Este trabalho teve por objetivo estudar a redução por hidrogênio de sínteres produzidos com coque e carvão vegetal. Para isso, foram realizadas sinterizações utilizando 3 tipos de sinter feeds hematíticos. Os sinter feeds foram caracterizados através de análise granulométrica, análise química, difração de raios-X, microscopia óptica e microscopia eletrônica de varredura. Os primeiros ensaios de sinterização visaram a produção de sínter de retorno para as sinterizações posteriores. Misturas adicionando o sinter feed resíduo do processo de pelotização de minérios (SFRP) foram sinterizadas para avaliar o efeito da adição deste subproduto no processo de sinterização. Um teste foi realizado para verificar o efeito da redução de finos presentes no sínter de retorno no processo de sinterização. Foram realizados 6 ensaios de sinterização substituindo o coque por carvão vegetal como combustível do processo. As substituições foram de 0%, 8%, 16%, 25%, 50% e 100%. As amostras com substituições de 0%, 50% e 100% foram reduzidas em termobalança, durante 6 horas, em temperatura de 1000°C, utilizando uma mistura de gases contendo Argônio 10% Hidrogênio. As amostras que apresentaram a melhor e a pior redutibilidade foram estudadas através de cálculos cinéticos, a fim de determinar os mecanismos de reação envolvidos durante a redução dos óxidos. A etapa de caracterização microscópica dos sínteres e reduzidos foi realizada de modo que tornou possível comparar a amostra de sínter antes e após o processo de redução. Os resultados mostraram que, para as misturas produzidas, o sínter fabricado com carvão vegetal diminuiu os índices de produção da sinterização e de resistência do sínter. Contudo, o sínter produzido utilizando somente carvão vegetal como combustível, apresentou maior redutibilidade. Os cálculos cinéticos indicaram, tanto para o sínter produzido com carvão vegetal quanto para o sínter produzido com coque, que o mecanismo controlador nos primeiros instantes (entre 50 e 55 minutos) é a reação química. No sínter produzido com carvão vegetal, o mecânismo muda para o controle misto. No sínter produzido com coque, o mecânismo muda para a difusão. Ensaios interrompendo o tempo de redução em 40min, 80min e 120min (40min + 40min + 40min), foram realizados com a amostra de sínter produzido com 8% de carvão vegetal. Nesta etapa, foi possível identificar os fenômenos de nucleação e crescimento da fase de ferro metálico sobre a estrutura do sínter. / This work aimed to study the sinter reduction by hydrogen produced with charcoal and coke breeze. Three kinds of hematitic sinter feeds were used. The materials were characterized by particle size analysis, chemical analysis, X-ray diffraction optical and scanning electron microscopy. The inicial sintering tests aimed to produce return fines for subsequent sintering. Mixtures adding the sinter feed residue from the pellets process were sintered to evaluate the addition effect of this product in the process of sintering. A test was conducted to verify the effect of elimination of fines present in the sinter return sintering process. Six sintering tests were conducted replacing coke breeze by charcoal as process fuel. The replacements were 0%, 8%, 16%, 25%, 50% and 100%. The samples with substitutions of 0%, 50% e 100% were reduced in thermobalance for 6 hours at a temperature of 1000°C using a blend of gases containing Argon 10% Hydrogen. The samples which presented the best and the worst reducibility were studied through kinect calculations to determine the reaction mechanisms involved during the reduction of oxide. The step of microscopic characterization of reduced sinters was carried out in a way that made possible to compare the sinter sample before and after the process of reduction. The results showed the sinter made with charcoal decrease the sinter rates of production and resistance. However, the sinter made using only charcoal as fuel presented better reducibility. The kinect calculation denotes both for the sinter made with charcoal and sinter made with coke breeze the controlling mechanism in the initial stages (between 50 and 55 minutes) is the chemical reaction. For the sinter produced with charcoal the controlling mechanism switches for mixed control. The sinter produced with coke breeze, the mechanism switches for diffusion. Tests interrupting the reduction time for 40min, 80min e 120min (40min + 40min + 40min) were produced with sinter sample produced with 8% with charcoal. At this stage it was possible to identify the phenomena of nucleation and growth phase of metallic iron on the sinter structure.

