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化成處理是用化學或電化學(electrochemical)處理金屬表面得到
金屬化合物
(compound of the metal)的覆層(coating).其目的有改進耐蝕性
(corrosion protection),塗裝附著性(paint bonding),金屬著色
(metal coloring),及化學研磨(chemical polishing)等作用.化成處理的種類
- 鉻酸鹽處理(Chromate conversion coatings)
- 磷酸鹽處理(Phosphate conversion coating)
- 金屬著色(Colaring of metals)
- 化學研磨(Chemical polishing)
- 2鉻酸鹽處理(Chromate Conversion Coatings)
鉻酸鹽處理應用在鍍鋅
(Zinc),鎘(Cadmium),銀(Silver),銅(Copper),黃銅(Brass), 錫(Tin)零件.鋁,鋅壓鑄品(Zinc Die-cast) 熱浸零件或其他金屬合金也有被鉻酸鹽處理的.一般採用簡單沒(immersion)在鉻酸鹽水溶液中但也有用噴霧法(spraying),刷洗法(brushing)或電解法(electrolytic method).
17.2
鉻酸鹽處理的影響因素- 基材金屬的作用(Effect of bases Metals)
- pH的影響(Effects of pH)
- 六價鉻的濃度(Hexavalent Chromium Concentration)
- 活性度(Activators)
- 處理時間(Treatment Time)
- 溶液溫度(Solution Temperature)
- 溶液攪拌(Solution Agitation)
- 溶液雜質(Solution Contamination)
- 水洗(Rinsing)
- 乾燥(Drying)
- 2.2鉻酸鹽處理的評估(Evaluation)
- 目測試驗(visual test): 用肉眼觀測顏色,均勻性(uniformity),光澤性(smoothness),附著性(adhesion)從顏色及虹色(iridescence)可辨別覆層厚度.
- 加速腐蝕試驗(accelerated corrosion tests): 最常用的是ASTM B-117鹽霧噴射測試以評估耐腐蝕性
- 濕度試驗(humidity tests): 此試驗較煙霧試驗更有用除非是海洋環境(marine atmospherp).做評估較實際狀況的耐腐蝕性
- 水試驗(water tests): 浸在蒸餾水中測試腐蝕生成物的情形
- 化學分析(chemical analysis): 用化學分析法測試六價鉻的含量做為耐蝕性的評估
- 點試驗(spot tests): 用分析溶解覆層並作用基材的情形評估耐蝕性
- 塗裝性能評估(performance tests for organic finishes): 測試塗裝覆著性及耐蝕性其方法有鉛筆硬度測定(pencil-hardness)膠帶測試(tape tests)彎曲測試(bending tests)及衝擊試驗(impect tests)
- 2.3電解鹽處理
17.3
磷酸鹽處理(Phospate Coatings) 磷酸鹽處理是將金屬基材(metal substrates)的表面轉化成新的非金屬(non-metallic)及非導電性(non-conductive)表面.磷酸鹽處理的主要目的有: - 塗裝的表面調節處理(precondition surfaces),使表面對塗料能接受(receive)且能保留(retain)及防止塗料下層間之腐蝕(under-paint corrosion).
- 塑膠塗裝(plastic coatings)的表面前處理以加強結合力(bonding).
- 金屬成型加工(metal forming operation)的表面調節處理(precondition),以利抽製成型劑的作用.
改進腐蝕性使臘
(wax)及防鏽油(rust-preventive oils)的作用更好17.3.1
磷酸鹽處理反應機構(Mechanism)大部份金屬磷酸鹽
(metal phosphates)不溶於水,但溶於礦物酸(mineral acids),當金屬浸入磷酸鹽水溶液中,輕微的酸浸漬(pickling)作用發生,金屬被溶解,氫氧產生,而酸化的濃度減少,則金屬離子轉化成金屬磷酸鹽沉積在金屬表面上.活性劑(activators)及其他添加劑可加速反應及改變造結算晶粒構造(modify microcrystalline structure)常用水的活性劑有硝酸鹽(nitrates),過氧化物(peroxides)等.磷酸鹽化成鍍層形成的反應如下:12Fe+8NaH2PO4+10H2O+7O2---2Fe3(PO4)2*8H2O+2Fe3O4+4Na2HPO4
Fe+2H3PO4---Fe(H2PO4)+H2
3Zn(H2PO4)---Zn3(PO4)+4H2O
2Zn(H2PO4)2+Fe(H2PO4)+4H2O---Zn2Fe(PO4)2*4H2O+4H3PO4
17.3.2
磷酸鹽處理的流程 清潔 磷酸鹽處理 水洗 酸 洗 乾 燥 Clean Phosphating Rinse Acidified Dry off17.3.3
磷酸鹽處理的功能 (no - 淨化表面及使表面成非鹼性狀態(non-alkaline condition).
- 改進表面均勻性(uniformity).
- 增加表面的接觸面積增加附著力.
- 產生微洞(micro-cavities),內鎖(interlocking)被覆層,吸收及保住(hold and retain)潤滑油或成型加工劑及防銹劑.
- 防止金屬刮傷(scoring and scratching).
- 防止電化腐蝕(electrochemical and scratching).
- 防止塗裝物質與金屬基材之作用.
- 抑制腐蝕的擴散.
17.4
金屬著色配方組成(coloring of metal) - 鋼鐵染黑(blackening of low carbon and low alloy steel)
例
1 苛性鈉 醋酸鈉 重鉻酸鈉 水 溫度例
2苛性鈉
硝酸鉀 亞硝酸鉀 溫度
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