Rcaction mechanism between Mg(NH₂)₂ and LiH are investigated with a B3LYP method of density functional theory. Geometries and harmonic vibration frequencies of reactants,intermediates,transition states and products are calculated at B3LYP/6-311G(d,P) level.Vibration analysis and intrinsic reaction coordinates(IRC) calculation at the same level are applied to validate connection of stationarv points. It indicates that the reaction has three stages.They are the first step of hydrogen substitution,the second step of hydrogen substitution and isomerization after removal of hydrogen.There are two pathways, in which a channel of the second step of alignment hydrogen suhstitution reaction is the main channel.The two hydrogen atoms in H₂ released are from Mg(NH₂)₂ and Lilt.

A sound isolator with axisymmetric periodic groove structures is given for eliminating drill collar wave.Sound isolation effect with different groove's depth (H),length,number,section shape and thickness of the drill collar is studied.With rectangle section shape,decreasing thickness of the drill collar and increasing H,isolation effect of the acoustic isolator can be increased.It can get a maximum of 36 dB sound attenuation which meets requirement of the sound isolator in LWD.