CS258819B1 - Bath additive for electrolytic polishing of metallic materials - Google Patents

Abstract

The composition of the additive for baths for electrolytic plating of metal materials based on orthophosphoric and sulfuric acid, suitable especially for polishing stainless steel, is addressed. The additive is formed by a colloidal dispersion of the compound Me2O3 . 3 P2Os . 6 H2O, where Me is a symbol for a metal, forming stable oxides in which this metal is trivalent, for example aluminum, iron, chromium. The additive enables the operation of polishing baths at low current density.

Description

The present invention relates to a bath additive for the electrolytic polishing of metallic materials based on inorganic acids, in particular orthophosphoric acid and sulfuric acid.

Electrolytic polishing of metallic materials is a special case of anodic metal dissolution, which achieves a smooth, glossy surface by controlling solution composition and working conditions. The essence of the process is a significantly higher current density on convex ridges than at other locations on the rough surface. To achieve the necessary differentiation of the current density on the polished surface, solutions of a special composition, usually based on phosphoric acid, with other components such as sulfuric acid, chromium oxide and the like are formulated. When using -2 of these solutions, high current densities, typically 3 to 100 A.dm, are required for polishing.

With the need for electrolytic polishing of large-scale installations, for example of the order of 10 to 22 meters, such current densities are difficult to achieve. Therefore, special solutions have been developed for the electrolytic polishing of large-scale devices, enabling polishing at relatively low current densities, for example 2 to 10 A.dm. An essential component of these solutions is the addition of organic, usually non-ionic, substances which increase the viscosity of the solution and thereby promote the concentration polarization of the anode required to achieve the polishing effect. It has been reported that the organic additives or their reaction products in the bath also act as corrosion inhibitors. Conventional additives with this effect are multifunctional alcohols such as ethylene glycol, glycerol and the like. The disadvantage of such formulated solutions is that the additives of organic substances significantly complicate and increase the cost of waste water disposal, for example considerably increase biological oxygen consumption, are a nutrient medium for mold growth and the like.

The disposal of waste water containing these components is demanding both in terms of investment and operating costs. Replacement of the organic components of polishing solutions with inorganic compounds is for example the subject of U.S. Pat. No. 4,372,831, according to which the function of the organic bath components inhibiting the etching function of H 2 O ions on the metal surface is replaced by an addition of polyphosphates such as sodium. at current -2 densities above 8 A.dm.

The disadvantages of the prior art in this field are largely eliminated by the bath additive for the electrolytic polishing of inorganic acid-based metallic materials, in particular orthophosphoric acid and sulfuric acid, according to the invention. The substance of the invention is characterized in that the additive consists of a colloidal dispersion of the compound MejOj. 3 PjOj · ⁶ HjO, where Me is a symbol for the metals forming stable oxides of this composition, especially for aluminum Al, iron Fe and chromium Cr.

The invention is based on the determination of the specific properties of solutions of polymeric compounds which are formed in a system of H ₂ O, P ₂ O 3, ^Me 2 O 3 additive in a polishing solution containing sulfuric and phosphoric acid. Since the polymer complex has the character of anions and the viscosity of its solution increases significantly with concentration, the additive is particularly effective in electrolytic polishing by increasing the viscosity of the solution at the polished metal: solution phase interface and thereby concentration polarization. The additive according to the invention not only completely eliminates the disadvantages of the organic components of the electrolytic polishing solutions, but by its specific properties it makes it possible to achieve more advantageous technical parameters, in particular lower effective current densities and total electrical charge required to achieve the desired surface condition.

The invention eliminates the need for the use of organic additives, such as glycol, glycerol and others, in a polishing bath, which complicates and increases the cost of wastewater disposal. The additive according to the invention in the polishing solution greatly increases its viscosity, especially in the immediate vicinity of the metal-solution interface, as a result of the increased concentration of negatively charged colloidal particles on the positive-charged anodized polarized surface. The increased viscosity and concentration of the additive near the interface leads to a marked increase in polarization, favorably affecting the polishing process. The higher effect of the invention is particularly manifested in that, in addition to completely removing the organic additives, it allows polishing at low current densities, shortens the polishing time and reduces the total consumption of electric charge.

The invention is explained in more detail below by way of example of a possible specific embodiment thereof.

He did

A base solution containing 350 gl ^-1 phosphorus pentoxide Ρ2 ^Ο 5 ' ^{K tons} was used to electrolytically polish stainless steel. 200 ml.l ^{-1 of the} colloidal dispersion of compound A12O ₃ was added to the base solution. 3 P ₂ ° 5 · ^6H 2 ° 's ^{for srovn4n} prepared and used as a standard solution with addition of 100 ml of glycerol and 50 ml of water per 1 1 of the basic solution _2. Polishing in both solutions was carried out at an anode current density of 10 A.dm and the gloss was assessed visually after passing an electrical charge of 1.2, 2.4 and 3.6 MC.m.

To achieve a gloss and smoothness of the ethanol-defined surface, a solution according to the invention was used

-2 -2 of the invention required a surface electric charge of 1.2 MC.m and in a comparative solution of 2.4 MC.m

Example 2

The electrolytic polishing of the same austenitic chromium-nickel steel with a matt surface followed the same procedure as in Example 1, except that a colloidal dispersion of FeO ₃ · ^p 2 ° 5 · ® ^H 2 ° ^{in an} amount of 150 ml was used as an additive. l The result was the same as in the first example. An additive consisting of a colloidal dispersion of Cr 1 O ₃ was used with the same effect. Ρ ₂ Ο ^. 6 H ₂ 0.

The invention can be used in mechanical engineering for polishing, in particular large-area installations.

Claims (1)

A bath additive for the electrolytic polishing of metallic materials based on inorganic acids, in particular orthophosphoric acid and sulfuric acid, characterized in that it consists of a colloidal dispersion of the compound Me ₂ O ₃ . 3 P ₂ O ₅ . 6 H ₂ 3 3, where Me is a feature for the metals forming stable oxides of said composition, especially for aluminum, iron and chromium.