Pressure slip casting of coarse grain oxide ceramics

This contribution investigates the pressure slip casting of large coarse grain oxide ceramic bodies with a water soluble organic additive system. This organic additive system allows the preparation of a stable and pumpable slip containing alumina rich magnesia aluminate spinel of a size of up to 3 mm and an easy demolding of crack free, dimensionally stable bodies with negligible gradients due to sedimentation. Cut out samples of fired bodies are examined on apparent porosity, dynamic elastic modulus, modulus of rupture, and pore size distribution. Computer tomography showed very homogenous and dense bodies. The effects of different maximum grain sizes as well as possible sedimentation and segregation of the slip on the mechanical properties and microstructure are evaluated by using the Student's t-test. The most promising results of this study indicate that it is possible to reproducible fabricate coarse grain ceramics for refractory and other high temperature applications by pressure slip casting.     

Research on Composite Slag Dam Cast with Magnesia Castables and Alumina Magnesia Castables

To enhance the service life of magnesia based slag dam,composite slag dam was designed to be cast with alumina magnesia castables in slag line and magnesia castables in molten steel zone.Workability of the magnesia castables for the slag dam was improved and a suitable vibration shaping method was adopted to combine it with alumina magnesia castables.The result shows:(1)workability and setting performance of magnesia castables can be improved to match with alumina magnesia castables by adjusting setting ret...     

The effect of nano-Cr2O3 on solid-solution assisted sintering of MgO refractories

The effect of Cr₂O₃ particle size on the densification of magnesia refractories was investigated. Magnesia grains (<45 μm) were mixed with 2 wt% of micro-Cr₂O₃ (2 μm) and nano-Cr₂O₃ particles (10–20 nm) and sintered at 850–1450 °C, for 5 h in air. The progress of the densification and phase evolution of samples was studied with the support of X-ray diffraction phase analysis (XRD), Fourier transformer infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). It was shown that the densification of magnesia was enhanced by reducing the particle size of the added chromia to the range of 20 nm. According to the phase analysis results, the higher dissolution rate of Cr₂O₃ in MgO in the MgO–Cr₂O₃ system was responsible for the faster densification of nano-Cr₂O₃ containing mixes.     

镁质强化瓷装饰用无铅无镉溶出大红釉的研究

研制一种适用于镁质强化瓷装饰用大红釉。该釉以包裹型镉硒为色料,以长石一石灰为基釉混合生料釉,氧化气氛烧成,烧成温度为1150-1270℃,釉料无铅镉溶出。同时研究了基釉的组成、升温速率、保温时间和燃烧气氛对呈色效果的影响,并获得了制备镁质强化瓷装饰用无铅无镉溶出大红釉制备技术。     

Enhancement of ionic conductivity and thermal stability of CaO-stabilised zirconia (CSZ) with MgO addition by scavenging effects

The effects of magnesia (MgO) addition on the ionic conductivity and thermal stability of CaO-stabilised zirconia (CSZ) was investigated by structural and morphological analysis. MgO was added to CSZ using a solid-state reaction, and a secondary phase was not observed via XRD of all specimens sintered at 1600°C. However, Mg₂SiO₄ and Mg-rich phases were detected in the microstructure of CSZ doped with 5 and 10?mol-% MgO, respectively. Ionic conductivity increased with an increase in MgO content, and CSZ doped with 5?mol-% MgO exhibited a maximum value of 0.819?S?cm^?1 measured at 1500°C due to the scavenging of Si impurities. The thermal diffusivity increased from 0.517 (CSZ) to 0.649?mm^2?s^?1 (5?mol-% doped CSZ), and the thermal expansion coefficient of 0.5?mol-% doped CSZ was maximal at 9.855?μm/m°C. The value of mol-% doped CSZ decreased to 8.937?μm/m°C as it was affected by the Mg–Si phase formation.     

镁氧类水泥膨胀剂的作用机理及影响因素

本文介绍一种新型油井水泥膨胀剂———镁氧类膨胀剂的组成、膨胀性能及应用情况。分析了膨胀机理和影响膨胀的因素，包括膨胀剂的煅烧温度、细度，水泥浆的养护温度、养护压力、水灰比、水泥的碱度等。掺有这种膨胀剂的水泥具有防气窜功能，可用于钻井堵漏、修井和固井作业。     

Preparation and characterization of magnesia-supported chromium catalysts for the fluorination of 1,1,1-trifluoro-2-chloroethane (HCFC-133a)

Chromium oxides dispersed on various supports by precipitation method were tested for the catalytic fluorination of HCFC-133a to HFC-134a. Catalytic activity decreased in the order of MgO>Al₂O₃>MgF₂>TiO₂>ZrO₂. The most active Cr/MgO, when properly activated and pre-fluorinated before the reaction, shows superior activity to other catalysts that have been reported so far. Isolated (monomeric) Cr(VI) species that was formed during an optimized thermal activation were changed into fluoride (Cr_xF_y) and oxyfluoride (Cr_xO_yF_z) form of monomeric and oligomeric Cr species during the pre-fluorination with HF, the latter of which are believed to be active sites for the reaction. High pre-fluorination temperature accelerates the formation of crystalline Cr₂O₃ due to the formation of crystalline MgF₂ from MgO which anchors the isolated Cr(VI).     

The effect of phase formation during use on the chemical corrosion of magnesia–chromite refractories in contact with a non-ferrous PbO–SiO2 based slag

One of the main factors limiting the lining lifetime in pyrometallurgical smelters is continuous refractory oxides dissolution in the slag bath. The overall wear is accelerated when the slag infiltrates the porous brick and the dissolution thus occurs in a larger part of the lining. This work investigates the possibility of preventing deep infiltration by sealing off the pores with newly formed phases. Static finger tests at constant temperature (1200 °C) were performed in contact with a synthetic non-ferrous PbO–SiO₂–MgO slag, showing the formation of forsterite (Mg₂SiO₄) throughout the refractory sample by the reaction between SiO₂ (slag) and MgO (refractory). This phase grows with time, eventually sealing off the pores near the interface with the bath. The phase grows too slow to prevent full infiltration of the refractory but creates an equilibrium state in the sealed off part of the sample, ceasing the chemical corrosion in that part of the sample.     

烧结合成致密尖晶石的试验研究

采用粒度≤0.058mm、MgO质量分数为96.28%的轻烧镁砂和粒度≤0.043mm的αAl2O3为原料,分别在50MPa、100MPa、150MPa和200MPa的成型压力以及1600℃、1650℃、1700℃、1750℃和1800℃的烧成温度下进行合成尖晶石的试验研究。结果表明:通过控制合理的工艺参数,特别是m(MgO):m(Al2O3)的比约为1:1,成型压力约100MPa,烧成温度>1700℃时,可一步煅烧制得体积密度>3.30g·cm-3、尖晶石含量较高的致密镁铝尖晶石。     

锆英石对镁砂烧结性及其制品性能的影响

探讨了锆英石对镁砂烧结性能的影响 ,并研究了由这种合成镁锆砂制成的镁砖的性能。结果表明 :锆英石能显著提高镁砂的烧结性能 ;利用合成镁锆砂制成的镁砖以高熔点的第二固相为结合相 ,性能明显优于普通镁砖