TRANSITION PATHS BETWEEN PHASE-IV, PHASE-III AND PHASE-II OF AMMONIUM-NITRATE PREDICTED FROM X-RAY-POWDER DIFFRACTOMETER AND DIFFERENTIAL SCANNING CALORIMETER DATA BY PARTIAL LEAST-SQUARES REGRESSION

Ammonium nitrate solid phase transition paths between phases IV, III a nd II were explained and predicted, on the basis of X-ray powder diffr action (XRD) and differential scanning calorimetry (DSC) data by apply ing partial least-squares regression (PLS) and principal component ana lysis (PCA). The samples were clustered according to their different t ransition paths with the PLS and PCA models, and the transition paths were predicted with PLS component clusters. The best PLS clusters were formed by a few first components. Prediction of the transition path w ith the PLS clusters made a semiquantitative prediction of the transit ion energy possible. In PCA, principal components 6 and 11, which best clustered the samples, explained 7% of the variation of the XRD data. The clustering showed that most of the variance is due to other facto rs than those affecting the transition path. The correlation between t he structural data and the transition energies obtained by differentia l scanning calorimetry was calculated by PLS method. The correlation b etween the predicted and the observed energies of an independent predi ctor set varied from zero to over 0.7 depending on the 2theta range. T he PLS analysis of the XRD and DSC measurements proved that the differ ent phase transition paths are of structural origin.