Sintering evaluation of doped lanthanum gallate based on thermodilatometry

The sintering behavior of La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ oxide-ion conductor was systematically investigated by thermodilatometry. The shrinkage data obtained with heating rates of 4, 7, 10 and 12?°C?min^?1 were analyzed by the constant rate of heating model and by construction of the master sintering curve. Validation of the master sintering curve was carried out by measurements of density in conventionally sintered specimens. Slight anisotropy of shrinkage data was found and changes to the basic equation of density was proposed to account for this effect. Plotting the data determined by the constant rate of heating model versus density allowed an easy identification of the density range of constant activation energy. The activation energy (865?kJ?mol^?1) obtained from the master sintering curve correlates quite well with that (874?kJ?mol^?1) obtained by the constant rate of heating model.     

Sintering of clay-chamotte ceramic composites for refractory bricks

Clay-chamotte composites were realized for manufacturing refractory bricks. We used two kaolinitic refractory clays mined in Cameroon and two calcined clays (chamottes) with a large grain size (0.1–4 mm). Clay-chamotte composites containing various quantities of chamotte (0–50 wt%) were shaped and sintered at 1200–1350 °C. The structural characteristics of composites indicated the presence of quartz from the initial clay, cristobalite and mullite. SEM observations revealed very heterogeneous microstructures where porosity is weakly distributed and large pores are entrapped at the vicinity of large chamotte and quartz grains. In general, the global porosity increases with the chamotte content. A specific interpretation of the matrix role on the global sintering behaviour reveals that only a part of the matrix acts effectively. Since the most part of the global porosity is within the matrix, it is distributed in matrix zones, which participate effectively to sintering and in inert matrix zones where larger pores occur. The global mechanical strength is controlled by the matrix behaviour, but the high porosity of this phase is unfavourable to high strength values. Besides, the occurrence of larges pores and local cracks at large grain interfaces from thermal stresses are critical flaws, which reduce the mechanical strength.     

Synthesis of lanthanum chromite using the sol-gel method

Synthesis of lanthanum chromite using the sol-gel method is considered. The effect of the amount of gel-forming agent and the heat treatment time and temperature on the completion of synthesis is investigated. The optimum parameters of the process are presented. The possibility of replacing the powder obtained by vibration crushing of electrically melted lanthanum chromite with powder synthesized by the sol-gel method in the production of miniature ceramic articles is demonstrated. Translated from Steklo i Keramika, No. 6, pp. 15 – 17, June, 1998.     

Investigating the solid phase synthesis of lanthanum chromite

Conclusions We studied the kinetics of solid phase synthesis of lanthanum chromite and solid solutions based on it in the system La₂O₃-Cr₂O₃-CaO-O₂.A relationship was obtained between the degree of conversion in the system and the synthesis temperature, the exposure time, and the CaO concentration. The synthesis of pure LaCrO₃ from oxides is quantitatively complete at 1695 K and with an exposure time of 2 h. The presence in the original mixture of CaCO₃ leads to the formation, in addition to LaCrO₃, of the compound -Ca(CrO₂)₂, and then with increase in the synthesis time to 10 h, at 1695 K, to the formation of solid solutions of the type La_1–xCa_xCrO₃ (x0.25). We determined the constants for the crystal lattices for the synthesized solid solutions.The technological parameters determined for the solid-phase synthesis can be used in work on the preparation of resistor elements made of lanthanum chromite.Translated from Ogneupory, No. 3, pp. 9–12, March, 1990.     

Rational electrothermal conditions for operation of lanthanum chromite electric heaters

A calculation of temperature fields is given for solid and tubular lanthanum chromite electric heaters. A triple diagram of “heater temperature — furnace temperature — specific surface power” is developed for heaters of generally employed sizes in the range of 1000 – 2000°C. Translated from Steklo i Keramika, No. 2, pp. 20–22, February, 2000.     

Tape casting of strontium and cobalt doped lanthanum chromite suspensions

Lanthanum chromite (LaCrO₃) is currently the most widely studied material as interconnector layers for solid oxide fuel cells (SOFC). The complexity of microstructures and geometries of SOFC devices, which are usually built-up by lamination of the different constitutive layers, make it necessary a precise control of processing parameters to achieve the desired combination of properties. Much effort has been devoted to the processing of electrodes and electrolytes but the other layers, such as that of interconnecting material, have received scarce attention. This work deals with the preparation and optimisation of the rheological behaviour of concentrated suspensions of Sr- and Co-doped LaCrO₃ and the subsequent tape casting to produce homogeneous thin sheets to be used in the SOFC stack.The starting powder was produced by combustion synthesis from the corresponding nitrates and urea as a fuel, and had a final composition of La_0.80Sr_0.20Cr_0.92Co_0.08O₃. These powders were dispersed in ethanol with commercial copolymers (Hypermer, KD6) to solids loading of up to 58 wt%. The binding system (BS) consisted of a mixture of a binder, polyvinyl butyral-co-vinyl alcohol-co-vinyl acetate (PVA-PVAc), and two plasticizers, polyethyleneglycol (PEG400) and benzylbutylphthalate (BBP). The effect of the binding system content and the binder-to-plasticizer ratio on the tape casting performance and the characteristics of the green and the sintered tapes, were studied, as well as the influence of the casting parameters (casting speed and blades height).     

