Ammonium Perchlorate Crystals Research Articles

Effect of pretreatment on the sublimation of ammonium perchlorate

The effects of pretreatments on the sublimation of pure ammonium perchlorate (AP) were studied by differential thermal analysis. The addition of inorganic salts (doping), or preheating, lead to desensitisation of the sublimation process, whereas it was sensitised by precompression. Sublimation increased with decrease in the particle size of the AP from 500 to 200 microns, but decreased with a further decrease in size from 200 to 100 microns. The results are interpreted in terms of gross imperfections and strain in the AP crystals.

Effect of pretreatment on the sublimation of ammonium perchlorate

AbstractThe effects of pretreatments on the sublimation of pure ammonium perchlorate (AP) were studied by differential thermal analysis. The addition of inorganic salts (doping), or preheating, lead to desensitisation of the sublimation process, whereas it was sensitised by precompression. Sublimation increased with decrease in the particle size of the AP from 500 to 200 microns, but decreased with a further decrease in size from 200 to 100 microns. The results are interpreted in terms of gross imperfections and strain in the AP crystals.

Thermoluminescence of irradiated ammonium perchlorate crystals

The thermoluminescence of single crystals of ammonium perchlorate irradiated with X rays, uv light, or high energy electrons has been measured between 80 and 420 K. With a heating rate of 5 K/min. prominent peaks occur at 95, 113, 134, 246, and 320 K; an additional peak is found at 347 K after longer irradiation times. The absorption spectrum of uv-irradiated ammonium perchlorate has also been measured and shows bands at 300, 360, and 610 nm. A comparison of these data with chemical and spectroscopic evidence obtained by other workers has permitted the probable identification of ClO3−, ClO−, ClO2, and F centres as radiation products. Three thermoluminescent peaks remain unassigned.

The electrical conductivity of ammonium perchlorate single crystals

The electrical conductivity of single crystals of ammonium perchlorate has been studied from 25 to 180°C. Plots of log σT vs 1 T show two linear regions, one from 25 to 100 and another from 100 to 180°C. Activation energies for the conduction processes in the low- and high-temperature regions are 0.12 and 1.04 eV, respectively. The conduction is a bulk process and not a surface mechanism. Conduction in the low-temperature region is predominantly due to the migration of protons and is sensitive to the concentration of interstitial H 2O molecules which act as proton donor and acceptor sites. In the high-temperature region, conduction is due to migration of NH 4 + through cation vacancies. Detailed mechanisms are postulated both for electrical conduction and for the electrode reactions.

Behavior of Several Catalysts in the Combustion of Solid Propellant Sandwiches

Theme T two-dimensional solid propellant sandwich has evolved as convenient test vehicle for theories dealing with both physical and chemical behavior of composite solid propellant ingredients. It allows detailed observation of the binder-oxidizer interface over range of test conditions. Sandwiches have been used by several investigators. Hightower and Price used laminated, two-dimensional sandwiches of single crystals of ammonium perchlorate and hydrocarbon binder. They considered this configuration to be a compromise between the complexity of the three-dimensional 'combustion zone' and the naivety of one-dimensional approximation. Jones investigated the catalytic behavior of Harshaw Catalyst, Cu 0202 and ferric oxide, Fe2O3 in solid propellant sandwiches of polycrystalline ammonium perchlorate (AP) and carboxyl terminated polybutadiene (CTPB). Hydroxyl terminated polybutadiene (HTPB) was substituted for CTPB and the behavior of the same catalysts over the pressure range 600-3200 psia was investigated. The sandwich vertical burn rate, the normal regression rate of the oxidizer and qualitative details of the deflagration process were obtained by cinephotomacrography. The current study has extended the investigation to include two additional catalysts,

Polarized Raman study of lattice modes in ammonium perchlorate at low temperatures

The Raman spectra of oriented single crystals of ammonium perchlorate have been measured as a function of temperature between 12 and 300 K. The results are consistent with the assignment of NH 4ClO 4 to the D 2 h 16 space group at all temperatures. A weak B 1 g mode at 180 cm −1 is assigned as an NH 4 + libration. Anomalous temperature dependence is observed for low frequency B 1 g and B 3 g lattice modes. Detailed results are presented for these modes in the range 18–80 K.

