基于“冷烧结”技术的ZnO-PTFE(聚合物)基纳米复合压敏陶瓷性能的研究

ZnO varistor ceramics have been widely used as protecting devices against voltage transients in electronics circuits and electrical system. Recently, a brand new “Cold Sintering Process” (CSP) technology (<300oC) was proposed to make co-firing of ceramic and polymer come true. It was found that the ZnO-polytetrafluoroethylene (PTFE) composite co-fired via CSP had a high breakdown field and varistor behavior. However, its nonlinear coefficient and dielectric loss still need to be further improved, and currently the study on the dielectric and mechanical property is an emergent task. In this proposal, the CSP technology will be adopted for grain boundary design of the ZnO-PTFE samples based on organic insulating phase (PTFE) and nano-inorganic filler, which will provide the support for exploring the origination of the varistor behavior, enhancing the nonlinear coefficient, and restraining the dielectric loss. The synergistic effect from PTFE and nano-inorganic filler that may inhibit the growth of grain size and influence I-V, dielectric and mechanical properties will be studied. A grain boundary barrier model based on grain-polymer boundary-grain structure will be proposed to explain the conductance mechanism of ZnO-PTFE composite. We believe the proposal will provide both theoretical foundation and experimental guidance for developing new Ceramic-Polymer materials via CSP.

ZnO压敏陶瓷被广泛应用于电子设备、电力系统等过电压保护领域。最近，采用新型的“冷烧结”（Cold Sintering Process）（＜300oC）技术，实现了陶瓷和聚合物的共烧，发现ZnO-聚四氟乙烯（PTFE）共烧的陶瓷复合材料具有高的击穿场强和压敏特性，但该材料的非线性系数和介质损耗有待改善，介电、力学等性能亟待深入研究。本项目拟采用“冷烧结”技术，以PTFE为绝缘相、无机纳米填料为改性剂对ZnO陶瓷进行晶界设计，探索ZnO-PTFE基压敏陶瓷高击穿场强的来源，以及提高非线性系数和降低损耗的方法。研究PTFE与无机填料的协同作用对ZnO陶瓷微观晶粒生长的抑制和对宏观I-V、介电与力学性能的影响规律，提出基于陶瓷晶粒-聚合物晶界-陶瓷晶粒结构的晶界势垒模型，揭示ZnO-PTFE基压敏陶瓷的电导机理。通过本项目，为基于“冷烧结”技术的陶瓷-聚合物基新材料的开发提供理论依据和实验指导。

ZnO压敏陶瓷作为避雷器的核心部件，被广泛应用电子设备、电力系统等过电压保护领域。新型的“冷烧结”技术烧结温度低，可用于冷烧共烧陶瓷-聚合物复合材料。本项目提出运用“冷烧结”工艺制备电气性能和机械性能优异的陶瓷-聚合物压敏陶瓷复合材料。首先，采用“冷烧结”技术制备了不同配比的ZnO-PTFE陶瓷复合材料，发现通过调控PTFE的体积分数，可以细化晶粒尺寸和优化晶界结构，从而调控ZnO-PTFE电气性能、力学性能及表面疏水特性，并揭示了“冷烧结”制备陶瓷的致密化机制和复合陶瓷材料的性能调控机制，明确了工艺参数-微观结构-宏观力学和电气等性能之间的内在联系，形成了如下重要结果：（1）ZnO-PTFE基陶瓷复合材料的微观结构受“冷烧结”工艺参数、PTFE和无机填料含量等共同作用的影响。压强、温度和辅助液相浓度等会影响复合材料的致密化，从而实现对微观形貌的调控。PTFE以及其它无机氧化物掺杂可以改变ZnO晶粒生长动力学，抑制其晶粒增长。（2）ZnO-PTFE基陶瓷复合材料的电气性能受PTFE和无机氧化物掺杂的共同作用。PTFE和无机填料在陶瓷颗粒之间形成高阻态晶界，发现ZnO-PTFE-CoO-Mn2O3复合压敏陶瓷电位梯度可达4546.87 V/mm，非线性系数为10.35。（3）发现PTFE可改善ZnO陶瓷复合材料的机械韧性，可将纯ZnO的弹性模量从76.84 GPa下降到ZnO-PTFE(20 vol%)的39.67 GPa。（4）随着PTFE体积分数的增大到40 vol%，ZnO-PTFE基陶瓷复合材料表现出优良的超疏水特性，疏水角和滚动角分别可达162°和7°。因此，采用“冷烧结”技术，以聚合物和无机填料为绝缘相调控晶界特性，不仅有望制备出具有高电气的新型ZnO 基压敏陶瓷，还可以提高陶瓷的机械韧性，这也将为“冷烧结”技术在其它陶瓷-聚合物共烧领域的推广应用及新材料的开发奠定理论基础和实验依据。