Preparation of Al2O3-mullite thermal insulation materials with AlF3 and SiC as aids by microwave sintering

Al₂O₃-mullite composites were prepared under the synergy effect of AlF₃ and SiC aids by microwave heating. The phase composition, microstructure, porosity, flexural strength, thermal shock resistance, and thermal conductivity were investigated. The XRD results revealed that the content of mullite phase steadily increased with the increasing of AlF₃ content. The microstructure showed that the lower content (≤1 wt%) of AlF₃ led to the formation of granular mullite and the higher content (≥3 wt%) of AlF₃ led to the formation of mullite whiskers, which could form an interlocking structure. In addition, the SiC hot spots can also promote the generation of mullite whiskers by microwave sintering. The thermal shock resistance was significantly improved by the interlocking structure of mullite whiskers. The residual rate of flexural strength of the composite with 3 wt% AlF₃ was 86%. The composite with 3 wt% AlF₃ additives got its optimized thermal conductivity from 30°C to 950°C, the value was between 0.819 and 1.021 W/(mK), which possess excellent thermal insulation performance.     

二氧化钛对黑色Al2O3陶瓷性能的影响

以超微细a-氧化铝粉为主要原料,添加适量过渡金属氧化物以及不同分量的TiO2粉末,采用传统粉末冶金技术、干压烧结法制备了黑色Al2O3陶瓷。对制备工艺中的原料准备、压制成型、烧结过程进行了讨论,并对其导电性能进行了测试分析。实验结果表明：TiO2是一种良好的添加剂,它不仅可以降低烧成温度,还有利于Al2O3陶瓷黑色的形成,改善其电气性能。     

0.73ZrTi2O6–0.27MgNb2O6 microwave dielectric ceramics modified by Al2O3 addition

0.73ZrTi₂O₆–0.27MgNb₂O₆ ceramics with various Al₂O₃ contents (0‐2.0 wt%) were prepared by conventional ceramic route. The effects of Al₂O₃ on the phase composition, microstructure, conductivity, and microwave dielectric properties were systematically investigated. The coexistence of a disordered α–PbO₂‐type phase and a rutile second phase was found in all compact ceramics with low Al₂O₃ contents (x = 0, 0.5, and 1.0 wt%), while a corundum phase was detected when Al₂O₃ additive increased to 1.5 and 2.0 wt% based on X‐ray diffraction results. With the addition of Al₂O₃, the decreased grain size of the matrix phase was observed using field‐emission scanning electron microscope, accompanied with increased resistivity and band‐gap energy. Additionally, Al₂O₃ additives efficiently improved the quality factor of the ceramics. After sintering at 1360°C for 3 hours, the ceramic with 1.0 wt% Al₂O₃ exhibited excellent microwave dielectric properties: a dielectric constant of 43.8, a quality factor of 33 900 GHz (at 6.6 GHz), and a near‐zero temperature coefficient of resonant frequency (3.1 ppm/^°C).     

Al2O3陶瓷高温釉氢烧失光原因的研究

本文总结并实验对比了国内外的几种高温釉,从而提出釉料化学性质、釉料中氧化铁等变价元素以及原料矿物组成是导致氢烧釉面失光的主要因素,并成功试制出适宜于氧化铝陶瓷以及1450℃金属化工艺的高温釉。     

凝胶注模法制备多孔氧化铝陶瓷的研究

采用凝胶注模和加造孔剂的工艺,用甲基丙烯酸—羟乙酯(HEMA)取代丙烯酰胺(AM)作为单体,用十二烷基硫酸钠作为造孔剂,将样品于1600℃下保温2小时烧结,成功制备出了气孔率为80%的结构均匀的氧化铝多孔陶瓷。     

Mg3B2O6 microwave dielectric ceramics fabricated by combining cold sintering with post-annealing process

It is difficult to get pure-phase Mg₃B₂O₆ (abbreviated as MBO) ceramics by the traditional high-temperature solid-state reaction method. In this paper, pure-phase MBO ceramics were successfully densified and obtained by combining the cold sintering and post-annealing process. The relative density of MBO ceramics was ∼80% cold sintered at 150°C/90 min/800 MPa, which was further improved to ∼91% by post-annealing at 900°C, 400°C lower than that of the traditional high-temperature sintering process (∼1300°C). X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and Raman results demonstrated that the secondary phase of MgO was effectively eliminated, and dense microstructure was observed by the cold-sintering process plus post-annealing treatment. Finally, the microwave dielectric properties of MBO were evaluated with ε_r: 5.15–6.37, Q×f: 5942–16 686 GHz, τ_f: −48.45–69.72 ppm/°C.     

