Particle Standards: Their Development and Application

Abstract

With the increase in the importance of dispersed materials (powders, aerosols, emulsions etc.) to trade, there is an increasing awareness of the need to verify that instruments which measure particle properties, particularly size, are operating within defined limits of accuracy. As a minimum, this process requires some form of verification with reference to standard particles whose properties are known in relation ultimately to the international standards of mass and length (so-called traceability chain). In some cases, a formal calibration to establish instrument response in terms of size, shape or concentration may be required. This article reviews the particle standards that are available to establish the performance of measurement equipment, placing most emphasis on particle size, as this is the variable that is generally of most importance to industry. However, secondary properties, such as shape, density and refractive index, influence the response of many types of particle size analyzer. Attempts to provide standard materials that may enable independent assessment to be made of the effect of some of these variables on instrument performance are therefore also considered.