新型共沉淀法制备铁酸镍纳米材料

以FeSO4·7H2O和NiCl2·2.5H2O为原料,采用新型化学共沉淀法制备了纳米尺寸的NiFe2O4粉体,并在不同温度下进行处理,利用XRD、TEM等手段研究了其结构特性.研究表明,350℃以上的热处理开始促进粉末的长大和晶化过程,随着温度的升高,晶化程度增强,粉末粒径增大.当热处理温度为600℃时,材料结晶较好,晶粒粒径约为24nm,粒度均匀.     

Absorbing properties investigation of SrFe12O19-NiFe204 composite nanopowders with core- shell structure

以Fe（NO3）3、Ni（NO3）2和Sr（N0s）2为主要原料,通过两步柠檬酸盐溶胶一凝胶法,制备出核一壳结构SrFe12O19-NiFe2O4磁性纳米复合粉体。采用XRD、TEM、VSM及矢量网络分析仪对合成的粉体的结构、形貌及吸波性能进行了分析研究。结果表明,复合粉体的相结构与NiFe2O4含量有关,当SrFe12O19与NiFe2O4的质量比为1：2、烧结温度为1050℃时,复合纳米粉体的相与NiFe2O4接近,核一壳结构SrFe12O19-NiFe2O4纳米复合粉体的饱和磁化强度（Ms）（51．4emu／g）比单体SrFel201。纳米粉体（42．6emu／g）的大;但矫顽力（H。）（336Oe）比单体SrFel2019纳米粉体的小,在SrFel2019与NiFe204的矫顽力5395-160Oe之间。在频率为8-18GHz范围内,微波吸收逐渐增强,当频率为12GHz时,SrFe12O19-NiFe2O4纳米复合粉体的微波吸收达到最大值-9．7dB,是一种性能优良的吸波材料。     

La2 CuO4前驱物粉体的自蔓延燃烧合成及其晶化

分别采用硝酸盐自蔓延燃烧法和醋酸盐／硝酸盐自蔓延燃烧法低温合成了La2CuO4前驱物粉体,研究了在不同条件下制备的前驱物粉体的晶化行为。在硝酸盐自蔓延燃烧法合成前驱物粉体时,燃烧反应十分剧烈,在前驱物粉体中发现有Cu单质存在,Cu单质的存在不利于在低温合成单一相La2CuO4粉体。在硝酸盐自蔓延燃烧法基础上,以醋酸盐部分取代硝酸盐,大幅度降低了自蔓延燃烧温度,可以通过调整尿素的用量来改变氧化剂的总氧化价O与还原剂的总还原价F之比,使自蔓延燃烧温度连续可调。用醋酸盐／硝酸盐自蔓延燃烧法合成的前驱物粉体在较低温度焙烧处理,得到了单一相La2CuO4粉体。自蔓延燃烧温度对前驱物的组成和焙烧产物的组成和显微形貌有显著影响。自蔓延燃烧温度连续可调为得到具有可控制显微形貌的目标产物提供了可能。     

低温固相反应工艺对NiFe_2O_4纳米粉体形貌的影响

为了改善NiFe2O4纳米粉体气敏性,采用低温固相反应法制备了不同形貌的NiFe2O4纳米粉体.以FeSO4·7H2O、NiSO4·6H2O和NaOH作为反应物,充分研磨制备前驱体,通过先抽滤后600℃热处理和先600℃热处理后抽滤制备了两种NiFe2O4纳米粉体,通过X射线衍射和扫描电镜考察了不同制备工艺对纳米晶粒尺寸及形貌的影响.XRD和SEM分析结果表明:两种制备工艺均能生成NiFe2O4尖晶石相.先抽滤后热处理制备的NiFe2O4纳米粉体颗粒尺寸约为80nm,颗粒呈立方体结构.而先热处理后抽滤制备的NiFe2O4纳米粉体,由于热处理过程中存在Na2SO4相,使得NiFe2O4纳米粉体颗粒呈圆形片状结构分布,颗粒尺寸为50nm,厚度约10nm.     

