碳化硅晶须改性反应烧结碳化硅陶瓷的显微结构及性能

以碳化硅晶须为增强体、碳化硅--碳为基体制备晶须增强反应烧结碳化硅复合材料,研究了碳化硅晶须、碳含量对复合材料显微结构与性能的影响。结果表明:碳化硅晶须经高温反应烧结后仍保持表面的竹节结构,且晶须增强体与反应烧结碳化硅基体间形成适中的界面结合强度;材料断口处有明显的晶须拔出,当碳黑含量为6%(质量分数)时,随着晶须含量的增加,材料的抗弯强度从200MPa提高到310MPa(晶须含量15%),当碳黑含量为18%时,随着晶须含量的增加,材料断裂韧性从3.3MPa·m1/2提高到4.3MPa·m1/2;碳化硅晶须含量过高时,晶须的"搭桥"效应导致材料中含有较多的游离硅,限制了材料力学性能进一步提高;微氧化处理使材料表面形成致密、均匀的氧化膜,可显著提高反应烧结碳化硅的抗弯强度和断裂韧性。     

用低纯碳化硅微粉烧结碳化硅陶瓷

用工业尾料低纯W3.5 μm SiC微粉为原料,在N2保护下烧结碳化硅(SiC)陶瓷.研究了低纯SiC微粉中杂质对SiC陶瓷力学性能的影响,对比了微粉提纯后材料的性能与结构.通过扫描电镜、金相显微镜分析材料的显微结构.结果表明:微粉杂质中SiO2、金属氧化物在SiC烧结温度下的放气反应是影响陶瓷材料力学性能的主要因素.由低纯SiC粉制得的材料的烧结密度达到(3.15±0.01)g/cm3,抗折强度达到(441±10)MPa.     

二次炭粒对PCRBSC显微结构的影响

用二次炭粒制备了纯碳反应烧结碳化硅(PCRBSC),研究了二次炭粒的密度、粒径及颗粒粘结状态对烧结体显微结构的影响。结果表明:当二次炭粒的密度为0.844 g/cm~3、粒径小于37μm时,烧结体中几乎没有fC的存在,但二次炭粒密度过低会导致fSi含量增加;加入粘结剂可以改善二次炭粒高温时的粘结强度,防止烧结开裂而出现硅线。     

喷雾造粒对固相烧结SiC陶瓷的影响

采用离心式喷雾造粒技术对SiC浆料进行造粒,研究了喷雾造粒对SiC粉体的流动特性、成型行为、烧结性能、力学性能及显微结构的影响机制。研究结果表明:喷雾造粒后,碳化硅粉体流动性得到较大改善,素坯密度增加,微观结构致密;固相烧结后,碳化硅陶瓷的烧结性能提高,陶瓷显微结构得到改善。     

碳化硅木质陶瓷的显微结构及力学性能

以汉麻秆芯碳化后的碳粉为原料,分别采用注浆和干压成型工艺制备素坯,通过反应烧结制备出碳化硅木质陶瓷.研究了注浆成型工艺中悬浮稳定剂的种类和添加量对浆料性能的影响.采用激光共聚焦显微镜、扫描电子显微镜和X射线衍射仪等分析了碳化硅木质陶瓷的显微结构、物相组成及力学性能.结果表明:采用注浆成型制备的碳化硅木质陶瓷力学性能优异,实测的游离硅含量同理论计算结果一致,说明渗硅过程中硅碳反应充分,烧结体显微硬度、弯曲强度、弹性模量和断裂韧性分别为22.3 GPa、397 MPa、290 GPa和3.0 MPa·m1/2.     

氧化镧对镁橄榄石晶体结构及性能的影响

以低品位菱镁矿与天然硅石为原料,以氧化镧为添加剂,通过固相反应烧结制备镁橄榄石.研究讨论了氧化镧对镁橄榄石材料相组成、晶胞参数、微观结构及常温性能的影响.用XRD和SEM法对烧后试样的相组成和显微结构进行研究.利用X' pert plus软件对试样中镁橄榄石相的晶胞参数进行计算.按国家标准,检测镁橄榄石试样的体积密度、显气孔率、吸水率和常温耐压强度.结果表明:加入适量氧化镧可以促进了低品位菱镁矿轻烧氧化镁粉与天然硅石中通过固相反应烧结合成制备镁橄榄石.氧化镧加入量为1.2％时,镁橄榄石的晶胞体积最大,镁橄榄石中引入氧化镧所造成的结构缺陷加速了离子扩散速度,而过量的氧化镧会进入晶界液相中.综合以上分析,氧化镧的引入量为1.2％时,镁橄榄石材料综合性能最好,其体积密度为2.44 g/cm3,显气孔率为23％,吸水率为9.5％,常温耐压强度为30.1 MPa.     

