P. Gębara

Combustion synthesis of silicon by magnesiothermic reduction

GRAPHICAL ABSTRACT ABSTRACT Magnesiothermic reduction of silica is a powerful method for producing silicon owing to its simplicity, low reduction temperature and low production cost. However, the inevitable formation of magnesium silicide (Mg2Si) limits the use of this method. A new approach was developed in this research to prevent the formation of Mg2Si by using alumina as a consumer of gaseous magnesium. Utilizing this approach, highly pure silicon was produced by firstly purifying the silica regent by acid-leaching. It was then subjected to magnesiothermic reduction regimes in order to optimize the power input and molar Mg/SiO2 ratio to minimize Mg2Si production. Silicon products were analyzed by X-ray powder diffraction (XRD) and quantitative Rietveld refinement. Optimum electrical power and molar ratio were found to be 3.75 kW and 2.25:1, respectively. The silicon product was examined by glow discharge mass spectrometry which indicated that its purity was 99.96%, with 0.10 ppm of B and 0.15 ppm of P, making it an attractive material for solar cell generation.

Effects of Co, Ni, and Cr addition on microstructure and magnetic properties of amorphous and nanocrystalline Fe86−xMxZr7Nb2Cu1B4 (M = Co, Ni, CoCr, and Cr, x = 0 or 6) alloys

Abstract Mössbauer spectra and thermomagnetic curves for the Fe86−xMxZr7Nb2Cu1B4 (M = Co, Ni, CoCr, and Cr, x = 0 or 6) alloys in the as-quenched state and after the accumulative annealing in the temperature range 600–800 K for 10 min are investigated. The parent Fe86Zr7Nb2Cu1B4 amorphous alloy is paramagnetic at room temperature, and substitution of 6 at.% of Fe by Co, Ni, and CoCr changes the magnetic structure – the alloys become ferromagnetic, whereas replacing 6 at.% of Fe with Cr preserves the paramagnetic state. After the heat treatment at 600 K, the decrease of the average hyperfine field induction, as compared to the as-quenched state, is observed due to the invar effect. After this annealing, the Curie temperature for all investigated alloys decreases. The accumulative annealing up to 800 K leads to the partial crystallization; α-Fe or α-FeCo grains with diameters in the range of 12–30 nm in the residual amorphous matrix appear.

Investigation of critical behavior in the vicinity of ferromagnetic to paramagnetic phase transition in the Fe75Mo8Cu1B16 alloy

The main goal of this work is to study the critical behavior in the as-quenched and annealed NANOPERM Fe75Mo8Cu1B16 alloy in the vicinity of the critical temperature TC. The second order phase transition from ferro- to paramagnetic state was confirmed by the positive slope of Arrott plots. The critical exponents (β, γ, and δ) have been revealed using the Kouvel-Fisher method. Moreover, the Kouvel-Fisher analysis revealed the detailed Curie temperature for all investigated samples.

Modeling hysteresis curves of La(FeCoSi)13 compound near the transition point with the GRUCAD model

Abstract The paper presents a new approach to modeling of magnetic properties and the influence of temperature on hysteresis loops in La(FeCoSi)13 magnetocaloric compound. The GRUCAD hysteresis model has been used for analysis of magnetic behavior in the vicinity of the magnetic phase transition. The modeling results are in a qualitative agreement with experiment.