Papers by Keyword: Reducing Atmosphere

Abstract: The possibility of making welded steel joints using arc welding in a reducing medium of carbon monoxide was studied. A method was proposed to eliminate its negative biological effect by heating the feed gas above its flash point, followed by oxidation till carbon dioxide was obtained. Welding modes have been selected to ensure the formation of a quality welded joint. Comparative studies of welded joints obtained using an oxidizing atmosphere of carbon dioxide and a reducing atmosphere of carbon monoxide were carried out. A chemical and metallographic analysis of welded joints was performed. The thermodynamic substantiation of chemical reactions in which carbon and microalloying additives can participate was presented. It was established that the main difference between the proposed welding method and those used at present was the suppression of oxidative processes in liquid metal due to the presence of a reducing atmosphere.

Abstract: Lead-free MnO doped 0.955K_0.5Na_0.5NbO₃-0.045Bi_0.5Na_0.5ZrO₃ (abbreviate as KNN-0.045BNZ) ceramics have been prepared by a conventional solid-state sintering method in a reducing atmosphere. The addition of MnO suppresses grain growth and eliminates the liquid phase. MnO dopant changes the crystalline structures of KNN-0.045BNZ ceramics from the classical Morphotropic Phase Boundary (MPB) with rhombohedral phase (R) and tetragonal phase (T) to the suppressed MPB with R/T phase. The 0.4% MnO doped KNN-0.045BNZ ceramics show an excellent electrical properties with quasi static piezoelectric constant d₃₃=300 pC/N, Curie temperature T_C = 350 °C, insulation resistivity ρ=4.83 × 10¹¹ (Ω・cm), and high field piezoelectric constants =438 pm/V (at E_max = 25 kV/cm). The results indicate that the 0.4%Mn doped KNN-0.045BNZ ceramic is a promising lead-free piezoelectric candidate material for commercial applications.

Abstract: Magnetizing roasting followed by magnetic separation is a compound technique for the beneficiation optimization of Huangmei refractory limonite. The natural limonite samples are obtained from Huangmei, Hubei province. The samples are characterized by TG-DTG-DSC. The content of major components is analyzed by SEM-XRAY, which is found that the sample iron mainly occurs in the form of limonite, with impurities including quartz, kaolinite, and barite. The feasibility of oxidized iron ore magnetic roasting limonite by multi-grade dynamic state magnetizing roasting is investigated. The effects of operation parameters such as roasting atmosphere, temperature and roasting duration are analyzed. The results show that: in the condition of the volume fraction of CO is 2% to 5%, the temperature is 700-780°C, and the roasting duration is 20 to 30 minutes. By multi-grade dynamic state magnetizing roasting, the grade of roasting limonite is nearly 33%, and the feasibility of separation is effective. A good index is created through simple mineral processing, the iron grade of concentrate reaches to 60% and the iron recovery rate reaches to 83.94%. It reveals that the multi-grade dynamic state magnetizing roasting device has a remarkable effect on roasting limonite.

Abstract: Our objective was to make transparent glaze using oak ash which has a high content of CaO and contains P₂O₅. However, the melting point of oak ash is above 1340^°C, making it difficult to make transparent glaze using only oak ash. In order to lower the melting point of oak ash, flux materials were mixed to oak ash and melting characterization was carried out. Feldspar, which is largely composed of Na₂O and K₂O andlimestone largely composed of CaO were used as the flux materials. The materials were added 10, 20 and 30wt%, respectively, in order to produce the glaze. Depending on the type and amount of flux materials added, the samples were fired at temperatures between 1280~1320^°C in the reducing atmosphere. As the amount of feldspar added was increased, the melting point decreased substantially. Samples with limestone added did not melt completely even at temperatures 1300^°C and wollastonite phase was observed in the glaze layer.

Abstract: To optimize operational parameters of fluidized-bed lignite gasification technology. Experiments have been conducted with Huolinhe (HLH) and Xiaolongtan (XLT) lignite ashes to investigate the mineral transformation behaviors under reducing atmosphere by X-ray diffraction (XRD). The results show that the initial melted parts are primarily result from wustite interacted other minerals under reducing atmosphere. Wustite can react with aluminosilicate minerals to form some low-melting eutectic compounds, and lead to its initial melting temperature 200 °C below the deformation temperature. Mullite is formed at 1000 °C or so, and its content increases and then decreases with the temperature increase, and reaches maximum at 1200 °C. Gehlenite and anorthite come from the reaction between calcium oxide and mullite. Owing to the generation of some gases during mineral transformation under weak reducing atmosphere, many holes are formed on the surface of molten ash.