Thermal decomposition of ammonium perchlorate single crystals

The thermal decomposition of large single crystals of pure ammonium perchlorate and ammonium perchlorate doped with Ba2 + or SO 2− 4 ions has been investigated over the temperature range 220–290°C. Comparative studies were also made with compressed pellets of the pure powder and with small single crystals containing macroscopic flaws. The kinetic results were analyzed using a computer technique which permits a very detailed examination of various kinetic models. This reveals that the “induction period” (α < ∼ 0.01) is very complex and comprises a desorption step, a linear process, an exponential process, and the beginnings of an Avrami process. The latter three processes are identified with (i) the inward growth of rapidly formed surface nuclei, (ii) “branching” of surface nuclei, and (iii) nucleation in the bulk crystal. Kinetic parameters are obtained for these three processes and also for the growth of nuclei in the bulk crystal. This model fits the kinetic data over the complete range of α(0–1), or 1 × 10 −5 < α < 1 if the desorption step is not included. The mechanism of the reaction and possible effects on this of Ba 2+ and SO 2− 4 doping are discussed briefly.

Effect of fast neutron, gamma-ray, and combined radiations on the thermal decomposition of ammonium perchlorate single crystals

The thermal decomposition kinetics have been determined for ammonium perchlorate crystals subjected to a fast neutron irradiation or to a fast neutron irradiation followed by a gamma-ray irradiation. Qualitatively, the radiation induced changes are similar to those obtained in this and in previous studies, with samples exposed only to gamma rays. The induction period is shortened and the rate constants, obtained from an Avrami-Erofeyev kinetic analysis, are modified. The acceleratory period constant increases and the decay period constant decreases. When compared on an equal deposited energy basis, the fast neutron induced changes are appreciably larger than the gamma-ray induced changes. Some, or all, of the fast neutron induced effects might be attributable to the introduction of localized regions of concentrated radiation damage (``spikes'') by lattice atom recoils which become thermal decomposition sites when the crystals are heated.

Co-crystallization of isomorphic substances

A theoretical model is developed to predict the separation factor in the co-crystallization of a compound with an isomorphic impurity. This model envisions reversible surface reactions for the crystallization of each of the two substances and predicts that the separation factor depends on the overall rate constants of the forward and the reverse reactions. According to this model the separation factor approaches the ratio of the equilibrium constants at small rates of crystallization and approaches the ratio of the forward rate constants at large rates of crystallization. Moreover, this theory shows how isomorphic impurities can concentrate in the solid phase upon crystallization. These theoretical conclusions were in agreement with the experimental results obtained from the crystallization of ammonium perchlorate with KMnO 4 and K +-impurity. The average values of the separation factors were obtained for these two systems.

Electrical Conductivity of Pure and Doped Ammonium Perchlorate Crystals

The conductivity of single crystals of pure ammonium perchlorate and of ammonium perchlorate doped with Ba2+ and with [Formula: see text]ions has been measured at a frequency of 1591 Hz between room temperature and 260 °C. All three systems display a marked increase in conductivity at the temperature of the orthorhombic → cubic phase transition. It is suggested that this sudden increase in conductivity is more probably due to secondary effects (specifically, dislocation generation) than to the actual change in crystal structure. The general similarity between the results for pure and doped crystals tends to support a proton transfer mechanism for a.c. conductivity that does not involve vacancies. However, vacancies may be important in d.c. conductance mechanisms.

Electrical conductivity of ammonium perchlorate

The a.c. electrical conductivity both of compressed pellets and of single crystals of ammonium perchlorate has been measured at a frequency of 1591 Hz from room temperature up to decomposition temperatures. The observed effects of annealing and partial decomposition emphasize the need for considerable caution in accepting various defect models for the conductivity that have been proposed in the literature.

Application of Internal Reflectance Spectroscopy to the Study of Solid Propellant: II. Thermal Decomposition of Ammonium Perchlorate

Abstract The infrared spectra of the surfaces of ammonium perchlorate crystals while being heated up to 250°C have been obtained using Internal Reflectance Spectroscopy. The crystal transformation, from rhombic to cubic, is apparently observed.

Proton transfer conduction in ammonium perchlorate

The electrical conductivity both of compressed pellets and of single crystals of ammonium perchlorate has been measured from room temperature up to decomposition temperatures. Special attention has been paid to the effects of thermal cycling experiments up to various maximum temperatures. These experiments disclose that, except in very carefully annealed samples, the low temperature region (< 127°C) is structure sensitive. The low temperature conductivity is increased by several orders of magnitude by either thermal decomposition, or the adsorption of water or of ammonia. The kinetics of annealing, and of sorption and desorption of ammonia, have been studied; they differ for pellets and single crystals and show that in pellets surface adsorption is the most important phenomenon but in single crystals diffusion predominates. These complex results can all be interpreted in terms of a model which involves the formation of proton defects (NH 3 molecules on lattice cation sites) by proton transfer from NH 4 + ions to water or ammonia molecules. The migration of a proton defect is only weakly temperature-dependent but defect formation requires energies of between 0·5 and 1 eV depending on the acceptor.

