Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/46—Electroplating: Baths therefor from solutions of silver
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/10—Electroplating with more than one layer of the same or of different metals
  • C25D5/12—Electroplating with more than one layer of the same or of different metals at least one layer being of nickel or chromium
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/60—Electroplating characterised by the structure or texture of the layers
  • C25D5/615—Microstructure of the layers, e.g. mixed structure
  • C25D5/617—Crystalline layers
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D7/00—Electroplating characterised by the article coated

Definitions

• the present invention generally relates to a silver-plated product and a method for producing the same. More specifically, the invention relates to a silver-plated product used as the material of contact and terminal parts, such as connectors, switches and relays, which are used for on-vehicle and/or household electric wiring, and a method for producing the same.
• plated products wherein a base material of copper, a copper alloy, stainless steel or the like, which are relatively inexpensive and which have excellent corrosion resistance, mechanical characteristics and so forth, is plated with tin, silver, gold or the like in accordance with required characteristics, such as electrical and soldering characteristics.
• Tin-plated products obtained by plating a base material of copper, a copper alloy, stainless steel or the like, with tin are inexpensive, but they do not have good corrosion resistance in a high-temperature environment.
• Gold-plated products obtained by plating such a base material with gold have excellent corrosion resistance and high reliability, but the costs thereof are high.
• silver-plated products obtained by plating such a base material with silver are inexpensive in comparison with gold-plated products and have excellent corrosion resistance in comparison with tin-plated products.
• the materials of contact and terminal parts are also required to have good wear resistance against the insertion and extraction of connectors and/or the sliding movements of switches.
• silver-plated products are soft and easy to wear. For that reason, if the silver-plated product is used as the material of a connecting terminal or the like, there is a problem in that the insertion and extraction and/or the sliding movement cause the adhesion thereof to easily cause the adhesive abrasion thereof. There is also a problem in that the surface of the connecting terminal is shaved to enhance the coefficient of friction thereof to enhance the insertion force thereof when the connecting terminal is inserted.
• Patent Document 1 JP 2009-79250 A (Paragraph Numbers 0003-0004)
• the silver-plating film is caused to contain an element, such as antimony, as the method of Patent Document 1, the improvement of the wear resistance is not sufficient although silver is alloyed to improve the hardness thereof. For that reason, it is desired to provide a silver-plated product having a more excellent wear resistance.
• the inventors have diligently studied and found that it is possible to provide a silver-plated product having a more excellent wear resistance than that of conventional silver-plated products while maintaining the high hardness thereof, and a method for producing the same, if the silver-plated product is produced by a method for forming a surface layer of silver on a base material by electroplating at a liquid temperature of not lower than 30 °C and at a current density of 1 to 15 A/cm 2 in a silver-plating solution which is an aqueous solution containing silver potassium cyanide, potassium cyanide and a mercaptothiazole wherein the concentration of the mercaptothiazole in the silver-plating solution is not lower than 5 g/L.
• a silver-plated product is produced by a method for forming a surface layer of silver on a base material by electroplating at a liquid temperature of not lower than 30 °C and at a current density of 1 to 15 A/cm 2 in a silver-plating solution which is an aque
• a method for producing a silver-plated product comprising the steps of: preparing a silver-plating solution which is an aqueous solution containing silver potassium cyanide, potassium cyanide and a mercaptothiazole; and forming a surface layer of silver on a base material by electroplating at a liquid temperature of not lower than 30 °C and at a current density of 1 to 15 A/cm 2 in the silver-plating solution, wherein the concentration of the mercaptothiazole in the silver-plating solution is not lower than 5 g/L.
• the concentration of the mercaptothiazole in the silver-plating solution is preferably not lower than 10 g/L.
• the concentration of the mercaptothiazole in the silver-plating solution is preferably not higher than 30 g/L, and more preferably not higher than 25 g/L.
• the current density in the electroplating is preferably in the range of from 2 A/cm 2 to 10 A/cm 2 .
