Band 106, Heft 9

A series of new equations have been developed, based on the pseudo-steady state approximation, to describe the kinetics of gas–solid reactions involving two reaction interfaces. These formulae can be applied to cases where two solid product layers (stoichiometric compounds or solid solution products) are involved, or to one solid product layer and one volatile species (formed by the reaction of solid product with gas). For the latter case, when either the solid product layer is dense, or the diffusion process is the controlling step, the relationship is equivalent to the widely-used Tedmon model.

This study is aimed at fabricating ultrahigh-purity silicon ingots from silicon cutting sludge – a byproduct of the ingot for solar cells cutting process. Firstly, silicon powder from the silicon cutting sludge was recovered by 1 st purification, such as ultrasonication, centrifugation, and acid treatment before preparation of the silicon ingots. After the 1 st purification, the silicon cutting sludge yielded silicon powder with a purity of 99.7612 %. The 1 st -purified silicon powder was subjected to 2 nd purification – 3 cycles hydrogen plasma arc melting (HPAM), resulting in ultrahigh-purity silicon ingot with a purity of 99.9999 %. HPAM has been verified to be an effective process for removal of B and P – the major impurities of silicon for semiconductors and solar cells – to levels of total ≤ 0.3 ppm.

For the purpose of powder injection moulding, a specific method is presented to identify the parameters for a combined rheological constitutive model. This model is a combination of three models used in powder injection moulding and accounts for the effects of the temperature, shear rate and particle size of the powder. The data obtained from experimental measurements were used for identification of the model parameters. The model with identified parameters could be used to realize accurate simulations.

The isothermal section of the Nd–Mn–As ternary system at 800 °C has been constructed in this work by using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy techniques. This isothermal section consists of 11 single-phase regions, 19 two-phase regions and 9 three-phase regions. The maximum solubility of As in (Mn) is about 2.602 at.% As and that of Mn in Mn 3 As and NdAs is below 1 at.% Mn. The highest solid solubility of Nd in MnAs is less than 1.25 at.% Nd. The decomposition temperature of NdAs 2 → NdAs + As is about 668 °C. The phase Nd 3 As could be slowly composed by peritectic reaction L + NdAs → Nd 3 As at higher temperature. The phase Mn 3 As still exists under this experimental condition. No ternary compound was found to exist in this section at 800 °C.

To fully understand the mechanism of forming fcc Co in electrodeposition, the effect of bath temperature and pH on the structure of electrodeposited Co nanowires is studied by means of X-ray diffraction and scanning electron microscopy. At −3.0 V and pH 2.5, the fraction of fcc Co decreases with increasing temperature, ranging from 1 (25 °C, pure fcc Co) to 0 (45 °C, pure hcp Co). The formation of hcp Co can be attributed to larger critical clusters formed at higher temperatures. The pH value has no appreciable effect on the formation of fcc Co nanowires. This is because the H adatoms produced at the cathodic surface can penetrate quickly through the thin Au film and desorb into air.

Microstructure, tensile strength and dry sliding wear studies of Al-15Si, Al-15Si-4.5Cu alloys with and without grain refinement and modifications are presented. Experimental alloys such as Al-15Si and Al-15Si-4.5Cu were conventionally melted and gravity die cast. For grain refinement, 1 wt.% of Al-1Ti-3B and for modification, 0.17 wt.% of aluminum phosphide (AlP) and 0.4 wt.% of Al-10Sr were added to the alloy melt. The results reveal refined microstructure due to grain refinement, modification, improved hardness, higher tensile strength and better sliding wear. Moreover, Al-15Si-4.5Cu alloy (untreated and treated) showed improved mechanical properties as compared to conventional hypereutectic Al–Si alloy.

In this study, the mechanical properties of B 4 C-reinforced AlSi7 foams produced by using a powder metallurgy method were investigated. For this purpose, Al foams containing B 4 C at various ratios (0, 2, 4 and 6 %) were prepared with dimensions of 30 × 30 × 14 mm and 110 × 15 × 14 mm for compression and bending tests. Both tests were performed at a 1 mm min –1 strain rate. According to the experimental results, the compressive stress of B 4 C-reinforced/unreinforced AlSi7 foams, whose relative densities were close to each other, for 10 % strain increased about 15 % with the addition of B 4 C. Although energy absorption values of B 4 C-reinforced/unreinforced AlSi7 foams were in a complex correlation for 60 % strain, the amount of absorption energy increased with the increase in relative density and the amount of B 4 C. Bending strength increased due to strain hardening that occurs with the addition of B 4 C to AlSi7 foams. While maximum bending strength was 0.9 kN in unreinforced materials, it was ∼1.15 kN in 6 % B 4 C-reinforced AlSi7 foams. Thus, the bending strength of B 4 C-reinforced materials is higher by ∼ 28 %.

