硅树脂添加量对氧化铝基陶瓷型芯性能的影响

以氧化铝粉末为基体,添加具有粘结性和一定陶瓷产率的硅树脂粉末,通过干压成型和无压烧结制备出氧化铝基陶瓷型芯,重点研究了硅树脂添加量对氧化铝基陶瓷型芯性能的影响。结果表明:硅树脂在裂解过程中会形成二氧化硅,二氧化硅与氧化铝基体发生反应形成新相莫来石。由于硅树脂在交联和裂解过程中会释放大量气体,导致烧结体失重,且气体的逸出会抑制由烧结引起的收缩,因此,随着硅树脂添加量增加,产生的气体量增加,烧结体的失重率增加,收缩率降低。硅树脂含量的增加使得烧结体的气孔率变大和体积密度减小,烧结体的室温抗弯强度逐渐减小。硅树脂的添加虽然降低了其室温强度,但是保证了陶瓷型芯的尺寸精度。     

固相含量对热固性硅树脂压注法制备的硅基陶瓷型芯性能的影响

以热固性硅树脂作为增塑剂,无定形二氧化硅粉末作为基体材料,利用压注法制备了硅基陶瓷型芯,研究了硅基陶瓷浆料的流变性能以及基体固相含量对陶瓷型芯性能的影响。研究结果表明:在固相含量为50vol%,添加1 wt%的分散剂时可以获得具有较好流动性的硅树脂陶瓷浆料,浆料呈现剪切变稀的特性;随着基体固相含量从45vol%增加到54vol%,陶瓷型芯的失重率和收缩率逐渐减小,体积密度逐渐增大,显气孔率逐渐减小,室温抗弯强度逐渐增大。在54 vol%固相含量时,获得收缩率为1.43%,体积密度为1.60 g·cm-3,室温强度为7.93 MPa的型芯样品。     

硅树脂粘结球形SiO_2陶瓷型芯的制备及性能研究

以球形SiO_2颗粒为基体、硅树脂为粘结剂,通过干压法制备多孔SiO_2陶瓷型芯,研究了硅树脂添加量和烧结温度对陶瓷型芯性能的影响。研究结果表明:硅树脂作为粘结剂通过交联、裂解从而实现对球形SiO_2颗粒的包覆和粘结,明显改善了球形SiO_2颗粒的烧结性能。在1 350℃烧结温度下,随着硅树脂含量增大,型芯样品的失重率不断增大,收缩率反而不断减小;在硅树脂含量为20%时,收缩率仅为0.42%,能较好地保证型芯的尺寸精度;硅树脂含量为10%时,在1 300℃烧结2 h,陶瓷型芯室温抗弯强度为11.8 MPa、线性收缩率为0.49%、显气孔率为30.9%,综合性能最佳。     

添加锆英粉矿化剂的氧化铝基陶瓷型芯试验研究

针对氧化铝基陶瓷型芯不易烧结、脱芯困难的问题,采用电熔刚玉粉为型芯基体材料,添加锆英粉为矿化剂,研究了不同终烧温度下氧化铝基陶瓷型芯室温和高温性能。结合型芯物相组成和断口形貌观测结果,分析了高温烧结过程中莫来石的形成机理,确定了型芯的适宜终烧温度为1 420℃。采用制备的氧化铝基陶瓷型芯拉制出了定向叶片,并进行了脱芯试验,型芯脱出性能良好。     

蓝晶石对氧化铝基复合陶瓷型芯性能的影响

在刚玉粉料中添加蓝晶石,利用原位合成方法制备了氧化铝基复合陶瓷型芯,讨论了蓝晶石含量以及烧结制度对氧化铝基复合型芯几种性能的影响.结果表明:烧结温度对氧化铝基复合陶瓷型芯蠕变性能影响较大,蓝晶石含量变化影响次之;随着蓝晶石含量增加,陶瓷型芯气孔率增加,线收缩率减小,线膨胀系数减小.随着烧结温度增加,陶瓷型芯气孔率减小,线收缩率增加.     

