阳极氧化(中英对照)

Anodize Alumina and Dyeing
2、Anodize treatment
The natural formed alumina on the surface of aluminum product is too thin and corrasive to defend, even to be colored. Manmade oxidated film is mainly used application chemistry oxidation and anodic oxidation. Put aluminum made products into the alkalescent and faintly acid liquor, some parts of metal reacts and then natural formed oxidation film on its surface will be thicker and get some other passivated film. This kind of process is called chemistry oxidation. We mainly use chemistry oxidation film including chromic acid film and phosphate film. Both of them are thin and have good absorption, easy to color and seal. In the Form-3, we introduce the chemistry oxidation of aluminum made products. Chemistry oxidation film is thinner than anodic oxidation film, but the corrosion stability and rigidity is weaker than anodic oxidation, also it is hard to color, the light fastness is weaker after coloring. So here, we just introduce anodic treatment
for pigmentation and match colors.
Form-3 chemistry oxidation crafts for aluminum products
2.1 General idea of anodic oxidation
2.1.1、The principle of anodic oxidation film
Put the product that takes aluminum or aluminum alloy for anode into electrolyte. After electrolysis, oxidation aluminum will be formed on the surface. This kind of process is call anodic oxidation of aluminum and aluminum alloy. In the whole process, the cathode should be the material which has good stability in electrolyte liquor, such as plumbum, stainless steel and aluminum etc.. The principle of anodic oxidation of aluminum is the same as water electrolyte when the current through out, the hydrogen will be released on the cathode while the oxygen will be released on the anodic. But the released oxygen is not only molecule oxygen, but also atom oxygen (O) and ion oxygen. We always use molecule oxygen to express. To oxidate the anodic aluminum by the oxygen it release, and then form anhydrous oxidation aluminum film. Not all the released oxygen are reacted with aluminum, a part of it will be separated out as gaseity.
2.1.2、The choice of anodic oxidation electrolyzing solution
The precondition for the formation of anodic oxidation film is that electrolyte can dissolve the oxidation film, but not all this kind of electrolyte can get oxidation film or similar film.
Form-4 lists acidic electrolyte of which applies to anodic oxidation.
Form-4 acidic electrolyte used in oxidation
2.1.3、 Kinds of anodic oxidation
Divided by current: DC anodic oxidation, alternating current anodic oxidation, impulse current oxidation. Divided by electrolyte: vitriol, oxalic acid, chromate, mix-acid and the natural color anodic take for the sulfonic organic acid as main liquor oxidation. Divided by film molecule: common film, film build, porcelain film, lucency film and prevent film used semiconductor. Form-5 introduces the common ways and crafts of anodic oxidation of aluminum and aluminum alloy. And the most popular one is DC sulphuric acid anodic oxidation.
Form-5 common ways of anodic oxidation of aluminum and aluminum alloy
2.1.4、Strcuture and quality of anodic oxidation film
Anodic oxidation film is composed by two stories. The holey and thick out film formed upon the inside film which is thick and dielectric properties. The inside film is called prevent film (also called active film). Study by electron microscope, the film has many tube holes in length and breadth. They through out the whole oxidation film. The principal axis around by holes is a six-edge beehive made by thick oxidation aluminum, and it is also called crystalloid cell. The whole film is formed by innumerable such crystalloid cells. Bar is formed by aluminum without water, thin and dense, and it also has high rigidity and can prevent the current through. Its thickness is about 0.03-0.05μm, take 0.5%-2.0% of the whole film. Holey out film of the oxidation film is formed by non-crystalloid oxidation aluminum and little hydration oxidation aluminum, also some cation of electrolyte. When we use vitriol as electrolyte, the content of sulphate is 13%-17% on usual. Most of the excellent character of oxidation film depends on the thickness of out film and holey rate that has intimate relationship with conditions of anodic oxidation.
2.2 DC vitriol anodic oxidation
2.2.1、 Mechanism of oxidation film shaped
