煤气中HCl对热风炉耐火材料侵蚀过程的研究

通过对高炉煤气中HCl侵蚀热风炉耐火材料的研究发现,HCl气体可以促使黏土砖中硅酸盐玻璃质和隐晶质铝硅酸盐向晶体莫来石和方英石的转化。 HCl气体还可以促使硅砖中的方英石向鳞石英转化,颗粒结晶度明显变差,容易导致硅砖内部颗粒因膨胀不均匀而产生龟裂现象。     

莫来石结合Al2O3-SiC浇注料的显微结构特征

借助SEM和EDAX研究了莫来石结合Al2O3 -SiC浇注料的显微结构特征。结果表明 :在莫来石结合Al2 O3 -SiC浇注料中 ,莫来石相与填充在其间隙的玻璃相形成连续基质 ;刚玉颗粒与基质中SiO2 反应生成的二次莫来石与基质中的原生莫来石交错存在 ,构成网状结构 ;SiC颗粒表面高温氧化生成的SiO2 膜 ,改善了SiC颗粒与基质的润湿性 ,是其与基质直接结合的媒介。     

碳化硅泡沫陶瓷中烧结助剂对莫来石生成的影响

添加几种烧结助剂如硅溶胶、氧化铝、黏土、苏州土和石英的不同组合,研究了烧结助剂对碳化硅泡沫陶瓷中莫来石相生成的影响.实验结果表明：在1 400℃烧结1 h的过程中,氧化铝、黏土和硅溶胶的组合会显著促进莫来石的生成,从而提高碳化硅泡沫陶瓷的高温强度和耐火度.莫来石相在较低温度下的大量生成主要归功于黏土产生液相,以及硅溶胶中非晶态氧化硅对氧化铝颗粒的包裹作用,从而降低了扩散距离.     

沭阳兰晶石及其合成莫来石试验报告

本试验采用X-衍射分析、扫描电镜及热膨胀等测定手段综合分析了沭阳兰晶石的特殊热性能及矿物组成.通过测定沭阳兰晶石在1300℃分解并转化为莫来石和方石英引起16～18%的体积膨胀,同时变体膨胀随颗粒细度的提高而降低,一般200目以下的颗粒膨胀率仅为4～8%.当温度提高至1550℃时产生收缩,矿物组成主晶相为莫来石和少量的液相,并具有低的热膨胀性能.试验表明沭阳兰晶石具有的特殊热性能是发展我国不定形耐火材料及人工合成莫来石的良好天然原料.     

杂砂岩碱集料反应特征

杂砂岩集料所含的石英组分是引起碱集料反应的主要活性来源,研究该集料中的石英溶出及其在碱溶液中的行为特征,结果发现:石英颗粒尺寸和相应的硅溶出速度之间存在着一定的相关性,即:石英颗粒尺寸越小,其比表面积越大,同等条件下相应的硅溶出速度越大;石英颗粒的结构特征变化规律与杂砂岩试样本身的碱活性大小之间不存在相关性.集料中的铝主要来源于γ-Al2O3纳米相、黑云母和白云母,其对溶液中硅溶出的影响机理不同.集料中的铝溶出生成铝硅酸盐从而引起溶液中溶出硅含量的降低,砂浆或混凝土碱集料反应膨胀率的大小与溶液中所谓的"自由硅"含量有关,即"自由硅"含量越大,同等条件下的碱集料反应膨胀越大.这些相关性对于实际工程应用非常重要,由此可望建立评价杂砂岩碱活性敏感性的直接测试方法.研究还发现通过添加高铝粉可抑制碱集料反应产生的膨胀.     

