S. Ribeiro

Substitution of pure Y2O3 by a mixed concentrate of rare earth oxides (CRE2O3) as sintering additive of Si3N4: a comparative study of the mechanical properties

Abstract In this work the substitution of pure yttrium oxide (Y2O3) by a mixed concentrate of yttrium and rare earth oxides (CRE2O3), produced at FAENQUIL-DEMAR, as sinter additive in gas-pressure sintered Si3N4 ceramics has been investigated. CRE2O3 presented similar behavior compared to pure Y2O3 in relation to the sinterability, intergranular phases formed, microstructure and mechanical properties. As this alternative additive is obtained at a cost of only 20% than that of commercial Y2O3, CRE2O3 demonstrated great potential as additive in the sintering of Si3N4 ceramics.

Incorporation of conjugated linoleic and alpha linolenic fatty acids into Pimedolus maculatus fillets

The objective of this study was to investigate the fatty acid composition of Pimedolus maculatus fillets of fish fed with different diets. The fish were submitted to an adaptation period (over 30 days) and fed only a control diet (diet I). After this period, the fish were divided into two groups: one group received a diet enriched with flaxseed oil (diet II), and the other received a diet enriched with conjugated linoleic acid (CLA) (diet III). Subsequent collections were undertaken after 25 and 50 days. Compared to the control samples, fish fed diet II showed an increase in concentrations of total fatty acid omega-3 (n-3) in the fillets, with an improvement ratio of n-6/n-3. The incorporation of CLA into fish fed diet III was successful. Supplementing the diet of Pimedolus maculatus with CLA and flaxseed oil led to improvements in nutritional quality and fatty acid profile of the fish fillets.

Application of Enzymes in Sunflower Oil Extraction: Antioxidant Capacity and Lipophilic Bioactive Composition

A 23 factorial design with center point in triplicate was used to evaluate the application of different enzymes in extraction of sunflower oil, comparing its quality with the oil obtained by conventional methods (solvent and pressing) in relation to antioxidant capacity, phytosterol and tocopherol contents, and fatty acid composition. Three enzymes were used; Pectinex Ultra SPL, Celluclast 1.5 L and Alcalase 2.4 L; and three factors were evaluated: enzyme concentration, sample/water ratio and extraction time. Enzymatic aqueous extraction produced oil with better quality in relation to some of the evaluated parameters: highest antioxidant capacity against peroxyl radicals (371 µmol Trolox g-1 of oil), total phytosterols (183 mg 100 g-1 of oil) and omega-3 fatty acid content, as well the lowest content of saturated fatty acids. The application of enzymes in sunflower oil extraction represents an environmentally friendly methodology, free of toxic solvent residues and providing a final product of high quality.

Characterization of Si3N4-Al interface after corrosion tests

Silicon nitride is a covalent ceramic material of high corrosion resistance and mechanical stability at elevated temperatures. Due to these properties, its use in metallurgical processes, such as the casting of alloys, is increasing. Therefore, the characterization of the interface between Si3N4 and the casted metal is of great importance to investigate possible interactions, which might deteriorate the ceramic mould or contaminate the metal. In this work, the use of Si3N4 as crucible material for Al-casting has been studied, by investigating the corrosion attack of liquid Al at a temperature of 1150 oC during 30 days in air. The interface was characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. It has been found that due to superficial oxidation two oxide layers form - SiO2 on Si3N4 and Al2O3 on Al - which effectively hinder further reactions under the conditions studied, confering high corrosion resistance to the Si3N4 crucible.

Incorporation of Alpha-linolenic Acid (18:3n-3) in Surubim-do-Iguaçu (Steindachneridion melanodermatum)

One hundred and eighty freshwater fish, Surubim-do-Iguaçu, were distributed into three cages and fed for 25 and 50 days with control diet based on soybean oil and diet supplemented with linseed oil, rich in fatty acid 18:3n-3. The objective this work was to evaluate the incorporation of 18: 3n-3 acid during the experiment. Total lipids were extracted and fatty acids were separated in the gas chromatograph coupled to a flame ionization detector and quantified. The fish that were fed during 50 days diet supplemented with flaxseed oil, incorporated alpha-linolenic acid on your filet, increasing the amount of this fatty acid of 9.76 mg g to time zero to 20.64 mg g LT . The best reason n-6/n-3 was found in fillets with 50 days containing flaxseed, 4.45. Thus, it is concluded that the addition of linseed oil rations brings development and improved fatty acid profile in Surubim do Iguaçu fillets.

Obtenção in situ do compósito alfa-SiAlON-SiC

The objective of this work is to obtain in situ a-SiAlON-SiC composites, by silicon nitride solid solution development, during sintering, using rare earth and yttrium oxide mixture (CRE3O3) as stabilizer of the a-Si3N4 phase. A fraction of 20 vol.% of AlN-CRE2O3 mixture was mixed to 80 vol.% of Si3N4. Different contents of b-SiC powders were mixed to the Si3N4-AlN-CRE2O3 powder mixture. The powder mixtures were milled and compacted by uniaxial and cold isostatic pressing. The green bodies were sintered at 1950 °C during 1 h under 1 MPa of N2 pressure. The sintered samples were characterized by X-ray diffraction and scanning electron microscopy, in order to assess the crystalline phases and microstructural aspects, respectively. The results revealed the presence of a-SiAlON and b-SiC as the only crystalline phases present in the material. No partial crystallization of remaining intergranular phase was detected. No a-SiAlON solubility variation was observed by the use of different SiC contents, but different grain of a grains are related to SiC addition in the mixtures.