Radiation-induced Dislocations in Ammonium Perchlorate Crystals

THE exposure of ammonium Perchlorate crystals to radiation before heating accelerates the decomposition rate and shortens the induction period1–4. Furthermore, the thermal, chemical and radiolytic decomposition of ammonium Perchlorate5–7 and the radiation-induced etching of NaN3 and KN3 (ref. 8), have been shown to be intimately related to dislocations. We wish to describe measurements indicating that the radiation-induced effects can be attributed to dislocations which are generated during irradiation.

ESR studies of restricted random motion of NH 3+ radicals in γ-irradiated ammonium perchlorate crystals

The ESR spectra of 14NH 3 + radicals in γ-irradiated crystals of ammonium perchlorate were observed in the temperature range 77–300°K. It was found that the radicals rotate in random fashion about two distinct directions in the unit cell, jumping from one orientation to the other. The temperature variation of the correlation time for the nitrogen-14 hyperfine interaction was investigated.

A photomicrographic and electron microscopy study of nucleation in ammonium perchlorate

The nucleation processes associated with the formation of thermal decomposition sites in single crystals of ammonium perchlorate have been studied by optical and electron microscopy. In crystals subjected only to heating the nucleation sites appear to be randomly distributed on the c face ; however, on the m face some are randomly distributed but others lie along lines in specific crystallographic directions. When crystals are strained, in any of several different directions, before thermal decomposition the nuclei are strongly alined on both faces. These alined nuclei lie, with few exceptions, in the same crystallographic directions as similarly alined p its formed by chemical etching. Consequently, it is concluded that the decomposition nuclei preferentially form where dislocations intersect the crystal surface. During heating at 170 to 210 °C the first-formed nuclei are widely distributed and appear to be on the surface. These and subsequently formed nuclei appear to cease growing when they reach a critical size. Additional nuclei continually appear between previously formed ones until a completely reacted layer is formed. (At these low temperatures complete reaction corresponds to the decomposition of only 30 % of the original material.) Further decomposition occurs in two ways. In one, the reaction progresses inward and roughly parallel to the surface as successively deeper layers of nuclei are formed. In the other, the reaction produces bands, possibly at an accelerated rate and with the formation of additional internal nuclei, along (001) planes in the [010] and [510] directions. Scanning electron microscope examination shows that these bands, as well as other parts of the reacted surface, consist of porous residue of ammonium perchlorate.

The deflagration of single crystals of ammonium perchlorate

By means of high-speed motion photography the deflagration rate of single crystals of pure ammonium perchlorate was measured from the deflagration pressure limit to 5000 psia at ambient temperatures of 89, 23, and −28°C. The 23°C burning rate isotherm, which was consistently lower than the 89°C isotherm and above the −28°C isotherm, rose to a relative maximum, dropped to a relative minimum, and then rose again as the pressure was increased to 5000 psia. The −28°C isotherm was measured between 415 and 565 psia and between 2000 and 4500 psia and had an apparent discontinuity between these two pressure regions. Within the accuracy of the data the deflagration rate was not influenced by the pressurization gas, either nitrogen or helium, by the crystallographic axis of the deflagration wave proceeding through the crystal, or by natural convection.

Deflagration rate, surface structure, and subsurface profile of self-deflagrating single crystals of ammonium perchlorate

Pure ammonium perchlorate single crystal self deflagration, determining energy transfer mechanisms from pressure effects, combustion characteristics and subsurface profile

Surface temperature of deflagrating ammonium perchlorate crystals.

Surface temperature of deflagrating ammonium perchlorate crystals calculated from crystal phase transition thickness

Electrical Conductivity of Ammonium Perchlorate

Zirkind and Freeman1 have pointed out the increase in the electrical conductivity of ammonium perchlorate crystals on irradiation with 0.637-MeV caesium-137 γ-rays. In this communication, results are reported from an investigation of the electrical conductivity of ammonium perchlorate solid as a function of temperature and gaseous atmosphere. Data concerning the electrical conductivity of ammonium perchlorate were not found in the literature.