• the concentration of the silver potassium cyanide in the silver-plating solution is preferably in the range of from 50 g/L to 200 g/L, and the concentration of the potassium cyanide in the silver-plating solution is preferably in the range of from 20 g/L to 120 g/L.
• the concentration of silver in the silver-plating solution is preferably in the range of from 20 g/L to 120 g/L, and the concentration of free cyanide in the silver-plating solution is preferably in the range of from 5 g/L to 50 g/L.
• the electroplating is preferably carried out at a liquid temperature of not higher than 50 °C.
• the base material is preferably made of copper or a copper alloy, and an underlying layer of nickel is preferably formed between the base material and the surface layer.
• a silver-plated product comprising: a base material; and a surface layer of silver which is formed on the base material, the surface layer having an average crystallite size of not greater than 23 nm and having a Vickers hardness HV of 100 to 160, the surface layer containing not less than 0.3 % by weight of carbon, not less than 0.4 % by weight of sulfur and not less than 0.1 % by weight of nitrogen.
• the surface layer preferably contains 90 to 99 % by weight of silver.
• the surface layer preferably contains not higher than 2 % by weight of carbon, and preferably contains not higher than 2 % by weight of sulfur.
• the base material is preferably made of copper or a copper alloy, and an underlying layer of nickel is preferably formed between the base material and the surface layer.
• the present invention it is possible to provide a silver-plated product having a more excellent wear resistance than that of conventional silver-plated products while maintaining the high hardness thereof, and a method for producing the same.
• a surface layer of silver is formed on a base material by electroplating at a liquid temperature of not lower than 30 °C and at a current density of 1 to 15 A/cm 2 in a silver-plating solution which is an aqueous solution containing silver potassium cyanide, potassium cyanide and a mercaptothiazole wherein the concentration of the mercaptothiazole in the silver-plating solution is not lower than 5 g/L.
• a mercaptothiazole is thus added to a silver-plating solution as an organic addition agent, it is considered that it is possible to incorporate the mercaptothiazole into a silver-plating film (a surface layer of silver) by electroplating to suppress the movement of transformation in the silver-plating film to enhance the hardness of the silver-plated product to improve the wear resistance thereof while decreasing the coefficient of friction of the silver-plated product by the lubricating effect of the organic addition agent.
• the mercaptothiazole has a dithioimino carbonate structure to easily dissociate protons thereof to have a high solubility in an aqueous solution to be easily incorporated into the silver-plating film, so that it is possible to improve the deposition rate of the silver-plating film.
• the deposition rage is high, it is possible to improve the abrasion resistance thereof unlike N-allylthiourea and 2-mercaptobenzimidazole.
• the concentration of the mercaptothiazole in the silver-plating solution is preferably not lower than 10 g/L and preferably not higher than 30 g/L (more preferably not higher than 25 g/L) .
• the electroplating for forming the silver-plating layer is preferably carried out at a current density of 2 to 10 A/dm 2 .
• the concentration of silver potassium cyanide in the silver-plating solution is preferably 50 to 200 g/L and more preferably 70 to 180 g/L.
• the concentration of potassium cyanide in the silver-plating solution is preferably 20 to 120 g/L and more preferably 30 to 100 g/L.
• the concentration of silver in the silver-plating solution is preferably 20 to 120 g/L, more preferably 30 to 110 g/L and most preferably 40 to 100 g/L.
• the concentration of free cyanide in the silver-plating solution is preferably 5 to 50 g/L, more preferably 10 to 45 g/L and most preferably 15 to 40 g/L.
• the electroplating for forming the silver-plating layer is preferably carried out at a liquid temperature of not higher than 50 °C , more preferably carried out at a liquid temperature of not higher than 45 °C, and most preferably carried out at a liquid temperature of not higher than 40 °C,
• the base material is preferably made of copper or a copper alloy.