溶胶-凝胶法制备氧化铝系复合膜的研究进展

介绍了采用溶胶-凝胶法制备Al2O3系复合膜的研究发展现状以及掺入不同外加组分后Al2O3膜的结构特点及其影响机理,同时指出了用溶胶-凝胶法制备氧化铝系复合膜过程存在的问题及发展趋势。     

Fabrication and characterizations of Ho3Sc2Al3O12 magneto-optical transparent ceramics

Currently, Faraday isolators and rotators for high-power lasers are popular research topics; therefore, finding magneto-optical materials with excellent Verdet constants and thermal properties is crucial. In this study, novel holmium scandium aluminum garnet (HoSAG) magneto-optical ceramics were fabricated using vacuum sintering. This study improved the traditional ball milling method and pre-synthesized powders with great sinterability after secondary ball milling and sieving. Different pre-synthesis temperatures were found to have significant effects on the particle size and micromorphology of the synthesized powders. HoSAG ceramics with 0.05 wt% MgO sintering aid and held at 1700°C for 30 h reached a transmittance of 76.7% at 1550 nm. Meanwhile, HoSAG transparent ceramics maintain higher transmittance in the infrared region (>1500 nm) than terbium gallium garnet (TGG) crystals, indicating better application prospects. The Verdet constants of HoSAG magneto-optical ceramics at 405, 532, 808, and 1064 nm were −421.5, −181.2, −65, and −32.3 rad T⁻¹ m⁻¹, respectively, which are slightly less than those of TGG magneto-optical ceramics. Moreover, the thermal conductivity of HoSAG ceramics at 300.00 K was 4.89 W m⁻¹ K⁻¹, which is comparable to that of the TGG ceramics.     

Al2O3＋TiC陶瓷中Al2O3与TiC化学反应抑制的研究

本文通过Ｙ－盐溶液的形式加入到Ａｌ２Ｏ３粉料中,制备了Ｙ２Ｏ３表面固溶的Ａｌ２Ｏ３粉料,对其阻止Ａｌ２Ｏ３与ＴｉＣ之间的化学反应进行了研究。研究结果表明：采用Ｙ－盐溶液加入Ｙ２Ｏ３,Ｙ原子能均匀的分散在Ａｌ２Ｏ３的表面,高温时Ｙ２Ｏ３在Ａｌ２Ｏ３表面形成固溶体层,少量的Ｙ２Ｏ３加入量（０．３５ｗｔ％）,就能有效的阻止Ａｌ２Ｏ３与ＴｉＣ之间的化学反应。     

Design and fabrication of Al2O3f/SiCN composite with excellent microwave absorbing and mechanical properties

A new kind of structural and functional integration ceramic matrix composite material was prepared from high-performance alumina (Al₂O₃) fibers and absorbing silicon carbonitride (SiCN) ceramics via a combination of polymer infiltration pyrolysis (PIP) and chemical vapor infiltration (CVI) methods. The Al₂O₃ fiber annealed at its cracked temperature had enhanced permittivity, because the sizing agent on the Al₂O₃ fiber surface was cracked into pyrolysis carbon. For PIP + CVI Al₂O_3f/SiCN composites, PIP SiCN matrix with low conductivity was used as the matching phase, while CVI SiCN matrix with medium permittivity and dielectric loss was regarded as the reinforcing phase distributed in porous PIP SiCN matrix and inter-bundles of Al₂O₃ fiber to improve their mechanical and microwave absorption properties. The fracture toughness and flexural strength of Al₂O_3f/SiCN composite were determined to be 9.4 ± 0.5 MPa m^1/2 and 279 ± 28 MPa, respectively. Based on the design principles for impedance matching, the Al₂O_3f/SiCN composites before and after oxidation were used as loss and impedance layers, respectively. It was found that the optimized composite had the lowest reflection coefficient (RC) of −70 dB and the effective absorption bandwidth covering the whole X-band. In conclusion, Al₂O_3f/SiCN composite can serve as a high-temperature structural material with excellent microwave absorption properties for aerospace applications.     

