反应烧结Al_2O_3-SiC制品的性能和结构研究

研究了SiC和添加剂对Al2 O3-SiC制品性能的影响。结果表明 :加入的SiC(10 %～ 15% )能在基质中形成紧密的网络结构 ;利用添加剂与碳素材料的反应 ,促进了制品的烧结 ,从而改善了制品的结构与强度。该结果为制取性能优良的烧成Al2 O3-SiC复合材料提供了依据     

固溶反应对MA-Al2O3材料结构和性能的影响

以电熔镁铝尖晶石为主要原料并加入少量烧结刚玉细粉部分替代尖晶石细粉,或以白刚玉为主要原料并加入少量电熔镁铝尖晶石细粉替代白刚玉细粉,制备了两组MA-Al₂O₃材料。研究刚玉与镁铝尖晶石之间的固溶反应对材料性能及显微结构的影响。结果表明：1)在两组材料中均发生了固溶反应,使得镁铝尖晶石的富铝程度增大,镁铝尖晶石中的氧化铝含量(w)由约76%增加到80%以上,从而加强了试样骨料与基质的结合,减少结构缺陷,改善了材料的高温性能;2)在以镁铝尖晶石为主要原料的MA-Al₂O₃材料中,加入烧结刚玉可使其常温耐压强度增大,改善其高温抗蠕变性和抗热震性;3)在以白刚玉为主要原料的MA-Al₂O₃材料中,加入镁铝尖晶石细粉,其常温耐压强度、高温抗蠕变性和高温抗折强度均有大幅度提高。     

添加Fe2O3、Al2O3和SiO2纳米粉对MgO烧结性能的影响

以烧结镁砂为主原料,分别以粒度20～60 nm的SiO2纳米粉、粒度20～40 nm的Fe2O3纳米粉和粒度50 nm的Al2O3纳米粉(纯度(w)均为99.9%)为添加剂,设计了添加剂加入量(w)分别为1%、3%、5%(其余为烧结镁砂)的9种试样。配料后,外加10%(w)的分散剂和5%(w)的丙酮,研磨10min后,以100 MPa压力制成2.54 mm×2.54 mm的试样,在电炉中以5℃.min-1的升温速度分别升温至1 300、1 500和1 620℃保温4 h,冷却后分析试样的体积密度、显气孔率、相     

Al2O3-MgAl2O4复相骨料对刚玉-尖晶石浇注料抗渣性能的影响

为研究Al₂O₃-MgAl₂O₄复相骨料对刚玉-尖晶石浇注料抗渣性能的影响,在基质中添加与不添加尖晶石细粉的2种情况下,分别以板状刚玉骨料和Al₂O₃-MgAl₂O₄复相骨料制备了刚玉-尖晶石浇注料。先利用FactSage反应热力学软件计算了1 600℃时板状刚玉和Al₂O₃-MgAl₂O₄复相骨料与熔渣之间的反应热力学,并采用浸泡法研究了2种骨料的抗渣性能,再采用静态坩埚法研究了2种骨料对浇注料抗渣性能的影响。结果表明：与板状刚玉骨料相比,Al₂O₃-MgAl₂O₄复相骨料侵蚀层中的裂纹细而少,遭受熔渣侵蚀后不易剥落,其过渡层中既有CA₆相也有尖晶石相,而且尖晶石相中固溶有Fe、Mn元素,该骨料不仅通过形成CA     

