CS251888B1 - A method for removing ionogenic substances from the surface of electronically conductive materials - Google Patents

Abstract

The issue of corrosion protection is addressed, namely a method of removing inorganic substances from the surface of electron-conducting materials, in which the electron-conducting material is connected as the cathode of an electrolytic system with an insoluble anode and an electrolyte formed by a solution of acid salts, the anions of which have corrosion-inhibiting properties.

Description

The invention solves a method of removing iiomogenních substances with the surface of the electron conductive materials, especially those that contaminate the surfaces of the electron conductive material during processing anebo- in contact with contaminated environment and often cause ^one of their subsequent deterioration by corrosion.

When processing electronically conductive materials, especially metals and alloys, and exposing them to atmospheres or other environments, surfaces are contaminated with corrosive active ionic substances, most commonly soluble salts. It is generally known that the type of anioint determines the stimulatory or inhibitory effect of salt solutions in addition to the pH of the solution. The anions of Cl ', Br ^- , J - and SO4 ^{- 2} are considered to be particularly aggressive, of which Cl' and SO - ² - ions are the most common component of both technological and external environments. Significant sources of these ions during processing include, for example, heat treatment environments, cleaning and surface treatment solutions, water, atmosphere, etc. The stimulation function of said anions is their chemisorption and subsequent chemical bonding with ions of the underlying material, especially metal, passivating anions OH ^- , O ^2- . The resulting salts promote corrosion by their hygroscopicity, which induces the formation of a liquid ionic conductive layer on the surface even at moisture values lower and higher than those corresponding to the condensation of water vapor to liquid water. Hydrolytic processes lower the pH of the electrolyte surface solution and the ainioins are released for recurring chemisorption at the anodic sites of the surface. The autoicatalytic course of coirose can be described by the following sequence of reactions, where Me is the symbol for the glo-forming ion Me ²⁺ , the x-symbol for the stimulating antan:

Me - 1 H 2 O

MeOH

Me OH acLs ~~ l

MeOH áds

I, i-O H ad-s

MeX (+ 2 H) (OH) 2 + 2

2H X -

The formation of the corrosion products according to reaction 5 is unacceptable for many applications. Reaction 4 may be a component of the processes leading to dangerous phenomena of structural corrosion, corrosion under other physical influences, especially static or dynamic stress! cracking and corrosion fatigue. The metal salts formed by reactions 1 to 4 sealed under the coatings are a frequent cause of undercoating and osmotic degradation.

Doisuid known and used methods for the removal of inogenic substances consist in washing the surfaces with water or aqueous solutions containing degreasing and surfactant components. Also, the use of ultrasonic cleaning with these compositions is not effective enough.

The drawbacks of the prior art are largely overcome by the method of removing ioinogenic substances from the surface of the electronically conductive materials of the invention. Its essence is that the electron-conductive material engages as a cathode of an electrolytic system with an insoluble anode and an electrolyte formed by a solution of acid salts whose anions have corrosion inhibiting properties. It is preferred that the electrolyte is a solution of the water-soluble, in particular, alkali salts of orthophosphoric, pyrophosphoric, tri- to hexametaphosphoric, tetraboric, chromic, molybdenum, tungsten, aliphatic and cyclic, mono- and dicarboxylic acids and hydroxy acids having 2 to 8 carbon atoms, for example, sodium phosphate, dipotassium chromene, sodium benzoate, sodium salicylain, sodium gluconate. The pH of the electrolyte solution is in the range of 8 to 13, the cathode current density in the range of 0.01 A. dm ^-2 to 10 A. dm ^-2 . It is preferred that the electrolyte solution surrounding the cathode be enriched with oxygen to suppress the concomitant formation of molecular hydrogen, which reduces the efficiency of the process of the invention.

The method according to the invention is based on utilizing the possibility of inducing a reversal of reactions 2 to 4 by connecting electronically conductive materials contaminated with corrosive stimulating impurities as the cathode of the electrolysis system, in which the anode is an insoluble material with sufficient electron content.

