液相烧结大晶粒UO2及其烧结动力学分析

大晶粒二氧化铀(UO₂)芯块因具有低辐照肿胀、低裂变气体释放及优异的燃料包壳相互作用效应(PCI),而成为未来先进反应堆关注的候选燃料。本文采用液相烧结工艺制备大晶粒UO₂芯块，研究了液相烧结对UO₂芯块烧结性能、显微结构和烧结动力学的作用机制和影响规律。结果表明：通过添加金属铀粉形成的液相烧结可明显促进UO₂芯块的致密化速度，液相烧结UO₂芯块的烧结特征指数为2.937,烧结机理主要为晶界扩散，烧结激活能为103.00 kJ/mol,低于普通UO₂芯块的烧结激活能(110.65 kJ/mol);液相烧结UO₂芯块晶粒生长指数为2.831,晶粒生长活化能为463.97 kJ/mol,低于普通UO₂芯块晶粒生长激活能(510 kJ/mol),加入的金属铀粉形成的液相烧结可促使晶粒长大；添加金属铀粉液相烧结工艺具有不引入非铀杂质元素、加快芯块致密化速度和增大芯块晶粒尺寸的多重作用。     

反应烧结制备Li2Zn2Mo3O12微波介质陶瓷及其微波介电性能研究

采用反应烧结法制备了具有超低烧结温度的Li₂Zn₂Mo₃O₁₂微波介质陶瓷,研究了烧结温度对Li₂Zn₂Mo₃O₁₂陶瓷的烧结特性、物相组成、微观结构以及微波介电性能的影响。XRD表明：在550～650℃范围内,温度对陶瓷的物相组成影响不大;随着烧结温度的升高,Li₂Zn₂Mo₃O₁₂陶瓷的体积密度、相对密度、介电常数(ε_r)和品质因数(Q×f)均呈先增大后减小的趋势,谐振频率温度系数(τ_f)在-(70～90)×10^-6/℃波动。在625℃烧结2 h获得最大体积密度和相对密度：4.25 g/cm³和96.4%,以及优异的微波介电性能ε_r=10.9,Q×f=69 459 GHz,τ_f=-84×10<...     

二硅化钼喷涂粉末的制备及其涂层组织结构

以粒度为1~2μm的MoSi₂粉末为原料,采用喷雾干燥和真空烧结制备了喷涂用MoSi₂团聚粉末. 分别用平均粒度为9.68μm的MoSi₂粉末和团聚造粒MoSi₂粉末(38~72μm)为喂料, 大气等离子喷涂制备了二硅化钼涂层,分析了涂层的微观组织结构. 研究结果表明,喷雾干燥造粒后的近球形粉末在1300℃真空烧结1h后,粉末流动性和松装密度分别为17.1s/50g和2.16g/cm³,比烧结前分别增加了57.0%和46.0%.平均粒度为9.68μm 的MoSi₂粉末制备的涂层主要是由Mo和Mo₅Si₃等富钼相组成. 团聚粉末制备的涂层主要由MoSi₂相组成,涂层较致密, 内部出现了类似“网状”的组织结构.     

无铅压电陶瓷KNN常压烧结及其电学性能

用常压烧结法制备K_0.5Na_0.5NbO₃陶瓷。研究烧结温度与陶瓷密度和电学性能的关系。研究表明在1065℃~1120℃范围内, 温度对陶瓷的密度有显著影响。当烧结温度为1100℃时, 密度达到4.35 g/cm³ (占理论密度的95%); 1100℃烧结的陶瓷表现出最好的电学性能, 压电常数最大118 pC/N, 相对介电常数最大达538, 介电损耗最小仅4.7%, 剩余极化强度为15.37 μC/cm², 矫顽场为13.16 kV/cm。陶瓷样品在206℃从正交结构转变到四方结构, 居里温度为410℃。     

