Ammonium Perchlorate Single Crystals Research Articles

Dynamic measurement of internal strain on composite solid propellant constituents during laser induced combustion

Binder melt flow and ammonium perchlorate (AP) cracking have been topics for research for a long time. Both impact the burning rate dependence on pressure and the binder flow. Rapid depressurization of the combustion vessel is the most common tool used to study binder melt flow by studying the ripples on the quenched surface. Laminate propellants were used to study fundamental combustion phenomena such as the melt flow over the oxidizer/binder interface AP/hydroxyl-terminated polybutadiene (HTPB). This study starts with thermally induced strain measurements in single crystals of AP with thicknesses 1- to 2.5-mm and neat HTBP slabs then finishes with laminates of AP/HTPB. A CO2 laser ignited and burned samples over a range of heat fluxes. First ever in- situ mapping of the two-dimensional thermally-induced internal strain generated at ignition to steady state combustion were imaged using a high-speed polarization camera. Heating of the surface produced strain fields in the AP, HTPB, and laminate provide information on the thermal diffusion during the ignition and fully developed combustion. This paper demonstrates how using polarized high-speed video, the binder melt flow was more accurately observed and AP cracking mechanisms can be better studied.

Simulation of the Dynamic Breakdown of Ammonium-Perchlorate Single Crystals

Dynamic breakdown of ammonium perchlorate single crystals is numerically simulated. A system of differential equations that describe processes in an equivalent circuit of a pulsed voltage oscillator, a kinetic equation of impact multiplication of electrons, and a heat-balance equation are simultaneously solved. The breakdown strength of ammonium perchlorate is calculated in the dynamic mode versus interelectrode distance and leading edge of a high-voltage pulse. The calculated results are in reasonable agreement with the experimental data on the dynamic breakdown of ammonium perchlorate.

Моделирование электрического пробоя монокристаллов перхлората аммония в динамическом режиме

A numerical simulation of the electrical breakdown in dynamic mode of single crystals of ammonium perchlorate has been carried out. The system of differential equations was solved, which described the processes in the equivalent circuit of the pulse voltage generator together with the kinetic equation of impact electron multiplication and the heat balance equation. The dependences of the electric strength of ammonium perchlorate in dynamic mode on the interelectrode distance and the duration of the leading edge of a high voltage pulse were calculated. Obtained numerical simulation results are in good agreement with the known experimental data of electrical breakdown of ammonium perchlorate in the dynamic mode.

Growth Rate Dispersion at the Single‐Crystal Level

AbstractEvidence of growth rate dispersion for symmetry‐related opposite faces of centrosymmetric single crystals of ammonium perchlorate is provided. Crystallization experiments conducted by evaporation of a stagnant aqueous solution at room temperature show that some $ ({\rm{hkl}}) $ faces have high and irregular normal growth rates, in time and space, whereas the corresponding $ ({\rm{\overline h}}\;{\rm{\overline k}}\;{\rm{\overline l}}) $ faces crystallize slowly and steadily. The $ ({\rm{hkl}}) $ faces presenting high and irregular crystal growth also form repetitive inclusions, whereas $ ({\rm{\overline h \;\overline k \; \overline l}}) $ faces are not involved in any formation of vacuoles. As a consequence, it is possible to retrace the crystallization history of a single crystal by analyzing the location of series of inclusions showing the progressive displacement of its center of gravity.

Spectroscopic Study of Shock-Induced Decomposition in Ammonium Perchlorate Single Crystals

Time-resolved Raman scattering measurements were performed on ammonium perchlorate (AP) single crystals under stepwise shock loading. For particular temperature and pressure conditions, the intensity of the Raman spectra in shocked AP decayed exponentially with time. This decay is attributed to shock-induced chemical decomposition in AP. A series of shock experiments, reaching peak stresses from 10-18 GPa, demonstrated that higher stresses inhibit decomposition while higher temperatures promote it. No orientation dependence was found when AP crystals were shocked normal to the (210) and (001) crystallographic planes. VISAR (velocity interferometer system for any reflector) particle velocity measurements and time-resolved optical extinction measurements carried out to verify these observations are consistent with the Raman data. The combined kinetic and spectroscopic results are consistent with a proton-transfer reaction as the first decomposition step in shocked AP.

