RESUMO O material CuCr2O4 foi sintetizado pela reação de combustão em solução e tratado termicamente na faixa de 600 à 1100oC, afim de verificar a evolução das fases. O composto foi carcterizado estrutural e morfologicamente por meio das técnicas de Difração de Raios X (DRX), refinamentos pelo método de Rietveld, Microscopia Eletrônica de Varredura com canhão de elétrons por emissão de campo (MEV-FEG) e espectroscopia na região do Infravermelho com transformada de Fourrier. O comportamento da sinterização do material foi analisado por meio da dilatometria. Por meio dos padrões da difração de raios X (DRX) observou-se a formação da fase pura da Cromita de Cobre na faixa de 700-1000°C, a qual é corroborada pelo Refinamento Rietveld. Quanto a morfologia, as fases puras da cromita de cobre apresentaram formas de poliedros regulares. Por meio da dilatometria observou-se que o material apresentou uma expansão seguida de retração associada a mudança estrutural do material.

ABSTRACT CuCr2O4 material was subjected to solution combustion synthesis and heat-treated in the range of 600 to 1100oC in order to analyze its phase evolution. The structure and morphology of the composite were characterized by X-ray diffraction (XRD), Rietveld refinement, field emission gun scanning electron microscopy (FEG-SEM) and Fourier transform infrared spectroscopy (FTIR), while its sintering behavior was analyzed by dilatometry. The XRD patterns revealed the formation of pure phase copper chromite in the range of 700-1000°C, which was confirmed by Rietveld refinement. This pure phase copper chromite exhibited a regular polyhedral shaped morphology. The dilatometric analysis indicated that the composite underwent thermal expansion followed by shrinkage, which were attributed to structural changes in the material.

RESUMO A cobaltita de níquel (NiCo2O4) de estrutura do tipo espinélio apresenta baixa estabilidade térmica em torno dos 400 °C, que ocasiona a perda de NiO, afetando de maneira significativa as propriedades físicas e estruturais do material produzido. Neste trabalho a cobaltita de níquel foi preparada pelo método dos precursores poliméricos. O material foi calcinado a 350 °C e tratado termicamente nas temperaturas entre 450 – 650 °C. O produto obtido foi caracterizado por Termogravimetria e Calorimetria Exploratória Diferencial (TG/DSC), Difração de Raios X (DRX), Refinamento Rietveld, Espectroscopia Raman, Microscopia Eletrônica de Varredura e caracterização magnética. Os resultados mostraram que é possível se obter a fase cobaltita de níquel independente do tratamento térmico empregado. As análises magnéticas mostraram um comportamento magnético diferente para cada temperatura de tratamento do composto sintetizado.

ABSTRACT Nickel cobaltite, NiCo2O4, with a spinel-like structure has low thermal stability at around 400 °C, which causes loss of NiO, thus significantly affecting the physical and structural properties of the material. In this work, nickel cobaltite was prepared by the polymeric precursor method. The material was calcined at 350 °C and heat-treated at temperatures ranging from 450 to 650 °C. The resulting product was analyzed by thermogravimetry and differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), Rietveld refinement, Raman spectroscopy, scanning electron microscopy (SEM) and a magnetic characterization technique. The results of these analyses indicated that the nickel cobalt phase can be obtained regardless of the heat treatment applied. The magnetic analysis revealed that the magnetic behavior of the synthesized compound varied as a function of each treatment temperature.

Several wood species from the Amazon region are used in the manufacture of furniture, which leaves behind large amounts of waste (slabs, sawdust, sanding dust and bark), thus causing serious environmental impacts. An interesting alternative for the use of these wastes is the manufacture of particleboards. However, few studies have focused on the behavior of Amazonian tree species and the wastes resulting from production with this type of material. This paper discusses the potential use of Tauari (Couratari oblongifolia) wood waste as a raw material for the production of particleboards, using castor oil-based bi-component polyurethane adhesive. Experimental boards were prepared with dry wood particles and a castor-oil polyurethane adhesive content of 16%. The boards, whose nominal density was 1000 kg·m-3, were subjected to uniaxial compression (5 MPa) at 90, 110 and 130ºC for ten minutes. The particleboards were characterized by performing the following tests: Apparent density (D AP), Moisture (M), Water Absorption (WA), Thickness Swelling (TS), Static bending strength: MOR (Modulus of rupture) and MOE (Modulus of elasticity), Perpendicular Tensile Strength (IB - internal bonding) and Screw Pullout (SP), according to the Brazilian NBR 14.810:2006 standard. The results indicate that, regardless of the processing temperature, the average density of Tauari particleboard is 930 to 941 kg·m-3, with higher IB and TS than those specified by the NBR 14810-2 and ANSI A208.1 standards, enabling this product to be classified as high-density particleboard suitable for industrial and commercial use.