Abstract: To obtain an indicator for evaluating the amount of corrosion of water wall tube materials in a coal-fired boiler, we investigated the effect of H₂S and SO₂ concentration on the amount of corrosion of Fe-2.25wt.%Cr-1wt.%Mo (STBA24) alloy at 773K in N₂-CO-CO₂-H₂-H₂O-H₂S-SO₂ mixed gases. As a result, it was clarified that the amount of corrosion and the scale structure were not affected by concentrations of H₂S and SO₂ when they were above 150ppm and 200ppm, receptively, at fixed P_O2 and P_S2. Therefore it appears that the amount of corrosion in this range of concentrations can be evaluated only from the correlation between P_O2 and P_S2. In contrast, under the condition of less than 150ppm SO₂ or less than 200ppm H₂S, the amount of corrosion was affected by the concentrations of SO₂ and H₂S. Therefore, it appears that the concentrations of SO₂ and H₂S are necessary to evaluate the amount of corrosion when the concentrations of SO₂ and H₂S are less than 150ppm and 200ppm, respectively. An indicator for evaluating the amount of corrosion was able to be proposed as a function of H₂S and SO₂ concentrations in coal combustion atmospheres. Introduction

Abstract: The optimized composition and sintering process of the low sintering X7R-type temperature-stable dielectric ceramics based on Barium Titanate in reducing atmosphere have been investigated. Flux aids SiO2-B2O3-Li2O were used in the experiments. The influence of composition and the content of flux agent on the microstructures and properties of ceramics materials were systemically studied. The X7R-type dielectric ceramics materials could be sintered at low temperature of 950oC in H2/N2 atmosphere, by optimizing flux content and adjusting process parameters. The dielectric constant of ceramics was effectively improved using two-step sintering process.

Abstract: CO sensing properties of various transition metal oxide-loaded SnO2 sensors were investigated in a reducing atmosphere such as wet H2 gas. Among transition metal oxide-loaded SnO2 sensors used in the present study, 5wt%CuO-loaded SnO2 sensor exhibited the highest sensitivity to 1% CO in wet 50% H2 at around 150 °C, while it showed no sensitivity in dry 50% H2. From XRD analysis, CuO was reduced to metallic Cu in a reducing atmosphere at above 150 °C. H2-temperature-programmed reduction (H2-TPR) and diffuse reflectance fourier transform infrared (DRIFT-IR) spectroscopy measurements were carried out to discuss the sensor response mechanism.

Abstract: The function of regenerators is to use the thermal energy of the waste gases to preheat the combustion air and thereby provide better heat transfer via a high flame temperature. Satisfactory furnace operation can only be achieved if the regenerator chambers are in good condition. Today, environmental issues play a major role in the selection of regenerators and checkers refractories. The impact on the environment has been studied on 35 side-fired flat glass furnaces. Firstly, we will describe in this paper the issues raised by increased carry over and CO content observed in various furnaces with different types of checker packing such as basket weaves, box blocks and cruciforms . Secondly, we will talk about how the impact on health and waste/recycling solutions is analyzed and should be taken into consideration before ordering refractories. Finally, some new materials are now appearing on the market. The fact that China dominates magnesia production (51% of the world production) entails the rise of new raw material sources for the basic refractories used for checker bricks. Besides that, the refractories suppliers are continuously improving their materials to offer glassmakers new solutions to overcome the actual issues in the regenerators. These new sources of materials have been analyzed in R&D and are now considered as potential solutions which need further testing under industrial conditions.

Abstract: In these years, glass industry has several problems to solve which are derived from environmental protection, energy saving, resource saving, demands for high quality glass and so on. Refractory for the glass melting also has some problems corresponding to the glass industry, such as more corrosive service circumstance, less glass contamination from the refractory, recycling and so on. NOx reduction, one of the environmental protection, brings the oxy-fuel combustion and/or the reducing atmosphere operation of glass melting into the glass industry. Under the reducing atmosphere, some kind of refractories can not endure for a long period of time and under the oxy-fuel combustion, refractories ought to endure around 3 to 4 times more severely corrosive circumstance. Thus, the problems of refractory that are corresponding to the glass industry are explained and discussed in this presentation. The solutions for the above are also discussed and presented, if possible in the presentation.