Saulo Roca Braganca

Recycling of iron foundry sand and glass waste as raw material for production of whiteware

The purpose of this study was to evaluate the production feasibility of triaxial whiteware using sand from cast iron moulds as a raw material instead of silica, and recycled glass in place of feldspar. Formulations were prepared using sand, glass waste, and white-firing clay such that only 50% of the composition was virgin material (clay). The ceramic bodies were formed by pressing and fired at different temperatures (between 1100 and 1300°C). Specimens were characterized in terms of green density prior to firing; and their flexural strength, linear shrinkage, and water absorption were measured after firing. The microstructure was determined by scanning electron microscopy. Possible environmental impacts of this recycling process were also evaluated, through solubility and leaching tests, according to Brazilian standards. Gaseous emissions during the firing process were also analysed. The results showed that it is possible to produce triaxial ceramics by using such alternative raw materials.

Heat Transfer in Steelmaking Ladle

The heat transfer in a steelmaking ladle was studied. The evaluation of heat transfer of the steel was performed by measuring steel temperature in points including all refining steel process. In the ladle, the temperatures in the refractories and the shell were also measured. To evaluate the thermal profile between the hot and cold faces of the ladle in the slag line position, an experiment which shows the importance of thermal contact resistance was carried out. Higher heat losses in the tapping and the vacuum were verified. The temperature measurements of the ladle indicate distinct thermal profiles in each stage of steel refining. Moreover, as each stage of the process depends on the previous one, the complexity of the ladle thermal control is incremental. So a complete model of heat losses in the ladle is complex.

Waste glass in porcelain

In this work, the feldspar used as a flux in typical porcelain was replaced by waste glass, and the resulting batch composition contained 50% kaolin, 25% quartz and 25% waste glass. The properties of this porcelain with glass powder (GP) were compared to traditional porcelain (TP), which utilizes feldspar. The samples were fired at different temperatures, ranging from 1200 °C to 1400 °C. Technical parameters, such as water absorption, modulus of rupture and KIC, phase analysis by XRD, and microstructure by SEM were analysed. The results indicated that the lower fracture toughness and MOR of GP is a consequence of the peculiar microstructure of this porcelain. The reduction in firing temperature and the use of a cheaper substitute for feldspar makes GP also an attractive economical alternative.

Microestrutura e propriedades de porcelanas

The microstructure of traditional porcelain sintered at different temperatures was analyzed and related to technical parameters . The morphology of the phases was investigated. Quartz, primary mullite and secondary mullite were found. The results were supported with experimental data using EDX and X-ray diffraction analysis. The properties of the sintered samples show to be strongly affected by vitreous phases, and this determine the quality of the ceramic pieces. The best sintering temperature was also a consequence of vitreous phase properties, like porosity. The crystalline phases were found responsible for the achieved stren gth .The microstructure of traditional porcelain sintered at different temperatures was analyzed and related to technical parameters. The morphology of the phases was investigated. Quartz, primary mullite and secondary mullite were found. The results were supported with experimental data using EDX and X-ray diffraction analysis. The properties of the sintered samples show to be strongly affected by vitreous phases, and this determine the quality of the ceramic pieces. The best sintering temperature was also a consequence of vitreous phase properties, like porosity. The crystalline phases were found responsible for the achieved strength .

Aspectos teóricos e práticos sobre a resistência mecânica de porcelanas

The properties of traditional porcelain, including its mechanical strength, are a consequence of the ceramic processing that formed the piece, and then, raw materials and their characteristics, forming process, firing atmosphere, time and temperature. These parameters determine the complexities of microstructure and phase development, which are difficult to be controlled and makes almost impossible to predict porcelain final properties. Since the last century, many theories have been developed to explain the strength of porcelain, and some have recently been revised and improved due to the development of new analytical techniques. This work shows an overview on the literature, which comprises new discussions and theories about porcelain strength, including authors´ own investigations.

