煅烧制度对合成轻质微孔莫来石骨料性能的影响

各类工业窑炉和热工设备的隔热保温是节能的重要方面。使用轻质耐火材料是实现节能的有效方法。开发和应用高性能轻质不定形耐火材料对实现节能意义重大。研制具有优良隔热性能的耐火骨料对开发高性能轻质浇注料有重要作用。以工业氧化铝、硅石粉为主要原料,采用加入可燃物的方法制备莫来石轻质合成料。根据坯体料的DSC-TG和大试样热重分析设置了不同的煅烧制度,比较了两种煅烧制度：一为单调升温,然后保温;另一为在高低两个温度分段保温。研究了两种煅烧制度对合成轻质微孔莫来石骨料莫来石化率及体积密度、气孔率性能的影响。结果表明,无烟煤约在600℃烧失,坯体料自1200℃开始发生莫来石化反应,试样经1350℃×6h热处理后的孔径分布3-7μm左右,莫来石转化率60%。     

煅烧温度与保温时间对合成莫来石材料结构与性能的影响

本研究是利用铝型材厂污泥与叶腊石合成莫来石材料.主要探讨煅烧温度和保温时间对莫来石合成料中形成的晶相、微观形貌及其含量的影响;从中确定较佳的煅烧温度和保温时间.采用XRD法和SEM法表征各试样形成的晶相和显微结构;用Rietveld Quantification 法确定各试样中各晶相的含量.实验结果表明不同煅烧温度和保温时间各试样形成的主晶相都是莫来石固溶体(Al4.59Si1.41O9.7),确定较佳煅烧反应温度为1600 ℃,较佳煅烧保温时间为3 h,对应的莫来石固溶体含量为96.4wt%.     

氧化铝-莫来石复合粉对莫来石烧结行为的影响

将莫来石先驱体溶胶预先引入到硫酸铝水溶液中 ,干燥后经 12 0 0℃煅烧获得氧化铝 -莫来石复合粉料。研究了该粉料与硅溶胶混合获得的混合粉的烧结行为 ,并与氧化铝、莫来石晶种和硅溶胶三相混合获得的混合粉的烧结行为进行了分析比较。其中 ,两种混合粉料均是以理论莫来石组分进行配比 (Al2 O3∶SiO2 =72∶2 8) ,并且两种混合粉中莫来石晶种的质量分数均为 5%。实验结果表明 :前者在 1450℃烧结 2 0min即实现完全莫来石化 ,其显微结构为晶须状莫来石 ;后者在 150 0℃烧结 2 0min实现完全莫来石化 ,其显微结构为针状莫来石     

玉米淀粉造孔剂对富铝煤矸石合成轻质莫来石料的影响

为了综合利用煤矸石,以天然富铝煤矸石矿为原料,聚乙烯醇(PVA)为结合剂,玉米淀粉为造孔剂,于1 500℃保温3 h反应烧结合成轻质莫来石料,研究了造孔剂加入量(其质量分数分别为10%、20%、30%、40%、50%)对轻质莫来石烧结性能以及显微结构的影响。结果表明:随着玉米淀粉加入量的增大,合成的轻质莫来石料体积密度明显降低,显气孔率和线收缩率显著增大,玉米淀粉的添加量以40%(w)为宜,此时合成的轻质莫来石料的体积密度和显气孔率分别为1.21 g·cm-3和62%;合成的轻质莫来石料的主晶相为莫来石,次晶相为刚玉,莫来石晶体呈柱状发育,刚玉晶粒被莫来石晶粒包裹,构成了疏松的空间网络结构。     

烧成温度和保温时间对红柱石基材料烧结性能的影响

以高纯度南非红柱石(有4～1mm、<1mm和<0.088mm三种粒级,且4～1mm的颗粒料为1500℃3h煅烧过的熟料)和活性氧化铝细粉(粒度<0.044mm)为原料,经配料、混练、成型、干燥后,将一部分试样分别在1300℃、1400℃、1500℃和1600℃下保温3h煅烧;另一部分试样在1600℃下分别保温1h、3h、6h和9h煅烧,待试样随炉冷却至常温后,检测其体积密度、显气孔率、耐压强度和烧成线变化率等,并采用XRD、SEM等手段分析各试样的物相组成和显微结构,以研究烧成温度及保温时间对高纯度红柱石的莫来石化程度及对红柱石基材料烧结性能的影响。结果表明:提高烧成温度对促进高纯红柱石的莫来石化十分有效,延长保温时间对于促进制品的烧结作用很大;高纯红柱石基材料需在1600℃下保温3h烧成,才能使红柱石完全莫来石化;欲使材料烧结良好且玻璃相含量低,物相较纯,则保温时间要达到6h左右。     

