Volume 32, Issue 2

Silicon is the most common material used in solar cells. High cost of silicon restricts the widely use of PV power. In order to make solar cells more accessible and affordable, it is strongly needed to develop a new and low-cost production process of solar energy silicon (SoG-Si). Electrodeposition of SoG-Si films appears to be a cost saving technique since solidification and sawing steps which contribute significantly to the overall cost of solar cells will be bypassed. Electrodeposition of SoG-Si has been evaluated during the last three decades, and some of them have shown promising results. Thermodynamic and kinetic considerations which relate to the electrodeposition of silicon are discussed, and progresses towards the developments of the electrodeposition of silicon in high temperature molten salts are reviewed in this paper.

This work has aims to study and develop the novel nanostructural quaternary thin film material for cutting tools and other applications with both high hardness value and good thermal stability at high temperature. The quaternary compound of TiAlCrN superhard coating material was deposited on tungsten carbide (WC-Co) substrates using cathodic arc deposition techniques at the deposition temperature of 623 K. The structures of the coatings were fundamentally examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and atomic force microscopy (AFM). The coating hardness and elastic modulus tests were performed and investigated by nanoindentation testing method. The maximum hardness and elastic modulus values as measured by nanoindentation tests are at 53 GPa and 887 GPa, respectively. Scratch tests were performed on thin films deposited in various conditions. The critical loads to the coating failure of the resultant coatings are above 75 N.

In this work, an Nb-14Si-24Ti alloy (at.%) was prepared by liquid-metal-cooled directional solidification (DS) and then heat treated (HT) at 1450°C for 100 h. The effects of the withdrawal rate and heat treatment on the microstructure were investigated. The results show that the DS samples consisted of Nb SS dendrites, Nb 3 Si blocks and eutectic Nb SS /Nb 3 Si. As the withdrawal rate increased, the microstructure became finer, the volume fraction of eutectic Nb SS /Nb 3 Si increased and the morphology of eutectic cell transformed from petaloid to regularly arranged granular morphology. The microstructure of the HT samples consisted of Nb SS and Nb 3 Si. The metastable phase of Nb 3 Si did not discompose through the eutectoid reaction. The dendritic Nb SS connected through diffraction and the secondary dendrite arm got coarser. The boundary of eutectic Nb SS /Nb 3 Si became blurry and the black Ti-rich phase of the DS samples in this region disappeared. The Nb 3 Si connected to form the continuous matrix. The granular Nb SS of eutectics spheroidized and the lamellar Nb SS of eutectic interconnected and became more bending distributed uniformly in the Nb 3 Si matrix.

Three different steel compositions with 1, 3 and 5 mass% Si were prepared using atomized iron (ASC.100.29) and 0.35 mass% natural graphite powders. The mixed powders were cold pressed at 700 MPa and sintered at 1200 °C for 30 min under pure Ar gas atmosphere. Some of the sintered specimens was quenched from 850 °C and then tempered at 100 °C for 1 h. The other sintered specimens were annealed at intercritical heat treatment temperature of 750 °C for 10 min and rapidly water-quenched. The experimental results showed that in as-sintered specimens inhomogeneously dispersed typical pearlitic structure in the ferrite matrix formed and its amount decreased with increasing Si content. In intercritically annealed specimens, the microstructure obtained was a mixture of partially transformed martensite and ferrite + pearlite. In quenched plus tempered specimens, beside tempered martensite, ferritic structure formed and its amount increased with increasing Si content. The wear tests were carried out under dry sliding conditions using a pin-on-disk type machine at constant load, speed and sliding distance. It was seen that, in all specimens, the friction coefficient and the wear rate both increased with increasing Si content. The increase of these values was less in the heat treated specimen than the as-sintered specimen.

We have successfully synthesized Sb 2 O 3 nanostructures using ultrasonic waves. We have also synthesized a brominated compound via a simple chemical reaction. In order to improve the thermal stability of the polymeric nanocomposites, Sb 2 O 3 and brominated compound were added to the poly methyl methacrylate (PMMA) acrylonitrile-butadiene-styrene (ABS), cellulose acetate (CA) and poly styrene (PS). The influence of flame retardant additives on the thermal properties of polymer matrixes was studied using thermogravimetric analysis (TGA) and derivative thermogravimetric analysis (DTG). We found that the thermal decomposition of the nanocomposites shifts towards higher temperatures as a result of synergistic effect between Sb 2 O 3 and brominated compound. The nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy.

