Fabrication and characterization of NiCr-based films with high resistivity and low temperature coefficient of resistance

As a metal alloy,NiCr films have a relatively high resistivity and low temperature coefficient of resistance (TCR) and are widely used in electronic components and sensors.However,the resistivity of pure NiCr is insufficient for high-resistance and highly stable film resistors.In this study,a quaternary NiCrAlSi target (47:33:10:10,wt.%) was successfully used to prepare resistor films with resistivities ranging from 1000 to 10 000μΩcm and TCR within±100 ppm/K.An oxygen flow was introduced during the sputtering process.The films exhibit hightemperature stability at 450℃.The films were analyzed using Auger electron spectroscopy,x-ray diffraction,time-of-flight secondary-ion mass spectrometry,and x-ray photoelectron spectroscopy.The results show that the difference in the oxide proportion of the films caused the differences in resistivity.The near-zero TCR values were considered to be due to the competition between silicon and other metals.This study provides new insights into the electrical properties of NiCr-based films containing Si,which will drive the manufacturing of resistors with high resistivity and zero TCR.

Determination of rock mass integrity coefficient using a non-invasive geophysical approach

Determination of rock mechanical parameters is the most important step in rock mass quality evaluation and has significant impacts on geotechnical engineering practice.Rock mass integrity coefficient(KV)is one of the most efficient parameters,which is conventionally determined from boreholes.Such approaches,however,are time-consuming and expensive,offer low data coverage of point measurements,require heavy equipment,and are hardly conducted in steep topographic sites.Hence,borehole approaches cannot assess the subsurface thoroughly for rock mass quality evaluation.Alternatively,use of geophysical methods is non-invasive,rapid and economical.The proposed geophysical approach makes useful empirical correlation between geophysical and geotechnical parameters.We evaluated the rock mass quality via integration between KV measured from the limited boreholes and inverted resistivity obtained from electrical resistivity tomography(ERT).The borehole-ERT correlation provided KV along various geophysical profiles for more detailed 2D/3D(two-/three-dimensional)mapping of rock mass quality.The subsurface was thoroughly evaluated for rock masses with different engineering qualities,including highly weathered rock,semi-weathered rock,and fresh rock.Furthermore,ERT was integrated with induced polarization(IP)to resolve the uncertainty caused by water/clay content.Our results show that the proposed method,compared with the conventional approaches,can reduce the ambiguities caused by inadequate data,and give more accurate insights into the subsurface for rock mass quality evaluation.

Corrected Formula of Bed Resistance Coefficient for Plane Numerical Simulation of Tidal Current

By means of a logarithm law for the velocity profile, a corrected formula of bed resistance coefficient, which involves many factors such as gradient of still water depth, variation of surface elevation, flow direction, and so on, is derived from the 3D governing equations of tidal current by averaging over the whole water depth. Theoretical analysis and application have shown that the 2D plane tidal current numerical model would be more reasonable and could be applied to steep bottom topography when the corrected bed resistance coefficient is used, therefore the results of reproduction simulation and engineering calculation would be more scientific and reasonable.

Study on resistance coefficient in compound channels

This paper presents a further study of the Manning and Darcy-Weisbach resistance coefficients, as they play a significant role in assessing the cross-sectional mean velocity, conveyance capacity and determining the lateral distribution of depth mean velocity and local boundary shear stress in compound channels. The relationships between the local, zonal and overall resistance coefficients, and a wide range of geometries and different roughness between the main channel and the flood plain are established by analyzing a vast amount of experimental data from a British Science and Engineering Research Council Flood Channel Facility （SERC-FCF）. And the experimental results also show that the overall Darcy-Weisbach resistance coefficient for a compound channel is the function of Reynolds number, but the function relationship is different from that for a single channel. By comparing and analyzing the conventional methods with the experimental data to predict composite roughness in compound channels, it is found that these methods are not suitable for compound channels. Moreover, the reason why the conventional methods cannot assess correctly the conveyance capacity of compound channels is also analyzed in this paper.

Analysis of sliding electric contact characteristics in augmented railgun based on the combination of contact resistance and sliding friction coefficient

The contact resistance between the armature and rails is an important indicator of the contact characteristics in electromagnetic launches.As the contact resistance depends not only on the contact state but also on the contact stress and temperature,there are some limitations in analyzing the contact characteristics using only the contact resistance.In this paper,the contact characteristics of the augmented railgun are analyzed by the combination of contact resistance and sliding friction coefficient.Firstly,the theoretical calculation model of the contact resistance and friction coefficient of the augmented electromagnetic railgun is established.Then the contact resistance and friction coefficient are calculated by the measured values of the muzzle voltage,rail current and armature displacement.Finally,the contact characteristics are analyzed according to the features of the waveforms of the contact resistance and the friction coefficient,and the analysis conclusions are verified by experimental rail images.The results showed that:the aluminum melt film gradually formed on the contact surface reduces the contact resistance and the friction coefficient;the wear and erosion of the armature cause deterioration of the contact state;after the transition,the reliability of the sliding contact between the armature and rails decreases,resulting in an increase in contact resistance.

