Mini-Encyclopedia of Papermaking Wet-End
Part Two: Definitions and Concepts
Papermakers use the word "ash" in two ways. In its most general sense, the word means "filler" or "mineral content." The word also refers to the material that is left over when paper is incinerated at a defined temperature and for a defined time. A relatively high temperature of incineration, such as 900 degrees Centigrade, can drastically change the chemical composition of the filler. For instance calcium carbonate is converted to CaO, which has a mass only 56% that of the filler. Kaolin clay looses water under such conditions; the anhydrous clay has 86% the mass of the hydrous filler clay. A moderately low temperature of incineration, e.g. 500 degrees Centigrade, may leave most of the filler in its original form. To convert "percent ash" data to "percent filler" it is necessary to know the relative amounts of the different fillers and their respective losses on ignition. The relative amounts of, say clay versus calcium carbonate, can be determined by x-ray fluorescence analysis of the incinerated ash.
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