High temperature thermal conductivity of platinum microwire by 3ω method

The 3ω method for thermal conductivity measurement has emerged as an effective technique applicable to micro/nanowires and thin films. This paper describes the adaptation of the method to temperatures as high as 725 K enabling reliable thermal conductivity measurements on such samples for which previously published methods have been found inadequate. In the technique, a sample wire is heated by applying a sinusoidal current at an angular frequency ω, which causes a temperature and resistance variation at an angular frequency, 2ω, leading to a voltage signal at 3ω. The sample is connected as a four-terminal resistor to a digital lock-in amplifier, which is used to detect the in-phase and out-of-phase 3ω voltages resulting from the applied 1ω current. The data are fitted by varying the values of the thermal resistance and diffusion time, both of which are functions of thermal conductivity. Measurements are made at steady state temperatures between 300 and 725 K. Meaningful measurements at elevated temperatures require that thermal losses be understood and minimized. Conduction losses are prevented by suspending the sample above the mounting substrate. Convection losses are minimized by maintaining a vacuum of ~10(-5) torr inside the sample chamber. To minimize radiation losses, an appropriately sized sample is shrouded with a double heat-shield, with the inner shield temperature near that of the sample. Using the 3ω method, the thermal conductivity of platinum was determined to vary between 71.8 and 80.7 Wm(-1) K(-1) over the temperature range of 300 to 725 K, in agreement with published values measured for bulk samples.     

Thermal conductivity measurements using 1ω and 3ω methods revisited for voltage-driven setups

1ω and 3ω methods are widely established transient measurement techniques for the characterization of thermal transport in bulk-materials, thin films, and 1D nano-objects. These methods are based on resistance oscillations of a heater caused by Joule-heating from a sinusoidal current at frequency 1ω which lead to changes in the 1ω voltage and produce a voltage component at 3ω. Although the usual formalism for analyzing the measurement data assumes an ideal current source, voltage-driven measurement setups are employed in many cases. In this context, we find that there has been lack of clarity if a correction generally has to be considered when analyzing the measurement data from voltage driven setups. In this work, Fourier-analysis is employed to show that a correction is not required for 1ω methods and for 3ω measurements that use common-mode-subtraction. Experimental results are presented for a line heater on a fused silica substrate with known thermal properties, and for an individual nickel wire with diameter of 150 nm.     

Note: Non-destructive measurement of thermal effusivity of a solid and liquid using a freestanding serpentine sensor-based 3ω technique

A non-destructive thermal effusivity characterization method described as a freestanding serpentine sensor-based 3ω technique was reported. This freestanding serpentine sensor was fabricated by the mature flexible printed circuit production technique. Expression for the temperature response of the freestanding serpentine sensor with respect to the thermal effusivity of the test sample was presented. The technique was further verified by measuring four kinds of standard samples at room temperature. Experimental results which well agree with reference values demonstrate the new technique is of great application value to thermal effusivity characterization of solids, liquids, and structures to which the conventional 3ω technique is not applicable, e.g., solids with porous surfaces.     

The freestanding sensor-based 3ω technique for measuring thermal conductivity of solids: principle and examination

In recent two decades, the 3ω technique has been proven to be valuable for characterizing thermophysical properties of materials from nanoscale to bulk, but some inherent deficiencies in this technique such as laborious and repeated four-pad micro strip heater/sensor deposition process and flimsiness of the micro heater/sensor limit its practical applications. Here, the authors report a novel 3ω technique, based on a freestanding sensor replacing the conventional 3ω heater/sensor adjacent to the specimen surface. A zigzag temperature response curve of the new sensor instead of the classical straight line was observed and used to extract the specimen thermal conductivity. Experimental results which excellently agree with calculation values show that the new technique is of great application value to thermal properties characterization of amorphous bulks and hundreds of microns thick wafers.     

Multi-variable measurements and optimization of GMAW parameters for API-X42 steel alloy using a hybrid BPNN–PSO approach

This research addresses multi criteria modeling and optimization procedure for Gas Metal Arc Welding (GMAW) process of API-X42 alloy. Experimental data needed for modeling are gathered as per L₃₆ Taguchi matrix. Model inputs include work piece groove angle as well as the five main GMAW process parameters. The proposed back propagation neural network (BPNN) simultaneously predicts weld bead geometry (WBG) and heat affected zone (HAZ). Image processing technique along with Bridge Cam and AWS gauges are used to take accurate measurements of WBGs and HAZs. The adequacy of the developed BPNN is established through comparisons against measured process outputs. Measurements indicate that the BPNN model simulates GMAW process with average errors of 0.33 to 0.82%. Next, the BPNN model is implanted into a particle swarm optimization (PSO) algorithm to simultaneously optimize HAZ and WBG characteristics. The hybrid BPNN–PSO determines process parameters values and groove angle so as a desired WBG is achieved while HAZ is minimized. Verification tests demonstrate that the proposed BPNN–PSO is quite efficient for in multi-criteria modeling and optimization of GMAW.     

