Preparation Of TiN-Based Composites As High-Temperature Microwave Absorption Materials

With the advancement of science and technology in the field of advanced military and aerospace equipment,the electromagnetic wave absorbing?EWA?materials used in high-temperature environment must possess both refractory and stable microwave absorbing properties without being affected by temperature changes.Up to now,researches on high-temperature absorbing materials mainly focus on insulated ceramics filled with semiconducting carbon,silicon carbide and metal oxides,etc.Usually,single component dielectric-based materials do not exhibit satisfactory absorption at wide band range due to severe impedance mismatch and limited absorbing mechanism.In addition,the effective absorption mechanisms were limited within the permittivity and Ohmic loss properties of the absorbents.And the wave absorption performance was dramatically affected by fluctuation of the environmental temperatures and thus the working temperature range was limited.Therefore,developing new type of excellent high-temperature absorbing materials with low density,oxidation resistance and stable properties has important scientific significance and application prospects.Titanium nitride?Ti N?has excellent wave-absorbing properties,as well as low density,high temperature resistance?Tm=2950°C?,high conductivity and high strength,which is a new type of promising high-temperature wave-absorbing materials to be used in various demanding environments.However,up to now,fewer researches on the absorption performance and electromagnetic mechanism of Ti N have been conducted,especially the investigations on its high temperature absorption performance.Broad effective absorption bandwidth is another requirement for the EWA materials.In the gigahertz or microwave range,introducing magnetic components into the dielectric base materials is considered as an effective strategy.Besides,the effective regulation of the dielectric and magnetic losses and the significant synergistic effects including interfacial polarizations and impedance matching caused by the heterogeneous electromagnetic couplings could also provide excellent electromagnetic wave dissipation.Based on the above considerations,in this study,the Ti N matrix composites with various morphology,structure and composition were prepared through electrostatic spinning and thermal nitriding processes.The electromagnetic properties in the range from room temperature to high temperature?873 K?were studied systematically.Furthermore,the evolution of the electromagnetic properties with increased temperature and the high temperature electromagnetic response mechanisms were investigated as well;meanwhile,the optimization of their high temperature absorption performance and the expansion of their effective frequency band range were realized.The main research contents and results in this work are summarized as follows:1.Preparation and High-Temperature Microwave Absorption Properties of Ti N nanoparticlesThe Ti N nanoparticles were prepared from precursor of titanate nanotubes?NTA?by thermal nitriding reaction.The Ti N nanoparticles were homogeneously mixed with the wave-transparent silicon dioxide?Si O₂?in a certain ratio to prepare waveguide sample blocks.The high temperature electromagnetic properties?293?873 K?in the X-band?8.2?12.4 GHz?of the samples were tested.The results show that when the filler contents was low?5.0 wt.% and 10.0 wt.%?,the dielectric properties increased first and then decreased with increasing the temperature.As the filler content increased to 20.0 wt.% and 30.0 wt.%,the dielectric loss performance improved,but the excessive conductivity started to change against the impedance matching performance and decrease the absorption performance.Taking into consideration of the impedance matching and the dielectric loss properties,the sample?T-10?with a filler content of 10.0 wt.% exhibited best high temperature absorption with a maximum reflection loss?RL?of-14.1 d B and effective absorption bandwidth?RL <-10 d B?of 2.75 GHz at 873 K,it is shown that the as-prepared Ti N nanoparticles are a promising material for high temperature absorption.2.Preparation and High-Temperature Microwave Absorption Properties of Magnetic Ti N/Fe₂Ni₂ N CompositesThe magnetic Ti N/Fe₂Ni₂ N nanoribbon composites were prepared through the combination of electrostatic spinning and thermal nitriding reaction.Studies on the room temperature electromagnetic properties of Ti N/Fe₂Ni₂ N nanoribbons with different filler content show that the dielectric properties of the composites are gradually enhanced with increasing filler content.When the filler content was only 15.0 wt.%?R-15?,the maximum reflection loss of the composite can reach-44.0 d B and the effective absorption bandwidth cover almost the entire test band from 2.0?18.0 GHz.Furtherly,the Ti N/Fe₂Ni₂N-nanoparticle composites were prepared by an in-situ thermal nitriding reaction in one step and their high-temperature electromagnetic properties were studied.The results show that the Ti N/Fe₂Ni₂ N magnetic nanoparticles exhibit good wave absorption performance throughout the tested frequency band from 2.0?18.0 GHz,the sample?F-20?with a filler content of 20.0 wt.% has a maximum reflection loss of-32.4 d B at 10.6 GHz and 373 K with the thickness of 2.8 mm.The effective absorption range of the sample?F-30?with a filler content of 30.0 wt.% covers almost the entire test temperature and frequency range.The introduction of the magnetic component Fe₂Ni₂ N improved the impedance matching performance,at the same time,the polarization sites provided by the heterogeneous interfaces promoted additional polarization loss ability,which is conducive to the optimization of the high-temperature absorption performance and effective frequency range.3.Preparation and High-Temperature Microwave Absorption Properties of Ti N/BN CompositesTo further optimize the impedance matching performance of Ti N under high temperature conditions and to better embody their dielectric loss performance.The Ti N/BN nanocomposites were prepared by an in-situ thermal nitriding reaction using NTA and boric acid?H3BO3?as precursors.The sample 5-1 was chosen as the absorbent to investigate the room temperature electromagnetic properties of the composites under different filler contents.The results show that,when the filler content was 60.0 wt.%,the Ti N/BN composites showed the excellent electromagnetic wave absorption properties with the highest reflection loss of-29.1 d B at the thicknesses of 1.6 mm.Furthermore,the high-temperature electromagnetic properties of Ti N/BN were investigated.The results showed that the Ti N/BN composite has the best hightemperature absorption performance with the filler content of 20.0 wt.%.When the temperature was controlled at 873 K,the reflection loss can reach-16.6 d B at 9.5 GHz.Furthermore,by comparing Ti N nanoparticles,it is shown that the introduction of BN can not only realize the optimization of the Ti N hightemperature impedance matching properties and absorption performance,but also effectively improve the high-temperature stability of the electromagnetic properties.This work provides meaningful design ideas and experimental basis for the comprehensive optimization of the high-temperature absorbing materials.