【作者】 李广慧；

【导师】 杨辉；

【作者基本信息】 浙江大学 ， 材料学， 2008， 博士

【摘要】 纳米氧化物如ZrO₂、TiO₂等过渡金属氧化物及稀土金属氧化物,由于其独特的性质在材料、能源及环保等领域受到广泛关注,其性能表征与应用成为近年来材料领域研究和应用开发的热点。这些氧化物性能往往与其晶型、形貌与尺度、表面特性等结构特征密切相关,而上述材料特征大多可通过制备方法进行调节和控制。目前制备这类氧化物纳米材料常用的方法包括气相法、沉淀法及溶胶凝胶法等,但这几种方法存在结晶度差或制备成本高等缺点,在制备结构、形态、尺寸可控的纳米材料方面没有显著的优势。本文针对PZT陶瓷在高温烧结时PbO挥发量大,导致环境污染及材料性能劣化这一电子陶瓷材料产业难题,结合纳米材料因高比表面和烧结活性而具有显著降低陶瓷材料烧结温度能力的特点,开展相关纳米粉体可控制备的基础研究,并在规模化生产水平上研究纳米粉体改性技术在降低PZT陶瓷烧结温度、改善陶瓷制备工艺、提高材料性能方面的作用,获得实用的纳米改性陶瓷生产工艺条件与产业化技术。据此,本文选择ZrO₂和TiO₂为研究对象,在对热液法实现纳米晶可控合成、表征和性能系统研究的基础上,研究其对PZT压电陶瓷（嘉康公司P612配方,用于生产频率元件）的改性作用及其实用化生产技术。研究内容及主要成果如下:1.在水介质中制备出ZrO₂纳米粉体。通过X射线衍射（XRD）、热重分析（TG）、红外光谱（FT-IR）及酸溶性实验对所制备的ZrO₂纳米晶前驱体溶胶的结构进行确定。此外,根据前驱体凝胶在不同升温速率下的差热分析（DTA）结果,依据Johnson-Mehl-Avrami（JMA）方程分别采用Owaza法和Kissinger法对ZrO₂纳米粉体相变动力学进行了研究,计算获得两种方法下的相变活化能分别为173.49kJ·mol^-1和159.49 kJ·mol^-1。产物粉体的XRD及透射电镜（TEM）分析结果表明,产物中四方相与单斜相的比例可通过反应条件进行可大范围的调节:当反应物ZrOCl₂与KOH摩尔比由1:4变为1:12.5时,180℃反应10小时后产物中四方相体积含量由18.63%增加到60.06%。此外,当反应温度为180℃、反应物ZrOCl₂与KOH摩尔比为1:12.5时,产物中单斜相含量随反应时间的延长而增加。不过,在水介质合成条件下通过改变反应物配比、反应温度及反应时间尚无法实现任意相组成ZrO₂纳米粉体的合成。2.在水作为反应介质制备ZrO₂纳米粉体的研究基础上,以无水乙醇取代水作为反应介质进行ZrO₂纳米粉体合成制备研究,分别考察了KOH、NaOH及NH₄OH等沉淀剂对产物相组成及形貌的影响。结果表明,在较低的140℃温度下反应3小时后,氨水条件下制备的产物为无定形相,而以NaOH和KOH为沉淀剂所制备产物均为ZrO₂纳米晶,且四方相含量分别为48.26%和100%。以KOH为沉淀剂制备ZrO₂纳米粉体时,分别考察了沉淀剂溶液浓度、反应温度、反应时间及表面活性剂等参数对产物组成及形貌的影响,发现表面活性剂对产物组成及形貌没有显著影响,而其余参数的改变均对产物产生显著影响。在NH₄OH为沉淀剂的体系中,考察了反应温度和反应时间对产物组成的影响。结果显示,即使在较高的反应温度（220℃,10小时）及较长的反应时间（180℃,36小时）等条件下,产物仍主要由四方相组成,低温稳定单斜相比例不高。综合ZrO₂纳米粉体制备过程中各因素对产物的作用结果发现,以KOH为沉淀剂时可通过改变反应时间实现纯四方相至纯单斜相范围内任意相比例ZrO₂纳米粉体的可控合成。此外,对无水乙醇为反应介质所制备纳米ZrO₂粉体的发光性能进行了研究,发现经250nm紫外光激发后,在402nm处可观察到ZrO₂纳米粉较强的发射峰,同时该粉体表现出较好的红外发射性能。3.在ZrO₂材料制备及应用研究中,稀土离子及其他过渡金属离子掺杂ZrO₂基结构材料及功能材料占有相当的比例,其中稀土Nd³⁺掺杂ZrO₂纳米粉体的制备及性能研究尚未见报道。本文考察了水介质中NH₄OH、KOH及NaOH等沉淀剂对ZrO₂∶Nd纳米粉体组成的影响,研究了以KOH为沉淀剂时掺杂离子浓度及热液反应温度对产物组成的影响规律。将名义掺杂量为5%的ZrO₂∶Nd纳米粉体在不同温度下煅烧2小时,研究发现ZrO₂∶Nd纳米粉体在不高于875℃温度下煅烧后主要由四方相组成,经1000℃煅烧后单斜相含量显著增加,但仍保留相当部分四方相,表明Nd³⁺掺杂可提高ZrO₂纳米粉体的热稳定性。在此基础上,对Nd³⁺离子掺杂稳定的机理进行了初步探讨。4.在课题组前期溶胶-凝胶法制备TiO₂薄膜的基础上,本文以钛酸丁酯为原料,通过热液法制备了TiO₂纳米粉体并研究了其部分添加对PZT压电陶瓷烧结性能、电性能及机械性能的作用。XRD分析结果表明产物由金红石和锐钛矿混合组成,金红石相占26.79%。通过Pb(Zr_0.53Ti_0.47)O₃压电陶瓷中纳米TiO₂部分替代微米粉体原料,研究纳米改性对PZT压电陶瓷烧结性能、电性能及机械性能的影响,以及对制成频率元件的性能影响作用。结果表明,在组成中以纳米TiO₂取代20%微米TiO₂对烧结有明显的促进作用。而纳米改性PZT压电陶瓷可以在保持原有介电及压电性能的同时,居里温度由改性前的300℃提高到400℃,使其可在更高的温度下使用。一般认为,掺杂是改变PZT压电材料的居里点的有效途径,本文研究结果揭示了一条通过非掺杂机制改变PZT压电材料居里点的新途径和技术。小试研究结果表明,纳米改性后陶瓷振子的耐高低温冲击性能得到显著提高,未改性振子在-55℃与85℃之间循环冲击200次后带宽变化率达49.9%,已丧失压电性能,而改性振子带宽变化不大,变化率仅为2.4%。5.上述研究结果已在嘉康电子有限公司进行了纳米改性压电陶瓷及频率元件的中试放大与生产。企业中试生产结果表明,通过纳米改性技术可以获得性能稳定的陶瓷产品与频率元件。在综合制造成本仅增加0.2%的条件下,改性后压电陶瓷产品的机械性能得到明显改善,耐高低温冲击性能获得了根本性的改善,达到了提高产品性价比的效果。更多还原

【Abstract】 Transition metal oxides（ZrO₂,TiO₂,etc.）and rare earth metal oxides have attracted extensively interests in the fields of materials,energy and environmental protection,etc.because of their unique chemical and physical properties. Nevertheless,the performances of these oxides depend on their structure features, such as phase form,morphology and size,and surface status,etc.Recently, preparation,properties and potential applications of nanometer oxides have been widely studied because of their excellent performances.Many approaches, including gaseous method,precipitation method and sol-gel method,etc.can be used to prepare above mentioned nano-materials.However,upon these approaches,one will obtain difficultly nano-materials with controllable structure, morphology and particle size.In addition,most of these preparation protocols require the calcination procedure to obtain the materials with high crystallinity, which will result in high cost.In general,the sintering temperature