The surface of anodic aluminum products uniformity oxidates in short time, in vitriol liquor. And because of vitriol liquor, parts of the weak point of film (such as grain boundary, densed point of impurity, defect of cystal lattice and deformed of structure) dissolve can make self-metal touch with electrolyte and the current also can transmit on. Newly formed oxygen ion is used to oxidate new metal and spread the hole bottom as a center. After assembly, there will be a new film formed between the old film and metal. It seems like that parts of old dissolved film is pieced up again. With the oxidation’s time going on, the film dissolve and pieced up again and again, the oxidation developed in depth, thus oxidation film formed by thin and densed inside film, thick and holey out film will grow continually on the surface. It is until the end of oxidation the thickness of inside film (prevent film, dielectric, active film) will not be changed, but the position will be moved in deep while the outside film get more and more thick.
2.2.2、Calculation for the thickness of oxidation film
We can calculate the thickness of oxidation film based on the formula of Faraday No.2 law.
σ= Kit
σ presents the thickness of oxidation film (μ m). i presents the density of current (A/dm2). t presents th e time of oxidation (min). k is a coefficient (when the density of alumina γ=kg/m3, k=0.309). When we use the formula to calculate, the precondition is all the current through is used to separate alumina out, and the density should be thought of purify of alumina and film. But it is different with the fact. In order to make k more fit for actuality, we should also think of the efficiency of current and density of film and holey rate, that is:
K = 1.57η/γ
Η presents current efficiency (the rate of quantity s eparated out actually in electrode and separating quantity converted with the whole current). k is different in different countries. In the USA, k is 0.328,0.285-0.355, in Japanese, k is 0.352,0.364,0.25, in China and Russia, k
is 0.25.
2.2.3、Element affect the grow and quality of oxidation film.
The dissolve speed of film will be increase 3 times when the temperature of electrolyte grown up from 20℃ to 30℃. The oxidate metal and the thickness of alumina film on the surface will
increase with the increase of density of current. The consistency of vitriol has little effective to the thickness of film, but in order to get the film which is medium thickness holey and easy to be colored,better corrosion stability, the consistency should be 15%-20%, deionized water needs chlorin ion< 15mg/L, iron ion<1mg/L, sulfate ion <30mg/L, resistance rate should be 5 ×10 or 5×10 Ω·cm. The content of impurity should be controlled in aluminum ion 20g/L, copper ion 2g/L, iron ion 5g/L, chlorin ion 0.1g/L. The thickness increased with the anodic oxidation time. When the thickness grow to some degree, because of film resistance increase, the ability of electricity conduct decrease, the speed of film grow will be low down. Though to lengthen oxidation time, thickness will not be increased. Anocid oxidation film of different aluminum alloy has different color. Pure aluminum film is achromation and transparent, the polish of metal is remained. Add little magnesium to high pure aluminum the color pf film will not change with extend the time of oxidation, but when the content of magnesium is over 2%, film color will change into dark and muddy. When anodic alumina and silicon alloy, silicon can’t be oxidate or dissolve, and part of it will form with film, so the film color is dark and gray. When enlarge the content of silicon, use hydrofluoric acid to marinate the alloy before oxidation, the film color will be better. When the content of silicon is over 5%, this kind of metal doesn’t suitable to make shining colored products, and when the content attach 13%, it is hard to make anodic oxidation. When the alloy contains little copper, the film is green. And film will darker and thinner with the increase of copper. Some other deformed anodic oxidation of aluminum alloy is introducted in Form-6. Aluminum alloy is anodic oxidate in vitriol liquor, the form grow and dissolve of oxidation film on the surface cause the change of resistance, and the current, density of current. In the actual operation, the voltage should not high quickly or the fil m can’t be formed uniformity.
Form-6 result of some anodic oxidate aluminum alloy
Note: 1-excellent 2-good 3-suitable 4-passable 5-unsuitable 6-only suit for dark color 2.2.4、Anodic oxidation for architecture aluminum stuff
