Papers by Keyword: Magnesia

Abstract: Compounds of alumina APC-2011 SG with niobia, silica and magnesia were sintered at 1400°C/3h, in order to evaluate their ballistic performance. The content of niobia (Nb₂O₅) was 4.0 to 8.0 wt.%; silica (SiO₂) was 0.8 wt.%; and magnesia (MgO) at 0.15 wt.%. Sintered samples were characterized by hardness, densification and energy absorption at impact. Ballistic tests were performed by ceramic discs firmly glued to steel plates and then subjecting the target to impact using 7.62 mm projectile shot from a rifle with a throw distance of 5 m. The energy absorbed by the disintegration of the ceramic discs was estimated by the residual velocity. The fracture surfaces of the samples were observed by scanning electron microscopy. It was verified for the first that the addition of high amounts of Nb₂O₅ to the alumina with the presence of SiO₂ and MgO increases the presence of vitreous phase in the contours of alumina grains and improved the properties of the material for use in ballistic protection.

Abstract: In this paper, the flow characteristics of a lightweight formed magnesia composite usingsuper absorbent polymer as base material for biological panels were evaluated. The experimentalparameters were evaluated with respect to the flow of the mortar according to the water binder ratio(W/B), the volume ratio of fine aggregate (Vs/Vm), the amount of foaming agent (FM) and theamount of super absorbent polymer (SAP). Statistical analysis was performed on the flow obtainedthrough the experiment and the influence coefficient on the flow quality was obtained. The flowquality prediction model equation of the magnesia composite is proposed through the obtainedinfluence coefficient. The proposed model equation shows that the experimental and predicted valuesare over 90%.

Abstract: In this paper, the compressive strength quality characteristics of lightweight formedmagnesia composite using super absorbent polymer as basic material for biological panels wereevaluated. The experimental parameters were evaluated with respect to the compressive strength ofthe mortar according to the water binder ratio (W/B), the volume ratio of fine aggregate (Vs/Vm), theamount of foaming agent (FA) and the amount of super absorbent polymer (SAP). Statistical analysiswas performed on the compressive strength obtained through the experiment and the influencecoefficient on the compressive strength quality was obtained. The compressive strength qualityprediction model equation of the magnesia composite is proposed through the obtained influencecoefficient. The proposed model equation shows that the experimental and predicted values are over80%.

Abstract: Micropowder MgCO₃ was added into magnesite as raw materials to prepare magnesia using a two-step calcination method. The sample magnesite was characterized use X-ray diffraction (XRD) and scanning electron microscopy (SEM). Experimental results showed that the sample insulated at 1600° C for 3 hours before and after sintering presented a linear change rate of 15.6 % in the case of without adding micropowder MgCO_3, the prepared magnesia had a bulk density of 2.31 g/cm³ and apparent porosity of 32.8 %, while MgO grain size was 3.11 μm. In the case of adding 8 % micropowder MgCO₃, the sample magnesite before and after sintering showed a linear change rate of 17.9 %. The bulk density, apparent porosity of prepared magnesia were 2.46 g/cm³ and 28.1 % respectively, while the grain size of MgO was 5.15 mm.

Abstract: At the present paper, a process of magnesia (MgO) synthesis from East Java dolomite through hydrochloride acid leaching, precipitation and calcination as well as characteristic of the product is discussed. Results of the experimental works show that the dissolution rate of magnesium and calcium from dolomite in hydrochloride acid solution was very rapid. Complete magnesium extraction was obtained by the leaching test with acid concentration of 1.5 molar, particle size distribution of -325#, solid-liquid ratio 1:20 (g/mL), stirring speed 200 rpm at room temperature after only 10 seconds. Precipitation of Mg(OH)₂ by the addition of 20% (v/v) CaO slurry into pregnant leach solution resulted in 97.5% Mg precipitation after 1 minute. Solution pH must be maintained at a level of 10-10.5 by adjusting CaO addition in order to minimize calcium co-precipitation and to obtain high purity of Mg(OH)₂ precipitate. Calcinations of Mg(OH)₂ were performed at temperature range of 550-800°C in which 99% of crystal water removal took place after 5 minute at temperature of 800°C. Lower temperature requires longer time of crystalline water removal from Mg(OH)₂. XRF analysis showed MgO purity of 88% with the main impurities of calcium and chloride. XRD analysis detected the presences of calcium as calcite (CaCO₃) and portlandite (Ca(OH)₂) as impurities in the MgO product. SEM analysis of the MgO powder revealed a nano size of MgO with particle diameter of about 50 nm.

Abstract: The lining of steel converters and ladles consists of magnesia-graphite refractories. The steel industry is the biggest consumer of refractories, about 70% of the total production of these materials. For this reason, it is very important to recycle them for the production process. The aim of this work is to carry out the physicochemical and microstructural characterization of post-mortem magnesia-graphite refractories from a steel plant, in order to achieve their incorporation to the manufacture of ceramic masonry to be used in the construction industry. The obtained results indicate acceptable properties in these industrial wastes in relation to the physicochemical and environmental characteristics and the feasibility of reusing them in the mentioned applications.

Abstract: In this paper, a new process for the production of the primary magnesium is introduced using the dolomite as the raw material. The magnesia and calcium carbonate were prepared from dolomite by acidification. The content of magnesium oxide can reach 98.92% about the magnesia obtained. The magnesia is used to produce primary magnesium by aluminothermic reduction under vacuum condition. The reduction ratio of MgO can be up to 86.14% under the temperature of 1200°C for 5hrs, briquetting pressure of 10MPa and the molar ratio of MgO to Al of 3:2. The content of magnesium is more than 99.90%. The major phases in the briquette residue are corundum and spinel, which can be used as refractory.

Abstract: The porous mullite ceramics doped with such metal oxides as ZrO₂, WO₃ and MgO in quantity of 5 wt% were prepared by slip casting method. The mullite phase was the main and dominant phase of ZrO₂-, WO₃- and MgO-doped samples, which were sintered at the temperatures of 1650°C, 1500°C, respectively. The ZrO₂, WO₃ and MgO had the positive effect on the increase of porosity and decrease of thermal conductivity of porous mullite ceramics and the degree of this effect was in the order of ZrO₂<MgO<WO₃.

Abstract: The phase composition and particle size of the boron mud is investigated by X-ray diffractometry (XRD), scanning electron microscope (SEM) and laser particle size analyzer. The mainly phase composition of the boron mud are magnesite (MgCO₃) and forsterite (Mg₂SiO₄). The mainly phase composition of the calcined boron mud are forsterite (Mg₂SiO₄) and a small amount magnesia (MgO). the sizes of the boron mud are about 2~6μm and a few of them are bigger and less than 10μm and the particle size of less than 10μm is about 60%.

Abstract: Preparation of the tundish coverture fluxes by the blast furnace slag can recycle utilization of solid wastes discharged from iron and steel industry. Calcium fluoride and magnesia can play an important role for the basic performance of tundish coverture fluxes. The impact on the melting temperature, viscosities and surface tension of the tundish coverture fluxes from the content of calcium fluoride and magnesia were studied. The results showed that: When the content of CaF₂ increased from 10% to 25%, the melting temperature, the viscosity and the surface tension were decreased by 50°C, 0.3 Pa·S and 0.039 N/m respectively. The viscosity was brought down of 0.02 Pa·S, the surface tension was increased by 0.03 N/m, and the difference between the lowest and highest melting temperature was about 3°C when the content of MgO changed from 5% to 11%.