Muxing Guo

First-principles study of electronic and optical properties in wurtzite Zn1−xCdxO

A first-principles study has been performed to evaluate the electronic and optical properties of wurtzite Zn1-xCdxO up to x=0.25. We have employed the Perdew-Burke-Ernzerhof (PBE) form of generalized gradient approximation within the framework of density functional theory (DFT). Calculations have been carried out in different configurations. With the increasing Cd concentrations, the band gap of Zn1-xCdxO is decreased due to the increase of s states in conduction band. The results of imaginary part of dielectric function indicate that the optical transition between O 2p states in the highest valence band and Zn 4s states in the lowest conduction band has shifted to low energy range as the Cd concentrations increase. Besides, the optical band gap decreases from 3.2 to 2.84 eV with increasing Cd concentrations from 0 to 0.25. Meanwhile, the bowing parameter b, which has been obtained by fitting the results of optical band gap, is about 1.21 eV. The optical constants of pure ZnO and Zn0.75Cd0.25O, such as optical conductivity, loss function, refractive index and reflectivity, have been discussed.

Electronic and optical properties of Ti1−xCdxO2: A first-principles prediction

A first-principles study has been carried out to evaluate the electronic and optical properties of rutile Ti1−xCdxO2 as a possible photocatalytic material. It was found that Cd incorporation lead to the enhancement of p states in the top of valence band and the decrease of band gap. The optical transition between Cd p and O p enhances gradually and shifts to high energy range with increasing Cd concentration. Furthermore, optical absorption of Ti1−xCdxO2 increases in the visible range.

Behaviour of magnesia-carbon refractories in vacuum-oxygen decarburisation ladle linings

Abstract Magnesia–chromite bricks are commonly used in the working lining in vacuum–oxygen decarburisation ladles. However, they are expensive and potentially environmentally-unfriendly. The possibilities of employing magnesia–carbon refractories were investigated through industrial testing combined with post-mortem assessments, thermodynamic calculations and mechanical considerations. Pitch bonded magnesia materials cannot be used in the slagline owing to the MgO–C reaction and extrinsic oxidation of carbon by reducible slag components (mainly CrOx), resulting in carbon removal, slag infiltration and direct MgO corrosion. Combined with turbulent slag motion this leads to hot erosion. Direct carbon burnout and the MgO reaction are the main causes for their failure in the freeboard. However, pitch bonded magnesia refractories are able to compete with magnesia–chromite bricks in the ladle bottom and in the lower metal bath region, where levels of turbulence and slag infiltration are limited. Simultaneously, both the MgO–C reaction and the extrinsic oxidation of carbon are restrained by, respectively, the inhibiting effect of a mechanical barrier and the non-wetting behaviour of steel towards the magnesia refractory component.

Dissolution and diffusion behavior of Al2O3 in a CaO-Al2O3-SiO2 liquid : An experimental-numerical approach

A technique to study the dissolution and diffusion behavior of Al2O3 in CaO–Al2O3–SiO2 liquids is presented. The dissolution of spherical Al2O3 particles at elevated temperatures is observed using confocal scanning laser microscopy and interpreted by means of numerical simulations with a lattice Boltzmann dissolution model. The dissolution mechanism is identified as diffusion-controlled and an estimate of the effective binary diffusion coefficient and its activation energy is obtained. The technique is readily applicable to other systems.

Origin and sedimentation of Cu-droplets sticking to spinel solids in pyrometallurgical slags

Cu-droplet losses in slags are an important problem in Cu-industry, limiting the metal recovery. An important cause responsible for the entrainment of copper droplet losses in slags is their sticking behaviour to spinel solids. In the present study, the interaction between spinel solids and Cu-droplets is investigated in an industrially relevant slag system (PbO–CaO–SiO2–Cu2O–Al2O3–FeO–ZnO) using two complementary experimental set-ups. Firstly the influence of the sedimentation time is studied and secondly the presence of entrained (sticking) droplets is studied as a function of height in the slag layer. Based on the experimental results, a mechanism that explains the sticking Cu-droplets is proposed. Finally, a model describing the sedimentation of sticking and non-sticking droplets is formulated based on the experimental data.

