亚白刚玉对红柱石细粉烧结性能的影响

为了考察亚白刚玉对红柱石基耐火材料烧结性能的影响,以南非红柱石细粉和亚白刚玉细粉为原料,研究了亚白刚玉加入量(加入质量分数分别为5%、10%、15%、20%、25%、30%和35%)对红柱石细粉在不同温度(1 150、1 200、1 250、1 300、1 350、1 400、1 450、1 500和1 600℃)煅烧后莫来石化和烧结性能的影响。结果表明,引入亚白刚玉后,红柱石细粉的烧结性能受控于原生莫来石化反应和二次莫来石化反应的膨胀效应,以及高温液相促进烧结的综合作用。低于1 350℃时,系统中发生的主要是原生莫来石化反应,系统的烧结行为主要受原生莫来石化反应的膨胀效应影响,亚白刚玉加入量对红柱石细粉的烧结性能影响不大。高于1 400℃时,系统中将产生二次莫来石化反应并主导系统的烧结行为,二次莫来石化反应的程度随着亚白刚玉加入量的增加而增大,红柱石细粉的烧结性能也随之恶化。可见,以亚白刚玉作为添加剂来提高红柱石基耐火材料的莫来石含量,进而改善其高温性能时,应该根据制品的性能指标要求,合理确定最佳亚白刚玉加入量和煅烧温度。     

红柱石基材料中添加SiC细粉的作用

在以高纯红柱石和活性Al2O3细粉为主要原料的试样中,分别加入0、3%、6%、9%和12%的SiC细粉(粒度<0.088mm),试样经1600℃3h烧成后,用XRD、SEM等方法分析试样的相组成和显微结构,并检测试样的体积密度、显气孔率、抗折强度、烧成线膨胀率、抗热震性及蠕变率等,研究了添加SiC细粉对高纯度红柱石基材料的矿物组成、显微结构、烧结状况以及抗热震性与抗蠕变性的影响。结果表明:适量SiC细粉的加入能提高材料中的莫来石含量,促进基质中莫来石晶体的生长,改善材料的组织结构并促进材料的烧结,改善其抗热震性和抗蠕变性;SiC细粉在高纯红柱石基材料中的加入量以6%~9%为宜。     

氧化铝原料对红柱石基耐火材料莫来石化行为的影响

研究了几种氧化铝原料对红柱石基耐火材料莫来石化行为的影响。对试样XRD数据的分析结果表明,所引入的烧结氧化铝、活性氧化铝和棕刚玉都对红柱石的分解转化有不同程度的抑制作用,其中棕刚玉对红柱石分解转化的抑制作用尤为强烈,原因在于引入的TiO2。但TiO2对二次莫来石的生成没有影响。红柱石的分解转化受制于高温液相中的氧化铝浓度。活性氧化铝加入量小于20%时,其加入量增加,对红柱石分解转化的抑制作用随之增大。氧化铝原料的反应活性取决于其在高温液相中的溶解速度。     

氧化铝纤维/红柱石复合材料的制备与性能

笔者针对红柱石和氧化铝纤维广泛的应用前景，通过两者的复合来提高红柱石制品的使用性能，采用传统无压烧结工艺制备氧化铝纤维增强红柱石基复合材料。探讨了红柱石细粉的粒度、氧化铝纤维的加入量和烧成温度对氧化铝纤维增强红柱石基复合材料物理性能以及常温力学性能的影响。结果表明：随着红柱石细粉粒度的降低，氧化铝纤维团聚现象加剧，由于纤维与基质的界面结合力较强，原料粒度的变化对材料常温力学性能影响不大；当氧化铝纤维加入量为5％。10％时，材料的体积密度最大，常温耐压强度和抗折强度最好，超过10％后由于纤维的团聚，材，料的力学性能显著下降；当烧成温度超过1400℃后纤维与基体开始反应，随着烧成温度的进一步提高，纤维遭到破坏的程度加剧。     

废镁铬砖细粉的加入对镁质浇注料烧结性的影响

将水泥回转窑烧成带废镁铬砖经处理后制成细粉料,用它代替镁质浇注料中的镁砂原料,研究了废镁铬砖细粉的加入对SiO2微粉结合镁质浇注料烧结性的影响.结果表明:加入适量的废镁铬砖细粉对于提高镁质浇注料的烧结程度和强度均有作用 ,但加入量不能太多.本实验条件下加入量为8%时,其烧结性能良好.对高温烧后试样的SEM及XRD分析可知,由于废镁铬砖细粉的加入而生成的尖晶石固溶体是促进镁质浇注料烧结、增加其结构致密性的原因.     

