高导热氮化铝基微波衰减材料的制备及性能研究
发布时间：2018-07-17 21:35
【摘要】：微波衰减材料广泛应用于微波电真空器件、消极电子对抗和微波测量系统中。由于AlN具有良好的综合性能,包括高热导率、良好的化学和热稳定性、高的电阻率,极其适合作为微波衰减复合材料的基体。导电颗粒W、SiC作为衰减剂,具有与AlN匹配的热膨胀系数、高熔点、较高的热导率；碳纳米管(CNTs)作为衰减剂,具有吸收频带宽、衰减量大、用量少等优点。由于碳纳米管与金刚石本征热导率很高,因此AlN和W、CNTs、SiC、金刚石的复合可以获得综合性能优异的新型高导热微波衰减材料。 本课题系统的研究了混粉方式、烧结温度、烧结保温时间、衰减相含量等因素对AlN基复合陶瓷微观组织、介电性能和导热性能的影响,并在此基础上制备出具有较高的致密度以及导热和介电性能优异的AlN基复合陶瓷。 通过磁力搅拌混粉制备的复合陶瓷有较高的介电损耗,但烧结体致密度低,CNTs分散性差；通过高能球磨混粉和添加W可以提高烧结致密度,有效改善CNTs在基体中的分散均匀性。高能球磨时间对复合陶瓷的性能也有一定的影响,随着球磨时间的增加,样品的致密度先增大后降低,介电损耗降低；球磨20min后制备的复合陶瓷致密度最高,球磨10min后制备的AlN-5vol%W复合陶瓷介电损耗在大多数频率范围内介电常数ε≈25。 SPS烧结温度对AlN/W复合陶瓷烧结致密度和介电性能影响较大,随着烧结温度从1450℃提高到1700℃,复合陶瓷的晶粒逐渐发育、长大,介电损耗降低,介电常数降低。烧结保温时间对AlN/W复合陶瓷表面形貌和致密度影响较小 W和CNTs的含量对复合陶瓷的性能有直接的影响,随着CNTs含量的增加,复合陶瓷中的孔隙数增多,而W可以有效的提高烧结体致密度；在AlN/W中添加CNTs,可以提高复合陶瓷的介电损耗。在AlN-10vol.%W中添加lvol%CNTs制备的复合陶瓷具有优异的介电性能,在70KHz-1MHz频率下介电常数为ε17.5。 在制备AIN-SiC复合陶瓷中,随着SiC含量的增加,介电损耗和介电常数均增加,但致密度会下降。纳米SiC优于微米SiC,呈现出优异的介电损耗性能。在频率为12.4-18GHz的范围内,AIN-SiC复合材料的介电损耗tanδ≥0.2,介电常数ε'在10-40之间。 最后,论文重点考察了A1N/金刚石复合陶瓷,其热导率和吸波性能受到基体中金刚石含量的影响,热导率随金刚石的添加量逐渐减小,且当金刚石含量为lvo1.%,复合陶瓷的导热性能最好,最大热导率为104.92W/(m·K). AlN-15vol.%Dia复合陶瓷综合性能较好,介电常数ε'为9.592,介电损耗tanδ≤13.1。金刚石发生sp2与sp3杂化,即生成一些可导电的非晶碳。陶瓷基体中出现了可导电颗粒,会使陶瓷的介电常数和介电损耗都增加,其损耗以电导损耗为主。复合陶瓷中添加15%和20%金刚石的介电损耗正切值高,是由于二者的致密度都很低,电磁波在穿过样品时,材料内部的缺陷可能会产生自激振荡,阻碍电磁波传递,使电磁损耗加大。AlN陶瓷的导热机理是声子导热,晶界的增多会使声子的自由程加长,并且晶界对声子传递有阻碍作用,金刚石本征热导率高,其对热导的提高大于对声子的阻碍作用。
[Abstract]:The microwave attenuation material is widely used in microwave electric vacuum device , passive electronic countermeasure and microwave measuring system . Because AlN has good comprehensive performance , including high thermal conductivity , good chemical and thermal stability , high resistivity , it is very suitable as matrix of microwave attenuation composite material .
Carbon nanotubes ( CNTs ) as an attenuation agent have the advantages of wide absorption frequency band , large attenuation amount and less dosage , etc . As the intrinsic thermal conductivity of the carbon nanotubes and the diamond is high , the composite of AlN and W , CNTs , SiC and diamond can obtain the novel high thermal conductivity microwave attenuation material with excellent comprehensive performance .
In this paper , the effects of powder mixing mode , sintering temperature , sintering time and phase content on microstructure , dielectric properties and thermal conductivity of AlN - based composite ceramics were studied . AlN - based composite ceramics with higher density and excellent heat conductivity and dielectric properties were prepared .
The composite ceramic prepared by magnetic stirring and mixing has higher dielectric loss , but the density of the sintered body is low , and the dispersibility of CNTs is poor ;
High - energy ball milling and adding W can improve the sintering density and effectively improve the dispersion uniformity of CNTs in the matrix . The high - energy ball milling time has certain influence on the properties of the composite ceramics . With the increase of the milling time of the ball , the density of the sample increases first and then decreases , and the dielectric loss is reduced ;
The composite ceramic prepared after ball milling for 20 min has the highest density , and the dielectric loss of the prepared AlN - 5vol % W composite ceramic after ball milling for 10min is 蔚 鈮，
本文编号：2131009
[Abstract]:The microwave attenuation material is widely used in microwave electric vacuum device , passive electronic countermeasure and microwave measuring system . Because AlN has good comprehensive performance , including high thermal conductivity , good chemical and thermal stability , high resistivity , it is very suitable as matrix of microwave attenuation composite material .
Carbon nanotubes ( CNTs ) as an attenuation agent have the advantages of wide absorption frequency band , large attenuation amount and less dosage , etc . As the intrinsic thermal conductivity of the carbon nanotubes and the diamond is high , the composite of AlN and W , CNTs , SiC and diamond can obtain the novel high thermal conductivity microwave attenuation material with excellent comprehensive performance .
In this paper , the effects of powder mixing mode , sintering temperature , sintering time and phase content on microstructure , dielectric properties and thermal conductivity of AlN - based composite ceramics were studied . AlN - based composite ceramics with higher density and excellent heat conductivity and dielectric properties were prepared .
The composite ceramic prepared by magnetic stirring and mixing has higher dielectric loss , but the density of the sintered body is low , and the dispersibility of CNTs is poor ;
High - energy ball milling and adding W can improve the sintering density and effectively improve the dispersion uniformity of CNTs in the matrix . The high - energy ball milling time has certain influence on the properties of the composite ceramics . With the increase of the milling time of the ball , the density of the sample increases first and then decreases , and the dielectric loss is reduced ;
The composite ceramic prepared after ball milling for 20 min has the highest density , and the dielectric loss of the prepared AlN - 5vol % W composite ceramic after ball milling for 10min is 蔚 鈮，
本文编号：2131009
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