Preparation And Characterization Of A Low-Melting Point Glass Matrix Composite Reinforced With Fibers

For the problem that the polymer enclosure materials which used for the outdoor surge protection devices of mobile base station have poor heat resistance and it is easy to catch fire when subjected to lightning strike,this thesis proposed a Si C fiber with high electrical resistivity reinforced inorganic glass matrix composite used for the enclosure.Firstly,this thesis explored the preparation process of La₂Ti₂O₇ interface layer on Si C fiber cloth by sol-gel method.And the phase composition,microscopic morphology and high temperature stability of the interface layer were analyzed.Secondly,the glass matrix precursor sol was synthesized using NaOH,aluminum silicate and H₃BO₃.The effect of raw material ratio on processing temperature was explored.And the structure of the matrix material at different heat treatment temperature was characterized by X-ray diffraction analysis（XRD）and Fourier transform infrared spectroscopy（FT-IR）.Finally,the preparation process of the Si C fiber with high electrical resistivity reinforced inorganic glass matrix composite and the effect of the heat treatment process of the composite preforms on the flexural strength of the composites were studied,and the breakdown strength was tested.The main conclusions are as follows:（1）After heat treatment at 500℃,700℃,800℃and 900℃for 3h,the incomplete crystalline La₂O₂CO₃ phase,La₂Ti₂O₇ phase with weak diffraction peak,crystalline La₂Ti₂O₇phase only,crystalline La₂Ti₂O₇ phase with enhanced diffraction peak were observed respectively.La₂Ti₂O₇interface layer prepared by 2 impregnation of 2wt%precursor sol and sintering at 500℃preferably has coverage integrity,uniform thickness and no obvious defects.After heat treatment at 700℃,750℃and 800℃for 2h respectively,it was found that with the increase of the temperature,defects such as cracks on the interface layer become more and more obvious.（2）As the amount of NaOH decreases,the processing temperature of the glass matrix gradually decreases.And then,as the amount of H₃BO₃ increases,it decreases further.The raw material weight ratio which has relatively low processing temperature is NaOH:aluminum silicate:H₃BO₃=18.80:10.08:2.40.The glass matrix is amorphous at 700-800℃.And its network structure is mainly composed of[Al O₄]and[Si O₄]tetrahedral units connected by bridging oxygen.（3）When the composite preform was heat treated for 1h,the flexural strength of the composite increased from 25.03MPa to 85.10MPa with the temperature rising from 700℃to750℃,and the corresponding open porosity and volume density from 39.80%and 1.26g/cm³changed to 16.44%and 1.71g/cm³,respectively.When the holding time was increased to 2h at 750℃,the flexural strength reached 123.58MPa,and the corresponding open porosity and volume density were 12.84%and 1.85g/cm³,respectively.Therefore,the relatively superior heat treatment process for composite preforms was 750℃for 2h.The breakdown strength of the composite measured by AC and DC modes respectively can reach 400-460V/mm and500V/mm.