基于高岭土制备轻量微孔莫来石骨料结构与性能研究

以高岭土细粉和α-Al2O3微粉为主要原料,采用原位分解法制备轻量微孔莫来石骨料,研究了铝硅摩尔比及热处理温度对轻量微孔莫来石骨料结构与性能的影响.结果表明:经过1400～1600℃热处理后,富铝莫来石试样中除主要物相莫来石相外,还残余一定量刚玉相,接近理论莫来石组成试样及富硅试样均仅检测到莫来石相;所制备的轻量骨料孔径分布主要集中于0.1 ～4 μm范围,均具有微孔结构;随着热处理温度的升高,骨料的体积密度上升,显气孔率下降,耐压强度上升;经1500℃热处理后,富铝试样体积密度为2.49 g/cm3、显气孔率为25.6％、耐压强度为146 MPa;接近理论莫来石组成试样及富硅试样体积密度均小于1.95 g/cm3、显气孔率大于38.0％,1000℃时导热系数均小于0.77 W/(m·K).     

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。     

Y2O3对合成微孔轻质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。轻质耐火材料的应用是实现节能的有效措施。开发和应用高性能轻质不定形耐火材料对实现能源节约和提高能源利用率意义重大。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。本工作以工业氧化铝、硅石粉为主要原料,采用烧烬可燃物法制备微孔轻质莫来石骨料,研究了Y2O3加入量对合成微孔轻质莫来石骨料性能的影响。结果表明引入Y2O3可促进合成料的固相反应和烧结过程。随着Y2O3含量的增加,合成微孔莫来石骨料的耐压强度显著提高,自4.5MPa提高到15MPa;引入Y2O3后合成料的气孔更小,分布更均匀。     

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%。     

煅烧制度对合成轻质微孔莫来石骨料性能的影响

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:一种为单调升温,然后保温;另一种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%。     

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、...     

改进刚玉-莫来石轻质耐火砖性能研究

研究了原料配比、烧成温度和保温时间及有机燃尽物对刚玉-莫来石轻质耐火砖性能的影响。通过对各种影响因素的分析,提出了改进刚玉-莫来石轻质耐火砖性能的方法及理论依据。     

莫来石加入量对SiC-莫来石材料性能的影响

以SiC颗粒(2～1mm、≤1mm)、SiC细粉(≤0.066mm)、莫来石细粉(≤0.074mm)和SiO2微粉(≤0.045mm)为原料,在w(SiC细粉)=40%的基础配方中分别以质量分数为5%、10%、15%、20%和25%的莫来石细粉取代相应量的SiC细粉,并外加2%的SiO2微粉,成型后分别在1300℃和1500℃的大气气氛中煅烧3h,测定试样煅烧前后的质量变化率以及烧后试样的显气孔率、常温抗折强度和抗热震性,并用扫描电镜观察试样的显微结构。结果表明:在SiC自保护氧化的作用下,试样的抗氧化性较强,而且随着莫来石加入量的增大,1300℃烧后试样的氧化程度减小,1500℃烧后试样的氧化程度先减小,至15%后又增大;1300℃烧后试样比1500℃具有较高的抗热震性,并且随着试样中莫来石加入量的增大,烧后试样的抗热震性提高。     

蓝晶石含量对球形45莫来石轻骨料浇注料显微结构及性能的影响

为改善含球形45莫来石轻骨料浇注料的体积稳定性和显微结构,引入了不同含量的蓝晶石(w=8%、10%、12%、14%、16%).采用X-射线衍射仪、扫描电子显微镜等对1300℃保温3 h煅烧后试样的物相组成、显微结构与性能进行了表征.研究发现:随着蓝晶石含量的增加,1300 ℃煅烧后试样的强度显著降低,线变化率由-0.87%逐渐增加至0.64%,骨料基质结合程度先变好后变差.综合考虑各项性能,含12%蓝晶石的试样综合性能最优:1.73 g/cm3的体积密度,36.8%的显气孔率,29.3 MPa的耐压强度,0.18%的线变化率,0.58 W/(m· K)的导热系数(800 ℃)和1339 ℃(T0.6)的荷重软化温度.     

Preparation of Short Mullite Fibers from Kaolin via the Addition of Foaming Agents

Short mullite fibers were fabricated by adapting the kneading–drying–calcination (KDC) process. The effect of foam forming on the formation of mullite fiber from kaolin via the KDC process, with the addition of a foaming agent, was examined. In the present study, doped sodium phosphates promoted the growth of mullite fiber and the formation of a glass matrix—effects that were ascribed to the P₂O₅ and Na₂O components, respectively, of the sodium phosphates. In particular, the addition of sodium phosphates greatly reduced the treatment time that was required for dissolution of the glass matrix in hydrofluoric acid. The addition of 10 mass% of sodium dihydrogen phosphate and calcination at 1500°C for 10 h were the optimum conditions for a short treatment time and the formation of long fibers.     

Acicular Mullite Crystals in Vitrified Kaolin

The microstructure of vitrified kaolin ceramic tapes has been studied via scanning and transmission electron microscopy (SEM and TEM). The sintered samples contained crystalline phase of predominantly stoichiometric mullite (3Al₂O₃·2SiO₂), which consisted of high aspect ratio, acicular crystals that are often referred to as secondary mullite. These crystals were interlocked and embedded in an aluminosilicate glass matrix of inhomogeneous composition. The glass matrix contained an average of ∼3.63 wt% K as determined by energy-dispersive X-ray analysis (EDS), whose composition could be approximated to 5Al₂O₃·16SiO₂·0.1MgO·0.3K₂O·0.15TiO₂·0.12Fe₂O₃. The acicular crystals have approximately the stoichiometric composition of Al₂O₃:SiO₂= 3:2. They have grown along a specific crystallographic orientation along the [001] axis. The crystal growth front exhibited facetting on the {110) planes with microfacetting on both the {100) and {010) planes.     

