|Place of Conferral||北京|
|Keyword||反相微乳法 喷墨打印技术 陶瓷墨水 二步烧结 微珠ntc热敏电阻|
负温度系数(Negative Temperature Coefficient，简称NTC)热敏电阻陶瓷材料已经发展成了具有多种不同材料体系、不同制备方法、不同相结构、不同应用需求的材料和元器件，广泛应用在生产生活的各个方面。近年来，随着电子工业和科学技术的不断发展，测、控温精度要求的不断提高，以及极端环境条件下对NTC热敏电阻产业需求的不断增长，高精度、快响应、小型化的NTC热敏电阻元件得到了更加广泛的关注。因此，微珠形NTC热敏电阻成为了新的研究热点。为了系统的研究微珠形NTC热敏电阻材料，本论文首次尝试采用喷墨打印技术，将其应用于微珠形NTC热敏电阻的制备。本文分别以NTC热敏电阻中比较典型的Mn1.2Co1.5Ni0.3O4 (MCN)系和Ni0.9Mn1.8Mg0.3O4 (NMM)系为研究对象，分别采用反相微乳法和共沉淀法，合成出了MCN和NMM粉体材料，重点研究反相微乳法中ω值(ω＝c[水溶液]/c[表面活性剂])、煅烧温度和反应温度对MCN粉体微观形貌和晶相结构的影响；采用分散法配制出分散稳定性良好的NTC陶瓷墨水，针对不同材料体系不同合成方法的粉体，分别研究了有机溶剂、分散剂，pH值对其分散稳定性的影响；比较研究了传统烧结和二步烧结对微珠形 NTC陶瓷材料的微观结构和电学性能的影响规律，揭示了微珠形NTC陶瓷材料的二步烧结机理。主要研究内容包括如下几点：⑴ 采用反相微乳法，选择曲拉通X-100-正己醇-环己烷为微乳体系，合成出超细MCN陶瓷颗粒，重点研究了ω值(ω＝c[水溶液]/c[表面活性剂])和煅烧温度对MCN陶瓷颗粒晶相结构和微观形貌的影响。通过TG/DSC、XRD、FT-IR、TEM以及HRTEM表征分析，说明随着ω值增大，其晶相结构从四方晶相向立方晶相转变，而后又伴随少量四方尖晶石相析出，而且粒径分布也会相应增大，从3 nm增加到18.63 nm，原因是ω值显著影响水核的体积和油水界面膜的强度，从而影响其成核过程和核生长过程，阳离子发生重排，晶相结构发生变化；当煅烧温度从300-800 ℃变化时，陶瓷粉体由四方尖晶石相向立方尖晶石相过渡，而对陶瓷粉体的粒径尺寸大小影响不大。当煅烧温度为600 ℃时，呈现出单一的结晶性较好的立方尖晶石相。因此，确定ω值为2，煅烧温度为600 ℃时，可获得结晶性良好粒径分布较小的MCN纳米陶瓷粉体。而共沉淀方法合成出的MCN粉体，在850 ℃煅烧时，呈现出单一的立方尖晶石相，粒径分布在40 nm左右，这为后面陶瓷墨水的配制奠定了很好的基础。⑵ 通过研究反相微乳法中反应温度对MCN粉体晶相的影响，根据XRD和HRTEM分析，发现在反应温度为60 ℃下，不经过煅烧就可以形成单一的结晶性较好的四方尖晶石相结构的MCN粉体，并且粒径分布均匀，尺寸为20 nm左右。结合元素面扫分析和能谱分析，表明在一个MCN纳米颗粒中元素分布均匀并且组成成分基本和初始比例相同，同时对反相微乳法中纳米颗粒形成的机理进行了分析和探讨。⑶ 以MCN系陶瓷墨水为研究对象，根据沉降实验、金相显微镜和zeta电位分析，研究了反相微乳法和共沉淀法对陶瓷墨水配制的影响。确定陶瓷墨水的成分组成和性能参数分别为：反相微乳法以70 wt%去离子水作有机溶剂，0.5 wt%聚丙烯酸PAA作分散剂，固含量为 30 wt%，pH值为9时，平均粒径为20 nm，其陶瓷墨水可稳定分散两个月左右；共沉淀法以乙二醇与乙醇质量比9:1的混合溶剂作溶剂，聚乙烯醇缩丁醛PVB为分散剂，含量为0.8 wt%，固含量为20 wt%，pH值为9，其陶瓷墨水可稳定分散72 h左右。粘度和表面张力均符合和满足喷墨打印设备的参数要求（粘度为1–30 mPa s，表面张力25-50 mNm-1）可顺利实现喷打。⑷ 首次采用喷墨打印技术，结合上述共沉淀法和反相微乳法配制出的陶瓷墨水，在平行导线上实现了微珠形MCN陶瓷材料成型。重点研究了传统烧结和二步烧结对微珠形MCN陶瓷材料微观结构和电学性能的影响。二步烧结可在较低烧结温度下更易获得致密度较高，晶粒尺寸较小且分布均匀的MCN陶瓷微珠材料。综合比较，烧结温度为T1-1300 ℃，T2-1200 ℃的二步烧结条件时，MCN微珠陶瓷材料获得较好的电学性能，R25为2208.6 KΩ，B值为4320 K，Ea为0.373 eV，α25为-4.8%/K。另外，由于不同粉体墨水合成方法制备出的微珠材料晶相结构不同，MCN微珠材料电学性能也差别较大，具有立方晶相的MCN陶瓷微珠材料具有较小的室温电阻(2776 Ω)和材料常数B值(3191 K)。⑸ 针对海洋温度传感器对NTC器件小尺寸快响应的要求，采用新颖的喷墨打印技术在平行导线上制备了NMM微珠形陶瓷材料，通过优化喷打工艺和烧结工艺，可以有效调节微珠珠体尺寸的大小。结合二步烧结，在二步烧结温度为T1-1300 ℃，T2-1250 ℃时可获得致密性较高、晶粒尺寸较小的NMM陶瓷微珠材料，微珠平均尺寸为140 μm左右，室温电阻值为98331 Ω，材料常数B值4183 K，激活能0.365 eV，电阻温度系数为-4.8 %/K，时间常数为58 ms。
Negative Temperature Coefficient (NTC) thermistor ceramic materials have been developed into a variety of different systems, different preparation processes, different phase structures, and different application demands of sensors and components, and they are widely utilized in every aspect of domestic and industrial applications. In recent years, the continuous developments of electronics industry and technology, the continuous increase of requirements of precise temperature control and measurement, and the continuous growth of NTC thermistor industry demands in the extreme environment make high precise, high reliable and miniaturized NTC thermistors a wide application and concern. Therefore, NTC microbead ceramic materials have become a new research hotspot.In this paper, inkjet printing technique is applied in the fabrication of NTC microbead materials and sensors for the first time, taking the Mn1.2Co1.5Ni0.3O4 (MCN) system and Ni0.9Mn1.8Mg0.3O4 (NMM) system as the research object respectively. It provides feasibility for the