Rheological properties of aqueous α A1₂O₃ suspensions: Influence of dispersant concentration

Abstract

The effects of concentration of polyacrylic acid as a dispersant on rheological properties of aqueous alumina suspensions have been investigated under steady and oscillatory shear conditions. At solid volume fractions between 0.45 and 0.6, a high degree of particle stabilization is achieved when 0.2 wt% of polyacrylic acid is added. At lower dispersant concentrations, suspensions exhibit pronounced irreversible thixotropic behaviour, whereas at higher dispersant concentrations, time dependent effects on the flow properties are not detectable. When the saturation adsorption limit of the polyelectrolyte on AI,O, is reached, further addition of the dispersant appreciably changes the flow behaviour, as well as the viscoelastic response of investigated suspensions. The data under steady shear are described by application of the generalized Casson model, and for the analysis of viscoelastic data the generalized Maxwell model is used. Keywords: a alumina suspensions, irreversible thixotropy, yield stress, viscoelastic properties, particle stabilization.ighly concentrated aqueous suspensions are very H important raw materials in advanced ceramic processing, such as slip casting, injection molding, etc. The formulation and preparation of highly concentrated suspensions implies rational criteria in order to achieve a high degree of particle stabilization resulting in relatively low viscosity and adequate viscoelastic properties. When stable highly concentrated alumina suspensions are to be prepared in aqueous disperse media, it is necessary to select the type of particle stabilization (based on electrostatic, steric or electrosteric repulsion) and to find the additive amount necessary to reach the optimal conditions. In several industrial applications of highly concentrated ceramic suspensions, particle stabilization by addition of polyelectrolytes appears to be favourable in order to overcome the problems connected with ageing and processing of multiphase systems.Ammonium and sodium salts of polyacrylic (PAA) and polymethacrylic (PMAA) acids are widely used in the ceramic industry as dispersants for aqueous suspensions. The functional groups of these polymers are carboxylic groups, which can be COOH or COO-, depending on the pH of the solution. Cesarano I11 et al. (1988) studied the influence of PAA and PMAA on the stability of aqueous alumina suspensions. They showed that at pH values exceeding the zero point of charge (zpc) on the surface of the alumina particles, these polymers are hlly dissociated and polyelectrolyte adsorption in this pH range is still controlled by the minority *Author to whom correspondence may be addressed. E-mail address: Andreja.Valant@,uni-lj.si of positive surface sites, even though the net surface charge is negative. When pH increases, the amount of adsorbed polymer necessary to provide stabilization decreases. Above pH 9, high-affinity-type polymer adsorption does not occur and the presence of excess polymer in solution is inevitable. In order to reach the saturation adsorption limit there ...

Influence of pH and Time on the Stability of Aqueous Alumina Suspensions Containing Sodium Polyacrylates: A Revisited Process

“…It was chosen to use this alumina and a high solid content, aiming to reproduce real conditions in some industrial applications. [1,2,4,5,[15][16][17][18] For the acrylic polymer with higher molecular weight (158,000 g=mol), it is observed an increase in the viscosity starting from pH 5. Probably, a smaller number of particles is recovered by the polymer and so the steric stabilization is not efficient.…”

“…[16][17][18] In this work, it was investigated the effect of the addition of a synthetic polymer (sodium polyacrylate) on the stability of aqueous alumina suspensions with high solid content. Although many works have been made with polyacrilates as stabilizing agents of alumina suspensions, [1,2,4,5,[15][16][17][18] few consider the joint use of several techniques. Viscometric results are correlated with zeta potential and particles size, determined by Fiber Optic Quasi-Elastic Light Scattering (FOQELS) technique.…”

“…[4] The polymers most commonly employed in dispersions, in the ceramic industry, are ammonium and sodium polyacrylates. [5][6][7][8][9] In systems with high concentration of particles, as is the case in this work, it is necessary to consider the interaction forces between them. These forces can be attractive or repulsive, depending on pH, among other conditions.…”

"Estabilização de suspensões aquosas de alumina pela adição de taninos e quitosana quaternizada"

“…A viscosidade é, portanto, a constante de proporcionalidade entre as variáveis taxa e tensão de cisalhamento. Um fluido que obedece à equação de Newton, [Brown, 1988;Zupancic, 1999…”

Biomacromoléculas carboximetiladas: atuação como agentes de estabilização de suspensões aquosas de alumina

“…(Hirata;Nishimoto;Ishima, 1992;Zupancic;Lapasin;Kristoffersson, 1999;Guo et al, 1998;Yokosawa, 1996;Greenwood;Kendall, 2000;Vasconcelos et al, 2003;Wu et al, 2010) Na literatura, pouco constam trabalhos sobre estabilização de suspensões cerâmicas utilizando-se macromoléculas e/ou polímeros de fontes naturais, (Yokosawa;Yokosawa;Cerrutti, 2005;Cerrutti et al, 2010), a utilização dos sintéticos, como o PAA, continua sendo a opção mais utilizada. (Tallon et al, 2007;Tallon;Limacher;Franks, 2010;Wu et al, 2010;Lu;Su, 2010;Yoon et al, 2010) Em trabalhos anteriores a este, foram desenvolvidos estudos visando a obtenção de suspensões cerâmicas estáveis utilizando macromoléculas (polieletrolíticas ou não) oriundas de fontes naturais, tais como cosmédia guar (leguminosa originária da Índia), (Yokosawa, 1996) lignossulfonato de sódio, (Yokosawa;Frollini, 2002a;Yokosawa, 2002b), taninos (Mimosa Acácia) e trimetilquitosana, (Cerrutti, 2005;Cerrutti, et al, 2009).…”