硅线石材料的预处理及其莫来石化行为

研究了硅线石材料的预处理及其莫来石化行为。结果表明：本文设计的少污染、无需专用设备的酸洗工艺能满足除杂的要求。采用搅拌球磨的方法获得的微细硅线石粉料有利于莫来石的转化;借助于X-射线衍射图详细地分析了三种温度下硅线石的莫来石化行为,在低于理论温虔1545℃的情况下,已有部分莫来石生成,在1650℃×4h的条件下,可彻底地转化为莫来石和玻璃相,并用HF萃取法测定这一条件下的莫来石转化率。最后,通过合适工艺获得了平均粒径为2.8μm的合成莫来石粉料。     

南非红柱石细粉的烧结行为和莫来石化研究

采用南非红柱石细粉(粒度≤0.088mm)为原料,粉体在200MPa下成型为36mm×10mm试样,选择煅烧温度为1200～1600℃(温度间隔50℃),研究了南非红柱石细粉的烧结行为。通过对试样烧后线变化率、体积密度、显气孔率及XRD分析数据进行处理,分析了红柱石分解和莫来石化反应的行为特征。结果表明:1200℃左右已有莫来石生成;1500℃红柱石分解完全。随着温度的升高,红柱石和莫来石两者的消长主要出现在1300～1400℃,而反应过程有如下先后顺序:材料膨胀,红柱石分解,莫来石生成。温度低于1400℃,莫来石化反应膨胀和基质烧结同时存在,出现局部膨胀和局部烧结排除气孔共存的现象,导致显气孔率的变化趋势与烧后线变化率及体积密度的变化趋势不对应。高于1450℃,液相促进烧结起主导作用,材料大幅度收缩。1400℃煅烧后试样的线收缩率最小。     

硅线石材料的预处理及其莫来石化行为

研究了硅线石材料的预处理及其莫来石化行为。结果表明：本文设计的少污染、无需专用设备的酸洗工艺能满足除杂的要求。采用球磨的方法获得的微细硅线石粉料有利于莫来石的转化；借助于X－射线衍射图详细地分析了三种温度下硅线石的莫来石化行为，在低于理论温度1545℃的情况下，已有部分莫来石生成，在1650℃×4h的条件下，可彻底地转化为莫来石和玻璃相，并用HF萃取法测定这一条件下的莫来石转化率。最后，通过合适工艺获得了平均粒径为2．8μm的合成莫来石粉料。     

高岭土加入量对合成轻质微孔莫来石性能的影响

以高岭土、工业氧化铝、硅石粉为起始原料,采用湿法共磨,注浆成型,利用高岭石热分解过程中形成一次莫来石及高活性的无定形SiO2,合成高纯轻质微孔莫来石.研究了高岭土加入量及煅烧温度对轻质莫来石体积密度与莫来石生成量的影响.结果表明,随配比中高岭土加入量的增加,莫来石的体积密度有下降的趋势,且有利于莫来石相含量的提高.高的煅烧温度虽能增加莫来石相的生成量,但不利于莫来石合成料的轻质化,适宜的煅烧温度为1450℃.     

