Sol-gel法制备ZrO2/钙铝硅系微晶玻璃复合材料的研究

采用Sol-gel法制备ZrO_2/钙铝硅系微晶玻璃复合材料,通过差热分析、X射线衍射和扫描电镜等测试手段对其显微结构及各项性能进行探讨。研究结果表明:所制得的复合微晶玻璃主晶相为t-ZrO_2和β-CaSiO_3,抗折强度为132.53MPa,适用于制备高强度牙科材料。     

锂霞石复合氧化铝陶瓷材料性能的研究

以预合成锂霞石、氧化铝微粉、钛白粉等为原料，经1600℃烧成，制备合成了锂霞石—氧化铝复合陶瓷，材料经过1100℃到常温空冷循环10次后，L1、L2、L3的抗折强度分别增加了83.7%、43.8%、29.2%，继续进行20次、30次热震试验，材料抗折强度基本不发生变化，具备非常优良的热震性能。利用XRD及SEM等测试方法，研究了锂霞石—氧化铝复合陶瓷热震前后强度变化的机理。结果表明，经热震试验后，材料中的Li AlO₂、LiAl₅O₈、Al₂SiO₅、LiAlSi₃O₈等晶相和玻璃相转变为Al₂O₃和LiAlSiO₄等晶相，材料微观结构得到改善，裂纹减少，晶粒结合程度更加紧密，提高了材料的抗折强度。     

信息集锦

高强度云母陶瓷云母陶瓷是一种特种工程材料。目前生产云母陶瓷采用两种方法：一种是结晶玻璃法，另一种是烧结法。但这两种方法生产的云母陶瓷抗折强度不够理想，不能超过150MPa。如用前种方法生产，其抗折强度一般在100～140MPa范围内。用后种方法生产，其抗折强度一般在120～130MPa范围内。因此需要研制一种抗折强度可达到150MPa以上的高强云母陶瓷。近年来，日本在这方面作了一系列的研究工作，研制成功一种高强云母陶瓷。这种云母陶瓷是用氟金云母和氧化铝为主要原料，加入氟化初和氟化钙外加剂，经烧成而成。其原料组成为氟金云母…     

不同成分对白榴石合成及性能的影响

采用熔体冷却析晶法制备了白榴石。利用X射线衍射分析、扫描电镜、热膨胀系数测试、抗折强度测试研究了不同的成分及析晶温度对白榴石析晶、热膨胀系数及其对牙科材料增强作用的影响。结果表明,当化学成分接近白榴石理论含量,Al2O3微过量,析晶温度为1100℃时,样品的析晶能力最好,热膨胀系数最高为20.13×10-6℃-1(20~500℃)。并且,白榴石掺杂可以有效提高牙科玻璃陶瓷的抗折强度和热膨胀系数,当掺杂量为50%时,材料的抗折强度提高到127.43 MPa,热膨胀系数提高到15.72×10-6℃-1。     

氧化铝微粉在轻质隔热浇注料中的应用研究

以超轻氧化铝质骨料为主要原料,铝酸钙水泥为结合系统,研究了不同含量氧化铝微粉对轻质隔热浇注料性能的影响。结果表明,轻质隔热浇注料的体积密度随着热处理温度的提高呈现先减小后增大的变化规律,并且随着氧化铝微粉含量的增加,体积密度增大。轻质隔热浇注料的抗折强度和耐压强度随着热处理温度的提高呈现先减小后增大的变化规律,并且当氧化铝微粉含量为5％时,材料的抗折强度和耐压强度最大。     

石英玻璃对Li2O-Al2O3-SiO2系统微晶玻璃性能的影响

向水淬后的Li2O-Al2O3-SiO2系统玻璃粉中加入石英玻璃粉，参照玻璃粉末的DTA曲线确定晶化温度，采用烧结法制备出了低膨胀微晶玻璃材料。运用XRD分析了材料的晶相种类，测定了材料的热膨胀系数、密度、抗折强度等性能，分析讨论了石英玻璃粉对材料性能的影响结果表明，石英玻璃粉含量增大，材料的热膨胀系数值减小。密度值增大，抗折强度值降低，析出主晶相为β-锂辉石固溶体。     

