共查询到19条相似文献,搜索用时 109 毫秒
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莫来石晶须的生长机理研究 总被引:3,自引:0,他引:3
本研究采用湿化学法制备莫来石晶须,主要讨论了晶须生长机理。研究结果表明,高温下产生的AIF3和SIF4气相在莫来石晶核表面通过气—固化学反应形成高长径比莫来石晶须。 相似文献
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以含稀土的石膏为原料运用常压酸化法合成硫酸钙晶须,探讨了不同工艺条件对生成的硫酸钙晶须形貌的影响,同时还考察了晶型助长剂的种类和晶型助长剂的含量对硫酸钙晶须生长的影响,利用SEM和XRD分别对硫酸钙晶须的表面形貌、物相特征做了表征分析。实验得到制备硫酸钙晶须的最佳的反应条件:稀土石膏质量浓度为0.22 g/mL、反应时间为25 min、盐酸浓度为2.8 mol/L、反应温度为70 ℃、陈化时间为4 h,在此条件下合成的硫酸钙晶须平均长度为61 μm,平均长径比为30.5;通过对比实验选出了CuCl2作为促进硫酸钙晶须生长的助长剂,在添加5%(质量分数)的CuCl2的情况下可使硫酸钙晶须长径比从30.5增至41,长度从61 μm增至81 μm。 相似文献
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《耐火材料》2016,(6)
基于低成本和废料资源化利用的目的,以质量分数分别为31.8%的煤矸石,68.2%的氢氧化铝,外加3%的金属氧化物(V_2O_5、MnO_2或MgO)为添加剂,于1 500℃保温1 h煅烧后制备了莫来石晶须增强刚玉耐火材料试样,并与未添加金属氧化物的试样对比。采用XRD、SEM等对试样物相及显微结构进行了分析,并探讨了添加不同金属氧化物对莫来石晶须生长和长径比及试样性能的影响。结果表明:添加金属氧化物后,莫来石晶须的长径比都出现了下降,其中添加V_2O_5的试样对晶须长径比的影响最小,MnO_2次之,添加MgO的试样影响最大。当添加金属氧化物MnO_2时,试样具有最大的抗折强度,这主要是由于试样中莫来石晶须长径比合适(13.5),以及莫来石是主晶相,刚玉是次晶相所致。 相似文献
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以脱硫石膏为原料,采用水热法再结晶工艺,研究了氯化镁、柠檬酸、十二烷基苯磺酸钠(SDBS)和油酸钠对硫酸钙晶须生长行为的影响。结果表明:在一定温度下,水热再结晶产物晶相均为半水硫酸钙;未加添加剂的脱硫石膏经水热转化可以形成硫酸钙晶须,但产物长径比小,晶须短而粗。氯化镁对晶须的生长无明显促进作用;柠檬酸会抑制晶须的生长;SDBS对晶须的生长有一定的促进作用,但产物形貌不均匀,出现颗粒状硫酸钙;油酸钠对晶须生长有较好的促进作用,可获得形貌均匀、长50~200μm、直径约1μm的高长径比的针状晶须,经煅烧可得到稳定化的无水死烧硫酸钙晶须。在此基础上探讨了油酸钠在水热转化过程中对晶须生长的作用机理。 相似文献
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燃烧合成法是一种高效能、低消耗的陶瓷材料合成方法。简要介绍了燃烧合成方法特点,评述了近年来燃烧合成氮化硅陶瓷晶须的研究进展,详细总结了原料选择、多种添加剂(如铁、稀土氧化物、铵盐等)对氮化硅晶须最终形貌和性能的影响, 总结了工艺参数,尤其是氮气压力和堆积密度对晶须生长的影响,并详细讨论了在燃烧合成过程中晶须的生长机理。 相似文献
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氮化硅晶须的研究现状 总被引:3,自引:0,他引:3
本文首先综述了近年来对晶须生长机理的研究,然后重点介绍了氮化硅晶须的制备方法以及影响其生长的因素,并阐述了氮化硅晶须增强复合材料的现状。指出了加强晶须的基础研究,从质量和成本考虑是今后的发展方向。 相似文献
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Wataru Nakao Shuntaro Mori Jun Nakamura Koji Takahashi Kotoji Ando Masahiro Yokouchi 《Journal of the American Ceramic Society》2006,89(4):1352-1357
To improve fracture toughness and encourage excellent self-crack-healing ability, mullite/SiC particle/SiC whisker multi-composites and mullite/SiC whisker composites were hot pressed. The crack-healing abilities and mechanical properties of these sintered composites were investigated. Based on the obtained results, the usefulness of the mullite composite as a material for springs was discussed. The part of mullite/15 vol% SiC whisker/SiC 10 vol% particle containing healed cracks retained high reliability over the whole measured temperature range. When the crack-healing ability was endowed by SiC whiskers alone, the parts containing the healed pre-cracks were found to have a heat-resistance limit temperature. Mullite/15 vol% SiC whisker/10 vol% SiC particle multi-composite had the best potential as a material for springs used at high temperatures, because it had an adequate crack-healing ability as well as shear deformation ability almost two times stronger than that of monolithic mullite. 相似文献
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Hao Yan Shile Chen Ying Lang Hongkang Wei Chuanjin Tian Chang-An Wang 《International Journal of Applied Ceramic Technology》2022,19(6):3116-3126
Porous mullite matrix ceramics have excellent thermal and mechanical properties suitable for applications such as in thermal insulation. However, their applications are limited by processing defects from nonuniform sintering shrinkage and the trade-off between high porosity (preferred for low thermal conductivity) and high mechanical strength. Herein, we seek to minimize the sintering shrinkage by near-net-size preparation and improve the strength by in situ formed whisker network structure. Gelcasting forming technology and pressureless sintering were used to prepare porous mullite matrix ceramics using kyanite and α-Al2O3 powders as the starting materials and