Al2O3纤维增强SiO2气凝胶复合材料的制备及其隔热机理

以正硅酸乙酯为先驱体,采用溶胶-凝胶工艺制备SiO2溶胶,将其与Al2O3纤维复合,经超临界流体干燥技术制得SiO2气凝胶复合绝热材料。采用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、压力试验机、平板导热仪等测试手段对样品的微观形貌、抗压强度以及热导率等进行了研究。讨论了材料的绝热机理,并对进一步降低SiO2气凝胶热导率的途径进行了概述。结果表明:添加Al2O3纤维能够明显增强SiO2气凝胶的综合力学性能;经过1000℃热处理的复合材料仍保持SiO2气凝胶的纳米多孔结构,这赋予复合材料优异的绝热特性。当Al2O3纤维添加量为8%(质量分数)左右时,可使复合材料同时具有较低的热导率(λ=0.051W/(m.K),298K)和较高的抗压强度(σbc=1.977MPa)。     

Al2O3纤维对SiO2基陶瓷型芯的烧缩阻滞

向SiO₂基体粉料中添加Al₂O₃纤维,采用热压注法制备Al₂O₃/SiO₂陶瓷型芯。分析Al₂O₃纤维含量对陶瓷型芯性能的影响。研究结果表明：Al₂O₃纤维含量对Al₂O₃/SiO₂陶瓷型芯的线收缩率、体积密度和抗弯强度均有较大的影响。当Al₂O₃纤维含量大于1wt%时,Al₂O₃/SiO₂陶瓷型芯的线收缩率大幅度降低,稳定在0.335%左右,体积密度随之降低,稳定在1.790 g · cm^-3左右;当Al₂O₃纤维含量为1wt%时,陶瓷型芯抗弯强度达最大值20.48 MPa。分析了Al₂O₃纤维对Al₂O₃/SiO₂陶瓷型芯烧结收缩的阻滞作用机制。     

Al2O3含量对PVDF/PVC/Al2O3共混中空纤维膜的影响

以聚偏氯乙烯(PVDF)、聚氯乙烯(PVC)和纳米氧化铝(Al2O3)三元共混,制备中空纤维膜,探讨Al2O3含量对膜性能的影响。结果表明,由于适量Al2O3的加入,中空纤维膜膜孔结构明显改善,大孔减少,微孔增多;亲水性明显提高。Al2O3为最佳含量3%时,水通量和截留率分别达到了289L/(h·m2)和77.2%。     

Al2O3、TiO2溶胶涂覆粉煤灰/黄土支撑体制备陶瓷膜的研究

用溶胶-凝胶法制备了Al₂O₃、TiO₂两种溶胶,分别涂覆在粉煤灰/黄土支撑体表面制备陶瓷膜,并利用热重分析仪、X-射线衍射仪对膜材料的热稳定性、晶相组成进行分析,并对陶瓷膜的微观形貌、孔隙率、膜通量、膜通量恢复率进行测试与表征。结果表明,烧结温度及干燥条件能有效控制陶瓷膜晶相变化及膜层完整性,Al₂O₃、TiO₂膜材料分别在50,25℃时干燥,600℃时烧结,制得的Al₂O₃膜材料为γ-Al₂O₃,TiO₂膜材料为金红石相TiO₂;Al₂O₃、TiO₂陶瓷膜的孔隙率分别为28.56%、34.12%,膜通量分别为1 092.67和2 983.33 L/(m²·h),膜通量恢复率分别为97%、89%。与未覆膜的支撑体相比,Al₂     

纳米SiO2/Al2O3复合改性对环氧树脂绝缘性能的影响

以双酚A型环氧树脂E51为基体,纳米SiO₂/Al₂O₃为辅助填料,采用低温等离子体协同偶联剂对纳米填料进行接枝处理,控制低温等离子体处理时间,制备出纳米SiO₂/Al₂O₃/E51三元复合绝缘材料,研究纳米填料对环氧树脂复合材料介电性能、闪络电压、热分解温度及击穿强度等的影响。结果表明,纳米SiO₂填充量为3%,纳米Al₂O₃填充量为1.5%,并且采用偶联剂协同低温等离子体的处理时间为30 s时,复合试样各项电气性能均得到显著提升。初始分解温度较未改性时提高22℃;闪络电压较未改性时提高20.9%;击穿强度较未改性时提高23.1%。这一结果为提高环氧树脂电气性能提供了新的研究思路。     

