Romualdo Rodrigues Menezes

The use of granite wastes as ceramic raw materials

The granite industry generates a large quantity of wastes that pollute and damage the environment. This work aim to characterize and evaluate the possibilities of the use of granite sawing wastes, generated by the industries from Northeast region, as alternative ceramic raw materials for production of ceramic bricks and tiles. Samples of granite sawing wastes were collected from industries located at Paraiba, Ceara and Pernambuco states, and afterwards were characterized for the determination of their particle size distribution, specific mass, surface area (BET) and chemical analyses, differential thermal analysis, GTA, X-ray diffraction, and scanning electron microscopy. After characterization, technological tests were performed in ceramic compositions with the objective of evaluation of the possibilities of the addition of wastes in ceramic masses for the production of ceramic bricks and tiles. The main results show that the wastes have physical and mineralogical characteristics similar to the conventional ceramic raw materials and ceramic bodies. Moreover, the ceramic pieces prepared using the wastes have technical characteristics according to the Brazilian standards for ceramic bricks and tiles.

O estado da arte sobre o uso de resíduos como matérias-primas cerâmicas alternativas

Os residuos industriais e urbanos vem-se tornando um dos mais serios problemas que a sociedade moderna enfrenta. Sua deposicao de forma inadequada provoca a degradacao do meio ambiente e a contaminacao dos mananciais de agua e do solo. Por outro lado, tecnicos da industria cerâmica se deparam com a escassez de reservas de materias-primas de boa qualidade em locais economicamente viaveis de exploracao. Assim, este trabalho objetiva apresentar uma visao geral da possibilidade de utilizacao dos residuos industriais e urbanos como materias-primas cerâmicas alternativas, enfocando a industria cerâmica como uma fonte economicamente viavel e ecologicamente correta para reciclagem de residuos.

Utilization of kaolin processing waste for the production of porous ceramic bodies

The kaolin processing industry generates large amounts of waste in producing countries such as Brazil. The aim of this study was to characterize kaolin processing waste and evaluate its suitability as an alternative ceramic raw material for the production of porous technical ceramic bodies. The waste material was physically and chemically characterized and its thermal behaviour is described. Several formulations were prepared and sintered at different temperatures. The sintered samples were characterized to determine their porosity, water absorption, firing shrinkage and mechanical strength. Fired samples were microstructurally analysed by X-ray diffraction and scanning electron microscopy. The results indicated that the waste consisted of quartz, kaolinite, and mica, and that ceramic formulations containing up to 66% of waste can be used for the production of ceramics with porosities higher than 40% and strength of about 70 MPa.

Microwave fast sintering of submicrometer alumina

Commercially available alumina powder with high-purity submicrometer particle size and narrow particle size distribution was fully densified by a microwave hybrid fast firing technique. The alumina compacts were surrounded by susceptor material, which helped the heating of the samples, and sintered in a microwave oven at a frequency of 2.45 GHz and a power level of 1.8 kW. The sintered samples reached densities of 99% in sintering cycles of 30 to 40 minutes, a much shorter time than conventional sintering processes. The sintered samples showed uniform microstructures with powder particle size/average grain size rations higher than 1:2.

Kaolin processing waste applied in the manufacturing of ceramic tiles and mullite bodies

In the last few years, mineral extraction and processing industries have been identified as sources of environmental contamination and pollution. The kaolin processing industry around the world generates large amounts of waste materials. The present study evaluated the suitability of kaolin processing waste as an alternative source of ceramic raw material for the production of ceramic tiles and dense mullite bodies. Several formulations were prepared and sintered at different temperatures. The sintered samples were characterized to determine their porosity, water absorption, firing shrinkage and mechanical strength. The fired samples were microstructurally analysed by X-ray diffraction. The results indicated that ceramic tile formulations containing up to 60% of waste could be used for the production of tiles with low water absorption (~ 0.5%) and low sintering temperature (1150 °C). Mullite formulations with more than 40% of kaolin waste could be used in the production of bodies with high strength, of about 75 MPa, which can be used as refractory materials.

Microwave Fast Sintering of Ceramic Materials

Microwaves are electromagnetic waves with wavelengths ranging from 1m to 1 mm, which correspond to frequencies between 0.3 and 300 GHz. This frequency range lies just above radio waves and just below visible light on the electromagnetic spectrum (Katz, 1992). The possibility of processing ceramics by microwave heating was discussed over 50 years ago by Von Hippel (1954a), and experimental studies on microwave processing of ceramics were started in the mid 1960s by Tinga and Voss (Tinga & Voss, 1968). Since then, the results of many investigations into microwave sintering and joining of ceramics have been reported (Bykov et al., 2001). Activity in this field began to accelerate in the mid-1970s because of a shortage of natural gas, prompting the investigation of microwave heating and sintering of several ceramic materials in the late 1970s and 1980s.