铝硅凝胶粉对刚玉莫来石气幕挡墙性能和显微结构的影响

以临界粒径为1 mm的板状刚玉为骨料,以白刚玉为细粉,以ρ-氧化铝和硅微粉为结合剂,添加不同量的铝硅凝胶粉,浇注成型制备了中间包用刚玉莫来石质气幕挡墙,研究了铝硅凝胶粉对材料物理性能和孔径分布的影响.结果表明:随着铝硅凝胶粉的加入,试样致密度提高,强度增大;在热处理过程中,凝胶粉反应生成莫来石,体积膨胀,促进致密化,降低气孔孔径;加入较多时,使得试样过烧结.在本实验条件下,铝硅凝胶粉加入4％时,刚玉莫来石气幕挡墙性能较好.     

红柱石及其引入方式对铝硅质浇注料性能的影响

为充分发挥红柱石在铝硅质浇注料中的优异性能,分别以特级矾土、棕刚玉为主要原料配以红柱石制备铝硅质浇注料.检测试样在不同温度下的抗折强度及体积密度、显气孔率及线膨胀率,并对烧后试样的物相组成及显微结构进行表征,以研究红柱石及其引入方式对不同配置的铝硅质浇注料性能的影响.研究结果表明:红柱石以细粉形式引入的铝硅质浇注料,在高温下莫来石反应及二次莫来石化较为充分,试样体积密度、高温抗折强度相对较高,线膨胀率相对较低;相比棕刚玉配置的浇注料,红柱石对矾土配置浇注料性能的改善更为明显,红柱石分解及二次莫来石化相对较为容易,产生的莫来石将矾土熟料紧密连接,有效改善试样的物理性能.     

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。     

镁砂对高铝质可塑料性能影响

以高铝矾土、二氧化硅微粉和氧化铝微粉为原料,以磷酸二氢铝和磷酸为结合剂,制备了用于CFB锅炉的高铝质可塑料,重点研究镁砂细粉用量对高铝质可塑料性能的影响.按照不定形耐火材料检测标准对热处理后耐火可塑料的常温力学性能、致密性及耐磨性能进行检测,通过XRD和SEM分析手段对热处理后试样的物相组成和微观结构进行表征.结果表明:镁砂对可塑料起到促凝和促烧结作用,随着镁砂加入量增大,促凝时间缩短,经110℃热处理后试样常温强度逐渐增大,经1100℃热处理后试样常温强度呈先增大后减小趋势.当镁砂加入量为5％,1100℃热处理后试样常温强度和结构致密性可处于最高值,耐磨性有所降低,试样矿物相组成中包括刚玉、莫来石和堇青石相.     

水泥窑用低导热多层复合砖的研究(Ⅱ):原料对工作层硅莫砖性能的影响

为了克服非均质天然铝矾土熟料给低导热多层复合砖工作层用硅莫砖性能带来的波动,以粒度均为5~3、3~1和1 mm的M60或M70矾土基烧结莫来石为骨料,以粒度均0.074 mm的M60莫来石、M70莫来石、80均化料、85均化料为细粉,掺入碳化硅、红柱石、白泥等原料,在1 490℃保温3 h制备了硅莫砖试样,并研究了各原料对试样显气孔率、体积密度、烧后线变化率、常温耐压强度、抗热震性、荷重软化温度等性能的影响。结果表明:采用M60或M70矾土基烧结莫来石为骨料,分别以M60、M70、80均化料、85均化料为细粉,掺入碳化硅和红柱石的试样性能比较稳定,可以避免以天然矾土为原料引起的试样高温性能波动的问题;以M70为骨料,80均化料为细粉,加入12%(w)的碳化硅细粉,加入10%~12%(w)的红柱石细粉的试样经高温煅烧后的主晶相为莫来石和碳化硅,莫来石柱状晶粒发育完好,且形成了网络交错的微观结构,碳化硅和玻璃相均匀分布在莫来石晶粒周围,具有良好的力学性能和较高的荷重软化温度。     

Andalusite: A promising material for manufacturing high-quality refractories

The process of mullitization of andalusite is reviewed to show that this phase transformation is based on the mechanisms of a pseudomorphism that fixes the grain shape and the chemistry of solid-phase processes. Mullite is oriented in correspondence with the generating crystal of andalusite along the C axis. A single crystal of andalusite transforms into a compound consisting of a mullite single crystal with capillary pores filled with a glass phase saturated with amorphous silica. The capillaries form a network of well-connected tubular pores with a micron cross section, and they are positioned along the C axis common for the newly formed mullite and the original andalusite. About 80% of the glass phase remains in pores of capillaries of the formed mullite. The results of the study were tested in reactions between andalusites of various grain compositions and powder alumina and are now used for fabricating unshaped refractory mixtures with an ultralow content of cement and cement-free mixtures with finely milled andalusite and alumina.     