The ionically conductive component of the system is an aqueous electrolyte solution, which ensures that, during electrolysis, aggressive conditions do not arise for the material whose surface is to be free of ibnogein substances. In such a connection, the following processes take place on the material to be purified, i.e. the cathode:

4 MeX -ř --8 4 Q. (ds θ?

kanodě

MeQH ads

The efficacy of reaction 8 is reduced by concurrent reaction +

h i- 2e> 2 H-> H ^ *

In order to suppress it, the pH of the electrolyte solution pH > 8 and the enrichment of the cathode environment with oxygen, for example by blowing air, are advantageous.

The resulting ad-compounds carry passivity, the stimulating amions are extracted to the anode and can be completely removed from the surface.

The composition of the electrolyte solution is selected to provide the desired pH and to contain non-stimulating, inhibitory anions. Suitable are, for example, the lithium, sodium and potassium salts of orthophosphoric acid, polymetaphosphoric acid, boric or tetraborous acid, chromic, molybdenum, tungstic, mono- and dicarboxylic aliphatic or aromatic acids or hydroxy acids, e.g.

The invention and its effects are explained in more detail by way of examples of a specific embodiment thereof.

Example 1

Destimulation of MgA18 alloy castings

When casting in sand, the metal is protected against oxidation by powdered sulfur. Oxidation fumes in the form of MgSCl or MgSCl2 deposit on the surface of the castings and are mostly removed during the subsequent passivation treatment of the surface. However, they cannot be removed from surface pores and shrinkage in such a way that, in a subsequent four-day condensation chamber test according to ČSN 03 8131, salts emit efflorescence from the pores and shrinkage,

which the technical conditions do not allow. The following procedure was used to remove stimulating ions: the castings were alternatively nested in * ro * zt * o * sk: (a) sodium phosphate 20 May g · I ' ¹ chromian dipotassium 10 g · l ' ¹ (b) disodium tetraborate 30 G I- ¹ (c) sodium benzoate 20 May g · l ^-1 nxinohydrogenphospharečnan disodium 20 May g · l- ¹ d j disodium oxalate 10 G and-' salicylam sodium 10 g · l ^-1 sodium gluconate 10 g · I- ¹ dipotassium tungstate 10 g · l- ¹ tripotassium orthophosphate 20 May g · 1- ’ Potassium molybdenum 10 g · 1-1

The pH of each solution was adjusted to pH < 8, 12 with acetic acid or phosphoric acid and sodium hydroxide. The anode of stainless steel sheet 16Ci18Ni9 had dimensions roughly the same as the cast surface. Electrolysis conditions were defined by cathode current density in A. dm ' ² = 0.1; 0.5; 1, 2, 5 and electrolysis time in minutes = 1; 5; 10; 20; 30. After completion of the electrolytic extraction of the anions, the castings were removed under power, rinsed with water and dried with warm air. In the four-day test according to CSN 03 8131, the results summarized in the table where x equals efflorescence effluents from pores, 0 without efflorescence effluents were obtained for electrolyte solution a]:

Current density 1

And. dm ' ²

Electrolysis time (minutes)

10 20 30

0.1 x x

0,2 x x

0.5 x x

XX x 0

0 0

Extraction results in other electrolyte solutions were similar.

Example 2

Extraction of sulphates from rust on gray iron castings

Gray iron castings weighing 1 kg to 10 kg were stored in a free atmosphere contaminated with sulfur dioxide for a long time. After machining the functional surfaces, the unworked parts should be painted. In the rust caused by atmospheric corrosion, a dense distribution of sulphate nests was found, which would cause rapid degradation x x 0 x 0 0 x 0 0

0 0

0 0

0 0 undercoating. Sulphate nests were identified by decals on developed and stabilized photo papers developed in K3Fe (CN) 6 solution. The castings were hung on the cathode rod of the electrolyzer after brushing of the rust-free rust. The working solution contained 10 g. I ^-1 disodium phosphate and 30 g. I ^-1 · trisodium phosphate. Lead plate was used as the anode. The electrolytic extraction was carried out at an approximate current density of 0.5 A. . divot ^'2 and waveform extraction ionogehních substances from the rust was observed decals like in the original casting. The course of the extraction, expressed as the areal distribution density, is expressed in the table:

Electrolysis time (minutes) Area of distribution of sulphate nests on oibtisl over 100 cm ² in cm ² xs

default state 8.5 2 1 6.8 2.3 2 4.9 1,8 5 2.7 1.1 10 1,8 0.6 20 May 0.7 0.15 30 0.15 0.04 60 0.07 0.01

x = sample diameter;

s = standard deviation

At a current density of approximately 1 A. dra ² , the time efficiency of extraction was about 50% higher. During the electrolytic extraction of the anions after rinsing with water and drying, the layer formed on the lead anode was analyzed and its composition was found to correspond to a mixture of lead phosphates and lead sulphates. After the sulphate extraction, the rinsed and dried rust layer was compact and substantially harder compared to the starting material. It was found by X-ray diffraction analysis that it contained a higher proportion of Fe3Oi, which was apparently produced by the conversion of the unstable components of the initial rust during electrolysis. Organic coatings with an inhibitory base layer applied to the surface treated in this way showed no tendency to undercorrupt in tests according to ČSN 67 3094 than the same coatings made on the blasted surface of castings.

Example 3

Electrolytic decontamination of metals used for electrical and electronic circuits

For many technical purposes it is required that the surfaces of metal parts are not contaminated with homogeneous substances. Conventional cleaning methods, including ultrasonic cleaning, are not effective enough. To verify the extent to which electrolytic deanionation allows the problem to be solved, the following procedure was performed. Samples of commonly used metals, namely carbon steel, tin, copper, moisazi, FeNi40 alloy and also carbon, were artificially contaminated with a known volume of 0.1 M NaCl solution. The amount of salt retained on the samples was determined by determining the loss of concentration of C18 in the contaminant solution and indicated below as 100%. The samples were placed in a plating drum with an anodized stainless steel anode. The electrolyte solution used was 10 g of disodium tetraborate. I ' ¹ , benziaam. sodium 10 g. I ^-1 . Electrolysis was performed at approximate processing time (minutes)

AND

Electrolytic removal of ionic substances is therefore significantly more effective than electroless scrubbing.

The invention can be used to remove ionogenic substances from metal surfaces, for example copper, silver, gold, beryllium, magnesium, cathode on the cathode 1A. dm ' ² . At the same time, the same contaminated samples were washed in a similar device with water. The time course of decontamination was monitored by determining the Cl- ¹ content of the solution and is expressed in the table after the pirioiploin ina NiáCl.

Decontamination efficiency in% with cathode delainilonation dm ^{2 without} current

56 30 76 48 97 60 99 85

Mia, tin, lead, chromium, molybdenum, iron, nickel, rhodium and others, their alloys and alloys with other elements containing at least 50 atomic percent of the base element as well as carbon and silicon.

Claims (5)

What is claimed is: 1. A method for removing ionic substances from a surface of electronically conductive materials, characterized in that the electronically conductive material is connected as a cathode of an electrolytic system with an insoluble ahotiotic and an electrolyte formed by an acid salt solution whose anions have corrosion inhibitory properties. 2. The method according to claim 1, wherein the electrolyte is a solution of water-soluble, in particular, alkali salts of orthophosphoric, pyrophosphoric, trieth hexametaphosphoric, tetraborate, chromium, molybdenum, tungsten, aliphatic and cyclic mono- and dicarboxylic acid and hydroxyl acids. carbon atoms of 2 to 8, for example sodium phosphate, dipotassium chromate, sodium benzate, sodium sialicylate, sodium gluconate. 3. The process of claims 1 to 2 wherein the pH of the electrolyte solution is in the range of 8 to 13. 4. The method of claims 1 to 3 wherein the current density at the cathode is in the range of 0.01A. dm ” ² to 10 A. dm ' ² . 5. A method according to claims 1 to 4, characterized in that the electrolyte solution in the vicinity of the cathode is enriched with oxygen.