using MoO3 to promote the growth of mullite whiskers. The results showed that the sintering shrinkage could be compensated by the volume expansion from solid-state reaction during reaction sintering. The in situ formed three-dimensional (3D) whisker network further reduced sintering shrinkage and effectively improved the strength of the ceramics. An ultralow sintering shrinkage of .78% was achieved. The near-net-shape porous mullite matrix ceramics strengthened by 3D whisker network had a high porosity of 63.9%, a high compressive strength of 83.8 MPa and a high flexural strength of 53.5 MPa. 相似文献
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《Ceramics International》2023,49(7):10238-10248
High-strength ceramics were prepared from high alumina fly ash (HAFA) and activated alumina as raw materials with magnesia as a sintering additive. The growth kinetics and influence mechanism of secondary mullite whiskers were investigated. Meanwhile, the effects of the Al2O3/SiO2 mass ratio (A/S) and the amount of magnesia on the content and morphology of mullite in the green body were investigated, so as to emphasize the effect of the liquid phase in the sintering process on the growth of secondary mullite whiskers. The results showed that the aspect ratio of secondary mullite whiskers increased significantly after adding activated alumina to increase the A/S ratio of raw materials. When 30 wt% activated alumina was added, the mullite content increased by 5.39%, and the whisker length increased from 1.36 μm to 4.18 μm. The addition of magnesia improved the liquid phase formed during the sintering process and the K value method was used to determine the sintering liquid phase content under various conditions. It was observed that increasing the magnesia level by 1 wt% could raise the liquid phase content by 5–7%. When the total liquid content of the system was 30–40%, the growth activation energy in the diameter direction of the whisker reduced significantly, promoting the growth of secondary mullite whiskers along the C axis. The morphology of mullite gradually developed from fibrous to long columnar crystal, making it combine more densely with the green body matrix. Furthermore, the staggered long columnar mullite crystal structure changes the fracture mode of ceramics from intergranular to transgranular fracture, which fully uses the high mechanical strength of mullite. As a result, the fracture energy and strength of ceramics are significantly improved. 相似文献
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《Journal of the European Ceramic Society》2017,37(7):2649-2655
It has been proved that the secondary structure assembled on each fiber in the porous fiber network can catch the ultrafine particles easily in filtration process. In this work, three different networks without (naked fiber) or with different secondary structure (mullite whisker/mullite fiber or corundum plate/mullite fiber) were prepared to investigate the influence of secondary structure on the high temperature mechanical property and the soot oxidation. The mullite whisker/mullite fiber (MW/MF) network exhibited the best high temperature compress resistence and lowest soot oxidation temperature. The soot oxidation start temperatures were 434 °C and 443 °C in the mullite whisker/mullite fiber (MW/MF) and corundum plate/mullite fiber (CP/MF) webs respectively, which was lower than that in the Naked mullite fiber (MF) web (473 °C). Thus, fiber webs assembled with secondary structures have been shown to be promising filter with effective soot oxidation activity. 相似文献
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为了提高粉煤灰的高附加值利用,分别以氢氧化铝和粉煤灰漂珠作为海胆状莫来石前驱体的铝源和硅源,氢氧化铝和粉煤灰为莫来石晶须前驱体增强剂的铝源和硅源,AlF3和V2O5为晶须促进剂和烧结助剂,采用固相法原位制备了莫来石陶瓷材料。主要研究了增强剂与海胆状莫来石前驱体的配比(质量比分别为3:7、4:6、5:5、6:4、7:3)对制备的莫来石陶瓷材料性能、物相组成和显微结构的影响。结果表明,随着增强剂与海胆状莫来石前驱体的配比从3:7增大至7:3,试样中形成的晶相全为莫来石,材料内部更加致密,体积密度和抗压强度逐渐增大,总气孔率逐渐减小,增强剂的引入提高了材料的线变化率和抗热震性能,但降低了材料的重烧线变化率,材料的残余抗压强度及残余强度比先增加后减小。当增强剂与海胆状莫来石前驱体的质量比为6:4时综合性能较佳。 相似文献
