种影响规律,实验过程中按照不同钙硅比配入原料,采用水热合成法制备水化硅酸钙,实验最终得到了钙硅比对产物水化硅酸钙物相微观结构以及聚合度的影响规律.对实验产物进行XRD分析发现,随着钙硅比的升高,分析结果中出现了Tobermorite(托勃莫来石)以及硬钙硅石的相.通过对产物SEM分析发现,随着钙硅比的升高,产物颗粒表面微观结构变得疏松.通过红外分析发现,产物聚合度随着钙硅比的升高而降低.     

Hydrothermal Formation of Calcium Silicate Hydrates

The kinetics of solution of quartz and the crystallization of calcium silicate hydrate during hydro-thermal treatment of single crystals of quartz in saturated lime solutions were studied. Microscopic examination of sections of the product layer showed that the calcium silicate hydrate was of fibrous crystal habit and grew radially from nucleating centers in a general direction away from the quartz surface. X-ray diffraction established that the mineral was mainly xonotlite. The crystallization of the mineral did not follow the receding surface of the quartz; the product layer was extended only on the surface in contact with the lime solution. The silicate ions apparently diffused preferentially through the product layer although separate measurements proved that the membrane had no selective action against the diffusion of calcium ions. Plots of the weight of xonotlite versus square root of time gave straight lines indicating that the process was diffusion-controlled at 235° and 335°C.     

Synthesis and characterization of calcium silicate insulating material using avian eggshell waste

This work focuses on the synthesis of calcium silicate insulating material via solid state reaction using avian eggshell waste as alternative calcium source. The calcium silicate formulations were mixed in a molar ratio SiO₂:CaO (1:1) and fired at 1100 °C for 24 h. The calcium silicate formulations were characterized by XRD, TG-DTA, dilatometry, SEM/EDS, and thermophysical properties (thermal diffusivity, heat capacity per unit volume, and thermal conductivity). The synthesized calcium silicate materials are composed mainly of wollastonite with minor amounts of larnite and rankinite. It was found that a processing of the avian eggshell waste (raw eggshell waste and calcined eggshell waste) had an influence on the thermophysical properties. Calcium silicate pieces were prepared by uniaxial pressing at 82 MPa, curing, and then testing to determine their use as thermal insulating material. The microstructure was evaluated by SEM. The results showed that both raw and calcined avian eggshell wastes could be used as an alternative calcium source in the calcium silicate formulation. It was found that the calcium silicate pieces reached low thermal conductivity values (0.252–0.293 W/mK). Thus, the developed calcium silicate materials using avian eggshell waste act as a good thermal insulation ceramic material.     

CaO-MgO-SiO2-H2O体系的热力学基础研究

本文从热力学角度系统研究了CaO-MgO-SiO2-H2O体系及钢渣中钙镁硅矿物在水热条件下的反应特性,结果表明：在CaO-MgO-SiO2-H2O系统中,CaO优先与SiO2反应生成水化硅酸gO只能与剩余的SiO2反应生成水化硅酸镁：MgO固溶时,可促进托勃莫来石向硬硅钙石转化。而对白钙沸石向白钙镁沸石的转化影响不大,不固溶MgO时,低温型水化硅酸钙向高温型转化温度提高,钢渣鲁镁硅矿物中,镁蔷薇辉石活性最大,透辉石活性最差,钙镁橄榄石和镁黄长石介于前两者之间。