Desulfurization kinetics of coal combustion gases

Desulfurization of the gases from coal combustion was studied, using limestone (marble) as the sorbent in a fluidized-bed reactor. The kinetic parameter, k, was measured by analyzing the reduction in SO2 emissions in relation to time when a batch of limestone was introduced directly into the combustor chamber. The influence of sorbent composition and particle size was also studied. The CaO content in the limestone was more important than the MgO content. Sorbent particle size showed a strong influence on the reaction time and efficiency of desulfurization. The results of this work prove that marble type is very important in the choice of sorbent for a desulfurization process. A magnesian limestone showed a better performance than a dolomite. Therefore, the magnesian limestone is more efficient for a shorter particle residence time, which is characteristic of the bubbling fluidized bed.

FBC desulfurization process using coal with low sulfur content, high oxidizing conditions and metamorphic limestones

A metamorphic limestone and a dolomite were employed as SO2 sorbents in the desulfurization of gas from coal combustion. The tests were performed in a fluidized bed reactor on a bench and pilot scale. Several parameters such as bed temperature, sorbent type, and sorbent particle size at different Ca/S molar ratios were analyzed. These parameters were evaluated for the combustion of coal with low-sulfur/high-ash content, experimental conditions of high air excess and high O2 level in fluidization air. Under these conditions, typical of furnaces, few published data can be found. In this work, a medium level of desulfurization efficiency (~60%) for Ca/S = 2 was obtained.

Produção de porcelana de ossos e caracterização de suas propriedades técnicas

Porcelains from bone ash are widely accepted and present high market value, however, their manufacture and research are still restricted to few countries. As a great producer of cattle, Brazil presents great potential for the recycling of cattle bone into ceramic materials. In this work, it was realized a comparative investigation of technical properties of a typical porcelain composition manufactured from bone ash according to English traditional composition and a traditional porcelain. The results revealed that it is more difficult to sinter bone porcelain in fast firing cycles, once it showed shorter firing intervals compared to traditional porcelains. However, the higher mechanical strength and better aesthetic qualities, especially its whiteness, make bone porcelains very attractive materials in terms of industrial applications potential.

The behavior of heavy metals in the process of desulfurization of Brazilian coal combustion gases by the addition of limestone

The concentrations of heavy metals in two kinds of Brazilian coals at 100° C (acid digestion) and at 850° C were studied (ashes the obtained in muffle furnace with and without addition of limestone). Data were analyzed by flame atomic absorption, using the air acetylene flame. For Pb, Zn, Ni, Mn and Cu the metal concentration obtained the acid digestion were higher than metal concentration were obtained in tests in the muffle furnace. This behavior observed in the muffle furnace occurs because these metals are fixed in stable sulfated compounds in the ashes, which are difficult to dissociate at flame temperature, and also due to the volatile character of the metals, mainly Pb and Zn. There was a constant concentration in the ashes in of Cr the acid digestion and muffle furnace tests. Results from tests using an XRD apparatus indicated, he formation of sulfated compounds in the ashes for both. coals. The analysis using microprobe electronic showed retention of metals like Ni, Mn, Cu, Fe, Ti and Ca. For both coals, the low mobility of most of the metals studied occured due to the alkaline pH of sulfated ashes. These metals in the ash from coal combustion in fluidized bed reactor were also studied and showed similar results, enabling a scale-up to pilot scale.

Use of Wollastonite as a Flux for Bone China Bodies

The utilization of wollastonite as a flux in bone china was investigated in this work. Ceramic industry is always looking to optimize the use of fluxes as a way of reducing energy costs associated with firing. Wollastonite is added in ceramic formulations as an auxiliary flux and allows fast firing production. However, its use in bone china has not been tested before. In the present work, two formulations were prepared, comparing the traditional formulation to another in which the conventional flux (potash feldspar) was partially replaced by wollastonite. The firing behavior, technical properties, microstructure, and phase development were analyzed. A slip with wollastonite was also developed to analyze its rheology. Wollastonite body achieved a reduction of firing temperature, a large plateau for firing, and optimal slip stabilization for casting pieces.