MTES含量对Al2O3/有机硅/SiO2杂化涂层性能的影响

以正硅酸乙酯（TEOS）、甲基三乙氧基硅烷（MTES）、二苯基二甲氧基硅烷（DDS）和仲丁醇铝（ASB）为原料,制备Al₂O₃/有机硅/SiO₂杂化涂层,测试了涂层的物理性能、耐热和电化学阻抗,研究了MTES含量对其性能的影响。结果表明:随着MTES含量的增加,硬度和耐冲击性先增大后减小;柔韧性和附着力良好且变化不大;当n（ASB）:n（TEOS）:rn（MTES）:n（DDS）=1:3:9:1时,Al₂O₃/有机硅/SiO₂杂化涂层的耐热和耐蚀性能最佳。     

多孔Al2O3f/Al2O3复合材料研究进展

作为20世纪90年代兴起的一类连续陶瓷纤维增强陶瓷基复合材料,连续氧化铝纤维增韧氧化铝(Al₂O_3f/Al₂O₃)复合材料已经发展为与C_f/SiC、SiC_f/SiC等非氧化物复合材料并列的陶瓷基复合材料。以多孔基体实现基体裂纹偏转成为Al₂O_3f/Al₂O₃复合材料主要的增韧设计方法,形成的多孔Al₂O_3f/Al₂O₃复合材料具有优异的抗氧化性能和高温力学性能,可在高温富氧、富含水汽的中等载荷工况中长时服役,是未来重要的热结构材料。经过近30年的发展,多孔Al₂O_3f/Al₂O₃复合材料已被应用于航空发动机、燃气轮机等热端部件。本文综述了多孔Al₂O_3f...     

Al2O3颗粒形貌对注凝成型ZrO2/Al2O3陶瓷性能的影响

采用3种不同形貌的Al₂O₃原料对注凝成型制备ZrO₂/Al₂O₃（ZTA）陶瓷工艺中悬浮体的流变性能进行了研究。以低毒的单体N,N-二甲基丙烯酰胺（DMAA）制备了ZrO₂/Al₂O₃坯体和陶瓷。讨论了3种不同形貌的Al₂O₃原浆料的分散剂用量、球磨时间和固含量对浆料流变性的影响。Al₂O₃粉体呈扁平状有利于降低浆料的黏度,Al₂O₃粉体呈棒状对生坯强度的提高有利。制得的3种ZrO₂/Al₂O₃坯体颗粒间结合紧密,抗弯强度分别达到21.45,19.87,25.90 MPa。Al₂O₃粉体呈颗粒状有利于最终陶瓷力学性能的提高,陶瓷的抗弯强度及断裂韧性分别为680 MPa和7.49 MPa·m^1/2,453.1 MPa和6.8 MPa·m^1/2,549.4 MPa和6.34 MPa·m^1/2。     

溶胶-凝胶法在PMMA上制备SiO2-Al2O3涂层过程的研究

采用溶胶-凝胶法,以无机盐AlCl     

BaFe12O19/SiO2-B2O3-K2O 微晶玻璃陶瓷的低温合成及其微波性能

采用柠檬酸sol-gel工艺合成了BaFe₁₂O₁₉/SiO₂-B₂O₃-K₂O微晶玻璃陶瓷, 并对其介电常数及其磁导率在100MHz～ 6 GHz 下的变化规律进行了研究。结果表明: BaFe₁₂O₁₉/SiO₂-B₂O₃-K₂O微晶玻璃陶瓷可以在850℃/5 h的条件下烧结而成, 其合成过程与体系中的Ba/Fe 密切相关; 其介电常数基本不随测试频率的变化而变化; 其磁导率实部随测试频率的增加而下降。      

The mechanism of simultaneous sintering and phase transformation in alumina

The sintering behaviour of boehmitic alumina gels during the transformation to the stable phase has been studied using dilatometry, transmission electron microscopy, X-ray analysis and differential thermal analysis. The specimens for transmission electron microscopy were prepared from gel specimens, sintered to various predetermined temperatures, using an ion-beam thinning technique. The transmission electron microscope study and X-ray analysis have revealed a characteristic sintering behaviour which is associated with the to phase transition. The transformation to the phase occurs by a nucleation and growth process. During the growth process considerable redistribution of the fine porosity existing within the transition alumina matrix occurs, in the form of large elongated interconnected pores trapped within the nucleating grains. These pores grow rapidly to a size approximately one hundred times that of the grains. This process results in a rapid fall-off in sintering rate at the end of the transformation. A study of the/ interphase interface by transmission electron microscopy has led to the development of a model that accounts satisfactorily for the redistribution of the porosity.     