automation formation of NTC microbead ceramic materials, through optimization parameters of the entire preparation process. MCN nanoparticles are synthesized via reverse microemulsion method for the first time at the low calcination temperature, even at room temperature, and the effects of R value, calcination temperature, reaction temperature and reaction concentration on the microstructure and phase structures of MCN nanoparticles are investigated systematically. The high solid content NTC ceramic inks with good dispersibility are prepared via the dispersion method for the first time. For the NTC powders of different material systems and different synthetic methods, the effects of organic solvent, dispersing agents, pH value on the dispersion and stability of their ceramic inks are studied. Comparative study on the conventional sintering and two step sintering (TSS), the influence on the microstructure and electrical properties of NTC microbead materials are investigated, and the TSS mechanism has been revealed.The main research results include as following:⑴ MCN ultrafine ceramic nanoparticles are successfully synthesized by the reverse microemulsion method in a triton X-100/ n-hexanol/ cyclohexane system. The effects of R value, and calcination temperature on the microstructure and phase structures of MCN nanoparticles are systematically investigated and characterized by TG/DSC, XRD, FT-IR, TEM and HRTEM. The results show that the tetragonal spinel phase is transformed to the cubic spinel structure with the R value increasing. As the R value further increases, there is a little tetragonal spinel structure appeared and particle size increased. It is attributed that the R value could change the water pool volume and the strength of the oil-water interfacial film, which affect the nucleation process and the nuclear growth process. This maybe causes the rearrangement and migration of Mn or Co cations between the octahedral interstices and tetrahedral interstices. When the calcination temperature changes from 300-800 ℃, MCN nanoparticles transfer the tetragonal spinel phase to the cubic spinel phase, and the particle size has little change. At the calcination temperature of 600 oC, the position and relative intensity of all diffraction peaks match well with the pure standard cubic spinel phase as well as no other diffraction peaks of impurity are observed. Therefore, at the R value is 2 and the calcination temperature is 600 oC, MCN nanoparticles maintain the highly crystalline and a narrow and uniform particle size distribution. MCN powders calcined at 850 ℃ prepared by the coprecipitation method show the single cubic spinel phase and the particle size approximately 40 nm, which have laid a good foundation for the preparation of ceramic inks.⑵ MCN nanoparticles show the pure tetragonal spinel phase and the well dispersed particle size distribution about 20 nm synthesized via reverse microemulsion method at the reaction temperature of 60 oC without calcination. The STEM-EDX mapping measurement shows that the atomic distributions of the Mn, Co, and Ni elements are homogeneous mixed in the each nanoparticle, which indicate the formation of ceramic particles without calcination, The EDS result shows a certain amount proportion of Mn, Co, Ni and O absorption peaks and the element composition nearest to the initial nominalconstitution of MCN samples prepared by reverse microemulsion method. Meanwhile, the reverse microemulsion process mechanism has been studied.