Fixation of Chromium in Wood from Dichromate and Chromate Salt Solutions

It has been reported that treatment of wood surfaces with aqueous solutions of chromium trioxide imparts some beneficial properties like weather resistance and some degree of water repellency. The work presented here aims at finding alternative ways of fixing chromium in wood with the avoidance of the very acidic and strong oxidant conditions of chromic acid solutions. This is because these solutions may affect the strength of wood, and are known to have a very high human toxicity. In this study, chromium has been fixed into wood from hexavalent chromium solutions at pH's of similar to 1.5 (CrO3 aq.), similar to 3.8-3.9 (K2Cr2O7 aq.) and similar to 9.5-10.3 (K2CrO4 aq.). For the CrO3-solutions the effects of temperature and reaction time an the fixation of chromium were investigated. For the dichromate and chromate solutions, fixation experiments were carried out with Cr-concentration and reaction times as variables. It is shown that a 3%-fixation level of chromium in small wood specimens can be attained from dichromate and chromate solutions without significant mechanical damage to wood. On the other hand, even diluted CrO3-solutions (0.01 M) impart serious strength reductions in wood at temperatures of 90 degrees C and higher when reacted for 8 hours, and the chromium content of wood resulting from such treatment is of the order of only 1%.