Effect of pH on rheology of aqueous Al2O3/SiC colloidal system

Journal of Advanced Ceramics, Jun 2014

The rheological behavior of aqueous Al2O3/SiC suspensions at different pH values was investigated by rheological measurement. Experimental results showed that at pH = 3–6, Al2O3 and SiC particles have opposite surface charges, and the binary suspensions have lower viscosity than the unary suspensions at shear rates of 0–300 s−1. Furthermore, at pH = 3–12, the stability of the Al2O3 component seemed to dominate the overall rheological behavior of the Al2O3/SiC binary suspensions. The tendency mentioned above showed little variations in various ionic strengths, particle diameters and component fractions.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

https://link.springer.com/content/pdf/10.1007%2Fs40145-014-0102-4.pdf

Effect of pH on rheology of aqueous Al2O3/SiC colloidal system

Journal of Advanced Ceramics 2226-4108 Effect of pH on rheology of aqueous Al2O3/SiC colloidal system Xiaoqing ZHANG 0 Yanli ZHANG 0 Han CHEN 0 Lucun GUO 0 0 College of Materials Science and Engineering, Nanjing University of Technology , Nanjing 210009 , China The rheological behavior of aqueous Al2O3/SiC suspensions at different pH values was investigated by rheological measurement. Experimental results showed that at pH = 3-6, Al2O3 and SiC particles have opposite surface charges, and the binary suspensions have lower viscosity than the unary suspensions at shear rates of 0-300 s1. Furthermore, at pH = 3-12, the stability of the Al2O3 component seemed to dominate the overall rheological behavior of the Al2O3/SiC binary suspensions. The tendency mentioned above showed little variations in various ionic strengths, particle diameters and component fractions. alumina; silicon carbide; mixed colloidal dispersion; rheology - The dispersion and stability of a colloidal system are the main issues in colloidal processing. These properties influence not only the green compacts and sintering performance, but also the quality of the final products. Understanding and predicting the stability of a ceramic colloidal suspension is of particular interest [ 1–5 ]. Numerous related studies have been reported in the literature [ 6–10 ]. Unary suspension, which is composed of one kind of particles, has been extensively studied, but the behavior of multiple suspension (i.e., suspension with several types of particles) is much less understood although dispersion of such system is commonly found in nature and in various applications [ 11–14 ]. One of the major reasons is the complexity of the phenomena involved. The stability of multiple system depends not only on many basic parameters, such as nature of solvent and particles, ionic strength, and size and charge of particles, but also on the interactions among the particles, including electrostatic force and van der Waals force. For a two-component system containing different particles A and B, the forces of A–A, B–B and A–B are involved. The two kinds of particles differ in various factors, such as Hamaker constant and surface charge. The factors such as volume fraction and number ratio affect the total energy of a colloidal system simultaneously. Internal structures are difficult to observe experimentally at a microscopic level [ 15–19 ]. Probing the experimental system in such detail is not an easy task, specifically the system with more components and dispersants. Some interesting experimental results on multicomponent system have been found in previous studies. Wang et al. [ 20,21 ] revealed that the addition of salt improves the colloidal stability in systems that contain different particles in a certain pH range between the isoelectric points (IEPs) of the two types of particles. Uricanu et al. [22] studied the stability in colloidal mixtures containing particles with a large disparity in size. The results supported that the composite heteroparticles behave in many ways like a silica sol, as the small silica particles are adsorbed onto the latex ones and the surface characteristics of latex cores are modified simultaneously. In recent years, alumina matrix composite ceramic materials attracted widespread attention due to their excellent mechanical properties, especially alumina/silicon carbide ceramics [ 23 ]. The study of dispersion properties about Al2O3/SiC colloidal system is of great significance to the subsequent process. The present study aims to investigate the effects of pH, ionic strength, particle size and component fraction on the rheological behavior of aqueous Al2O3/SiC binary suspension, focusing on the comparison with the unary suspensions of Al2O3 and SiC and the surprising stability of initially oppositely charged particle mixtures. 2 Experimental 2. 1 Material All of the experiments were conducted with Al2O3 (Zhengzhou Aluminum Co., Henan, China, purity > 99% (in mass)) and SiC (Jiangsu Leyuan Factory, Jiangsu, China, purity > 99% (in mass)). The average particle sizes (D50) of the powders were 31.63 μm and 0.92 μm, respectively, which were characterized by laser diffraction (NSKC-IA, Nanjing University of Technology, China). The Al2O3 powder was ground into different particle diameters (1.44 μm and 0.55 μm) for further use. Scanning electron microscopy (SEM) photographs of 1.44 μm Al2O3, 0.55 μm Al2O3 and 0.92 μm SiC are shown in Fig. 1, observed with a scanning electron microscope (JSM-6360LV, JEOL Led., Tokyo, Japan). The IEP values of the powders were obtained from Zetasizer (3000HSA, Malvern Instruments Ltd., Malvern, UK). 2. 2 Sample preparation The ceramic powders were dispersed in deionized water. The pH was then adjusted to the desired value using standardized analytical-grade HCl or NaOH solution. NaCl was used to adjust ionic strength. Finally, the mixture was ball-milled using an agate grinding ball as media at a (...truncated)


This is a preview of a remote PDF: https://link.springer.com/content/pdf/10.1007%2Fs40145-014-0102-4.pdf

Xiaoqing Zhang, Yanli Zhang, Han Chen, Lucun Guo. Effect of pH on rheology of aqueous Al2O3/SiC colloidal system, Journal of Advanced Ceramics, 2014, pp. 125-131, Volume 3, Issue 2, DOI: 10.1007/s40145-014-0102-4