Low-temperature thermal decomposition of large single crystals of ammonium perchlorate

Similarities and differences in the thermal behaviour of deuterated and nondeuterated ammonium perchlorate provide insights into the mechanism of its thermal decomposition. Thermal decomposition of NH 4 ClO 4 and ND 4 ClO 4 always begins in the bulk of the crystals. In both cases decomposition stops when the degree of conversion is about 30%, giving porous products which undergo the same phase transition as the parent single crystals. Thermal decomposition of the deuterated sample is slower, the volume fraction of pores appears to be lower and the sample has a small quantity of ‘snow’ on the surface. These effects are best rationalized as caused by proton transfer at the intersections of dislocations in the bulk of the crystals.

Thermomechanical model and temperature measurements for shocked ammonium perchlorate single crystals

A consistent thermomechanical material model was developed for unreacted ammonium perchlorate (AP) single crystals for shock compression normal to the (210) and (001) crystal planes. Building on previous work, the mechanical response for both orientations was described using a single isotropic elastic-plastic model and an overstress model to describe rate-dependent yielding. Velocity interferometer measurements to 12 GPa were performed to extend the AP Hugoniot curve to higher stresses. The specific heat cv, the coefficient of thermal pressure (∂P/∂T)V, and the isothermal bulk modulus BT were determined from Hugoniot and isothermal compression curves, along with available data at atmospheric pressure. Time-resolved Raman spectroscopy experiments were carried out under stepwise loading to obtain temperatures in the shocked state. Calculated temperatures using our material model are in good agreement with the temperatures obtained from our experiments, thus providing validation for our modeling approach.

Shock wave response of ammonium perchlorate single crystals to 6 GPa

Plane shock wave experiments were carried out on ammonium perchlorate single crystals compressed along [210] and [001] orientations to peak stresses ranging from 1.2 to 6.2 GPa. Quartz gauge and velocity interferometer techniques were used to measure the elastic and plastic shock wave velocities, and stress and particle velocity histories in the shocked samples. The measured Hugoniot elastic limit (HEL) was 0.48±0.09 GPa. Above the HEL and up to about 6 GPa, the data show a clear two-wave structure, indicating an elastic-plastic response. Time-dependent elastic precursor decay and plastic wave ramping are discernable and orientation dependent in the low stress data. However, the orientation dependence of the peak state response is small. Hence, data for both orientations were summarized into a single isotropic, elastic-plastic-stress relaxation model. Reasonable agreement was obtained between the numerical simulations using this model and the measured wave profiles. At a shock stress of about 6 GPa and for the time duration and crystal orientations examined, we did not observe any features that may be identified as a sustained chemical reaction or a phase transformation.

Effect of the duration of the front edge of the voltage pulse on the electric breakdown of ammonium perchlorate

The results of a study of the effect of the front edge duration of a voltage pulse (τ) on the electric breakdown of ammonium perchlorate single crystals are submitted. Experiments have shown that at τ 1.5 µs. It is shown that the electric breakdown of ammonium perchlorate results from an impact generation of electrons. The impact generation rate of electrons versus electric field and the diameter of the through channel being formed during electric breakdown in ammonium perchlorate are estimated.