Architecture aluminum stuff is the main product of anodic oxidation, 75%-85% of these products are used vitriol to oxidate. According to China Architecture Stuff Standard, the thickness of oxidation film should more than 10μm. The best technology parameter for anodic oxidation aluminum is electrolyte liquor vitriol 15%±2%. The content of aluminum ion should less than 5g/L, temperature of liquor should be 21±10℃, density of current should be （1.3±0.05）A/dm2, time is (for LD31 alloy)30min, to 10μm,60min should reach 18μm(voltage:18V), the liquor should be
dispensed by pure water.
2.3 Other anodic oxidation
2.3.1、Anodic oxidation with oxalic acid
Most aspects that affect anodic oxidation with vitriol also affect oxalic acid anodic oxidation. We can use direct current, alternating current and DC & alternating current alternative to do the anodic oxidation with oxalic acid. At the same condition, the film get from alternating current is more soft and less elasticity than DC; oxidation with DC, the film will easy to be hole corrade while use alternating current will prevent, and by the increase of alternating current, the corrosion stability will be improved, but the color will darken, the pigmentation is weaker than vitriol film. The density of dissociate oxalic acid in electrolyte is 3%-10%, 3%-5% in common, per A·h consume about 0.13-0.14g, 0.08-0.09g aluminum in per A·h dissolved in electrolyte and form oxalic acid aluminum. And this needs oxalic acid with 5 times of the amount for aluminum. The consistency of aluminum ion should be controlled in below 20g/L, when the consistency of aluminum reaches 30g/L, the liquor will invalidotion. Oxalic acid electrolyte liquor is sensitive for chlorid, anodic oxidate pure aluminum and aluminum alloy, the content of chlorid should be controlled in 0.04-0.02g/L, and we’d better to dispense the liquor with pure water. The higher the temperature of electrolyte is, the thinner the film is. In order to get thicker film, we should inlarger ph of liquor. When we use lead, graphite and stainless steel to be the cathode of DC anodic oxidate, the area rate is （1：2）-（1：1）. Oxalic acid is weak acid with weak solvency, so we should cool products and electrolyte when oxidate aluminum. Thickness and color of oxalice acid film is different because of different alloy, film of pure
aluminum is light yellow and silver, and the film of alloy is darker, such as yellow and copper yellow. After clean the oxidate film, if we don’t dye, we can also use 3.43×10 Pa steam to seal
for 30-60 min.
2.3.2、Chrome acid anodic oxidation
The crafts of anodic oxidation with chrome acid is introduced in Form-4. We should analyse the density of liquor frequently during oxidation, add chrome anhydride at suitable time. We can use lead, iron and stainless steel to be the cathode of electrolyte, area rate of cathode should better be （5：1）-（10：1）. When tervalent chrome ion becomes more and more , we can use electrolysis to change them into Cr6+. Anodic oxidation will be affected when the content of sulfate over 0.5%. So we can add some barium hydroxide or barium carbonate to get the deposition of barium sulfate. The content of chlorid should be controlled in 0.2g/L. We’d better diluteor change qnother liquor when the content of chrome is over 70g/L. The ways of chrome acid anodic oxidation contains voltage periodically change and permanent voltage to anodic oxidate.
2.3.3、Anodic oxidation for horniness
Horniness anodic oxidation is a kind of craft for hard oxidation film on the surface of aluminum and aluminum alloy. The thickness of honiness film can reach 250μm, rigidity of film on the surface of pure aluminum is 12000-15000Mpa while alloy is 4000-6000Mpa, similar as sclerous chromeplate floor, the wearable is the best under the lower load, hole rate of horniness film is about 20%, lower than common vitriol film. Form-7 lists some crafts of anodic oxidation for horniness.
Form-7 Crafts of anodic oxidation for horniness
2.3.4、 Anodic oxidation with porcelain
Anodic alumina and aluminum alloy in oxalic acid, citric acid, boracic acid with titanium salt、zirconium salt or thorium salt liquor, the hydroxid of such kinds of salt come into the holy of oxidate film that make the surface of products looks like opaque and compact which like porcelain enamel, or have some special reflet which likes plastic. This kind of process is called anodic oxidation with porcelain. It same as common vitriol anodic oxidation, the only difference is that anodic oxidation with porcelain suitable under the high DC (115-125V) and liquor with high temperature(50℃-60℃), the electrolyte should be mix round frequently and pH also should
be adjusted in 1.6-2.
铝制品表面的自然氧化铝既软又薄，耐蚀性差，不能成为有效防护层更不适合着
色。