改性松果活性炭去除Cr6+的研究

为了提高水中Cr⁶⁺的去除效率，以松果粉末(PC)为原料，利用H₃PO₄改性法制备了低成本高比表面的改性松果活性炭(PCAC)。采用扫描电子显微镜、X射线衍射仪、傅里叶红外光谱仪和全自动比表面积分析仪对PCAC表面理化性质变化进行表征。通过静态吸附实验探究其对Cr⁶⁺的吸附性能，测定了溶液初始pH、PCAC投加量和吸附时间对Cr⁶⁺吸附性能的影响。根据吸附动力学和吸附等温线，探讨了PCAC对Cr⁶⁺的吸附机理。结果表明：经H₃PO₄改性制备的PCAC比表面积和孔隙体积分别为1669.2m²/g和0.851cm³/g,高于未改性的PC;对于100mg/L Cr⁶⁺模拟废水，最佳吸附条件：pH=2、PCAC投加量0.5g、吸附时间3h,此时PCAC对Cr⁶⁺的去除率最大且为99.97%;吸附动力学数据拟合分析，拟二级动力学模型较好...     

低损耗SrY0.15Ce0.85O2.925陶瓷的烧结特性、相结构及微波介电性能研究

采用固相反应法制备了SrY_0.15Ce_0.85O_2.925陶瓷材料，利用XRD、SEM和微波矢量网络分析仪研究了材料的相组成、结构、烧结特性和微波介电性能。结果表明，当烧结温度为1 450℃时，SrY_0.15Ce_0.85O_2.925陶瓷的综合性能最佳：体积密度为5.2 g/cm³,相对密度达到92.7%,Q×f=21 503 GHz,ε_r=23.83,τ_f=-46.43×10^-6/℃。以上结果表明，SrY_0.15Ce_0.85O_2.925陶瓷可以作为现代移动通讯器件的备选材料。     

多孔铝基陶瓷型芯的制备及其性能

为了解决铝基陶瓷型芯难于烧结和不易脱芯的难题, 在样品中加入了一定量的SiO₂. 利用干压法制备了多孔氧化铝基陶瓷型芯样品, 研究了不同SiO₂的添加量、烧结温度和保温时间对样品性能的影响. 研究结果表明: 经1500℃烧结保温2 h和1600℃烧结降温2 h的样品, 其线收缩率变化不大. 经1700℃烧结保温2 h的样品, 由于SiO₂的挥发导致样品的气孔率升高, 抗弯强度明显降低. 经1500℃烧结保温2 h的样品综合性能最好, 当SiO₂添加量为10wt%时, 样品的线收缩率为1.1%, 抗弯强度为63 MPa, 气孔率为35.5%, 体积密度为2.29 g/cm³; 当保温时间≥4 h时, 其线收缩率、抗弯强度、气孔率和体积密度变化不大, 有望成为高温型芯的候选材料.     

304不锈钢表面纳米铝改性有机硅涂层的高温氧化和电化学行为

研究了纳米铝改性有机硅高温涂层的固化、抗650℃高温氧化性能和耐3.5% NaCl水溶液电化学腐蚀性能。当聚氨酯:有机硅的质量分数达到1:3或更高时,有机硅涂料可以在24 h内完成常温固化。制备出的纳米铝改性有机硅高温涂层表面致密,没有微观裂纹等缺陷。纳米铝改性的有机硅涂层显著提高了304不锈钢抗氧化性能,经1028 h氧化实验,基体几乎没有发生氧化,涂层没有出现开裂和剥落。纳米铝改性的有机硅涂层还显著提高了氧化后的304不锈钢耐氯化钠水溶液腐蚀性能,无涂层的304不锈钢氧化后形成的氧化膜低频阻抗仅3.2 Ω·cm²,而涂装涂层的不锈钢的低频阻抗约为1.1×10⁵ Ω·cm²。     

