激光熔覆Al2O3+TiO2复合陶瓷涂层的微观结构

研究了４５＃钢表面Ａｌ２Ｏ３＋ＴｉＯ２复合陶瓷激光熔覆层的微观组织和相结构、Ａｌ２Ｏ３＋ＴｉＯ２复合陶瓷激光熔覆涂层由α－Ａｌ２Ｏ３,ＴｉＯ２,γ－ＴｉＯ２,γ－Ａｌ２Ｏ３及Ａｌ２ＴｉＯ５相组成,消除了等离子喷涂层的层状组织特征,形成了大致方向的柱状晶,晶内为溶入了Ｔｉ及少量底层元素的α－Ａｌ２Ｏ３;晶界为由ＴｉＯ２和Ａｌ２Ｏ３形成的Ａｌ２ＴｉＯ５相,溶有少量的Ｃｒ,Ｆｅ,Ｙ取代了Ａｌ２ＴｉＯ５     

复合添加剂对钛酸铝稳定性的影响

探讨了复合添加剂对Ａｌ２ＴｉＯ５ 烧结性能、抗折强度、热膨胀系数和稳定性的影响，利用ＸＲＤ、ＳＥＭ 等手段分析了材料的物相组成和显微结构。结果表明， 利用复合添加剂在不提高Ａｌ２ＴｉＯ５ 热膨胀系数的情况下，获得了具有较高强度的稳定化Ａｌ２ＴｉＯ５ 。     

填料对室温硫化硅橡胶包覆材料性能的影响

研究了四种填料［Ｃｒ２Ｏ３、ＴｉＯ２、Ａｌ２Ｏ３、和Ａｌ（ＯＨ）３］对火箭推进剂用双组分室温硫化（ＲＴＶ）硅橡校包覆材料力学性能和烧蚀性能的影响。结果表明，Ａｌ（ＯＨ）３能够较大幅度地提高硅橡校的拉伸强度，但却随着Ａｌ（ＯＨ）３添加量的增加，硅橡胶的线烧蚀率也增加。ＴｉＯ２可以降低硅橡校的线烧蚀率。确定了四种填料对硅橡胶拉伸强度贡献率的大小顺序。     

增加TiO2,Nb2O5晶核剂对烧结微晶玻璃结构与性能的影响

在Ｌｉ２Ｏ－ＭｇＯ－Ａｌ２Ｏ３－ＳｉＯ２系玻璃中，加入不同含量的ＴｉＯ２或Ｎｂ２Ｏ５为晶核剂，经过粉碎，混和，成型，烧结能制得致密的微晶玻璃，微晶玻璃的强度比示添加ＴｉＯ２或Ｎｂ２Ｏ５的样品有所提高，当ＴｉＯ２，Ｎｂ２Ｏ５含量增加，微晶玻璃强度也相应增加，加入ＴｉＯ２或Ｎｂ２Ｏ５添加物对微晶玻璃的热膨胀系数影响较小，电子显微归咎表明，晶体颗粒随着添加物ＴｉＯ２或Ｎｂ２Ｏ５的增加而减小，Ｘ光衍射结果     

Al2O3/AgCuTi钎料/Nb连接的微观结构及性能

在钎焊温度１０９３Ｋ、钎焊时间３－６０ｍｉｎ条件下,对Ａｌ２Ｏ３／（Ａｇ７２Ｃｕ２８）９７Ｔｉ３／Ｎｂ接头进行钎焊试验。结果证实：（Ａｇ７２Ｃｕ２８）９７Ｔｉ３钎料能有效实现Ａｌ２Ｏ３／Ｎｂ连接并可获得较高的连接强度;在１０９３Ｋ,１５ｍｉｎ条件下,剪强度达２２３ＭＰａ。通过ＸＲＤ及ＥＤＳ检测,证明界面反应产物为ＴｉＯ和Ｔｉ２Ｏ。结果ＳＥＭ及试样断口形貌,初步探讨分析了钎焊时间对接头强度的影响。钎     

影响（Ba_（0．65）Pb_（0．35））TiO_3系PTC陶瓷电阻率的因素

在合成的（Ｂａ０．６５Ｐｂ０．３５）ＴｉＯ３中分别掺入了Ａｌ２Ｏ３，ＳｉＯ２，Ｌａ２Ｏ３，ＭｎＯ２和ＴｉＯ２．讨论了每种掺杂物与烧成气氛和升温制度对常温电阻率的影响，找出了ＰＴＣ陶瓷的最佳组成；１ｍｏｌ（Ｂａ０．６５Ｐｂ０．３５）ＴｉＯ３，０．００２ｍｏｌＡｌ２Ｏ３，０．００４ｍｏｌＳｉＯ２，０．０１ｍｏｌＴｉＯ２，０．００３ｍｏｌＬａ２Ｏ３，０．０００２ｍｏｌＭｎＯ２．这种ＰＴＣ陶瓷的表面温度为２７０℃，常温电阻率为５～８×１０３Ω·ｃｍ，时任性为２４０ｖ／ｍｍ．     