An electron spin-resonance study of radicals in single crystals

An ESR study of centres in x-irradiated ammonium perchlorate single crystals is carried out that is aimed at resolving the controversy that has recently arisen over the possible occurrence of low-temperature phase transitions in the compound (room temperature structure: orthorhombic; space group Pnma). The ESR spectra are recorded as a function of the orientation of the magnetic field H in the three orthogonal crystallographic planes at 300 K, 77 K, and 4.2 K, and also as a function of temperature for H parallel to the principal z-component of the hyperfine coupling tensor. The analysis of the spectra shows that while the -tensor remained axial over the entire temperature range 2.0052(3), 2.0055(3), 2.0057(3) and 2.0090(3), 2.0096(3), 2.0105(3) at 300 K, 77 K, and 4.2 K respectively), , which is rhombic at room temperature , , and at 300 K) becomes more axial as the temperature is lowered , , and at 77 K, and , , and at 4.2 K). No changes in the spectra attributable to any phase transition were observed, and we conclude that does not undergo any phase transition below room temperature. Furthermore, it is found that during radiative decomposition the mirror-related Cl - O bonds, even though weaker than the other Cl - O bonds, do not break, thus confirming our earlier conclusion that mirror symmetry is preserved during radiation damage.

Nanosecond and picosecond laser-induced cracking and ignition of single crystals of ammonium perchlorate

Nanosecond and picosecond laser irradiations have been used to study the decomposition of ammonium perchlorate (NH4ClO4) crystals, a main component of propellants. Chlorate (NH4ClO3) decomposition product was detected via X-ray photoelectron spectroscopy. The decomposition is initiated amid associated mechanical deformations and microcracking processes occurring on a time scale commensurate with actual frequencies of energetic crystal decompositions pertinent to propellant combustion. Optical, scanning electron and atomic force microscopy methods have been applied to characterization of the laser-damage zones. Individual initiation or residual “hot spot” sites have been detected in the electron and atomic force microscope images, and are related to the cracking behaviour of the perchlorate allotropic phases. Evidence of the 240°C orthorhombic to rock-salt type cubic transformation was obtained in nanosecond laser irradiations through a remnant microstructure of ultrafine cracks whose intersection points marked an array of decomposition sites. A dislocation model description is given for the connected cracking and decomposition site observations.

Relating deformation to hot spots in shock-loaded crystals of ammonium perchlorate

The purpose of this work is to perform a microscopic-scale study of the role that crystal defects have in forming hot spots during shock loading of large, optical quality, pure single crystals of ammonium perchlorate (AP). The crystals were immersed in mineral oil at various distances from a detonator that provided the shock. The small explosive donor permitted recovery of the crystals for quantitative chemical analysis of decomposition and microindentation hardness testing. Hardness testing was also performed on an unshocked crystal to determine 1) the slip systems associated with primary and secondary deformation in accommodating the indenter and 2) the crack propagation directions at the surface as well as into the crystal. High-speed photographs of the shock-loaded crystals showed slip and cracking systems identified by hardness testing. Some of the systems were luminous. In addition, when a crystal with a large indentation was shocked near its reaction threshold, significant light appeared in the vicinity of the identation following shock passage. As such, preferred chemical reactivity in AP has been associated with its deformation systems and the presence of large strain centers.

Temperature-dependent Raman study of ammonium perchlorate single crystals: Evidence for NH4+ quantum rotation below 30 K.

We report a detailed temperature-dependent Raman study of oriented single crystals of ${\mathrm{NH}}_{4}$${\mathrm{ClO}}_{4}$ and ${\mathrm{ND}}_{4}$${\mathrm{ClO}}_{4}$ in the lattice-mode region from 10 to 300 K. Based on the deuterium shift, characteristic changes in bandwidth with temperature, structural information, etc., we have assigned the Raman bands in the lattice-mode region, which provides deeper insight into the dynamics of ammonium ions in the lattice. We have observed temperature-dependent sidebands by \ifmmode\pm\else\textpm\fi{}19 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ (10 K) from the main bands associated with some of the internal and lattice modes of the ${\mathrm{NH}}_{4}^{+}$ ion below 30 K. These spectral features have been explained in terms of a model in which the ${\mathrm{NH}}_{4}^{+}$ ion rotates almost freely about one of the axes coinciding with the N-H(2)...O(1) bond while it performs librational motion about the two perpendicular axes below 30 K.

