Use of phase diagrams in studies of refractories corrosion

Abstract

Typical applications of phase diagrams to specific of refractories corrosion has been highlighted,3-7 and problems of refractories corrosion are highlighted.a few cases such as attack of Al 2 O 3 -SiO 2 refractoriesSaturation solubilities of refractories components in molten slags can be estimated using existing by alkali oxides well studied,4,6,7 their use is far from phase diagrams. These can then be used to predict ubiquitous.the corrosion behaviour, and qualitatively compareThis paper seeks to emphasise applications of phase the corrosion resistance, of a refractory in different diagrams to specific refractories corrosion problems slags or different refractories in the same slag. using typical examples. Previously reported experi-If the slag is not saturated with refractories mental results which were not well explained have components, using relevant phase diagrams, the been re-analysed and earlier discrepancies clarified conditions under which solid reaction product using the relevant phase diagrams. phases form at refractories/slag interfaces can be predicted, which assists understanding of direct and indirect dissolution. By checking the Significance of saturation solubility of compatibility between impurities or additives and refractories oxide phases in liquid slag refractories components at high temperatures, their influence on corrosion resistance can be Dissolution of solid oxides in liquid slag is governed predicted, aiding their selection. Phase diagrams by: (a) chemical reaction (or solution) at the also reveal that atmosphere affects refractories refractories/slag interface or ( b) transport (or corrosion resistance by altering the valence of diffusion) of reacting species.8 In the latter case, some components (in particular, iron oxide) in the dissolution rate can be expressed in terms of the refractories and/or slags. The compatibility Nernst equation between refractories and slags indicates the corrosion resistance of different refractories, J=D(C s −C m )/d . . . . . . . . . . (1) assisting refractories selection for specific applications. Finally, phase diagrams can be used where D is the diffusion coefficient (m2 s−1), C m and to assist design of refractories composition. C s are, respectively, concentration and saturation Repeated experimental corrosion test results show solubility of refractory in the slag (g m−3), and d is good agreement with phase diagram predictions. the effective boundary layer thickness (m). Therefore, use of the information which is Increasing D or decreasing d (i.e. increasing available in existing phase diagrams can reduce D/d) increases dissolution rate J. Besides this, it is the need for expensive and time consuming clear from equation (1) that the value of C s −C m experiments to evaluate high temperature strongly influences dissolution rate. If the slag is corrosion of refractories (and other ceramics).

A review of factors affecting the composition of early Egyptian glasses and faience: alkali and alkali earth oxides

“…The recently proposed two-stage model, based on the archaeological evidence excavated at QantirePi-Ramesse (Rehren and Pusch, 2005; and in good agreement with ideas put forward earlier based on the cuneiform texts , assumes a low-temperature (800e900 C) first melt to produce semi-finished glass, followed by a second step at considerably higher temperatures (1000e1100 C) to produce a good glass free of residual batch material, and coloured in one of the available colours. The maximum content of lime in soda-lime-silica glass is determined by the melting temperature (Shugar and Rehren, 2002); according to the relevant phase diagram (Shahid and Glasser, 1972), the maximum lime content in glass of typical LBA composition rises from around 6 wt% at 900 C to around 10 wt% at 1000 C. This increase in lime content in the melt limits the efficiency of the parting layer as a refractory material (Zhang and Lee, 2000) and explains the observed failure of the parting layer particularly in high-fired crucibles (Pusch and . Further experimental work (Merkel and Rehren, 2007) and analyses of archaeological finds from the glassmaking site of Qantir-Pi-Ramesses (Schoer and Rehren, 2007;Tanimoto, 2007; Tanimoto and Rehren, submitted for publication) have shown how the parting layer gets increasingly absorbed into the glass as the furnace temperature increases, to the stage where it completely disappears and the glass sticks to the ceramic vessel.…”

Artigo revisão - A relação entre a corrosão e a microestrutura: a chave para o desenvolvimento de concretos refratários espinelizados de alto desempenho

“…Isso ocorre, pois no contato em altas temperaturas, as fases presentes no material refratário tendem a reagir com a escória líquida, a fim de se diminuir o gradiente químico existente e atingir o equilíbrio termodinâmico [26,35]. Nesse sentido, a composição química do refratário a ser aplicado em zonas de elevado ataque químico é selecionada de maneira a minimizar essa disparidade química.…”

Simulação termodinâmica e sua aplicação na avaliação do desempenho de materiais refratários

“…Felizmente, estes dados podem ser determinados por meio de cálculos termodinâmicos ou diagramas de equilíbrio. Verifi cando a diferença entre as concentrações e as solubilidades de saturação dos principais componentes do refratário na escória, sua resistência relativa ao ataque pelo líquido pode ser estimada, e assim, a infl uência das composições dos refratários na resistência a corrosão pode ser prevista [10]. Por exemplo, a Fig.…”