方石英的含量对氧化硅陶瓷型芯性能的影响

以石英玻璃粉为基体,方石英为矿化剂,陶瓷铸造蜡为增塑剂,利用热压注法制备了氧化硅陶瓷型芯,研究了方石英添加量对氧化硅陶瓷型芯性能的影响。研究结果表明:随着方石英添加量的增加,陶瓷型芯样品中石英玻璃析晶含量先增大后减小,样品的收缩率及高温挠度逐渐减小,高温强度先增加后减小,显气孔率随方石英添加量的增加逐渐增大。经验证,在烧结温度为1 200℃下,方石英的最佳添加量为5%时,氧化硅陶瓷型芯的综合性能最好。     

电熔莫来石含量对硅基陶瓷型芯性能的影响

以石英玻璃粉为基体,电熔莫来石为矿化剂,石蜡为增塑剂,通过热压注法制备硅基陶瓷型芯,研究了电熔莫来石添加量对硅基陶瓷型芯综合性能的影响。研究结果表明:随着电熔莫来石含量的增加,样品的室温抗弯强度、高温抗弯强度、高温挠度逐渐降低,收缩率随电熔莫来石含量的增加先减小后增大,显气孔率随电熔莫来石含量的增加先增大后减小。当电熔莫来石的添加量为10%时,型芯样品的综合性能最佳,其收缩率为0.83%,显气孔率为31.49%,体积密度为1.50 g/cm~3,室温抗弯强度为12.28 MPa,高温强度为18.17 MPa,高温挠度为0.95 mm。     

凝胶注模成形空心叶片用氧化铝陶瓷型芯性能研究

采用凝胶注模成形方法制备氧化铝陶瓷型芯材料,研究其气孔率、体积密度和室温抗弯强度随固相体积含量和烧结温度的变化规律。结果表明,在所研究的固相含量范围内,随着固相含量的不断增加,氧化铝陶瓷型芯的气孔率逐渐减小,体积密度和抗弯强度逐渐增大。在所研究的烧结温度范围内,随着烧结温度的不断升高,氧化铝陶瓷型芯的气孔率逐渐减小,体积密度和抗弯强度逐渐增大。当固相含量为50vol.%,在1 300℃烧结后,型芯样品的抗弯强度为13.3 MPa;在1 600℃烧结后,型芯样品的抗弯强度增加到57.6 MPa。     

精密铸造用氧化铝基复合陶瓷型芯

利用原位合成方法制备了几种氧化铝基复合陶瓷型芯,讨论了MgO含量对氧化铝基复合型芯几种性能的影响.研究结果表明:随着MgO含量增加,陶瓷型芯气孔率先增加后减小;线膨胀系数先减小后增大:碱浸出速率减少.当MgO含量为1%(质量分数),经过1500℃烧结5 h后型芯,蠕变量最小.通过实验分析,讨论了MgO含量对陶瓷型芯综合性能影响的机理.     

精密铸造用氧化铝基复合陶瓷型芯

利用原位合成方法制备了几种氧化铝基复合陶瓷型芯，讨论了MgO含量对氧化铝基复合型芯几种性能的影响。研究结果表明：随着MgO含量增加，陶瓷型芯气孔率先增加后减小；线膨胀系数先减小后增大；碱浸出速率减少。当MgO含量为1％（质量分数），经过1500℃烧结5h后型芯，蠕变量最小。通过实验分析，讨论了MgO含量对陶瓷型芯综合性能影响的机理。     