烧结温度对莫来石/石英质经济型陶粒支撑剂性能的影响

以阳泉长青Ⅲ级铝矾土和砂土为原料,在1420~1540℃下烧结制备了莫来石/石英质经济型陶粒支撑剂,研究了烧结温度对莫来石/石英质经济型陶粒性能的影响,并与目前市场上的支撑剂进行了详细的对比,得出这是一种性能优于天然石英砂、成本低于人造陶粒支撑剂的一种经济型陶粒支撑剂;并采用XRD和SEM等手段对陶粒支撑剂的性能和物相形貌进行了表征和分析。结果表明:在1510℃下烧结制备的陶粒支撑剂体密度为1.39 g·cm-3,视密度为2.78 g·cm-3,35 MPa下的破碎率为5.54%;在该温度下,莫来石晶相已经发育完全,且石英颗粒填充在莫来石形成的网络空间结构中,烧结致密化程度较高。     

流化床燃煤固硫灰渣微观结构研究

分别用X射线衍射、红外光谱和扫描电镜研究固硫灰渣矿物组成、硅酸盐阴离子聚合度和颗粒形貌。并与煤粉炉粉煤灰进行对比。结果表明：与粉煤灰不同，固硫灰渣基本不舍莫来石；固硫灰渣[SiO4]和[AlO6]聚合度均低于粉煤灰；固硫灰渣的颗粒形貌极其不规则且疏松多孔。研究发现，固硫剂和生成温度对固硫灰渣微观结构影响很大。     

Al2O3对ZTM陶瓷结构与性能的影响

本文研究了氧化铝对ZTM陶瓷结构和性能的影响.发现在烧结过程中,氧化铝可固溶于莫来石颗粒形成富铝型柱状莫来石,产生的体积膨胀增强了基质对氧化锆颗粒的约束,使材料中的四方氧化锆相对含量增加,其强韧化效果进一步发挥,明显改善了材料的力学性能.     

Al2O3在莫来石中固溶对ZTM/Al2O3陶瓷结构与性能的影响

研究了加入氧化铝对ZTM陶瓷结构和性能的影响.发现在烧结过程,氧化铝可固溶于莫来石颗粒形成富铝型柱状莫来石,并因其产生的体积膨胀增强了基质对氧化锆颗粒的约束,使材料中的四方氧化锆相对含量增加,其强韧化效果进一步发挥,明显改善了材料的力学性能.     

宋代建盏的科学研究

五、建盏的显微结构和毫纹的生成机理在光学显微镜下证实,不管它们的釉外观如何差异,建盏的胎质一般皆为含氧化铁的粘土所构成,除了明显地呈一轴晶正光性的残留石英颗粒之外,可以看到层状粘土矿物残骸,其附近如有低熔液相存在则会发育成尺寸较小的莫来石晶丛。胎中的氧化铁在     

Sintering of clay-chamotte ceramic composites for refractory bricks

Clay-chamotte composites were realized for manufacturing refractory bricks. We used two kaolinitic refractory clays mined in Cameroon and two calcined clays (chamottes) with a large grain size (0.1–4 mm). Clay-chamotte composites containing various quantities of chamotte (0–50 wt%) were shaped and sintered at 1200–1350 °C. The structural characteristics of composites indicated the presence of quartz from the initial clay, cristobalite and mullite. SEM observations revealed very heterogeneous microstructures where porosity is weakly distributed and large pores are entrapped at the vicinity of large chamotte and quartz grains. In general, the global porosity increases with the chamotte content. A specific interpretation of the matrix role on the global sintering behaviour reveals that only a part of the matrix acts effectively. Since the most part of the global porosity is within the matrix, it is distributed in matrix zones, which participate effectively to sintering and in inert matrix zones where larger pores occur. The global mechanical strength is controlled by the matrix behaviour, but the high porosity of this phase is unfavourable to high strength values. Besides, the occurrence of larges pores and local cracks at large grain interfaces from thermal stresses are critical flaws, which reduce the mechanical strength.     

Transient liquid phase diffusion process for porous mullite ceramics with excellent mechanical properties

Porous mullite ceramics were fabricated by the transient liquid phase diffusion process, using quartz and fly-ash floating bead (FABA) particles and corundum fines as starting materials. The effects of sintering temperatures on the evolution of phase composition and microstructure, linear shrinkage, porosity and compressive strength of ceramics were investigated. It is found that a large amount of quartz and FABA particles can be transformed into SiO₂-rich liquid phase during the sintering process, and the liquid phase is transient in the Al₂O₃-SiO₂ system, which can accelerate the mullitization rate and promote the growth of mullite grains. A large number of closed pores in the mullite ceramics are formed due to the transient liquid phase diffusion at elevated temperatures. The porous mullite ceramics with high closed porosity (about 30%) and excellent compressive strength (maximum 105?MPa) have been obtained after fried at 1700?°C.     