Cr2O3微粉加入量对Al2O3-Cr2O3质耐火材料性能的影响

以电熔铬刚玉和白刚玉为主要原料,用Cr₂O₃微粉部分替代电熔铬刚玉细粉,研究了Cr₂O₃微粉加入量对Al₂O₃-Cr₂O₃质耐火材料常温和高温性能、物相组成和显微结构的影响。结果表明,随着Cr₂O₃微粉加入量的增加,原位形成了(Al_1-xCr_x)₂O₃固溶体,促进了烧结,材料的显气孔率先降低后升高,且(Al_1-xCr_x)₂O₃固溶体的晶格常数呈线性增加,符合Vegard定律。材料的常温抗折强度和常温耐压强度随Cr₂O₃微粉加入量的增加先升高后降低,在Cr₂O₃微粉加入量为15%(质量分数)时强度达到最大值。而当Cr₂O₃微粉加入量为20%(质量分数)时,由于有挥发现象,材料显气孔率上升,强度下降。材料高温抗折强度随Cr₂O₃微粉加入量的增加而增加,材料的残余强度保持率呈先降低后升高的趋势。     

添加Al2O3的Y-TZP基层状陶瓷力学性能

用15%(体积分数)Al2O3/3Y-TZP作为中间层,以20%(体积分数)Al2O3/3Y-TZP作为外层,采用干压、等静压法成型,并通过无压烧结制成了三层复合材料.通过测定材料的收缩率,对烧结收缩引起的应变进行了估算,提出:烧结收缩率也是层状材料设计的主要因素之一.实验结果表明:层状复合材料与15%(体积分数)Al2O3/3Y-TZP单层材料相比,应力方向平行于界面的抗弯强度提高了11.8%,由482MPa提高到539MPa;应力方向垂直于界面的韧性提高了21.2%,由9.9MPa*m1/2提高到12.0MPa*m1/2.     

Na2O-Al2O3-Fe2O3系烧结过程中铝、铁的反应行为

以Al2O3, Fe2O3和Na2CO3为原料,对Na2O-Al2O3-Fe2O3系烧结过程中的反应行为进行了详细研究. 基于溶出率与时间、温度的关系,证明Na2O×Al2O3和Na2O×Fe2O3的生成反应动力学都服从Zhuralev-Lesokin-Tempelman模型,表观活化能分别为186.59和80.92 kJ/mol,表明Na2O×Fe2O3比Na2O×Al2O3在动力学上更易形成;Al2O3易与Na2O×Fe2O3反应形成Na2O×Al2O3和Fe2O3,在1273 K烧结30 min,所得熟料Al2O3溶出率达98.51%;Fe2O3对Na2O×Al2O3的形成有双重作用,在1273 K下可加速Na2O×Al2O3的形成,超过1323 K,促使Na2O×Al2O3分解成Na2O和b-Al2O3,且随着温度升高或时间延长,分解程度增高,从而导致熟料中Al2O3溶出率显著降低.     

Sintering behavior and morphology control of porous Al2O3-SiO2 ceramics for radome applications

Ceramics from porous Si₃N₄ and its derivatives SiAlON and Si₂N₂O were once considered the most promising high-temperature wave-transmitting materials. However, their large-scale application in the field of radomes is greatly restricted due to their poor oxidation resistance, high preparation costs, and expensive raw materials. Therefore, the development of low-cost porous oxide ceramics remains of significant interest to the field of high-temperature wave transmission. Surprisingly, mullite ceramics, which are representative of the Al₂O₃-SiO₂-system of ceramics, are ultra-low-cost materials with the potential to replace ceramics from Si₃N₄ and its derivatives. In this paper, integrated porous Al₂O₃-SiO₂-system ceramics were successfully prepared for load-bearing/wave-transmitting applications, using inexpensive calcined kaolin and alumina powder as the main raw materials. Calcined kaolin can provide seeds for the growth and development of mullite crystals in the ceramic system. High-strength and high-porosity ceramics were obtained with the mullite morphology controlled through the molar ratio of Al₂O₃ to SiO₂ and the resulting content of mullite seeds. With increasing of mullite seed content, the length and radial width of mullite whiskers with “interlocking structure” gradually change from rod-shaped “long and thick” to needle-like “short and thin.” The prepared porous Al₂O₃-SiO₂ ceramics have high flexural strength, fracture toughness, and good dielectric properties.     

