Study On Phase Formation And Reaction Kinetics Of Al-B System

There are so few materials could satisfy people’s requirements of energetic materials that the metalic borides have begun to drawn more and more attention worldwide, which made AIB2become a hot concern of scientists for high calorific value of Al. It was restricted in the field of application for the materials can not be prepared with mass pure amounts. To solve the problem depends strongly on the knowledge of physical-chenistry of Al-B system. Therefore, the thermodynamics and kinetics of Al-B were systemically studied in this thesis. A reaction model of Al-B system was established. And the microstructure defects formed during the fabrication process of AlB2and its related effects were also investigated. It can be restricted in the field of applicaton for the material can not be prepared with mass amounts.The physical-chemistry characteristics for the Al-B system were systemically investigated by thermodynamics calculation, diffusion couple and differential scanning calorimetry (DSC). The results of DSC experiment show that the solid-solid state doesn’t react. The result of DSC indicates that the Al melting and liquid-solid state reaction (Al(l)+2B(s)=AlB2(s)) occur in the Al-B system during rising temperature. Based on the results of the Al-B system thermodynamics and kinetics research, the reaction model of Al-B system has been established that can describe the mechanisms of the phase formation and formation of microstructure defects well.The formation mechanism of holes during sintering reaction for Al-B system was explored by using the proposed reaction model of Al-B system. The experimental and analyzed results indicate that the reaction between Al and B converting into AlB2take places at the sites of initial B, and the holes form at sites of Al particles. Under special sintering time condition and the sintering temperature prolonging after the certain extent, the sample apparent density starts to reduce, and opening holes increase greatly, also shuting holes reduce. However the difference is not much later. With the sintering time expanding in the special sintering temperature, the opening porosity, the apparent density and the true density change are not large. The Al-B system react quickly.And the atomic proliferation migration is quite full, the pellet contact surface and shuts the hole eliminate completely in the short time. In addition, the formation of AlB2phase could induce the volume expansion in the B range, between the holes production and the volume expansion will have the interaction, the hole has suppressed the partial volume expansion.The villiaumite and the powder reaction sintering law could fabricate AIB2. We choose the sintering reaction law because we need the pure AlB2powder to energetic materials. I have analyzed AlB2phase, and calculated the content of AlB2with XRD and RIR Law in the different conditions. Few Al is surplus in sintering process. When using the excessive low pure amorphous B powder, few Al is still surplus. However, with excessive high pure amorphous B powder, Al phase disappeared. Using twice sintering, we couldn’t make Al reduce instead of introducing the new impurity. Al phase do not occur any more with the gland sintering. But the gland sintering is not suitable for producing the mass AIB2. The AIB2should be grinded into powder for the energetic material, therefore apparent and tap density have been tested. Its flowing property is not good and the compression ration is high.