以改良式無電電鍍法製備高熱穩定性之鈀複合薄膜

Prepation of thin dense palladium composite membranes with enhanced stability by an improved electroless plating technique

紀岩勳(Yen-Hsun Chi)

指導教授 ： 黃金花

國立清華大學/工學院/材料科學工程學系/博士(2015年)

https://doi.org/10.6843/NTHU.2015.00592

摘要

本研究係以改良式無電電鍍法製備出同時具有高氫氣滲透率與高熱穩定性之鈀/多孔不銹鋼複合膜。研究內容分成三部份，由於多孔不銹鋼基材之孔徑分佈不均，故首先探討利用兩階段方式修飾多孔不銹鋼管之可行性，其概念是先利用10 μm之氧化鋁粒子將多孔不銹鋼之表面大孔加以修飾，待大孔形成均勻小孔後，再利用1 μm之氧化鋁粒子將表面粗糙度降低。其次則是利用層狀雙金屬氫氧化物(LDH)取代1 m之氧化鋁粒子進行第二階段之多孔不銹鋼管表面修飾，探討LDH層作為表面修飾層與中間阻障層之實用性。最後則是探討在無電電鍍程序中，若施一轉速(0-200 rpm)於經修飾後之多孔不銹鋼基材上，不同轉速對鈀金屬沉積速率與鈀膜層微結構之影響。
在「以兩階段方式修飾多孔不銹鋼基材」部份，實驗結果顯示利用10 m與1 m氧化鋁粒子兩階段修飾多孔基材表面，可將原有基材平均孔徑10-20 m減小至1 m以下。以無電電鍍法析鍍鈀金屬於該基材，膜厚僅4.4 μm時即可獲得緻密鈀膜，其薄膜結構為Pd/1 m Al2O3/10 m Al2O3/PSS。在溫度500C時，薄膜之氫氣滲透率可達75.5 m3/m2 h bar0.5且選擇率(H2/He)為1124。相較於未經修飾之多孔不銹鋼管，膜厚在31.5 m時才可達相同緻密程度，且氫氣滲透率僅有15.3 m3/m2 h bar0.5。實驗結果證明兩階段修飾法不僅可有效修飾基材表面，還可保有原先基材透氫量80%，此結果使達緻密時所需膜厚下降約7倍，氫氣滲透率亦提升約5倍。
其次在「利用層狀雙金屬氫氧化物(LDH)取代1 μm之氧化鋁粒子」部份，實驗結果顯示利用10 μm氧化鋁粒子與LDH層修飾後之多孔不銹鋼表面，可將原有基材平均孔徑10-20 m減小至1-3 m。以無電電鍍法沉積鈀金屬於該基材表面上，膜厚約在7.85 m時即可獲得緻密鈀膜，其結構為Pd/LDH/10 m Al2O3/PSS。在溫度400C時，薄膜之氫氣滲透率可達76.7 m3/m2 h bar0.5且選擇率(H2/He)為3817。將此鈀膜管在400C純氫氣氛下長期測試1500小時，實驗結果顯示，氫氣通量與H2/He選擇率皆為一定值，證明利用LDH層進行表面修飾，不僅可有效修飾基材表面亦可做為中間阻障層，避免在高溫下鈀膜層與多孔基材發生金屬互擴散而降低鈀膜管之氫氣滲透率。
最後「在無電電鍍程序中，若施一轉速於經修飾後之多孔不銹鋼基材上，不同轉速對鈀金屬沉積速率之影響」部份，實驗結果顯示，鈀金屬之析鍍速率會隨轉速增加而增加，意即在相同析鍍時間下，其鈀金屬轉化效率可有效提升。利用無電電鍍法配合旋轉多孔不銹鋼基材方式，可鍍製出膜厚僅5.0 m之緻密鈀膜，其結構為Pd/LDH/10 m Al2O3/PSS。此外，相較於傳統無電電鍍法，此方式製備出之鈀膜層較為平整且均勻，可提升鈀膜管在高溫滲氫時之熱穩定性。在400C時，氫氣滲透率高達78 m3/m2 h bar0.5且選擇率(H2/He)超過400。在14次的升降溫(0 ~ 400C)測試期間內(350小時)，鈀膜管之氫氣滲透率與選擇率(H2/He)皆為一定值，證明膜管具備良好之熱穩定性。
綜合上述研究結果可知，多孔不銹鋼基材經由10 m Al2O3與LDH層兩階段修飾後，可將原有平均孔徑10-20 m減小至1-3 m，此時以無電電鍍法結合旋轉多孔基材方式，可製備出同時具有高氫氣滲透率與良好熱穩定性之緻密鈀膜管。