• an underlying layer of nickel is preferably formed between the base material and the surface layer.
• This underlying layer of nickel can be formed by electroplating in a publicly-known nickel-plating bath (preferably a sulfamic acid bath), such as a Watts bath or a sulfamic acid bath.
• the preferred embodiment of a silver-plated product according to the present invention comprises: a base material; and a surface layer of silver which is formed on the base material, the surface layer having an average crystallite size of not greater than 23 nm and having a Vickers hardness HV of 100 to 160, the surface layer containing not less than 0.3 % by weight of carbon, not less than 0.4 % by weight of sulfur and not less than 0.1 % by weight of nitrogen.
• the content of silver in the surface layer is preferably 90 to 99 % by weight, more preferably 92 to 99 % by weight, and most preferably 95 to 99 % by weight.
• the content of carbon in the surface layer is preferably not lower than 0.5 % by weight, and preferably not higher than 2 % by weight (more preferably not higher than 1 % by weight).
• the content of sulfur in the surface layer is preferably not lower than 0.6 % by weight and preferably not higher than 2 % by weight (more preferably not higher than 1.5 % by weight).
• the content of nitrogen in the surface layer is preferably not lower than 0.2 % by weight and preferably not higher than 2 % by weight (more preferably not higher than 1 % by weight and most preferably not higher than 0.5 % by weight).
• the content of potassium in the surface layer is preferably 0.1 to 2 % by weight and more preferably 0.2 to 1 % by weight.
• the ratio (C/S) of the content (atomic concentration at%) of carbon to the content (atomic concentration at%) of sulfur in the surface layer is preferably 1.5 to 2.5.
• the ratio (SIN) of the content (atomic concentration at%) of sulfur to the content (atomic concentration at%") of nitrogen in the surface layer is preferably 1.0 to 2.5.
• the ratio (C/N) of the content (atomic concentration at%) of carbon to the content (atomic concentration at%) of nitrogen in the surface layer is preferably 2.5 to 4.0.
• an underlying layer of nickel is preferably formed.
• a rolled sheet of oxygen-free copper (C1020 1/2H) having a size of 67 mm x 50 mm x 0.3 mm was prepared as a base material (a material to be plated).
• the material and a SUS plate were put in an alkali degreasing solution to be used as a cathode and an anode, respectively, to carry out electrolytic degreasing at 5 V for 30 seconds.
• the material thus electrolytic-degreased was washed with water, and then, pickled for 15 seconds in a 3% sulfuric acid to be washed with water.
• the material thus pretreated and a nickel electrode plate were used as a cathode and an anode, respectively, to electroplate (dull-nickel-plate) the material at a liquid temperature of 55 °C and at a current density of 5 A/dm 2 for 60 seconds in a dull-nickel-plating solution of an aqueous solution containing 540 g/L of nickel sulfamate tetrahydrate, 25 g/L of nickel chloride and 35 g/L of boric acid, while stirring the solution at 500 rpm by means of a stirrer.
• the thickness of the substantially central portion of the dull-nickel-plating film was measured by means of an X-ray fluorescent analysis thickness meter (SFT-110A produced by Hitachi High-Tech Science Corporation). As a result, the thickness was 1 ⁇ m.
• the material having the underlying plating film and a titanium electrode plate coated with platinum were used as a cathode and an anode, respectively, to electroplate the material at a room temperature (25 °C) and at a current density of 2.0 A/dm 2 for 10 seconds in a silver strike plating solution of an aqueous solution containing 3 g/L of silver potassium cyanide (KAg(CN) 2 ) and 90 g/L of potassium cyanide (KCN), while stirring the solution at 500 rpm by means of a stirrer. After a silver strike plating film was thus formed, it was washed with water for sufficiently washing away the silver strike plating solution.
