Effect of heat input and weld chemistry on mechanical and microstructural aspects of double side welded austenitic stainless steel 321 grade using tungsten inert gas arc welding process

Stainless steel 321 is a stabilized austenitic grade that prevents the formation of chromium carbides at the grain boundaries and subsequently reduces the risk of corrosion attack at the weld surface by forming titanium carbide. It is primarily used in industries such as pressure vessels, boilers, nuclear reactors, carburetors and car exhaust systems. In order to assess the effect of gas tungsten arc welding process parameters on weld penetration, the proposed Taguchi L₉ orthogonal matrix has been selected with two factors and three levels for welding austenitic stainless steel 321 by adjusting the welding current and welding speed. Bead-on-plate experiments were performed on base metal of 6 mm thick plate by changing the process parameters, and corresponding weld bead measurement and macrostructure images are examined. Maximum depth of penetration −3.3017 mm is achieved with a heat input −1.4058 kJ/mm, i. e., welding current-220 A and welding speed-120 mm/min. Double-side arc welding technique is used to obtain full penetration on 6 mm thick plate. The quality of the weldment was assessed using non-destructive radiography inspection. Mechanical integrity and microstructural characteristics of the weldments were studied using tensile (transverse and longitudinal), bend, impact, microhardness, optical microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction analysis, ferrite number measurement and scanning electron microscope. The results reveal that the double side-tungsten inert gas weldment have better mechanical properties. It is corroborated from the weld metal microstructure that it contains γ-austenite, δ-ferrite and titanium carbides (intermetallic compounds). X-ray diffraction analysis and energy dispersive x-ray spectroscopy plots confirm the increase in the ferrite phase in weld metal. The ferrite measurement results show that the ferrite volume in the base metal and weld metal is 1.2 percent and 6.1 percent respectively. In addition, the higher δ-ferrite volume in the weldment helps in attaining superior mechanical integrity. Fractography shows that the failure mode of the weld metal and the base metal is ductile.     

Growth of homogeneous polycrystalline Si1-xGex and Mg2Si1-xGex for thermoelectric application

Homogeneous polycrystalline Si_1-xGe_x were grown using a Si(seed)/Ge/Si(feed) sandwich structure under the low temperature gradient less than 0.4 °C/mm. It was found that the composition of the Si_1-xGe_x was controlled by the growth temperature. The homogeneous Mg₂Si_1-xGe_x was synthesized by heat treatment of the homogeneous Si_1-xGe_x powders under Mg vapor. The Mg₂Si_1-xGe_x sample with the relative density of 95% was synthesized by spark plasma sintering technique. The resistivity and the Seebeck coefficient of the Si, Ge, Si_1-xGe_x and Mg₂Si_1-xGe_x samples were evaluated as a function of temperature. It indicated that Seebeck coefficients of the Si_1-xGe_x and Mg₂Si_1-xGe_x samples were higher than those of Si and Ge. Moreover, the Seebeck coefficient of Mg₂Si_0.7Ge_0.3 sample was higher than that of Mg₂Si_0.5Ge_0.5 and Si_0.5Ge_0.5 samples.     

Monte Carlo simulation of transport process of the sputtered species in the facing target sputtering technique

In facing target sputtering (FTS) technique two targets facing each other are sputtered simultaneously and the particles are collected in the off axis position. When these two targets constitute two different materials having different sputtering yields, the deposited films show a gradation in composition along the axis parallel to the targets. The process parameters involved, increase the complexity of understanding the composition profile of the deposited films. Here an attempt has been made to simulate the transport behavior of the sputtered species, which leads to the theoretical realization of the variation in composition. The simulation has been performed for SmCo system using the Monte Carlo approach based on the empirical formula proposed by Sigmund and Thompson. The theoretical results have been compared with the experimental results obtained and are explained in detail.     

Temperature dependent grain-size and microstrain of CdO thin films prepared by spray pyrolysis method

CdO thin films on glass substrate were prepared by home built spray pyrolysis unit from aqueous solution of Cd(CH₃COO)₂·2H₂O at different substrate temperatures. X-ray diffraction (XRD) studies indicate the formation of polycrystalline cubic CdO phase with preferential orientation along (111) plane. X-ray line broadening technique is adopted to study the effect of substrate temperature on microstructural parameters such as grain size and microstrain. Scanning electron microscopy (SEM) shows that the film prepared at 250°C consists of spherical shape grains with size in nanometer range and is comparable with the XRD studies.     

Structural and magnetic property studies on low temperature chemically synthesised one-dimensional Zn1−xNixO nanorods

One-dimensional Zn_1?xNi_xO nanorods have been established through a facile surfactant/template free low temperature hydrothermal route, which involves the direct growth of the nanorod-like structures from an aqueous alkaline phase. The monophasic wurtzite structure of the Ni-doped ZnO nanocrystallites were initially studied using the X-ray diffractograms and their rod-like morphological appearance and homogeneity were analyzed through the aid of electron microscopes. Moreover, the substitution of Ni ions was found to contain the oxygen related vacancies and defect states in the nanostructures, through suppressing the E₂(high) and E₁(LO) modes in the Raman spectra. A similar trend was also observed in the subband gap emission, over the visible region of the emission spectra. The magnetic property studies on the Zn_1?xNi_xO semiconducting nanorods revealed the presence of paramagnetic characteristics at room temperature and antiferromagnetic interactions at 20 K.     