This thesis is focused on the study of the influence of plasma activation of powder ceramic materials on sintered microstructure. In this experiment Diffuse Coplanar Surface Barrier Discharge (DSCBD) device was used for plasma treatment and two materials were chosen to be investigated – Al2O3 (TAI) and ZrO2 doped with 3 mol % Y2O3 (TZ). Two methods of powders dispergation in suspension were used – ultrasound and ball milling. The effect of using of DCSBD on alumina and zirconia powders was investigated by mercury intrusion porosimetry, dilatometry and by evaluation of final relative densities and grain sizes. Generally, was investigated that plasma surface activation of ceramic particles has measurable influence on the final microstructure. In comparison with the non-plasma treated alumina powders, plasma activated powders disperged with ultrasound and ball milling achieved lower values of grain size at comparable relative densities. In case of zirconia powders was observed that plasma treated powders achieve higher relative densities, if ultrasound was used. On the other hand, plasma treated zirconia powders disperged with ball milling achieve lower relative densities compared with non-plasma treated zirconia powders. Final sintering trajectory of plasma treated TZ powders disperged with ultrasound is comparable to the sintering trajectory of non-plasma treated zirconia powders disperged with ball milling and vice versa. Plasma surface treatment is the way of more ecological friendly preparation of suspension and its stabilization than the conventional stabilization methods using chemical additives.

Cold sintering process (CSP) je nová metoda pro slinování keramik a skel. Tato metoda vede ke snížení teploty (

abstract: The hierarchical silica structure of the Coscinodiscus wailesii diatom was studied due to its intriguing optical properties. To bring the diatom into light harvesting applications, three crucial factors were investigated, including closely-packed diatom monolayer formation, bonding of the diatoms on a substrate, and conversion of silica diatom shells into silicon. The closely-packed monolayer formation of diatom valves on silicon substrates was accomplished using their hydrodynamic properties and the surface tension of water. Valves dispersed on a hydrophobic surface were able to float-up with a preferential orientation (convex side facing the water surface) when water was added. The floating diatom monolayer was subsequently transferred to a silicon substrate. A closely-packed diatom monolayer on the silicon substrate was obtained after the water evaporated at room temperature. The diatom monolayer was then directly bonded onto the substrate via a sintering process at high temperature in air. The percentage of bonded valves increased as the temperature increased. The valves started to sinter into the substrate at 1100°C. The sintering process caused shrinkage of the nanopores at temperatures above 1100°C. The more delicate structure was more sensitive to the elevated temperature. The cribellum, the most intricate nanostructure of the diatom (~50 nm), disappeared at 1125°C. The cribrum, consisting of approximated 100-300 nm diameter pores, disappeared at 1150°C. The areola, the micro-chamber-liked structure, can survive up to 1150°C. At 1200°C, the complete nanostructure was destroyed. In addition, cross-section images revealed that the valves fused into the thermally-grown oxide layer that was generated on the substrate at high temperatures. The silica-sintered diatom close-packed monolayer, processed at 1125°C, was magnesiothermically converted into porous silicon using magnesium silicide. X-ray diffraction, infrared absorption, energy dispersive X-say spectra and secondary electron images confirmed the formation of a Si layer with preserved diatom nano-microstructure. The conversion process and subsequent application of a PEDOT:PSS coating both decreased the light reflection from the sample. The photocurrent and reflectance spectra revealed that the Si-diatom dominantly enhanced light absorption between 414 to 586 nm and 730 to 800 nm. Though some of the structural features disappeared during the sintering process, the diatom is still able to improve light absorption. Therefore, the sintering process can be used for diatom direct bonding in light harvesting applications. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2018

No description available.

Existing laser sintering systems have several advantages over alternate additive manufacturing technologies but suffer from limitations inherent to the use of a single, self-contained powder bed. This powder bed design limits the ability of the machine to print multiple materials in a single print cycle, obscures the part during printing which can lead to material waste, and presents significant obstacles to embedding during printing. I present here an additive manufacturing process that uses an upward-directed laser to fuse monolayers of material powder onto a substrate through a clear surface. The powder on the glass can then be replenished or replaced, and new powder can be fused to the previous powder layer. This is repeated until a solid, multi-layer hanging print is formed. This process eliminates the need for a large powder bed as well as allows the sintering of different powders in a single layer. I demonstrate this method by using a 445 nm laser to fabricate a multi-material pattern of Nylon-12 and TPU as well as producing direct metal laser sintered (DMLS) copper components. I also demonstrated the ability of this technology to print hybrid powder/resin components and embed during the printing process.