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Fabrication of Oriented SiC-Whisker-Reinforced Mullite Matrix Composites by Tape Casting 总被引:1,自引:0,他引:1
Dense SiC-whisker-reinforced mullite composites with up to 50 vol% whiskers can be obtained by tape casting and hot pressing. The tape casting process results in high degrees of SiC whisker orientation as determined visually and by X-ray diffraction. The ability to achieve dense composites with as much as 50 vol % whiskers is attributed to the higher percolation threshold of aligned whiskers. The factors affecting the degree of whisker orientation during tape casting are described using a fluid dynamics model derived from Jeffery's equations and show that the orientation of anisometric particles is enhanced primarily by the casting rate and particle aspect ratio. 相似文献
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Triplicane A. Parthasarathy Randall S. Hay Robert Ruh 《Journal of the American Ceramic Society》1996,79(2):475-483
The effect of 33.5 vol% SiC whisker loading on high-temperature deformation of 1 wt% MgO-38.5 wt% zirconia-mullite composites was studied between 1300° and 1400°C. At strain rates of 10−6 to 5 × 10−4 /s the creep resistance of zirconia-mullite composites without SiC reinforcement was inferior to monolithic mullite of similar grain size. Analysis of the results suggested that the decreased creep resistance of mullite-zirconia composites compared to pure mullite could be at least partially explained by mechanical effects of the weaker zirconia phase, increased effective diffusivity of mullite by zirconia addition, and to the differences in mullite grain morphology. With SiC whisker reinforcement, the deformation rate at high stress was nearly the same as that of the unrein-forced material, but at low stress the creep rates of the SiC-reinforced material were significantly lowered. The stress dependence of the creep rate of unreinforced material suggested that diffusional creep was the operative mechanism, while the reinforced material behaved as if a threshold stress for creep existed. The threshold stress could be rationalized based on a whisker network model. This was supported by data on other whisker-containing materials; however, the threshold stress had a temperature dependence that was orders of magnitude higher than the elastic constants, leaving the physical model incomplete. The effects of residual stresses and amorphous phases at whisker/matrix interfaces are invoked to help complete the physical model for creep threshold stress. 相似文献
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Zhuohao Xiao Xianglin Li Shijin Yu Xinyuan Sun Xiuying Li Min Wu Chuanhu Wang Tianshu Zhang Sean Li Ling Bing Kong 《Ceramics International》2018,44(12):13841-13847
Mullite ceramics with hollow whisker structure have been synthesized firstly through ordinary sintering process. The effects of Bi2O3 and processing, on mullitization behavior and morphology development of mullite ceramics, derived from the mechanochemically activated mixture of Al2O3 and SiO2, were investigated in this paper. When the content of Bi2O3 was less than 10?mol%, the mullite grains show a short rod-like morphology, without the formation of whisker. As the content of Bi2O3 was increased to more than 10?mol%, the formation temperature of mullite was decreased from 1400?°C to 1100?°C. After sintering at 1400?°C, well-developed mullite whiskers with hollow structure were formed. The formation process and growth mechanism of hollow structural whiskers in mullite ceramic doped with high content of Bi2O3 were discussed in detail. 相似文献