Electromagnetic Properties And High Temperature Wave Absorption Performance Of Doped Titanium Nitride Powder

With the development of electromagnetic area and the promotion of electronic products, electromagnetic environment becomes more and more complicated. So it becomes urgency to research the electromagnetic absorbing materials. As the limitation and deficiency of traditional electromagnetic wave absorbing materials, developing new absorbing material system makes a big difference.Ti N has many applications because of its excellent mechanical properties, corrosion resistance, oxidation resistance, low density, high melting point, high conductivity and thermal conductivity. And its absorption mechanism can be fused with the resistance type and the dielectric type with its semiconductor properties, so has the potential in the field of electromagnetic wave absorbing. But its high electrical conductivity lead to the impedance mismatch problem. Therefore, this paper takes Ti N as the main material and studies its electromagnetic wave absorbing performance, then carries out the optimization and modification through carbon doping.Ti N and Ti N(1-x)Cx(x = 0.2, 0.4, 0.6, 0.8) were prepared by two steps of Sol-gel and solid gas reaction. We studied the influence of preparation temperature and atmosphere on the products. Through thermodynamic analysis and experimental study, we confirmed the nitriding temperature was 900?, the atmosphere was nitrogen. However, the carbon-doping temperature was 1700, and the atmosphere was argon.We analyzed the phase and morphology transformation of Ti N during carbon doping by XRD, XPS, SEM and other analytical methods. We found that carbon could completely dope into Ti N crystal and form successive substitutional solid solution Ti N(1-x)Cx(x = 0, 0.2, 0.4, 0.6, 0.8). The XRD peak shifts to the left with carbon doping and the lattice constant had a liner relationship with the carbon amount: y=4.2331+0.0813 x. Raman and XPS results confirmed that carbon was completely doped into Ti N and then lead to the increase of the unit cell, distortion and defect. The morphology analysis shows that the grain size of powder changed from 300 nm to submicron after carbon doped.We analyzed the electromagnetic property transformation of Ti N during carbon doping by four-probe method and coaxial line method. It is found that with the doping of carbon, C replaced the lattice position of N and formed covalent bond with Ti with no free electron remained. So the conductivity of Ti N(1-x)Cx decreased as expected. In order to get suitable electromagnetic parameters, we analysed the percolation phenomenon of Ti N(1-x)Cx/paraffin compound and then found the percolation threshold of Ti N(1-x)Cx(x = 0, 0.2, 0.4, 0.6, 0.8) sample was 80%. After measuring the electromagnetic parameters of samples, we calculated the reflection loss and found that Ti N has high dielectric loss, but exist no absorbing ability because of impedance mismatch.With the carbon doped into Ti N, the impedance matching of Ti N(1-x)Cx(x=0.2, 0.6, 0.4, 0.8) was optimized and then the reflection loss gradually increased. Finally, the reflection loss of Ti N0.2C0.8 reached-40.1d B and the bandwidth less than-10 d B was from11.1 to 13.6GHz with the thickness of 1.32 mm. Further study found that the absorption peak of Ti N(1-x)Cx(x = 0, 0.2, 0.4, 0.6, 0.8) are accord with the "one quarter" wavelength resonance model. The samples had different matching thickness at differnet frequencies. In order to optimize electromagnetic absorbing performance, Ti N0.2C0.8 was orderly composited with low dielectric materials by multi-layer optimization methord, and this methord show good effect on improving electromagnetic absorbing performance.In order to prepare Ti N(1-x)Cx sample for high temperature electromagnetic parameters test, we Fe coating to optimize the preparation process of Ti N(1-x)Cx sintered samples, and the relative density were all over 90% after optimazation. Due to the special requirements of high temperature wave absorbing materials, we analyzed the oxidation resistance transformation of Ti N before and after carbon doping. Finally, the relationship between the permittivity and temperature was calculated from microscopic view. We found that the permittivity became lager with temperature increased because of dipole prolarization. Then we predicted the change trend of high temperature wave absorbing performance, briefly analyzed the foreground and optimization scheme of Ti N(1-x)Cx in high temperature wave absorbing application.