CHEMICAL ACOUSTIC EMISSIONS FROM GAS EVOLUTION PROCESSES RECORDED BY A PIEZOELECTRIC TRANSDUCER

The information of frequency domain power spectra obtained from acoust ic emission (AE) signals by fast fourier transform (FFT) program for d ifferent gases evolution processes are investigated. The different pro cesses include different metals in dilute inorganic acids for evolving hydrogen gases, different carbonate/bicarbonate solutions dropping in to dilute inorganic acids for evolving carbon dioxide gases, bubbling nitrogen into above-mentioned salt solutions of corresponding reaction products and the above-mentioned salt solutions background without ga s evolution. Averaged power spectra from these systems and their corre sponding characteristics are examined. The characteristic frequencies for a given system are found to be more or less reproducible, while th e corresponding maximum power intensities are varied to a large extent but still kept up to the same order of magnitude. The AE signals can be used for chemical pattern recognition. The principal component anal ysis (PCA) with appropriate frequency selection procedure can give sat isfactory classification of AE signals for different gas evolution sys tems. The back-propagation algorithm of multilayer feed-forward networ k can give better recognition of AE signals for different metal-acid b uffer solution reaction processes. In addition, the AE energetic param eters are linearly related with solution pH, which opens some new poss ibilities for analytical application of AE signals. (C) 1998 Elsevier Science S.A. All rights reserved.