牙科用Y-TZP/云母微晶玻璃复合材料的研制

以K2O-MgO-Al2O3-SiO2-F系统的微晶玻璃为基础,与不同量的Y-TZP粉体进行复合,制备出了用于牙科修复的新型全瓷材料。借助于DTA,XRD,SEM等对该材料的主晶相种类和显微结构进行了研究,并测试了复合材料的抗折强度、体积密度、维氏硬度、热膨胀系数和耐酸(碱)性等理化性能。实验结果表明:复合材料的主晶相为氟金云母、t-ZrO2和少量的m-ZrO2;其具有优于天然牙齿和牙釉质的力学性能,化学性能稳定、审美效果良好,适用于制作前牙冠、贴面、嵌体等口腔修复体。     

锆英石和氧化铝加入量对镁质浇注料性能的影响

研究了锆荚石和氧化铝的加入量对镁质浇注料常温物理性能、热震稳定性、高温抗折强度（１４５℃,１ｈ）及抗渣性能的影响。结果表明：锆英石和氧化铝的加入均降低了镁质浇注料的常温强度,提高了其热震稳定性,但对高温抗折强度影响不大;适量锆英石和氧化铝的加入均能改善镁质浇注料的抗渣渗透性。     

不同铝基原料对MgO-Al-C材料性能和显微结构的影响

以烧结镁砂骨料、电熔镁砂细粉、Al粉、N220炭黑为原料,酚醛树脂为结合剂,制备MgO-Al-C材料,研究了三种铝基原料(造粒氧化铝微粉、氧化铝空心微珠、六铝酸钙)对其常温抗折强度、高温抗折强度、抗热震性及抗氧化性的影响,并借助XRD和SEM对其物相组成及显微结构进行分析。结果表明,造粒氧化铝微粉是多孔结构,可吸收热应力,加入量为1%(质量分数,下同)时,可提高材料的常温抗折强度和抗热震性,明显改善材料的抗氧化性。氧化铝空心微珠是中空结构,可缓冲热应力,加入量为3%时,可明显提高材料的常温抗折强度,并具有较高的抗热震性和抗氧化性。六铝酸钙的热膨胀系数较低,可赋予材料较好的韧性,加入量不超过5%时,样品具有较好的抗热震性。     

纳米氧化铝对天然橡胶/顺丁橡胶/丁苯橡胶复合材料性能的影响

研究了纳米氧化铝用量对天然橡胶/顺丁橡胶/丁苯橡胶复合材料的性能及在玻璃路面与沥青路面的抗湿滑性能的影响。结果表明,纳米氧化铝用量小于10.0份时,对复合材料的力学性能、0℃和60℃下的损耗因子影响不大,但随纳米氧化铝用量的增加,复合材料的耐磨性能下降,压缩生热增加。当摩擦面为玻璃路面时,随着纳米氧化铝用量的增加,复合材料的抗湿滑性能提高。当摩擦面为沥青路面时,纳米氧化铝的用量对复合材料的抗湿滑性能影响不大,路面的平均构造深度为抗湿滑性能的主要影响因素。     

Mullite/SiAlON/Alumina Composites by Infiltration Processing

The formation of mullite/SiAlON/alumina composites was studied by infiltrating a SiAlON/alumina-base composite with two different solutions, followed by thermal treatment. The base composite was prepared from a mixture of tabular Al₂O₃ grains, fume SiO₂, and aluminum powders. The mixture was pressed into test bars and nitrided in a nitrogen-gas (N₂) atmosphere at 1480°C. The infiltrants were prehydrolyzed ethyl polysilicate solution and ethyl polysilicatealuminum nitrate solution. The composites were infiltrated under vacuum, cured at 100°C, and precalcined in air at 700°C. This infiltration process was repeated several times to produce bars that had been subjected to multiple infiltrations, then the bars were calcined in a N₂ atmosphere at 1480°C to obtain mullite/SiAlON/alumina composites. The infiltration process increased the percentage of nitrogenous crystalline and mullite phases in the matrix; therefore, a decrease of the composite microporosity was observed. The infiltration increased the mechanical strength of the composites. Of the two composites, the one produced using prehydrolyzed ethyl polysilicate as the infiltrant had a higher mechanical strength, before and after being subjected to a severe thermal shock.     