稀土氧化物对常压烧结氮化硅陶瓷性能的影响

高导热氮化硅陶瓷是大功率电力电子器件散热的关键候选材料。研究采用稀土氧化物(Re₂O₃)和氧化钛(TiO₂)烧结助剂体系, 通过低温常压烧结方法来制备氮化硅陶瓷, 以有效降低成本, 满足实际应用的需求。系统研究了烧结助剂种类及含量对Si₃N₄陶瓷的致密化行为、热导率、显微结构以及力学性能的影响。研究发现随着稀土离子半径的增大, 材料的致密度和热导率均呈现下降趋势, 添加Sm₂O₃后样品最高密度仅为3.14 g/cm³。但是当Sm₂O₃-TiO₂烧结助剂含量为8wt%时, 样品断裂韧性可达5.76 MPa•m^1/2。当添加Lu₂O₃且烧结助剂含量为12wt%时, 材料的密度可达3.28 g/cm³, 但是大量存在的第二相导致热导率仅为42.3 W/(m∙K)。研究发现该材料具有良好的断裂韧性。经1600℃退火8 h后, Er₂O₃-TiO₂烧结助剂样品的热导率达到51.8 W/(m∙K), 基本满足一些功率电路基板材料的实际应用需求。     

TC4合金微弧氧化涂层的组织结构与高温氧化行为研究

为了提高TC4合金的高温抗氧化性能,采用微弧氧化方法在NaAlO₂+Na₃PO₄电解液体系中,于钛合金表面制备抗氧化陶瓷涂层。通过XRD、SEM、EDS等方法,表征涂层的相组成和微观结构,用纳米压痕仪测试涂层硬度与弹性模量,并研究了微弧氧化涂层的抗高温氧化及抗热震性能。结果表明：微弧氧化涂层表面多孔,涂层以Al₂TiO₅和金红石型TiO₂相为主。微弧氧化涂层的纳米硬度为(7.8±0.6) GPa,显著高于TC4合金[(4.0±0.2) GPa]。微弧氧化涂层在700℃循环氧化80 h后,单位面积增重仅0.73 mg/cm²,远小于TC4合金的增重(20 mg/cm²),表现出良好的高温抗氧化性能。经700℃热冲击25次后,涂层未出现剥落现象,展现出良好的抗热震性能。由此可见,微弧氧化涂层能有效阻止氧的扩散,显著降低了钛合金基体的氧化速率,改善了钛合金的抗高温氧化性能。     

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.     

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.     

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.     

Numerical study of methods of linearization of the output characteristics of radio-frequency sensors of the level of dielectric media

Different constructions of the sensing elements of radio-frequency level sensors based on sections of long lines are numerically investigated by means of the Matlab program for the purpose of minimizing the measurement error caused by the nonlinearity of the output characteristic. It is shown that the nonlinearity is lowest for U-shaped designs. The nonlinearity factor KN may be regulated by varying the capacitance of a correcting capacitor connected to the input of the sensing element and (or) the length of one of the sections of the long line. In selecting an optimal capacitance of the correcting capacitor KN ≤ 0.15% for control media with dielectric permittivity in the range 2.2–30.     

Possibilities of Decreasing the Errors of Determination of the Height of the Pole of a Sessile Drop of Melt

We analyze the possibilities of decreasing the errors of measuring the height of the pole of a sessile drop of melt above its equator by determining the position of the equator according to the midpoints of vertical chords of the image of the drop. The optimal distance between these chords and the edge of the image of the drop is chosen within 10–20% of the radius of the equator. The proposed method guarantees the same level of errors of evaluation of the height of the pole and the radius of the equator, which enables one to substantially increase the accuracy of evaluation of the capillary constant and the surface energy of the melt according to the geometric parameters of the sessile drop.     

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.     

Analysis of anisotropy of properties on the basis of studies of texture of coarse-grained ingots of thermoelectric materials

An analysis of anisotropy of the properties of a Bi₂Se_0.3Te_2.7 solid solution was carried out using construction of demonstrative surfaces for thermoelectric effectiveness and thermal expansion coefficients. It is shown that the texture is an important factor forming anisotropy of properties and technological fitness of ingots for manufacturing modules. Anisotropy of properties based on the studies of the ingot textures obtained using the float-zone method and Bridgman method (growing thermoelectric plates in a flat cavity) was studied.     

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.