| Silicone rubber（SR）has been widely used in the field of high-voltage and ultra-high voltage power transmission because of its good performance such as electrical insulation,weather resistance,high and low-temperature resistance,hydrophobicity and hydrophobic migration.However,SR may suffer from tracking and erosion damage with the continuous increment of the voltage in the polluted or humid environment,losing the electrical insulation performance and even causing a fire,which severely threatens the safety and stability of the power system.Traditionally,the tracking and erosion resistance of SR was mainly improved by adding a large amount of inorganic hydroxide（≥45 wt%）,but its mechanical properties and processability were deteriorated.In recent years,our group found that a platinum（Pt）and nitrogen-containing silane（NS）catalytic system could improve the tracking and erosion resistance of SR by promoting the formation of a ceramic-like barrier layer on the SR surface under the arc discharge.Nevertheless,the ceramic barrier layer is caducous under the arc bombardment,airflow purging or rain scouring due to its poor strength and compactness.It is difficult to meet the requirement of SR for long-term service in the heavily polluted ultra-high voltage environment.Hence,in this dissertation,we mainly focus on the key issue of how to promote the efficient ceramization of SR to improve tracking and erosion resistance.The main contents and results are as follows.（1）A ceramifiable silicone rubber composite（Pt-NS/FP/SR）with outstanding flame retardancy was prepared by simultaneously introducing Karstedt’s catalyst（Pt）andγ-aminopropyltriethoxysilane（NS）into silicone rubber composite（FP/SR）using fluorophlogopite（FP）as ceramic filler,in which the fluxing agent was needless.Compared with FP/SR,when the content of FP,Pt and NS was 40 phr,15 ppm and 2.0 phr,respectively,the limiting oxygen index of Pt-NS/FP/SR increased to 37.5%from 31.5%,and the vertical burning test reached a UL-94 V-0 rating.After heating at 1000 oC for 1 h,the organic-to-inorganic conversion rate of Pt-NS/FP/SR was increased to 28.1%from 6.83%,and the three-point flexural strength of the ceramic was as high as 14.4 MPa.It was revealed that Pt and NS synergistically catalyzed the radical coupling reaction of the silicone rubber chains at high temperature,resulting in the organic-to-inorganic conversion of silicone rubber matrix and the formation of an amorphous SiOC ceramic structure,which enhanced the adhesion with silica and FP to form a rigid and compact ceramic.Therefore,the flame retardancy of Pt-NS/FP/SR was improved remarkably.（2）The effect of low-melting point fluxing agents,such as boron oxide（BO）,low-melting-point glass frit and lithium carbonate,on the organic-to-inorganic conversion of methylvinypolysiloxane containing a platinum-nitrogen system was studied,in which the platinum-nitrogen system（Pt-PPMDS）was composited of Karstedt’s catalyst（Pt）and piperazinylpropylmethyldimethoxysilane（PPMDS）.On this basis,the effect of BO and Pt-PPMDS on the ceramization of SR was investigated in depth.It was found that the silicone rubber composites（BO/Pt-PPMDS/SR）had excellent ceramifiable properties when the content of BO,Pt and PPMDS was 0.4 phr,15 ppm and 2.0 phr,respectively.After heating at 1000 oC for 1 h,BO/Pt-PPMDS/SR transformed into a rigid ceramic with a flexural strength of 6.0 MPa.FTIR,XRD,11B-NMR and XPS results showed that the SR matrix converted to SiOC-like ceramic under the catalysis of Pt-PPMDS.Meanwhile,BO transformed from[BO3]to[BO4]with a similar structure to SiO2 and SiOC-like ceramic at high temperature and entered the ceramic by forming a Si-O-B structure,which strengthened the network structure of the ceramic and made BO/Pt-PPMDS/SR transform into a hard and compact ceramic.（3）A small amount of organo-modified montmorillonite（OMMT）was introduced into SR containing Karstedt’s catalyst（Pt）and aminopropyltriethoxysilane（NS）to prepare a tracking-resistant silicone rubber with good ceramifiable properties.When the content of OMMT,Pt and NS was 0.50 phr,15 ppm and 2.0 phr,OMMT/Pt-NS/SR reached 1A4.5 level in the inclined plane（IP）test and the eroded mass was only 0.48%.After heating at 1000 oC for 1 h,OMMT/Pt-NS/SR transformed into a rigid ceramic with a flexural strength of 4.20 MPa.SEM,FTIR and XRD results revealed that the two-dimensional structure of OMMT had a good barrier and skeleton enhancement effect.Moreover,OMMT and Pt-NS could synergistically promote the organic-to-inorganic conversion of silicone rubber chains to form a hard and compact SiOC-like ceramic.When subjected to arc bombardment,OMMT/Pt-NS/SR ceramized rapidly and formed a compact and arc ablation-resistant ceramic barrier on the surface.Hence,the generation and development of tracking were effectively inhibited,thereby improving the tracking resistance of OMMT/Pt-NS/SR.（4）A tracking-resistant silicone rubber（FPNs/Pt-NS/SR）with efficient ceramization was fabricated by introducing a small amount of fluorophlogopite nanosheets（FPNs）into SR containing Karstedt’s catalyst（Pt）and aminopropyltriethoxysilane（NS）.When 0.50 phr FPNs,15 ppm Pt and 2.0 phr NS were added,FPNs/Pt-NS/SR had excellent tracking resistance of1A4.5 level and the eroded mass was only 0.35%.After heating at 1000 oC for 1 h,the organic-to-inorganic conversion rate of FPNs/Pt-NS/SR was increased to 40.2%,and the flexural strength of the ceramic was as high as 7.54 MPa.It was found that FPNs had a good barrier and skeleton enhancement effect,and could cooperate with Pt-NS to promote the efficient ceramization of SR.Moreover,FPNs also endowed FPNs/Pt-NS/SR with good hydrophobic and charge dissipation properties,which reduced the deposition of contaminants on the surface and the generation of dry band arc.Thus,the tracking resistance of FPNs/Pt-NS/SR was improved significantly.（5）Polyborosiloxanes（PBS）with different B/Si molar ratio were synthesized through the condensation reaction among boronic acid,vinyltrimethoxysilane and octamethylcyclotetrasiloxane.A tracking resistant silicone rubber（PBS/Pt-NS/SR）with efficient ceramization was fabricated by introducing PBS and Pt-NS into SR.When 1.0 phr PBS,15 ppm Pt and 2.0 phr NS were added,PBS/Pt-NS/SR had excellent tracking resistance of 1A4.5 level and the eroded mass was only 0.39%.It was revealed that PBS and Pt-NS synergistically promoted the organic-to-inorganic conversion of silicone rubber matrix to form SiOC-like ceramic.Meanwhile,the Si-O-B structure formed between PBS and the silicone rubber matrix during the thermal degradation was also beneficial to improve the compactness and strength of the SiOC-like ceramic.Hence,the surface of PBS/Pt-NS/SR ceramized efficiently to form a hard and compact ceramic protective layer under the strong arc discharge,which improved the tracking resistance of PBS/Pt-NS/SR. |