Fabrication and Characterization of an Ultra-High-Temperature Carbon Fiber-Reinforced ZrB2–SiC Matrix Composite

A novel carbon fiber-reinforced ZrB₂–SiC matrix composite was fabricated by heaterless chemical vapor infiltration through infiltration of SiC matrix into a carbon fiber-ZrB₂ powder preform. The C/ZrB₂–SiC composite presented a flexural strength of 148 MPa, a fracture toughness of 5.6 MPa·m^1/2, and a good oxidation and ablation resistance.     

Mullite/Alumina Particulate Composites by Infiltration Processing: III, Mechanical Properties

The effect of incorporating mullite into alumina by an infiltration process on the mechanical properties was investigated. Data for Young's modulus, strength, and fracture toughness for various composite compositions were compared with those for the unreinforced matrix (alumina). Measurements of Young's modulus by a resonance technique showed that the addition of mullite decreased Young's modulus. Up to 14 vol%, these changes were close to those expected, but above this mullite content, the decrease was more dramatic and indicated specimen damage during processing. The addition of mullite led, in some cases, to increases of more than 60% in both the strength (biaxial flexure) and indentation fracture toughness. These increases have been attributed to the method of introducing mullite and the resulting residual compressive surface stresses. The strength of the indented composite bodies deviated from the ideal behavior, indicating the probability of R -curve behavior in these materials.     

Processing and Properties of a Porous Oxide Matrix Composite Reinforced with Continuous Oxide Fibers

A process to manufacture porous oxide matrix/polycrystalline oxide fiber composites was developed and evaluated. The method uses infiltration of fiber cloths with an aqueous slurry of mullite/alumina powders to make prepregs. By careful manipulation of the interparticle pair potential in the slurry, a consolidated slurry with a high particle density is produced with a sufficiently low viscosity to allow efficient infiltration of the fiber tows. Vibration-assisted infiltration of stacked, cloth prepregs in combination with a simple vacuum bag technique produced composites with homogeneous microstructures. The method has the additional advantage of allowing complex shapes to be made. Subsequent infiltration of the powder mixture with an alumina precursor was made to strengthen the matrix. The porous matrix, without fibers, possessed good thermal stability and showed linear shrinkage of 0.9% on heat treatment at 1200°C. Mechanical properties were evaluated in flexural testing in a manner that precluded interlaminar shear failure before failure via the tensile stresses. It was shown that the composite produced by this method was comparable to porous oxide matrix composites manufactured by other processes using the same fibers (N610 and N720). The ratio of notch strength to unnotch strength for a crack to width ratio of 0.5 was 0.7–0.9, indicating moderate notch sensitivity. Interlaminar shear strength, which is dominated by matrix strength, changed from 7 to 12 MPa for matrix porosity ranging from 38% to 43%, respectively. The porous microstructure did not change after aging at 1200°C for 100 h. Heat treatment at 1300°C for 100 h reduced the strength for the N610 and N720 composites by 35% and 20%, respectively, and increased their brittle nature.     

Microstructure and mechanical properties improvement of the Nextel™ 610 fiber reinforced alumina composite

The alumina slurry with high solid content was prepared, and a rapid lamination route for fabricate the Nextel? 610 fiber reinforced alumina composite was proposed in this work. The microstructure and mechanical properties of the as-received all-oxide composite were investigated by a series of techniques. The shrinkage cracks in matrix were reduced, while porous structure in composite was maintained. The N610/alumina composite has weak matrix and weak interface, as the Young’s modulus of the alumina matrix and the interfacial shear strength of the composite are 140.8±2.5GPa and 129.1±14.6MPa. The mechanical properties of the composite are much higher than lots of oxide/oxide composites, given its flexural strength, interlaminar shear strength and the fracture toughness are 398.4±5.7MPa、27.0±0.5MPa and 14.1±0.9MPa·m^1/2, respectively. The flexural strength of the virgin composite keep stable at 25–1050 °C, while dramatically decrease at 1100–1200 °C.     