Electro-and photochemical studies of gold (Ⅲ) bromide towards a novel laser-based method of gold patterning

In this report, we demonstrate a novel technique for the microscopic patterning of gold by combining the photoreduction of Au~ⅢBr₄^-to Au~ⅠBr₂^-and the electrochemical reduction of Au~ⅠBr₂^-to elemental gold in a single step within solution. While mask-based methods have been the norm for electroplating, the adoption of direct laser writing for flexible, real-time patterning has not been widespread. Through irradiation using a 405 nm...     

Determination of complex permittivity and permeability of lanthanum iron garnet filled PVDF-polymer composite using rectangular waveguide and Nicholson–Ross–Weir (NRW) method at X-band frequencies

In our previous work, the lanthanum iron garnet-filled PVDF-polymer nanocomposite has been prepared. The reflection and transmission coefficients (S-Parameters) of PVDF-13% LIG were measured using rectangular waveguide in conjunction with a microwave vector network analyzer (VNA) at X-band frequencies (8–12 GHz). In order to determine simultaneously the real and imaginary parts of complex permittivity and permeability of nanocomposite sample the Nicholson–Ross–Weir (NRW) method was applied based on the measurement of the S-Parameters of the materials. The general observations of the results indicate that the decreasing in real and imaginary part of complex permeability and real part of complex permittivity resulted in increasing the frequency; meanwhile imaginary part of permittivity tends to become constant when frequency increased.     

Broad-band and high-temperature ultrasonic transducer fabricated using a Pb(In(1∕2)Nb(1∕2))-Pb(Mg(1∕3)Nb(2∕3))-PbTiO3 single crystal∕epoxy 1-3 composite

In this paper, 1-3 composites based on Pb(In(1∕2)Nb(1∕2))-Pb(Mg(1∕3)Nb(2∕3))-PbTiO(3) (PIMNT) single crystal and high-temperature epoxy were fabricated with various volume fractions of PIMNT single crystal ranging from 0.4 to 0.9. The electrical properties were studied as functions of PIMNT volume fraction and temperature, and it revealed that the nature of ultrahigh electromechanical coupling coefficient (0.82-0.93) and low acoustic impedance (17-19 MRayl) of the composites can be retained within a wide temperature range from room temperature to 185?°C. Single element ultrasonic transducer using the PIMNT 1-3 composite was fabricated and characterized as a function of temperature. It was found that the transducer can still work normally at high temperatures, such as 165?°C, possessing a bandwidth of 95% and insertion loss of -27 dB.     

Discrimination of particles by the scintillation pulse shape (in the electron energy range of 0.5–4.0 MeV) using the zero-crossing method

The ratios of the fast to slow components of scintillation pulses produced by neutrons and γ rays have been calculated on the basis of experimental data for several energies in the range of 0.5-4.0 MeV of the electron equivalent. The procedure for discriminating between neutrons and γ rays by measuring the zero-crossing time of a bipolar pulse formed by RC circuits has been simulated for organic scintillators using the Monte Carlo method in the range of 0.012-4.000 MeV of the electron equivalent. It is shown that pulse shape discrimination of particles based on the zero-crossing technique allows rejection of γ-ray background down to a level of 10-4 at particle energies of >100 keV of the electron equivalent (for energies of <50 keV, the γ-ray background is suppressed to a level of 10^-1- 10^-2 and this technique becomes ineffective in principle).     

A data processing method for determining instantaneous angular speed and acceleration of crankshaft in an aircraft engine–propeller system using a magnetic encoder

This paper presents a method for determining the instantaneous angular speed and instantaneous angular acceleration of the crankshaft in a reciprocating engine and propeller dynamical system from electrical pulse signals generated by a magnetic encoder. The method is based on accurate determination of the measured global mean angular speed and precise values of times when leading edges of individual magnetic teeth pass through the magnetic sensor. Under a steady-state operating condition, a discrete deviation time vs. shaft rotational angle series of uniform interval is obtained and used for accurate determination of the crankshaft speed and acceleration. The proposed method for identifying sub- and super-harmonic oscillations in the instantaneous angular speeds and accelerations is new and efficient. Experiments were carried out on a three-cylinder four-stroke Saito 450R model aircraft engine and a Solo propeller in connection with a 64-teeth Admotec KL2202 magnetic encoder and an HS-4 data acquisition system. Comparisons with an independent data processing scheme indicate that the proposed method yields noise-free instantaneous angular speeds and is superior to the finite difference based methods commonly used in the literature.     

Development of a new theory of thermal cutting processes 3. Influence of cutter’s front angle on the cutting temperature and influence of preheating of the blank on the cutting force

Within the framework already established, attention turns to the influence of the cutter’s front angle on the cutting temperature and to the influence of preheating of the blank on the cutting force.     

