掺碳SiC颗粒对MOSi2复合材料性能的影响

研究分析了掺碳SiCp/MoSi2复合材料的相组成、室温和高温力学性能、高温抗氧化性能、耐磨性能以及电阻率.结果表明(SiCp+C)/MoSi2复合材料主要由MoSi2,α-SiCp,Mo5Si3和β-SiC组成.材料的密度和相对密度分别为5.12g/cm3和91%;Vickers硬度,抗弯强度和断裂韧性分别为12.2GPa,530MPa和72MPa.m1/2;800℃的Vickers硬度为8.0GPa,1200℃和1400℃的抗压强度分别为560MPa和160MPa.材料的抗氧化性能优良.在Al2O3和SiC磨盘上表现出优异的耐磨性能.电阻率为40.2μΩ.     

熔渗温度对MoSi2（Cr5Si3）-RSiC复合材料显微结构和性能的影响

以RSiC为基体,通过酚醛树脂浸渍裂解(PF-PIP)和MoSi2-Si-Cr合金活化熔渗(AMMI)复合工艺制备具有三维互穿网络结构的MoSi2(Cr5Si3)-RSiC复合材料。借助于X射线衍射、扫描电子显微镜、力学性能和电阻率测试等研究了熔渗温度对复合材料组成、显微结构、力学性能和导电性能的影响。采用改进型混合规则探讨了复合材料互穿网络结构和界面结合性对其导电方式的影响。结果表明:不同温度所制备的复合材料主要组成均为SiC、MoSi2和Cr5Si3;随着熔渗温度的升高,复合材料气孔率和体积电阻率下降,密度、抗弯强度和弹性模量提高。当熔渗温度为1 900℃时,复合材料的气孔率、密度、抗弯强度、弹性模量和体积电阻率分别为1.4%、3.5g/cm3、99.2MPa、313.60GPa和124.2mΩ·cm。当熔渗温度较低时(1 700℃),复合材料的导电方式与颗粒增强复合材料的导电方式接近,随温度升高,复合材料的导电方式与传统复合材料的导电方式差别增大。     

热压烧结法制备碳化钛/氧化铝复合材料

把TiC颗粒和金属Al以AlTiC中间合金的形式引入Al2O3陶瓷中,用过渡液相热压烧结法制备了TiC/Al2O3复合材料,并对其微观结构与力学性能进行了研究。结果表明:在1450℃,30MPa条件下,热压烧结制备的TiC/Al2O3复合材料中TiC与Al2O3能稳定共存,材料的断裂韧性和Vickers硬度均有明显提高。材料的Vickers硬度平均超过23.5GPa,断裂韧性超过8.7MPa·m1/2,密度低于纯Al2O3的。由于添加相AlTiC和Al2O3的成本均较低,因而找到了一种低成本制造高性能TiC/Al2O3复合材料的方法。     

直接浸渗法制备MoSi2/SiC复合材料

本文通过直接浸渗法制备了致密的MoSi2/SiC复合材料,在室温下该材料的强度为248±25MPa,1600℃下的强度为205±20MPa,室温下显微硬度为12.6GPa,断裂韧性为3.6MPa·m1/2.同时分析了复合材料的相组成;观察了材料的显微结构;讨论了热处理工艺和成型工艺对烧结体性能的影响.     

热压烧结Ti3SiC2材料的性能研究

热压烧结摩尔比为2TiC/Ti/Si/0.2A1的混合粉末制备的含铝Ti3SiC2材料的力学性能、电性能、热性能和高温氧化性能得到了研究.试样的抗压强度、弯曲强度、断裂韧性和维氏硬度分别为854MPa、420MPa、5.8MPa·m1/2和3.5～5.0GPa;25℃和800℃时的电导率分别为4.3×103和1.0×106 S·m-1;热膨胀系数为9.0×10-6 K-1.固溶在基体中的Al改变了材料的氧化机理,氧化过程中Al的向外扩散代替了Ti的向外扩散,并在表面形成致密的以α-Al2O3为主要成分的氧化膜,提高了材料的抗氧化性能.     

