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、...     

高纯莫来石原料合成工艺研究

利用工业氧化铝与煤系轻烧高岭土或高纯石英砂为原料合成高纯莫来石,研究了添加剂(分别为滑石、ZnO和锆英砂)、合成温度、工艺过程对莫来石相含量及体积密度的影响。采用XRD定量分析的K值法计算出莫来石相的含量。结果表明:用工业氧化铝与煤系高纯高岭土合成出的莫来石相含量高于用石英砂与工业氧化铝合成的试样,在其中加入1%ZnO和1%锆英砂作添加剂的试样(其w(Al2O3)=68%),在氧化气氛下采用1380℃3h和1580℃3h二次保温煅烧工艺,合成的莫来石相含量达到97%,体积密度达到2.89g·cm-3。     

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。     

莫来石轻质骨料的制备及性能研究

以蓝晶石细粉为原料，核桃壳粉为造孔剂，硅溶胶为结合剂，制备了莫来石轻质骨料。研究了煅烧温度(分别为1 300、1 400、1 500、1 600℃,保温时间均为180 min)和保温时间(分别为60、120、180 min,煅烧温度均为1 500℃)对莫来石轻质骨料体积密度、显气孔率、烧后线变化率、物相组成和显微结构的影响。结果表明，在1 500℃保温60 min所得莫来石轻质骨料的综合性能最优，其体积密度为1.18 g·cm^-3,显气孔率为59.8%,烧后线变化率为2.58%,莫来石相含量为86%(w)。     

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%。     

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%。     

温度对煤系煅烧高岭土物化性能影响的研究

煅烧高岭土是一种性能独特的新型无机非金属矿物粉体材料。实验以山西煤系硬质高岭岩为原料，研究了煅烧温度对煤系高岭土白度、吸油率、堆积密度、遮盖率(光散射系数)及活性(活性Al2O3含量)等物理化学性能的影响。结果表明：在650～1150℃范围内煤系煅烧高岭土的白度随温度升高而显著提高；堆积密度略有增大；活性在650～980℃范围内显著提高，但在1050℃后下降。遮盖率在650～950℃之前随温度升高显著增强，但在950℃后基本上不再变化。吸油率指标在650～1150℃范围内基本上不变化。950℃以下，煅烧高岭土的物相以偏高岭石相为主；950～1050℃，煅烧高岭土的物相已转变为硅铝尖晶石和部分莫来石。当煅烧温度达到1150℃时，煅烧高岭土已转变为莫来石相。     

镁橄榄石骨料的合成及其对镁橄榄石质耐火材料性能的影响

采用XRD分析了镁橄榄石碎矿细粉及其分别经1200～1600℃3h煅烧后的物相组成,研究了煅烧温度和轻烧MgO加入量对镁橄榄石合成骨料显气孔率和体积密度的影响以及合成骨料对镁橄榄石质耐火材料常温物理性能的影响。结果发现:(1)镁橄榄石原料经1200～1600℃3h煅烧后,物相组成没有明显改变,主要以镁橄榄石相为主。(2)随着煅烧温度的提高,合成骨料的显气孔率先降低后增高,体积密度先增大后减小;以不同煅烧温度合成的骨料为主要原料制备的镁橄榄石质耐火材料试样经1600℃3h处理后收缩趋势增大,显气孔率逐渐下降,体积密度增大,抗折强度没有明显变化,耐压强度缓慢增大。(3)随着轻烧MgO加入量的增加,合成骨料的显气孔率先降低后增高,体积密度先增大后减小;轻烧MgO含量为10%时,合成骨料的显气孔率最小,体积密度最大;以添加轻烧MgO的合成骨料为主要原料制备的镁橄榄石质耐火材料试样收缩增大,显气孔率降低,体积密度增大,抗折强度先下降后增高,耐压强度先增高后降低。     

发泡剂对偏高岭土基地质聚合物轻质材料性能影响

以偏高岭土为原料,水玻璃为碱激发剂,化学发泡法制备了偏高岭土地聚合物基轻质材料;研究了不同发泡剂及表面活性剂十二烷基苯磺酸钠对偏高岭土地质聚合物的体积密度及强度的影响,结果表明:随着铝粉、双氧水加入量的增加,体积密度及强度变化明显,发泡效果较好;十二烷基苯磺酸钠加入量为0.2%,双氧水的加入量为0.7%时,铝粉的加入量为0.15%时,体积密度为分别为1.061 g/cm~3、1.035 g/cm~3,强度分别为6.7334 MPa、9.5347 MPa。     

二氧化锰及其复合添加剂对莫来石刚玉复相材料的影响研究

通过对样品的体积密度、气孔率、物相组成和表面形貌的分析,确定二氧化锰及其复合添加剂对莫来石刚玉复相材料与烧结刚玉材料性能的影响。通过添加二氧化锰及氧化钇复合添加剂的方法,在低于传统煅烧温度50℃的条件下,制备出了性能优异的莫来石刚玉复相材料,材料的物相组成稳定,莫来石含量在62%左右,刚玉相含量在38%左右,体积密度、气孔率等指标都要优于传统煅烧温度煅烧制备的莫来石刚玉复相材料原样,且耐火度也达到国家标准。     

Synthesis of high-performance mullite ceramics based on associated rare-earth kaolin

The objective of this work was to prepare high-purity, high-strength mullite ceramics from low-cost, associated rare-earth kaolin (AREK). A reaction sintering process using calcined AREK and γ-Al₂O₃ powders was used to synthesize high-performance mullite ceramics. Mineralogical, morphological, and chemical characteristics of AREK were given. The effects of associated REEs in kaolin and sintering temperature on the microstructural evolution, phase transformation, and physical properties of mullite were studied. The results showed that the mullite contents were 98.8%, the maximum aspect ratio was 8.22 μm, the relative density was 93.04%, and the micro-Vickers hardness and flexural strength were 10.63 GPa and 184.24 MPa, after sintering at 1500°C for 4 h. For comparison, calcined without rare-earth kaolin was also employed as a raw material to synthesize mullite ceramics, and the mullite content prepared by sintering the two kaolin clays at 1320–1480°C for 4 h was quite similar. However, mullite prepared using AREK forms secondary mullite in the temperature range of 1480–1500°C with a significantly higher mullite content, and therefore, the advantages of preparing mullite based on AREK as the raw material are high purity, low mullitization temperature, and high strength.     

