【作者】 汪潇；

【导师】 杨留栓； 黄金亮；

【作者基本信息】 河南科技大学 ， 有色金属冶金， 2008， 硕士

【摘要】 Bi₂O₃-ZnO-Nb₂O₅（BZN）系微波介质陶瓷作为一类很有发展前途的低温烧结陶瓷,自问世以来,已受到人们的广泛关注。在以往对立方焦绿石结构的Bi_1.5ZnNb_1.5O₇陶瓷的研究中,粉体多由传统的固相法制备。固相法制得的粉体易团聚,容易引入杂质,煅烧温度高（⁸00℃）。陶瓷粉体的性能将影响陶瓷的烧结性能和电性能。为了克服固相法的不足,本论文采用水热法和熔盐法制备Bi_1.5ZnNb_1.5O₇陶瓷粉体,系统的研究不同工艺对合成粉体物相和显微组织的影响,以及对陶瓷烧结性能和介电性能的影响。采用水热法,以Bi（NO₃）₃·5H₂O,ZnO和Nb₂O₅为原料,以KOH作为矿化剂,合成单相Bi_1.5ZnNb_1.5O₇纳米粉体。结果表明:水热条件的变化对水热合成Bi_1.5ZnNb_1.5O₇粉体的物相和晶粒尺寸有很大影响,但对其形貌影响不大。TEM表明,合成的粉体均呈颗粒状,粒径30⁵0nm。当Nb:Bi=2.0（摩尔比）时,随KOH浓度增加和反应时间的延长,粉体粒径先变小,后变大,相应的比表面积变化正好与之相反;随温度升高,粉体粒径逐渐减小,比表面积逐渐增大,但在180℃后,其减小的趋势已很不明显。在KOH浓度为1.8mol·L^-1,220℃水热反应24h的条件下,合成粉体的比表面积最大,为28.8m2·g-1,相应的粉体粒径最小,为51nm;由Scherrer公式计算得到的粉体晶粒也最小,为43nm。将固相法与水热法合成的粉体按一定比例混合后烧结的Bi_1.5ZnNb_1.5O₇陶瓷试样,物相并不发生改变。随纳米粉体掺入量X（wt%）的增加和烧结温度的提高,介电常数ε先增大,后减小,介电损耗tanδ变化与之相反。掺入纳米粉体后,晶粒得到细化,但烧结致密度下降。当X=20,30,在晶粒细化的同时,出现了少量晶粒的急剧长大,介电性能相应变差。总体看来,在X=10,1000℃烧结陶瓷样品的ε最大,约148,tanδ最小,约3.365×10^-4,表现出更高的频率稳定性。以各组分氧化物为原料,KCl为熔盐,采用熔盐法在800⁹50℃得到（α+β）复相粉体,在950¹000℃可以合成单相颗粒状的Bi_1.5ZnNb_1.5O₇粉体。合成温度对粉体形貌和尺寸影响较大,随温度升高,粉体粒径增大,呈明显的颗粒状,且棱角分明;熔盐含量和保温时间对其影响相对较小。当料盐比为1:1（质量比）时,在1000℃保温2h,粉体粒径约2⁵μm。与固相法相比,合成粉体分散性较好,粒度分布比较均匀,无团聚现象,但合成温度较固相法高,粉体粒径也比固相法大。烧结样品最大致密度与固相法相当,但烧结温度略有升高。在1050℃时熔盐法制备的陶瓷样品的ε= ¹55,tanδ= ³.1×10^-3。更多还原

【Abstract】 Microwave dielectric ceramics based Bi₂O₃-ZnO-Nb₂O₅（BZN） system have been widely noted as a promising low temperature cofiring ceramics system since they were explored. In the course of previous study on the cubic pyrochlore phase Bi_1.5ZnNb_1.5O₇, the powders were prepared by the conventional solid state method （CS）. The solid state reaction lead to agglomeration and impurity easily, and the calcining tmperature of the powders prepared by CS is high （about 800℃）. The capability of powders will affect on the bulk density and dielectric behaviors of ceramics. To overcome the shortcomings of CS, the Bi_1.5ZnNb_1.5O₇ powders was synthesized by hydrothermal method（HTM） and molten salt synthesis（MSS） in this paper, and the systemic investigations were focused on the effects of different HTM parameters on the phase and microstructure of the powders and the bulk density and dielectric behaviors of ceramics.The single-phase Bi_1.5ZnNb_1.5O₇ nanopowder was successfully synthesized by HTM from the starting materials: Bi（NO₃）₃·5H₂O, ZnO, Nb₂O₅ and the mineralizer: KOH. The results show that the hydrothermal conditions have obvious effects on the phase and the grain sizes of Bi_1.5ZnNb_1.5O₇ nanopowders, but not obvious on the morphology. TEM photographs reveal that the powders present the regularly granular shape and its sizes are about 30⁵0nm. With the increase of KOH concentrations and reaction times, the sizes of Bi_1.5ZnNb_1.5O₇ nanopowders initially became small, and then big, but the tendency of the specific surface areas was reverse when the molar ratio of Nb to Bi was two. With the increase of synthesis temperature, the sizes of the powders also became increasingly small, and the specific surface areas became big, but the tendency was not very obvious when the synthesis temperature is above 180℃. The maximal specific surface area of the nanopowders is 28.8 m²·g^-1, the minimal powders’size is 51 nm and the minimal grain size calculated by Scherrer equation is 43nm when the Bi_1.5ZnNb_1.5O₇ powder is synthesized under the hydrothermal conditions with a synthesis temperature of 220℃, a reaction time of 24 h and a KOH concentration of about 1.8 mol·L^-1.The phase of Bi_1.5ZnNb_1.5O₇ samples did not change when the ceramics was sintered using the compound of powders synthesized by HTM and CS. With the increase of X （wt%）, the mass of nanopowders and sintering temperature, the dielectric constantsεinitially increased, and then decreased, and the change of dielectric losses tanδwas even reverse. The grain sizes of the ceramics samples became fined when the nanopowders synthesized by HTM was mixed with the powders synthesized by CS, but the bulk density decreased. However, when the X was 20 or 30, a few of grains grew unusually, and the dielectric behaviors decreased. As a whole, it can be obtained that the maximal dielectric constant is 148 and the minimal dielectric loss is 3.365×10-4 when X is 10.The phases ofαandβcould be obtained when the powders were synthesized by KCl molten salt synthesis at 800⁹50℃using the component oxides as raw materials. The phase ofαcould be obtained at 950¹000℃. The effect of synthesizing temperature on the morphology and sizes of the powders is obvious but the mass ratio of raw materials to salt and reaction times are not. With the increase of synthesis temperature, the powders appear to be grained shape and its sizes increase. The size of the powders synthesized by MSS at 1000℃for 2h is about 2⁵μm when the weigh ratio of the raw materials to salts is one. Comparing with CS, the powders synthesized by MSS does not appear the tendency of agglomerate, but its sizes were bigger and synthesis temperature were high than those by CS. The bulk density of ceramics samples synthesized by MSS corresponds to those by CS, however, the sintering temperature lightly increased. The dielectric constant is about 155 and the dielectric loss is about 3.1×10-3.更多还原