Al_2O_3-TiCN/Co-Ni复合材料制备及力学性能

用真空热压烧结法制备了Al2O3-Ti C0.5N0.5/Co-Ni复合材料,用扫描电子显微镜、能谱仪、电子万能试验机和Vickers硬度仪等测试分析了不同烧结参数对样品显微组织及力学性能的影响。结果表明:当烧结温度1 650℃,压力25 MPa,保温时间30 min时,样品的相对密度、抗弯强度(σmax)、断裂韧性(KICmax)和Vickers硬度(HV)的最大值分别达到99.6%,σmax=1 100 MPa,KICmax=10.5 MPa·m1/2和HV=23.7 GPa,样品断口形貌存在混晶断裂特征。     

直接浸渗法制备MOSi2/SiC复合材料初探

通过直接浸渗法制备了致密的MoSi2/SiC复合材料,在室温下该材料的强度为(248±25)MPa,1600℃下该材料的强度为(205±20)MPa,室温下显微硬度为12.6 GPa,断裂韧性为3.6 MPa·m1/2.同时分析了Si分压对材料表面形貌的影响.     

放电等离子制备Ti3AlC2/TiB2复合材料及性能

采用放电等离子烧结(spark plasma sintering,SPS)工艺制备了Ti3AlC2/TiB2复合材料,并研究了复合材料的性能.研究表明:在1 250℃,30MPa烧结8min,可以获得相对密度达98%以上的致密Ti3AlC2/TiB2块体材料;在Ti3AlC2中添加TiB2能大幅度提高材料性能,当TiB2含量为30%(体积分数,下同)时,Ti3AlC2/30%TiB2复合材料的Vickers硬度达到10.39GPa,电导率为3.7×106 S/m;当TiB2含量为10%时,抗弯强度为696MPa,断裂韧性为6.6MPa·m1/2.用电子显微镜对复合材料的显微结构分析表明:Ti3AlC2/TiB2复合材料的晶粒为层状结构.     

熔渗温度和熔渗相组成对三维互穿网络结构(Mo,Ti)Six-RSiC复合材料组成、微观结构、力学和热学性能的影响

以RSiC为基体,通过MoSi2-Si-Ti合金活化熔渗(AMMI)工艺来制备三维互穿网络结构的(Mo,Ti)Six-RSiC复合材料。采用XRD、SEM、力学性能、热膨胀测试等方法研究了熔渗温度和熔渗相组成对复合材料组成、微观结构,力学和热膨胀系数等性能的影响。结果表明:采用AAMI法可获得具有三维互穿网络结构的(Mo,Ti)XSi2-RSiC复合材料,材料的组成主要为SiC、Si、TiSi2和(Mo0.2Ti0.8)Si2;随预熔配方中MoSi2含量和熔渗温度的增加,复合材料的室温力学性能均先增大后减小,采用MoSiTi-2配方1700℃熔渗所得复合材料的力学性能最佳,其弯曲强度、弹性模量和断裂韧性分别为136.8MPa、217.3GPa和2.45MPa·m^1/2,相比基体分别提高约44%,158%和75%;MoSiTi-2-S2.6-1700在1200℃的热膨胀系数约为4.51×10^-6℃^-1,且基体密度对复合材料CTE的影响高于熔渗相组成;随温度升高,复合材料的弯曲强度增加,1400℃时,其弯曲强度为189.4MPa,比室温提高了约38%;随氧化时间增加,MoSiTi-2-S2.6-1700的室温力学性能先增加后降低,氧化60h时,材料的弯曲强度和弹性模量达到最大,分别为146.8MPa和212.08GPa,与未氧化试样相比提高了约16.2%和51.7%,即使氧化100h,材料的力学性能仍高于初始值。     