Computer simulation of a 1.0 GPa piston–cylinder assembly using finite element analysis (FEA)

The paper reports a preliminary study of the behavior of a high performance controlled-clearance piston gauge (CCPG) in the pressure range up to 1 GPa through finite elemental analysis (FEA). The details of the experimental characterization of this CCPG has already been published (Yadav et al., 2007 [1]). We have already pointed out that the use of Heydemann–Welch (HW) model for the characterization of any CCPG, has some limitation due to the fact that the linear extrapolation of the cube root of the fall rate versus jacket pressure (v^1/3–p_j) curve is assumed to be independent of the rheological properties of the pressure transmitting fluids. The FEA technique addresses this problem through simulation and optimization with a standard ANSYS program where the material properties of the piston and cylinder, pressure dependent density and viscosity of the pressure transmitting fluid etc. are to be used as the input parameters. Thus it provides characterization of a pressure balance in terms of effective area and distortion coefficient of the piston and cylinder. The present paper describes the results obtained on systematic studies carried out on the effect of gap profile between piston and cylinder of this controlled-clearance piston gauge, under the influence of applied pressure (p) from 100 MPa to 1000 MPa, on the pressure distortion coefficient (λ) of the assembly. The gap profile is also studied at different applied jacket pressure (p_j) such that p_j/p varied from 0.3, 0.4 and 0.5.     

Disc cutters’ layout design of the full-face rock tunnel boring machine (TBM) using a cooperative coevolutionary algorithm

In rock TBM design the disc cutters’ layout design of the full-face rock tunnel boring machine (TBM) is one of the key technologies. However, there are few published papers in literatures for various reasons. In this paper, based on the engineering technical requirements and the corresponding cutter head’s structure design requirements, a nonlinear multi-objective disc cutters’ layout mathematical model with complex constraints and the corresponding multi-stage solution strategy are presented, in which the whole disc cutters’ layout design process is decomposed into the disc cutters’ spacing design and the disc cutters’ plane layout design. A numerical simulation method based on the FEM theory is adopted to simulate the rock chipping process induced by three TBM disc cutters to determine the optimal cutter spacing. And a cooperative coevolutionary genetic algorithm (CCGA) is adopted to solve the disc cutters’ plane layout design problem. Finally, a disc cutters’ layout design instance of the TBM is presented to demonstrate the feasibility and effectiveness of the proposed method. The computational results show that the proposed method can be used to solve the disc cutters’ layout design problem of the TBM and provide various layout schemes within short running times for the engineers to choose from.     

The parameters measurement of air–water two phase flow using the electrical resistance tomography (ERT) technique in a bubble column

The air–water two-phase flow is investigated in a bubble column with a height of 2 m and a diameter of 0.282 m by using the Electrical Resistance Tomography (ERT) technique. The flow characterization are measured by applying ERT sensors of three vertical sections with superficial gas velocities in the range 0.027–0.156 m/s. Based on the cross-correlation technique and dynamic gas disengagement (DGD) theory, the bubble Saunter diameters are obtained and the local axial velocity about two phases flow can be calculated. The results show that with increased gas superficial velocity the distribution of bubble size is gradually widespread. Moreover, the local velocity of gas bubble swarm has a center peak distribution with increased gas superficial velocity.     

Sorption and Preconcentration of Vanadium,Chromium, Manganese,and Lead on Silica Gel Modified with (3‐Mercaptopropyl) Trimethoxysilane

Abstract

3‐mercaptopropyltrimethoxysilane, (CH₃O)₃SiCH₂CH₂CH₂SH, loaded on silica gel was used as a preconcentration sorbent for V, Cr, Mn and Pb prior to their determination by graphite furnace atomic absorption spetrometry (GFAAS). Surface characteristics and surface area of the silica gel before and after chemical modification were determined by elemental analysis. The retention and recovery of the analyte elements were studied by applying batch and column techniques. The experimental parameters, such as the effect of pH of the sample, shaking time in batch technique, flow rate of the eluent, the concentration of acid solution in the column section, and the amount of silica on retention and elution have been investigated. All elements were quantitatively (≥90%) recovered in the batch technique with R.S.D. values of 3.0 for vanadium, 1.8 for chromium, 1.7 for manganese, and 0.4 for lead. The same recoveries were obtained in the column techniques for all elements, while manganese in sea water could not be succesfully recovered. Detection limits of the method for vanadium, chromium, manganese, and lead are 1.1, 1.4, 1.3, and 0.8 ng, respectively.     

Influence of the Addition of Vanadium Nitride on the Structure and Specifications of a Diamond–(Fe–Cu–Ni–Sn) Composite System

This article discusses the influence of the addition of vanadium nitride on the mechanical and operational properties of diamond composite material based on metallic bond comprised of iron, copper, nickel, and tin obtained by sintering in a mold at 800°C for 1 h with subsequent hot repressing. It has been established that the addition of vanadium nitride in the amount of 2 wt % to diamond–(51Fe–32Cu–9Ni–8Sn) increases the ultimate compressive strength from 846 to 1640 MPa and bending strength from 680 to 1120 MPa, as well as decreases the wear intensity of the composite material from 0.0069 to 0.0033 g/km. The mechanism of improving the tribological properties has been revealed.