【作者】 胡伟；

【导师】 刘韩星；

【作者基本信息】 武汉理工大学 ， 材料物理与化学， 2015， 博士

【摘要】 随着微波通讯技术在航天航空领域的快速发展,低介微波介质陶瓷材料已成为近20年来的研究热点,具有低的烧结温度(T<1000℃)、低的介电常数(εr<9)、高的品质因数(Q×f>35000 GHz)和低的谐振频率温度系数(τf<±5ppm/℃)的陶瓷材料变的越来越重要。结合目前低介微波介质陶瓷的研究现状及存在的问题(烧结温度高和Q×f值低),本文选取α-Ca Si O3基陶瓷为研究对象,系统的研究了组成设计、烧结工艺、相逆转和微观结构对α-Ca Si O3基陶瓷微波介电性能的影响。报道了α-Ca Si O3相可以相逆转为β-CaSiO3相,并通过TG-DSC和晶体结构来分析其相变机理。主要研究内容和结果如下:(1)研究了不同晶相的粉体对α-Ca Si O3陶瓷微波介电性能的影响,并通过添加TiO2来调节α-Ca Si O3陶瓷的谐振频率温度系数。结果表明:使用1260℃下煅烧的Cyclo-CaSiO3相粉体制备的α-CaSiO3陶瓷具有优异的微波介电性能:εr=6.92,Q×f=26611 GHz,τf=-11.14 ppm/℃;1300℃下煅烧的Pseudo-CaSiO3相粉体制备的α-CaSiO3陶瓷微波介电性能较差:εr=6.95,Q×f=18649 GHz,τf=-7.07 ppm/℃。TiO2能有效的调节材料的谐振频率温度系数,α-Ca SiO3与TiO2反应生成的CaTiSiO5相分布在α-Ca SiO3陶瓷的晶界处,抑制了α-CaSiO3陶瓷晶粒的异常长大,TiO2的添加量为2wt%时,α-CaSiO3-TiO2陶瓷在1300℃烧结时的微波介电性能为:εr=7.86,Q×f=16491 GHz,τf=0.76 ppm/℃。(2)研究了SiO2对α-CaSiO3陶瓷相变和微波介电性能的影响。结果表明:SiO2可以抑制α-CaSiO3陶瓷晶粒生长使内应力增加,从而抑制Cyclo-CaSiO3相相变为Pseudo-CaSiO3相并有效的提高陶瓷的微波介电性能,当SiO2的添加量为6wt%时,α-CaSiO3-SiO2陶瓷在1350℃烧结时的微波介电性能为:εr=7.37,Q×f=33714 GHz,τf=-11.08 ppm/℃。(3)通过添加Al2O3来提高α-CaSiO3陶瓷的Q×f值。结果表明:Al2O3和α-CaSiO3反应生成的Ca2Al2SiO7相分布在α-CaSiO3晶粒的晶界处,抑制α-CaSiO3陶瓷晶粒异常长大并明显的提高了陶瓷的Q×f值,当Al2O3的添加量为2wt%时,α-CaSiO3-Al2O3陶瓷在1250℃烧结时的微波介电性能为:εr=7.39,Q×f=39523 GHz,τf=-13.28 ppm/℃。并通过添加2.5wt%的TiO2调节α-CaSiO3-2wt%Al2O3陶瓷的温度系数接近于零(εr=7.88,Q×f=24412 GHz,τf=-0.52 ppm/℃)。(4)研究了B2O3低温助烧剂对α-CaSiO3陶瓷微波介电性能的影响及α-Ca Si O3相相逆转为β-CaSiO3相的作用机理。结果表明:B2O3低温助烧剂可以将α-CaSiO3陶瓷的烧结温度降低到1100℃。1100℃烧结时陶瓷的主晶相由α-CaSiO3相相逆转为β-CaSiO3相,1125℃时β-CaSiO3相又相变为α-CaSiO3相。α-CaSiO3相粉体经过相逆转制备的β-CaSiO3陶瓷在1100℃烧结时的微波介电性能(εr=6.45,Q×f=31914 GHz,τf=-35.36 ppm/℃)优异于β-CaSiO3相粉体制备的β-CaSiO3陶瓷。(5)研究了Li2CO3低温助烧剂对α-CaSiO3-2wt%Al2O3陶瓷微波介电性能的影响,并分析了相逆转机理。结果表明:Li2CO3可以将α-CaSiO3-2wt%Al2O3陶瓷的烧结温度降低到975℃。800℃烧结时陶瓷的主晶相由α-CaSiO3相相逆转为β-CaSiO3相。经过相逆转制备的β-CaSiO3-Li2Ca4Si4O13陶瓷在975℃烧结时的微波介电性能(εr=6.86,Q×f=47067 GHz,τf=-35.82 ppm/℃)远远优异于β-CaSiO3相粉体制备的β-CaSiO3-Al2O3陶瓷。(6)通过低温助烧剂对α-CaSiO3相相逆转为β-CaSiO3相的控制,并添加7wt%的CaTiO3调节陶瓷的温度系数接近于零。最终使用α-CaSiO3相粉体在975℃下制备出了性能优异的β-CaSiO3-CaTiO3陶瓷(εr=8.07,Q×f=40573GHz,τf=0.45 ppm/℃),满足了实际应用的要求。更多还原

