Hua Zhi Gu

Finite Element Analysis on Temperature-Stress of Permeable Refractory Ceramic under Working Process in Ladle

According to the practical physical dimension and processing parameters of ladle with bottom gas blowing in a factory, a geometrical model was established and mesh structure was completed, Eulerian multiphase model and porous media model were adopted for the two-phase flow in ladle, which was coupled, the effect of temperature field and thermal stress in course of working process of permeable- gas refractory ceramic was studied by finite element approach. The correlations between processing, structure, and high-temperature mechanical properties were discussed, and the material and structure of permeable-gas ceramic were designed to optimum. The results show that: The steady gas flow rate can avoid wearing of permeable-gas refractory ceramic from cataclysm of temperature-stress; After the material and structure of permeable-gas refractory ceramic are optimized, the effect on ceramic wearing of temperature-stress in condition of oxygen washing is weakened. It is an important guiding for prepara- tion of permeable-gas refractory ceramic with long life, which will make for highly active refining ladle.

Potash Erosion Resistance of Chromium-Containing Materials

Compared with the traditional entrained flow gasifier, coal catalytic gasifier has the advantages of low reaction temperature, high production efficiency and low energy consumption, but it also has higher requirements for potash erosion resistance. Chromium-containing material is commonly used as lining material for gasification furnaces. In this paper, potash erosion resistance of chromium-containing raw materials and products were respectively researched by using powder tabletting sintering and potassium vapor erosion method. The potash erosion resistance are characterized by XRD and SEM. The study show that:(1)There are obvious potassium salt deposition on the surface of chromium-containing raw materials and products after potash erosion experiment. Potash reacts with chrome-corundum and magnesium-chrome spinel to form K2CrO4,and reacts with chromium oxide to form K2Cr2O7 at 750°C. (2)Potassium vapor enters into chromium-containing products through pores and leads to crack formation and volume change, which destroy the structure and reduce high temperature volume stability of material.

Oxidation Resistance and Mechanical Enhancement of Ferro-Silicon Nitride on Silica Sol Bonded SiC Castable

Silica sol bonded SiC castable have obvious advantages of slag resistance and thermal stress damage resistance. However, they are not widely used due to their weak oxidation resistance at high temperature. Ferro-silicon nitride is added to improve the oxidation resistance of SiC castable. The efficiency of SiC castable in the presence of different contents of ferro-silicon nitride was evaluated through sintered properties, isothermal oxidation behaviors and microstructural analysis. The results show that sample with 5wt% ferro-silicon nitride possessed good mechanical behavior after heat treatment due to its acceleration for the formation of SiC whiskers. At 1500 °C, Isothermal oxdation curve indicated that the oxidation progress performed two-stage model controlled by chemical reaction at the earlier period and diffusion at the later period. Sample with 5wt% ferro-silicon nitride present faster oxidation rate (kc) at the earlier stage versus the contrast sample (0.025 mg·cm-2·min-1 vs 0.087 mg·cm-2·min-1), and slower oxidation rate (kd) at the later stage (0.145 mg·cm-2·min-1 vs 0.137 mg·cm-2·min-1). After 470 min isothermal oxidation test, the weigh gain of sample with 0 wt% ferro-silicon nitride exceeded the sample with 5wt% ferro-silicon nitride.

Preparation and Electrochemical Properties of Graphene/MnO2 Nanocomposites for Supercapacitors

In the present work, we demonstrated a facile process to prepare graphene/MnO2 composites via a simple hydrothermal method at 120 °C using KMnO4 and graphene oxide as raw materials followed by reduction with or without hydrazine. The electrochemical performance of the graphene/MnO2 composites were investigated in a neutral electrolyte of Na2SO4. Among these samples, the sample rGM3 prepared without hydrazine show uniform morphology and the best electrochemical performance. The specific capacitance of rGM3 is 169 F g-1 at a specific current of 0.2 A g-1. It exhibits a maintenance of 75.5 % of the initial capacitance after 1000 cycles. The results manifest that the graphene/MnO2 composites can be potentially applied in supercapacitors.

Effects of Atmospheric Conditions on Slag Corrosion Resistance of Lightweight Al2O3-MgO Castables

By adopting dynamic induction furnace corrosion test, the corrosion mechanism of lightweight Al2O3-MgO castable with different environmental oxygen partial pressure was investigated through macro- and micro-analysis, XRD and thermodynamic simulation. The atmospheric condition was set to P(O2) = 0.21 atm or P(Ar) = 1.0 atm. The attained results showed that a reduced slag corrosion but intensified slag penetration happened at low environmental oxygen partial pressure condition. With P(O2) = 0.21atm, Mn and Fe in slag were present in the form of divalent and/or trivalent cations and were incorporated into spinel to form MnFe2O4 solutions and MgAl2O4 solutions during corrosion process. Since Fe, Mn ions are largely consumed, liquid with high viscosity formed and the continuing infiltration was suppressed. Under P(Ar) =1.0 atm, corrosion on castable aggregates was significantly weakened, and the reaction products under this condition are mainly MgAl2O4 and CA6.

