Anodize Alumina and Dyeing2、Anodize treatmentThe 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 treatmentfor pigmentation and match colors.Form-3 chemistry oxidation crafts for aluminum products2.1 General idea of anodic oxidation2.1.1、The principle of anodic oxidation filmPut 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 solutionThe 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 oxidation2.1.3、 Kinds of anodic oxidationDivided 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 alloy2.1.4、Strcuture and quality of anodic oxidation filmAnodic 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 oxidation2.2.1、 Mechanism of oxidation film shapedThe 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 filmWe can calculate the thickness of oxidation film based on the formula of Faraday No.2 law.σ= Kitσ 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/γΗ 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, kis 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 willincrease 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 alloyNote: 1-excellent 2-good 3-suitable 4-passable 5-unsuitable 6-only suit for dark color 2.2.4、Anodic oxidation for architecture aluminum stuffArchitecture 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 bedispensed by pure water.2.3 Other anodic oxidation2.3.1、Anodic oxidation with oxalic acidMost 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 purealuminum 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 sealfor 30-60 min.2.3.2、Chrome acid anodic oxidationThe 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 horninessHorniness 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 horniness2.3.4、 Anodic oxidation with porcelainAnodic 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 shouldbe 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。
