Investigation Of Property And Design Of Ceramizable Silicone Rubber With High Thermal Stability

Ceramicizable silicone rubber composites have gradually become a new type of flame retardant thermal protection material due to their advantages of heat resistance,ablation resistance and electrical insulation after burning,and are often used in military and civilian fire and flame retardant fields.In order to make the silicone rubber composite material have good shape stability and excellent ceramic effect under high temperature use.This topic modified the silicone rubber composites by selecting different types of functional fillers,and explored the high temperature mechanical properties,shape dimension and ceramic evolution of the composites.In this paper,a silicone rubber ceramizable composite material was mainly studied and prepared,and the high temperature properties of the silicone rubber composite material and the microstructure evolution during the ceramization process were discussed under the optimal system,and the following conclusions were drawn:（1）By adjusting the ratio of CaSiO₃/B₂O₃,when the temperature is lower than800℃,boron oxide plays a leading role in the linear shrinkage,and when the temperature exceeds 800℃,the volume expansion of calcium silicate due to the crystal phase transformation causes the linear shrinkage.impact is more pronounced.At 900℃,when B₂O₃:CaSiO₃=15:15,the flexural strength and linear shrinkage of the composites reached an ideal balance,the flexural strength reached 18.5Mpa,and the shrinkage ratio was 8.1%;The XRD and SEM analysis showed that the low melting point compound formed by MgO-Al₂O₃-SiO₂ formed a local connection network in the silicone rubber composite before 700℃,and the crystal structure of CaSiO₃ changed with the increase of temperature.It causes volume expansion,which offsets and slows down the volume contraction caused by liquid phase cooling.（2）With the introduction of BN/B₄C mixed fillers,at lower temperatures（below800℃）,the flexural strength of ceramizable silicone rubber composites gradually increases,and there is no significant difference in size,and the strength of the ceramic body mainly passes through the system.The generated liquid phase（low melting point compound,glassy B₂O₃,etc.）forms an interconnected and cross-linked network along the gap;when the temperature is high（over 800℃）,the flexural strength and dimensional changes of the composite material first increase and then decrease.,the ceramic phase structures and crystal transformations such as Ca（Mg,Fe,Al）（Al,Si）₂O₆,Ca（Mg,Fe）Si₂O₆,etc.generated in the material are dominant,which can effectively protect the heat and improve the composite materials.High temperature residual strength.When the BN/B₄C ratio is 20:30（at 800℃）,the bending strength and dimensional shrinkage of the composite achieve the best results of 13.28MPa and6.73%,respectively.（3）Fiber-containing silicone rubber composites were prepared by using GF of different sizes and GFC as reinforcing materials.When the addition amount is the same,the composite materials with fibers of different sizes above 800℃can obtain ceramic products with complete shape and certain strength after ablation,especially the reinforcement effect of 0.5mm GF is the most obvious.Only 3.61%.In contrast,although there is no obvious dimensional shrinkage after ablation of the GFC composite,the thermal decomposition of the adhesive at high temperature produces a large number of voids,which greatly reduces the bending strength to 8.6MPa.After a short-time high temperature treatment,the composite material reinforced with 0.5mm GF showed a gradual multi-layer structure,and the surface of the sample showed a ceramic phase within 3 minutes,and the porcelain was fast and the degree of porcelain was high;after 10 minutes of treatment,The bending strength of the sample was significantly increased to 4.75MPa.The microstructure shows that the three types of fibers are entangled and interspersed in the ablation product,and are covered by the liquid phase in the system.The layer-by-layer resistance to thermal oxygen erosion greatly improves the mechanical properties and shape stability of the composite.