Nesse trabalho, foram caracterizados, pela primeira vez, azulejos históricos portugueses do Centro Histórico de São Luís (CHSL) do Maranhão. A caracterização foi realizada através dos ensaios de microscopia ótica, difração de raios X (DRX) e análise química, visando ao uso dessa informação para a determinação das possíveis matérias-primas utilizadas na sua fabricação, bem como a provável temperatura de queima desses materiais. Os resultados mostraram que a microestrutura desses materiais é constituída por poros de tamanhos variados, apresentando incrustações de calcita e grãos de quartzo de tamanhos inferiores a 500 µm, distribuídos numa matriz de cor rosa-amarelo, onde foram identificadas, por DRX, as fases minerais calcita, gelhenita, wollastonita, quartzo e amorfo. A partir da informação obtida, é possível inferir que as matérias-primas originais estiveram constituídas, provavelmente, por mistura de argilas caoliníticas (Al2O3·2SiO2·2H2O), ricas em carbonatos de cálcio e quartzo ou misturas de argilas caoliniticas, quartzo e calcita. Essas matérias-primas originais não atingiram a temperatura de cocção de 950ºC.

This work involved the first-ever characterization of antique Portuguese ceramic wall tiles in the Historic Center of São Luis do Maranhão, Brazil. The tiles were characterized by optical microscopy, X-ray diffraction (XRD) and chemical analysis to identify the possible raw materials used in the fabrication process, as well as the firing temperature of these materials. The results indicate that the microstructure of these materials consists of pores of varying sizes with calcite incrustations and quartz grain sizes smaller than 500 µm distributed in a pinkish yellow matrix, which were identified by XRD as calcite, gehlenite, wollastonite, quartz, and amorphous mineral phases. Based on this information, it can be inferred that the original raw materials probably consisted of a mixture of kaolinitic clays (Al2O3·2SiO2·2H2O) rich in calcium carbonates and quartz, or mixtures of kaolinitic clays, quartz and calcite, which did not reach the pre-firing temperature of 950ºC.

Nesse trabalho, foram caracterizadas algumas argilas coletadas nos municípios de São Luís, Rosário, Pinheiro e Mirinzal. A caracterização foi realizada através dos ensaios de difração de raios X, massa específica real, capacidade de troca de cátions (CTC), área superficial, distribuição granulométrica, análise química, análise térmica (TG-DTA) e limites de Atterberg. Ensaios tecnológicos de retração linear, antes e após a queima, absorção de água e tensão de ruptura a flexão, em três pontos, foram realizados em corpos de prova prensados uniaxialmente a 20 MPa e tratados termicamente em 850, 950, 1050, 1150 e 1250ºC. Os resultados obtidos permitiram identificar duas argilas de queima branca, constituídas de quartzo, caolim, feldspato e anatásio, com excelentes propriedades para uso em cerâmica branca. As restantes são queima vermelha e possuem composição mineralógica de quartzo, caolim, feldspato, montmorilonita, hematita e goetita. Estas últimas apresentaram valores moderados de plasticidade e são adequadas para aplicações em cerâmica vermelha.

This work involved the characterization of clays collected in the municipalities of São Luis, Rosário, Pinheiro and Mirinzal (state of Maranhão, Brazil), based on specific mass, specific surface area, cation exchange capacity (CEC), particle size distribution, X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TG-DTA) and Atterberg limits. Technological tests for ceramic applications were also carried out on compacts pressed under 20 MPa and heat-treated at 850, 950, 1050, 1150 and 1250ºC. Our results indicated that two of the clays composed of kaolinite, quartz, and anatase with high plasticity limits, have excellent properties and can be used in the whiteware industry. The other ones are red-firing clays and have a mineralogical composition of quartz, kaolin, feldspar, montmorillonite, hematite and goethite. The latter showed low and moderate values of plasticity, which makes them suitable for the production of heavy clay products.

Tests involving the Classical Nucleation Theory (CNT) often disregard the size dependence of surface energy. Thus, the surface energy of critical nuclei is assumed to be a macroscopic quantity that depends only on the temperature of a flat surface. However, because the size of critical nuclei changes with temperature, σcl(T) should be described as a function of both temperature and size of critical nuclei. The present work examines the temperature dependence of macroscopic surface energy, decoupling it from the size dependent part. Tolman, Rasmussen and Vogelsberger's equations are used to decouple the dependence of surface energy on size, using experimental data for the following silicate glasses Li2O.2SiO2 (LS2) and Na2O.2CaO.3SiO2 (N1C2S3). These equations are successful in obtaining a decrease in σcl(T), in agreement with theoretical predictions. For all the values of δ , Tolman's equation produces the lowest values of σcl(T). Nevertheless, they are very close to the liquid/vapor surface energy (σlv), which contradicts the Stefan's rule (i.e. σcl/σ lv << 1). Therefore, it is demonstrated that the assumption of the curvature dependence of surface energy does not suffice, per se, to explain the discrepancy between the experimental and theoretical values of nucleation rates.