Al_2O_3改性环保型酚醛树脂的制备与研究

采用偶联剂KH-550对Al2O3表面进行处理,并将其添加到酚醛树脂(PF)中,成功制备了有机-无机杂化PF。通过红外光谱(FT-IR)仪、差示扫描量热(DSC)仪、扫描电镜(SEM)和材料试验机等对改性PF的结构、耐热性、微观形貌、力学性能和电学性能等进行分析。结果表明:Al2O3表面出现了Si-O键,说明KH-550成功处理了Al2O3;改性PF固化速率最快时所对应的峰值温度降低了8℃,使树脂固化更容易进行;当w(Al2O3)=5.0%时,复合材料的综合性能最好,其拉伸强度为664 MPa,弯曲强度为973 MPa,冲击强度为252 MPa,表面电阻率为4.00×1014Ω/cm,体积电阻率为1.93×1014Ω.cm。     

Al2O3陶瓷的动态力学性能研究

本文采用ＳＨＰＢ装置对９５瓷、９７瓷和９９瓷的动态力学性能进行实验研究。结果表明Ａｌ２Ｏ３陶瓷在高冲击载荷下其抗压强度增高,其增加幅度随Ａｌ２Ｏ３含量增加而加大,并分析了机理。     

Characterization of green Al2O3 ceramics surface machined by tools with textures on flank-face in dry turning

Green Al₂O₃ ceramics through cold isostatic pressing were produced. Scratch tests were performed to evaluate the machinability. Texturing was applied on the flank-face of the WC/Co tools by laser. Tools with textures on the flank-face were adopted in dry cylindrical turning of the green Al₂O₃ ceramics. Characterization of green ceramic surfaces machined by flank-face textured tools was studied. Results revealed that green ceramics had good enough machinability in cutting tests and scratch tests. There were no visible cracks on the surface after machining. Flank-face textured tools could improve the surface integrity during processing green Al₂O₃ ceramics. Mechanisms responsible were found that derivative-cutting behavior by flank-face textures was able to remove visible hard inclusions on surfaces of green ceramics, which made the surfaces much smoother. More tiny ceramic powders generated by the phenomenon were pressed on the surfaces of green ceramics, which made further efforts on improving surface quality. Machining parameters had significant impacts on surface integrity. Within machining parameters, surface quality became better and compaction area was found on surfaces of green Al₂O₃ ceramics with the increase of cutting depth, but there were still visible hard inclusions and spalling of materials on the surface after machining.     

Al2O3对CaO-Al2O3-SiO2系微晶玻璃晶化和性能的影响

以CaO-Al2O3-SiO2三元系微晶玻璃为研究对象,从玻璃析晶动力学方面进行研究,通过DTA和SEM等分析方法,对微晶玻璃析晶行为进行研究,利用析晶活化能E和析晶参数n值来分析析晶机理;实验结果表明:析晶参数n=2,体系属于整体析晶。随着Al2O3含量的增加,析晶温度有升高的趋势,析晶活化能增大,有利于玻璃的烧结;试样密度增大,显微硬度增加。     

Al2O3含量对PbO-CaO-B2O3-SiO2系玻璃析晶行为与烧结性能的影响

PbO-CaO-B₂O₃-SiO₂系玻璃粉体是耐高过载低温共烧陶瓷(LTCC)生瓷带的主要组成部分。玻璃粉体的析晶行为影响烧结性能,进而决定基板的使用性能。本文研究了Al₂O₃含量对PbO-CaO-B₂O₃-SiO₂系玻璃析晶行为与烧结性能的影响。结果表明:向PbO-CaO-B₂O₃-SiO₂系玻璃中引入Al₂O₃可抑制玻璃析晶,防止高膨胀晶相的析出,并提高玻璃烧结密度;不含Al₂O₃的PbO-CaO-B₂O₃-SiO₂玻璃粉体析晶峰温度为862 ℃,烧结过程中析出方石英晶相,20~200 ℃的平均线膨胀系数高达260.8×10^-7 ℃^-1;引入2.1%(质量分数)Al₂O₃可显著抑制玻璃析晶,700 ℃烧结后膨胀系数降低至72.9×10^-7 ℃^-1,介电常数显著增大,由6.30提高至7.02。     

Al2O3-ZrO2系无收缩的致密陶瓷

研究了利用无机原料以反应烧结法合成Al2O3-ZrO2系无收缩的陶瓷的可能性。为使收缩率达到零,作为活性反应组分,除了ZrAl3金属间相之外,还利用了超细铝粉,后者是采用导线通过电爆破法制取的。查明,由于加入15%金属铝,使试样的几何尺寸变化几乎为零,此时制取的试样的气孔率<1.5%,强度达750MPa。