Temperature-dependent Raman study of ammonium perchlorate single crystals: The orientational dynamics of the NH+4 ions and phase transitions

A detailed temperature-dependent study of the Raman spectra of oriented single crystals of NH4ClO4 is reported in the spectral regions of lattice modes and internal vibrations of the ClO−4 and NH+4 ions between 10 and 300 K. The internal modes of the ClO−4 ions show splitting into several components due to site and correlation field effects. The linewidth, frequency shift, and intensities of some of the internal modes of the ClO−4 and NH+4 ions and the frequency shift of a few lattice modes show anomalous temperature dependence around 180 and at 40 K. These anomalies have been explained in terms of phase transformations associated with the changes in hydrogen bonding strength and reorientational freedom of the NH+4 ions in the lattice. The low temperature transition at 40 K exhibits a sharp and discontinuous anomaly in some of the spectral parameters measured in this study which is associated with order–disorder-type transition. The measured linewidth of the ν′1 mode in the diagonal scattering configuration can be understood in terms of vibrational dephasing of the ν1 excited state due to vibrational–librational coupling. The estimated activation energies in the 50–160 K and 10–40 K temperature ranges are found to be 141 and 51 cm−1, respectively, which correspond to the observed NH+4 librational frequencies.

On the adhesion between Hydroxyl‐Terminated Polybutadiene Fuel‐Binder and Ammonium Perchlorate. Performance of bonding agents

AbstractA simple method to evaluate the adhesive force between solid oxidizer and polymeric fuel‐binder is presented. As an illustration, hydroxyl‐terminated polybutadiene (HTPB) sticks including several different bonding agents are bonded on ammonium perchlorate (AP) single crystals, and stress‐strain history until rupture occurs is obtained by applying uniaxial tensile stress perpendicularly to the adhesion surface. Further, whether each bonding agent reacts with AP or not was analysed with pursuing infrared absorption spectra. The hypothesis that the interfacial adhesive force arises from hydrogen bonding force is proposed.

Direct current conduction in ammonium perchlorate single crystals

The dc electrical conductivity of pure and doped ammonium perchlorate (AP) has been studied in two different crystal orientations, with the electric field applied perpendicularly to either (001) or (210) planes. The conductivity along the direction of the c axis was found to be lower than that normal to (210) by a factor of 5 to 10. The dc electrical conductivity of AP is decreased by Pb 2+ ions but increased by SO 2− 4 and CrO 2− 4 ions. The conductivity of pure AP and of Pb 2+-doped AP displays two regions with activation energies for conduction of 0.56 and 0.87 eV, respectively. The conductivity of the anion-doped crystals has a single activation energy, 0.66 eV for SO 2− 4 and 0.72 eV for CrO 2− 4. Exposure to ammonia enhances the conductivity of pure AP. A proton conduction mechanism is proposed that takes due regard of the structure of AP. The effect of the various additives on the conductivity are attributed to their influences on the formation of charge-carrying protons.

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.

The electrical conductivity of strontium doped ammonium perchlorate single crystals: A. G. Kennan and M. G. Ohanian. Department of Chemistry, University of Miami, Coral Gables, Florida 33124

The electrical conductivity of strontium doped ammonium perchlorate single crystals: A. G. Kennan and M. G. Ohanian. Department of Chemistry, University of Miami, Coral Gables, Florida 33124

The electrical conductivity of ammonium perchlorate single crystals: A. G. Keenan and M. G. Ohanian. Department of Chemistry, University of Miami, Coral Gables, Florida 33124

The electrical conductivity of ammonium perchlorate single crystals: A. G. Keenan and M. G. Ohanian. Department of Chemistry, University of Miami, Coral Gables, Florida 33124