Effects of Matrix Densification Based on Particle Packing on Lightweight Al2O3-MgO Castables

The property of refractory matrix was dominated by both the maineral composition and particle packing behaviors. In this study, the theoretical packing density of refractory castables was calculated to design the particle size distribution (PSD) of its matrix. Four lightweight Al2O3-MgO castables with different matrix PSD (represented by q-value) were prepared and examined. Results show that a suitable q-value was needed to ensure acceptable properties including sintering characteristics, strength and slag resistance, which deteriorated distinctly at high q ( > 0.31). For the sample with q = 0.28, the matrix showed dense and uniform mirostructure, and the properties of castable reached a favorable compromise among sintering characteristics (apparent porosity = 14.8%, bulk density = 3.02g∙cm-3, permanent linear change < 0.6%), strength (cold modulus of rapture = 12.4MPa, cold crashing strength=155.5MPa), and resistance against both slag corrosion (Ic = 22.4%) and penetration (Ip = 11.5%). The sample with q = 0.25 showed the highest strength and resistance against slag corrosion, but its slag penetration resistance was lower due to the existence of cracks between aggregates and matrix.

The Improvements for the Siliceous Self-Flow Castable with Adding Nano SiO2

In order to make up for the deficiencies due to the molding process,and improve the mechanical properties and sintering performance of self-flow castable,in this paper, we used nano SiO2 which had high surface activity as admixture. We added 0wt%, 0.1wt%, 0.2wt%, 0.3wt% of nano SiO2, and then test the linear change, Flexural strength, compressive strength,and refractoriness under load after dried at 110°Cfor 24h and heat treatment at 1400°C for 8h.The results showed that: with the increase of nano SiO2, self-flow value of self-flow castablel decreased, the flexural strength and compressive strength of the sample increased after dried at 110°C for 24 h, the strength of the self-flow castable was improved after formed.After heat treatment at 1400°C for 8h, linear change of the sample remained the same, Tridymite content, flexural strength and compressive strength increased, apparent porosity decreased, refractoriness under load lowered.

Preparation and Properties of Low-Temperature Glaze Used in Coke Oven Cordierite Bricks

According to analyze service condition and extent of damage of cordierite bricks used in coke oven, the experiment was prepared by using spodumene powder, cordierite powder and fused silica as main starting materials, borax as the flux. The effect of borax on melting properties and thermal shock resistance of low-temperature glaze used in coke oven cordierite brick was investigated. The results showed that the melting temperature of glaze is close to the theoretical calculation, Seger formula can be equally applied to metallurgical industry. With the amount of borax increasing, the melting temperature of the glaze reduced. When the amount increased to 22%, borax dissolved in the mullite phase, which increased the content of glass phase in glaze. When the temperature is 1000°C, glaze layer formed and spreaded evenly on the surface of cordierite lining bricks and didn’t flowing. After five thermal shock, glazed surface didn’t appear crack, the requirements were achieved that glaze can be generated in the carbonization chamber temperature of coke oven without pre-firing. When the amount of borax continues to increase, the viscosity of glaze decreases, which results in flowing.

Influence of nanoAl2O3 Powder on the Properties of Microporous Corundum Aggregates

With Al2O3 micro-powder as main raw material, a kind of microporous corundum aggregate was prepared by adding nanoAl2O3 powder. Effect of nanoAl2O3 powder on the properties of microporous corundum aggregates and its sintering mechanism were studied. The results show that, the closed porosity of sinter is too low when adding too less nanoAl2O3 powder; however, excessive nanoAl2O3 powder would lead to the separation of grain boundary and pores during the sintering process, partial crystal grow up abnormally, the relative density of sinter reduces. Microporous corundum aggregate with 5.2% apparent porosity and 9.2% closed porosity can be obtained with 3wt% nanoAl2O3 powder in this study.

Research on Mechanochemical of Silica and its Composite Powders

Silca and its composite powders added different amount of microsilica were ground in a planetary ball mill (QM-3SP4) at various grinding period with addition of a certain number of grinding aid. The effects of mechano-chemical on particle size, crystal size and lattice deformation in grinding process were analyzed. The phase compositions and size compositions of the treated powders were investigated by X-ray Diffraction (XRD) and Laser Particle Size Analyzers. With the increase of grinding time, the particle size decrease, the specific surface area increase, and the more amount of microsilica added, the smaller particle size the powders had after grinding. The XRD results showed that the diffraction peak intensity of powders weaken and gradually widen. The surface of the particle happened to amorphization, and occurred grain refinement and lattice distortion. Comparing with other treated powders, the change of the powders with the microsilica addition of 5% was larger. Even though the grinding time reached to 30h, the crystal transformation of SiO2 has not been detected.