纳米晶莫来石粉体的高压致密化研究

利用高压烧结法研究纳米晶莫来石粉体。以100℃的升温步幅从1 100℃加热到1 500℃,使用高压凹陷砧型装置在4GPa压力下合成晶粒大小为51nm的莫来石粉体。根据致密化温度函数分析致密试样的物相组成和晶体结构参数。经XRD分析表明,新相(蓝晶石和刚玉)的生成改变了烧后试样的密度。采用高压法可以获得相对致密的烧结体。由于莫来石晶粒生长的各向异性,其微观结构呈针状。在1 400℃煅烧的细长莫来石晶粒的长度达到5μm左右,升高到1 500℃后晶粒变粗并保持原来的针状结构。莫来石粉体的维氏硬度随着烧成温度的升高而增大(直到1 400℃),然而在1 500℃由于晶粒粗化试样的维氏硬度呈下降趋势。     

原料及热处理制度对合成微孔轻质莫来石骨料性能的影响

研制具有优良隔热性能的耐火骨料对开发高性能轻质浇注料有重要作用。以w(α-Al2O3)=95%,w(β-Al2O3)=3%~5%的工业氧化铝A或w(γ-Al2O3)=70%~80%,w(α-Al2O3)=5%~10%,w(三水铝石)=5%~10%的工业氧化铝B,硅石粉为主要原料,采用烧烬可燃物法制备了微孔轻质莫来石骨料,研究了两种具有不同特性的工业氧化铝和不同热处理制度对合成微孔轻质莫来石骨料性能的影响。结果表明:(1)以工业氧化铝B为原料制得的轻质莫来石骨料的体积密度要普遍低于以工业氧化铝A为原料的,且以工业氧化铝B为原料得到的莫来石骨料的常温耐压强度随热处理温度升高而增加。(2)以不同工业氧化铝为原料合成骨料的莫来石的转化率在1500℃之前大致相当,均为60%(w)左右,得到的微孔轻质莫来石骨料的平均孔径约为3~5μm。(3)以γ相为主的工业氧化铝B更适合作原料,合适的热处理制度为1350℃6h。     

矾土基合成莫来石质多孔陶瓷的研制

采用发泡法与添加造孔剂相结合,以高铝矾土和高岭土为骨料,长石作熔剂,并添加适量的煤、MgSO4和CaSO4作发泡剂,煤为造孔剂,PVA为粘结剂,干压成型后于1500℃左右烧成制备了莫来石质多孔陶瓷。制得的多孔陶瓷莫来石生成量高达90%以上,其气孔分布均匀,孔径分布范围为100～300μm;气孔率高达52.3%（闭孔气孔率为38.7%,开孔气孔率为13.6%）;体积密度为0.9731g/cm3;抗压强度为25.1317MPa;导热系数为0.143W/（m.K）的多孔陶瓷。     

Strength Degradation of Nonrandom Porous Ceramic Structures under Uniaxial Compressive Loading

Nonrandom porous mullite ceramics with controlled pore geometry have been fabricated using a lost mold process, where the molds were fabricated using the fused deposition process from CAD data. The pore geometry of molds was varied to achieve different pore sizes and shapes. These porous ceramic structures were then tested under uniaxial compression to evaluate their strength degradation for different pore volumes created by varying pore sizes and shapes. The finite element method (FEM) has been used to understand the effect of these porosity parameters based on stress concentrations along pore boundaries. Strength degradation of porous ceramics was found to be related to the increase in stress concentration along the pore boundaries in three-dimensional nonrandom porous ceramics.     

Effects of calcining conditions of kaolinite on pore structures of mesoporous materials prepared by the selective leaching of calcined kaolinite

This paper describes the effects of calcining conditions of kaolinite on pore structures of the porous materials obtained from the selective leaching of calcined kaolinite using KOH solution. Mesoporous -Al₂O₃ was the predominant crystalline phase in the samples calcined in the temperature range between 950°C and 1050°C for 24 h. The mean specific surface area of these samples was approximately 250 m² · g^–1 and the mean total pore volume was approximately 0.8 ml · g^–1. The pore size distribution curves of these samples showed a sharp peak at around 2–3 nm pore radius. This peak was sharper for the sample calcined at 1000°C for 24 h. On the other hand, the pore sizes of the sample calcined at 1100°C for 24 h increased abruptly to 10–20 nm and this change corresponded to the formation of mullite in the sample. The pore sizes of the samples calcined at 1100°C varied with calcining time. The specific surface area and total pore volume decreased, the longer the calcining time of the samples, and this was correlated with an increase in the amount of mullite in the samples.     