BN/Al2O3 复合粉末及其聚合物基复合材料的制备与导热性能

采用固-液相共混法制备了多种BN/Al₂O₃复合粉末,通过冻融法和表面修饰法对BN进行了改性处理,改变表面修饰剂类型和摩尔比得到了前驱体和烧结态BN/Al₂O₃复合粉末,并利用机械混合法制备了聚合物基BN/Al₂O₃复合材料,并测试分析了其导热性能。结果表明,经冻融处理的BN分散性和界面相容性明显优于未经冻融处理的BN。多巴胺对BN的改性效果优于聚乙二醇。采用多巴胺作为表面修饰剂且BN与Al(NO₃)₃的摩尔比为1:1时,能够得到纳米Al₂O₃均匀包覆的微米BN粉末,即BN/Al₂O₃微纳复合粉末,其聚合物基复合材料的导热系数可达0.62 W·m^-1·K^-1,是纯聚合物导热系数的3倍,是采用纯微米BN粉末制备的聚合物基复合材料导热系数的1.5倍。在BN表面附着的Al₂O₃可以形成层状热传导通道,能够有效提高聚合物基BN/Al₂O₃复合材料的热导率。     

The influence of powder characteristics on mechanical properties of Al2O3–TiC–Co ceramic materials prepared by Co‐coated Al2O3/TiC powders

Ultrafine Al₂O₃–TiC–Co (ATC) ceramic is prepared in order to improve the bending strength and fracture toughness of ceramic materials. The ultrafine Co‐coated Al₂O₃ and TiC powders have been synthesized by electroless plating at room temperature, and the composite powders were sintered by hot‐pressing to compact ATC samples. The average bending strength, average hardness and average fracture toughness values of ATC ceramic with different particle sizes and Co contents were investigated. The toughening mechanism of the ultrafine ATC ceramic was studied by transmission electron microscopy (TEM) and ceramic performance testing methods. The results show that the relative density, bending strength and fracture toughness values increase remarkably with the increase of Co content. The ultrafine grain of original powders is beneficial to improve the relative density, strength and toughness values of ATC ceramic. The Co phase hinders the growth of ATC ceramic grains during sintering. The Co phase forms a three‐dimensional mesh skeleton structure during sintering, improving the fracture toughness and strength of the composite ceramic.     

Al_2O_3/MoS_2复合涂层的制备及摩擦磨损性能

以大气等离子喷涂工艺制备的Al_2O_3陶瓷涂层为模板,利用陶瓷涂层中存在的孔隙和微裂纹,采用水热反应在其内部原位合成具有润滑特性的MoS_2,制备出Al_2O_3/MoS_2的复合涂层。结果表明,通过水热反应在陶瓷涂层原有的微观缺陷中成功合成了MoS_2,合成的MoS_2固体粉末呈类球形状,并且这球状的粉末是由纳米片层状的MoS_2搭建组成的。摩擦试验结果表明,与纯Al_2O_3涂层相比,复合涂层中由于MoS_2润滑膜的形成,其摩擦因数和磨损率都显著降低,且载荷越大,复合涂层的摩擦性能越好。     

过渡材料对等离子喷涂Al2O3梯度陶瓷涂层性能影响

针对Al2O3陶瓷涂层结合强度低、孔隙率高的实际,选择NiAl金属间化合物和金属铜粉作为过渡材料,利用等离子喷涂制备Al2O3梯度陶瓷涂层,并对梯度涂层进行组织形貌观察,测试结合强度和孔隙率.结果表明,梯度涂层的组织表现出宏观的不均匀性和微观连续性的分布特征,NiAl和Cu是金属基体与Al2O3涂层之间过渡层的理想材料,可以有效地提高涂层的结合强度,而Cu-Al2O3梯度涂层又比NiAl-Al2O3梯度涂层结合强度高;梯度涂层的孔隙率远低于双涂层的孔隙率,在Cu-Al2O3梯度涂层中随Al2O3含量的增加,涂层的孔隙率降低,而且孔隙率低于NiAl-Al2O3梯度涂层.     