of ceramics can be significantly decreased by addition of nanomaterials due to their high specific surface area and sintering activity.However,heavy volatilization of PbO from sintering of PZT ceramics at high temperatures will lead to the problems of environmental pollution and performance deterioration.In this dissertation,based on the investigations about the preparation of nanomaterials,we investigated the effects of the nanomaterials on lowering the sintering temperature and improving the preparation techniques and performance of PZT ceramics in an industrial scale.Nano-ZrO₂ and nano-TiO₂ with controllable phase and morphology were prepared via hydrothermal and solvothermal methods,respectively.And their effects on the sintering and electric properties of PZT ceramics（P612 Composition,Zhejiang Jiakang Electronics Co.Ltd.）were investigated and discussed as well for the aim of obtaining practical industrial technique.The main contents are as follows.1.Nano-ZrO₂ was synthesized via the hydrothermal method.The sol precursor was characterized by X-ray diffraction（XRD）,thermogravimetric analysis（TG）, FT-IR,and the solubility of xerogel of the precursor in nitric acid,etc. Furthermore,phase transition activation energy was obtained by Johnson-Mehl-Avrami（JMA）equation according to the DTA results of the gel precursors at various heating-up rates.Results show that the values of activation energy calculated according to Owaza method and Kissinger method are 173.49 kJ·mol^-1and 159.49 kJ·mol^-1,respectively.Results from XRD patterns and TEM images indicate that the phase composition can be effectively adjusted in a large range by changing the initial molar ratio of Zr⁴⁺/OH^- and the hydrothermal reaction time.With reaction condition at 180℃for 10 hours,the volume fraction of the tetragonal ZrO₂ increases from 18.63%to 60.06%as the initial molar ratio of Zr⁴⁺/OH^- decreases from 1:4 to 1:12.5.Also,the volume fraction of the monoclinic ZrO₂,which was prepared at 180℃with 1:12.5 molar ratios of Zr⁴⁺/OH^-,increases with the hydrothermal reaction time.However,in the water medium we failed to prepare ZrO₂ with fully changeable phase composition by adjusting the reaction condition such as molar ratio,reaction temperature or reaction time,etc.2.Nano-ZrO₂ was prepared via the solvothermal method using ethanol as the solvent,and the effects of precipitators（KOH,NaOH and NH₄OH）on phase composition and morphology were investigated.It is found that the product prepared at 140℃for 3 hours with NH₄OH as the precipitator is mainly amorphous,while the products prepared with either NaOH or KOH as the precipitator in the same condition are in the crystalline form of tetragonal and（or） monoclinic phase,and the volume fraction of tetragonal ZrO₂ is 48.26%and 100%,respectively.The effects of precipitator concentration,reaction time and temperature,and surfactant,etc.on the preparation of ZrO₂ were investigated when KOH was used as the precipitator.It is showed that both reaction time and temperature have significantly effects on the preparation while the effect of the surfactant is negligible.As for the NH₄OH precipitator system,the effects of reaction temperature and time on the phase composition of the prepared product were also investigated.It is found that the prepared products are mainly in the form of tetragonal phase and contain little monoclinic phase even at a relatively high temperature（220℃for 10 hours）or after a long heat-treatment（180℃for 36 hours）.Summarily,the phase composition of products can be effectively controlled to any ratio from