SiCp1/ZrB2超高温陶瓷的制备及性能

研究了碳化硅晶片(SiCp1)增韧二硼化锆(ZrB2)陶瓷的制备及其力学性能.采用热压烧结方法,在烧结温度1950℃、保温时间1h、压力20MPa、流动氩气气氛下,制备了高致密度的SiCp1/ZrB2复合材料.通过X射线衍射分析、扫描电子显微镜、三点弯曲法和单边切口梁法对SiCp1/ZrB2陶瓷复合材料的物相、显微结构和力学性能进行了研究,结果表明:随着SiCp1的加入,SiCp1/ZrB2复合材料的相对致密度和断裂韧性都得到了较大提高,当SiCp1添加量为15%(体积分数)时,相对致密度达到99%,断裂韧性达到(8.35±0.26)MPa·m1/2,抗弯强度达到(522±49)MPa.用轧膜法制备的SiCp1定向排列的SiCp1/ZrB2复合材料的力学性能略有下降.     

骑式摩托车油箱喷涂工艺的改进

面对日益激烈的市场竞争,摩托车油箱外观质量越来越成为影响销售的因素之一。文章介绍了改进工艺后的油箱涂装,该涂装体系提高了油箱外观的丰满度,降低了油箱涂装的生产成本。     

茶多酚提取方法进展

本文综述了国内外现有茶多酚提取方法的现状以及近期的研究进展，并对其优缺点进行了评价。这将有助于中低档茶的综合利用和茶多酚的进一步开发应用。     

SEDIMENTATION OF BINARY MIXTURES OF PARTICLES OF UNEQUAL DENSITIES AND OF DIFFERENT SIZES

A model is developed for the sedimentation from a suspension of two particle species of unequal densities and of different sizes. The composition and the thickness of various layers in the sediments are predicted using graphical and analytical methods. The model predictions were in excellent agreement with experimental results, when the particle size ratio was ≥ 108. When size ratio of the particles was 2.60 and 4.31 the agreement occurred in about 50 percent of the cases.     

HEASUREHENT OF INSTANTANEOUS RATES OF LOSS OF VOIATILE COMPOUNDS DURING DRYING OF DROPS

A novel technique serves to monitor instantaneous rates of loss of a volatile solute from a suspended drop during drying. A highly sensitive electron capture detector is used to monitor concentrations of SF6 released into a flowing gas stream from a suspended, drying drop. Simultaneously, the appearance and morphological development of the drop are monitored with a video camera. This provides the wherewithal of relating instantaneous rates of loss of the volatile solute to particular events during the development of particle morphology.

Initial experiments have been carried out with drops of aqueous solutions of glucose, sucrose, maltodextrin and coffee extract. The results clearly display the onset of the volatiles-retentive selective diffusion phenomenon. There is also substantial loss of the volatile component later in the drying process, when the drops undergo repeated ex ansion, bursting and cratering due to the formation of internaf bubbles. These experiments appear to be the first quantitative demonstration of major losses accompanying changes in drop morphology.     

用两个形状指数表征粉煤灰颗粒形貌的研究

引用两个形状指数表征颗粒形状的概念,即先将颗粒形状近似为椭圆,再将椭圆图像分离:以圆为基准的颗粒宏观形状指数δ;以光滑椭圆为基准的颗粒轮廓凹凸度,即微观形状指数ζ。分析和发展了近似椭圆模型。并运用图像分析仪对粉煤灰、水泥样品进行实验。结果表明,粉煤灰颗粒的两个形状指数δ和ζ都大于水泥颗粒。证明粉煤灰颗粒的球形度、表面光滑度优于水泥,而且,随着粒径增大,δ和ζ呈下降趋势,表明磨制颗粒越粗。(?)粒形状越不规则。文中还运用近似椭圆模型再现了颗粒的模拟图像。     

典型煤碳燃烧特性研究和数值模拟

本文以三种典型煤的碳燃烧为研究对象，分别采用简单一维沉降燃烧方式和等温加热燃烧方式，实验研究了煤在快速加热条件下，其碳的初期和中，后期燃烧过程。以实验为基础，建立了煤的碳燃烧模型，变工况数值模拟了煤的碳燃烧过程，揭示了煤不同条件下的单颗粒碳燃烧特性。     