氧化对Al2O3—TiB2陶瓷刀具材料磨损特性的影响

研究了Ａｌ２Ｏ３－ＴｉＢ２陶瓷刀具材料的高温氧化特性以及氧化对刀具耐磨性能的影响。结果表明，随ＴｉＢ２含量的增加，Ａｌ２Ｏ３－ＴｉＢ２的氧化活化能降低，抗化能力下降。Ａｌ２Ｏ３－ＴｉＢ２刀具材料在加工淬火钢时，因切削高温的氧化作用在刀具表面生成的ＴｉＯ２既可将轻刀具的粘结磨损，又能起到固体润滑剂的作用，从而降低摩擦系数，因而提高刀具的耐磨性能。     

添加剂对BaTiO_3基PTC陶瓷性能的影响

本文研究了Ｎｂ_２Ｏ_５、 Ｙ（ＮＯ_３）_３、 ＴｉＯ_２、及 Ａｌ_２Ｏ_３、 ＳｉＯ_２对 ＢａＴｉＯ_３半导体陶瓷性能的影响。结果表明室温电阻率的波动随不同施主掺杂物量的改变而不同。Ｙ（ＮＯ_３）_３在较宽范围内变化时,试样的室温电阻率能保持较好的稳定性。同时对ＴｉＯ_２及Ａｌ_２Ｏ_３、ＳｉＯ_２都能提高ＰＴＣ效应的机理进行了解释。     

添加Cr2O3对Al2O3-TiC陶瓷烧结及纳米结构形成的影响

研究了Ａｌ２Ｏ３－ＴｉＣ陶瓷材料中Ｃｉ２Ｏ３添加剂对该陶瓷材料烧结致密度和力学性能的影响。Ｃｒ２Ｏ３与ＴｉＣ在高度有化学反应发生,反应产物在高温产生的液相有助于陶瓷材料的烧结。Ｃｒ２Ｏ３与Ａｌ２Ｏ３形成的连续固溶体,使Ａ２ｌＯ３晶格的活化从而也促进了Ａｌ２Ｏ３－ＴｉＣ陶瓷材料的烧结。ＴＥＭ研究表明：Ｃｒ离子高温时在ＴｉＣ中具有较高的溶解度,降温后淀析出许多纳米级含Ｃｒ的颗粒,使Ａｌ２Ｏ３－ＴｉＣ陶     

4Al＋3TiO_2＋3C化学反应的差热分析研究

通过差热分析曲线和物相分析等研究了４Ａｌ＋３ＴＯ_２＋３Ｃ普通化学反应和自燃烧化学反应的特点。研究结果表明，在一定的升温速率下Ａｌ、ＴｉＯ_２、Ｃ相互之间均能发生相互化学反应；随着升温速率的提高，Ａｌ、ＴｉＯ_２、Ｃ任意两组元之间的相互化学反应受到抑制。运用４Ａｌ＋３ＴｉＯ_２＋３Ｃ自蔓延高温合成反应制备了Ａｌ_２Ｏ_３－ＴｉＣ陶瓷复合材料。     

Mechanical, thermal and ablative properties of interply continuous/spun hybrid carbon composites

The mechanical and thermal properties of interply hybrid carbon fiber (continuous and spun fabric)/phenolic composite materials have been studied. Hybrid carbon/phenolic composites (hybrid CP) with continuous carbon fabric of high tensile, flexural strength and spun carbon fabric of better interlaminar shear strength and lower thermal conductivity are investigated in terms of mechanical properties as well as thermal properties.Through hybridization, tensile strength and modulus of spun type carbon fabric reinforced phenolic composites (spun CP) increased by approximately 28% and 20%, respectively. Hybrid CP also exhibits better interlaminar shear strength than continuous carbon fabric/phenolic composites (continuous CP).The in-plane thermal conductivity of hybrid CP is 4-8% lower than that of continuous CP. As continuous filament type carbon fiber volume fraction increases, the transversal thermal conductivity of hybrid CP decreases.The erosion rate and insulation index were examined using torch test. Spun CP has a higher insulation index than continuous CP and hybrid CP over the entire temperature range. Hybrid CP with higher content of spun fabric exhibits higher insulation index as well as lower erosion rate.     

