以脈衝電流燒結氧化鋁/奈米碳材複合材料及其性質分析

Preparation of alumina/nano-carbon composites by pulsed electric current sintering and their performance

林鐘榮(Chung-Jung Lin)

指導教授 ： 段維新

國立臺灣大學/工學院/材料科學與工程學研究所/博士(2019年)

https://doi.org/10.6342/NTU201902458

摘要

近期氧化鋁奈米複合材料發展新增對電子元件中散熱基板的需求，本研究嘗試添加少量0.57~8.5 vol％的奈米碳(nano-carbons包括:奈米碳管、石墨烯或奈米鑽石)與氧化鋁粉末混合製漿，再壓成生胚片後以脈衝電流燒結技術(PECS)使奈米複合材料緻密化，期望透過添加高導熱的奈米碳材料，大幅改善氧化鋁的導熱性和韌性。
由於石墨烯及奈米碳管緻密化過程中在晶界累積形成阻礙以及奈米鑽石在緻密化過程中發生釘扎效應(pinning effect)，在添加少量石墨烯及奈米鑽石的確略微提高氧化鋁之導熱率，但隨著奈米碳添加量的增加，卻反使導熱率快速下降。在校正孔隙率和晶粒尺寸的影響之後，顯示添加少量的奈米碳對於導熱率的增加有所助益，但是超過臨界值後，添加奈米碳後將使導熱率急速下降。
本論文討論三種不同奈米碳(nano-carbons)對於氧化鋁複合材料之熱物理性能的影響，並且若要發揮的優異熱傳導性，必須同時考慮到結構特徵與熱傳方向。其中，二維石墨烯的最佳傳熱方向是平面的，但卻恰好垂直於熱傳的目標方向；一維奈米碳管的最佳傳熱方向是沿軸向，但由於奈米碳管的纏繞效應，傳熱的結果顯示是隨機的，熱傳效益也可能相互抵消，未能發揮CNT的優良傳熱性能。零維的納米金剛石是目前最好的添加劑，因為它沒有特定的傳熱方向，並且該結構不會在晶界處產生阻礙，這會影響緻密化。這項工作的結果表明奈米鑽石和PECS技術的巨大潛力適合陶瓷複合材料的各種工程應用。

關鍵字

石墨烯 ； 奈米碳管 ； 奈米鑽石 ； 氧化鋁奈米複合材料 ； 熱傳導

並列摘要

The latest developments in power electronics have increased the demand for heat-dissipating substrates. The present study prepared the alumina slurry with the addition of a small amount (0.57 to 8.5 vol%) of nano-carbon (carbon nanotubes, graphene or nanodiamonds). The slurry was compressed into a green compact. The nanocomposite was prepared using the pulsed electric current sintering (PECS) method.
The nano-carbons (graphene/nanodiamond/CNT, less than 1 vol%) play the role of heat transfer in the nanocomposites. In terms of the structural characteristics, and the heat transfer, the best heat transfer direction for 2D-graphene is its planar direction. It happens to be perpendicular to the heat transfer direction of the target. The best heat transfer direction of 1D-CNT is along the axis direction. Because of the entanglement of CNT, the direction of heat transfer is random, and the efficiency of heat transfer might offset each other. Therefore, the CNT failed to play an excellent role in heat transfer.
Zero-dimensional nanodiamond is currently the best additive because it has no specific heat transfer direction, and its specific surface area is smaller compared to that of graphene and CNT. Moreover, its presence does not affect the densification. The present study shows that a small amount of nanodiamond (less than 1 vol%) leads to a better heat transfer than pure alumina.

並列關鍵字

graphene ； CNT ； nanodiamond ； alumina composite ； thermal conductivity

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