热压烧结Al2O3-ZrB2-SiC复相陶瓷的高温力学性能研究

为提高Al2O3陶瓷的高温力学性能,采用热压烧结工艺(烧结温度1 800℃,烧结压力20 MPa,保温1 h)制备了Al2O3-ZrB2-SiC复相陶瓷(简称AZS),并研究了ZrB2含量对Al2O3基陶瓷高温抗折强度和抗热震性的影响。结果表明:1)在Al2O3基陶瓷中加入第二相ZrB2能有效改善材料的高温抗折强度和高温强度保持率,在1 000和1 200℃时,加入20%体积分数ZrB2的AZS陶瓷试样具有最高的高温抗折强度,而加入24%体积分数ZrB2的AZS陶瓷试样具有最高的高温强度保持率。2)AZS陶瓷的抗热震性能优于纯Al2O3陶瓷。经100℃温差急冷后,加入20%体积分数ZrB2的AZS陶瓷具有最高的残余强度,比纯Al2O3陶瓷提高了17.2%;经300和500℃温差急冷后,加入24%体积分数ZrB2的AZS陶瓷都具有最高的残余强度,比Al2O3陶瓷分别提高了35.3%和20.9%。     

骨料种类对铁水包用Al2O3-SiC-C砖性能的影响

骨料作为耐火材料的重要组成部分,决定着材料的各项性能。分别以粒度均为5～3、3～1和≤1 mm的高铝矾土、电熔棕刚玉、板状刚玉为骨料,以电熔白刚玉(≤0.045 mm)、SiC(≤0.075 mm)、活性α-Al₂O₃微粉(≤0.045 mm)和鳞片石墨(≤0.15 mm)等为基质,以热固性酚醛树脂为结合剂制备了Al₂O₃-SiC-C砖,研究了骨料种类(高铝矾土、电熔棕刚玉、板状刚玉)对Al₂O₃-SiC-C砖常温力学性能、高温力学性能和抗渣性能的影响。结果表明：以板状刚玉为骨料时,由于其较高的致密度和较低的杂质含量,使得Al₂O₃-SiC-C砖具有最优的高温力学性能和抗渣性能;以高铝矾土为骨料时,由于其较高的气孔率和杂质含量,导致试样高温力学性能和抗渣性最差。     

Al2O3-尖晶石浇注料性能的研究

采用电冶矾土刚玉为骨料,研究了基质中MgO/Al     

烧结板状刚玉的制备及性能研究

烧结板状刚玉具有优异的体积稳定性、抗热震性、机械强度、耐磨性和抗酸碱侵蚀能力,极高的耐火度,优越的抗蠕变性和抗剥落性等特性,具有广泛的应用前景。采用超高温竖窑工艺制备烧结板状刚玉,研究了产品的显微结构和物理性能。结果表明,经1 900℃高温烧结后形成了板片状组织,晶内含有大量的圆形闭口气孔。物理性能测试表明,其体积密度为3.68 g/cm3,显气孔率小于3%,吸水率小于0.8%。     

反应烧结碳化硅材料的抗热震性能研究

通过对比不同温差热震后材料的残余强度 ,对反应烧结碳化硅材料的抗热震性能进行了研究。结果表明 :反应烧结碳化硅材料的抗热震性能与显微组织密切相关 ,低游离硅含量与小粒径的反应烧结碳化硅材料具有较好的抗热震断裂性能 ,而高游离硅含量或大碳化硅粒径的材料具有相对优异的抗热震损伤性。对反应烧结碳化硅材料的抗热震性与显微组织的关系进行了探讨。     

添加Al粉对反应烧结碳化硅性能和结构的影响

以SiC、炭黑和热固性酚醛树脂为主要原料,配制成Al粉外加量分别为0和4％(w)的两种试样,经混料、成型、180℃固化、800℃炭化后,在石墨坩埚中用单质Si掩埋,在真空条件下分别经1550、1600、1650和1700℃烧成反应烧结碳化硅.结果表明:1)未添加和添加4％(w)Al粉的试样经1550～1700℃烧成后,...     

Processing and microstructure development in Al2O3-SiC ‘nanocomposites’

Composites consisting of Al₂O₃ + 5 vol.% 0·15 μm SiC particles were prepared by pressureless sintering. The optimum conditions for achieving dense and uniform microstructures by conventional ceramic processing are given in detail. The SiC particles were found to strongly inhibit grain growth of the Al₂O₃ matrix. Densification was also significantly retarded by these ultra-fine particles, and possible explanations for this behavior are discussed.     