pure tetragonal phase to pure monoclinic phase by adjusting the reaction time when KOH is used as the precipitator.In addition,the luminescent property of nano-ZrO₂ prepared via the solvothermal method was also investigated.The photoluminescence spectrum of nano-ZrO₂ shows that,under 250 nm excitation,there is a strong emission peak at 402 nm.Unexpectedly,the nano-ZrO₂ shows good infrared emission performance.3.Rare earth metal ions and transition metal ions doped ZrO₂ occupy a large fraction in the based-ZrO₂ structure materials and functional materials.Herein,we reported the preparation of ZrO₂:Nd for the first time and investigated the effects of the precipitators（NH₄OH,KOH and NaOH）on the preparation of ZrO₂:Nd in the water medium,and also the effects of Nd³⁺concentration and reaction temperature on the phase composition using KOH as the precipitator in the water medium.The nano-ZrO₂:Nd with nominal doping content of Nd/Zr of 5mol%prepared via the hydrothermal method are calcined at various temperatures for 2 hours,and results show that the nanoparticles calcined at 875℃below are mainly tetragonal, and that the fraction of the monoclinic phase increases remarkably after calcination at 1000℃,indicating that introduction of Nd³⁺into ZrO₂ can improve the thermal stability of tetragonal ZrO₂.The stabilization mechanism of Nd³⁺in ZrO₂ is also preliminarily discussed.4.Nano-TiO₂ was prepared via the hydrothermal method using titanium n-butoxide as the starting material,and the effect of addition of nano-TiO₂ on the sintering performance,electric performance and mechanical performance of PZT ceramics were investigated.XRD results show that the prepared products contain 26.7%rutile and 73.3%anatase.Alter partial replacement of micro-TiO₂ by nano-TiO₂,the sintering performance,electric performance and mechanical performance of the PZT ceramics and the performance of the corresponding frequency device were also investigated.It is found that 20%replacement of micro-TiO₂ by nano-TiO₂ can benefit the sintering of PZT ceramics to a large extent.The modified PZT ceramics have the dielectric and piezoelectric performances equivalent to the formerly unmodified ones but the curie temperature rises from 300℃to 400℃, which will favor the higher work temperature of PZT piezoelectric ceramics. Generally,doping is a common way to adjust effectively the curie temperature of the piezoelectric ceramics.Present work offers a novel approach and technique to adjust the curie temperature without the modification of nominal composition of PZT ceramics.The change of band width for ceramic frequency device,which is a parameter requiring as small as possible for practical application,decreases from 49.9%of un-modified ceramic to 2.4%for nano-modified one after 200 times shock cycles between -55℃and 85℃.At the same time,the bending strength and tenacity of the nano-modified PZT ceramics are improved remarkably from 81.53 MPa to 97.9 MPa and from 1.15 MPa.m^1/2to 1.42 MPa.m^1/2,respectively.5.Above results have been verified in Zhejiang Jiakang Electronics Co.Ltd. under mass production level,and the obtained technique is applied to produce frequency devices.It is found that the resistance ability to temperature shock can be improved for both the nano-modified PZT ceramic and the frequency devices while the overall cost of nano-modified frequency devices only increases by 0.2%. Therefore,the overall performance of frequency devices is significantly improved, and the ratio of performance to the cost is promoted significantly with present technique.更多还原