Anisotropy of Expansion Coefficient and Slag Resistance of Spinel Carbon Bricks

Effects of the pressure direction on the thermal expansion and slag corrosion resistance were investigated and anisotropic microstructures of flaky graphite in spinel carbon bricks were examined. The experimental results show that slag corrosion velocities in the direction parallel to the pressure direction display a decrease of 34% compared to those in the vertical direction. Meantime, the linear expansion coefficient in the direction parallel to the pressure direction is 2.45 times as large as that in the vertical pressure direction. Slag corrosion velocities of spinel carbon bricks soaked in the AOD melting slag display a 46%-47% decrease compared to those of magnesia carbon bricks. The microstructure observation shows that spinel carbon bricks have a high degree of preferred orientation.

Uphillshift decision strategy of an AMT off-road vehicle based on generalized road resistance coefficient

In order to improve the shift decision strategy for an off-road vehicle with automated manual transmission（AMT）,the generalized road resistance coefficient is defined based on the longitudinal dynamics analysis.Vehicle mass and generalized road resistance coefficient are estimated using the recursive least square（RLS）method with multiple forgetting factors.The improved shift schedule is designed based on the generalized road resistance coefficient under uphill road condition.The simulation and real vehicle test verify the effectiveness of improved shift strategy and the improvement of vehicle dynamic performance.

Negative Temperature Coefficient of Resistivity in Bulk Nanostructured Ag

The change of the temperature coefficient of resistivity (a) with the particle size, dp, and the grain size, dc, in the nanostructured Ag bulk samples was investigated. dp and dc were controlled by heating the nano-Ag powders over the temperature range from 393 to 453 K. The electrical resistance measurements of the nanostructured Ag bulk samples obtained by compacting the Ag powders after heat treatments showed a change in the sign of a with dP and dc. When dp and dc are smaller or equal to 18 and 11 nm below room temperature or 20 and 12 nm above room temperature, respectively, the sign of the temperature coefficient of resistivity changes from positive to negative. The negative a arises mainly from the high resistivity induced by the particle interfaces with very lowly ordered or even disordered structure, a large volume fraction of interfaces and impurities existing in the interfaces, and the quantum size effect appearing in the nano-Ag grains.

Determination of rock resistant coefficient based on Mohr-Coulomb criterion for underwater tunnel

According to the load-structure method, the wall rock with lining can bear the load caused by the surrounding rock, and the rock resistant coefficient (RRC) is a key parameter for evaluating the capacity of this wall rock. Based on the Mohr-Coulomb yield criterion, this paper develops a formula for calculating the RRC, which has been applied to the real engi-neering project, such as Xiamen Xiang’an East Passage Underwater Tunnel Project. The fact shows that this formula is helpful for designers to determine the RRC value.

Thin Film Chip Resistors with High Resistance and Low Temperature Coefficient of Resistance

High resistance thin film chip resistors(0603 type) were studied,and the specifications are as follows:1 k? with tolerance about ±0.1% after laser trimming and temperature coefficient of resistance(TCR) less than ±15×10-6/℃.Cr-Si-Ta-Al films were prepared with Ar flow rate and sputtering power fixed at 20 standard-state cubic centimeter per minute(sccm) and 100 W,respectively.The experiment shows that the electrical properties of Cr-SiTa-Al deposition films can meet the specification requirements of 0603 type thin film chip resistors when the deposition time was about 11 min and deposition films were annealed at 500 ℃ for 120 min.The morphologies of Cr-Si-TaAl film surfaces were examined by scanning electron microscopy(SEM).The analysis suggests that Ta and Al may be distributed in CrSi2 film with mixed form of several structures(e.g.,bridge-like,capillary-like or island-like structures),and such a structure distribution is responsible for high film resistance and low TCR of Cr-Si-Ta-Al film.

Experimental Study on Rotation Resistance Coefficient of Motor Bogie for Type A Vehicle

Rotation resistance coefficient is an important operating parameter for vehicle bogies, which influences the dynamic behavior of vehicles directly. A research on the rotation resistance coefficient of type A vehicle motor bogies was conducted by means of theoretical calculation, dynamic simulation, test certification, and so on. Result of the simulation analysis shows that the rotation resistance coefficient relates to air springs stiffness and negotiated curve radii, and it varies proportionally with the change of air springs horizontal stiffness. The greater the rotation angle is, the greater the factor becomes. The certifications made under the operating conditions(e.g., different air spring status, different rotation speeds) indicate that the rotation resistance coefficient increases with the increase of the rotation speed. The anti-yaw dampers can contribute to the rotation resistance torque acted on bogie, and the greater the rotation speeds are, the greater the torque generated by the anti-yaw dampers is. The results suggest that the theoretical analysis and dynamics simulation are in accordance with the results from the bogie bench tests, which meet the requirements in EN14363 and the indicators in vehicles safe operation.

