The transitions in phases II–III–IV in high purity ammonium nitrate

Abstract

The phase changes in high-purity ammonium nitrate were studied by a differential thermal analysis (DTA) apparatus designed for constant heating and cooling rates and continuous cycling for ~,3-gram samples. On the basis of DTA and X-ray diffraction data very consistent behavior is observed. Phase IV--~ IIl transformation on heating in the range 43 ~ to 51 ~ and Phase II---~ IV transformation on cooling in the range 49 ~ to 53 ~ are demonstrated. The III-+ II transition at about 86 ~ is seen with repeated temperature cycling. This repeatable behavior not consistently seen by investigators using other techniques is believed to be due to the high purity material and constant heating and cooling rates.The literature on the thermal behavior of NH~NO3 (ammonium nitrate) is voluminous; and although it extends back for more than 50 years, it still leaves the reader without a statement of the unambiguous phase relations for the material. Each investigator has reported on a special set of conditions, and the reader has the dilemma of deciding whether the anomalies described are related to the special conditions imposed by the experimenter, are the peculiar characteristics of the salt, or are both.The crystalline modification of NH~NO3 are given as follows [1 ]: Phase I cubic 169.6 ~ to 125.2 ~ Phase II tetragonal 125.2 ~ to 84.2 ~ Phase III orthorhombic 84.2 ~ to 32.1 ~ Phase IV orthorhombic 32.1 ~ to -16 ~ Phase V tetragonal below -16 ~ Phase VI above 160 ~ at pressure >9000 kg/cm ~ Phase VII below -170 ~The fusion temperature and the 125.2 ~ temperature inflections are unambiguous, and Phases VI and VII are not in the scope of this paper. The behavior of the material at 32 ~ and 85 ~ appears to be irregular.

Influence of frequent rhombic-monoclinic crystal transformation and of moisture content on ammonium nitrate crystal transformation energies

“…Further increase in moisture content, in the investigated interval, does not influence the temperatures observed. The temperatures determined with this technique under the given conditions agree with those in the literature [1][2][3][4]16] (Fig. 2).…”

“…The shapes of the DTA curves and the temperatures of the crystal transformations for ammonium nitrate generally agree well with the literature data [2,4,10,12,15], but in the case of [1] only for the samples with higher water contents. Brown and McLarsen [1] have suggested that the IV ~IlI phase transformation takes place only in the presence of moisture, via a dissolution and recrystallization mechanism involving drastic structural change.…”

“…The energies of ammonium nitrate crystal transformations from rhombic into monoclinic, from monoclinic into trigonal and from trigonal into cubic were observed as functions of the number of previous crystal transformations and the moisture content.The phase transformations of ammonium nitrate have been extensively investigated by DTA, DSC and dilatometry [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The structures of the phases have also been investigated [16][17][18][19][20][21][22].…”

Phase Stability of Ammonium Nitrate with Organic Potassium Salts

“…These have shown that the phase behavior of AN strongly depends on the experimental conditions, such as humidity [26], crystallization method [7], thermal history of sample [7], sample size [27], pressure [28,29], purity of sample [30], sample weight [31].…”

Minol IV, A New Explosive Composition Containing Ammonium Nitrate-Potassium Nitrate Solid Solution. Part 1

“…At atmospheric pressure, the stability regions of forms I through V of AN are given (16,17) as follows: I -169.6C (m.p.) to 125.2'C; II to 84.2*C; III to 32.2'C; IV to -i7 0 C,; V below -170C.…”