凝胶注模成型制备高性能的氮化硅陶瓷(Ⅱ)-冷等静压、粉料氧化处理和气压烧结对材料性能的影响

在对氮化硅粉料进行助烧剂包覆和凝胶注模成型的基础上,研究了冷等静压凝胶注模成型氮化硅坯体、氧化氮化硅包覆料和气压烧结制度对凝胶注模成型氮化硅陶瓷的抗弯强度和韦泊尔模数的影响冷等静压有利于提高凝胶注模成型氮化硅陶瓷的力学性能.合适的粉料氧化制度和烧结制度都能提高材料的抗弯强度和韦泊尔模数.实验采用优化的工艺,制备出的氮化硅陶瓷的三点弯曲强度和两参数韦泊尔模数(20个试样)分别高达944.7±29.5MPa和33.9.     

凝胶注模成型工艺制备羟基磷灰石陶瓷

采用凝胶注模成型工艺成功地制备出羟基磷灰石(HAp)陶瓷,研究了单体、引发剂用量及固相含量等因素对坯体强度的影响.结果表明,由单体含量为2%(质量分数)、引发剂加入量为5%(质量分数)、固相含量为60%(质量分数)的浆料凝胶注模而成的坯体强度最高(>31MPa).SEM形貌分析表明,经凝胶注模工艺制备的陶瓷,其结构均匀并有较高的气孔率;颗粒与颗粒之间的有机物粘连是获得高强度坯体的主要原因.     

氧化铝陶瓷凝胶注模成型工艺的研究

探讨了陶瓷凝胶注模成型的机理和特点,研究了固相体积含量、pH值、分散剂等对制备低粘度、高固相体积含量的氧化铝陶瓷悬浮液的影响.实验结果表明,固相体积分数为55%,浆料的粘度可以满足注模的需要时坯体抗弯强度可达30MPa.控制pH值为9左右,加入8%(质量分数)的PMAA-NH4分散剂,可制得粘度低、流动性好适宜于复杂形状制品注模的陶瓷浆料.     

较大规格SnO_2坯体的凝胶注模成型及抑制其卷曲变形的工艺研究

在凝胶注模成型制备平板状陶瓷坯体的过程中,坯体在固化后极易发生卷曲变形,严重制约了该技术在平板陶瓷成型领域的应用。本文使用SnO2粉体,通过制备高固含量、低粘度的浆料,并在此基础上改变凝胶注模成型工艺中固化剂的引入方式,从而制备出较大规格无卷曲变形的平板SnO2坯体。     

钛酸铝陶瓷水基注凝成型工艺

本文采用水基凝胶注模成型工艺,通过控制技术参数,制备了固相含量为62%,粘度达到280mpa·s的钛酸铝陶瓷浆料.研究了抽真空时间对致密度以及固化时间的影响.随着有机单体和交联剂含量的增加,坯体的弯曲强度逐渐增大.通过分析影响因素,并改善制备条件,能够制备出强度为33.4MPa、可进行机加工的陶瓷坯体.     

超高压成型对碳化硅陶瓷微观结构的影响

以两面顶为成型设备,利用其超高压力(4.5GPa)来提高素坯的相对致密度,从而降低坯体的烧结温度、缩短烧结时间,并制备出高致密度的细晶碳化硅陶瓷。结果表明,经超高压成型后,碳化硅素坯的平均相对致密度为65.7%。与冷等静压成型后的坯体(45.5%)相比,提高了大约20%。在低压流动氮气保护下,超高压成型的坯体于1900℃下无压烧结30min,烧结体的致密度达到了98.3%,其晶粒尺寸在200nm左右。     

高精度复杂形状碳化硅陶瓷制备工艺研究

研究了一种复杂形状碳化硅陶瓷制品制备工艺—陶瓷素坯加工工艺(GCM,Green ceramic machining).采用凝胶注成型工艺制备出简单形状碳化硅陶瓷素坯,通过数控机床对素坯陶瓷进行三维加工.研究了凝胶注模成型碳化硅陶瓷素坯强度以及显微结构,并对其加工性能(钻孔、挖槽)以及加工工艺参数进行的研究,优化了加工工艺参数并制备出了复杂形状的高精度碳化硅陶瓷制品.     

Y2O3含量及制备工艺参数对Y—TZP纳米粉烧结体性能的影响

用化学共沉淀法制备了Ｙ２Ｏ３含量不同的两种Ｙ－ＴＺＰ纳米粉体；采用了不同压力不冷等静压成形制备素坯；研究了Ｙ２Ｏ３含量，素坯成型压力及烧结温度对Ｙ－ＴＺＰ陶瓷体密度，组织结构及机械性能的影响。     

Y_2O_3含量及制备工艺参数对Y－TZP纳米粉烧结体性能的影响

用化学共沉淀法制备了Ｙ２Ｏ３含量不同的两种Ｙ－ＴＺＰ纳米粉体；采用不同压力下冷等静压成形制备素坯；研究Ｙ２Ｏ３含量、素坯成型压力及烧结温度对Ｙ－ＴＺＰ陶瓷体密度、组织结构及机械性能的影响。     

纳米Y-TZP凝胶注模成型的研究

对纳米Y－TZP的浆料进行了凝胶注模成型．有机单体丙烯酸胺和交联剂N,N-亚甲基双丙烯酸胺的加入,不但起到使浆料凝胶的作用,还可以大大降低浆料粘度,改善浆料的流变性．有机单体、交联剂、引发剂均有其合适的用量范围．与干压法、等静压法相比,用凝胶注模法成型的素坯密度高、显微结构均匀、烧结体的断裂韧性也较等静压法高．     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.