化学结合法低温制备氧化铝泡沫陶瓷的研究

以磷酸二氢铝为粘结剂、电熔α氧化铝粉末为原料、聚氨酯海绵为模板低温制备出了氧化铝泡沫陶瓷.研究了浆料固相含量对氧化铝泡沫陶瓷微观形貌、线收缩率、体积密度和抗折强度的影响.结果表明:随浆料固相含量的增加,烧成氧化铝泡沫陶瓷的通孔率逐渐降低、体积密度与抗折强度逐渐提高,线收缩率均低于1％.在浆料固相含量为60％时,可制备出体积密度为0.83 g/cm3、抗折强度为(2.21±0.43) MPa、通孔率优异的泡沫陶瓷.     

反应烧结工艺对碳化硅陶瓷微结构及性能的影响

研究了脱胶温度、加硅量、升温速率及重烧次数对反应烧结碳化硅陶瓷金相组织、体积密度、力学性能和微观结构的影响.结果表明:经800℃脱胶,硅与碳化硅生坯的质量比为0.9∶1,升温速率为1.0 ℃/min时,反应烧结碳化硅陶瓷产品的性能最好,体积密度为3.09 g/cm3,维氏硬度为26.82 GPa,弯曲强度为388 MPa,断裂韧性为4.49MPa·m1/2.对渗硅不充分的不合格品进行重烧可以有效提高产品的致密度和力学性能,但是,重烧次数过多会引起晶粒粗化,从而导致力学性能下降.     

淀粉为造孔剂制备碳化硅多孔陶瓷

以微米碳化硅基体,氧化铝和氧化钇为烧结助剂,淀粉为造孔剂,采用无压烧结技术制备碳化硅多孔陶瓷.通过测试合成多孔陶瓷的密度、收缩率、力学强度以及扫描电子显微镜(SEM)和X-射线衍射(XRD)等研究了不同造孔剂含量对SiC粉体的力学性能、微观形貌和物相的影响.研究表明:随造孔剂含量的升高,碳化硅陶瓷密度和强度降低,气孔率增加,而造孔剂含量对碳化硅陶瓷的物相组成基本没有影响.     

SiC-石墨复相陶瓷的反应连接法焊接特性

为研究料浆涂覆工艺及反应连接法焊接Si C-石墨复相陶瓷的焊接特性,以w(Si C)=95%、w(石墨)=0的SG0和w(Si C)=65%、w(石墨)=30%的SG30两种陶瓷材料为母材,以硅粉和活性炭粉按n(Si)n(C)=1 1.2配制的65%固相体积分数的混合料浆(分散介质为酚醛树脂和酒精)为焊料,采用涂覆法及反应烧结工艺进行Si C-石墨复相陶瓷的焊接,并对焊接接头的抗弯强度、焊缝的显微形貌以及物相组成进行了测试及分析。结果表明:焊缝具有与母材类似的微观结构及物相组成,焊缝与基体结合紧密;对比SG0-SG30和SG30-SG30两种焊接试块的抗弯强度,其中具有同质母材的焊接试块SG30-SG30的接头抗弯强度较高,达到了81.96 MPa。     

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.     

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。     

COMPARISON OF METHODS OF ANALYSIS OF GYPSUM1

The different analytical methods proposed for the evaluation of gypsum have been subjected to an experimental test. A combination method, consisting of a fusion with KHCO₃ and determination of CaO by KMnO₄ titration, the SO₃ by Andrews method of titration of BaCrO₄ has been found to give very reliable results with the least consumption of time.     

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。     

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.     

环氧树脂羟基值测定方法的研究

利用乙酸酐、吡啶和浓硫酸混合的乙酰化试剂测定环氧树脂中羟基值含量的方法具有操作简便、滴定终点明显和分析结果误差小等优点。     

制备板状玻璃炭工艺中固化曲线的确定

固化处理是在玻璃炭制备工艺中很关键的阶段．在差热分析和热失重分析的基础上．建立了玻璃炭（GC）固化升温曲线，并与等速升温法作了比较．