Manufacture of mullite substrates from andalusite for the development of thin film solar cells

The purpose of this work is the manufacture of dense thin mullite substrates by tape casting of the natural silicate mineral andalusite. The targeted application for such substrates is the manufacture of thin film solar cells. Indeed, in addition to a good resistance at high temperature (up to 1200 °C), this application requires a good correspondence between the thermal expansion coefficient of the substrate and silicon film in order to lower the stresses in the film and in the substrate after cooling. The work was performed in three successive stages. First, the study of the transformation during sintering of andalusite+alumina mixtures. Second, the optimisation of the slurries and of the parameters for tape casting. Finally, green tapes prepared from various powder compositions were characterised before and after sintering. The addition of alumina to andalusite reduces the final amount of vitreous phase. This limits the risk of impurity diffusion in the silicon film. However, the addition of alumina also slows down the sintering process leading to more porosity in the substrates. A good compromise is obtained with an initial mixture of 80 wt.% andalusite with 20 wt.% alumina. In that case, the thermal expansion behaviour is very close to pure mullite and the mechanical properties of the substrates can be considered as sufficient for the targeted application.     

Phase Evolution,Microstructure, and Mechanical Properties of Alumina–Mullite–Zirconia Composites Prepared by Iranian Andalusite

This paper investigates the effects of Iranian andalusite and short milling times on alumina–mullite–zirconia composites. Andalusite powder was added at 0, 2.5, 5, and 10 wt% to an alumina–zircon mixture and the raw materials were milled for 1 or 3 h. The sintering of samples was carried out at the temperatures of 1550°C, 1600°C, and 1650°C for 3 h. Microstructural changes, phase composition, physical properties, and mechanical strength of the sintered composites were characterized by scanning electron microscopy, X‐ray diffraction, density, and strength measurement tests. Results show that andalusite promoted the decomposition of zircon and accelerated the reaction sintering of alumina–zircon, which leads to the formation of much more mullite phase and improvements to the composites’ thermal shock resistance up to about 50%.     

Sillimanite,Kyanite and Andalusite in China and Their Applications Part Ⅰ:Their Reserve,Distribution and Characteristics

Sillimanite, kyanite and andalusite areadvantageous natural refractory raw materials foraluminosilicate refractories to attain improved keyproperties. This paper are divided into two parts tointroduce their resource and technical characteristicin the first part, and their applications in refracto-ries in the second part to be succeeded. In this part,based on authors' knowledge and sources, informa-tion on their reserve, distribution, composition and     

Isothermal corrosion testing of frit furnace refractories

In this paper, the corrosion behaviour of aluminosilicate type refractories in frit melts is studied in an isothermal corrosion test setup. A refractory brick of largely andalusite and sillimanite composition was compared to another refractory brick of mullite and sillimanite composition, both of which were made by different manufacturers for use in different frit furnaces. The industrial frit used for corrosion tests was a commercial product used in a wall tile glaze formulation. Corrosion tests conducted under isothermal conditions provide quantitative and reproducible data about the corrosion performance of refractories. In this study, tests were performed by partially immersing a 15 mm × 15 mm × 115 mm refractory specimen into a frit melt at temperatures between 1404 and 1504 °C. The effects of temperature, duration of exposure and the refractory brick type were investigated using a statistically designed set of experiments. The ANOVA (analysis of variance) table indicated that temperature and test duration were the most important factor effects, as expected. Increasing both temperature and exposure duration led to an increased amount of corrosion as measured by the cross-sectional area loss of the corroded refractory specimen. Postmortem microstructural analysis was also done on the specimens, with extensive amount of ZnO·Al₂O₃ precipitation observed along the frit–refractory interface, where crystals of mullite and alumina were also found to precipitate. Increasing the amount of exposure time and temperature produced more ZnO·Al₂O₃ precipitation. As identified by SEM-EDS analysis, mullite crystals were in the needle-like morphology, while alumina crystals were generally cubic. Additional experiments were conducted by rotating the specimens in the melt at 50 rpm of rotational speed. Due to the reduction of boundary layer thickness, more dissolution was observed from the rotated specimens. In all specimens, corrosion was more pronounced in the bond phase than through the large filler grains of mullite and andalusite.     