• KAg(CN) 2 aqueous solution containing 3 g/L of silver potassium cyanide
• KCN potassium cyanide
• the silver-strike-plated material and a silver electrode plate were used as a cathode and an anode, respectively, to electroplate (silver-plate) the material at a liquid temperature of 35 ( ⁇ 0.5) °C and at a current density of 3 A/dm 2 for 200 seconds in a silver-plating solution of an aqueous solution containing 80 g/L of silver potassium cyanide (KAg(CN) 2 ), 39 g/L of potassium cyanide (KCN) and 12.4 g/L of 2-mercaptothiazole (a mercaptothiazole) (MT) (the aqueous solution containing 43.4 g/L of silver and 16 g/L of free cyanide), while stirring the solution at 500 rpm by means of a stirrer.
• the silver-plating film thus formed was washed with water, and then, dried with wind pressure by means of an air gun to obtain a silver-plated product.
• the thickness of the substantially central portion of the silver-plating film of the silver-plated product thus obtained was measured by means of the above-described X-ray fluorescent analysis thickness meter. As a result, the thickness was 5 ⁇ m.
• the Vickers hardness HV of this silver-plated product was measured in accordance with JIS Z2244 by applying a measuring load of 10 gf for 10 seconds using a micro-hardness testing machine (HM-221 produced by Mitutoyo Corporation). As a result, the Vickers hardness HV was 151.
• the crystallite sizes in vertical directions to each crystal plane of (111), (200) , (220) and (311) planes of the silver-plating film of the silver-plated product were calculated by the Scherrer's equation from the full-width at half maximum of each of peaks ((111) peak appearing at about 38°, (200) peak appearing at about 44° , (220) peak appearing at about 64° and (311) peak appearing at about 77° ) on the crystal planes on an X-ray diffraction pattern (XRD pattern) obtained by means of an X-ray diffractometer (Full-Automatic Multi-Purpose Horizontal X-ray diffractometer, Smart Lab produced by RIGAKU Corporation).
• XRD pattern X-ray diffraction pattern
• the calculated crystallite sizes were weighted on the basis of the orientation ratio of each of the crystal planes to calculate an average crystallite size by the weighted average of the crystallite sizes on the crystal planes.
• the average crystallite size of the silver-plating film was 61.0 angstroms (6.10 nm).
• a silver-plated product was produced by the same method as that in Example 1, except that the electroplating (silver-plating) for forming the silver-plating film was carried out at a current density of 5 A/dm 2 for 120 seconds.
• the thickness of the substantially central portion of the silver-plating film of the silver-plated product thus obtained was measured by the same method as that in Example 1, so that the thickness was 5 ⁇ m.
• the content of carbon in the silver-plated product was calculated by qualitatively and quantitatively measuring CO and CO 2 , which were produced when the silver-plated product was heated to 1350 °C in an oxygen gas stream to be melted, by an infrared detector by means of a carbon/sulfur analyzer (EMIA-810 produced by HORIBA, Ltd.).
• the content of sulfur in the silver-plated product was calculated as the content of sulfur in the silver-plating film by qualitatively and quantitatively measuring SO 2 , which was produced when the silver-plated product was heated to 1350 °C in an oxygen gas stream to be melted, by the infrared detector.
• the content of nitrogen in the silver-plated product was calculated as the content of nitrogen in the silver-plating film by quantitatively measuring N 2 , which was produced when the silver-plated product was melted in a helium gas stream by an electric power of 5000 W, by a thermal conductivity detector (TCD) by means of an oxygen/nitrogen/hydrogen analyzer (produced by LECO JAPAN CORPORATION).
• the obtained silver-plated product was dissolved in nitric acid (reagent for accurate analysis), it was diluted so as to cause the concentration of potassium in this nitric acid solution not to be higher than 2 mg/L. Then, the content of potassium in the silver-plated product was measured by an atomic absorption photometer (Deflection Zeeman Atomic Absorption Photometer ZA3300 produced by Hitachi High-Tech Science Corporation). The contents of silver, carbon, sulfur, nitrogen and potassium in the silver-plated product were regarded as the contents of silver, carbon, sulfur, nitrogen and potassium in the silver-plating film, since the contents of silver, carbon, sulfur, nitrogen and potassium in the base material were not greater than detection limit although they were obtained by the same methods as the above-described methods before the silver-plating film was formed.