Influence of MnO2 on the sintering behavior and magnetic properties of NiFe2O4 ferrite ceramics

The samples with small amounts of MnO₂ (0, 0.5, 1.0, 1.5, 2.0, and 2.5 wt%, respectively) were prepared via ball-milling process and two-step sintering process from commercial powders (i.e. Fe₂O₃, NiO and MnO₂). Microstructural features, phase transformation, sintering behavior and magnetic properties of Mn-doped NiFe₂O₄ composite ceramics have been investigated by means of scanning electron microscopy (SEM), differential thermal analyzer, X-ray diffraction (XRD), thermal dilatometer and vibrating sample magnetometer (VSM) respectively. The XRD analysis and the result of differential thermal analysis indicate that the reduction of MnO₂ into Mn₂O₃ and the following reduction of Mn₂O₃ into MnO existed in sintering process. No new phases are detected in the ceramic matrix, the crystalline structure of the ceramic matrix is still NiFe₂O₄ spinel structure. Morphology and the detecting result of thermal dilatometer show that MnO₂ can promote the sintering process, the temperature for 1 wt% MnO₂-doped samples to reach the maximum shrinkage rate is 59 °C lower than that of un-doped samples. For 1 wt% MnO₂-doped samples, the value of the saturation magnetization (M_s) and coercivity (H_c) is 15.673 emu/g and 48.316 Oe respectively.     

Microstructure and mechanical properties of Al2O3-Cr2O3 composite coatings produced by atmospheric plasma spraying

Al₂O₃, Al₂O₃-Cr₂O₃ and Cr₂O₃ coatings were deposited by atmospheric plasma spraying. Phase composition of powders and as-sprayed coatings was determined by X-ray diffraction. Electron probe microanalyzer was employed to investigate the polished and fractured surface morphologies of the coatings. Mechanical properties including microhardness, fracture toughness and bending strength were evaluated. The results indicate that the addition of Cr₂O₃ is conducive to the stabilization of α-Al₂O₃. Compared with the pure Al₂O₃ and Cr₂O₃ coatings, Al₂O₃-Cr₂O₃ composite coatings show lower porosities and denser structures. Heterogeneous nucleation of α-Al₂O₃ occurs over the isostructural Cr₂O₃ lamellae and partial solid solution of Al₂O₃ and Cr₂O₃ might be occurring as well. Furthermore, grain refining and solid solution strengthening facilitate the mechanical property enhancement of Al₂O₃-Cr₂O₃ composite coatings.     

Al2O3-nanodiamond composite coatings with high durability and hydrophobicity prepared by aerosol deposition

We attempted the room-temperature fabrication of Al₂O₃-based nanodiamond (ND) composite coating films on glass substrates by an aerosol deposition (AD) process to improve the anti-scratch and anti-smudge properties of the films. Submicron Al₂O₃ powder capable of fabricating transparent hard coating films was used as a base material for the starting powders, and ND treated by 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) was added to the Al₂O₃ to increase the hydrophobicity and anti-wear properties. The ND powder treated by PFOTES was mixed with the Al₂O₃ powder by ball milling to ratios of 0.01 wt.%, 0.03 wt.%, and 0.05 wt.% ND. The water contact angle (CA) of the Al₂O₃-ND composite coating films was increased as the ND ratio increased, and the maximum water CA among all the films was 110°. In contrast to the water CA, the Al₂O₃-ND composite coating films showed low transmittance values of below 50% at a wavelength of 550 nm due to the strong agglomeration of ND. To prevent the agglomeration of ND, the starting powders were mixed by attrition milling. As a result, Al₂O₃-ND composite coating films were produced that showed high transmittance values of close to 80%, even though the starting powder included 1.0 wt.% ND. In addition, the Al₂O₃-ND composite coating films had a high water CA of 109° and superior anti-wear properties compared to those of glass substrates.     

