Over recent years, owing to the need to increase productivity, it has been necessary among other things to increase the hot metal temperature in the blast furnace hearth. As a result, refractory lining wear becomes more intense. While publications present a host of comparative tests for hearth refractories and their performance, hardly any information is available in such publications regarding reaction mechanisms and further deterioration of these materials. Based upon comparative laboratory test results using two carbon materials of different concepts, the various reaction mechanisms and enhanced refractory lining deterioration for the blast furnace hearth have been identified. From an understanding of these wear mechanisms acting upon the hearth lining, it has been decided to introduce some practical operating measures, with a view to extending the blast furnace campaign.

A técnica de difração de raios X tem sido amplamente utilizada para a determinação de fases cristalinas em materiais cerâmicos. Em argilas, a grande quantidade de quartzo e seu elevado grau de orientação dificultam a identificação e caracterização das demais fases presentes. Baseando-se no princípio da sedimentação, é apresentado neste trabalho um método simples e confiável para a determinação de argilominerais em materiais argilosos.

Zeta potential is one of the most relevant parameters controlling the rheological behavior of ceramic suspensions. In this work, it was observed that for pH values below the isoelectric point (IEP), the positive value of zeta potential of water suspensions of α-quartz and α-cristobalite, experiences a sudden steep increase with the increase in specific surface area of the powders. For pH values above the IEP, the zeta potential values of crystalline forms of silica (α-quartz and α-cristobalite), get gradually more negative with the increase in pH. Conversely in the case of vitreous silica, for pH values above 6, there occurs a steep change towards more negative values of zeta potential than those presented by quartz and cristobalite. These findings have not yet been accounted for in the DLVO theory but may provide subsidies for better understanding of how to stabilize and destabilize crystalline and vitreous silica water suspensions.

Thermal diffusivity is a material physical property important in all problems involving non-steady state heat transfer calculations, being a decisive parameter in the response of materials subjected to thermal shock. In this work it is presented a fundamental study related to how the phase transitions may influence the thermal diffusivity behaviour as a function of temperature in the phase transforming SiO 2 . The experimental technique employed was the flash thermal diffusivity technique, and measurements were carried out from 100 o C up to approximately 1200 o C. It was found a strong dependence on the thermal diffusivity with the high and low temperature forms of the quartz and cristobalite phases.

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This paper looked into hot metal corrosion behavior for graphite refractory used in blast furnace hearth, consisting of 50% graphite and 50% anthracite, impregnated with TiO 2 , ZrO 2 carrying solutions. The method used for corrosion was the Finger Test, which was conducted in an induction furnace with 30 Â 30 Â 280 mm bar-shaped test specimens, and the hot metal and slag used were taken from the CSN #2 Blast Furnace runner, the test temperature was 1470 8C with a sixty-minute isotherm. After the corrosion test, the specimens were characterized by their dimensional variation, X-ray diffractometry and Scanning Electronic Microscopy (SEM).

Simultaneous grain growth of the lime (CaO) and periclase (MgO) phases was studied in a synthetic, hydroxide-derived doloma over the temperature range 1400" to 1700°C. The grain growth kinetic exponents were 5 and 6 and the activation energies 333 f 45 and 437 & 47 kJ/mol for the CaO and MgO phases, respectively. The large kinetic exponents are attributed to the topological restraints of the two phases on the growth of one another. The parameters suggest that the grain growth of the CaO may be governed by Ca2+ diffusion within the CaO phase for it is the continuous phase in the microstructure. In most instances for grain growth of the MgO phase, the Mg2+ must diffuse through the lime phase. and this process is believed to be limited by movement of associated defects involving Mg2+ within the CaO structure.

ABSTRACT:This study presents an investigation of the effect of the different crystalline phases of each blend component on miscibility when blending poly(vinylidene fluoride) (PVDF) and its copolymer poly[(vinylidene fluoride)-ran-trifluorethylene] [P(VDFTrFE)] containing 72 mol % of VDF. It was found that, when both components crystallized in their ferroelectric phase, the PVDF showed a strong effect on the crystallinity and phase-transition temperature of the copolymer, indicating partial miscibility in the crystalline state. On the other hand, immiscibility was observed when both components, after melting, were crystallized in their paraelectric phase. In this case, however, a decrease in crystallization temperatures suggested a strong interaction between monomers in the liquid state. Blend morphologies indicated that, in spite of the lack of miscibility in the crystalline state, there is at least miscibility between PVDF and P(VDF-TrFE) in the liquid state, and that a very intimate mixture of the two phases on the lamellar level can be maintained upon crystallization.