Research On Precursor-derived Tantalum Carbide Ceramics

Ultra-high temperature ceramic-based composite materials have potential applications in the aerospace,weapons,energy and other high-tech fields.TaC ceramics are one of the research hot spots of ultra-high temperature ceramics.TaC materials are mainly prepared by high temperature carbothermal reduction of tantalum oxide.In this paper,the hypoxia caremic precursor was prepared by the reaction of TaCl₅ with amine groups.The effects of synthesis factors on the composition of the precursor,the process of inorganicization and the structural properties of the ceramic products were studied.The precursors were synthesized by the reaction of Ta-Cl and-NH₂ groups.The effects of synthesis factors on the structure of the precursor were studied by using TaCl₅and ethylenediamine as starting material.The results showed that the condensation reaction occurred during the high temperature desalination process.PTNC precursor was prepared by vacuum desalting at room temperature for 1h at 320?for 1h.The results showed that the condensation reaction between Ta-Cl bond and N-H bond occurred during the high temperature process,and the deamination reaction occurred at the same time.The PTNC2 precursor reacted with Grignard reagent Allyl-MgCl.The modified precursors cotain-CH=CH₂.Based on the characterization and analysis of the inorganic process of the precursor,the study shows that the inorganic process of PTNC precursor could be divided into three stages:the first stage is room temperature to 300?,due to the condensation of the remaining Ta-Cl bond and N-H bond,the performance of HCl release,a small part of the carbon chain break to generate propane,the mass loss of about 2%;the second stage of 300 to 400?,the quality of the drive with the temperature increased rapidly,the final loss of quality 17%,The precursor carbon chain breaks to produce C₂H₂ and NH₃;the third stage is 400 to 1200?,is the precursor pyrolysis zone,the mass loss is12%,the precursor of the N atoms from the precursor molecular chain and the NH₃ gas was released.The fourth stage was above 1200?and the TG curve was almost unchanged,indicating that the precursor was inorganic.PTNC has a very low ceramic transition temperature,can be converted into TaC ceramic at 1200?,the preparation of TaC ceramic contains free carbon.After heat treated at 2000?,TaC ceramic mass loss of8.3%,TaC ceramic Ta and C atomic ratio of 1:1.6,containing a certain amount of surplus carbon.The pyrolysis process of the precursor of PTNC2 can be roughly divided into two stages.The first stage:room temperature to 600?,the mass loss of 38%is attributed to the release of NH3 and propylene.The second stage:600 to 1100?,the temperature of the precursor under further pyrolysis,the mass loss of about 3%is assigned to NH3removel.The third stage:1100 to 1500?,TG curve show no obvious change,indicating that the precursor is basically inorganic.PTNC2 precursor has a very low ceramic transition temperature,when the temperature achieved at 1000?the formation of TaC phase has been appeared.After treated at 1200?,PTNC2 can be converted into TaC ceramic.TaCl₅ and melamine as raw materials,preparation of TaC precursor?PTNC3?,and the composition of the precursor structure and the process of a preliminary study.Compared with PTNC precursor,PTNC3 precursor,prepared by TaCl₅+C₃N₆H₆reaction system,had higher N content and lower C content.Since the N content in PTNC3 is higher than that of PTNC,after pyrolysis the PTNC3 precursor at 1200?,the product consists of TaC phase,Also contains a certain TaN phase and Ta?CN?phase.