A new laboratory method to evaluate the influence of aggregate temperature on the binder-aggregate bonding: first results

In this paper, the effects of aggregates temperature reduction in asphalt mix manufacturing process have been analyzed in terms of complex modulus, fatigue and stripping resistance according to standard tests. The limits of these conventional standardized tests have been analyzed and a new method has been developed to estimate the bitumen-aggregate bonding quality when aggregate temperature is reduced. This method is based on the thermal contact resistance (TCR) assessment at the bitumen-substrate interface which reflects the contact imperfection at the microscopic scale. The study has shown that the TCR decreases when the aggregate temperature increases. Consequently, the TCR could be used as a bonding quality criterion in asphalt manufacturing condition when aggregates temperature is reduced. The results have been well correlated with a modified mechanical stripping test developed. It has been proved that when aggregates temperature decreases, the TCR increases and the stripping resistance decreases due to the poor bitumen-aggregates bonding.     

Effect of Excessive Bias Heating on a Titanium Microbolometer Infrared Detector

In a metal film infrared microbolometer, the responsivity is improved by high bias current to compensate for its low-temperature coefficient of resistance (TCR). However, what are the upper limits of this current without damaging the microbolometer element is not well understood. To study the effects of large bias current, we performed the destructive I-V measurements on an element of a 16$,times,$ 16 Ti-microbolometer array developed at our laboratory and report here the experimental observations of its electrical and physical damages.      

Transcrystallization kinetics at the poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/hemp fibre interface

Transcrystallization of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) on hemp fibres was investigated using polarized optical microscopy. Nucleation and growth of crystals of the transcrystalline region (TCR) were measured during isothermal treatments of samples located in a hot stage. The nucleation rate, nucleation density at saturation and growth rate of the TCR, were determined at crystallization temperatures between 320 and 363 K.The growth rate of crystals in the TCR is the same as that of spherulites in the bulk. Nucleation at the hemp fibres was properly described in terms of the heterogeneous nucleation theory and the transcrystalline growth agrees with the kinetics theory of polymer crystallization. From the empirical data we determined that the interfacial free energy difference function of PHBV on hemp fibres is Δσ = 4.4 erg/cm², lower than the one in the bulk. This indicates that the substrate is not neutral but contributes to the formation of the TCR.From the intensity of the depolarization light, measured under different cooling rates, we determined the activation energies for crystallization in the bulk and transcrystallization.     

Influence of beta phase decomposition on the temperature coefficient of resistivity of titanium alloys

The temperature coefficient of resistivity (TCR) of beta stabilized titanium alloys is sensitive to minor constitutional changes produced by quenching, ageing and precipitate reversion. The influence of omega and alpha phase precipitation on TCR is demonstrated for binary and ternary alloys of composition Ti₈₀(Nb + V)₂₀. It is concluded that TCR measurements provide a sensitive method for detecting the early stages of beta phase decomposition in these alloys.     

High temperature coefficients of resistance of VO2 films grown by excimer-laser-assisted metal organic deposition process for bolometer application

With bolometer application in mind, we prepared VO₂ films on TiO₂ (001) substrates by an excimer-laser-assisted metal organic deposition process at 300 °C or less. A metal-to-insulator transition of VO₂ is expected to induce high temperature coefficient of electrical resistance (TCR) useful for high-performance infrared sensors, but the practical use of crystalline VO₂ films has been prevented due to the accompanied wide hysteresis. In this study, by forming the epitaxial phase only near the substrate interface, the transition of the film was successfully broadened and the hysteresis disappeared. The maximum TCR of the film was more than -10%/°C near room temperature, and the temperature range in which TCR was higher than -4%/°C was very wide (280-320 K).     

导电炭黑填充硅橡胶的电阻温度系数

以炭黑(CB3100)为导电相,硅橡胶为基质制备导电复合材料。研究导电橡胶中炭黑质量分数对电阻温度系数的影响,并用填料对电阻温度系数的影响。以隧道效应理论为基础,给出了导电炭黑填充橡胶的电阻温度系数计算模型,结合实验得到温度对导电炭黑/硅橡胶电阻温度系数的影响主要体现在对其电阻率的影响;基体的体积热膨胀提高复合材料的电阻率,提高了正电阻温度系数;炭黑粒子间的隧道效应降低复合材料的电阻率,增强了负电阻温度系数;在炭黑/硅橡胶中加入少量碳纳米管,利用碳纳米管和炭黑的协同补强效应,使复合材料的导电性和稳定性提高。     

Simultaneous measurement of resistivity and temperature coefficient of resistivity of metallic thin films with the transient hot-strip method

The recently described transient hot-strip method for measuring thermal transport properties of solid insulators has been developed for simultaneously measuring the resistivity ?_F and the temperature coefficient of resistivity (TCR) α_F of metallic thin films. The experimental arrangement is similar to the well-known four-probe technique but the constant current pulse passed through the thin film is sufficiently high to increase its mean temperature by about 1 K. By measuring the time-varying increase or decrease in the resistance, information is obtained not only about the resistivity but also about the TCR.The main advantage of the method is the possibility to measure ?_F and α_F simultaneously without increasing or decreasing the temperature of the film by more than 1 K, i.e. without measurably changing the properties of the film.The method has been tested on unannealed copper films at room temperature.     