Pozolanic activity of kaolin processing residues for use in masonry mortars.

The kaolin processing industry generates large amounts of waste, which is indiscriminately dumped in open-air sites. This work evaluates the technical suitability and pozolanic activity of kaolin processing wastes for the production of mortars. The wastes were characterized by particle size distribution and chemical composition determination, X-ray diffraction and thermal differential and gravimetric analyses. The pozolanic activity index was determined using lime and Portland cement. Cement:lime:sand mortars were formulated and the kaolin wastes replaced cement by 5, 10, 15 and 20% on weight basis. The kaolin wastes were used in their natural condition and after thermal treatment at 600 °C for 2 h. Test specimens were produced and their compression strength determined. The results indicated that the waste consists of quartz, kaolinite and mica, and that the use of the fired waste improves the mortar strength at 28 days by up to 150%.

Influence of Firing Conditions on Properties of Red Ceramic

In the ceramic industry, the firing is one of the main stages of the production process. There are two heating rates prevailing at this stage: low heating rate (long residence time) and high heating rate (fast residence time), the low rate is more used in traditional ceramics. This study aims to evaluate the influence of firing conditions on technological properties of three compositions of clay, used in the manufacture of red ceramic products. Initially, the mixtures were characterized subsequently were extruded, dried and submitted to firing at temperatures at 900 and 1000 °C with heating rates of 1, 2, 5, 15, 20 and 30 °C/min. The crystalline evolution of the different samples was analyzed using X-ray diffraction and the technological properties were determined. For the mechanical resistance, it was not observed significant change with the increase of the temperature and heat rate

Análise da expansão por umidade e absorção de água de pisos cerâmicos comerciais em relação à composição química e à quantidade estimada de fase vítrea

Moisture expansion is the size increase of the ceramic body due to water adsorption and can have a great influence in the ceramic material service life. This work aims to relate the moisture expansion and water absorption of commercial ceramic tiles with their chemical composition and estimated glassy phase content, calculated from the phase equilibrium diagram of the system SiO2.Al2O3.K2 O using the lever rule. Samples of twenty three commercial ceramic tiles were studied. The chemical composition of the samples was obtained (wet route) and their moisture expansion and water absorption were determined (according to the Brazilian standard NBR 13818). The specific surface area of some samples was also determined, using the nitrogen adsorption methodology (BET). The results obtained generally show an inverse proportionality between the moisture expansion and the water absorption, for the majority of the samples. The analysis using the phase diagram suggests an inverse proportionality between the water absorption and the estimated glassy phase content and a direct proportionality between the moisture expansion and the quantity of glassy phase.

Influência das variáveis de processo na obtenção de argilas organofílicas

As argilas bentoniticas, usadas como agente viscosificante e nanocompositos, nao podem ser usadas sem um previo tratamento orgânico para que suas superficies se tornem hidrofobicas e possam ser dispersas em meios orgânicos. Estas argilas depois de tratadas sao chamadas de argilas organofilicas, e sao geralmente obtidas atraves da adicao, em meio aquoso, de um agente organofilizante, geralmente um tensoativo, ionico, anfotero ou nao ionico. O processo de organofilizacao, composto de varias etapas, nem sempre garante a obtencao de argilas organofilicas de boa qualidade, sendo importante destacar as variaveis de processo bem como a escolha das materias-primas a serem utilizadas. Propoe-se entao um estudo detalhado das variaveis envolvidas no processo de dispersao das argilas bentoniticas, e tambem no processo de organofilizacao procurando relacionar as viscosidades aparente e plastica das dispersoes argilosas com a eficiencia do processo de organofilizacao. O processo de organofilizacao sera controlado pelos resultados de difracao de raios X e termogravimetria. As variaveis de processo tanto envolvidas na dispersao das argilas quanto na organofilizacao, do ponto de vista da caracterizacao, nao tem grande influencia na incorporacao do tensoativo as argilas bentoniticas, sendo influentes o tipo de argila e tensoativo e a presenca de sodio como agente defloculante, o que e muito importante de vista industrial pela melhor operacionalidade das condicoes de processamento.