Based on the measurement of roll forces during the laboratory hot rolling of flat samples graded in thickness, the new phenomenological type of mean flow stress model was developed and applied on plain-carbon and HSLA steels. The obtained models describe with a very good accuracy the hot deformation resistance characteristics in the temperature range 1123 to 1463 K, large effective strain, and strain rate in the useful range of approximately 10 to 100 s −1 . Difficulty in the mathematical description of the influence of temperature on mean flow stress in the wide range of temperature by a single equation was solved by introducing another constant in the temperature member of the conventional model. The newly proposed model solves by phenomenological means a frequent problem of heteroscedasticity of relative deviations between the calculated and experimental values of mean flow stress values depending on temperature. It becomes more reliable from the viewpoint of the operational application, e.g. fast prediction of mean flow stress values and power/force parameters necessary in the steering systems of hot rolling mills.

It is an important issue to calculate the physicochemical properties of aluminosilicate melt based on some known data. However, it is also a difficult issue to do so, especially for a multicomponent slag system since the available data are very limited due to the difficulty of experimental measurement at high temperature. In this paper, a method is suggested to resolve this problem, which is particularly significant. This model can be well used to estimate the electrical conductivity, viscosity, molar volume and surface tension of aluminosilicate melt.

Influence of the methodology of mathematical processing of experimental data on the calculated value of the activation energy in hot forming was evaluated for three very different alloys: iron aluminide, low-alloyed steel and magnesium alloy. Application of the mean strain rates is appropriate but calculations with use of nominal strain rates of the plastometric tests do not give significantly different results. Calculations based on the processing of the simplified power dependence between strain rate and peak stress can give the results differing very substantially from those that were gained by the solution of the complex hyperbolic relationship. This has negative impacts, particularly at prediction of the maximum flow stress in the broad range of forming conditions, represented by the Zener-Hollomon parameter.

Mercury selenide nanostructures were synthesized from the reaction of N , N ′-bis(salicylidene)propane-1,3-diamine mercury complex, (Hg(Salpn)) as a novel precursor, via sonochemical method. The effect of different surfactant on the morphology and particle size of the products was investigated. Products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy and X-ray energy dispersive spectroscopy (EDS).

This paper presents and analyzes the responses of non-alloy structural steel (1.0044) subjected to uniaxial stresses at high temperatures. This research has two important determinants. The first one is determination of stress-strain dependence and the second is monitoring the behavior of materials subjected to a constant stress at constant temperature over time. Experimental results refer to mechanical properties, elastic modulus, total elongations, creep resistance and Charpy V-notch impact energy. Experimental results show that the tensile strength and yield strength of the considered material fall when the temperature rises over 523 K. Significant decrease in value is especially noticeable when the temperature rises over 723 K. In addition, engineering assessment of fracture toughness was made on the basis of Charpy impact energy. It is visible that when temperature raises then impact energy increases very slightly.

A series of nanocomposites consist of organic polyimide and organo-modified clay content varying from 0 to 10 mass%, were successfully prepared by in situ polymerization. Polyimide used as a matrix of nanocomposite was prepared through the reaction of 1,2-bis(4-aminophenoxy)ethane (BAE) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) in N,N-dimethylacetamide (DMAC). The resulting nanocomposite films were characterized by FT-IR spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA).

Boron-doped BaTiO 3 precurors (BaTi 1−x B 2x O 3+X ) were prepared via the glycol-glycerol complexes of boron, titanium (IV), and barium. With optimum composition, ceramics with dielectric properties comparable to those of pristine BaTiO 3 ceramic sintered at 1300°C can be obtained after sintered at temperature less than 900°C (room-temperature dielectric constant ∼4000, dielectric strength ∼7.0 kV/mm). The appreciable decrease in sintering temperature is attributable to (a) addition of boron dopant as substitute of titamium rather than to stochiometric BaTiO 3 , and (b) application of glycol-glycerol solvents/ligands in the synthesis of precursors, which guarantees the compositional homogenization of the final ceramics.

The α - β transition ( T Q  = 578°C) is studied in quartz by analyzing the experimental heat capacity C p data taken from the literature, using a power-law formula. Values of the critical exponent α for C p are extracted below and above T Q , which describe the α - β transition as a second order transition in quartz. The α values obtained here are compared with the predictions of the theoretical models.