剪力对梁变形影响的分析

本文用材料力学的分析方法,导出了一个计入剪力时梁的挠曲线的微分方程式。为了估计剪力对梁变形的影响,在集中力作用下梁内剪力用一个单值连续的反三角函数表示。由能量法确定了截面因子数值之后,定量地给出计入剪力时梁变形的分析结果。其结果和弹性力学的结来是一致的。     

酚醛树脂热降解动力学研究

用热失重非等温法对不同甲醛,苯酚魔鬼洋比的酚树脂进行了热降解动力学研究。结果表明,甲醛,苯酚摩尔比为１．５时,酚醛树旨的热发活化能最高。耐热性最好。     

氢气纯度分析方法准确性的探讨

ONACCURACYOFANALYSISOFOFHYDROGEN1前言我公司目前应用的氢气纯度分析方法有两种,一种是爆炸反应法,另一种是焦性没食子酸吸收法。几年来,人们对两种分析方法的准确性曾有过褒贬不一的评论。这里我们也谈谈自己粗浅的观点。2爆炸法测定氢气纯度一定量的氢气样品与适量的空气之均匀混合物因反应后生成液体水而引起气体体积减少,减少的体积等于参加反应气体体积之和。其中l／3为氧气,2／3为氢气。根据氢气取样量和反应前后混气体体积之差,以及氢气在反应中的体积比例关系,可计算出样品的氢气纯度。计算公式式中：A一混…     

ANALYSIS OF RECENT MEASUREMENTS OF THE VISCOSITY OF GLASSES

Viscosity of Simple Soda-Silicate 500° to 1400°C Comparison of the results given by English with those of Washburn, Shelton and Libman, indicates a discrepancy in the absolute values of log₁₀ viscosity amounting to 0.6, those of Washburn et al., being relatively too high. If correction for this is made, the isothermal curves of log₁₀ viscosity as a function of soda content are smooth up to 50% Na₂O, showing no inflection. The observations as a function of temperature T are all represented within accidental error by an equation of the type where all three constants vary regularly with the composition. Change of Viscosity of Glass (6SiO₂, 2Na₂O) due to Molecular Substitution of CaO, MgO and Al₂O₃ for Na₂O The effect is clearly brought out by plotting (from the results of English) the change of log₁₀η due to the substitution as a function of temperature. The curves each show a sharp bend at a temperature between 840° and 1050°C, which is designated the aggregation temperature T_a. If we divide these curves by the corresponding percentage substituted, we get curves for each oxide which are straight and parallel below the aggregation temperatures, the slopes (increase of change of log₁₀η per 100°C) being −0.056 (CaO), −0.055 (MgO), −0.018 (A1₂O₃) per per cent oxide substituted. For substitution of 1/2 molecule the slopes are −0.325 (CaO), −0.23 (MgO) and −0.18 (Al₂O₃) per 100°. At the aggregation temperature the change of log₁₀η per per cent is a minimum, 0.03 to 0.06 for CaO, 0.12 for MgO, 0.07 for Al₂O₃. Evidence of Aggregation in Glasses, from viscosity Measurements The sharp bends in the plots of change of log₁₀η due to substitution of an oxide for Na₂O, suggest the beginning of molecular aggregation at these temperatures. These aggregation temperatures are close to the devitrification temperatures, but the effect on the viscosity curves cannot be due to actual devitrification since it does not change with time. Taking the aggregation temperatures as equal to devitrification temperatures, additional isotherms are roughly sketched into the equilibrium triangle of the system Na₂O-CaO-SiO₂. Change of Viscosity of Glass (4SiO₂, 2Na₂O) due to of Substitution of B₂O₃ for SiO₂ The change of log₁₀η (from the results of English) is plotted as a function of temperature, and also the change of log₁₀η per per cent B₂O₃. The curves are more complex than for the substitution for Na₂O.