第二十一讲真空卷绕镀膜

(接2022年第1期88页) 3.5.2 海绵导电化 真空磁控溅射技术是海绵卷导电化处理非常行之有效的方法,也是目前国际上最先进的工艺方法.它可以解决采用化学镀或涂导电胶的方法在海绵镍中产生微量元素污染的问题,提高电池充电次数和使用寿命,同时又可以消除原方法产生的环境污染.其产品的主要特点是泡沫镍杂质少、面电阻小、抗拉...     

低温下胶基导电复合材料力敏特性试验研究

对炭黑/硅橡胶导电复合材料进行了低温条件下的力敏特性试验研究。测试结果表明,胶基导电复合材料在低温下仍具有优良的拉伸敏感性(最低温度达到-35℃)及压缩敏感特性。拉伸时,试样电阻随拉伸变形的增大而增大,电阻与应变(最大应变达到20%)之间具有良好的线性关系;压缩时,试样电阻与压缩应力之间也表现出较好的线性关系。研究结果表明,胶基导电复合材料是较低负温下应变及应力测试的理想敏感元件,特别对于大变形测试具有明显优势。     

滴胶/炭黑心电电极的制备及性能表征

以高透明水晶胶A胶,B胶和纳米级炭黑为反应原料,采用共混-模压成型法制备了滴胶/炭黑纳米复合导电材料。利用FT-IR、TGA和SEM对该复合材料组分、结构和形貌进行表征,并尝试将该导电复合材料与纯棉无纺布结合制备滴胶型心电电极,同时考察了该类心电电极的导电性能。结果表明,通过共混-模压成型法成功制备了纳米炭黑分散均匀的导电滴胶/炭黑纳米复合材料,其弹性模量为2.45 MPa,电导率为0.399μS/cm,制备的滴胶/炭黑心电电极电导率为7.051μS/cm,具有优异的导电性能,能够采集到稳定的人体心电信号,心电波谱单元清晰、稳定,信噪比高,可满足市场化应用要求。     

碳纤维导电复合材料的电学性能研究

研究了FR－4溴化环氧树脂玻璃布和碳纤维导电纸层压复合面状发热板的电学性能,结果表明：溴化环氧树脂固化过程对其电性能产生影响,对于不同规格的导电纸,其电阻下降率不同。面状发热板的电阻在升温和降温过程中存在不同程度的偏离,呈现PTC或NTC效应,数次热循环后,可以使室温电阻保持恒定。发热板的电阻随通电时间的延长而逐渐下降并趋于稳定,通断电次数对基电阻影响不大,在长期通电使用下能保持其功能稳定性,发热板的功率密度与表面温度呈现良好的线性关系。     

导电橡胶电阻弛豫行为研究

实验制备了炭黑填充型导电橡胶,介绍了导电橡胶的导电特性,阐述了导电橡胶的电阻弛豫行为,研究了炭黑填充量、厚度、压力、温度对导电橡胶电阻弛豫行为的影响,并讨论了导电网络与电阻弛豫行为的关联性。研究表明随着炭黑填料质量分数的增加,导电橡胶的电阻弛豫时间缩短;增加厚度其电阻弛豫时间延长;增加压力能够缩短其电阻弛豫时间;在正温度效应和负温度效应的转折点处其电阻弛豫时间最长。     

一种基于碳黑/聚四乙烯吡啶纳米复合物的新型湿度传感器

以4-羟-2,2,6,6-四甲基哌啶氮氧自由基(TEMPO)为引发剂,通过本体聚合方法制备聚四乙烯吡啶(P4VP)接枝纳米碳黑(CB)复合材料,以溴丁烷和1,4-二溴丁烷分别与之进行季胺化和交联季胺化反应,制得了新型电阻型湿敏材料.测试了该类纳米复合湿敏材料的温度响应特性,发现其在低湿环境下也具有较好的导电性,而且材料的导电行为同时存在离子导电和电子导电两种机理.通过改变碳黑与聚合物的相对比例,使聚合物产生季胺化以及交联季胺化反应等,可以调控两种导电机理的复合材料在电响应中所起的作用,从而改变其湿敏响应特性,制备可以全程响应的电阻型湿度传感器.     

拉伸应变下镍包碳纤维填充导电橡胶取向及电阻响应

导电橡胶因其超高的弹性和良好的导电性而在柔性电子材料领域受到广泛关注。受载时导电填料重新排列会产生相应的电阻变化。本研究选取镍包碳纤维（Nickel coated carbon fiber,CF-Ni）填充于基胶聚二甲基硅氧烷（Polydimethylsiloxane,PDMS）中制备导电橡胶。基于MATLAB平台,观察了导电橡胶中CF-Ni纤维的静态分布,并构建了纤维取向率的计算方法;随后施加动态应变载荷,选用3D打印的样品,在拉伸应变下,对其进行了纤维在胶体中取向变化的同步观察。结果表明:CF-Ni纤维沿拉伸应变方向发生偏转,最大偏转角度可达20°; CF-Ni纤维的取向分布及拉伸应变下纤维的偏转会对导电橡胶的电学性能产生影响,在60%的应变量下,CF-Ni/PDMS表面电阻最大变化为600%。导电橡胶电阻对拉伸应变载荷的响应为CF-Ni/PDMS用于制备柔性传感器奠定了基础。      

基于GEM模型的炭黑/硅橡胶拉伸传感器的工作原理分析

分析了电阻率和电阻几何系数对基于炭黑/硅橡胶的力敏导电橡胶的"正拉力-电阻特性"(positivetensile coefficient of resistance,PTCR)的影响程度,揭示了力敏导电橡胶拉伸过程的电阻变化机理。在一定拉伸范围内(40%),当导电填料用量处在渗流区中心时,电阻率的增大是引起PTCR效应的主要原因。随着导电填料用量的增大,电阻几何系数的增大成为引起PTCR效应的主要原因。在某一特定导电填料范围内,力敏导电橡胶的"正拉力-电阻特性"还与拉伸长度有关。拉伸长度较小时,电阻几何系数的增大在PTCR效应中占主导;拉伸长度较大时,电阻率的增大在PTCR效应中占主导。     

碳纳米管导电纸的制备及改性研究

以纸纤维作为载体,碳纳米管(CNTs)为导电剂,采用普通造纸的工艺制成碳纳米管导电纸。通过对碳纳米管的石墨化处理改性导电纸性能,采用X射线衍射、热重分析、扫描电子显微镜、四探针电阻仪、矢量网络分析仪等对其表征。研究表明,当纸纤维和碳纳米管加载比为1∶1时,碳纳米管经石墨化改性后,导电纸电导率和导热系数大幅增大,在175~2 700 MHz频段,电磁屏蔽效能提高到-28~-35dB,对比未石墨化碳纳米管导电纸屏蔽效能平均提高10dB。     

高压开关设备导电回路电阻量值溯源路径及测量不确定度评定

该文提出的高压开关设备导电回路电阻量值溯源路径和溯源方法,使高压开关导电回路电阻的测量及量值溯源和标准器的校准形成一个完整的系统,给出的测量结果不确定度评定适合于通流能力为100A,标称值为10-5～10-2Ω的直流电阻计量器具的校准.该文确立的高压开关设备导电回路电阻量值溯源图,拓展了《直流电阻计量器具检定系统》检定规程,为高压开关设备导电回路电阻量值的准确测量提供了科学合理的方法.     

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.     

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.     

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.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。