低温燃烧合成法制备纳米NiFe_2O_4

以九水硝酸铁、六水硝酸镍、水溶性肼类燃料为原料,添加金属离子络合剂、分散剂等为辅助剂,利用溶液燃烧合成法制备了纳米NiFe2O4粉体。利用XRD、TEM、SEM等测试方法对产物进行了表征,并研究了不同燃料、络合剂用量、分散剂用量、煅烧温度对粉体粒径和形貌的影响。实验结果表明,在以水溶性肼为燃料、络合剂2g、分散剂2g、煅烧温度800℃、煅烧时间2h时,可获得粒径均匀的纳米NiFe2O4粉体。所得产物的粒径范围为40～80nm,结构膨松,分散性良好。     

尖晶石型Ni0.8Zn0.2Fe2O4纳米晶体的?制备及电磁性能研究

以金属离子的柠檬酸盐为前驱体,通过sol-gel自燃烧的合成方法制备了镍锌铁氧体(Nio.8Zno.2Fe2O4)纳米晶体.采用FT-IR、DSC-TG、XRD、TEM波导等方法对产物以及产物的电磁性能进行了表征.结果表明,在前驱体中,金属离子与柠檬酸以络合物的形式存在.凝胶在220℃完成自燃烧反应.随着热处理温度的升高,粉体的粒径逐渐增大.纳米晶体在8～12GHz的测试条件下具有介电损耗与磁损耗.随着涂层厚度的增加,混合媒质的微波反射率逐渐增加,反射率吸收峰随着厚度的增加向低频移动.     

尖晶石型Ni0.8Zn0.2Fe2O4纳米晶体的制备及电磁性能研究

以金属离子的柠檬酸盐为前驱体，通过sol-gel自燃烧的合成方法制备了镍锌铁氧体（Ni0．8Zn0．2Fe2O4）纳米晶体。采用FT-IR、DSC-TG、XRD、TEM波导等方法对产物以及产物的电磁性能进行了表征。结果表明，在前驱体中，金属离子与柠檬酸以络合物的形式存在，凝胶在220℃完成自燃烧反应，随着热处理温度的升高，粉体的粒径逐渐增大，纳米晶体在8-12GHz的测试条件下具有介电损耗与磁损耗，随着涂层厚度的增加，混合媒质的微波反射率逐渐增加，反射率吸收峰随着厚度的增加向低频移动。     

铁氧体/碳复合吸收剂的水热法制备及电磁性能研究

采用固相法制备BaZn2Fe16O27铁氧体,将其与葡萄糖溶液混合水热反应,得到铁氧体/碳复合粉体。通过XRD、SEM等表征手段,研究了复合粉体的物相组成、显微结构,并用网络分析仪分析了不同水热反应温度下复合粉体的电磁特性。结果表明,葡萄糖在水热反应后发生碳化,接枝在片状铁氧体表面,得到了铁氧体/碳复合吸收剂;与单一的铁氧体相比,在2～18GHz频段内,复合粉体的磁损耗有所增加,介电损耗明显增加;在水热反应温度为160℃时,复合粉体的介电损耗值达到最大,介电损耗和磁损耗在2～18GHz频段内出现多个损耗峰,有利于电磁波的吸收,并且拓宽了吸波频带,增加了其电磁性能,使得吸波效果进一步增加。     

纳米FeNi粉体的吸波性能研究

利用液相还原法制备了纳米FeNi粉体。利用XRD和SEM分别对FeNi粉体的物相、形貌进行了分析,并通过矢量网络分析仪,利用同轴方法对FeNi粉体/固体石蜡复合材料进行了电磁参数的测定。研究表明,制备出的铁镍复合粉体主要成分为FeNi;FeNi粉体为球形,直径约为100 nm,分布均匀。利用实验所得到的数据模拟了FeNi复合材料不同厚度涂层的吸波性能,当涂层厚度为2 mm时,复合材料的吸收峰值R达到-6.25 d B,小于-4 dB带宽从13.24~16.47GHz;在2~18 GHz频率范围内,当涂层厚度为4 mm时,FeNi粉体/固体石蜡复合材料出现了两个吸收峰,其值都小于-4.5 dB。     

TiC-Al2O3/Fe3Al复合粉末的燃烧合成

以天然钛铁矿为主要原料,采用燃烧合成技术制备了TiC-Al2O3/Fe3Al金属间化合物/陶瓷基复合材料.研究了预热时间和热处理对燃烧合成过程及产物的影响.研究结果表明:随着预热时间的延长,燃烧温度和燃烧波速率都增加,产物晶胞参数增大,合成更为完全,无序固溶相进行有序化转变的程度增大.当预热5min时,Fe3Al有序金属间化合物的量明显高于无序固溶相,但继续延长预热时间很难将无序相消除;在750℃下进行热处理,可以制备出以Fe3Al金属间化合物为主要成分的复合粉体.     

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.     

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.     

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.     

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。     

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.     

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.