Measurement of the Temperature Coefficient of Resistance in Metallic Films with Nano-thickness

The temperature coefficient of resistance (TCR) values of gold and aluminum films deposited on glass substrates were obtained in the range of thickness from 20 nm to 200 nm at 298 K and atmospheric pressure conditions. Applying an electrical current and measuring simultaneously the corresponding changes of voltage (i.e., electrical resistance), and the change of temperature on the thin films, the TCR value was estimated. The measured TCR values show a decrement with the film thickness reduction, and their values are approximately 13.0 % lower than their corresponding bulk values mainly for thinner films. A comparison with previously reported cooper TCR values and the values estimated with the Tellier–Tosser model show good agreement with differences of about 5.0 % between them.     

Properties of evaporated Ni-Cr films with an aluminum content of about 50%

Films with an aluminum content of about 50% in Ni-Cr were produced as a continuation of investigations on multicomponent thin alloy films based on Ni-Cr, because an additional zero transition for the temperature coefficient of resistance (TCR) of these thin films was indicated in the earlier investigations. The alloy films were evaporated in high vacuum onto ceramic substrates and measurements of the TCR and the stability were carried out. It was found that the TCR is less than ±50 ppm K^-1 for aluminum concentrations between 45 and 65 at.%. Such films are suitable for the production of metal film resistors.     

Experimental Study on Thermal Contact Resistance at the End of a Carbon Nanotube

A carbon nanotube (CNT) has a very high intrinsic thermal conductivity and is expected to be used in a variety of thermal applications. However, the thermal contact resistance (TCR) between a CNT and ambient material still remains unclear. Some analytical and molecular dynamics studies have been reported, but there is no reliable experimental method to quantitatively investigate the interface issues. This article reports on a new technique for measuring the TCR at the end of an individual CNT by using a platinum hot film sensor. Two methods are introduced to obtain the TCR between a multi-walled CNT and a SiO₂ surface, and both methods were confirmed to give an identical TCR.     

Fabrication of Ta3N5-Ag nanocomposite thin films with high resistivity and near-zero temperature coefficient of resistance

In this study, we investigate as-deposited Ta₃N₅-Ag nanocomposite thin films with near-zero temperature coefficients of resistance (TCRs) that are fabricated by a reactive co-sputtering method; these films can be used in thin-film embedded resistors. In these films, the TCR approaches zero due to compensation between Ag (+TCR) and Ta-N (−TCR) at resistivities higher than 0.005 Ω-cm.Taking into account the fact that Ag counterbalances the resistivity of the Ta₃N₅-Ag thin film, we performed reactive co-sputtering at a nitrogen partial pressure of 55%, corresponding to a resistivity of 0.384 Ω-cm. The resistivity and power density changed, respectively, from 1.333 Ω-cm and 0.44 W/cm² for silver to 0.0059 Ω-cm and 0.94 W/cm² for the Ta₃N₅-Ag thin film. A near-zero TCR of + 34 ppm/K was obtained at 0.94 W/cm² in the Ta₃N₅-Ag thin film without heat treatment.     

Electrical and structural properties of Ta-N thin film and Ta/Ta-N multilayer for embedded resistor

Ta/Ta-N multilayer has been developed to control temperature coefficient of resistance (TCR) in a thin-film embedded resistor with the incorporation of Ta layer (+ TCR) inserted into Ta-N layers (− TCR). Electrical and structural properties of sputtered Ta, Ta-N and the multilayer films were investigated. The stable resistivity value of 0.0065 Ω·cm in β-Ta film was obtained, and phase change from fcc-TaN to orthorhombic Ta₃N₅ in Ta-N films was observed at nitrogen partial pressure of 22%. The multilayer of Si/Ta(60 nm)/Ta₃N₅(104 nm)/Ta(60 nm)/Ta₃N₅(104 nm) showed TCR value of − 284 ppm/K, where TCR of Ta was − 183 ppm/K and that of Ta₃N₅ was − 3193 ppm/K.     

