Fundamental studies and applications of low-temperature combustion synthesisas as well as improvements of NTC resistor process

• Main Authors: Huang Kuan Tung, 黃冠棟
• Other Authors: Chien-Chong Chen
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/10601989806406603377

碩士 === 國立中正大學 === 化學工程研究所 === 89 === This thesis divides into two parts. The first part is for fundamental studies and applications of low-temperature combustion synthesis. The studied system is to prepare α-alumina powder by combustion synthesis between aluminum nitrate and fuels such as urea and carbohydrazide. The main goal is to study the influences on reaction behavior and product properties by fuels and other process parameters such as reaction atmosphere, heating temperature, diluent, excess fuels, etc. The second part is for improvements of NTC resistor process, where an accurate quantitative method based on XRD to determine on mixing efficiency is proposed. And, preparation of spinel metal oxide materials for NTCR was carried out. The results of the process parameters on the low-temperature combustion synthesis were summarized as followed. The reaction atmosphere dramatically changes the combustion behavior. When combustion was performed in air, the flame ignited at the dish edge and propagated in an inward fashion due to the thermal convection and richness of oxygen at the dish edge. On the other hand, for the nitrogen atmosphere, the liquid phase reactants ignited simultaneously such that flame covered the whole dish and the combustion time was much shorter. Product particle size of combustion taken place in nitrogen was smaller than that in air, because of sintering degree was smaller in nitrogen. Next, the product particle size was increased with the increasing heating temperature, due to the less sintering extent. The reactant density R, defined as the ratio of reactant to dish volume, also influenced the combustion. When R decreased, the product particle size increased. However, if R was further reduced to a threshold value, the reaction failed to ignite. The effect of diluent had the similar effect as the reactant density. If the amount of diluent was raised, the product particle size was reduced. When excess fuel participated the combustion, it resulted in retardation of liquid phase reaction and enhancement of the released gas. Thus, the product particle size was decreased. Next, if mixing in liquid phase was adopted, the product particle size decreased with the increasing mixing speed. Extra addition of solid nitrogen sources could also decrease the product particle size. For the study on NTCR process, grinding of initiative powders (Mn3O4, Co3O4 and NiO) could reduce the particle size effectively. A method to determine the mixing efficiency of the above three powders based on the XRD was introduced. It utilized the linear relationship between the content of a certain powder component and its intensity of the XRD characteristic peak. An experimentally determined diagram of mixing efficiency was established. Moreover, by the least squares method a quadratic function relating the powder content and the XRD intensity could be easily used to determine the mixing efficiency. The estimated relatively error was less than 3%. Next, the NTCR intermediate powders, such as NiMn2O4, NiCo2O4 and MnCo2O4, were successfully synthesized by the low-temperature combustion synthesis. With this success, it can simplify the NTCR process.