J. E. Zorzi

Moldagem por injeção em baixa pressão de peças complexas de cerâmicas avançadas produzidas com pós submicrométricos

A moldagem por injecao em baixa pressao (MIBP) tem constituido, nos ultimos anos, uma excelente alternativa para a producao de pequenos lotes de pecas cerâmicas diversificadas e com formas complexas. Esta tecnica de conformacao e relativamente simples e barata, mas apresenta diversos problemas na etapa de extracao dos ligantes, principalmente quando o po cerâmico e muito fino e as pecas possuem grande secao transversal. Neste trabalho e descrita uma metodologia especifica para a producao de pecas cerâmicas por moldagem por injecao a baixa pressao de alumina submicrometrica (0,4 mm), incluindo a formulacao da mistura para injecao, bem como detalhes do processo de extracao dos ligantes orgânicos utilizados na moldagem. Para o desenvolvimento deste processo fez-se necessario (i) entender melhor o processo de MIBP, (ii) desenvolver a formulacao da mistura de po cerâmico e aditivos orgânicos, (iii) confeccionar moldes adequados para a injecao a baixas pressoes e (iv) otimizar os parâmetros de injecao. A metodologia desenvolvida neste trabalho, possibilita a confeccao de pecas cerâmicas complexas, com secao transversal relativamente grande, permitindo uma producao robusta de pequenos lotes de pecas cerâmicas diversificadas com otima qualidade e excelente reprodutibilidade.

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.

Dureza e resistência ao desgaste da camada de ZrN formada por nitretação a plasma sobre zircônia parcialmente estabilizada com ítria

Samples of yttria partially-stabilized zirconia were molded by uniaxial pressing, sintered and nitrided in an atmospheric pressure microwave plasma. This procedure leads to the formation of a ZrN layer whose growth rate and thickness reached 4 µm.min-1 and 500 µm, respectively. The samples were characterized by means of hardness and wear resistance tests. The nitrided surface exhibits superior hardness and wear resistance similar to that of the zirconia substrate.

Constante de mola de molas cerâmicas injetadas a baixa pressão

The machining of sintered ceramic parts is a difficult process, mainly due to the hardness and brittleness of these materials, which implies in high production costs. Therefore, great efforts have been made to improve the forming processes of green ceramics, or create new processes to obtain the near net shape parts. The production of ceramic parts with complex shapes, free of defects, is a task that involves great difficulties. Ceramic springs exhibits shapes extremely difficult to be molded and therefore are currently commercially produced mainly by machining, a process which is difficult and expensive. An alternative for the production of ceramic springs is by low-pressure injection molding. For the development of ceramic springs for technological applications, it is required in addition to getting parts intact and free of defects, to measure some of its properties, including the spring constant. Since these springs are usually applied at high temperatures, it becomes important to carry out the measurement of resistance imposed by the spring to elastic deformation at different temperatures. Accordingly, in this work we describe the assembly of an experiment for the measurement of the spring constant of low-pressure injection molded ceramic springs, both at ambient temperature and at high temperatures, using the dynamic impulse excitation method to measure the frequency of vibration of a suspended spring inside a furnace. Results are presented for a helical spring of alumina from room temperature to1100 oC to illustrate the application of this technique.

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.

Instrumentação para espectroscopia de ressonância de ultrassom

The resonant ultrasound spectroscopy technique (RUS) allows the simultaneous determination of all components of the tensor of elasticity for the material that constitutes the sample. In this work, an automated device for ultrasonic resonance spectroscopy was assembled which enables the analysis of small samples in the form of parallelepipeds, cylinders or spheres. The application of this device is exemplified by the determination of the elastic constants of polycrystalline samples of alumina and nickel. The results differ from the expected values by, at most, 2.6% and 0.91% for alumina and nickel, respectively, and demonstrate the usefulness of this device in determining the elastic stiffness of small samples.

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.