Volume 106, Issue 8

The effect of carbon on nitrogen solubility in slag was investigated for the ternary CaO–MgO–SiO 2 and the quaternary Al 2 O 3 –CaO–MgO–SiO 2 slag systems at 1873 K under controlled oxygen and nitrogen potentials. Gas–slag equilibration experiments were conducted using molybdenum and graphite crucibles. In the absence of carbon, the nitrogen solubility was very low. The presence of carbon greatly increased the nitrogen solubility in slag. The total nitrogen content was found to increase with SiO 2 and MgO concentration for the carbon saturated slags. Low levels of cyanide were found by wet chemistry with considerable uncertainty. The results analyzed by different methods ruled out cyanide formation being the main reason for the large increase in nitrogen solubility in the presence of pure carbon.

The PbO–Al 2 O 3 system has been extensively studied in literature. In the present study, experimental work was conducted in which equilibria between phases were investigated under air between 600°C and 800°C by X-ray diffraction. Three intermediate compounds reported in literature were confirmed, which are PbAl 12 O 19 (1PbO:6Al 2 O 3 ), PbAl 2 O 4 (1:1) and Pb 2 Al 2 O 5 (2:1). Results support a widely accepted version of the phase diagram in which these compounds exist. On the basis of the results obtained in this study and data considered from literature, a thermodynamic modeling according to the Calphad approach was performed, where all intermediate phases were considered as stoichiometric compounds and where the liquid phase was described by a two-sublattice ionic liquid model. Good agreement has been obtained from thermodynamic optimization in comparison with experimental results.

Phase equilibria in the Co–Fe–Ti ternary system were investigated by means of the equilibrated alloy method with X-ray powder diffraction and electron probe microanalysis. No ternary compounds were found. The experimental results indicated the existence of seven two-phase and one three-phase regions at 600°C, five two-phase and two three-phase regions at 800°C, and six two-phase and two three-phase regions at 950°C. The solubility of Co in TiFe 2 was determined to be larger than 54 at.% at all investigated temperatures, and the solubilities of Fe in TiCo 3 and Ti 2 Co showed an appreciable increase with increasing temperature. The three-phase equilibrium in the Ti-rich corner at 800°C was revealed to be ((β-Ti) + Ti(Fe, Co) + Ti 2 Co) rather than ((α-Ti) + Ti(Fe, Co) + Ti 2 Co) reported in previous investigations. Based on the experimental data obtained in the present work, three isothermal sections at 600, 800 and 950°C were established.

A hot-rolled Ni–Ti–Fe alloy was subjected to 50% cold rolling by laboratory rolling mill and was subsequently annealed at 800°C for 1.5 h. This sample was then deformed through another 10% reduction in thickness by two different routes (i) conventional cold rolling and (ii) marforming (rolling in liquid nitrogen) followed by annealing under identical conditions. The grain refinement during normal cold rolling was attributed to relatively large presence of dislocations in the ND // <110> grains in the starting microstructure. The regions of higher dislocation densities became gradually textured to ND // <111> orientation, with cold rolling. Marforming (deformation in liquid nitrogen following phase transformation) on the other hand led to more significant grain refinement and also change in the bulk texture. The objective of this study was to compare the grain refinement and microstructural modification produced through marforming with that obtained in conventional cold deformation.

Isothermal compression tests of TC4 titanium alloy over a temperature range of 973 K to 1123 K and strain rate range of 0.1 s −1 to 30 s −1 showed that dynamic recrystallization (DRX) occurred under all deformation conditions. To model the flow stress taking into account the DRX behavior, the model was divided into two stages by the critical strain of DRX (∊ c ) calculated using the Poliak–Jonas method. The flow stress in the first stage with no DRX (∊ ≤ ∊ c ) was described by the Estrin–Mecking equation. The flow stress in the second stage with DRX (∊ > ∊ c ) was expressed by the interaction of work hardening, dynamic recovery, and DRX. The function relationship between the principal parameters in the flow stress model and the deformation conditions described by the Zener–Hollomon parameter was also analyzed. The prediction of the constructed flow stress model agreed well with the experimental results.

High-speed steel is successfully fabricated by solid state sintering of Fe, Co, WC, Mo 2 C, Cr 3 C 2 and VC powders under vacuum. The sintering density, microstructure, phase structure, hardness, and transverse rupture strength of the specimens are examined. Results show that the density increases with increasing sintering temperature. Nearly full density is obtained without microstructural coarsening in the sintering temperature range of 1190–1210°C. The optimum sintering temperature for the steel is 1200°C. The suitable quenching temperatures range from 1200 to 1240°C. After heat treatments, the microstructure consists of a martensitic matrix (grain size ≈5 μm) with a homogeneous distribution of M C and M 6 C carbides (average size lower than 1 μm). The highest hardness of 68.5 ± 0.3 HRC and the maximum transverse rupture strength of 3.58 ± 0.12 GPa is obtained for the specimen tempered at 560°C.

