Abstract
摘要...本研究乃利用自製多孔陶瓷平板做為氧化鈦薄膜之覆製工作其主 要目的在於減少基材之平均孔洞並增加孔洞均一性及改善表面 之平整性, 以便能製作出更小孔洞之薄膜,使之能應用氣體分離之工業上;通常為製備 出分離氣體之薄膜多採用如溶膠－凝膠技術。 在此技術中薄膜的龜裂是 決定薄膜品質最重要之因素﹔然而影響薄 膜龜裂的因素眾多諸如:乾燥之 條件,燒結之溫度與速率,溶膠的特性等等;其中被覆基材之表面型態亦佔 一很重要之因素。若孔洞大小不均一,可能在乾燥的同時就會造成薄膜之 龜裂。故在覆上以溶膠－凝膠製備之分離層之前,吾人嘗試先配製0.5微米 以及30奈米之氧化鈦粒子利用真空過濾堆積基材之上,以形成薄膜之中間 層;於此吾人最主要在工作皆在於探討製程－微結構－特性三者間之關 係,亦即操作參數對孔隙度,孔徑大小,孔洞構造之影響,以及對氣體穿透性 之效應﹐以期得到最佳之成品。 首先﹐漿料 內粒子是否分散良好對於其是否有效地堆積於基材之上,於孔洞之顯微結 構乃至於其特性有著明顯地影響(分散性以及 覆膜時流動性差者,並不能 有效地使孔洞縮減);於此發現以0.5微米之氧化鈦在1ml Darvan 7/200ml D.I water中(濃度為0.654 Vol%粒徑儀顯示有90%粒子展現於0.5微米附 近,而同樣地情況對於30奈米氧化鈦粒子卻只有45%展現於50奈米左右;另 一方面﹐對於氧化鈦薄膜之晶相除了收燒結溫度影響以外,對於粒子與粒 子間之配位數亦是影響因素之一,然若晶相之成長對於孔洞之縮減大為不 利。在薄膜表面平整性言,覆膜後不論由SEM,AFM,或α-step平整性與孔洞 均一性大幅提昇,有助於日後以溶膠-凝膠法製備薄膜 之程序。就薄膜之 孔洞以及顯微結構而言,由水銀擠入法之觀察發現在1.6微米,0.1微米以 及0.03微米附近分別為基材,第一中間層,及第二中間層之孔徑分佈;藉由 控制操作變數－氧化鈦粒子之用量,發現對於第一層中間層薄膜之顯微結 構－厚度成一線性增加之關係;另外,對其他顯微結構如:薄膜平均孔 徑(0.40→0.125微米)以及孔隙度(23→35%),乃至於對於產品的性質－濾 材整體之穿透性(420x10-7→160x10-7 (mol/sec-Pa-m2))皆有著顯著之影 響。 .....最後針對自製多孔基材在溶氧量測之應用上,發現其所提供 之 氣泡遠小於傳統用之燒結玻璃﹐尤其在低氣體流速下尤為明顯,於此範 圍質傳係數並未隨著流速而迅速下降,乃因小氣泡所提供之大質傳表面積 。另由水穿透性實驗中,發現本研究所得之氧化鈦薄膜 孔徑較商業化產 品為小,但水穿透性相去不遠;而針對掃流過濾間接發現,基材部份粒子燒 結性不良,而薄膜粒子與基材之燒結性與附著性良好。 The objective of this work is to reduce the pore size and improve the surface roughness of the porous plate for making membranes with smaller pores . The sol-gel method was usually adopted to prepared the membrane for gas separation industries. Cracking,however, is the major problem to affedt the quality ofthe membrane, and the surface morphology of the support is one of the causes .A membrane often cracks upon drying if the pores are not uniform. TiO2 particles of 0.5um and 30nm were dispersed in water with Darvan 7 and then dipped in sequence onto the support and water was filtrated out by applying vacuum on the down stream side . The first and second intermediate membrane layer were formed with mean pore sizes 0.5um and 30nm, respectively. The main job of this work is to investigate the relationship amoung processing variables - microstructure - properties of the membrane and condition for producing the optimum products. TiO2 particles of 0.5um can be well dispersed in 200ml D.I water with 1ml Darvan 7 (0.654 Vol%) to show about 90% particles around 0.5um from LPA analysis. However, the 30nm particles show about 45% at 50nm indicating agglomeration between particles . The grain growth of the sintered TiO2 particles is affected by sintering temperature and the coordination number amoung the particles .Grain growth will accompany with increasing pore size. The surface roughness ofthe membranes will be greatly improved as shown from SEM, AFM and a-Step analysis .A flat surface will be advantageous to subsequent sol-gel process t o further reduce pore sizes. As for the microstructure,the membrane thickness is linear with the quantities of TiO2. The mean pore size (0.40→0.125 um) and overall permeability (420x10-7→160x10-7) (mol/sec-Pa-m2)) decreased, while th porosity (23→35%)is increased with thickness . If compared with commercial products, our membrane can offer smaller pore size, yet similar fluxes. When thporous support is tested as a bubble device,we found that the mass transfer coefficent (KL.a) is higher than commercial products made of sintered glasses, especially in the low gas flux region (Ug < 1cm/sec) .This mainly due to the very small bubble size associated with our porous support. When tested in crossflow operations, both the support and the membrane show decaying flux with time,suggesting that particles are gradually plugging the support. Nervertheless, the adhesive property between support and membrane is quitesatisfactory.