Mechanical properties of refractory castables bonded with hydratable magnesium carboxylate-boric acid

Hydratable magnesium carboxylate (HMC), which is similar to the properties of cement, can be used as a potential binder for refractory castables. However, its decomposition may lead to poor mechanical properties at medium temperatures (300 °C–1100 °C). This work investigated the effects of boric acid on the mechanical properties and microstructural evolution of castables bonded with hydratable magnesium carboxylate. The mechanical strength, bulk density, apparent porosity, thermal shock resistance, and sintering properties of the castables were evaluated. The results showed that the mechanical properties of HMC-bonded castables (HMCC) at various temperatures can be improved by adding boric acid. Boric acid reacts with HMC to form magnesium carboxylate borate ester (MCBE), which improves the bonding strength between HMC molecules. Thus, the cold modulus of rupture of HMCC containing boric acid dried at 110 °C are higher than that of calcium aluminate cement-bonded refractory castables (CACC). The decomposition temperature of MCBE is 77 °C higher than that of HMC, so MCBE can endow castables with better mechanical properties at 110 °C–500 °C. The B₄C obtained by MCBE pyrolysis could form a boron-rich liquid phase, which can accelerate the structural densification of castables via transient liquid phase sintering, thus improving the mechanical properties of castables at 500 °C–1100 °C. Moreover, boric acid can improve the thermal shock resistance of HMCC. The residual strength rate first increases and then decreases with an increasing boric acid, and reaches a maximum value of 29.7% (1 wt% boric acid is added), which is 2.3 times that of the CACC. The nanoindentation test showed that the microcracks in the matrix of 1 wt% boric acid castables are easy to initiate but difficult to propagate, so the microcracks are many and wavy.     

Mechanical and thermal properties of bisphenol A-based cyanate ester and diallyl phthalate blends

Cyanate ester resins are a high performance class of compounds. They have excellent mechanical properties, dielectric properties and thermal properties; however, their major drawback is their brittleness. An attempt was made to improve the impact strength of the cyanate ester resin. In the present study a commonly used cyanate resin, bisphenol A dicyanate (BADCy), was modified by the addition of diallyl phthalate (DAP) and was cured with benzoyl peroxide. The properties of the blends such as thermal and mechanical properties were investigated in detail by scanning electron microscope, dynamic mechanical analysis, thermogravimetric analysis, and mechanical measurement. The results indicate that the addition of the appropriate amount of DAP can effectively improve the impact toughness and the flexural strength while sacrificing the thermal properties of the blends. The maximum impact strength and flexural strength were observed on addition of 15 phr DAP content. However, the thermal stability of the blends was found to be lower than that of the unmodified BADCy resin.     

增容剂对PP/回收PET共混物性能的影响

采用熔融共混的方法,制备了聚丙烯(PP)/回收聚对苯二甲酸乙二酯(r-PET)共混物,研究了增容剂甲基丙烯酸缩水甘油酯接枝聚丙烯(PP-g-GMA)对共混物力学性能、热稳定性的影响。结果表明:增容剂的加入能提高共混物的拉伸强度和拉伸模量;加入增容剂能显著提高共混物的热分解温度,增容剂使r-PET的熔点降低;增容剂对PP的结晶性能影响与熔融温度有关。     

聚甲醛/纳米SiO2复合材料的力学性能、结晶行为及热稳定性研究

以改性纳米SiO2为填料,通过熔融共混工艺制备聚甲醛/纳米SiO2复合材料,对其力学性能、结晶行为及热稳定性进行了研究。结果表明:复合材料的拉伸强度和缺口冲击强度随着SiO2含量的增加呈先增大后减小的趋势,二者分别在SiO2质量分数为3%和1%时达到最大;而弹性模量的情况则有所不同,其随着SiO2含量的增加不断增大。DSC测试结果显示,纳米SiO2具有较好的形核作用,能够促进聚甲醛的结晶温度升高,但会抑制晶粒的生长,导致复合材料结晶度的降低。此外,纳米SiO2还能显著提高聚甲醛的热稳定性。与纯聚甲醛相比,复合材料的最大热分解温度在氮气和空气气氛下分别提高了约41.1℃和24.5℃。     

BCE/BMI/Nano-SiO_2复合材料的性能研究

采用熔融共混法制备了氰酸(酯BCE/)双马来酰亚胺预聚(体BMI)/纳米二氧化(硅nano-SiO2)复合材料,研究了nano-SiO2用量对复合材料耐热性能、静态力学性能和动态力学性能的影响,并利用扫描电镜分析了nano-SiO2在聚合物基体中的分散情况。结果表明:随着nano-SiO2用量的增加,BCE/BMI/nano-SiO2复合材料的冲击强度和弯曲强度均是先升后降,冲击强度、弯曲强度和储能模量均在nano-SiO2含量为2%时达到最大值;nano-SiO2的加入可以提高复合材料的耐热性,但随其用量的增加,nano-SiO2在基体中的分散性逐渐变差。     