ZnS:O 2− (ZSO) nanoparticles were synthesized using a low temperature solid-state reaction method. The effects of annealing conditions and the content of the surfactant polyethylene glycol (PEG) on photoluminescence (PL) properties of the ZSO nanoparticles were studied. It was found that annealing and adding PEG during the synthesis did not change the crystal structure of ZSO nanoparticles, and their average crystallite size increased with increasing annealing time and temperature, but decreased with increasing PEG content. The emission intensity of ZSO nanoparticles was found to be enhanced after annealing or using PEG during the synthesis. Optimal annealing conditions both in air and vacuum and the optimal content of PEG were obtained for achieving maximum emission intensity from the ZSO nanoparticles.

In this paper, the effects of using Cr 2 O 3 and ZnO 2 nanoparticles on the mechanical properties and durability of self-compacting mortars are investigated. A fraction of Portland cement was replaced with 1, 2, 3, 4 or 5 wt.% of either Cr 2 O 3 or ZnO 2 nanoparticles, and 25 wt.% fly ash. The rheological properties of these mortars were determined through the mini-slump flow diameter and V-funnel flow time tests. The mechanical and durability characteristics were evaluated by compressive and flexural strength, water absorption, electrical resistivity and rapid chloride permeability tests. The microstructure of the mortars was assessed through the use of scanning electron microscopy. The inclusion of 2 wt.% Cr 2 O 3 or 4 wt.% ZnO 2 nanoparticles had the best result in compressive and flexural strength tests. Also, mixtures containing either 3 wt.% of Cr 2 O 3 or 5 wt.% of ZnO 2 nanoparticles obtained the best result in terms of durability. It can be deduced that the properties of these mixtures are significantly improved by the addition of Cr 2 O 3 and ZnO 2 nanoparticles.

BaO addition to ternary (80– x )TeO 2 -20ZnO- x BaO ( x = 0–20 mol.%) glasses resulted in a decrease in ultrasonic velocities and independent elastic moduli; this result indicated that the rigidity of the glass network weakened possibly because non-bridging oxygen increased. Thermal analysis results showed that glass transition temperature increased as BaO content increased because of the stabilizing effect of Ba 2+ on the glass network. Additional analyses using bulk compression and ring deformation models revealed that the ratio between theoretical bulk modulus and experimental bulk modulus increased; this result indicated that the compression mechanism mainly involved isotropic ring compression. Furthermore, the increase in non-bridging oxygen formation with BaO addition caused a decrease in optical energy gap and an increase in refractive index. An increase in Urbach energy indicated that the degree of disorder in the glass system also increased.

Anodic aluminum oxide is a well-known template for nanofabrication. Structural features of anodic aluminum oxide, such as pore diameter, can be controlled by adjusting anodization operating conditions. In this paper we will describe how nanoporous alumina of different porosities was prepared using electrochemical anodization. The influence of anodization time, potential, and temperature on the formation of well-ordered porous anodic aluminum oxide was studied. Results from high-resolution field-emission scanning electron microscopy have shown that pore diameter increases with increasing potential, temperature, and anodization time. Optimal anodic aluminum oxide pore diameter and arrangement were obtained for samples anodized at 40 V, 30°C for 60 min.

Pelletization of ball milled powder, although a better technique for distributing nanoreinforcements into the metal melt, increases the production line. Here, we report our attempt to improve the distribution of nanoreinforcements without increasing the production line. We observed the effect of increase in a novel parameter, launching particle to constant reinforcement ratio (by weight; 1.5 wt.% Al 2 O 3 ), on the nanoreinforcement distribution and ultimate strength of composites fabricated by stir casting. The medium used for launching the nanoreinforcements into the Al–Cu matrix is aluminum powder prepared by ball milling. An increase in the launching particle to constant reinforcement ratio leads to an improvement in the nanoreinforcement distribution and tensile strength of the composite. The X-ray maps indicate the absence of iron contamination and iron intermetallics.

A manganese ferrite–graphene nanocomposite was designed and prepared by a hydrothermal method. The combination of MnFe 2 O 4 and graphene results in much improved electrochemical performance in lithium-ion batteries. The manganese ferrite–graphene (with 30 wt.% graphene) exhibits a highest reversible capacity of 1120 mA h g −1 with excellent cycling stability and rate capability. The superior electrochemical performance of the manganese ferrite–graphene system can be attributed to its unique structure and the concerted effects of MnFe 2 O 4 and graphene.

TiO 2 nanoplates decorated with Ag nanoparticles have been synthesized by a facile method. The as-prepared Ag/TiO 2 nanoplates have been characterized using transmission electron microscopy and X-ray diffraction. Transmission electron microscopy results show that TiO 2 nanoplates have a uniform side length of about 40 nm and mono-dispersed morphology, which implies that TiO 2 nanoplates may be pomising supports. Ag nanoparticles with diameter ranging from 10 to 20 nm can be observed to disperse homogeneously on the surface of TiO 2 nanoplates. The electro-oxidation of Ag/TiO 2 nanoplates for hydrazine oxidation has been investigated in detail. The results show that Ag/TiO 2 nanoplates have excellent electrocatalytic activity. The electro-oxidation of hydrazine may be an irreversible process being controlled by diffusion of hydrazine.