Study On Preparation And Performance Of Rare Earth Hydride

Rare earth hydrides have high energy and high activity.Their application in active fragments will greatly enhance the damage power of active fragments warheads and eliminate the phenomenon "hitting but not destroying" of traditional inert fragments.In this thesis,rare earth metal hydrides were synthesized by high temperature direct hydrogenation.The optimum synthesis process and the stabilization treatment process of rare earth hydrides were studied.Furthermore,the properties of the products were also studied.SEM,XRD and TA were used to characterize the products.Particularly,the following work was carried out:Firstly,the optimization of preparation process of rare earth metal hydride was studied with cerium hydride as the representative.The effects of hydrogen decrepitation process,the raw metal size and the composition of reaction gas on the preparation effect of cerium hydride were studied through comparative experiments.The results showed that the active cerium hydride products with excellent properties can be synthesized by the method that using hydrogen-argon mixture gas as reaction gas,combining with hydrogen decrepitation process,and reducing the size of raw metal block appropriately.Secondly,the properties of the cerium hydride samples were tested.The density of the samples was measured by oil discharge method.And the decomposition temperature and exothermic properties of the samples were analyzed by comprehensive thermal analysis.The results showed that the yield of cerium hydride samples was over 99%,while the density was 5.4099g/cm3,which was close to the theoretical maximum density.When heated to 1025℃,the samples were not completely decomposed.After mixing with ammonium perchlorate as oxidant,their heat release of DSC curve reached 4.056 kJ/g.Following,the thermal decomposition performance of the mixture of cerium hydride and ammonium perchlorate was studied.The optimum ratio of cerium hydride to ammonium perchlorate was determined by theoretical calculation and experiment.Firstly,the oxygen balance value of the mixed system was calculated.According to the negative oxygen balance theory,the ratio of cerium hydride to ammonium perchlorate was 60%:40%,and the contrast experiments were designed,in which the ratio were 75%:25%,65%:35%and 55%:45%respectively.The heat release from thermal decomposition of cerium hydride to ammonium perchlorate was calculated by DSC.The experimental results showed that the heat release capacity of cerium hydride to ammonium perchlorate was the best when the ratio was 60%:40%.The stabilization treatment of the cerium hydride samples was studied because rare earth metal hydrides are very active and will oxidize rapidly or even spontaneously ignite when exposed to the air.The results showed that the physical coating of organic substances such as stearic acid,PVB and MMA on the surface of cerium hydride can be achieved by using homogeneous reactor and rotating coating method,and the stability of cerium hydride can be improved.Among them,4%stearic acid had the best coating effect.In addition to cerium hydride,two another rare earth hydride,praseodymium hydride and terbium hydride,were prepared and studied,and their stabilization treatment was carried out.The results showed that 4%stearic acid could make the stability of praseodymium hydride and terbium hydride the best.The density of praseodymium hydride and terbium hydride were 5.5406g/cm3 and 7.0087g/cm3,respectively.The heat release from thermal decomposition was 2.887 kJ/g and 2.704 kJ/g when the praseodymium hydride and terbium hydride were mixed with oxidant.