Impact of inorganic waste fines on structure of mullite microspheres by reaction sintering

The impact of waste composition and morphology on the properties of the mullite microstructure were studied by reaction sintering two types of siliceous waste powders with calcined alum sludge. Stoichiometric mixtures of fly ash or rice husk ash with the alum sludge were shaped into mullite microspheres by droplet coagulation. The mullitization reaction was followed by HT-XRD with a distinct difference in onset temperature. The specific powder composition of fly ash (presence of primary mullite) shifted the onset temperature to higher values as compared to the rice husk ash mixture. After sintering at 1600?°C, the mullitization reaction resulted in the same yield for both samples. Although the mullite content in the microspheres was equal, distinct differences on the microstructure could be observed. Reaction sintering of the fly ash mixture resulted in lower total porosity with smaller pore sizes.     

不同造孔剂对煤矸石合成多孔莫来石性能影响的研究

以煤矸石为主要原料,高铝矾土熟料为调配成分,选取不同种类的造孔剂,通过模压成型的工艺,在1200℃下烧结制备多孔莫来石材料。通过TG-DTA、阿基米德法、XRD和SEM等检测手段,对制品的显气孔率、体积密度、力学性能和微观结构等进行研究。结果表明:在1200℃合成主晶相为莫来石的多孔莫来石材料;造孔剂的种类和粒径不同,造孔效果不同;随着造孔剂含量的增加,显气孔率增大,体积密度和抗折强度呈下降趋势。     

Preparation and characterization of porous mullite ceramics via foam-gelcasting

Porous mullite ceramics were prepared via foam-gelcasting using industrial grade mullite powder as the main raw materials, Isobam-104 as the dispersing and gelling agent, sodium carboxymethyl cellulose as the foam stabilizing agent, and triethanolamine lauryl sulfate as the foaming agent. The effects of processing parameters such as type and amount of additive, solid loading level and gelling temperature on rheological properties and gelling behaviors of the slurries were investigated. The green samples after drying at 100 °C for 24 h were fired at 1600 °C for 2 h, and the microstructures and properties of the resultant porous ceramic samples were characterized. Based on the results, the effects of foaming agent on the porosity level, pore structure and size and mechanical properties of the as-prepared porous mullite ceramics were examined. Porosity levels and pore sizes of the as-prepared samples increased with increasing the foaming agent content up to 1.0%, above which both porosity levels and pore sizes did not change. The compressive strength and flexural strength of the as-prepared sample with porosity of 76% and average pore size of 313 μm remained as high as 15.3±0.3 MPa and 3.7±0.2 MPa, respectively, and permeability increased exponentially with increasing the porosity.     

不同的烧失物对微孔莫来石性能的影响

莫来石的导热系数低、高温下体积稳定性好,适合用来制备轻质耐火材料。以硅石粉和工业氧化铝为起始物料,加入一定量的烧失物,通过在1350℃下煅烧6h制得了微孔莫来石轻质骨料。研究了碳黑、焦炭和无烟煤这三种烧失物对合成的莫来石骨料体积密度、气孔孔径分布、莫来石生成量及组织结构的影响。认为,不同的烧失物对微孔莫来石的体积密度、...     

Effects of Al2O3 crystal types on morphologies,formation mechanisms of mullite and properties of porous mullite ceramics based on kyanite

Porous mullite ceramics with different crystal shapes of mullite are fabricated by in-situ reaction with middle-grade kyanite as raw material, Al(OH)₃, γ-Al₂O₃, ρ-Al₂O₃ and α-Al₂O₃ as alumina sources. Effects of Al₂O₃ crystal types on morphology evolution and formation mechanisms of mullite, and properties of porous ceramics are investigated. Results show that mullite in the sample with Al(OH)₃ mainly shows acicular morphology, because its (001) plane has the minimum interplanar crystal spacing and maximal attachment energy, it grows fast along [001] direction by screw dislocation mechanism. With a successive slowdown in reactivities of Al(OH)₃, γ-Al₂O₃, ρ-Al₂O₃ and α-Al₂O₃, the amount and aspect ratio of mullite reduce, its growth mechanism gradually transforms into two-dimensional nucleation. Acicular mullite not only reinforces samples, but makes effective pore sizes smaller, which enable the sample with Al(OH)₃ to present low bulk density, high apparent porosity and linear changes, small average pore size and good mechanical strength.