SmFeO_3的制备及其多波段兼容隐身性能研究

采用固相法制得了SmFeO3粉体.借助XRD、SEM对SmFeO3粉体的物相组成和形貌进行了表征.此外,测试了SmFeO3的微波电磁特性及其吸波性能、红外辐射率以及1.06 μm波长处的反射率性能.结果表明,当煅烧温度为1250℃时,可以制得单一相的SmFeO3粉体;该粉体宏观呈现橙红色,微观颗粒尺寸大小为2～4μm的不规则块状.当单层SmFeO3材料的厚度为2.0mm时,反射损耗在15.8GHz左右出现约为-10dB的峰值,同时在14.3～16.8 GHz频率范围内反射损耗均达到-5dB.SmFeO3粉体在1.06μm波长处的反射率为0.31%,激光吸收性能强;红外辐射率为0.58,属于中低红外辐射率.     

铁基FeSiBPCu纳米晶软磁合金粉体的制备及电磁波吸收性能

通过高能球磨法制备Fe_(83.3)Si_4B_8P_4Cu_(0.7)纳米晶软磁合金粉体,研究了球磨时间对粉体结构、形貌、电磁参数及电磁波吸收性能的影响。采用XRD和SEM对粉体的微结构及形貌进行表征和观察,采用矢量网络分析仪在2～18 GHz范围内测量粉体的电磁参数,进而评价其吸波性能。结果表明,Fe_(83.3)Si_4B_8P_4Cu_(0.7)合金经20～140 h球磨后可形成平均颗粒尺寸为4.7～10.9μm的近球形粉体;粉体具有α-Fe纳米晶和非晶相组成的双相复合结构,α-Fe平均晶粒尺寸随球磨时间的延长逐渐减小而后维持在6 nm左右;合金粉体具有优异的软磁性能,经球磨100 h后粉体的饱和磁化强度达到最大值182.3 emu/g;粉体具有高的磁导率、合适的介电常数以及出色的吸波性能,由球磨100 h后的纳米晶粉体/石蜡构成的厚度为2 mm的复合样品在11.5 GHz下具有反射损耗最低值(RL_(min)为-44.0 dB),且有效吸收频率范围为9.2～15.0 GHz,有效吸收带宽可达5.8 GHz。     

粉煤灰空心微珠的Co-Ni-P化学镀及镀层的吸波性能

为了实现吸波材料的薄型化及轻量化,采用化学镀工艺对粉煤灰空心微珠(5μm级)进行表面电磁改性,制备出"核-壳"结构新型轻质复合粉体吸波材料,探讨了Co-Ni-P化学镀工艺参数对吸波性能的影响.借助SEM,EDS和微波矢量网络分析仪研究了施镀工艺参数对镀层形貌、成分与吸波性能的影响.结果表明,空心微珠表面镀层由粒径0.5...     

原位生长FeCo/rGo纳米复合材料的电磁波吸收性能研究

利用化学开发高性能吸波材料是解决电磁污染问题和实现军事装备雷达隐身的有效手段。基于化学原位生长策略,以金属离子Fe²⁺和Co²⁺为原料,采用一步水热法制备FeCo/rGo复合材料,并对其形貌、结构以及吸波性能进行测试和分析。结果表明,当FeCo和氧化石墨烯的复合比为1∶0.5在厚度1.9 mm时有效吸收带宽达到5.5 GHz,其最小反射损耗达到-54.14 dB。复合比为1∶1时则实现了1.3 mm, 4.5 GHz有效吸收带宽的吸波性能,这表明FeCo/rGo磁性材料有望成为一种极具应用价值的电磁吸波材料。     

PVP的添加对BaZn_2Fe_(16)O_(27)铁氧体吸波性能及其机理的影响

采用sol-gel法制备W型BaZn2Fe16O27铁氧体,借助XRD、SEM和网络分析仪等手段研究了PVP的添加对样品的电磁性能及吸波机理的影响。结果表明,添加PVP制备BaZn2Fe16O27铁氧体并不改变其物相组成,但是片状颗粒的厚度由1μm增加到5μm左右。添加2%PVP制得的样品在10~18 GHz频率范围内的相对输入阻抗更接近于1,并且在10~17 GHz频率范围内的磁损耗能力增强。通过适量添加PVP制备BaZn2Fe16O27铁氧体可以改善其吸波性能,其反射损耗峰值由-15.7 dB增加到-19 dB。     