人工制氧化膜主要是应用化学氧化和阳极氧化。

化学氧化就是铝制品在弱碱
性或弱酸性溶液中，部分基体金属发生反应，使其表面的自然氧化膜增厚或产生
其他一些钝化膜的处理过程，常用的化学氧化膜有铬酸膜和磷酸膜，它们既薄吸
附性又好，可进行着色和封孔处理，表-3介绍了铝制品化学氧化工艺。

化学氧
化膜与阳极氧化膜相比，膜薄得多，抗蚀性和硬度比较低，而且不易着色，着色后的耐光性差，所以金属铝着色与配色仅介绍阳极化处理。

表-3 铝制品化学氧化工艺
（一）阳极氧化处理的一般概念
1、阳极氧化膜生成的一般原理
以铝或铝合金制品为阳极置于电解质溶液中，利用电解作用，使其表面形成氧化铝薄膜的过程，称为铝及铝合金的阳极氧化处理。

其装置中阴极为在电解溶液中化学稳定性高的材料，如铅、不锈钢、铝等。

铝阳极氧化的原理实质上就是水电解的原理。

当电流通过时，在阴极上，放出氢气；在阳极上，析出的氧不仅是分子态的氧，还包括原子氧（O）和离子氧，通常在反应中以分子氧表示。

作为阳极的铝被其上析出的氧所氧化，形成无水的氧化铝膜，生成的氧并不是全部与铝作用，一部分以气态的形式析出。

2、阳极氧化电解溶液的选择
阳极氧化膜生长的一个先决条件是，电解液对氧化膜应有溶解作用。

但这并非说在所有存在溶解作用的电解液中阳极氧化都能生成氧化膜或生成的氧化膜性质相同。

适用于阳极氧化处理的酸性电解液见表-4。

表-4 氧化处理的酸性电解液
3、阳极氧化的种类
阳极氧化按电流形式分为：直流电阳极氧化，交流电阳极氧化，脉冲电流阳极氧化。

按电解液分有：硫酸、草酸、铬酸、混合酸和以磺基有机酸为主溶液的自然着色阳极氧化。

按膜层性子分有：普通膜、硬质膜（厚膜）、瓷质膜、光亮修饰层、半导体作用的阻挡层等阳极氧化。

铝及铝合金常用阳极氧化方法和工艺条件见表-5。

其中以直流电硫酸阳极氧化法的应用最为普遍。

表-5 铝及铝合金常用阳极氧化方
4、阳极氧化膜结构、性质
阳极氧化膜由两层组成，多孔的厚的外层是在具有介电性质的致密的内层上上成长起来的，后者称为阻挡层（也称活性层）。

