(1)色泽 ：浅灰色的金属
(2)比重：7.14
(3)原子量：65.37
(4)原子价 ：2
(5)标准电位 ：-0.7628v
(6)熔点：419℃
(7)原子序：30
(8)沸点：907℃
(9)密度：7.13
(10)特性：脆.比较硬.加热至100～150℃有较好的塑性.可延压及锻造加工,但到250 时又变脆.干燥空气中锌较安定,在水中及潮湿空气中表面易形成碳酸盐或氧化物的白色模层具有保护性,锌为两性金属,腐蚀于酸,.鰔及硫化物中,锌的标准电位较负,所以其镀层属于阳极性保护,成本低,加工容易,效果良好,很多刚铁零件镀锌,但不易做摩擦性的镀层。
(1)酸性镀锌(acid zinc plating)
(2)碱性非氰化物镀锌(alkaline plating )
(3)氰化物镀锌(cyanide zinc plating )
7.3 酸性镀锌
形状简单镀件和做油漆底层用的较多,其优缺点如下
优点
(1)可得光泽,平滑,镀锌层相似的镀层
(2)可直接镀在碳化,氮化的钢铁上和铸铁上
(3)电流效率较高
(4)废液处理容易,只需用高ph值将锌沉淀
(5)导电性佳,节省电原
(6)产生氢脆性小
(7)可在较高温下得到光泽镀层
(8)镀浴安定,毒性小,成本低
缺点
(1)镀浴腐蚀性强,镀槽及附属设备需加衬
(2)焊接及组合镀件不宜,会有渗流(bleadout)
(3)厚镀层延性差
(4)结晶粗糙
(5)均一性差
(6)过滤,冷却管及冷冻设备需要有
优点
1.毒性小
2.废液处理容易,只需将锌沉淀
3.成本低
4.均一性好
5.可用刚镀槽
缺点
1.镀浴成份需严格控制,每天要分析
2.前处理要求质量高
3.锌含量少时,电流效率降低
4.对金属杂质及硬水杂质敏感
5.镀层校氰化镀锌脆
6.需要添加剂,否则黑暗镀层出现
7.添加剂特殊,非一般性原料,需由厂商提供
7.4.1 Alkaline non-cyanide galvanizing bath (alkaline-non-cyanide bath)
Can be formulated in two ways
1. Anode zinc is dissolved in caustic solution
2. Zinc oxide dissolves with caustic
Its preparation procedure is as follows
1. Use a small amount of water to mix with zinc oxide in the plating tank to form a slurry, or better use another matching bath tank to make it
2. Slowly stir caustic soda and water into one-third of the water
3. Fully stir until the zinc oxide is completely dissolved
4. Add 6 lbs/100 gallons of zinc powder and stir for 30 to 60 minutes
5. Precipitate and filter or pour into the plating tank
6. Put in the anode zinc plate and use low current density electrolysis to remove impurities overnight
7. Analyze the content of zinc and caustic soda and adjust the composition
add additives
Its formula is as follows
Zinc oxide (zinc oxide) 1.5 oz/gal
Caustic soda 10 oz/gal
Additives (addition agents) according to the indicated amount
Bath temperature 70 ~ 115 F
advantage
1. It has a long history of use and rich experience
2. The pre-processing requirements are not strict
3. Excellent covering property
4. The analysis and control of bath components are relatively easy
5. The coating has good ductility
6. The plating bath is less corrosive
shortcoming
1. The plating bath is highly toxic and must be treated as cyanide waste
2. Heat treatment and cast iron parts cannot be plated
3. It needs to be operated at a higher temperature, otherwise the glossy coating will not be obtained, and the temperature needs to be above 105F
4. The conductivity of the plating bath is poor
5. At high current density, the current efficiency drops sharply
Jay Helsel - 《KTA-Tator，Inc》