Effect of pyrophyllite incorporation in porcelain composition on mechanical properties and microstructure

China clay (Kaolin) and quartz in the ratio of 1:2 was progressively replaced by pyrophyllite in a conventional porcelain mix. Addition of 15% pyrophyllite as a replacement of a combination of china clay and quartz decreased the linear shrinkage by 5.03% while fired strength was improved by about 31.5% compared to that of the conventional body fired at 1300 °C. Incorporation of pyrophyllite beyond 15% resulted in early vitrification of porcelain composition, although in lower proportion the effect is not so significant. Percentage of mullite was found to increase in the fired specimens even when kaolinite was progressively replaced by pyrophyllite. However, beyond 22.5% pyrophyllite addition, there occurred large volume of glass formation. Presence of large volume of glassy phase as well as formation of large pores of various shapes resulted in deterioration in ceramic properties. The size and shape of mullite crystals is to a large extent controlled by the fluidity of the liquid matrix from which they grow and this is again a function of temperature and composition.     

A novel and green preparation of porous forsterite ceramics with excellent thermal isolation properties

This work provides a novel and green approach to preparing porous forsterite ceramics by a transient liquid phase diffusion process based on fused magnesia and quartz powders without detrimental additives. The size of quartz particles markedly affected the sintering behaviors, phase composition, microstructure and properties of the porous forsterite ceramics. Fine quartz particles (D₅₀, 3.87?µm) accelerated the rate of the forsterite formation at elevated temperatures and promoted solid-state sintering behavior of the porous ceramics. Conversely, coarse quartz particles (D₅₀, 25.38?µm) reduced the rate of the solid state reaction and a large amount of unreacted SiO₂ and enstatite (MgSiO₃) phases transformed into a transient liquid-phase during the firing process. This effect resulted in a high porosity (approximately 58.89%) and formation of many large pores (mean pore size of 42.36?µm). These features contributed to the excellent thermal isolation properties of the prepared porous forsterite ceramics. The strength of the obtained porous ceramics (about 23.6?MPa) is relatively high compared with those of conventional ceramics.     

The effect of particle size of body components on the processing parameters of semi transparent porcelain

The effect of the particle size of quartz and K- feldspar on the sintering behaviour and technical properties of semi transparent porcelain were investigated. This study was implemented by “the Factorial Experimental Design Method” to determine the effect of factors on semi vitreous porcelain production. The sintering behaviour of the samples were examined by using an optical dilatometer. The phases and their respective amounts in the microstructure were determined by way of Rietvelt X- ray diffraction (XRD) technique. Furthermore, the values such as shrinkage, water absorption, bulk density, porosity, thermal expansion, light transmission measurements were taken on the samples and the microstructures were studied by SEM. It was observed that as the particle size of quartz and K- feldspar decreased; the viscosity of the liquid phase fell down, the relative amount of secondary mullite crystals increased and the large pores were removed among the particles and the densification rate increased. Data were analysed by Minitab 13.20 software, and assessed in relation to the amount of glassy phase and its viscosity. The effect of K- feldspar particle size on the densification of porcelain is less than the change of heat treatment and quartz particle size.     

Phase evolution and microstructural characterization of sintered ceramic bodies from contaminated marine sediments

The phase evolution during firing of ceramic bodies from three different contaminated marine sediments was investigated as a function of temperature. The mineralogical evolution examined by X-ray diffraction (XRD) revealed that quartz, which is a main crystalline phase in the original marine sediments, remains as a main phase in the sintered bodies. In addition, a glassy phase and new crystalline phases appear as result of different chemical reactions during firing. Scanning electron microscopy (SEM) showed a homogeneous microstructure composed by pores, crystals and a ceramic matrix. Energy X-ray dispersive spectroscopy (EDS) analyses permitted to distinguish the crystalline phases previously identified by XRD and also minor phases, which were not detected in the X-ray diffractograms.     

