Materials Science Forum Vols. 727-728

Abstract: The element phosphorus plays key role in plants metabolism. It is widely used as fertilizer. This element is usually found in insoluble forms (Ca₁₀(PO₄)₆F₂). The solubilization in phosphoric acid (H₃PO₄) is a process widely used in fertilizer industry. The impurities in the phosphate exert significant influence on recovery and productivity phosphoric process, besides affecting the quality of products. The objective of this work is to analyze the influence of some of these main impurities (iron, aluminum and magnesium) in the production process of phosphoric acid. A referential methodology (induced crystallization) of phosphoric acid production was developed. Samples of igneous phosphate concentrate contaminated with iron, aluminum and magnesium were prepared for the experiments. The reaction control parameters were similar to an industrial operation of phosphoric acid dihydrate process. Reductions in conversions, increases in viscosity and density of phosphoric acid were observed with increasing presence of these impurities. In the filtration step was found increase in resistivity of the cake with the increase of the impurities content. The iron mineral element promoted an increase in induction time of crystals nucleation.

Abstract: In this study, the production of metallic chromium via metallothermic process was investigated. A chromium oxide-rich residue from chromium plating industry was characterized. Aluminothermic reduction was performed in lab-scale using an open graphite crucible. The plating residue and the aluminum powder were processed in a SPEX mill, in order to promote its effective mixing and mechanical activation. Energy dispersive X-Ray (EDX) analyses in the scanning electron microscope (SEM) have shown the presence of metallic chromium in the reaction products.

Abstract: Titanium is a material used in biomedicine for osseous implants due to their low density and biocompatibility. Its use in this field is limited by the lack of similarity of their stiffness with the stiffness of bones. In order to reduce this difference, powder metallurgy offers ways to develop porous materials with a reduced stiffness. The main objective of this work is to develop titanium scaffolds by space-holder technique, concretely with using two different spacers: Ammonium bicarbonate and sodium chloride. It has been studied the best way for remove spacer of green compacts, which have been sintered in high vacuum. Materials obtained by using of two spacers, have been analyzed in order to value different results in porosity, microstructural and mechanical properties. The stiffness of new materials was obtained by testing of three points in bending. This research shows that the manufacturing method of porous materials for bone replacement using space holder technique with ammonium bicarbonate or sodium chloride, allows obtained samples with slightly difference in physical, microstructural and mechanical properties.

Abstract: The quality of the atmosphere inside a sintering furnace plays a key role in the final properties of the sintered part. Properties such as the hardness, ductility, dimensions, carbon content, microstructure and magnetic properties among others are influenced not only by time and temperature, but also by the composition, flow rate and stability of the atmosphere within the furnace. The different physical zones within the furnace require different degrees of oxidizing or reducing power to develop the optimum properties in the final sintered part. Presented in this paper are practical techniques and technologies developed over the last 30 years of experiences with production sintering furnaces. The concept of distributed atmosphere introduction, combined with the use of directional atmosphere injectors, flame curtains, and gas curtains are used to stabilize and maintain the atmosphere profile within the furnace. Optimum and proven designs for atmosphere injectors, flame curtains, gas curtains and exhaust systems are presented.

Abstract: The service life of stainless steel wire mesh belts in sintering furnaces is limited, because material deterioration results in wire fracture. A newly developed humidification system establishes a furnace atmosphere that maintains a protective oxide scale on the belt surface throughout the sintering process and at the same time creates an environment that is reducing to the sintered metal compact. This work includes thermodynamic calculations of the furnace atmosphere dew points that satisfy these oxidation / reduction criteria. Scanning Electron Microscopy, combined with Energy-dispersive X-ray Analysis, and mechanical testing methods have been used to compare belts that have undergone the same length of service in a nitrogen-hydrogen atmosphere and in an atmosphere that was modified using the newly developed humidification method. The material examinations have revealed that the new humidification system significantly extends the service life of stainless steel belts.

Abstract: Quasicrystalline materials have unique properties such as high hardness, excellent surface properties, good resistance to oxidation and corrosion and low electrical and thermal conductivities. These materials can be obtained by conventional methods of metallurgy. However, quasicrystals are quite weak and this characteristic complicates their use in the form of billets for the manufacture of mechanical components. For this reason, the evaluation of mechanical properties of quasicrystalline materials using conventional methods, such as tension, compression, fatigue, among others, is not feasible. One method to evaluate the mechanical properties of quasicrystals is through instrumented indentation, once it is a very efficient tool for the calculation of properties such as hardness, fracture toughness and modulus of elasticity. The latter was the property studied in this work and that it is an important design criterion for the manufacturing of quasicrystalline alloys for their use in industry.

Abstract: Nacrystalline WC-10wt.%Co powders were prepared by high energy milling and liquid phase sintered. The powders with different milling time were characterized by X-ray diffraction and SEM. After sintered the WC-10wt.%Co cemented carbides exhibits ultra fine grain sizes. Coercitive field and Vickers hardness measurements on the consolided samples detected a significant increase and decrease Vickers hardness with the milling time increase in sintered samples.

Abstract: Cu-Si-B alloys are a new generation of metal matrix for producing composites incorporated with diamonds for cutting tools. These alloys have been developed as a special matrix in order to improve the thermal properties of the diamond composites used in machining tool bits. Despite the industrial interest, not much has been reported on this type of composite matrix. In this work, samples of Cu-Si-B alloys were processed at high pressure and high temperature (HPHT) sintering conditions. The microstructure changes that occurred were evaluated. Microstructural aspects were observed by SEM. Compounds formed during sintering were studied by EDS. Wear tests were performed in sintered diamond particle incorporated composites. The results revealed significant advantages of Cu-Si-B alloy as matrix for these composites.

Abstract: Stainless steels are employed as filters, and in this application the amount of pores and their size distribution are very important. Here it is discussed a densification model, which takes into account both, grain size and density. After this model is applied to experimental data, the obtained parameters can be used for extrapolation in other sintering conditions, for example other temperatures and heating rates. The studied material is the austenitic alloy 316L.

Abstract: As a superhard material, next to diamond, the cubic boron nitride (cBN) is of great interest owing to its efficiency in machining ferrous alloys. In nature, only the hexagonal, hBN, exists. In practice, high pressure and high temperature (HPHT) synthesis has to be used to produce small cBN crystals. For larger size machining inserts, the powder-like cBN crystals need to be sintered at specific HPHT conditions using a metallic binder. The present work investigates the sintering of cBN inserts using a Ti-based binder at 7 GPa of pressure and 1800°C. The results disclosed relatively high hardness for the inserts and revealed their effectiveness in machining high strength steels.