Lapping composition

摘要

A lapping composition consists of plate alumina powder in which the proportion of grains having a grain size of at least twice the value of the average grain size is at least 0.2% by weight. A method of producing such a lapping composition comprises the steps of: (a) preparing a first abrasive powder which consists of plate alumina powder of a first average grain size by milling and classifying a sintered body of plate alumina obtained by calcining aluminium hydroxide; (b) preparing a second abrasive powder which consists of plate alumina powder by milling a sintered body of plate alumina obtained by calcining aluminium hydroxide and classifying the milled powder to give a second abrasive powder having an average grain size in the range from 1.3 to 2.3 times as large as the plate alumina powder of first average grain size, and (c) blending said first and second abrasive powders in proportions such that the weight fraction of plate alumina powder having a grain size of at least twice the value of the average grain size is not less than 0.2%.