The Study on Pipe Sudden Enlargem entLocal Resistant Coefficient

During the design of pipeline,the determination of local resistant coefficient is often come arcoss.The sudden enlargement local resistant coefficient ξ 1=1-A 1A 2 2 is determined through theory.In the paper,the sudden enlargement local resistant coefficient under the conditions of three kinds of A 1A 2 was studied in experiment.In the end ,the result shows that ξ 1 is related not only to two flow cross sections,but also to the velocity.Through experimental research,the relationship between ξ 1,A 1A 2 and V 1 was determined.In a word,the hydraulic calculation of pipeline can be done by taking correspondent ξ 1 ,according to the design velocity V 1 and A 1A 2.

Experimental Study on Influencing Factors of Resistance Coefficient and Residual Resistance Coefficient in Oilfield Z

In order to clarify the major influence factors of resistance coefficient and residual resistance coefficient, so as to provide the basis for optimizing the polymer flooding schemes in oilfield Z of Bohai Sea, artificial cores were made by simulated the characteristic parameters of real reservoir and the spacing of production-injection wells. The main parameters considered include reservoir permeability, polymer solution concentration and polymer injection rate. Core experiment of polymer flooding was taken by considering all the main parameters. The result showed that resistance coefficient and residual resistance coefficient decrease with the increase of core permeability. Resistance coefficient and residual resistance coefficient increase with the increase of concentration of polymer solution. The increment of displacement pressure in low permeability core is higher than in medium and high permeability core. The resistance coefficient increase with higher displacing velocity, and the increment in high permeability core is higher than in low permeability?core. The displacement velocity has little effect on the residual resistance coefficient. The experimental results can effectively guide the formulation of polymer flooding scheme in offshore oilfields, and optimize the appropriate injection rate and concentration of polymer solution for different properties of reservoirs, thus ensuring the effectiveness of polymer flooding in offshore oilfields.

Bogie's Rotational Resistance Coefficient Analysis Based on Novel Parallel Mechanism

In this paper,a novel parallel mechanism which can be used to evaluate body-to-bogie yawtorque is proposed.It can satisfy experimental testing for rotation resistance coefficient(RRC) with various types of bogies,different rotational speeds,and different states of air spring.Aiming at the problem that computing speed of Newton iterative method for solving rotational angle is incompetence to meet the real-time requirements,and also that other methods adopting physical device such as laser displacement sensor to solve rotational angle possess larger measurement error,the analytical techniques method used for solving rotational angle is presented.Finally,by using the upper-single-6-DOF motion platform as an authentic urging mean to simulate a real vehicle,the test was carried out under the speeds of 0.2 and 1.0(°)/s,with the air spring at the inflated and deflated states,respectively.The results showthat the RRC of the bogie under various conditions is less than 0.06,which meets the standard requirement EN-14363.It was also found that the speed of vehicles moving along curves and the state of air spring were key factors influencing the RRC.The feasibilities of this model and test method are verified in this study.

Positive temperature coefficient of resistivity effects of semiconducting (Bi(1/2)Na(1/2)) TiO_3-CaTiO_3-BaTiO_3 ceramics sintered in air atmosphere

Y^3＋-doped （Bi 1/2 Na 1/2） TiO 3-CaTiO 3-BaTiO 3 （BNCBT） positive temperature coefficient of resistivity （PTCR） ceramics sintered in air atmosphere were investigated in this study. （Bi 1/2 Na 1/2） TiO 3 （BNT） component can remarkably increase the onset temperature T c of PTCR ceramics with the expense of the resistivity R 25 increase. CaTiO 3 （9–27 mol%） component can decrease the resistivity, and adjust the effects of BNT phase on the T c point. For the sample containing 3 mol% CaTiO 3 , T c raises from 122 ℃ to 153 ℃ when only 0.6 mol% BNT added, while for the ones with higher CaTiO 3 content （9–27 mol%）, T c is only increased by a rate of 8–9℃/1.0 mol% BNT. The effects of BNT and CaTiO 3 components on R25/Rmin （negative temperature coefficient effect） are also discussed.