微波辐照煤系高岭土及其吸油性能

以山西煤系高岭土为原料,在1 800 W的功率下对3 g煤系高岭土进行微波辐照,以此提高煤系高岭土的吸油值。利用扫描电镜、X射线衍射仪、红外光谱分析仪、比表面积分析仪等对处理前后样品的形貌和结构进行表征。结果表明,随微波辐照时间的增加,煤系高岭土的吸油值呈先增加后降低的趋势,且在处理时间为17.5 min(最高温度达到1 100 ℃)时吸油值最高,达到74.4 g/100 g,较高岭土原土吸油值提升了61%,此时煅烧高岭土的吸附平均孔径最大且生成了少量的莫来石。随着处理时间的延长,煅烧高岭土出现烧结,导致内部孔隙闭合,吸油值降低。煅烧高岭土的吸油值与其吸附平均孔径以及孔径分布有关,生成少量莫来石对吸油值的提高有促进作用。     

煅烧煤系高岭土吸油性能与颗粒形貌关系研究

以山西朔州煤系高岭土为原料,利用三水氟化铝(AlF₃·3H₂O)添加剂能够促进莫来石晶须生长的特性,结合超声破碎处理制备高吸油值煅烧煤系高岭土,随后分析了颗粒形貌对粉体吸油值的影响。通过扫描电子显微镜、X射线衍射仪和比表面积分析仪等表征手段分析了AlF₃·3H₂O提高煅烧煤系高岭土吸油值的作用机理。结果表明:AlF₃·3H₂O的添加能够使煅烧煤系高岭土的颗粒表面产生大量莫来石晶须,颗粒表面产生的亚微米级莫来石晶须可显著提高样品的吸油值;此外对样品进行超声处理可以进一步提高其吸油值,当超声处理时间为45 min时,其吸油值可达到86.14 g/100 g;颗粒的圆形度对粉体的吸油值影响较大,高吸油值煅烧煤系高岭土的圆形度整体比普通煅烧煤系高岭土的圆形度低,且圆形度分布更集中。     

Sintering of magnesia refractories through the formation of periclase–forsterite–spinel phases

Effect of calcined kaolin additions on sinterability of dead-burned magnesia was studied through additions of Egyptian kaolin. Five batches containing powders of 100/0, 90/10, 80/20, 70/30 and 60/40 magnesia/kaolin, respectively, were mixed, dried and fired up to 1550 °C for 4 h. Their physical (bulk density and apparent porosity), mechanical (cold crushing strength) as well as refractory (thermal shock resistance and refractoriness under load) properties were tested according to the International Standard Specifications. The phase compositions of the fired batches were investigated using X-ray diffraction as well as scanning electron microscope to illustrate the effect of the different developed phases on the above properties compared with the main magnesia source itself. Generally, samples containing 10–20 wt.% kaolin are characterized by their high sintering, mechanical and refractory properties, so they are recommended for use as a lining for different parts of steel furnaces as well as heating zone of cement rotary kilns. Samples containing 30–40 wt.% kaolin with lower refractory properties can be used in the heat exchangers or as kiln furniture in ceramic industries.     

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).     

Self-formed mullite containing refractory barium silicate cements and their castable applications

Abstract

Six batches consisting of different percentages of barite, kaolin and calcined alumina were sintered at 1500–1600°C for 3 h to produce self-formed mullite containing barium silicate cements. The compositions of the cement mixes were investigated using X-ray diffraction. Physicomechanical, sintering and refractory properties were tested according to standard specifications. Each of the mixes, composed mainly of varying proportions of mullite and dibarium silicate minerals, showed different behaviour. The best compromise between cementing, sintering and refractory properties was provided by the mix prepared from 60 wt-% barite, 25 wt-% kaolin and 15 wt-% calcined alumina, consisting of about 54 wt-% dibarium silicate and 33 wt-% mullite. Self-formed mullite containing castable prepared from 15 wt-% of a fine powder of the chosen mix as the cement and 85 wt-% of graded aggregate of the same mix showed good volume stability, high mechanical properties, high thermal shock resistance as well as high loadbearing capacity.     

Mechanism of Secondary Expansion of High-Alumina Refractories Containing Calcined Bauxite

The use of some calcined bauxites in high-alumina refractories is limited by unusual and excessive secondary expansion. One such calcined bauxite was compared with pure alpha alumina to determine the crystalline changes responsible for the expansion, to determine the mechanism of the expansion, and to suggest means for control of the expansion. X-ray diffraction and petrographic techniques were used. The expansion was found to result from crystallization of secondary mullite by the action of impurities in aiding the diffusion of alumina and silica. Secondary mullitization and growth began at 1400°C. and caused as much as 23% expansion at 1600°C. The expansion was caused primarily by the mullite growth rather than by the true density changes associated with mullitization. Small sodium fluoride additions proved to be effective for controlling expansion.     

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.