關鍵字

氫氣 ； 鈀膜 ； 多孔不銹鋼 ； 無電電鍍

並列摘要

Thin dense Pd membranes for hydrogen filtration were deposited on modified porous stainless steel (PSS) tubes by an improved electroless plating technique. Three research parts are included. First, alumina oxide (Al2O¬) particles of two different sizes were subsequently used to modify the non-uniform pore distribution and the surface roughness of the PSS tubes. The principle of the modification was to use large Al2O3 particles (~10 μm) to fill larger pores on the surface, and leave the smaller pores intact. Small Al2O3 particles (~1 μm) were then used to further decrease the surface roughness. Moreover, instead of small Al2O3 particle, a layered double hydroxide (LDH) layer was chosen to reduce the surface roughness of the PSS and to be a middle layer retarding Pd/Fe interdiffusion. Finally, the influence the support rotation rate ranging from 0 to 200 rpm exerted during the Pd deposition process was analysed, and the permeation of hydrogen flux through the membranes was investigated.
First, the detailed manufacturing steps of the Al2O3 modification were investigated and optimized to achieve a continuous dense Pd membrane with a minimum thickness of 4.4 μm on the modified PSS tubes. The highest hydrogen permeance of the membrane (Pd/1 m Al2O3/10 m Al2O3/PSS) was 75.5 m3/m2 h bar0.5 at 500°C, with a selectivity coefficient (H2/He) of 1124 under a pressure difference of 8 bar. In comparison, the thickness and hydrogen permeance of a dense Pd membrane on unmodified PSS tubes were 31.5 μm and 15.3 m3/m2 h bar0.5, respectively, at 500°C.
Moreover, the LDH layers successfully instead of small Al2O3 particles to reduce the surface roughness of the PSS and to be a good diffusion barrier layer. The results indicated the membrane (Pd/LDH/10 m Al2O3/PSS) with thickness of ~7.85 m had a hydrogen permeance up to 76.7 m3/m2 h bar0.5 and selectivity coefficient (H2/He) of 3817 at 400°C. Thermal cycling between room temperature and 400C was performed and showed that the membrane exhibited good permeance and selectivity. Long-term evaluation (1500 hours) of the membrane at 400C showed static results of H2 flux and H2/He selectivity over the 1500 hours test period.
Finally, thin dense palladium (Pd) membranes (~ 5.0 m) were fabricated on rotating PSS supports using electroless plating. The influence the support rotation rate ranging from 0 to 200 rpm exerted during the Pd deposition process was analysed. The rate of Pd deposition increased as the support rotation rate increased during electroless Pd plating. Compared with conventional electroless plating methods, the proposed modified electroless plating using a support rotation technique yielded Pd membranes that had considerably more uniform and smooth surface morphology, which substantially enhanced the membrane stability. The membranes exhibited a hydrogen permeance as high as 78 m3/m2 h bar0.5 at 400°C. Moreover, the membranes were stable during long-term temperature cycling performed between room temperature and 400°C over a period of 350 hours. These results indicated that the electroless plating combined with support rotation process was a simple, effective method for preparing thin dense Pd membranes featuring high hydrogen permeation flux and high thermal durability.

並列關鍵字

hydrogen ； palladium ； porous stainless steel ； electroless plating

參考文獻

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