The expansion and stability of foams made from remelted aluminium alloy scrap has been studied. Foams made from scrap alloy contain oxide bi-films introduced from the swarf (machining chips and turnings) of LM26 alloy and these oxides act as stabilizing agents. The wettability of the oxides and hence the stabilisation is studied by varying the addition of Mg (0 to 2 wt.%) in the alloy. The viscosity of the melts with and without Mg addition is measured and correlated with foam expansion and stability. A detailed microstructural analysis of the base alloy and foam cell wall was conducted to obtain an understanding of the stabilisation behaviour of oxides.

In the present research, WC-12 %Co cermet coatings were deposited on AISI–321 stainless steel substrate using air plasma spraying. During the deposition process, the standoff distance was varied from 80 to 130 mm with 10 mm increments. Other parameters such as current, voltage, time, carrier gas flow rate and powder feed rate etc. were kept constant. The objective was to study the effects of spraying distance on the microstructure of as-sprayed coatings. The microscopic analyses revealed that the band of spraying distance ranging from 90 to 100 mm was the threshold distance for optimum results, provided that all the other spraying parameters were kept constant. In this range of threshold distance, minimum percentages of porosity and defects were observed. Further, the formation of different phases, at six spraying distances, was studied using X-ray diffraction, and the phase analysis was correlated with hardness results.

The dynamic tensile response of a polyurethane interlayer was investigated using a series of tests, including differential scanning calorimetry and dynamic mechanical analysis, quasi-static tension tests and Kolsky tension bar tests. The suitable geometry of the polyurethane interlayer was analyzed and high-speed photography was employed to study the uniform deformation of the specimen at high strain rates. The tensile stress–strain responses of the polyurethane interlayer were sensitive to temperature and strain rate. The polyurethane interlayer exhibited brittle behavior and the failure occurred both in quasi-static and dynamic loading conditions at −40 °C. The experimental results can provide guidelines to a typical aeronautical windshield design.

A linearized analysis of the Debye–Scherrer ring (D–S ring) is proposed in this paper. In our previous works, the authors reported on a technique to calculate stress from the Fourier series of the normal strain of a D–S ring and demonstrated a technique to calculate stress from an imperfect D–S ring. In fact, the same equation can be deduced by linearizing the equation for the D–S ring. We analyzed the data from our previous work to demonstrate this technique. In addition, we propose a data selection technique that uses the distance between the measured data and the hyperplane.

The exclusive effects of gas induced semi-solid parameters such as rheocasting temperature, agitation intensity and flow rate of gas injection into the melt on the average size and shape factor of primary α-Al particles and subsequently tensile properties of 319 aluminum alloy have been studied. Applying vigorous agitation and rapid heat extraction simultaneously in the early stages of solidification in order to achieve a slurry with fine and dispersed primary α-Al particles is essential. Hence, in order to investigate these two factors separately, three different types of graphite diffusion in three proportional gas flow rates have been used. It was found that a reduction in rheocasting temperature leads to a decrease in the average size of the primary α-Al particles and an increase in their sphericity and improvement of tensile properties as well. The average size of primary particles slightly decreases as the agitation intensity increases as expected; while a decrease in agitation intensity in a given gas flow rate leads to the formation of gas porosity. Also the gas was trapped due to an increase in gas flow rate at constant agitation intensity whereas the decrease in gas flow rate has no significant effect on morphology of primary α-Al particles.

In this paper ductile fracture of low carbon high strength steel is estimated following the phenomenological approach of continuum damage mechanics (CDM) evolved by Lemaitre. This assumes damage, corresponding to void growth and their coalescence during large deformation, to be isotropic and ductile in nature. The CDM formalism allows estimating the ductile behavior by a damage variable D . This is evaluated from elastic modulus degradation measurement of uniaxial tensile tests with loading–unloading cycles. The result obtained in terms of D C , the critical value of damage, is found to be 0.44. This gives a measure of ductile fracture from the CDM approach. Respective average D values corresponding to every elastic modulus degradation estimate are used for simulation of ductile behavior of the material. The simulation result closely approximates the experimental flow curve up to about 15 % of strain with minor deviation beyond this strain level up to fracture. The method shown provides a way to evaluate ductile behavior of a material conveniently.

β-Si 3 N 4 whiskers with a diameter of 0.2 – 1.7 μm and length of over 100 μm were synthesized by means of microwave sintering at 1550 °C for 30 min in a flowing nitrogen atmosphere. The β-Si 3 N 4 whiskers grew on Si 3 N 4 substrate without catalyst by the vapor–liquid–solid mechanism. Microwave energy and Y 2 O 3 –Al 2 O 3 –ZrO 2 additives played a significant role in the growth of β-Si 3 N 4 whiskers. The microwave energy provided an orientation temperature gradient and the additives formed the low viscosity glass phase at a low eutectic temperature.