热致性液晶/埃洛石纳米管/尼龙66导热原位混杂复合材料的结构与性能

采用熔融共混方法制备了热致液晶聚合物(TLCP)/埃洛石纳米管(HNTs)/尼龙66(PA66)原位混杂复合材料,研究了其导热性能、力学性能及微观形态。结果表明:在实验范围内,复合材料的导热性能及力学性能均随着HNTs含量的增加而提高,当HNTs质量分数增至40%时,复合材料的导热系数、热变形温度、拉伸强度、弯曲强度及弯曲模量分别提高了134%、144%、15.3%、31.9%、231%;扫描电子显微镜(SEM)显示,TLCP及HNTs均能在基体中均匀分散,并能观察到TCLP所形成的沿纤维轴方向取向的微纤及HNTs所形成的导热网链。     

Novel self-reinforcing ZrO2–SiO2 aerogels with high mechanical strength and ultralow thermal conductivity

Novel self-reinforcing ZrO₂–SiO₂ aerogels with high mechanical strength and ultralow thermal conductivity are fabricated by impregnating hydrolyzed ZrO₂–SiO₂ sol into wet gel matrix and drying. The ZrO₂–SiO₂ sol fills the macropores and defects of ZrO₂–SiO₂ aerogel matrix generating during the gelation process, which contributes to the improvement of the mechanical properties of the ZrO₂–SiO₂ aerogel matrix. The mechanical and thermal properties of the as-prepared ZrO₂–SiO₂ aerogel are investigated and discussed. The results show that the mechanical strength of the self-reinforcing aerogels obviously increases from 0.51 to 3.11?MPa with the increase of impregnation times, while the thermal conductivity of the aerogels slightly increases from 0.0235 to 0.0306?W?m^?1 K^?1. The novel self-reinforcing ZrO₂–SiO₂ aerogel could have interesting applications in aerospace and energy because of its outstanding mechanical and thermal properties.     

Thermal cycling behavior and bonding strength of single-ceramic-layer Sm2Zr2O7 and double-ceramic-layer Sm2Zr2O7/8YSZ thermal barrier coatings deposited by atmospheric plasma spraying

The single-ceramic-layer (SCL) Sm₂Zr₂O₇ (SZO) and double-ceramic-layer (DCL) Sm₂Zr₂O₇ (SZO)/8YSZ thermal barrier coatings (TBCs) were deposited by atmospheric plasma spraying on nickel-based superalloy substrates with NiCoCrAlY as the bond coat. The mechanical properties of the coatings were evaluated using bonding strength and thermal cycling lifetime tests. The microstructures and phase compositions of the coatings were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results show that both coatings demonstrate a well compact state. The DCL SZO/8YSZ TBCs exhibits an average bonding strength approximately 1.5 times higher when compared to the SCL SZO TBCs. The thermal cycling lifetime of DCL SZO/8YSZ TBCs is 660 cycles, which is much longer than that of SCL 8YSZ TBCs (150 cycles). After 660 thermal cycling, only a little spot spallation appears on the surface of the DCL SZO/8YSZ coating. The excellent mechanical properties of the DCL LZ/8YSZ TBCs can be attributed to the underlying 8YSZ coating with the combinational structures, which contributes to improve the toughness and relieve the thermal mismatch between the ceramic layer and the metallic bond coat at high temperature.     

Influence of silicon carbide as a mineralizer on mechanical and thermal properties of silica-based ceramic cores

Ceramic cores have been designed with compounds based on fused silica due to its excellent thermal stability and chemical inertness against molten metals. To endure the high temperatures present during investment casting, mineralizers have been widely used to enhance the flexural strength and shrinkage of ceramic cores. In this study, we demonstrated a silica-based ceramic core with silicon carbide as a mineralizer for improving the mechanical and thermal properties. The SiC in the silica-based ceramic cores can enhance the mechanical properties (i.e., flexural strength and linear shrinkage) by playing a role as a seed for the crystallization of fused silica to cristobalite. The SiC also improves the thermal conductivity due to its higher value compared with fused silica. The results suggest that using the optimal amount of silicon carbide in silica-based ceramic cores can provide excellent mechanical properties of flexural strength and linear shrinkage and improved thermal conductivity.