【Abstract】 With the rapid development of microwave communication technology in aerospace field, low dielectric microwave ceramics has become a research focus for recent 20 years, and the microwave dielectric materials with low sintering temperature(T < 1000°C), low dielectric constant(εr < 9), high quality factor(Q × f > 35000 GHz) and low τf(< ±5 ppm/°C) become more and more important. Based on the research status and problems(high sintering temperature and low Q × f) of low dielectric microwave ceramics, in this paper, α-Ca Si O3 ceramics were chosen as a study objective. The effect of composition design, preparation process, reverse phase transition and microstructure on the properties of α-Ca Si O3 ceramics were investigated.It was reported that the reverse phase transition appears from α-Ca Si O3 to β-Ca Si O3, and the mechanism of phase transition was analyzed by crystal structure and differential scanning calorimetry(DSC). The main research results are as follow:(1) The effects of calcined powders with different crystalline phases on the microwave dielectric properties of α-Ca Si O3 ceramics had been studied, and Ti O2 powder was added to adjust the τf value of α-Ca Si O3 ceramics. It shows that α-Ca Si O3 ceramics prepared with Cyclo-Ca Si O3 phase ceramic powder showed superior properties of εr = 6.92,Q × f = 26611 GHz,τf =-11.14 ppm/°C, and prepared with Pseudo-Ca Si O3 phase ceramic powder exhibited properties of εr = 6.95,Q × f = 18649 GHz,τf =-7.07 ppm/°C. Ti O2 can effectively adjust the τf value of α-Ca Si O3 ceramics, the addition of Ti O2 into α-Ca Si O3 ceramics resulted in the emergence of Ca Ti Si O5 phase which can inhibit the growth of α-Ca Si O3 grains by surrounding their boundaries. The α-Ca Si O3 ceramics containing 2wt% of Ti O2 sintered at 1300 °C showed microwave dielectric properties: εr = 7.86,Q × f = 16491 GHz,τf = 0.76 ppm/°C。(2) The influence of phase transition and internal stress on the microwave dielectric properties of α-Ca Si O3-Si O2 ceramics had been researched. The results show that the addition of Si O2 can inhibit the grain growth of α-Ca Si O3 and improve the internal stress, which inhibits phase transition from cyclo-Ca Si O3 phase to pseudo-Ca Si O3 phase and enhance the microwave dielectric properties obviously. The α-Ca Si O3 ceramics containing 6wt% of Si O2 sintered at 1350 °C showed dielectric properties: εr = 7.37, Q × f = 33,714 GHz and τf =-11.08 ppm/°C.(3) Al2O3 was selected as an additive to increase the quality factor of α-Ca Si O3 ceramics. It shows that the addition of Al2O3 into α-Ca Si O3 ceramics resulted in the emergence of Ca2Al2 Si O7 phase which can inhibit the growth of α-Ca Si O3 grains by surrounding their boundaries and improve the quality factor. The α-Ca Si O3 ceramics with 2wt% of Al2O3 sintered at 1250 °C showed superior properties: εr = 7.39,Q × f = 39523 GHz, τf =-13.28 ppm/°C. Moreover, the addition of 2.5wt% Ti O2 in α-Ca Si O3-2wt%Al2O3 ceramics could adjust the τf value near to zero( εr = 7.88,Q × f = 24412 GHz,τf =-0.52 ppm/°C).(4) The influences of B2O3 sintering aid on the microwave dielectric properties of α-Ca Si O3 ceramics and the mechanism of the reverse phase transition from α-Ca Si O3 to β-Ca Si O3 had been studied. It was found that with the addition of B2O3, the sintering temperature of α-Ca Si O3 ceramics is reduced to 1100 °C. The main crystal phase of ceramics transformed from α-Ca Si O3 to β-Ca Si O3 at 1100 °C, and then transformed from β-Ca Si O3 to α-Ca Si O3 at 1125 °C.The microwave dielectric properties of β-Ca Si O3 ceramics prepared by α-Ca Si O3 ceramic powder under phase reverse are: εr = 6.45,Q × f = 31914 GHz,τf =-35.36 ppm/°C, which is far more excellent than that of β-Ca Si O3 ceramics by β-Ca Si O3 ceramic powder.(5) The effects of Li2CO3 as sintering aid on the microwave dielectric properties of α-Ca Si O3-2wt%Al2O3 ceramics and the mechanism of the reverse phase transition had been studied. It shows that with the addition of Li2CO3, the sintering temperature of α-Ca Si O3-2wt%Al2O3 ceramics is reduced to 975 °C. The main crystal phase of the ceramics reversibly transformed from α-Ca Si O3 to β-Ca Si O3 when sintered at 800 °C. The microwave dielectric properties of β-Ca Si O3-Al2O3 ceramics prepared via the phase reversal are: εr = 6.86,Q × f = 47067 GHz,τf =-35.82 ppm /°C, which is much better than that of β-Ca Si O3 ceramics prepared by β-Ca Si O3 ceramic powder.(6) The microwave ceramics were obtained by low-temperature sintering aid control on α-Ca Si O3 reversed-phase transition to β-Ca Si O3 phase and Ca Ti O3 powder was added to adjust the τf value near to zero. Prepared using α-Ca Si O3 ceramic powder, β-Ca Si O3-Ca Ti O3 ceramics sintered at 975 °C have outstanding properties(εr = 8.07,Q × f = 40573 GHz,τf = 0.45 ppm/°C), which can be satisfied with the requirements of practical application.更多还原