• the silver-plating film was a film containing 0.7 % by weight of carbon, 1.1 % by weight of sulfur, 0.2 % by weight of nitrogen, 0.2 % by weight of potassium and the balance being silver (Ag purity: 97.8 % by weight) assuming that the total of the contents of silver, carbon, sulfur, nitrogen and potassium was 100 % by weight.
• the measurement of the Vickers hardness HV of the silver-plating film, the evaluation of the wear resistance thereof and the calculation of the crystallite sizes thereof were carried out by the same methods as those in Example 1.
• the Vickers hardness HV was 129. It was confirmed that the base material was not exposed after the reciprocating sliding movement was repeated 1,000 times, so that it was found that the wear resistance thereof was good.
• the average crystallite size of the silver-plating film was 148.7 angstroms (14.87 nm).
• a silver-plated product was produced by the same method as that in Example 1, except that a silver-plating solution of an aqueous solution containing 175 g/L of silver potassium cyanide (KAg(CN) 2 ), 95 g/L of potassium cyanide (KCN) and 18.5 g/L of 2-mercaptothiazole (a mercaptothiazole) (MT) (the aqueous solution containing 94.9 g/L of silver and 38 g/L of free cyanide) was used as the silver-plating solution and that the electroplating (silver-plating) for forming the silver-plating film was carried out at a current density of 5 A/dm 2 for 120 seconds.
• the thickness of the substantially central portion of the silver-plating film of the silver-plated product thus obtained was measured by the same method as that in Example 1, so that the thickness was 5 ⁇ m.
• the surface analysis of the silver-plating film of this silver-plated product was carried out by the same method as that in Example 2.
• the measurement of the Vickers hardness HV of the silver-plating film, the evaluation of the wear resistance thereof and the calculation of the crystallite sizes thereof were carried out by the same methods as those in Example 1.
• the Vickers hardness HV was 129. It was confirmed that the base material was not exposed after the reciprocating sliding movement was repeated 1,000 times, so that it was found that the wear resistance thereof was good.
• the average crystallite size of the silver-plating film was 109.1 angstroms (10.91 nm).
• a silver-plated product was produced by the same method as that in Example 3, except that the electroplating (silver-plating) for forming the silver-plating film was carried out at a current density of 7 A/dm 2 for 86 seconds.
• the thickness of the substantially central portion of the silver-plating film of the silver-plated product thus obtained was measured by the same method as that in Example 1, so that the thickness was 5 ⁇ m.
• the surface analysis of the silver-plating film of this silver-plated product was carried out by the same method as that in Example 2.
• the measurement of the Vickers hardness HV of the silver-plating film, the evaluation of the wear resistance thereof and the calculation of the crystallite sizes thereof were carried out by the same methods as those in Example 1.
• the Vickers hardness HV was 147. It was confirmed that the base material was not exposed after the reciprocating sliding movement was repeated 200 times, so that it was found that the wear resistance thereof was good.
• the average crystallite size of the silver-plating film was 175.7 angstroms (17.57 nm).
• a silver-plated product was produced by the same method as that in Example 1, except that a silver-plating solution of an aqueous solution containing 175 g/L of silver potassium cyanide (KAg(CN) 2 ), 95 g/L of potassium cyanide (KCN) and 70 mg/L of selenium (the aqueous solution containing 94.9 g/L of silver and 38 g/L of free cyanide) was used as the silver-plating solution and that the electroplating (silver-plating) for forming the silver-plating film was carried out at a liquid temperature of 18 ( ⁇ 0.5) °C and at a current density of 5 A/dm 2 for 120 seconds.