接触热阻对注塑制品冷却时间的影响

从塑件的瞬态热传导方程出发，推导出了存在在接触热阻时塑件的温度分布吸冷却时间计算的解析表达式，并通过几个简单例子讨论了接触热阻对冷却时间的影响，结果表明，存在热阻时，冷却时间显著增加，随着塑件厚度的增加，热阻的影响逐渐减小。     

Technological considerations when obtaining high-precision resistors with controllable temperature coefficient of resistance

The present paper deals with a study of the technological characteristics of thin film resistors to provide a control in obtaining temperature coefficients of resistance (TCR) of given value. The experimental results are for resistors produced by sublimation of NiCr alloys in vacuum. An analytical dependency of TCR on the sheet conductivity of the deposited layer is found. The resultant equation is proven experimentally and the results are presented graphically. The conditions, in which the deposition of thin NiCr layers of given low TCR values can be controlled, are determined.     

Electrical resistivity-constitution relationships in Ti-Fe and Ti-Ni alloys

The influence of minor modifications in constitution on the temperature coefficient of resistivity (TCR) of beta stabilized titanium-base alloys is demonstrated for binary alloys with iron and nickel. Correlations with constitutional data are reviewed to show that the negativity of TCR occurs over a narrow composition range, corresponding to the threshold for 100% beta stabilization. The results for Ti-Fe and Ti-Ni alloys show that slow quenching rates leading to diffusional transformers, such as the alpha and/or omega phase-precipitation reactions, cause the TCR to increase toward positive values.     

High-Temperature Heat-Shielding Panels with Thermochemical Cooling Based on the Reaction of Steam Conversion of Methane

A method is developed for thermohydraulic analysis of panel-type thermochemical reactors (TCR) with catalytic walls cooled by a gas mixture of methane with steam, in which an endothermal conversion reaction proceeds upon heating. The suggested method provides for all forms of heat transfer in the reactor, including the thermal conductivity of the metal frame in multichannel panels. The results of prediction study of the thermohydraulic characteristics and overall dimensions and weight of such reactors are analyzed.     

Reliability: How much is it worth? Beyond its estimation or prediction, the (net) present value of reliability

In this article, we link an engineering concept, reliability, to a financial and managerial concept, net present value, by exploring the impact of a system's reliability on its revenue generation capability. The framework here developed for non-repairable systems quantitatively captures the value of reliability from a financial standpoint. We show that traditional present value calculations of engineering systems do not account for system reliability, thus over-estimate a system's worth and can therefore lead to flawed investment decisions. It is therefore important to involve reliability engineers upfront before investment decisions are made in technical systems. In addition, the analyses here developed help designers identify the optimal level of reliability that maximizes a system's net present value—the financial value reliability provides to the system minus the cost to achieve this level of reliability. Although we recognize that there are numerous considerations driving the specification of an engineering system's reliability, we contend that the financial analysis of reliability here developed should be made available to decision-makers to support in part, or at least be factored into, the system reliability specification.     

Tolerancing of diffraction-limited Kirkpatrick-Baez synchrotron beamline optics for extreme-ultraviolet metrology

The recent interest in extreme-ultraviolet (EUV) lithography has led to the development of an array of at-wavelength metrologies implemented on synchrotron beamlines. These beamlines commonly use Kirkpatrick-Baez (K-B) systems consisting of two perpendicular, elliptically bent mirrors in series. To achieve high-efficiency focusing into a small spot, unprecedented fabrication and assembly tolerance is required of these systems. Here we present a detailed error-budget analysis and develop a set of specifications for diffraction-limited performance for the K-B optic operating on the EUV interferometry beamline at Lawrence Berkeley National Laboratory's Advanced Light Source. The specifications are based on code v modeling tools developed explicitly for these optical systems. Although developed for one particular system, the alignment sensitivities presented here are relevant to K-B system designs in general.     

Complex amplitude correlations of dynamic laser speckle in complex ABCD optical systems

Within the framework of complex ABCD-matrix theory, exact theoretical expressions are derived for the space-time-lagged cross-covariance functions of the fields valid for arbitrary (complex) ABCD-optical systems, i.e., systems that include Gaussian-shaped apertures and partially developed speckle. Specifically, we show and discuss the results for the three generic systems, i.e., free-space propagation, Fourier transform configuration, and imaging. To cope with various surface structures of varying rms surface heights, we apply two models in addition to employing the usual model for surfaces giving rise to fully developed speckle. The theoretical results found for free-space propagation are supported by interferometrically obtained data.     

Study of polymorphous silicon as thermo-sensing film for infrared detectors

In this work we have deposited and characterized pm-Si:H thin films obtained by plasma deposition. Our aim is to use pm-Si:H as thermo-sensing element for infrared (IR) detectors based on un-cooled microbolometers. We have studied the electrical characteristics of pm-Si:H that are figures of merit important for IR detection, as activation energy, thermal coefficient of resistance (TCR), room temperature conductivity (σ_RT) and responsivity under IR radiation. The influence of the substrate temperature (200 °C and 300 °C) on the pm-Si:H characteristics has been also studied. Our results shown that pm-Si:H is an excellent candidate to be used as thermo-sensing film for microbolometers, due to its large activation energy and TCR, with an improved σ_RT.