THE X-RAY STRUCTURE OF A SODIUM PEROXIDE HYDRATE, NA2O2-CENTER-DOT-8H(2)O, AND ITS REACTIONS WITH CARBON-DIOXIDE - RELEVANCE TO THE BRIGHTENING OF MECHANICAL PULPS

The main component of the solid originally believed to be a peroxosili cate with pulp-brightening properties has been shown to be Na2O2 . 8H( 2)O. The solid crystallizes in the monoclinic space group Cue, with an empirical formula H8O5Na, and with a = 14.335(3), b = 6.461(1), c = 1 1.432(2) Angstrom, beta = 118.28(3)degrees, and Z = 8. The centrosymme tric structure consists of a peroxide anion with an O-O distance of 1. 499(2) Angstrom. Each of these oxygen atoms is at the apex of an appro ximate square-based pyramid, the base of which consists of four oxygen atoms of water molecules. The bases of the two pyramids are staggered when viewed down the peroxide bond. Each sodium is at the centre of a n approximate octahedron of water molecules, four of which bridge othe r sodium atoms and two bridge to the peroxide anions. One hydrogen ato m of each of these two water molecules is terminal and the other two a re hydrogen bonded to peroxide oxygen atoms. The compound reacts very rapidly with CO2 in moist air to form Na2CO3, but in drier conditions, formation of the carbonate can take many days and proceeds via a perc arbonate, believed to be Na2CO4. This has been identified by infrared spectroscopy and X-ray powder diffraction and can persist for long per iods in dry air.