Particle Characterisation and Grinding Behaviour of Gamma-Alumina Slurries Prepared in a Stirred Media Mill

Stephen Adegbite

doi:10.5539/jmsr.v2n1p135

Abstract

This paper investigates gamma-alumina slurry preparation in a stirred media mill to develop protocols for the characterisation of slurries for coating onto monolithic catalyst supports. The relationship between the pH and the zeta potential of particles is determined. The gamma–alumina particles are found to be optimally stabilised at a pH of 4 and zeta potential of +41 mV. The grinding behaviour of gamma-alumina particles inside the mill is determined in terms of the number of stress events (SN), stress energy (SE) and the specific energy (Em,p). The visualisation of the particles at different stages of milling is done by scanning electron microscope (SEM). The results show that finer particles are produced by increasing milling duration from 0 – 240 min due to an increase in SN and that the use of smaller grinding media inside the mill produced finer particles due to an efficient consumption of Em,p.

Highlights

The emergence of the first cars equipped with monolith catalysts began in 1975 and today there are several hundred million monolith catalysts fitted in motor vehicles worldwide (Twigg, 2007)
The electrokinetic sonic amplitude (ESA) technique is such that when an alternating electrical potential was applied to the slurry, it caused the particles to vibrate in a manner that depends on their diameter and on the zeta potential at the frequency of the applied field
When there is a density difference between the particles and the aqueous suspension, this motion would generate an alternating acoustic wave of the same frequency as the applied field. This phenomenon is called the ESA effect and the particle diameter measured is termed the ESA diameter (Sarraf & Herbig, 2008). These results clearly show the strong dependence of the zeta potential and the ESA diameter of particles on slurry pH

Summary

Introduction

The emergence of the first cars equipped with monolith catalysts began in 1975 and today there are several hundred million monolith catalysts fitted in motor vehicles worldwide (Twigg, 2007). Demand for emission control technology is constantly increasing worldwide due to greater need for motorised transportation, new legislation for deployment in developing countries and tighter emission standards aimed at future zero emissions (Twigg, 2006). These factors will invariably increase the competition in the catalyst industry for the development of technologies to enhance automotive catalytic functions (Collins & Twigg, 2007; Jobson, 2004). The stabilisation of γ–alumina particles is necessary to prevent the van der Waals forces causing particle aggregation which affects the adhesion between the coating and the monolith surface

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