热解炭(PyC)/BN复合粉的制备及其吸波性能

以尿素、硼酸和热解炭(PyC)粉为原料, 利用化学转化法, 在1750℃、N₂气氛下反应6 h, 制备了PyC/BN复合粉。采用XRD、XPS、SEM、DTA/TGA对PyC/BN复合粉的物相组成、化学成分、表面形貌及抗氧化性能进行了表征, 并用矢量网络分析仪测试了PyC/BN复合粉在2~18 GHz频段内的吸波性能。结果表明: 生成的h-BN颗粒在PyC粉表面形成包裹层, 其尺寸为几十至几百纳米。相比于PyC粉, PyC/BN复合粉的抗氧化性能明显提高, 在1200℃时其质量仍剩余50%以上, 而PyC粉在940℃时已被氧化完全。同时, 由于波阻抗增大, 电子位移极化、界面极化、多重散射和λ / 4干涉相消作用, 使得PyC/BN复合粉在相同厚度下(d=2 mm), 其反射率峰值达到-27.2 dB, 反射率小于-10 dB的频宽为2.6 GHz; 且随着厚度的增加, 其反射率峰值均小于-10 dB, 并出现多重吸收峰。PyC/BN复合粉可作为理想的轻质、耐高温、强吸收的吸波剂应用于微波领域。

Synthesis and Microwave Absorbing Properties of PyC/BN Composite Powders

PyC/BN composite powders were synthesized via chemical reaction of boric acid, urea and PyC powders at 1750℃ for 6 h in nitrogen. The phases, chemical compositions, surface morphologies and oxidation resistance of PyC/BN composite powders were characterized by XRD, XPS, SEM and DTA/TGA instruments, respectively. The microwave absorption properties of PyC/BN composite powders were measured by using a microwave network analyzer in the frequency range of 2-18 GHz. The results show that generated h-BN particles are coated on the surfaces of PyC powders with the dimension from tens of nanometers to hundreds of nanometers. Compared with PyC powders, the oxidation resistance of PyC/BN composite powders is improved. The mass of PyC/BN composite powders remains over 50% at 1200℃ whereas PyC powders are oxidized completely at 940℃. Due to higher microwave impedance, electronic displacement polarization, interface polarization, multiple scattering and λ/4 destructive interference effect, the reflectivity peak of PyC/BN composite powders reaches -27.2 dB and the bandwidth of the reflectivity below -10 dB is 2.6 GHz under the same thickness (2 mm). And the reflectivity peaks are all less than -10 dB and multiple absorbing peaks appear with the increase of thickness. PyC/BN composite powders are supposed to be ideal microwave absorbers with lighter weight, high temperature resistance and strong microwave absorption.