FIXATION OF CHROMIUM IN WOOD FROM DICHROMATE AND CHROMATE SALT-SOLUTIONS

It has been reported that treatment of wood surfaces with aqueous solu tions of chromium trioxide imparts some beneficial properties like wea ther resistance and some degree of water repellency. The work presente d here aims at finding alternative ways of fixing chromium in wood wit h the avoidance of the very acidic and strong oxidant conditions of ch romic acid solutions. This is because these solutions may affect the s trength 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 (K 2Cr2O7 aq.) and similar to 9.5-10.3 (K2CrO4 aq.). For the CrO3-solutio ns the effects of temperature and reaction time an the fixation of chr omium were investigated. For the dichromate and chromate solutions, fi xation 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 s olutions without significant mechanical damage to wood. On the other h and, even diluted CrO3-solutions (0.01 M) impart serious strength redu ctions in wood at temperatures of 90 degrees C and higher when reacted for 8 hours, and the chromium content of wood resulting from such tre atment is of the order of only 1%.