用电子显微镜观察研究，膜层的纵横面几乎全都呈现与金属表面垂直的管状孔，它们贯穿膜外层直至氧化膜与金属界面的阻挡层。

以各孔隙为主轴周围是致密的氧化铝构成一个蜂窝六棱体，称为晶胞，整个膜层是又无数个这样的晶胞组成。

阻挡层是又无水的氧化铝所组成，薄而致密，具有高的硬度和阻止电流通过的作用。

阻挡层厚约
0.03-0.05μm，为总膜后的0.5%-2.0%。

氧化膜多孔的外层主要是又非晶型的氧化铝及小量的水合氧化铝所组成，此外还含有电解液的阳离子。

当电解液为硫酸时，膜层中硫酸盐含量在正常情况下为13%-17%。

氧化膜的大部分优良特性都是由多孔外层的厚度及孔隙率所觉决定的，它们都与阳极氧化条件密切相关。

（二）直流电硫酸阳极氧化
1、氧化膜成长机理
在硫酸电解液中阳极氧化，作为阳极的铝制品，在阳极化初始的短暂时间内，其表面受到均匀氧化，生成极薄而有非常致密的膜，由于硫酸溶液的作用，
膜的最弱点（如晶界，杂质密集点，晶格缺陷或结构变形处）发生局部溶解，而出现大量孔隙，即原生氧化中心，使基体金属能与进入孔隙的电解液接触，电流也因此得以继续传导，新生成的氧离子则用来氧化新的金属，并以孔底为中心而展开，最后汇合，在旧膜与金属之间形成一层新膜，使得局部溶解的旧膜如同得到“修补”似的。

随着氧化时间的延长，膜的不断溶解或修补，氧化反应得以向纵深发展，从而使制品表面生成又薄而致密的内层和厚而多孔的外层所组成的氧化膜。

其内层（阻挡层、介电层、活性层）厚度至氧化结束基本都不变，位置却不断向深处推移；而外早一定的氧化时间内随时间而增厚。

2、氧化膜厚度计算
阳极氧化生成的氧化膜厚度从理论上可按法拉第第二定律推导的公式进行计算。

σ= Kit
式中σ为阳极氧化膜厚度（μm），I为电流密度（A/dm2），t 为氧化时间（min），K为系数（当氧化铝密度γ=kg/立方米则K=0.309）。

上述公式计算的前提是以认为通过的电量全用于氧化铝析出，同时也把氧化铝及膜的密度视为纯净的氧化铝密集的值。

但实际情况并非完全如此，为了使K值更切合实际，应将电流效率和在这种工艺条件下所生成膜的密度或孔隙度考虑在内，即：
K = 1.57η/γ
式中η为电流效率（电极上实际析出的物质量与又总电量换算出的析出物质量之比）。

K实值各国取值大小各异，美国有取0.328、0.285-0.355，日本有取0.352、0.364、0.25，中国、俄罗斯取0.25。

3、影响氧化膜生长和质量的因素
当电解液的温度从 20度上升到30度，膜的溶解速度约增加3倍。

随电流密度的增加，制品被养护的金属量、表面生成的铝氧化膜厚度都随着增加。

硫酸浓度对氧化膜厚度的影响不大，为获得中等厚度、多孔而易于着色和封闭、抗蚀性较高的膜层，浓度最好为15%-20%；溶液用去离子水要求氯离子<15mg/L、铁离子<1mg/L、硫酸根离子<30mg/L，电阻率为5×10的5-6次方Ω·cm；溶液
中杂质允许的最大含量铝离子 20g/L，铜离子 2g/L，铁离子 5g/L，氯离子
0.1g/L。

随着阳极氧化时间的延长，氧化膜的厚度增加，到一定厚度后，由于膜厚电阻增加、导电能力下降，膜的生长速度减慢，有的合金即使延长氧化时间，膜的厚度也不会再增加。

不同的铝合金的阳极氧化膜有不同的色彩，纯铝上的膜无色透明，使金属的光泽完全保持下来；高纯铝添加少量的镁，膜色不会因氧化时间的延长而改变，当镁的含量超过2%，膜变暗浊色；铝硅合金阳极氧化时，硅不会被氧化或溶解，部分进入膜层使膜呈暗灰色。

含硅量大时，阳极氧化前先用氢氟酸浸泡，膜色会有所好转，一般含硅5%以上的合金不适合做光亮着色制品，含量达13%就难于进行阳极化处理；含铜的合金，当含量较少时，膜呈绿色，随铜含量的增加，膜薄，色调深暗。

某些变形铝合金的阳极氧化处理见表-6。

铝合金在硫酸溶液中阳极氧化，由于氧化膜在表面上形成、生长和溶解，引起电阻的变化，使过程中的电流、槽端电压及电流密度都随之发生变化。

实际操作中电压升高不宜太快，否则会使生成的膜不均匀。

表-6 某些铝合金阳极氧化处理效果
4、建筑铝型材阳极氧化工艺
建筑铝材是目前阳极氧化处理的主要产品，其中75%-85%是用常规硫酸法处理。

中国建筑型材标准规定氧化膜的厚度大于10μm。

建筑铝材阳极氧化工艺的最佳工艺参数为电解液硫酸15%±2%，铝离子含量小于5g/L，溶液温度
21±10C，电流密度（1.3±0.05）A/dm2，时间（对LD31合金）30min，则10μm；60分钟，则可达18μm（电压18V），溶液用纯水配制。