Ti活度对Al2O3/AgCuTi/Fe-Ni-Co钎焊接头机械性能和微观组织结构的影响

采用AgCuTi钎料实现了Al₂O₃陶瓷与Fe-Co-Ni合金的钎焊连接,并调查了不同钛含量的钎料对Al₂O₃/AgCuTi/Fe-Ni-Co钎焊接头机械性能和微观组织结构的影响。扫描电子显微镜(SEM), X射线能量色散光谱仪(EDS), X射线衍射仪(XRD)及电子万能试验机用于分析钎焊接头的机械性能和微观组织结构,结果表明:钛含量的增加明显提高AgCuTi钎料与Al₂O₃陶瓷的相互作用,在Al₂O₃/Ag-Cu-Ti界面生成一层由Ti-Al 和 Ti-O化合物组成的反应层。Al₂O₃/AgCuTi/Fe-Ni-Co钎焊接头的抗拉强度随钛含量的增加而增加,当钛含量提高到8wt.%时,抗拉强度达到最大值78Mpa。通过微观组织结构分析发现,采用AgCu4Ti在890℃保温5min的条件下可以获得较好的钎焊接头,典型接头的微观组织结构为Al₂O₃/TiAl+Ti₃O₅/NiTi+Cu₃Ti+Ag(s,s)/Ag(s,s)+Cu(s,s)+(Cu,Ni)/Fe-Ni-Co。采用AgCu8Ti获得的钎焊接头的界面反应层与AgCu4Ti差异不大,但反应层稍微增厚,并伴有TiO和Ti3Al在Al₂O₃/Ag-Cu-Ti界面生成。     

Bulk WC-Al2O3 composites prepared by spark plasma sintering

WC and WC-Al₂O₃ materials without metallic binder addition were densified by spark plasma sintering in the range of 1800-1900 °C. The densification behavior, phase constitution, microstructure and mechanical properties of pure WC and WC-Al₂O₃ composite were investigated. The addition of Al₂O₃ facilitates sintering and increases the fracture toughness of the composites to a certain extent. An interesting phenomenon is found that a proper content of Al₂O₃ additive helps to limit the formation of W₂C phase in sintered WC materials. The pure WC specimen possesses a hardness (HV₁₀) of 25.71 GPa, fracture toughness of 4.54 MPa·m^1/2, and transverse fracture strength of 862 MPa, while those of WC-6.8 vol.% Al₂O₃ composites are 24.48 GPa, 6.01 MPa·m^1/2, and 1245 MPa respectively. The higher fracture toughness and transverse fracture strength of WC-6.8 vol.% Al₂O₃ are thought to result from the reduction of W₂C phase, the crack-bridging by Al₂O₃ particles and the local change in fracture mode from intergranular to transgranular.     

High dielectric constant of (Ba0.96Ca0.04)(Ti0.85Zr0.15)O3 multilayer ceramic capacitors with Cu doped Ni electrodes

A nickel paste with Cu dopant was used as the internal electrodes in multi-layer ceramic capacitors (MLCCs) using barium titanate (Ba_0.96Ca_0.04)(Ti_0.85Zr_0.15)O₃ ceramic (BCTZ) with copper endtermination. The sintering behaviors of the MLCC and the interfacial structure between the Ni/Cu electrodes and the BCTZ dielectrics have been investigated. The thermal shrinkage and sheet resistance of the Ni/Cu alloys sintered at 1220 °C for 2 h in a reducing atmosphere were measured using thermal analysis techniques (TMA) and four-point probe equipment. The composition distributions, microstructures and line defects were examined using microstructural analysis techniques (SEM/HRTEM) coupled with energy-dispersive spectroscopy (EDS). The Cu alloyed with Ni significantly improves the continuity of the electrode in the MLCC; this is due to there being no mutual trigger reaction between Ni and BCTZ dielectrics. In terms of the electrical properties, the results showed that Ni paste with Cu dopant improves the dielectric constant of the MLCC, but the dielectric loss (tan δ) is a slightly when higher compared to standard MLCC.