Sintering of Al2O3-SiC composite from sol-gel method with MgO, TiO2 and Y2O3 addition

Al₂O₃-SiC composite ceramics were prepared by pressureless sintering with and without the addition of MgO, TiO₂ and Y₂O₃ as sintering aids. The effects of these compositional variables on final density and hardness were investigated. In the present article at first α-Al₂O₃ and β-SiC nano powders have been synthesized by sol-gel method separately by using AlCl₃, TEOS and saccharose as precursors. Pressureless sintering was carried out in nitrogen atmosphere at 1600 °C and 1630 °C. The addition of 5 vol.% SiC to Al₂O₃ hindered densification. In contrast, the addition of nano MgO and nano TiO₂ to Al₂O₃-5 vol.% SiC composites improved densification but Y₂O₃ did not have positive effect on sintering. Maximum density (97%) was achieved at 1630 °C. Vickers hardness was 17.7 GPa after sintering at 1630 °C. SEM revealed that the SiC particles were well distributed throughout the composite microstructures. The precursors and the resultant powders were characterized by XRD, STA and SEM.     

Oxidation behavior in wet oxygen environment of Al2O3 added reaction-sintered Si-B-C ceramics

The influence of Al₂O₃ addition on the oxidation behavior of Si-B-C ceramics at 1200 °C in O₂/H₂O (40/60) atmosphere was studied. Results showed that Al₂O₃ was enriched in the oxidized layer, and impeded the crystallization of oxide (cristobalite) during cooling. Denser oxidized layer and less weigh change were observed. Infrared spectra indicated that the addition of Al₂O₃ could weaken the tendency of bridged oxygen atoms (Si-O-Si, Si-O-Al) to become non-bridged oxygen atoms (Si-O-H) and enhance the degree of interconnection of the structural units. The above phenomenon was attributed to the fact that the bridging oxygen bond between Al and Si was not broken but protonated. The protonated bridging oxygen (Al-O(H)-Si) still acts as a linkage in the glass network, which results in higher viscosity of the aluminosilicates melt and lower reaction activity with steam, thereby significantly improving the oxidation resistance of Si-B-C in O₂/H₂O atmosphere.     

Characterization and tribological investigation of sol-gel Al2O3 and doped Al2O3 films

Thin films of Al₂O₃ and doped Al₂O₃ were prepared on a glass substrate by dip coating process from specially formulated ethanol sols. The morphologies of the unworn and worn surfaces of the films were observed with atomic force microscope (AFM) and scanning electron microscope (SEM). The chemical compositions of the obtained films were characterized by means of X-ray photoelectron spectroscopy (XPS). The tribological properties of obtained thin films sliding against Si₃N₄ ball were evaluated and compared with glass slide on a one-way reciprocating friction tester. XPS results confirm that the target films were obtained successfully. The doped elements distribute in the film evenly and exist in different kinds of forms, such as oxide and silicate. AFM results show that the addition of the doped elements changes the structure of the Al₂O₃ films, i.e., a rougher and smoother surface is obtained. The wear mechanisms of the films are discussed based on SEM observation of the worn surface morphologies. As the results, the doped films exhibit better tribological properties due to the improved toughness. Sever brittle fracture is avoided in the doped films. The wear of glass is characteristic of brittle fracture and severe abrasion. The wear of Al₂O₃ is characteristic of brittle fracture and delamination. And the wear of doped Al₂O₃ is characteristic of micro-fracture, deformation and slight abrasive wear. The introduction of ZnO is recommended to improve the tribological property of Al₂O₃ film.     