• a silver-plating solution of an aqueous solution containing 175 g/L of silver potassium cyanide (KAg(CN) 2 ), 95 g/L of potassium cyanide (KCN) and 70 mg/L of selenium the aqueous solution containing 94.9 g/L of silver and 38
• the thickness of the substantially central portion of the silver-plating film of the silver-plated product thus obtained was measured by the same method as that in Example 1, so that the thickness was 5 ⁇ m.
• the surface analysis of the silver-plating film of this silver-plated product was carried out by the same method as that in Example 2.
• the silver-plating film was a film containing not higher than 0.1 % by weight of carbon and the balance being silver (Ag purity: not less than 99.9 % by weight).
• the measurement of the Vickers hardness HV of the silver-plating film, the evaluation of the wear resistance thereof and the calculation of the crystallite sizes thereof were carried out by the same methods as those in Example 1.
• the Vickers hardness HV was 134. It was confirmed that the base material was exposed after the reciprocating sliding movement was repeated 80 times, so that it was found that the wear resistance thereof was not good.
• the average crystallite size of the silver-plating film was 278.0 angstroms (27.80 nm).
• a silver-plated product was produced by the same method as that in Example 1, except that a silver-plating solution of an aqueous solution containing 148 g/L of silver potassium cyanide (KAg(CN) 2 ), 140 g/L of potassium cyanide (KCN) and 8 mg/L of selenium (the aqueous solution containing 80.2 g/L of silver and 56 g/L of free cyanide) was used as the silver-plating solution and that the electroplating (silver-plating) for forming the silver-plating film was carried out at a liquid temperature of 16 ( ⁇ 0.5) °C and at a current density of 8 A/dm 2 for 75 seconds.
• a silver-plating solution of an aqueous solution containing 148 g/L of silver potassium cyanide (KAg(CN) 2 ), 140 g/L of potassium cyanide (KCN) and 8 mg/L of selenium the aqueous solution containing 80.2 g/L of silver and 56
• the thickness of the substantially central portion of the silver-plating film of the silver-plated product thus obtained was measured by the same method as that in Example 1, so that the thickness was 5 ⁇ m.
• the measurement of the Vickers hardness HV of the silver-plating film, the evaluation of the wear resistance thereof and the calculation of the crystallite sizes thereof were carried out by the same methods as those in Example 1.
• the Vickers hardness HV was 82. It was confirmed that the base material was exposed after the reciprocating sliding movement was repeated 50 times, so that it was found that the wear resistance thereof was not good.
• the average crystallite size of the silver-plating film was 750.0 angstroms (75.00 nm).
• a silver-plated product was produced by the same method as that in Example 1, except that a silver-plating solution of an aqueous solution containing 115 g/L of silver potassium cyanide (KAg(CN) 2 ), 60 g/L of potassium cyanide (KCN) and 40 mg/L of selenium (the aqueous solution containing 62.3 g/L of silver and 24 g/L of free cyanide) was used as the silver-plating solution and that the electroplating (silver-plating) for forming the silver-plating film was carried out at a liquid temperature of 25 ( ⁇ 0.5) °C and at a current density of 2 A/dm 2 for 300 seconds.
• a silver-plating solution of an aqueous solution containing 115 g/L of silver potassium cyanide (KAg(CN) 2 ), 60 g/L of potassium cyanide (KCN) and 40 mg/L of selenium the aqueous solution containing 62.3 g/L of silver and 24
• the thickness of the substantially central portion of the silver-plating film of the silver-plated product thus obtained was measured by the same method as that in Example 1, so that the thickness was 5 ⁇ m.
• the measurement of the Vickers hardness HV of the silver-plating film, the evaluation of the wear resistance thereof and the calculation of the crystallite sizes thereof were carried out by the same methods as those in Example 1.
• the Vickers hardness HV was 119. It was confirmed that the base material was exposed after the reciprocating sliding movement was repeated 100 times, so that it was found that the wear resistance thereof was not good.
