Effect of dispersants on the rheology of aqueous silicon carbide suspensions

Abstract

• This is a journal article. AbstractThe effect of cationic and anionic dispersants on aqueous suspensions of as-received and surface-modified silicon carbide particles has been studied via observation of the rheological behaviour. Only the cationic dispersants were effective for the as-received SiC, with polyethyleneimine being superior to Hyamine 2389 probably as a result of a greater electrosteric interaction. SiC particles modified using Al(NO 3 ) 3 behaved like alumina and so could be dispersed using the anionic dispersants ammonium polyacrylate and polymethacrylate. Such dispersions displayed no heteroaggregation when alumina was added, although the order of mixing could significantly affect the rheological behavior of the suspension. Nevertheless, the suspensions appeared robust to slight fluctuations in pH. I IntroductionAchieving adequate dispersion of ceramic powders is important for suspension-based ceramic green forming; it is generally necessary to prepare the suspensions with as high solid content and low viscosity as possible. Due to the wide use of alumina ceramics, the dispersion of these powders into water has been extensively studied and the dispersants used are commonly polyelectrolytes such as polyacrylic acid (PAA), polymethylacrylic acid (PMAA) and their (usually ammonium) salts [1,2,3,4,5]. However, there are very few reported papers on the dispersion of silicon carbide, SiC, powders into water.A small number of researchers have used ammonia or sodium hydroxide solutions to adjust the pH of their suspensions [6,7,8], whilst Si et al. [9] used tetramethylammonium hydroxide (TMAH). In both cases the aim was to maximise the zeta potential of the SiC particles in aqueous suspension. In contrast, Sano [10] used styrene-maleic acid copolymers, the resulting 33 vol% solid content suspension exhibited a viscosity of only 190 mPa s at a shear rate of 6.9 s -1 , whilst other promising dispersants are the weak cationic polyelectrolytes polyethyleneimine (PEI) and polyvinylimidazole (PVI). The former has been used for the flocculation of silica § , SiO 2 , suspensions [11] whilst the latter, which has similar properties to § The surface charge behaviour of SiO 2 and SiC is fundamentally similar because there is always a very thin layer of SiO 2 on the surface of SiC [12,13,14]. In both cases, therefore, the zeta potential is negative when the pH is higher than the point of zero charge (PZC), typically pH 3±1. The polyelectrolytes adsorb onto the surface of the particles due to the electrostatic attraction force between the particles and the ionised groups on the polymer segments, the level of adsorption also being dependent on the molecular weight of the polymer. 3PEI and shows good adsorption onto the surfaces of the particles, has been studied for dispersing SiC powder [15]. However, in neither case was a rheological study of the resulting suspensions reported.A further complicating factor when producing SiC ceramics is that sintering additives are usually required to generate liquid phases and h...

Synthesis of nanostructured cadmium and zinc sulfides in aqueous solutions of hyperbranched polyethyleneimine

“…Due to its large amount of side amino groups, the electron donation ability of PEI overweighs its steric situation in these reactions [34]. Moreover, and in addition to its role as a capping agent, PEI has recently been applied as a strong cationic surfactant for dispersion of submicron solid suspensions [45]. It can be suggested here that PEI could have played an interesting double role in obtaining nanosized Cd and Zn sulfides as it inhibited growth of ZnS and CdS particles beyond the nanoscale and facilitated the dispersion of nanoparticles as soon as they are formed in the aqueous medium in our experiments.…”

Effect of a Cationic Polymer, Polyethyleneimine, on Ni/SiC Co-Deposition

“…5,11,12,19 Polyethyleneimine (PEI) is a cationic polymer that was previously investigated as a dispersant for aqueous SiC suspensions. [20][21][22][23][24] These studies indicate that PEI is an effective dispersant for SiC particles in aqueous media. 20,22,24 In addition to dispersion studies, PEI has also been investigated as a suppressor in copper and nickel electrodeposition.…”

“…[20][21][22][23][24] These studies indicate that PEI is an effective dispersant for SiC particles in aqueous media. 20,22,24 In addition to dispersion studies, PEI has also been investigated as a suppressor in copper and nickel electrodeposition. 25,26 However, the effect of PEI on Ni/ceramic particle co-deposition has not been investigated to our knowledge.…”

Electroless copper-phosphorus coatings with the addition of silicon carbide (SiC) particles

“…The Si content increases with increasing pH values due to the dissolution of the thin layer of SiO 2 on the surface of SiC according to Eq. (4) below [31][32]. Consequently, the Si content increases in the composite.…”