Preparation And Corrosion Resistance Study Of B₄C Neutron Absorber Based On Al-Si Alloy

Because of lower neutron absorbing ability, higher heat transmit coefficient, and better corrosion resistance, Al-Si eutectic alloy may be an ideal base material for B₄C neutron absorber. The process and corrosion resistance of B₄C--Al-Si eutectic alloy, directly influence the absorbing ability and operational life, so it is necessary to investigate.The influence of forging process on mechanical properties and microstructure of the B₄C--Al-Si eutectic alloy powder have been studied in this paper. And the investigation of corrosion resistance for block samples has been carried out under different temperatures, different pH values for a long time. By macro-weight loss measuring, microscopic detection, and thermodynamics calculating, the corrosion rates, types and products at different conditions have been analyzed, the corrosion resistance and corrosion mechanism of samples at 25℃and 80℃have been investigated.It's shown that partial melting and metallurgical bonding of B₄C--Al-Si eutectic alloy is occured by sintering, showing a continuum of network structure, its plasticity is greatly increased, the compressive strength is up to 292MPa but the relative density does not change significantly, some pores are existed in the blocks. The plastic deformation of particles can make them meshing with each other by cold forging process, the spacing between particles is reduced and the pore is narrowed, so that the relative density of materials is up to 97% and the compressive strength is up to 356MPa.Corrosion solution temperature and pH value have a significant effect on the corrosion resistance of B₄C-Al-Si eutectic alloy. Macro-weight loss results show that after 14 days corrosion of weak acid/weak base solution, the samples weight loss in the weak alkaline solution is more than in the weak acid solution, and slight pitting is occured in the weak acid solutions, no significant weight loss and corrosion defects are appeared at 25℃, it's shown that the material is fully meet the corrosion standards by calculating the corrosion rate. Because more heat has been transfered into kinetic energy of molecules at 80℃, the reaction rate is increased with the molecular thermal diffusion accelerates, the weight loss phenomenon is more obvious than that at 25℃, it's also shown that the material is basicly meet the corrosion standards by calculating the corrosion rate. Microscopic detection and thermodynamic calculations show that the Al₂O₃ films are thin and dense on the surface of sample in the weak acid corrosion.Although the Al₂O₃ film and dilute H₂SO₄ solution can be reacted in the thermodynamic, but the dynamic obstacles are existed, so the corrosion rate is very slow, it can protect the Al matrix no further corrosion. However, the surface of Al₂O₃ film in the weak alkaline solution corrosion is less dense than the former, also the oxygen content is less than the former, it's shown that a chemical reaction is occured with Al₂O₃ films and dilute NaOH solution, it can not protect the Al matrix. Also the electrochemical corrosion is occured with Al matrix and dilute NaOH solution, the material corrosion will be occured layer by layer dissolution in dilute NaOH solution.Since most parts of our country atmosphere is humid weak acid, that means B4C--Al-Si eutectic alloy can meet the requirements of normal operation under the normal used temperature as a kind of ideal neutron absorber.