Morphology and growth of alumina inclusions in Fe–Al alloys at low oxygen partial pressure

Abstract The degree of supersaturation is a factor that influences the Al2O3 inclusion characteristics in steel. The influence of the addition of a large amount of Al in the molten steel on the formation, growth and morphology of Al2O3 inclusions was investigated by laboratory scale experiments. Consecutive steel samples were taken during the deoxidation process and subjected to chemical analysis (ICP-AES), automated image analysis (AIA) and scanning electron microscopy (SEM) assessment with respect to the extracted inclusions. The characterisation and quantification of Al2O3 particles show different growth processes, leading to variations in particle size distribution as well as in the morphology.

Wetting behaviour of Cu based alloys on spinel substrates in pyrometallurgical context

Metal droplet losses in slags are an important issue in copper industry. One significant aspect that promotes the entrainment of metal droplets in the slag is their attachment to spinel solids. In the present study, the wetting behaviour of copper alloys on spinel substrates has been investigated in the presence and absence of a slag phase. At first, the attachment was investigated using a synthetic slag containing spinel particles. Microstructural analysis of quenched slag reveals the presence of microdroplets sticking onto a surface of the spinel particles. Second, the metal–spinel interaction was investigated using the sessile drop technique. Wetting angle measurements were performed between Cu–Ag alloys and MgAl2O4 substrates. A non-wetting behaviour between the alloys and substrates was observed. The results suggest that the oxygen partial pressure and the amount of Ag in the alloy both influence the wetting behaviour.

Induced migration of non-magnetic particles and fabrication of metallic-based graded materials by applying a strong magnetic field

Strong magnetic fields e.g., 10 T are now frequently used during materials preparation. In the present paper, a method of metal-ceramics graded materials preparation is proposed by applying a strong magnetic field with a high gradient. Experimental and theoretical analyses are performed to investigate the effect of the strong magnetic field on the migration and interaction behavior of diamagnetic oxide particles in a liquid metal. The migration of micrometer or sub-micrometer sized particles is clearly enhanced by the magnetic field gradient. After being treated by the strong magnetic field, a self-assembly structure of the particles is achieved. Various factors such as the magnetic dipole-dipole interaction and chain-chain interaction, are governing the particles assembly. The present results provide direct evidence that nonmetallic particles of micrometer size or less can be manipulated in a conductive melt by applying a strong magnetic field and as a consequence graded materials can be prepared.

Ferroalloy quality and steel cleanliness

Abstract Ferroalloys are added during secondary steelmaking to impart special properties to the steel. Depending upon the ferroalloy quality this may lead to the formation of inclusions. The present knowledge lacks in the exact content of the individual elements and the nature of inclusions dispersed in the ferroalloys. In order to broaden the knowledge concerning ferroalloy quality, eight different ferroalloys (i.e. FeMo, FeNb, HCFeMn, LCFeMn, FeTi70, FeTi35, FeSi75 and FeP) were characterised for their impurity content. The samples were investigated for chemical analysis (inductively coupled plasma atomic emission spectroscopy and Leco combustion technique) and microstructural analysis (SEM energy dispersive spectroscopy). These impurities are linked to the ferroalloy manufacturing route. The inclusions observed in the microstructure are in good agreement with the inclusions extracted by the dissolution technique. In the present manuscript, the possible influence of ferroalloy quality over steel cleanliness is evaluated in the context of the impurities extracted and observed in the ferroalloys.

Effect of the strong magnetic field on the magnetic interaction between two non-magnetic particles migrating in a conductive fluid

This paper presents a theoretical analysis of the interaction between two non-magnetic particles migrating in a conductive fluid due to an imposed strong magnetic field. A repulsive force induced by the conductive fluid flow around the particles is first derived and calculated for a concrete example. From the numerical results, a counteracting behavior with the interparticle magnetic dipole-dipole attractive force is found to exist at a critical particle size which makes the particles controllable under strong magnetic fields (e.g., B> 10 T). This renders a better understanding of recent experimental results and provides a basis to control the particle size distribution using strong magnetic fields for materials processing. Copyright c EPLA, 2009