⑶ Taking the MCN system and Mn-Ni-Mg-O system as the research object, according to the sedimentation experiment, metallurgical microscope, and zeta potential analysis, the composition and performance parameters of MCN ceramic inks are as following: RM method choose the deionized water as solvent medium with 70 wt%, the polyacrylic acid (PAA) with molecule weight about 3000 g/mol as dispersant with 0.5 wt%, solid content with 30 wt%, pH value with 9, particle size with 20 nm, coprecipitation method choose the mixed sovlent with glycol and ethanol (mole ratio:9:1) as solvent medium, the PVB as dispersant with 0.8 wt%, solid content with 20 wt%, pH value with 9, and the viscosity (1–30 mPa s) and surface tension (25-50 mNm-1) must meet ink-jet printer system requirements. In addition, The MCN ceramic inks were very stable and homogeneous over two months and no obvious stratification.⑷ The MCN ceramic microbeads are formed by inkjet printing on the parallel wires using inkjet printingtechnique for the first time. Comparative study on the conventional sintering and two step sintering (TSS), and between NTC microbead and its bulk materials, the influence on the microstructure and electrical properties of NTC microbead materials are mainly focused. MCN nanoceramic microspheres with high denseand small grain size are successfully achieved by TSS process at a lower sintering temperature. The highest R25, B25/50, Ea and α25 values of 4846.7 KΩ, 4320 K, 0.401 eV and -5.24 %/K are achieved at sintering temperature of 1150 oC for these MCN nanoceramic microspheres, respectively. In addition, the electrical properties of MCN microspheres prepared via different methods is difference due to the different crystal structure. The MCN microspheres samples with cubic spinel structure have the relative resistance with 2776 Ω and material constant B value with 3191 K.⑸ We report a simple and effective in situ inkjet printing method for the fabrication of nanostructured and highly dense Ni0.9Mn1.8Mg0.3O4 (NMM) spinel oxide nanoceramic microbeads materials, in view of the requirements of small size and fast response for the ocean temperature sensors of NTC thermistors. The body size of NMM microbeads can be adjusted by the spacing of parallel wires and the quantity of inkjet printing. NMM nanoceramic microbeads with high denseand small grain size are successfully achieved at a lower sintering temperature with TSS process, and the body size of NMM microbeads on the wires are about 140 μm long and well densification. Through optimizing inkjet printing and sintering process, NMM microbeads are coated a thin film to fabricate the high performance, small size and fast response NMM sensors.That is the lower resistance values with 98331 Ω, the higher material constant with 4309 K as well as activation energy with 0.365 eV, and lower thermal time constant with 58 ms.
|陈龙. 微珠形NTC热敏电阻的喷墨打印技术制备及结构与电学性能研究[D]. 北京. 中国科学院大学,2016.|
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