Estimation of the Thermal Decomposition and Analysis of Evolved Species and Char of Wood Preservatives Using Thermogravimetric Analysis Combined with Spectrometric Techniques
Journal of the Faculty of Agriculture Kyushu University
Three types of wood preservatives, creosote oil (Creosote), chromated copper arsenate (CCA-3) and ammoniacal copper quats (ACQ-1) were studied, first by using thermogravimetric analysis (TGA) under different heating rates (5 or 40˚C/min), and then by using thermogravimetric analysis with infrared spectrometry (TGA-IR) and energy dispersive X-ray spectrometry (EDX). The results obtained from the TGA tests found that the decomposition temperature of each of the preservatives for the heating rate
... t 5˚C/min was lower than that at 40˚C/min. Regardless of different heating rate, the char (wt %) of the CCA-3 was more than that of the ACQ-1, and the amount of char for the Creosote was lower than that for either of the water-based preservatives. The IR response of all preservatives in the TGA-IR tests showed that at a heating rate of 5˚C/min, the absorbance of Creosote and ACQ-1 was higher than that of CCA-3. This indicated that the concentration of evolved species of CCA-3 was less than that of Creosote and ACQ-1. However, at a heating rate of 40˚C/min, the absorbance of CCA-3 and ACQ-1 was higher than that of Creosote. Considering the decomposition step (thermal time or temperature) at different heating rates in the TGA tests and the IR response from the TGA-IR analysis, the results obtained showed that at the slow-heating regime, the concentrations of CO 2 produced by Creosote and ACQ-1 were higher than that of CCA-3, but at the fast-heating regime, the concentration of CO 2 for ACQ-1 was higher than that of Creosote and CCA-3. The EDX analysis of all preservatives showed that the main element of the char for Creosote was C (82.75%) after combustion. The char of CCA-3 had an amount of Cr (34.99%) that was obviously more than that of As (11.89%) and Cu (16.69%) due to Cr being a stable element during combustion. The char of ACQ-1 left a high amount of inorganic metal elements, such as Cu (50.14%). These results, when compared to the chemical ingredients of all preservatives, enabled us to point out the kinds of evolved species for referencing the thermo-decomposition processes of the preservatives. The use of TGA for analyzing the thermal properties of three types of preservatives, in combination with TGA-IR and EDX analysis, has led to useful results, regarding the identification of thermal decomposition products (evolved species and char).