Zhou Dongxiang

Research on NTC thermally sensitive powder materials for thick-film thermistors

Abstract Negative temperature coefficient (NTC) thermally sensitive powder materials made of semiconductor ceramics are crucial for the fabrication of thick-film thermistors. This paper presents several new experimental methods and the results of research on NTC thermally sensitive semiconductor ceramics in the MnCoNi and MnCoNiRu systems. Formulation of the constituents, preparation methods and preparation techniques for the materials are also described.

Air-fired Ni for ohmic electrode of PTCR

The constitution and furing-technology of Ni paste were experimentally investigated. The experimental results show that the contact resistance could be lowered by adding glass powder and Boron powder, respectively used as adhesive and antioxidant when the content of Ni powder is higher than 65 wt%. By firing at 810 °C, Ni paste obtained could form a good ohmic contact to PTC ceramics, as shown by SEM iamges. In addition, we compared the electrical properties of PTCR ceramics measured with various electrodes and found that fired-Ni contact is superior to contacts made by fired-Al and sputtered-Ni.

The printing and firing process of A1 paste in PTC ohmic contact electrodes

Al electrodes are well known as ohmic contact electrodes for the PTC component, the influence of their thickness on final component properties was investigated by comparing their ohmic characteristics with the ones of InGa electrodes. After observing the Al paste physical and chemical behaviors during rising temperature by thermal analysis (DTA), the firing operation of Al electrodes could be divided into three main subsections: the temperature rising time (tr), the peak firing temperature (Tp) and the hold time at peak firing temperature (th). The effects of these three parameters on final component properties were discussed in detail.

Effects of NaNbO3-Co2O3 Co-additive on the properties of PZN-PZT ceramics

NaNbO3-Co2O3 co-added PZN-PZT (PZCNNT) ceramics were prepared using conventional solid state reaction. The piezoelectric and dielectric properties were measured. The experimental results show that the addition of 0.3mol% Co2O3 leads to low dielectric loss (tg δ) in PZCNNT ceramics and the proper addition of NaNbO3 not only improves piezoelectric properties but also decreases intensively dielectric loss and mechanical loss. The optimal ceramic having d33=310 pC/N, kp=0.59, ɛr=985, tg δ=0.0034, Qm=1380 was obtained.