Simultaneously improving mechanical and microwave absorption properties of a novel SiCf/SiOC & mullite hybrid ceramic matrix composite

For enhanced mechanical and microwave absorption properties at the same time, the SiC_f/hybrid matrix composites were fabricated by precursor infiltration and pyrolysis (PIP) method with polysiloxane (PSO) ethanol solution, alumina sols and silica sols. As the first layer of the hybrid matrix, the SiOC ceramic was pyrolyzed from PSO solution. The remained hybrid matrix was mullite, which sintered from alumina sols and silica sols. The effects of different content of PSO solution on the morphologies, flexure strength and reflection loss values of composites were studied. Additionally, the XRD patterns, Fourier Transform Infrared (FTIR) and Raman spectrum of hybrid matrix were also investigated. With the increasingly content of PSO solution from 0% to 10 % and 20%–60% in the first infiltration-pyrolysis process, the flexure strength of composites was increased from 175.18 MPa to 301.94 MPa and decreased from 263.33 MPa to 221.30 MPa, respectively. The complex permittivity was increased with the increasing content of PSO solution from 0%–40% due to the free carbon conductive network from excessive SiOC. Moreover, the complex permittivity of SiC_f/hybrid matrix composites with 50 % and 60 % content of PSO solution was reduced due to more open porosity and broken free carbon conductive network. Additionally, the maximum reflection loss values of SiC_f/hybrid matrix composite with 50 % PSO solution were over -60 dB and the effective absorption bandwidth (EAB) of this composite reaches 3.89 GHz in the X band.     

Fabrication of Cf/SiC Composites by Vapor Silicon Infiltration

Carbon fiber reinforced silicon carbide matrix composites were fabricated by the vapor silicon infiltration process. The density and the open porosity of the composite infiltrated at 1973 K were 2.25 g/cm³ and ∼6%, respectively. The flexural strength of the composite at ambient conditions was 300 MPa. When the infiltration temperature decreased, the density and flexural strength of the composite also decreased. However, the resulting composite materials exhibited non-brittle fracture behavior.     

Preparation and characterization of Nextel 720/alumina ceramic matrix composites via an improved prepreg process

In this work, the Nextel 720 continuous fiber reinforced alumina ceramic matrix composites (CMCs) were prepared by an improved prepreg process. The alumina matrix was derived from aqueous slurry, which consisted of organic glue, alumina sol, nanometer alumina powders, and micrometer alumina powders. This design provided a densely packed matrix for the CMC, and made the whole process relatively simple. The ratio of different alumina components in aqueous slurry was optimized to obtain good sintering activity, high thermal resistance, and excellent mechanical properties simultaneously. Furthermore, a preceramic polymer of mullite was used to strengthen the ceramic matrix through a multiple infiltration process. The final CMC sample achieved a high flexural strength of 255 MPa and a good high-temperature stability. After 24 h of heat treatment at 1100°C, 85% of the maximum flexural strength still had been retained.     

Influence of glass phase on Al2O3 fiber-reinforced Al2O3 composites processed by slip casting

The present work describes the processing of alumina fiber reinforced alumina ceramic preforms consisting of chopped Al₂O₃ fibers (33 wt%) and Al₂O₃ (67 wt%) fine powders by slip casting. The preforms were pre-sintered in air at 1100 °C for 1 h. A lanthanum based glass was infiltrated into these preforms at 1250 °C for 90 min. Linear shrinkage (%) was studied before and after glass infiltration. Pre-sintered and infiltrated specimens were characterized by scanning electron microscopy, energy dispersive X-ray, X-ray diffraction, porosimetry and flexural strength. The alumina preforms showed a narrow pore size distribution with an average pore size of ∼50 nm. It was observed that introducing Al₂O₃ fibers into Al₂O₃ particulate matrix produced warp free preforms with minor shrinkage during pre-sintering and glass infiltration. It was observed that the infiltration process fills up the pores and considerably improves the strength and reliability of alumina preform.     

Translucent Al2O3/LaAl11O18 Composite

A translucent alumina composite containing 1 vol% LaAl₁₁O₁₈, prepared by the hot isostatic pressing (HIP) method, displays both high translucency and high fracture toughness. Its total forward transmission at 600 nm is 75% (thickness 1 mm), and its bending strength and fracture toughness are estimated to be 574±15 MPa and 5.9±0.46 MPa·m^0.5, respectively. Its high translucency is due to the similarity of refractive index between the additive phase (LaAl₁₁O₁₈) and the matrix (alumina).