Controllable morphology and wettability of polymer microspheres prepared by nonsolvent assisted electrospraying

Polymethylmethacrylate (PMMA) microspheres with various morphologies are fabricated by nonsolvent assisted electrospraying. The morphology evolution is determined by nonsolvent properties including the solubility parameter, surface tension and viscosity, and nonsolvent induced phase separation is the main reason for the formation of the porous and/or hollow structures. It is found that nonsolvent possessing a high surface tension is beneficial to the formation of a hollow structure, while the large phase separation tendency between nonsolvent and the polymer can promote pore generation on the sphere surface. The nanosized pores, especially hierarchical pores, can enhance the hydrophobicity of the substrate surface coated with these microspheres. On the other hand, nonsolvent with a large viscosity could prevent the growth of the phase separated nuclei, leading to the presence of relatively small and discontinuous pores on the microsphere surface, which can finally cause the decrease of the contact angles. The surface pores of the electrosprayed microspheres are even eliminated if polymer additive, i.e., PVP, is incorporated into the polymer-solvent-nonsolvent solution. The addition of PVP renders the microsphere coated surface hydrophilic, which can be completely wetted by water droplets.     

Effects of heat treatment on the physical properties of lightweight aggregate from water reservoir sediment

Lightweight aggregates (LWAs) were produced from water reservoir sediment with added calcium oxide by employing four heat treatments, respectively, at temperatures in the range of 1170-1230 °C. The results show that LWAs produced at temperatures above 1200 °C meet European Union regulation EN-13055-1, which states that the unit weight of LWAs should be lower than 2000 kg/m³. The bulk density was easily lowered by extending the soaking time and increasing the heating rate. The ratio of strength to unit weight of the LWA produced at 1230 °C with a short soaking time and a fast heating rate was near that of a commercial product. The level of water adsorption was below 4%, which increased initially and then decreased due to pore connections and pore sealing. The formation of a glassy phase made the LWAs treated at higher temperature rough and sealed small pores (<0.1 mm) connected to the walls of large pores (>0.2 mm). The mineral phases of the LWAs were quartz, anorthite, and hematite.     

Effect of pyrophyllite on the mullitization in triaxial porcelain system

China clay (kaolin) was progressively replaced by pyrophyllite in a conventional porcelain mix. Addition of 5% pyrophyllite as a replacement of china clay improved the fired strength by about 24% compared to that of the conventional body fired at 1300 °C. Percentage of mullite was found to increase in the fired specimens when kaolinite was progressively replaced by pyrophyllite. However, beyond 7.5% pyrophyllite addition, amorphous SiO₂ released from pyrophyllite dehydroxylate inhibited further recrystallization of mullite. There was very insignificant change in the phase compositions with mixes having pyrophyllite content higher than 7.5%. Entire phenomenon has been explained on the basis of structural reorganization of pyrophyllite during dehydroxylation. Presence of large amount of undissolved quartz of smaller size as well as isolated pores in the microstructures of specimens containing pyrophyllite more than 7.5% are assumed to hinder the propagation of crack and thereby improving the mechanical properties. The size and shape of mullite crystals is to a large extent controlled by the fluidity of the liquid matrix from which they grow and this is again a function of temperature and composition.     

煤矸石陶瓷墙地砖的制备工艺研究

本试验以煤矸石为主要原料制备出陶瓷墙地砖。采用X射线衍射、扫描电子显微镜和阿基米德原理研究了样品的物相组成、显微结构、体积密度和吸水率。结果表明,煤矸石陶瓷墙地砖主要由玻璃相组成。并含有石英和莫来石晶相,其吸水率、体积密度、气孔数量和尺寸均随烧成温度的改变而改变。根据试验结果分析,1200～1240℃是较为适宜的烧成温度范围。