The automobile industry has set the demand regarding Powder Metallurgy (PM) parts for decades, since this near-net shape technology is a cost-effective manufacturing process allying good mechanical properties with dimensional and geometrical precision. Aiming at the future of the electric automobiles high production and demand, many changes are on the way to guarantee the competitiveness of PM against other manufacturing process. The high costs of alloying elements such as Ni and Cu, the changes in health and safety regulations as well as light weighting of components are the topics of major importance in the field of PM and focus of main R&D around the globe. The use of high temperature sintering and different alloying elements are possible solutions to overcome properties obtained by using Ni as an alloying element sintered at conventional temperatures. Materials with Cr, Mo and Si were investigated using high temperature sintering (1180°C and 1250°) in comparison to traditionally high Ni materials sintered at conventional temperature (1120°C). The dimensional stability, geometrical precision, density, and microstructure of ring-shaped specimens were studied by using a coordinate measuring machine (CMM) and the effect of HTS on the mechanical properties were estimated through the fraction of the load bearing section. The effect of HTS on the dimensional precision and geometrical stability was later investigated in real parts manufactured by industrial partners through an EPMA Club Project. The 4%Ni material sintered at 1120°C was also compared to Ni-less/Ni-free materials sintered at 1250°C using tensile testing, impact testing, and hardness. The use of HTS to improve the mechanical properties without impairing the dimensional and geometrical stability was confirmed in parts with both low and high complexity designs. This project sets the blueprint for future material developments using HTS as manufacturing process.

No description available.

No description available.

Thermotropic liquid crystalline polymers (TLCPs) possess a number of physical and mechanical properties such as: excellent chemical resistance, low permeability, low coefficient of thermal expansion, high tensile strength and modulus, and good impact resistance, which make them desirable for use in the storage of cryogenic fluids. Rotational molding was selected as the processing method for these containers because it is convenient for manufacturing large storage vessels from thermoplastics. Unfortunately, there are no reports of successful TLCP rotational molding in the technical literature. The only related work reported involved the static coalescence of two TLCP powders, where three key results were reported that were expected to present problems that preclude the rotational molding process. The first result was that conventional grinding methods produced powders that were composed of high aspect ratio particles. Secondly, coalescence was observed to be either slow or incomplete and speculated that the observed difficulties with coalescence may be due to large values of the shear viscosity at low deformation rates. Finally, complete densification was not observed for the high aspect ratio particles. However, the nature of these problems were not evaluated to determine if they did, in fact, create processing difficulties for rotational molding or if it was possible to develop solutions to the problems to achieve successful rotational molding. This work is concerned with developing a resin selection method to identify viable TLCP candidates and establish processing conditions for successful rotational molding. This was accomplished by individually investigating each of the phenomenological steps of rotational molding to determine the requirements for acceptable performance in, or successful completion of, each step. The fundamental steps were: the characteristics and behavior of the powder in solids flow, the coalescence behavior of isolated particles, and the coalescence behavior of the bulk powder. The conditions identified in each step were then evaluated in a single-axis, laboratory scale, rotational molding unit. Finally, the rotationally molded product was evaluated by measuring several physical and mechanical properties to establish the effectiveness of the selection method. In addition to the development and verification of the proposed TLCP selection method, several significant results that pertain to the storage of cryogenic fluids were identified as the result of this work. The first, and argueably the most significant, was that the selection method led to the successful extension of the rotational molding process to include TLCPs. Also, the established mechanical properties were found to be similar to rotationally molded flexible chain polymers. The biaxial rotationally molded container was capable of performing to the specified requirements for cryogenic storage: withstand pressures up to 34 psi at both cryogenic and room temperatures, retain nitrogen as a gas and as a cryogenic liquid, the mechanical preform retaining nitrogen, as both a gas and as a cryogenic liquid, and resist the development of micro-cracks during thermal cycling to cryogenic conditions. / Ph. D.