Deuteron NMR spectra of ND4ClO4 single crystal at low temperatures.
2H NMR spectra of ND4ClO4 single crystal were obtained at v0 = 44 MHz. Orientation and temperature (1.9-75 K) dependences were measured. Fitting the spectra gives the effective quadrupole coupling constants for all deuterons and the ground torsional level structure. The isotope reduction of the (A-T) and (A-E) tunnelling splittings, i.e., the ratios of the respective splittings for NH4+ and ND4+, were found to be different. The splittings at T = 24 K are about 60% of the helium temperature values. The spectrum undergoes intermediate narrowing by reorientations between 26 and 34 K and tunnelling related features in the spectra are eradicated. After reaching the extreme narrowing limit, a doublet with gradually decreasing separation was observed, what was attributed to averaging by torsional oscillations of increasing amplitude. At high temperatures (T > 75 K), the narrow spectrum reflects fast multiaxial reorientation of the ammonium ion.
An analysis of the NMR line shapes of the ammonium ion undergoing composite tunneling and reorientational motions at low temperatures
An analysis is made of the NMR line shapes of the rotationally tunneling ammonium (NH4+) ion which also undergoes rapid reorientataional jumps around its C3 or C2 symmetry axis. The proposed composite motion, believed to be brought about by the coupling of rotor states of the ion with lattice phonons, leads to line narrowing and offers an interpretation of experimental line shape and second moment data not explained previously. In particular, the proton resonance line shapes of (NH4)2SnCl6, NH4BF4, NH4ClO4, (NH4)2GeF6, (NH4)2PbCl6, and (NH4)2PtCl6 at liquid helium temperatures are discussed. The analysis suggests that proton magnetic resonance line shape measurements on single crystals may provide an assessment on the state of ordering of the tunneling and reorienting NH4+ ions.
Finite Difference Modeling on the Temperature Field of Substrate in Friction Surfacing
Friction surfacing is an advanced process of great potential, especially in the field of repair and reclamation of worn and damaged components. As a kind of thermal processing technology, the temperature profile and changes of the substrate in friction surfacing are important factors to get coatings of high quality. In this paper, the temperature field of the substrate during the process is simulated by finite difference method. The results are consistent with experiments, reappearing the temperature change of the substrate during friction surfacing, allowing further study on figuration and quality of coatings.