Research Of Fine-grained PTC Ceramic And Co-sintering Technology With Nickel Electrode

In order to meet the miniaturization of electronic components, chip-based, high-performance development needs, PTCR must also be moving in a small, multi-chip-oriented direction. To obtain high-performance multi-layer chip PTCR as much as possible, We must make multi-layer chip PTCR body in the vertical direction contains a number of grain, while the multi-layer chip PTCR body thickness of single-layer is 10-40μm, which requires the corresponding reduction in grain size. The single-layer must at least include many grain boundaries, so the grain size should be between 0.5μm and 2μm. Preparation of this paper, high-performance multi-layer chip PTCR was the target, hydrothermal method and solid-phase method of fine-grained BaTiO3-based PTC ceramics were used, which high-performance nickel electrodes and the matching issue of electrode and ceramic, the best tape casting process to obtain fine-grained ceramic, interface effects and atmosphere on the PTCR properties of multilayer chip relations, the relationship between re-oxidation method and the properties of multi-layer chip PTCR were researched.In this paper, powder by hydrothermal method and solid-phase powder as raw material, through improving the ratio of acceptor and dopant, improving pre-sintering temperature, decreasing sintering temperature, adding the equivalent of different ways, we reduced the glass-ceramic grain size and improved the electrical properties of PTC. By hydrothermal method using outsourcing as a raw material powder we got the PTCR with an average grain size of 2-5μm, room-temperature resistivity in the 100Ω·cm or so, lift-drag ratio greater than 104, but the hydrothermal method presence of barium titanium powder ratio imbalanced, impurities and other defects was difficult to further reduce its grain size; using the traditional solid-phase powder as raw material, by adjusting the Y/Mn, after pre-sintering at 1220℃,sintering at 1300℃including other methods we got the PTC with an average of grain size of 2μm, room-temperature resistivity of 205Ω·cm, lift-drag ratio greater than 104.Within the process of Ni inner electrode production for multilayer chip PTCR, in order to obtain good performance Ni electrode paste, sub-micron Ni powder was gotten by liquid-phase reduction method. Alcohol and pine oil phthalate ding ester were used for organic solvent, rosin was selected for organic binder. Ni electrode paste in the adding amount of 10 wt% BaTiO3 powder could promote a better match between electrode and ceramic, which was a good solution to the occurrence of stratification. The 15 wt% Cr powder was also joined in Ni electrode, adjusting the sintering temperature of electrode, increasing the use temperature of electrode which played the well-protected role of Ni electrode in re-oxidation process.We used the method of organic cast of which powders were gotten by solid-phase, through increasing the ratio of acceptor and doping appropriately, increasing the pre-sintering temperature, lowering sintering temperature and other methods we achieve a small grain size of ceramic which had good performance. By improving the solids extension of flow slurry, experiments showed that the PTC had a better lift-drag ratio, smaller grain size, lower electrical resistivity at room temperature. Through introducing Ca used for the A-bit diversified and using the method of high-energy ball milling we obtained the PTC of which grain size was 1.5μm, room-temperature resistivity was 150Ω·cm, density was 5.64 g/cm3, lift-drag ratio was up to 4.5 orders of magnitude.We studied the mechanism of the multilayer chip PTCR in the sintering surrounding of reducing oxygen, with the relationship between re-oxidation mechanism and the the performance of laminated body, the relationship between Ni-BaTiO3 interface effect and multi-layer chip PTCR properties were also researched. The green sheets with Ni paste as inner electrodes were sintered at 1240-1320℃for half an hour under a N2/H2 mixing gas with the oxygen partial pressure P(O2)=10-8-10-12 MPa, and then re-oxidation at 800℃for one hour to form multilayer PTCR. In the process of 1050-1280℃and high temperature down to 850℃, the heating rate and cooling rate were 400℃/h and 300℃/h. With this mechanism we got we got the PTC with an average of grain size of less than 1μm, room-temperature resistivity of 98.8Ω·cm, lift-drag ratio of 2.5 orders of magnitude. Interface effect experiments showed that an appropriate degree of metal-ceramic inter-diffusion on the formation of high performance multi-layer chip PTCR was very good, but too heavy inter-diffusion could worse the performance of multi-layer chip PTCR. Dispersion effects in ceramics cofired with Ni electrodes were benefit for the development of multilayer chip PTCR.