Improvement of the mechanical properties of SiC reticulated porous ceramics with optimized three-layered struts for porous media combustion

Silicon carbide reticulated porous ceramics (SiC RPCs) with three-layered struts were fabricated by polymer replica method, followed by infiltrating alumina slurries containing silicon (slurry-Si) and andalusite (slurry-An), respectively. The effects of composition of infiltration slurries on the strut structure, mechanical properties and thermal shock resistance of SiC RPCs were investigated. The results showed that the SiC RPCs infiltrated with slurry-Si and slurry-An exhibited better mechanical properties and thermal shock resistance in comparison with those of alumina slurry infiltration, even obtained the considerable strength at 1300 °C. In slurry-Si, silicon was oxidized into SiO₂ in the temperature range from 1300 °C to 1400 °C and it reacted with Al₂O₃ into mullite phase at 1450 °C. Meantime, the addition of silicon in slurry-Si could reduce SiC oxidation of SiC RPCs during firing process in contrast with alumina slurry. With regard to slurry-An, andalusite started to transform into mullite phase at 1300 °C and the secondary mullitization occurred at 1450 °C. The enhanced mechanical properties and thermal shock resistance of SiC RPCs infiltrated alumina slurries containing silicon and andalusite were attributed to the optimized microstructure and the triangular zone (inner layer of strut) with mullite bonded corundum via reaction sintering. In addition, the generation of residual compressive stress together with better interlocked needle-like mullite led to the crack-deflection in SiC skeleton, thus improving the thermal shock resistance of obtained SiC RPCs.     

Strength of additively manufactured alumina with different debinding and sintering heat treatments

Lithography-based ceramic manufacturing (LCM) utilizes slurries with low solids loading, which makes pressureless sintering to full density especially difficult. A further compounding issue in sintering to full density and establishing structure–property–processing relationships for LCM alumina is the fact that the current literature lacks consensus on heat treatments to achieve full densities. Treatment specifics that are recorded are frequently ambiguous and insufficiently detailed. In this work, temperatures and times for debinding and sintering schedules were varied to characterize the influence of heat treatment parameters on density, microstructure, and flexural strength of high-purity, LCM-formed alumina. Removing the bisque-fire from debinding and fine-tuning sintering parameters produced parts with full densities, high flexural strengths, and Weibull moduli that match or exceed the values documented in a round robin study of traditionally processed alumina.     

尖晶石对凝胶结合氧化铝空心球浇注料性能的影响

以5～3mm、3～2mm、2～1mm、1～0.2mm粒度氧化铝空心球为原料,引入二氧化硅微粉制成凝胶结合氧化铝空心球浇注料,研究了预合成镁铝尖晶石对凝胶结合氧化铝空心球浇注料性能的影响。用各种耐火制品检测设备和仪器对引入不同量尖晶石的试样性能进行了检测。结合氧化镁-氧化铝-二氧化硅相图进行理论分析,结果发现:尖晶石的引入促进了浇注料中刚玉相的烧结,提高了凝胶结合氧化铝空心球浇注料的常温耐压强度和显气孔率,降低了浇注料的体积密度。尖晶石对凝胶结合氧化铝空心球浇注料基质具有强化作用,有利于提高浇注料的热震稳定性     

红柱石基刚玉-莫来石复相陶瓷的显微结构及性能

以红柱石颗粒为主要骨料,辅以莫来石颗粒和刚玉颗粒,硅微粉、铝微粉为基质料,经混合、困料及成型后,经不同温度下烧成4h,制得莫来石基刚玉-莫来石复相陶瓷,分析了烧成温度对复相陶瓷的物相组成、显微结构、烧成性能、力学性能及热学性能。结果表明:红柱石在高温下转化成针状和柱状莫来石改善复相陶瓷的烧成性能和抗热震性能;在1480℃烧成时,红柱石刚玉-莫来石复相陶瓷具有优越性能,其抗折强度为15.4MPa,耐压强度为91.6MPa,热膨胀系数为5.5×10-6/K,1100℃下水冷的抗热震次数达到99次。