Sintering behavior of waste serpentine from abdasht chromite mines Abdasht chromite mines and kaolin blends

The aim of this study is investigating on sintering behavior of Abdasht waste serpentine and kaolin blends. According to this, three formulations of dry milled waste serpentine with 25%, 50% and 75% high grade kaolin were wet milled. The slurries were then dried, sieved and uniaxially pressed at 100 MPa and fired for 2 h soaking time at temperatures between 1100 and 1400 °C. Sintered samples were investigated by bulk density, apparent porosity, water absorption, linear shrinkage and phase changes with raising temperatures in order to characterize their sintering process. It was revealed that all samples were starting to melt at 1350 °C and the sintering was completed for all specimens at 1300 °C. The only phases of fully sintered samples were cordierite and enstatite. Cordierite concentration, however, increased with enhancing kaolin percentage in composition. The results of this study can introduce Abdasht waste serpentine as magnesium silicate source into the ceramic industries and may help to solve environmental problems caused by several million tones wastes in Abdasht chromite mines.     

Influence of free chromium oxide on some properties of ceramics made of lanthanum chromite

Conclusions The stability of the properties of materials made of lanthanum chromite is determined primarily by their original porosity, and to a less degree by the content of free chromium oxide. An increase in the stability of the properties may be obtained by using a material with the minimum content of free chromium oxide, and the maximum possible density.The change in the porosity of the material on the basis of electrofused lanthanum chromite containing free chromium oxide, during use at high temperatures, is connected with the predominant removal of the chromium oxide and the completion of sintering of the material with volatilization of the Cr₂O₃.The dynamics of the mass loss of lanthanum chromite depend not only on the nature of the volatilization (congruent or incongruent) but also on the material's porosity.Translated from Ogneupory, No. 1, pp. 26–29, January, 1989.     

Reaction of lanthanum chromite ceramic with Li2CO3 and KNO3 melts

Translated from Steklo i Keramika, No. 2, pp. 22–24, February, 1994.     

Sintering of fireclay-kaolin mixtures with refractory clay

It is shown that the sintering of fireclay-kaolin mixtures is intensified by the replacement of refractory easily sintering plastic clays by high-melting clay. Recommendations are given on the choice of the method for preparation and introduction of the mentioned additive into the mixture. The developed technology has been tested under industrial conditions. Translated from Steklo i Keramika, No. 6, pp. 25 – 27, June, 2000.     

Modification of refractory ceramic composites with coatings based on compounds of titanium and zirconium

This article describes the properties and features of formation of modifying coatings developed for refractory materials on the basis of compounds of titanium and zirconium. It also explains the principles behind the interaction of the resulting composites with melts of metallurgical slag and borosilicate glass.     

氧化物-非氧化物复合材料的显微结构特征

利用SEM、TEM及HREM研究了氧化物-非氧化物复合材料的显微结构特征。结果表明(1)在氧化物基体中引入非氧化物,非氧化物颗粒将穿插于氧化物颗粒构成的骨架中;在非氧化物基体中引入氧化物,氧化物颗粒将弥散于非氧化物颗粒构成的编织状结构的空隙处。(2)氧化物与非氧化物之间的结合方式可分为(a)直接结合(在没有助烧剂、直接烧结的情况下);(b)通过晶界非晶质薄膜相结合(在有助烧剂奉与的直接烧结和反应烧结的情况下)。(3)所研究的试祥中普遍存在有微裂纹,这些微裂纹将有助于材料抗热震性的改善。     

Sintering behavior of periclase–doloma refractory mixes

Steelmaking electric arc furnaces (EAF) hearth is usually built up with dry vibratable refractory mixes. During furnace operation, the refractory mix undergoes sinterization, slag attack, and chemical interaction with steel. Material sintering is needed in the upper part of the EAF hearth, in order to develop enough mechanical strength and wear resistance during operation. Densification of the upper layer also reduces steel infiltration from the hot surface.In this work, the sintering behavior of three dry vibratable commercial refractory materials for EAF hearth is reported. The characterization of the mixes includes chemical, mineralogical, and granulometric analyses. The study of sintering behavior is carried out by dilatometric analysis and microstructural and mechanical evaluation of sintered specimens.Results showed that the analyzed mixes mainly contain periclase and doloma, with a wide granulometric distribution and different content of minor components (mainly, iron oxides). Material sintering began at temperatures higher than 1200 °C and was associated to liquid phase formation. Differences in sintering mechanisms with distinct amounts of liquid phase involved were determined in the analyzed materials and related to their iron oxides contents. Well-sintered specimens with higher room temperature mechanical strength and lower porosities were obtained from the mix with highest iron oxide content.