Abstract The family of crystals known as Tutton's salts plays a significant role in physics and chemistry; because they are used in phase transition studies and to define models applied to materials. The importance of salts in material engineering is recent, as in applications in adiabatic degaussing refrigerators and solid-state anodes. Studies of the (NH4)2Ni(SO4)2∙6H2O and (NH4)2Co(SO4)2·6H2O are widely found in literature but do not occur for the mixture of both. In this research, we studied mixed crystals of the general chemical formula (NH4)2NixCo(1-x)(SO4)2·6H2O with x ranging from 0 to 1, utilizing x = 0.7. The objective is to study the modifications caused owing to the ion's weighted composition in the formation of the solid solution and compare it with the pure salts. For this, the growth of these crystals is discussed based on ICP-OES results and optical microscopy concerning the crystal growth theory. The discussion also relates the Raman spectra of the salts with molecular changes according to structured group theory, qualitatively characterizing its crystalline structure. Finally, a Single-crystal X-ray study solves and confirms the structure of pure salts and mixed salt, quantitatively characterizing their crystal structure.

RESUMO O compósito WC-10%Co também conhecido como Metal Duro de Carbeto de Tungstênico (WC) com Cobalto (Co) é um dos materiais mais produzidas pela indústria fabricante de metal duro, entretanto busca-se o melhor entendimento sobre o efeito de parâmetros de processo sobre as suas características estruturais, especialmente no que diz respeito à formação de fases metaestáveis – fases η. Neste trabalho, usamos o método de Rietveld aliado a difração de raios X (DRX), a microscopia eletrônica de varredura (MEV) e o Brunauer – Emmett – Teller (BET) para investigar a estrutura das matérias-primas utilizadas na produção de metal duro. Os tamanhos das partículas assim como as morfologias identificadas para os pós de WC e Co são reflexos do seu processo de fabricação que, introduzem tensões residuais para o pó de WC, a baixa cristalinidade e significante parcela de amorfo para o pó de Co. Estas características foram identificadas com a difração de raios X em comparação com o padrão de difração obtido e os bancos de dados cristalográficos. Após o processo de mistura dos pós foram quantificadas as fases e identificados os efeitos desse processo sobre as células unitárias de cada fase. Este trabalho mostra que a rota de caracterização empregada, com o uso do método de Rietveld, é eficiente para analisar a estrutura desses materiais durante seu processamento. Foi possível observar que o processo de mistura utilizando equipamento de moagem de alta energia promove alteração na densidade das células unitárias do WC “empurrando” átomos de Co para dentro de sua estrutura. Isso pode vir a acelerar o processo de dissolução de grande parte das partículas de WC durante a sinterização, contribuindo para a formação acentuada das fases metaestáveis eta – η, prejudicando o equilíbrio entre as propriedades mecânicas de dureza e tenacidade à fratura tornando a ferramenta ou peça muito dura e pouco tenaz.

ABSTRACT The composite WC-10% Co is one of the materials most produced by the hardmetal fabrication industry. However, a better understanding of the effect of process parameters on their structural characteristics is sought, especially with respect to the formation of metastable phases - η. In this work, we used the Rietveld Method with X - Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Brunauer - Emmett - Teller (BET) to investigate the structure of the raw materials used in the production of hardmetal. The particle sizes as well as the identified morphologies for the WC and Co powders are reflections of their manufacturing process, which introduce residual stresses for WC powder, low crystallinity and a significant amorphous portion for Co powder. These characteristics were identified with XRD in comparison to the obtained diffraction pattern and crystallographic databases. After the powder mixing process, the phases were quantified and the effects of this process were identified on the unit cells of each phase. This work shows that the characterization route using the Rietveld Method is efficient to analyze the structure of these materials during their processing. It was observed that the mixing process using high energy milling equipment promotes a change in the density of WC unit cells by “pushing” Co atoms into their structure. This may accelerate the dissolution process of most WC particles during sintering. And contribute to the accentuated formation of metastable phases eta – η, damaging the balance between the mechanical properties of hardness and fracture toughness making the tool or piece very hard and not very tenacious.