Thermomechanical Properties of β-Sialon Synthesized from Kaolin

β-Sialon powder was synthesized by the simultaneous reduction and nitridation of Hadong kaolin at 1350°C in an N₂–H₂ atmosphere, using graphite as a reducing agent. The average particle size of β-sialon powder was about 4.5 μm. The synthesized β-sialon powder was pressureless sintered from 1450° to 1850°C under a N₂ atmosphere. The relative density, modulus of rupture, fracture toughness, and microhardness of β-sialon ceramics sintered at 1800°C for 1 h were 92%, 248 MPa, 2.8 MN/m^3/2, and 13.3 GN/m², respectively. The critical temperature difference (ΔT_c) in water-quench thermal-shock behavior was about 375°C for the synthesized β-sialon ceramics.     

Evolution of Mullite Texture on Firing Tape-Cast Kaolin Bodies

Kaolin undergoes a series of phase changes on heating to elevated temperature, proceeding through kaolin, metakaolin, γ-Al₂O₃ spinel, and mullite. The morphologic evolution of the kaolin–mullite reaction series was investigated in the present study. A highly textured kaolin green body was prepared by a tape-casting technique, and the morphology evolution from kaolin flakes to mullite aciculars on firing from 450° to 1600°C was then monitored using X-ray diffractometry and scanning electron microscopy. Equiaxed mullite nuclei first appeared at 1000°C; the aspect ratio of the mullite grains then increased with increased firing temperature. The mullite aciculars rearranged their orientation in a glassy phase until they impinged on each other. A highly textured mullite specimen was prepared by firing the kaolin tape at a temperature >1500°C.     

硅线石含量对轻质莫来石-刚玉耐火材料的显微结构与性能的影响

以多孔球形莫来石为骨料,板状刚玉细粉、硅线石和粘土为基质,经1400 ℃、1500 ℃和1600 ℃保温3 h烧成,制备了四组轻质莫来石-刚玉耐火材料.采用X-射线衍射仪(XRD)和扫描电子显微镜(SEM)对试样的物相组成和显微结构进行表征,研究了烧成温度及硅线石含量(4%、6%、8%和10%)对试样常温物理性能和显微结构的影响.结果表明:(1)当硅线石含量不变时,随着烧成温度的升高,试样的显气孔率逐渐减小,体积密度逐渐增大,线收缩率逐渐增加,常温耐压强度先降低后升高;(2)当硅线石的含量从4%增加到8%时,经1400 ℃烧后,试样的显气孔率和体积密度变化不大,当硅线石含量超过8%时耐压强度显著下降;经1600 ℃烧后,随硅线石含量的增加,试样的体积密度减小,强度降低,线收缩率也由2.5%减小到1.5%;(3)当硅线石含量为6%、烧成温度为1400 ℃时,试样的线收缩率为0.86%,耐压强度为36.1 MPa,热导率为0.249 W/(m·K)(300 ℃),试样基质中气孔的d50为46.7 μm.     

硅源对高岭土合成ZSM-5分子筛的影响

以煤系高岭土为原料,分别以水玻璃、气相Si O_2、正硅酸四乙酯和硅酸为硅源,氢氧化钠为矿化剂,四丙基氢氧化铵为模板剂,合成了ZSM-5分子筛。随后,在氯化铵氛围下离子交换合成HZSM-5分子筛。利用XRD、SEM、FTIR、NH_3-TPD、BET对HZSM-5进行了表征。最后,利用甲醇制汽油(MTG)反应测试HZSM-5的催化性能。结果表明:以硅酸合成的HZSM-5分子筛催化效果优异,在MTG反应43 h后开始失活,高碳烃(C_(5+))类产物的选择性为41.75%。     

氟化铝添加量对碳化硅/莫来石复合多孔陶瓷性能的影响

本文以碳化硅(SiC)、气相SiO2、纳米Al2O3和AlF3·H2O为原料,制备出了碳化硅/莫来石复合多孔陶瓷,主要研究了AlFa·H2O添加量、烧结温度对多孔陶瓷抗弯强度、气孔率、孔径分布等性能的影响.用SEM、XRD研究了多孔陶瓷的微观形貌和物相组成.结果表明:AlF3·H2O对莫来石的生成有明显的促进作用,1300℃时,添加AlF3·H2O的样品中检测到莫来石相,多孔陶瓷气孔率随AlF3·H2O加入量增加而升高,而抗弯强度随其增高而先增加后减小,AlF3·H2O添加量为4wt％时,多孔陶瓷气孔率为42.8％,抗弯强度为31.1 MPa.     

Influence of Magnesia Addition on the Rheological Properties of Mullite Suspensions

Water-based suspensions of mullite that are used to form porous bodies through the impregnation of sponges were investigated. The rheological properties of the suspensions are strongly influenced by the amount of magnesia added, as well as the solid loading and the preparation procedure. Amounts of magnesia higher than 0.15 wt% change both the steady shear behavior from nearly Newtonian to plastic (with an increasing apparent yield stress) and time dependent, as well as the viscoelastic properties (the storage modulus increases more than 5 orders of magnitude). Similar effects are shown for long milling procedures, or solids loadings higher than 25 vol%, while the elastic properties are not strictly related to the total volume fraction. The results of the rheological characterization, under either continuous or dynamic conditions, are discussed in relation to the properties of the structure built up within the suspension. The density of the cast bodies increases with decreasing magnesia content.