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。     

铁氧体Ba(Zn_(1-x)Co_x)_2Fe_(16)O_(27)/环氧树脂复合材料吸波性能

采用化学共沉+高温助熔工艺制备了铁氧体Ba(Zn(1-x)Cox)2Fe16O27粉体,然后用模压法制备了铁氧体粉体/环氧树脂复合材料板,采用同轴电缆法测定了复合材料的电磁参数。研究表明,随着铁氧体中Co含量增加,铁氧体主相由BaZn2Fe16O27转变成Ba-Co2Fe16O27,材料磁损耗逐渐加强,复合材料与空气的电磁匹配特性在频率低于12GHz时较好。然后将M-玻璃纤维/环氧树脂复合材料置于铁氧体粉体/环氧树脂复合材料前端组合成多层复合材料结构,复合材料板与空气的电磁匹配性能和吸波性能都有很大提高。数据如下:当复合材料结构中x=0.75铁氧体吸波层厚度为2.0mm,结构总厚度5.3mm时,复合结构反射系数R的绝对值在2～8GHz时4dB、在8～18GHz时10dB的吸波性能。     

沉积温度对纳米碳管-铁粒子复合物的制备及吸波性能影响（英文）

采用金属有机化学气相沉积(MOCVD)工艺,以Fe(CO)_5为前驱体,在CNTs表面原位生长纳米级Fe粒子,通过改变沉积温度,调控复合粉体的形貌结构和吸波性能。用X射线衍射仪、场发射电子显微镜、透射电子显微镜和矢量网络分析仪对粉末的结构及电磁性能进行表征并对其吸波性能进行研究。结果表明,随着沉积温度升高(210～240℃),沉积到CNTs表面的Fe粒子逐渐增加;沉积温度过高时(270℃)会造成CNTS表面Fe粒子团聚。通过调节沉积温度,可以调控CNTs-Fe复合粉体的电磁性能。以吸波性能为考察指标,最终确定最佳的沉积温度为240℃。以沉积温度为240℃时所获样品的电磁参数,模拟计算出涂层厚度为2.9 mm时,反射率达到最小值为-28.3 dB,小于-10 dB的吸波带宽最大为6.1 GHz(10.2～16.3 GHz)。     

石英玻璃纤维表面吸波涂层包覆及其吸波性能研究

四针状氧化锌晶须(T-ZnOw)具有独特的三维四针状结构,具有材料增强、抗静电、吸波性等特性,是一种理想的介电损耗吸收剂。四针状氧化锌晶须(T-ZnOw)作为吸收剂、酚醛树脂为粘结剂配制吸波浆料,涂覆在石英玻璃纤维表面,制备新型的吸波纤维布。研究表明,T-ZnOw作为介电损耗吸收剂,能有效提高石英玻璃纤维的吸波性能;纤维电阻率会影响纤维的吸波性能,理想的纤维电阻率在0.21Ω·cm左右。调节处理温度可以有效调节纤维电阻率,最佳处理温度为850℃;涂层不连续周期分布纤维相较于涂层连续分布纤维能提高纤维低频吸波性能和宽频吸波性。     

吸波剂含量和涂层厚度对微波吸收性能的影响

以具有强磁损耗特性的磁粉、电阻型和电介质型物质作为吸波剂,制备出了具有阻抗渐变结构的3层复合雷达吸波涂层,研究了吸波剂用量和涂层厚度对吸波性能的影响.结果表明,增加表层、中层或底层吸波剂含量及涂层厚度,均能使吸波性能曲线向低频端方向移动,反之,吸波性能曲线向高频端方向移动;选择适当的吸波剂含量或者一定厚度的涂层才能拓宽、加深吸波性能.制得的试样中反射损耗可达-35.74和-39.25dB,其频宽(＜-10dB)分别为3.52和2.84GHz.     

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.     

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)。