ZrC-SiC nanopowders were prepared by carbothermal reduction of ZrO2 and SiO2 with carbon black in argon gas atmosphere, using microwave energy as an alternative heating source. The samples were ...characterized by XRD, SEM and BET surface area analysis. The results indicate that highly crystalline ZrC-SiC composites with a mean particle size of about 80 nm can be synthesized at a relatively low temperature (~1420 °C). Microwave-assisted heating to obtain the ZrC-SiC nanopowders significantly reduces the synthesis time to only 40 min when compared with the long reaction times involved in conventional carbothermal reduction, which requires about 8 hours to obtain ZrC and 2 hours to obtain SiC.
An aqueous colloidal processing method was proposed to prepare m-Li2ZrO3 bodies, with high green density and a homogenous microstructure, employing a pressureless forming technique. For this purpose, ...the preparation conditions of m-Li2ZrO3 aqueous suspensions were optimized considering colloidal processing variables, such as milling time (0–40 min), dispersant concentration (1–10 wt% of the solids content) and maximum solid loading (41–74 wt%). Particle size distributions and steady-state flow curves of the slips were analyzed, together with phase composition and microstructure of the ceramic bodies. The results show that after planetary ball milling for 30 min, the aqueous suspension with 63.1 wt% of m-Li2ZrO3, and a dispersant content equal to 10 wt% of the solid loading, yielded green bodies with bulk densities close to 66% TD by slip casting. Then, after the heat treatment process at 1100 °C for 12 h, bulk densities close to 88% TD were achieved. It was found that density values and microstructure of the green and sintered products bear a direct relationship to the particle size and the consistency of the slips.
In the context of the current global environmental paradigm, lithium zirconate-based materials (LZOs) are of great technological interest in the reduction of the carbon footprint. Due to their ...exceptional mechanical, thermal and chemical stability, high lithium atom density and outstanding tritium release behavior, LZOs have been studied as tritium breeding ceramics for fusion technology. Besides, given that they can selectively and reversibly absorb CO2 at high temperatures, LZOs could be used in the capture and industrial reuse of this gas. Moreover, in their most widespread use today, LZOs could be applied as nanocoatings on solid-state electrolytes and electrodes, constraining the formation of high resistive interfaces and slowing the evolution of dendrites, both in lithium-ion and solid-state batteries. Finally, there are some small contributions in the development of catalytic materials to produce biodiesel and air-hydrogen fuel cells based on LZOs, and also in the development of luminescent materials with photovoltaic applications. This article is the first review of the LZO system. It summarizes LZOs main applications and describes the latest advances in the technologies described above.
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Universidade ...Federal de Sao Carlos
One of the major motivations for the development of new synthesis routes is a continuing need for fast and energy-efficient methods that allow obtaining materials with differentiated technological characteristics and properties. The use of microwaves in materials synthesis has generated great interest in the scientific research due to its speed, simplicity and energy-efficiency. Among different synthesis methods which can be assisted by microwave energy, the carbothermal reduction is the most simple and effective method in ceramic materials production. The conventional carbothermal reduction is used to obtain zirconium carbide (ZrC). In this context, the purpose of this work was to study the synthesis by microwave-assisted carbothermal reduction of ZrC using a mixture of zirconia (ZrO2) and carbon black (C). The synthesis parameters evaluated in this work were: stoichiometry, ZrO2/C-forming process, microwave power, reaction time and pressure of inert gas (argon). Characterization by X-ray diffraction (XRD) analysis of the samples synthesized by this method showed that the formation of ZrC phase was enhanced by controlling the following parameters: microwave power and reaction time increases, conservation of theoretical stoichiometry ZrO2/C:1/3, less compression of the pelleted mixture before the reaction and moderate pressure of argon. The samples with the highest ZrC content were characterized by specific surface area (BET) and scanning electron microscopy (SEM). These characterizations revealed that microwave-assisted carbothermal reduction synthesis produced ZrC samples with average particle size of ~100-200nm, near the nanometer range, homogeneous morphology and reaction time of 30 minutes.
Uma das maiores motivações para o desenvolvimento de novas rotas de síntese é a necessidade contínua de métodos rápidos e eficientes em termos energéticos, que permitam a obtenção de materiais com características e propriedades diferenciadas em nível tecnológico. O uso de micro-ondas na síntese de materiais tem gerado um grande interesse na pesquisa cientifica devido a sua rapidez, simplicidade e eficiência energética. Entre os diversos métodos de síntese que podem ser auxiliados pela energia de micro-ondas, a redução carbotérmica é um dos mais simples e eficazes na produção de diversos tipos de pós cerâmicos. A redução carbotérmica convencional é usada na obtenção de diversos tipos de carbetos incluindo o de zircônio (ZrC), um material altamente refratário, potencialmente útil em aplicações de alta temperatura que exibe estabilidade em estado sólido e boas propriedades termomecânicas e termoquímicas. Neste contexto, esta dissertação visa estudar a síntese por redução carbotérmica assistida por micro-ondas para a obtenção de pós cerâmicos de ZrC a partir da mistura de pós de zircônia (ZrO2) e negro de fumo (C). Os parâmetros de síntese avaliados nesta pesquisa foram a estequiometria dos reagentes, o método de conformação da mistura ZrO2/C, a potência do micro-ondas, o tempo de reação e a pressão de argônio. As caracterizações mediante a difração de raios X (DRX) das amostras sintetizadas por este método revelaram que a formação da fase ZrC foi favorecida pelo controle dos seguintes parâmetros: aumento da potência e tempo de reação, conservação da estequiometria teórica ZrO2/C:1/3, menor compactação da mistura peletizada antes da reação, e pressão moderada de argônio. As amostras de ZrC, com menor presença de fase secundaria, foram caracterizadas pela determinação de área específica superficial (BET) e por microscopia eletrônica de varredura (MEV). Os resultados revelaram que, mediante a síntese por redução carbotérmica assistida por micro-ondas, foi possível obter pós cerâmicos de ZrC com tamanho médio de partículas entre ~100-200nm, morfologia homogênea e em tempos de reação de apenas 30 minutos.
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