Intermediate Si-Al spinel phase formation in phase transformation of diphasic mullite gel

Al₂O₃-SiO₂ diphasic mullite gel (Si/Al=1/3) has been synthesized by using Al(NO₃)₃·9H₂O and Ludox in basic conditions. Its phase transformation behaviour has been studied by qualitative and quantitative X-ray diffraction techniques. The results indicate that a noncrystalline alumino-silicate phase forms together with the slow crystallization of Si-Al spinel phase of a mullite-like composition up to 1250 °C. Thereafter, it transforms suddenly to orthorhombic mullite around 1325 °C. Earlier studies, e.g. alkali leaching, and measurement of co-ordination number of aluminium in 1000 °C heated diphasic gel, confirm Si-Al spinel formation as an intermediary phase.     

Effects of silica and titania modification additions on the microstructure of sintered alumina

The way in which silica and titania modification additions are introduced into alumina is shown to have a strong effect on the microstructure of sintered Al₂O₃-SiO₂-TiO₂ materials. By combining molecular layering and mechanical mixing, materials with a controlled pore structure can be obtained.     

磁场对材料固态相变影响的研究进展

介绍了磁场对金属材料固态相变影响的研究进展。磁场可改变相稳定性，诱发铁磁合金中的马氏体生成，提高Ms点的温度；影响生成相的形貌，在一些相的生成过程中施加磁场会使这些相的微观排列方向与磁场方向一致；此外磁场还有抑制再结晶、降低焊接试样内应力等效果。初步探讨了磁场对固态相变的作用机制。     

Creep of porcelain-containing silica and alumina

Hard porcelain ceramics find many applications because of their high hardness, high mechanical strength and moderate thermal-shock resistance. The addition of alumina as a filler to porcelain increases its strength at room temperature. In the present investigation, four-point-bend creep tests were carried out for porcelain-containing silica (SP-1) and alumina (AP-3) at 800, 900 and 1000°C. The creep data were analysed using a power-law creep, and the stress exponents were estimated. The activation energy for these two materials was found to be 45 kcal mol^–1. The viscosity of the feldspar glassy phase was also determined from the creep tests. The test samples were analysed by scanning electron microscopy (SEM). The X-ray diffraction results (XRD) show that the amount of crystalline phase in the material increases after creep testing.     

Influence of AlF3 and ZnF2 on the phase transformation of gamma to alpha alumina

This paper focused on the effect of AlF₃ and ZnF₂ additives on the phase transformation of gamma to alpha alumina. AlF₃ and ZnF₂ were found to be effective accelerating agents on the gamma to alpha phase transformation. A single phase of alpha alumina, with an average particle size of 22 nm, can be obtained at 920 °C with AlF₃additive. ZnF₂ can reduce the gamma to alpha transformation temperature to 900 °C, the average size of the particles is about 40 nm and the morphology of some particles is platelike with an aspect ratio of 2–4. The reduction of the transformation temperature was mainly attributed to the formation of intermediate compound of AlOF, which was considered to accelerate the mass transportation from transition alumina to alpha alumina. Moreover, mechanical milling and introducing alumina seeds uniformly worn from the milling mediums are also beneficial for reducing the transformation temperatures.     

Enhanced photoactivity and anatase thermal stability of silica–alumina mixed oxide additives on sol–gel nanocrystalline titania

Nanocrystalline titania with silica and silica–alumina mixed oxide as additives has been prepared through a sequential approach sol–gel method starting from titanyl sulphate in aqueous medium. The mixed oxide added titania shows increased anatase phase stability and high surface area. The complete transformation of anatase to rutile in the mixed oxide added titania occurs only above 1100 °C. The silica and silica–alumina added titania precursor even after calcination at 800 °C show specific surface area of 53 m² g^− 1 and 63 m² g^− 1 respectively. Further, the mixed oxide added titania sample shows excellent photoactivity compared to the commercially available Hombikat UV 100 titania, with respect to degradation of methylene blue. The addition of mixed oxide has resulted in better properties with respect to specific surface area, increased anatase to rutile phase transformation and photocatalytic activity of titania.     

Structural evolution in alumina gel

Thermal treatment and consequent dehydration modifies the structure of boehmite gel, which transits from a polymeric, partially disordered state to the crystalline -alumina via several transition phases. We have investigated the evolution of the microstructure and structural order in the lattice. The significance of particle morphology is brought out in the sintered gel powder pellet. The transparency of the gel glass, despite the large porosity confirms the absence of long range order upto the -phase.