【摘要】：微波衰減材料廣泛應用于微波電真空器件、消極電子對抗和微波測量系統(tǒng)中。由于AlN具有良好的綜合性能,包括高熱導率、良好的化學和熱穩(wěn)定性、高的電阻率,極其適合作為微波衰減復合材料的基體。導電顆粒W、SiC作為衰減劑,具有與AlN匹配的熱膨脹系數(shù)、高熔點、較高的熱導率；碳納米管(CNTs)作為衰減劑,具有吸收頻帶寬、衰減量大、用量少等優(yōu)點。由于碳納米管與金剛石本征熱導率很高,因此AlN和W、CNTs、SiC、金剛石的復合可以獲得綜合性能優(yōu)異的新型高導熱微波衰減材料。 本課題系統(tǒng)的研究了混粉方式、燒結溫度、燒結保溫時間、衰減相含量等因素對AlN基復合陶瓷微觀組織、介電性能和導熱性能的影響,并在此基礎上制備出具有較高的致密度以及導熱和介電性能優(yōu)異的AlN基復合陶瓷。 通過磁力攪拌混粉制備的復合陶瓷有較高的介電損耗,但燒結體致密度低,CNTs分散性差；通過高能球磨混粉和添加W可以提高燒結致密度,有效改善CNTs在基體中的分散均勻性。高能球磨時間對復合陶瓷的性能也有一定的影響,隨著球磨時間的增加,樣品的致密度先增大后降低,介電損耗降低；球磨20min后制備的復合陶瓷致密度最高,球磨10min后制備的AlN-5vol%W復合陶瓷介電損耗在大多數(shù)頻率范圍內(nèi)介電常數(shù)ε≈25。 SPS燒結溫度對AlN/W復合陶瓷燒結致密度和介電性能影響較大,隨著燒結溫度從1450℃提高到1700℃,復合陶瓷的晶粒逐漸發(fā)育、長大,介電損耗降低,介電常數(shù)降低。燒結保溫時間對AlN/W復合陶瓷表面形貌和致密度影響較小 W和CNTs的含量對復合陶瓷的性能有直接的影響,隨著CNTs含量的增加,復合陶瓷中的孔隙數(shù)增多,而W可以有效的提高燒結體致密度；在AlN/W中添加CNTs,可以提高復合陶瓷的介電損耗。在AlN-10vol.%W中添加lvol%CNTs制備的復合陶瓷具有優(yōu)異的介電性能,在70KHz-1MHz頻率下介電常數(shù)為ε17.5。 在制備AIN-SiC復合陶瓷中,隨著SiC含量的增加,介電損耗和介電常數(shù)均增加,但致密度會下降。納米SiC優(yōu)于微米SiC,呈現(xiàn)出優(yōu)異的介電損耗性能。在頻率為12.4-18GHz的范圍內(nèi),AIN-SiC復合材料的介電損耗tanδ≥0.2,介電常數(shù)ε'在10-40之間。 最后,論文重點考察了A1N/金剛石復合陶瓷,其熱導率和吸波性能受到基體中金剛石含量的影響,熱導率隨金剛石的添加量逐漸減小,且當金剛石含量為lvo1.%,復合陶瓷的導熱性能最好,最大熱導率為104.92W/(m·K). AlN-15vol.%Dia復合陶瓷綜合性能較好,介電常數(shù)ε'為9.592,介電損耗tanδ≤13.1。金剛石發(fā)生sp2與sp3雜化,即生成一些可導電的非晶碳。陶瓷基體中出現(xiàn)了可導電顆粒,會使陶瓷的介電常數(shù)和介電損耗都增加,其損耗以電導損耗為主。復合陶瓷中添加15%和20%金剛石的介電損耗正切值高,是由于二者的致密度都很低,電磁波在穿過樣品時,材料內(nèi)部的缺陷可能會產(chǎn)生自激振蕩,阻礙電磁波傳遞,使電磁損耗加大。AlN陶瓷的導熱機理是聲子導熱,晶界的增多會使聲子的自由程加長,并且晶界對聲子傳遞有阻礙作用,金剛石本征熱導率高,其對熱導的提高大于對聲子的阻礙作用。
[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，

本文編號：2131009