用双波长分光光度法测定锡铜锌合金镀液中铜、锌的含量

锡铜锌合金镀层已广泛应用于电子和机械产品的防护，为此，以5-Br-2-吡啶偶氮-5-二乙氨基酚（5-Br—PADAP）为显色剂，采用双波长分光光度法对新型环保锡铜锌合金镀液中的铜、锌含量进行同时测定。Cu^2＋的测量波长是555nm，参比波长是561nm；Zn^2＋的测量波长是538nm，参比波长是568nm。试验考察了酸度、甘油用量、显色剂用量、OP乳化剂用量以及干扰离子对测定的影响。结果表明：铜、锌含量在0-20μg／25mL范围内均服从郎伯-比尔定律，样品加标回收率为98％以上。该方法简便、快速，准确度高，不经分离可直接对锡铜锌合金镀液中的铜、锌进行快速测定，结果令人满意。

铜-锌合金镀液中锌的分析方法

用铬黑T作指示剂分析氰化物镀铜-锌合金镀液中的锌,在传统的测定方法中,需要使用剧毒氰化物和抗坏血酸抑制Cu2+离子的生成。为了消除氰化物的污染,研究了用三乙醇胺取代氰化钾的方法,三乙醇胺与Cu+离子生成稳定的络合物,在抗坏血酸存在的条件下,Cu+离子不能转变为Cu2+离子。测定时加甲醛破坏游离氰化钠,以铬黑T作指示剂,在pH=10的条件下用EDTA滴定锌。测定结果的相对平均偏差为0.71%,回收率为101.3%～101.9%。

酸性锡锌合金镀液中硫酸锌的分析方法

为了解决柠檬酸对EDTA容量法测定锌的干扰问题,制定了测定酸性锡锌合金镀液中硫酸锌的新方法。加双氧水将Sn(II)和Fe(II)分别氧化成Sn(IV)和Fe(III),然后用氟化钠掩蔽锡离子及铝杂质,用三乙醇胺掩蔽铁杂质,用二甲基二硫代氨基甲酸钠掩蔽铜杂质。在p H=10的条件下以铬黑T作指示剂,用EDTA标准溶液滴定锌。测定结果的相对平均偏差为0.17%,回收率为99.59%~100.41%。

Al和Mg对锌合金镀液抗高温氧化性能的影响

制备8种不同Al、Mg含量的锌合金镀液,采用SEM、XRD等分析方法,研究Al和Mg元素对锌合金镀液表面氧化的影响。结果表明:Mg含量增加会加剧镀液表面的氧化,而Al含量增加会抑制镀液表面氧化;在Mg含量为0.5%的合金镀液中,当Al含量≥0.1%时,氧化膜层中出现混合氧化物MgAl2O4相,减少了氧化膜层中MgO的含量;Mg含量为0.5%的镀液中添加0.075%的Al,其镀层具有良好的耐高温氧化性。

Surface pretreatment of Mg alloys prior to Al electroplating in TMPAC-AlCl_3 ionic liquids

It is difficult to directly electroplate Al on Mg alloys. The effects of pretreatment parameters on the corrosion resistance of films obtained on AZ31 Mg alloy surface were studied by using potentiodynamic polarization curves, to produce a compact interfacial layer as zinc-immersion deposition. After the substrate was pretreated under optimized conditions, aluminum was electrodeposited on AZ31 from TMPAC-AlCl3 room temperature ionic liquids. The depositions were characterized by scanning electron microscope equipped with energy dispersion X-ray. The results show that the traditional pretreatment of Mg alloys was successfully used for the Al-electroplating process from TMPAC-AlCl3 ionic liquids. The entire procedure includes alkaline cleaning, chemical pickling, surface activation （400 mL/L HF acid, 10 min）, zinc-immersion （20 min） and anhydrous treatment. A relatively compact zinc-immersion film was prepared on the substrate surface. A silvery-colored satin aluminum deposition was obtained on AZ31 from TMPAC-AlCl3 using direct current plating.