• the average crystallite size of the silver-plating film was 636.0 angstroms (63.60 nm) .
• a silver-plated product was produced by the same method as that in Example 1, except that a silver-plating solution of an aqueous solution containing 40 g/L of silver potassium cyanide (KAg(CN) 2 ), 39 g/L of potassium cyanide (KCN) and 1 g/L of N-allylthiourea (the aqueous solution containing 21.7 g/L of silver and 16 g/L of free cyanide) was used as the silver-plating solution and that the electroplating (silver-plating) for forming the silver-plating film was carried out at a liquid temperature of 25 ( ⁇ 0.5) °C and at a current density of 0.7 A/dm 2 for 857 seconds.
• a silver-plating solution of an aqueous solution containing 40 g/L of silver potassium cyanide (KAg(CN) 2 ), 39 g/L of potassium cyanide (KCN) and 1 g/L of N-allylthiourea the aqueous solution
• the thickness of the substantially central portion of the silver-plating film of the silver-plated product thus obtained was measured by the same method as that in Example 1, so that the thickness was 5 ⁇ m.
• the measurement of the Vickers hardness HV of the silver-plating film, the evaluation of the wear resistance thereof and the calculation of the crystallite sizes thereof were carried out by the same methods as those in Example 1.
• the Vickers hardness HV was 61. It was confirmed that the base material was exposed after the reciprocating sliding movement was repeated 30 times, so that it was found that the wear resistance thereof was not good.
• the average crystallite size of the silver-plating film was 455.6 angstroms (45.56 nm).
• a silver-plated product was produced by the same method as that in Example 3, except that the electroplating (silver-plating) for forming the silver-plating film was carried out at a liquid temperature of 25 ( ⁇ 0.5) °C and at a current density of 5 A/dm 2 for 120 seconds.
• the thickness of the substantially central portion of the silver-plating film of the silver-plated product thus obtained was measured by the same method as that in Example 1, so that the thickness was 5 ⁇ m.
• the surface analysis of the silver-plating film of this silver-plated product was carried out by the same method as that in Example 2.
• the measurement of the Vickers hardness HV of the silver-plating film, the evaluation of the wear resistance thereof and the calculation of the crystallite sizes thereof were carried out by the same methods as those in Example 1.
• the Vickers hardness HV was 131. It was confirmed that the base material was exposed after the reciprocating sliding movement was repeated not higher than 60 times, so that it was found that the wear resistance thereof was not good.
• the average crystallite size of the silver-plating film was 257.4 angstroms (25.74 nm).
• a silver-plated product was produced by the same method as that in Example 3, except that the electroplating (silver-plating) for forming the silver-plating film was carried out at a liquid temperature of 25 ( ⁇ 0.5) °C and at a current density of 7 A/dm 2 for 86 seconds.
• the thickness of the substantially central portion of the silver-plating film of the silver-plated product thus obtained was measured by the same method as that in Example 1, so that the thickness was 5 ⁇ m.
• the surface analysis of the silver-plating film of this silver-plated product was carried out by the same method as that in Example 2.
• the measurement of the Vickers hardness HV of the silver-plating film, the evaluation of the wear resistance thereof and the calculation of the crystallite sizes thereof were carried out by the same methods as those in Example 1.
• the Vickers hardness HV was 145. It was confirmed that the base material was exposed after the reciprocating sliding movement was repeated not higher than 60 times, so that it was found that the wear resistance thereof was not good.
• the average crystallite size of the silver-plating film was 269.8 angstroms (26.98 nm).
• Table 1 Silver-Plating Solution KAg(CN) 2 (g/L) KCN (g/L) MT (g/L) N-allyl thio urea (g/L) Se (mg/L) Ag (g/L) Free Cyanide (g/L) Ex.

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  • 2022-05-27 EP EP22832665.8A patent/EP4317536A4/fr active Pending

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