Crystal structure and properties of Al2O3-Cr2O3 solid solutions with different Cr2O3 contents

To enable the comprehensive application of Al₂O₃-Cr₂O₃ solid solutions, the crystal structures and properties of Al₂O₃-Cr₂O₃ solid solutions with different Cr₂O₃ contents were studied. It was observed that Al₂O₃ and Cr₂O₃ form a complete substitutional solid solution over the entire composition range at 1650 °C, with no compounds being formed. Lattice parameters “a” and “c” both increase linearly with an increase in the Cr₂O₃ content. The doping of the Cr³⁺ ions causes a more severe lattice strain in the c-axis direction. The diffraction angles of the diffraction peaks decrease in a linear manner with the increase in the Cr₂O₃ content. The relationship between the theoretical density of the solid solution and the Cr₂O₃ content could be fitted using a second-order polynomial. It was also observed that the linear expansion coefficient of the solid solutions decreases with an increase in the Cr₂O₃ content.     

ZrB2对Al2O3-ZrB2-SiC复相陶瓷室温力学性能影响

Al2O3陶瓷具有优异的室温和高温性能,但其脆性大,断裂韧性较低,限制了其应用.采用热压烧结工艺制备了应用于不同环境的Al2O3-ZrB2-SiC复相陶瓷(简称AZS),主要研究不同含量的ZrB2对Al2O3-SiC基陶瓷性能的影响.力学性能研究发现,当Al2O3陶瓷中ZrB2和SiC的体积百分比分别为20％和5％时,AZS3陶瓷具有最高的强度和韧性,分别为508.5MPa和6.65MPa· m1/2,相比纯氧化铝陶瓷的468.6MPa和5.56 MPa· m1/22提高了8.5％和19.6％.     

Effect of Al2O3 on mechanical properties of Ti3SiC2/Al2O3 composite

The effect of Al₂O₃ on mechanical properties of Ti₃SiC₂/Al₂O₃ composite fabricated by SPS was studied systematically. The results show that the hardness of the Ti₃SiC₂/Al₂O₃ composite can reach 10.28 GPa, 50% higher than that of pure Ti₃SiC₂. However, slight decrease in the other mechanical properties was observed with Al₂O₃ addition higher than 5–10 vol.%, which is believed to be due to the agglomeration of Al₂O₃ in the composite.     

Fabrication and microstructure evolution of Al2O3/ZrBN-SiCN/Al2O3 high-temperature oxidation-resistant composite coating

The oxidation-resistance of thin film sensors, particularly at high temperatures, is critical for the lifetime and performance of the sensor. The preparation and oxidation-resistance of an Al₂O₃/ZrBN-SiCN/Al₂O₃ composite film with a sandwich-structure was performed using reactive magnetron sputtering. The microstructure evolution of the composite film is examined herein using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analysis. Oxygen diffusion was significantly inhibited by the formation of crystalline Al₂SiO₅ and Zr-B-C amorphous phase inside the composite film. The Pt-13%Rh/Pt thin film thermocouple (TFTC) with the Al₂O₃/ZrBN-SiCN/Al₂O₃ composite film as a protective layer was fabricated and calibrated. Both the stability and lifetime of the TFTC was significantly enhanced for temperatures up to 1000?℃. The test error of the TFTC was reduced by half, compared with that of the TFTC with the Al₂O₃ protective layer, indicating an excellent oxidation-resistant performance of the composite film.     

Al2O3/Cu-O composites fabricated by pressureless infiltration of paper-derived Al2O3 porous preforms

Al₂O₃/Cu-O composites were fabricated from the paper-derived alumina matrix infiltrated with a Cu-3.2?wt% O alloy. Paper-derived alumina preforms with an open porosity ranging from ～ 14 to ～ 25?vol% were prepared by sintering of alumina-loaded preceramic papers at 1600?°C for 4?h. Pressureless infiltration at 1320?°C for 4?h of the preforms with Cu–O alloy resulted in the nearly dense materials with good mechanical and electrical properties, e.g. fracture toughness up to 6?MPa?m^0.5, four-point-bending strength up to 342?MPa, Young's modulus up to 281?GPa and electrical conductivity up to 2?MS/m depending on the volume fraction of copper alloy in the composites. The technological capability of this approach was demonstrated using prototypes in various engineering fields fabricated by lamination, corrugating and Laminated Object Manufacturing (LOM) methods.