Small-signal model for the single-electron transistor: part I

A simple small-signal model of the single-electron transistor is presented. The terminal voltage variations are considered to be sufficiently small to result in small current variations that can be expressed using linearized relations. The derivation of such relations and the development of an equivalent circuit to represent them are presented. Two-port analysis of the small-signal circuit of the single-electron transistor is proposed and explained using various parameters such as impedance parameters, admittance parameters, and hybrid parameters. The variation of the magnitude of these parameters is plotted with respect to frequency. The transconductance and drain resistances and their frequency variation are also discussed. The effect of parasitic capacitance on the proposed small-signal model is also analyzed.     

Studies on dissolution kinetics of dolime in electrothermal magnesium slag

The electrothermal process of magnesium metal production is a promising route, where large sized internally heated reactor is used for magnesium production resulting in less energy and labour intensive and high space-time yield process. However, the dissolution behavior of dolime in the electrothermal slag has been found critical for the process optimization. In this paper, the dissolution kinetics of the dolime in the slag was discussed. Quaternary slag (CaO-Al₂O₃-SiO₂-MgO) was prepared having basicity CaO/SiO₂ ≥ 1.8 and Al₂O₃/SiO₂ ≥ 0.26 for dolime dissolution studies by static hot dip method. Prior to the experiments, FactSage calculations were carried out varying temperatures and slag compositions. In the kinetic studies, dolime particles 10–15 mm size was added in slag melted at 1450, 1500 and 1550°C and samples were taken at various time intervals. The chemical analysis of slag sample was carried out to investigate the dissolution kinetics to establish the rate expression. The activation energy for the process was calculated for different models used in study and was found to be in the range of 130–270 kJ/mol. SEM analysis was done for surface analysis of reacted particles. This study would be helpful in optimizing the dolime charging rate during pilot scale trials for electrothermal magnesium production at CSIR-NML, Jamshedpur.     

Thermodynamic consideration and phase evolution during oxidation of tungsten–copper electrical contactor scraps

Present studies account the feasibility studies on isothermal oxidation of W–Cu hard metal electrical contractor scraps for recycling by roasting-leaching method. This was investigated as one of main processes to produce friable oxidized product amenable to subsequent leaching process. Oxidation is facilitated using scrap turnings instead of solid W–Cu contactor rods. The alloy oxidizes to Cu_xO, WO_x and CuWO₄ upon heating in the temperature range 400–1000°C under oxygen flow. Apart from oxidized W and Cu phases, significant amount of Cu nuggets formed initially at 450°C that rose gravimetrically up to 750°C, and then disappeared at higher temperature. The maximum weight gain was about 22% compared to initial weight when oxidation was carried out at 750°C. Oxidation beyond the temperature of 750°C corresponded to significant loss of tungsten by evaporation of WO₂ · (OH)₂ gaseous product. Thermal oxidation of W–Cu metal electrical contractor tip scraps produced porous and friable oxidized product of W and Cu.