Title: 雜質及前處理對電解電容器用鋁箔直流電蝕之效應
the effects of impurities and pretreatment on the DC-etching behavior of aluminum foil for electrolytic capacitor usage
Authors: 林文
Lin, Wen
涂肇嘉
George C. Tu
材料科學與工程學系
Keywords: 雜質;前處理;電解電容器;鋁箔;直流電蝕;impurity;pretreatment;electrolytic capacitor;aluminum foil;DC-etching
Issue Date: 1996
Abstract: 本論文在研究電解電容器用鋁箔之特性及原箔雜質與
前處理對其直流電蝕行為之影響。結果顯示中高壓用之鋁
箔具有高純度,高立方度,晶粒大於箔厚等特徵。低壓用鋁
箔純度略低,但立方度遠低於高壓用箔。為研究雜質鉛,
銦對鋁箔電蝕行為之影響,在諸多高壓用鋁箔中,選用兩
種電蝕形貌差異大者為研究箔材。結果顯示,鋁箔電蝕行
為與存於鋁箔內之鉛、銦等雜質含量及分佈有密切關連;
雜質在壓軋線的聚集會導致電蝕點沿壓軋線分佈,造成電
蝕分佈不均,同時不利於隧道蝕孔的發展。
經由置換還原法引入之沉澱鉛,銦等雜質可克服電蝕常發
生的壓軋線效應,提高電蝕效能。另外銦雜質對鋁電蝕點
之調質能力又強於鉛。這使得在引進銦的製程中,可在較
低溫度及較稀濃度情況下進行。
為研究雜質調質之機理,本論文亦以磷酸前處理取代雜質,
研究磷酸對鋁箔電蝕行為之影響。結果顯示,在高濃度磷
酸處理下可得到較密之隧道蝕孔分佈。由磷酸物種-pH值
之關係及ATR 分析之結果顯示:在低濃度時(<20 vol. %),
因其具較高pH值,有較多解離之單價磷酸根離子(由前處
理中引入)與氯離子競爭吸附於鋁箔表面,造成孔蝕電位
朝安定方向移動而得到較低的隧道蝕孔密度。另一方面,
在高濃度磷酸(>20 vol. %)中,其pH值較低,此時幾乎以
不解離之磷酸存在,大量的Al//AlH3PO4吸附局部電池,造成
孔蝕電位朝較活潑方向移動,而得到較高之隧道蝕孔密
度。但在非常高濃度之磷酸前處理時,由於非常大量的
AlH3PO4吸附位置互相接合而形成鈍態膜。此時會得到較安定孔蝕電位及
較低的隧道蝕孔密度。 綜觀本研究,三種表面
調質(或三種前處理)之方法(鉛,銦,磷酸引入鋁箔表面)均具
一共通原理。即:他們均以創 造眾多電化學局部電池來調整電
蝕效能,而優良之前處理 必須能提供適當且均勻分佈之局部電池。
The characteristics of aluminum foils for capacitor usage and
the effects of foil impurities and pretreatment on the
DC-etching behavior of foils were investigated in the present
work. The experiment shows that foils for high voltage usage
have high purity, high cube texture with grain
sizes larger than foil thickness. The foils for low voltage
usage have lower purity and cubicity. Two of the high
voltage foils with different etching behaviors were
chosen to study the effects of lead and indium impurities on the
etching behavior. Results showed that the
difference in etched morphology of the two foils are related
closely to the lead and indium content and their distributions
on foil surface. The impurities, such as lead
and indium, segregated along the rolling lines are considered
responsible for the resulted nonuniform etching pits and
inhibited etchability. Through
introducing the lead or indium impurities on foil surface by
immersion reduction method, the rolling line
effect can be improved or even overcome, and thus
enhance etchability. The modification of etchability by indium
appears stronger than that by lead. This facilitates
employing lower temperature and dilute concentration in the
indium-introducing process to optimize the etchability.
The phosphoric acid pretreatment was performed in order to study
its role as compared with that of the
impurity introducing. The composition-pH relationship of
phosphoric acid and ATR analyses showed that: in dilute (<20
vol. %) phosphoric acid with higher pH value,
the pitting potential would shift toward noble direction, this
is caused by more H2PO4- anions (introduced in
pretreatment process) being in competition with
Cl- to adsorb on aluminum surface and resulting in lower tunnel
density. On the contrary, in concentrated (>20
vol. %) phosphoric acid with lower pH value, H3PO4
species dominate almost exclusively, the numerous Al//Al H3PO4
adsorbed local cells would drive pitting
potential toward active direction and result in higher tunnel
density. In case that extremely concentrated phosphoric
acid being employed, the very high
population of AlH3PO4 adsorbed sites would connect together to
form a passive film and result in a noble pitting
potential with much less tunnel density.
Overhauling the present work, it is apparent that the three
modification (or pretreatment) methods,
including Pb, In and H3PO4 introducing onto aluminum surface,
possess a common theme. That is, they all tends to modified the
etchability by creating electrochemical local cells
on foil surface, and a useful pretreatment must be capable of
producing proper amount and uniformly distributed local cells.
URI: http://140.113.39.130/cdrfb3/record/nctu/#NT850159022
http://hdl.handle.net/11536/61598
Appears in Collections:Thesis