R. C. D. Cruz

Caracterização de matérias-primas cerâmicas do Vale do Rio Caí

da regiao nordeste do Rio Grande do Sul, limitada pelas regioes geomorfologicas da depressao periferica ao sul e pelas encostas do planalto meridional ao norte (Fig. 1). Constitui uma regiao de relevo muito peculiar chamada de rebordo do Planalto das Araucarias, que se estende da porcao sul dos patamares da bacia do Parana ate encontrar a depressao gaucha. Esta localizada entre 29° 50’ S e 29° 17’ S de latitude e 51° 41’ O e 51° 10’ O de longitude e regionalmente e denominada Encosta Inferior do Nordeste. A topografia que predomina e a de coxilhas (termo equivalente para colinas e lombas) tanto nas altitudes elevadas do planalto quanto nas baixas altitudes da depressao. A diferenciacao destas coxilhas se faz pelo processo de formacao dos solos. Enquanto no planalto sua origem e predominantemente basaltica, na depressao possui origem sedimentar e arenitica. Nestas ultimas, separando e permeando as coxilhas estao as planicies de alagamento do rio Cai e seus afluentes. A regiao e de baixa altitude (50 m) e apresenta relevo plano ou levemente ondulado ao sul, enquanto na regiao central a altitude media e de ate 200 m, com predominância de varzeas, encostas e morros. Ao norte predominam escarpas, vales profundos e elevacoes com ate 500 m de altitude. O clima da regiao e temperado subtropical umido, caracterizado por invernos frios e umidos e primaveras de temperaturas mais elevadas. O solo e predominantemente composto por argila vermelha com forte acidez natural [1].O rio Cai pertence a regiao hidrografica do Guaiba. Sua nascente esta localizada no planalto gaucho da Serra Geral, no municipio de Sao Francisco de Paula, em cotas que ultrapassam os 800 m de altitude. Seu curso de agua tem

Technological Characterization of Heavy Clay from the Caí River Valley in Brazil

This study presents the chemical, mineralogical, mechanical, physical and thermal properties of a clay widely available for use by the ceramic industry in southern Brazil. Some of the most important characteristics of the clay were studied, including its chemical and mineralogical composition, particle size distribution, thermal behaviour and green and after firing properties. The material was a kaolinitic primary clay with low organic content and high amount of finely divided quartz and goethite. This work is part of an effort to make available useful technical data on raw materials affecting ceramic business costs and to promote sustainable exploitation of mineral resources and improved practices in the local heavy clay industry.

Reactive processing of a non-additivated isotactic polypropylene: mechanical and morphological properties on molten and solid states

Isotactic polypropylene (iPP) is a thermoplastic with several desirable properties as it can be modified by additives and processing, making it one of the most versatile and popular polymers. In this context, we present a detailed study of morphological and mechanical properties of non-additivated iPP produced by reactive processing, mainly concerning the effect of controlled radicalar degradation on polymer structure in molten and solid states. Melt rheology and size exclusion chromatography analyses evidenced the reduction on viscosity and moduli in dependence of molecular weight by the addition of commercial peroxide. The behavior in solid state showed that smaller chains of degraded iPP at high temperatures exhibited greater mobility resulting in a more viscous response upon a mechanical loading. Moreover, β-form crystals were suppressed by molecular weight reduction as suggested by X-ray diffraction. This finding suggests that smaller chains have higher mobility, and consequently are less susceptible to shear deformations during processing.

Aditivo surfactante de fonte renovável para redução do consumo energético na extrusão de massas de cerâmica vermelha

The impact of surfactants on the semi-solid extrusion of clay masses is directly related to the performance associated with the mass flow and energy consumption. In this work, a formulation based on a ceramic mass used in the manufacture of structural blocks was formulated with the addition of surfactant obtained from a renewable source (tannin). The objective was to evaluate the impacts of tannin addition on the workability of the mass, reduction of energy consumption, the hardness of the extrudate, and properties of the dry and sintered bodies (e.g. flexural strength, linear retraction and water absorption). For the ceramic mass formulation with 1.0 wt% tannin, the results indicated a decrease of ~37% in wet mass hardness, increase in mechanical strength after drying (~29%) and firing (~15%), and ~75% reduction in specific energy consumption. The overall positive effects of surface modifier addition to the ceramic mass suggest that tannin can be used, safeguarding the economic criteria, without compromising the performance of the red ceramic blocks.

Obtenção de amidos termoplásticos para a extrusão de pós cerâmicos

Thermoplastic polymers can be used as organic vehicle (OV) in ceramic parts forming by extrusion. In this context, starch-based thermoplastics arise as a sustainable alternative to polyolefins conventionally used in ceramic slurry formulation. The initial step for the development of a feedstock (extrudable load) is the selection of the polymeric binder system, which is responsible for providing appropriate rheological properties during processing. Accordingly, in this work thermoplastic starches obtained in the presence of citric acid are characterized and evaluated as for the potential use in the extrusion of ceramic powders. The processability of the premixed starches was investigated in a twin-screw extruder and in a mixer torque rheometer. The variation of water and glycerol contents in the composition of the premixed starches significantly influenced the interactions between polymer chains, promoting changes in density and viscosity for most analysed samples. The thermoplastic starches were partly esterified as an effect of the citric acid presence in the system. Among all formulations investigated, the H-34 sample (hydrated and processed with 34% w/w of glycerol content) showed the best paste properties and can be further employed in ceramic powder forming processes.

Influência da cera de carnaúba no comportamento reológico de misturas usadas na moldagem por injeção em baixa pressão

The low-pressure injection molding (LPIM) has some advantages over other methods of forming ceramic parts with complex shapes. Among the advantages are the lower costs in the production of small and medium lots and less wear of molds and equipment. In this work, the effect of an organic additive used in LPIM been studied, carnauba wax, on the rheology of the mixture (feedstock). The ceramic powder used was alumina with particle size of about 0.4 micrometers. With additions of 5wt% and 10wt% of carnauba wax in the organic vehicle, viscosity decreases significantly, being much more pronounced at 10%, while above this value (15%), the viscosity decrease, but this reduction is less pronounced. In contrast, in feedstock without carnauba wax (0%), the viscosity is so high that the injection almost impossible at low pressures.

Efeito do processamento em misturas de alumina/ligantes orgânicos usadas na moldagem por injeção em baixa pressão

The low-pressure injection molding (LPIM) is a technique already being used in the production of ceramic parts with complex shapes and geometries. The homogeneity of the mixture of organic binder and ceramic powder is a determining factor which must be controlled to minimize defects formation while feedstock processing to LPIM. Typical defects of LPIM processing, such as air bubbles and agglomerates, generate density gradients in the mixtures, which, after shaping, have little possibility of removal. These imperfections compromise the performance of the products obtained by this technique. This work is focused on the evaluation of these inhomogeneities and how they can be correlated with density variation and the rheological behavior of these mixtures. Therefore, submicrometer aluminas, as received and deagglomerated, were added to a molten mixture of paraffin based binders, waxes and additives and processed in two different mixers, with and without vacuum. The presence of alumina agglomerates was observed in the powder as received, possibly generated during the calcination step. It was also observed that the type of mixer and vacuum application or not during the final processing step, has a major influence on the mixing time required to reduce the viscosity of the feedstock for injection.