以化學共沉法製備Mn-Ni-Al系NTC陶瓷混合 不同濃度硼之研究

Preparation of Mn-Ni-Al system NTC Ceramics Mixed difference Concentration Boron by the Chemical Coprecipitation

徐勝楹(Sheng-Ying Hsu)

指導教授 ： 胡毅

大同大學/工程學院/材料工程學系所/碩士(2006年)

摘要

根據電學公式可得知，當材料電阻愈低時，其產生出的焦耳熱也就愈小，所以降低NTC的電阻在電路設計的匹配上，將有更多選擇的空間，但NTC的電阻穏定性亦是相當重要的考慮因素；一般阻值愈低，穏定性愈差。因此為了改善低阻值NTC穏定性，化學共沉法是一可採用的粉末製備方法。化學合成法的原料是在溶液狀態下混合，粉體的均勻性高、平均粒徑小、化學活性較大，所以反應較傳統之固態反應法快且完全。故本研究是以化學共沉法製備Mn-Ni-Al系混合不同濃度硼之NTC陶瓷。本研究採用的共沉法是以硝酸鹽和草酸銨皆製備成0.2M之水溶液，並將之加熱混合，形成草酸鹽沉澱物。由實驗的結果得知以化學共沉法所製備之NTC：(1) 化學共沉法的製備之粉末在煆燒過程中重量損失在55%左右。(2) 試片之密度會影響銀膠的附著，密度值必需高於2.7g/cm3，銀膠才可以附著於試片上。(3) 燒結之緻密性隨著混合硼量的增加而有明顯的提升，且在燒結溫度900℃時，即可看出整體緻密性已有明顯提升。(4) 混合硼之試片在燒結時，硼會熔解附著於晶界上，造成晶界之電阻上升，而影響其導電性。(5) Mn-Ni-Al系NTC在25℃時之電阻率，隨著混合硼量的增加而增加。(6) Mn-Ni-Al系混合0wt% B，在燒結溫度1100℃時，ΔR/R隨時效時間增長並無多大改變，有較佳之穩定性。(ΔR/R＝0.17﹪、1.73﹪、0.1﹪)。

關鍵字

半導體陶瓷 ； 負溫度係數 ； 電阻

並列摘要

It is well known that a material is acquired to produce small joule-heat only when it has low resistance according to the electricity rule. Therefore reduce the resistance of NTC in the match for the design of circuit gives more space in chosen. In addition, the stability of NTC resistance is a quite important factor for consideration. In order to improve the stability of low resistance NTC , coprecipitation is a suitable method to prepare the NTC powders. The powders obtained from the coprecipitation are mixed in solution. This method gives high homogeneous in compositions, low mean grain size, and high chemical activation , so reflects the reaction faster and more complete than the traditional solid state route. The powder compositions of this study are by Mn-Ni-Al mixed difference concentration Boron primarily . From the experimental results of coprecipitation process, there are several conclusions. The powder was weight loss approximately 55﹪in calcination process by the chemical coprecipitation . It is affects the Ag paste by the sample density .The density value must be higher than 2.7 g/cm3 , then the Ag can paste with sample . The sintering densification is enhanced as the content of Boron increased , and it can observation the densification is obvious enhanced at sintering temperature 900℃ .When the sample were mixes Boron at sintering process , the Boron was pastes on grain boundary , therefore it affects the electric properties by the grain boundary resistivity is increased . The resistivity of Mn-Ni-Al system NTC at 25℃ is enhanced while the content of Boron increased . When the Mn-Ni-Al system NTC mixed 0wt% Boron at sintering temperature 1100℃, the ΔR/R value is change not many while the aging increased , and it has well stability (ΔR/R＝0.17﹪、1.73﹪、0.1﹪) .

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