發(fā)布時(shí)間：2018-04-30 01:40

  本文選題：Galfan + 鑭鹽轉(zhuǎn)化膜　； 參考：《華南理工大學(xué)》2016年碩士論文

【摘要】：熱浸Galfan(Zn-5%Al-0.1%RE)鍍層的耐大氣腐蝕性能比熱浸鍍鋅層更優(yōu)異,其應(yīng)用范圍在不斷的擴(kuò)展。與熱浸鍍鋅層一樣,熱浸Galfan鍍層在儲(chǔ)存運(yùn)輸過(guò)程中容易發(fā)生腐蝕,因此也需要進(jìn)行鈍化后處理,作為熱浸鋅鍍層常用的鉻酸鹽鈍化處理因其環(huán)保因素而不適用于熱浸Galfan鍍層。稀土鑭鹽能在Galfan鍍層表面形成化學(xué)轉(zhuǎn)化膜,并具有無(wú)毒無(wú)污染且耐腐蝕性好等優(yōu)點(diǎn)。目前,在熱浸Galfan鍍層表面研究鑭鹽轉(zhuǎn)化膜的報(bào)道較少。本文以La(NO3)3·6H2O為主鹽,H2O2為氧化劑和NaF為成膜促進(jìn)劑,采用化學(xué)浸泡法在熱浸Galfan鍍層表面獲得一層鑭鹽轉(zhuǎn)化膜,通過(guò)正交試驗(yàn)和單因素試驗(yàn)得到了成膜最佳工藝參數(shù)范圍:La(NO3)3·6H2O 20 g/L,H2O2 10 ml/L,NaF 0.1 g/L,成膜溫度T 70℃,處理時(shí)間t 10~30 min。成膜溫度和處理時(shí)間對(duì)鑭鹽轉(zhuǎn)化膜耐腐蝕性能的影響較大。采用掃描電子顯微鏡(SEM)、能譜儀(EDS)、原子力顯微鏡(AFM)、X射線光電子能譜(XPS)、X射線衍射(XRD)等測(cè)試手段研究鑭鹽轉(zhuǎn)化膜的表面形貌、結(jié)構(gòu)和化學(xué)成分,并探討了成膜機(jī)理。結(jié)果表明:(1)鑭鹽轉(zhuǎn)化膜優(yōu)先在熱浸Galfan鍍層的晶界及相界等活性區(qū)域成膜。隨著處理時(shí)間的延長(zhǎng),膜層的厚度增加。當(dāng)處理時(shí)間超過(guò)10 min后,膜層表面會(huì)出現(xiàn)裂紋并不斷增多變寬,當(dāng)處理時(shí)間為60 min時(shí),膜層發(fā)生局部脫落,當(dāng)處理時(shí)間超過(guò)120 min后,膜層表面會(huì)附著白色顆粒物,其主要成分為Zn(OH)2/ZnO;(2)熱浸Galfan鍍層表面鑭鹽轉(zhuǎn)化膜由La(OH)3/La2O3、Al(OH)3/Al2O3及Zn(OH)2/ZnO組成。在成膜過(guò)程可以分為兩個(gè)階段:前期以Al(OH)3/Al2O3、La(OH)3/La2O3沉積為主,后期以La(OH)3/La2O3、Zn(OH)2/Zn O沉積為主。采用中性鹽霧(NSS)試驗(yàn)、塔菲爾極化曲線(Tafel)和電化學(xué)阻抗(EIS)等測(cè)試手段研究鑭鹽轉(zhuǎn)化膜的耐腐蝕性能。采用劃痕試驗(yàn)研究膜層的自愈性能。結(jié)果表明:(1)熱浸Galfan鍍層表面鑭鹽轉(zhuǎn)化膜具有較好的耐腐蝕性能;(2)熱浸Galfan鍍層表面的鑭鹽轉(zhuǎn)化膜能同時(shí)抑制腐蝕反應(yīng)的陽(yáng)極過(guò)程和陰極過(guò)程,顯著提高基體的耐腐蝕性能。與未處理的熱浸Galfan鍍層相比,處理時(shí)間為10 min獲得的鑭鹽轉(zhuǎn)化膜的耐腐蝕性能最優(yōu),其極化電阻提高了30倍,腐蝕電流密度降低了約1個(gè)數(shù)量級(jí);(3)經(jīng)鑭鹽鈍化液處理的試樣的阻抗值較Galfan試樣明顯提高,當(dāng)處理時(shí)間小于10 min時(shí),膜層逐漸增厚,孔隙率逐漸降低,膜層變得連續(xù)致密,能有效的阻止電荷的轉(zhuǎn)移及電解質(zhì)在膜層中的擴(kuò)散,提高了基體的耐腐蝕性能。當(dāng)處理時(shí)間超過(guò)10 min后,膜層中出現(xiàn)裂紋并不斷增多變寬,最后發(fā)生脫落,使膜層變得不完整不致密,導(dǎo)致膜層對(duì)基體的保護(hù)作用減弱,降低了基體的耐腐蝕性能;(4)鑭鹽轉(zhuǎn)化膜具有一定的自愈性能。
[Abstract]:The atmospheric corrosion resistance of the hot-dip Galfan-Zn-5 / Al-0.1RE) coating is better than that of the hot-dip zinc coating, and its application range is continuously expanding. Like hot dip zinc coating, hot dip Galfan coating is prone to corrosion during storage and transportation, so it is also necessary to undergo passivation post treatment. Chromate passivation treatment is not suitable for hot dip Galfan coating because of its environmental protection factors. Rare earth lanthanum salt can form chemical conversion film on the surface of Galfan coating and has the advantages of non-toxic and pollution-free and good corrosion resistance. At present, there are few reports on the study of lanthanum salt conversion film on the surface of hot dip Galfan coating. In this paper, using La(NO3)3 6H2O as oxidant and NaF as film forming accelerator, a layer of lanthanum salt conversion film was obtained on the surface of hot-dip Galfan coating by chemical soaking method. By orthogonal test and single factor test, the optimum technological parameters of film formation were obtained: 1: Laanno _ 3, 3 6H2O, 20 g / L H _ 2O _ 2, 10 ml / L NAF, 0.1 g / L, T _ (70 鈩，

本文編號(hào)：1822539