Experimental Determination of Local Resistance Coefficient of Sudden Expansion Tube

Theoretical derivation of local resistance coefficient of sudden expansion tube is presented. Several assumptions are analyzed in the theoretical derivation. That the head loss shall be neglected is affirmed. Experimental data proves that the pressure before and after sudden expansion section is basically the same. That the friction force on the side face of control body is neglected is denied and it is pointed out that such neglect is the main cause for error between theoretical calculation and actual measurement. Experimental device for measuring local resistance coefficient is designed in combination with theoretical derivation process. Optimal gradually varied flow section is selected after sudden expansion pipe in Bernoulli equation based on variation of piezometer tube head. It is pointed out in accordance with experimental data analysis that the value of local resistance coefficient of sudden expansion tube determined through experimental data is closer to the actual situation during pipeline design.

金枪鱼延绳钓单丝和绳索的惯性力系数和阻力系数研究

金枪鱼延绳钓单丝和绳索的惯性力系数CM和阻力系数CD取值直接影响到渔具数值模拟的计算速度和精度。通过波浪水槽试验探究了7种金枪鱼延绳钓单丝和绳索材料在规则波条件下所受的波浪力,并在Morison方程的基础上,使用最小二乘法计算出相应材料的CM和CD;分析了CM和CD随KC数和雷诺数Re的变化情况。结果显示:同一波高下,试验材料所受波浪力随着波浪周期增加逐渐增加;同一波浪周期下,试验材料所受波浪力随波高增加逐渐增加;相同材料随着直径增加,所受波浪力增加;3种尼龙单丝随着KC数增加CD逐渐增加,CM变化不明显,趋于常数,随着雷诺数Re的增加CM和CD有逐渐增加的趋势;3种聚丙烯绳索CM随着KC数和雷诺数Re增加而增加,CD在低KC数时较为平稳,其随着雷诺数Re增加逐渐下降,趋于常数;涂沥青的聚丙烯绳索的CM和CD较为稳定。研究表明,本试验得出的CD和CM,可用于延绳钓渔具数值模拟。

偏组成堇青石陶瓷材料结构与性能

堇青石陶瓷具有热膨胀系数低、抗热震性好、耐高温等特点,被广泛应用于高低温急剧变化的环境。如何进一步降低堇青石陶瓷的热膨胀系数,提升其使用性能,仍然是国内外研究的热点,以单层片状结构的苏州高岭土、滑石和γ-Al_(2)O_(3)为原料,设计了不同的配比组成并制备了堇青石低膨胀陶瓷样品。采用XRD、SEM、CTE和EPMA等测试技术对样品的结构和性能进行了表征。探究了偏化学计量不同配比组成对合成堇青石陶瓷的结构与性能的影响。结果表明:偏镁样品(Si/Al为1.34时)合成的是单一的纯相堇青石;样品的热膨胀系数为1.91×10^(-6)℃^(-1) (25℃~800℃),抗折强度为50 MPa,气孔率为20%,体积密度为1.90 g·cm^(-3)。风冷热震循环试验(25℃~1000℃) 30次后抗折强度损失率仅为2.66%。偏镁组成中的MgO促进了高温液相的生成,液相传质推动高温化学反应充分进行,提高了样品中的堇青石含量(达到了99 wt.%),生成的堇青石晶粒定向排列,降低了样品的热膨胀系数,提高了样品的抗热震性。

炉腹煤气量指数和透气阻力系数在马钢2号高炉的应用

对炉腹煤气量指数X_(BG)和透气阻力系数K在马钢2号高炉的应用进行了总结。通过对2号高炉1年多的生产数据跟踪分析,结果表明:X_(BG)控制在63~64m/min,对应炉腹煤气量VBc控制在6300~6400m^(3)/min时,高炉稳定顺行,燃料比较为稳定;针对2号高炉炉腹渣皮厚、炉腹温度整体偏低现象,风压控制在靠上限水平,K值实际控制在4.25~4.75为宜,高炉运行状态良好。认为炉腹煤气量指数和透气阻力系数都是综合操作参数,在高炉日常操作中,可以用此来判断炉况,衡量强化程度,使炉况保持稳定顺行,技术经济指标改善。

核动力系统分析中细管簇当量元件阻力

为研究不同工况下核动力系统主管路的参数变化,需选择合适的阻力元件当量代替部件内部细管簇的流动阻力.根据流体流动规律,设计了一种圆弧渐缩渐扩式当量阻力元件,采用标准k-ε湍流模型探究该阻力元件对圆管内部流动的影响,对比分析得到阻力系数ζ与缩径比d/D和阻力元件长度L的基本规律,最后拟合并验证所得关系式.结果表明:该阻力元件对下游管道影响相对较小,可用于当量代替复杂部件内部流动阻力;排除雷诺数Re对该元件阻力系数ζ的影响,ζ与d/D和L均呈负相关,且d/D越小,L越短,中心轴向速度和湍动能变化越大,下游恢复区长度就越长;经验证,Re>3.0×106,d/D=0.5~0.9时,拟合的指数函数关系式预测的ζ更准确,并且该指数函数能够实现某蒸汽发生器内部细管簇的简化.