“奈米”是介於宏觀(Macroscope)與微觀(Microscope)兩個世界之間的一種尺度，而奈米粒子是指粒徑在1 ~ 100nm範圍的粒子。由於奈米級材的特性有異於一般塊材(bulk material)的特性，且目前沒有簡單的系統理論可以描述有關納米粒子之熱力學物性變化，因此本實驗選擇了SiO2作為研究的系統，探討納米尺度粒徑對粒子燒結的影響，作為切入此一研究主題的初步嚐試。
我們選擇了水玻璃法製造的粒徑規格7-10nm、10-13nm、50nm 、80nm（真茂企業股份有限公司提供）與TESO水解法合成30nm的 SiO2粒子在800℃、900℃、1000℃等溫度進行燒結，並以BET、SEM、DTA、密度測量、雷射光粒徑量測、XRD、ESCA等方法進行分析；以理論探討奈米級粒子顆粒大小與溫度高低如何影響燒結行為的機制。

結果顯示，7-10nm的SiO2粒子在800℃燒結的速度比10-13nm的SiO2粒子要快，50nm 及 80nm沒有燒結；且7-10nm及10-13 nm的SiO2粒子可能為粒子間進行頸部成長、小孔洞消失及大孔洞生成的燒結初始階段。在900oC以上7-10nm與10-13nm的SiO2 粒子燒結速度比800℃快，但在兩溫度下50 nm 及80 nm的SiO2 粒子並沒有燒結；且在900oC以上7-10 nm 與10-13nm的SiO2粒子燒結時是變成無孔洞的塊材，在800oC及以下則是變成有大孔洞的材料，另外，7-10nm在850 oC ，粒子基本上是結成塊材，但會有相當多之針孔(pinhole)留下。

晶相轉變方面，7-10nm的SiO2 粒子在900 oC燒結24小時，晶相從amorphous轉變為tridymite；在1000 oC燒結2小時，晶相轉變為cristobalite，再經16小時，晶相轉為tridymite。10-13nm的SiO2 粒子，在900℃燒結8小時即出現cristobalite的晶相。

30 nm SiO2粒子在800℃燒結中經歷了頸部成長、粒子接觸消失及大孔洞生成之燒結初始階段的過程；並且進入孔洞形成平衡形狀且繼續收縮的中間階段。但在800℃ 30 nm的燒結行為比較於7-10nm與10-13nm的SiO2粒子有不合理的現象，是我們目前無法說明的。

Nano-particles as particles in the size range of 1 to 100 nm, in which the characteristic length scale falls in between the microscopic and macroscopic worlds. Due to the unusual property falls in the nano-material as compared to the bulk material and that there is no simple theory that can describe the thermodynamic change of physical property well, we choose SiO2 as the system to study the size effect of nano-particles for sintering behavior.
We have the particle sizes of 7-10nm, 10-13nm, 50nm and 80nm produced by factory using the method of water-glass and 30nm synthesized by the hydolysis of TEOS. Several characterizations including BET, SEM, DTA, gravimetry, light-scattering, XRD and ESCA are employed to analyze the sintering mechanism effected by the particle size and sintering temperatures at 800℃,900℃ and 1000℃.

The 7-10nm was sintered faster than the 10-13nm at 800℃, however, there was no sintering for the 50nm and 80nm. The 7-10nm and 10-13nm may undergo the initial sintering stage with the phenomena of neck growing, disappearance of small pores, and large pores growing. For the 7-10nm and 10-13nm , the sintering was faster at 900℃than 800℃, however, the 50nm and 80nm still did not sinter at 900℃. The 7-10nm and 10-13nm would become the bulk material without pores when sintered above 900℃ and become the one with large pores below 800℃. Besides, the 7-10nm sintered at 850℃ would become the bulk material essentially with a lot of pinholes.

As for the phase transition, the morphology would change from amorphous to tridymite when 7-10nm was sintered for 24 hours at 900℃. And the morphology would change to cristobalite when 7-10nm was sintered for 2 hours at 1000℃ and then change to tridymite when sintered for 16 hr. The cristobalite may be present when 10-13nm was sintered for 8 hours at 900℃.

The 30nm would undergo the initial stage with the phenomena of neck growing, disappearance of small pores, large pores growing and then would enter the evolution of the intermediate stage with equilibrium shapes and continuous shrinkage. But up to now, we still can not explain the unreasonable phenomena for 30nm sintered at 800℃ compared with the same condition of 7-10nm and 10-13nm.

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