A heuristic reference recursive recipe for adaptively tuning the Kalman filter statistics part-1: formulation and simulation studies

Since the innovation of the ubiquitous Kalman filter more than five decades back it is well known that to obtain the best possible estimates the tuning of its statistics \({\mathbf{X}}_{\mathbf{0}}\), \({\mathbf{P}}_{\mathbf{0}}\), \(\Theta \), R and Q namely initial state and covariance, unknown parameters, and the measurement and state noise covariances is very crucial. The manual and other approaches have not matured to a routine approach applicable for any general problem. The present reference recursive recipe (RRR) utilizes the prior, posterior, and smoothed state estimates as well as their covariances to balance the state and measurement equations and thus form generalized cost functions. The filter covariance at the end of each pass is heuristically scaled up by the number of data points and further trimmed to provide the \({\mathbf{P}}_{\mathbf{0}}\) for subsequent passes. The importance of \({\mathbf{P}}_{\mathbf{0}}\) as the probability matching prior between the frequentist approach via optimization and the Bayesian approach of the Kalman filter is stressed. A simultaneous and proper choice for Q and R based on the filter sample statistics and other covariances leads to a stable filter operation after a few iterations. A typical simulation study of a spring, mass and damper system with a weak nonlinear spring constant by RRR shows it to be better than earlier techniques. Part-2 of the paper further consolidates the present approach based on an analysis of real flight test data.     

Low-temperature synthesis of hexamethylenetetramine-stabilised ZnS nanoparticles and its photocatalytic properties

ZnS nanoparticles have been synthesised at low temperature by short reaction (80°C for 2?h) via wet chemical route. The nanoparticles were stabilised using hexamethylenetetramine (HMTA) as surfactant in aqueous solution. The average particle size calculated from X-ray diffraction studies was about 4?nm with cubic zincblende structure. The presence of HMTA in the synthesised ZnS nanoparticles was confirmed by FTIR studies. A significant blue shift was observed in the optical absorption band edge for the ZnS nanoparticles as compared to the bulk, indicating a strong quantum confinement. The room temperature photoluminescence (PL) spectrum showed a broad green emission peak at around 502?nm. The photocatalytic property of HMTA-stabilised ZnS nanoparticles were investigated on the decolourisation of methylene blue aqueous solution under UV light irradiation.     

Removal and recovery of metal ions from acid mine drainage using lignite--A low cost sorbent

Acid mine drainage (AMD), has long been a significant environmental problem resulting from the microbial oxidation of iron pyrite in presence of water and air, affording an acidic solution that contains toxic metal ions. The main objective of this study was to remove and recover metal ions from acid mine drainage (AMD) by using lignite, a low cost sorbent. Lignite has been characterized and used for the AMD treatment. Sorption of ferrous, ferric, manganese, zinc and calcium in multi-component aqueous systems was investigated. Studies were performed at different pH to find optimum pH. To simulate industrial conditions for acid mine wastewater treatment, all the studies were performed using single and multi-columns setup in down flow mode. The empty bed contact time (EBCT) model was used for minimizing the sorbent usage. Recovery of the metal ions as well as regeneration of sorbent was achieved successfully using 0.1 M nitric acid without dismantling the columns.     

Mechanical and barrier properties of epoxy polymer filled with nanolayered silicate clay particles

The diglycidyl ether of bisphenol A (DGEBA) epoxy resin system filled with organo clay (OC) and unmodified clay (UC) were processed separately by two different curing agents. Triethylene tetramine (TETA) and Diaminodiphenyl methane (DDM) hardeners were used as curing agents. The nanocomposites were processed by shear mixing at different clay concentrations (1, 2, 3,5 and 10 wt%). The OC and UC were characterized by x-ray diffraction (XRD) technique. The morphology of the nanocomposites was obtained by XRD and Transmission Electron Microscopy (TEM). Bending and Impact tests conducted on these materials revealed that the organo clay filled epoxy resin showed good improvement in property over unmodified clay filled epoxy composites. The mass uptake of the nanocomposites was studied in the acid, base and water mediums. It is observed that the mass uptake in the acid medium is higher than in other mediums. The equilibrium mass uptake in all the mediums for nanocomposites was found to be lower compared to neat epoxy polymer system.     

利用计算机控制太阳能采暖系统

太阳能采暖系统采用微机监控系统后,既提高了系统运行水平,又提高了供热质量。系统投入自动运行后,供回水温度始终在规定的范围内运行。当水箱中的水温达不到规定范围时,电加热器会自动启动对供水进行加热直至达到规定值;同时,水箱中的水位过低或过高时,报警装置会自动启动报警并采取措施。通过实时曲线和报表还可以随时了解到系统运行时的详细情况,通过历史趋势曲线和历史报表查询任意时间段的历史数据,对整个系统有更全面的了解,以保证系统安全,经济地运行。