Combustion synthesis method was used to prepare NdB_(6)ultra-fine powders with B_(2)O_(3),Nd_(2)O_(3)and Mg powders as the raw materials.The basic thermody-namic data of NdB_(6) were estimated.The standard forma-tion ...Combustion synthesis method was used to prepare NdB_(6)ultra-fine powders with B_(2)O_(3),Nd_(2)O_(3)and Mg powders as the raw materials.The basic thermody-namic data of NdB_(6) were estimated.The standard forma-tion heat of NdB_(6) is-357.48 kJ·mol^(-1).The values of the heat capacity and the standard entropy are 96.87 and 86.60 J·K^(-1)·mol^(-1),respectively.The adiabatic tempera-ture of the reaction is 2726 K,which is higher than the thermodynamic criterion of 1800 K.This indicates that the combustion synthesis reaction of the B_(2)O_(3)-Nd_(2)O_(3)-Mg system could spontaneously take place by itself to generate NdB_(6).The NdB_(6) powders were characterized by X-ray diffractometer(XRD),scanning electron microscopy(SEM)and differential scanning calorimetry-thermo-gravimetry(DSC-TG).The results indicate that the com-bustion products consist of NdB_(6),MgO,and a few Mg_(3)B_(2)O_(6)and Nd_(2)B_(2)O_(6).The leached products consist of single NdB_(6) phase,and its purity is 98.6 wt%.When the sample preparation pressure is 20 MPa,the average parti-cle size of NdB_(6) powders is less than 500 nm.The antioxidant ability of NdB_(6) is very strong,which is oxi-dized step by step.The apparent activation energies of the oxidation reactions are 986.14 and 313.83 kJ·mol^(-1),respectively.In addition,the reaction orders are 4.10 and 3.75,respectively.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos. 51002025 and 51422403)
文摘Combustion synthesis method was used to prepare NdB_(6)ultra-fine powders with B_(2)O_(3),Nd_(2)O_(3)and Mg powders as the raw materials.The basic thermody-namic data of NdB_(6) were estimated.The standard forma-tion heat of NdB_(6) is-357.48 kJ·mol^(-1).The values of the heat capacity and the standard entropy are 96.87 and 86.60 J·K^(-1)·mol^(-1),respectively.The adiabatic tempera-ture of the reaction is 2726 K,which is higher than the thermodynamic criterion of 1800 K.This indicates that the combustion synthesis reaction of the B_(2)O_(3)-Nd_(2)O_(3)-Mg system could spontaneously take place by itself to generate NdB_(6).The NdB_(6) powders were characterized by X-ray diffractometer(XRD),scanning electron microscopy(SEM)and differential scanning calorimetry-thermo-gravimetry(DSC-TG).The results indicate that the com-bustion products consist of NdB_(6),MgO,and a few Mg_(3)B_(2)O_(6)and Nd_(2)B_(2)O_(6).The leached products consist of single NdB_(6) phase,and its purity is 98.6 wt%.When the sample preparation pressure is 20 MPa,the average parti-cle size of NdB_(6) powders is less than 500 nm.The antioxidant ability of NdB_(6) is very strong,which is oxi-dized step by step.The apparent activation energies of the oxidation reactions are 986.14 and 313.83 kJ·mol^(-1),respectively.In addition,the reaction orders are 4.10 and 3.75,respectively.
