Research On Preparing Colored Stainless Steel With Patterns By Cyclic Utilization Treatment

Because of their beautiful colors and predominant capabilities, colored stainless steels are highly welcomed by people and have great market value.Among the methods of preparing colored stainless steels, the acid-chemical coloring is the one that is most researching, fastest developing and highest industrializing. Although this method has many advantages as mild conditions, showy luster, good reproducibility and being not affected by sample shapes, and so on, it still exists some disadvantages as color singleness, lacking aesthetic feeling, poor uniformity of colored film, and the coloring deteriorative liquid, which is highly toxic, strongly acidic and complicated in composition, hasn't been coped with reasonably until now, etc.In order to solve such problems, the main researches of this dissertation were as follows.(1) The main aging reason of acid-chemical coloring solution and the influence on stainless steel coloring effect of the concentrations of foreign ions were researched. The coloring method coupling ultrasonic was put forward for the first time, whose influence on uniformity of colored film was observed.(2) The regulations and method of coloring patterns on stainless steel surface were researched. By means of the coloring potential-time curve, the regulations of coloring for multicolor and the main influence factors as coloring area, bottom color, surface covering, etc, were found out and discussed respectively for the first time. And then, the colored patterns were prepared on stainless steel surface by using the screen printing technique.(3) The method and process of cyclic utilization treatment of the coloring deteriorative liquid was researched. First, the chemical determination methods for analyzing the main components as Cr⁶⁺, Cr³⁺, Fe³⁺ , Ni²⁺ and H₂SO₄ in deteriorative liquid were established. Then, according to its particularities, the deteriorative liquid was cyclic utilization treated with the evaporating separation-electrochemical oxidation method, which was advanced for the first time, too. And the influence of main factors was also analyzed and discussed.The results show that:(1) The aging of coloring solution is mainly due to the content increasing of foreign ions in coloring liquid, which also influences on stainless steel coloring effect severesly. With the augmenting of concentrations of Cr³⁺, Fe³⁺ or Ni²⁺, the coloring initial potential is ascended, the coloring rate slowered, the coloring time prolonged, the luster of colored film darkled, and the tone deviated. Among the foreign ions, Cr³⁺ influences them the most severely, Fe³⁺ the least relatively and Ni²⁺ the middle. When the concentration of Cr³⁺ exceeds 45g/L, Fe³⁺ 30g/L or Ni²⁺ 8g/L, the coloring liquid can not be used for coloring any more.(2) The coloring with coupling ultrasonic can improve the uniformity of colored film obviously, and especially minish the color difference between the edge and the midst of colored film evidently. And the coloring potential-time curve of the coloring with coupling ultrasonic moves toward right and below, compared with the traditional acid-chemical coloring method. And the larger the given energy of ultrasonic, the more the descending value of the curve; the higher the frequency of ultrasonic, the clearer the moving rightward of the curve.(3) The regulations of coloring for multicolor are different from those of traditional coloring for monocolor. To obtain the identical aim color, the summation of potential difference of coloring for multicolor is less than the potential difference of coloring for monocolor. The coloring potential-time curve of coloring for multicolor shows the variation trend with ascending firstly, descending afterward and reascending finally, and exists the relaxation phenomenon. The color species of final showing in coloring for multicolor depend on the potential difference of bottom color, and the higher the potential difference of bottom color, the less the color species. Coloring areas and surface coverings hardly influence the coloring for multicolor, therefor, the results of laboratory experiments can be used to guide the industrial production directly. The beautiful, fine and multicolor patterns on stainless steel surface can be formed by the screen printing technique.(4) With methods of chemical titration and spectrophotography-standard addition, the concentrations of main components in coloring deteriorative liquid can be analyzed conveniently. The analyzed results are showed as follows: [Cr⁶⁺] = 85.02g/L, [Cr³⁺] = 28.94g/L, [Fe³⁺] = 20.36g/L, [Ni²⁺] = 2.14g/L, [H₂SO₄] = 376.45g/L.(5) Using the evaporating separation-electrochemical oxidation method, the coloring deteriorative liquid can be reutilized well, and the whole process of stainless steel coloring can be made green. Hereinto, the chromium (VI) and the ferric can be recovered and removed from coloring deteriorative liquid by the evaporating separation treatment for the first, respectively. And then, after the electrochemical oxidation treatment, the Cr³⁺ in residue deteriorative liquid can be oxidated to Cr⁶⁺ to realise the cyclic utilization of residual chromium and H₂SO₄, and the Ni²⁺ and the residue Fe³⁺ can also be separated further. The optimal conditions in electrochemical oxidation treatment are as follows: the anode is Pb-PbO₂ electrode, the anode liquid is residue deteriorative liquid being diluted 4 times, the cathode liquid 5% H₂SO₄, the anode current density 200A/m², the oxidation time 3.5 hours, the oxidation temperature 70℃. After treating, the conversion rate of Cr³⁺ 94.20%, the anode current efficiency 83.21%, the anode liquid can be recycled to confect new coloring liquid, and the cathode liquid can be reused to confect new anode liquid.