（三）其他阳极氧化
1、草酸阳极氧化
对硫酸阳极氧化影响的大部分因素也适用于草酸阳极氧化，草酸阳极氧化可采用直流电、交流电或者交直流电迭加。

用交流电氧化比直流电在相同条件下获得膜层软、弹性较小；用直流电氧化易出现孔蚀，采用交流电氧化则可防止，随着交流成分的增加，膜的抗蚀性提高，但颜色加深，着色性比硫酸膜差。

电解液中游离草酸浓度为3%-10%，一般为3%-5%，在氧化过程中每A·h约消耗
0.13-0.14g，同时每A·h有0.08-0.09g的铝溶于电解液生成草酸铝，需要消耗5倍于铝量的草酸。

溶液中的铝离子浓度控制在20g/L以下，当含30g/L铝时，溶液则失效。

草酸电解液对氯化物十分敏感，阳极氧化纯铝或铝合金时，氯化物的含量分别不应超过0.04-0.02g/L，溶液最好用纯水配制。

电解液温度升高，膜层减薄。

为得到厚的膜，则应提高溶液的pH值。

直流电阳极氧化用铅、石墨或不锈钢做阴极，其与阳极的面积比为（1：2）-（1：1）之间。

草酸是弱酸，溶解能力低，铝氧化时，必须冷却制品及电解液。

草酸膜层的厚度及颜色依合金成分而不同，纯铝的膜厚呈淡黄或银白色，合金则膜薄色深如黄色、黄铜色。

氧化后膜层经清洗，若不染色可用3.43×10的4次方Pa压力的蒸汽封孔30-60
分钟。

2、铬酸阳极氧化
铬酸阳极氧化工艺见表-4。

氧化过程中应经常进行浓度分析，适时添加铬酐。

电解的阴极材料可用铅、铁、不锈钢，最好的阳阴面积比为（5：1）-（10：1）。

当溶液中三价铬离子多时，可用电解的方法使其氧化成六价铬离子。

溶液中的硫酸盐含量超过0.5%，阳极氧化效果不好，硫酸根离子多时可加入氢氧化钡或者碳酸钡使其生成硫酸钡沉淀。

溶液中氯化物含量不应超过0.2g/L。

溶液中铬含量超过70g/L时就应稀释或更换溶液。

铬酸阳极氧化有电压周期变化的阳极氧化方法或恒电压阳极氧化法（快速铬酸法）两种。

3、硬质（厚膜）阳极氧化
硬质阳极氧化是铝及铝合金表面生成厚而坚硬氧化膜的一种工艺方法。

硬质膜的最大厚度可达250μm ，纯铝上形成的膜层微硬度为12000-15000MPa，合金的一般为4000-6000MPa，与硬铬镀层的相差无几，它们在低符合时耐磨性极佳，硬质膜的孔隙率约为20%左右，比常规硫酸膜低。

某些硬质阳极氧化工艺见表-7。

表-7 硬质阳极氧化工艺
4、瓷质阳极氧化
瓷质阳极氧化铝及铝合金在草酸、柠檬酸和硼酸的钛盐、锆盐或钍盐溶液中阳极氧化，溶液中盐类金属的氢氧化物进入氧化膜孔隙中，从而使制品表面显示出与不透明而致密的搪瓷或具有特殊光泽的类似塑料外观的处理过程。

瓷质阳极氧化处理工艺流程与常规硫酸阳极氧化基本一致，不同的是瓷质阳极氧化是在高的直流电压（115-125V）和较高的溶液温度（50-60度）、电解液经常搅拌、经常调节pH值使之处于1.6-2范围内的条件进行。