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
  • C25D3/66—Electroplating: Baths therefor from melts

Definitions

• This invention relates to a method of electroplating aluminum by using a fused salt and has as an object to provide aluminum plated metal sheets having a coating which is dense, adherent and resistant to corrosion by incorporating dehydrating substance on the surface of or in the plating bath whereby aluminum is plated in a moisture-free state.
• Electroplating of aluminum by means of a fused salt bath is usually performed by employing a bath essentially consisting of an aluminum halide incorporating a few other compounds for decreasing its melting point and satisfying other objects.
• aluminum halide is not entirely suitable because not only does it readily sublimate but it is also highly hygroscopic so that an ordinary fused salt bath absorbs moisture and oxygen from the surrounding air to be degraded rapidly and become usuitable for plating. Therefore, in order to obtain satisfactory plating with fused salts it is necessary to control the plating bath so that it can be used over a long period.
• an aluminum halide comprising the essential component of the bath for electroplating aluminum is strongly hygroscopic, so that it is inevitable to introduce into the plating bath absorbed moisture caused by the pretreatment of the articles to be plated or the moisture in the atmosphere. Such moisture acts as the source of oxygen ions, prevents satisfactory precipitation of aluminum, and results in the precipitation of dendritic aluminum which is liable to fall off. Thus, if some substance which can prevent introduction of moisture into the plating bath or which can collect the moisture introduced in the bath were used the above described difficulties could be avoided. We have found that by utilizing a suitable moisture absorbing substance it is possible to increase current efficiency, to prevent precipitation of dendritic aluminum and provide aluminum plating of excellent quality over a long period.
• An object of the present invention is to provide a method of electroplating aluminum in which deterioration of a fused salt bath is minimised.
• a further object of the present invention is to provide a method of electroplating aluminum in which a deten'orated bath may be regenerated.
• Another object of the present invention is to provide a method of electroplating aluminum to obtain an improved quality of plated aluminum.
• a suitable dehydrating substance such as silica gel particles, quartz sand and minute pieces of porous ceramic and the like is added to the surface of or in the plating bath essentially consisting of aluminum chloride.
• the plating operation is then performed in the absence of moisture to provide dense aluminum plating.
• the dehydrating substance utilized in this invention must withstand the high melting temperature of the fused salt, not react with highly reactive fused salt, have a strong aflinity for water, and not affect the plating operation, or the quality of the plating. In addition, it should not be expensive and should readily be regenerated.
• Such dehydrating substance is selected singly or in combination from the group consisting of silica gel particles, granules of silica, quartz sand, minute pieces of porous ceramics, adsol (a kind of sintered activated clay), diatomaceous earth, charcoals, graphite, carbon black, alumina gel particles, glass particles, glass fibers, asbestos, powder of anorthite, calcium sulphate, fluorspar, zeolite, acid clay, pumice stone and alumina particles.
• adsol a kind of sintered activated clay
• EXAMPLE I 30 g. of quartz sand prepared by heating it in vacuum by electron bombardment and made sufiiciently dehydrating were added to 1 liter (1.7 kg.) of a fused plating bath having a composition of 60 mol percent of aluminum chloride and 40 mol percent of sodium chloride. This had been before-hand left to stand in the atmosphere for such a long period that it caused to precipitate dendritic aluminum and make no use for an ordinary aluminum plating process. After adjusting the mixture, plating operation was again commenced. Plating ability was gradually recovered with time until finally a steel plate having a dense aluminum plating was obtained at a high current efficiency of more than 80%. The latter value is comparable to that of a fresh bath.
• EXAMPLE II 30 g. of heated and dehydrated silica gel particles were floated on the surface of one liter (1.7 kg.) of an electro'lytic bath consisting of 60 mol percent of aluminum chloride and 40 mol percent of sodium chloride and this was sealed off from the atmosphere. An aluminum plate was dipped in this bath and the bath was repeatedly used to plate aluminum on steel plates. With this bath, dense aluminum platings were obtained at high current densities of more than 80%, as in the initial stage of a plating operation even after one week.
• EXAMPLE III One liter of fused salt bath consisting of 60 mol percent of A101 and 40 mol percent of NaCl was prepared and placed in a beaker. A 50 x 100 mm. aluminum plate acting as the anode electrode was placed at the middle of the beaker and a 50 x 100 x 0.18 mm. steel plate to be plated was suspended in the bath opposite the anode electrode at a distance of 48 mm. Plating operations of ten minutes each were continuously repeated for four days at a current of 2 amps and voltages from 280 to 320 mv. During this period there were some rainy days so that the bath greatly deteriorated. Continuous plating under these conditions resulted in the following current efliciencies (in percent) of deposition: 39.4, 39.3, 51.2, 58.2, 60.6, 63.4, 62.0, 56.3, 47.5.
• the color of the plated surface was grey and the surface appearance was coarse, which showed that the quality of the plating had degraded owing to a large increase of oxygen ions.
• the resulted plated surface was white, flat and dense. These properties were identical to those of platings obtained from a fresh plating bath.
• the subject matter of this invention lies in the discovery that the basic reason for the deterioration of the plating bath and for inferior plating is the moisture absorbed or introduced into the bath and in a novel method of plating in the absence of moisture.
• aluminum can be plated to iron, copper, titanium, or any other metals which can be electroplated with aluminum and that the composition of the bath is not limited to those illustrated hereinabove.
• silica gel and quartz any other suitable dehydrating or moisture absorbing substances such as porous ceramic can be used as well.
• this invention provides a novel method of aluminum plating capable of producing electroplated articles of good quality at low cost.
• said moisture absorbing substance is a. member or some combination of members selected from the group consisting of silica gel particles, granulates of silica, quartz sand, minute pieces of porous ceramics, adsol (a kind of sintered activated clay), diatomaceous earth, charcoals, graphite, carbon black, alumina gel particles, alumina particles, glass particles, glss fibers, asbestos, powder of 6 anorthite, calcium sulphate, fluorspar, zeolite, acid clay and pumice stone.
• silica gel particles granulates of silica, quartz sand, minute pieces of porous ceramics, adsol (a kind of sintered activated clay), diatomaceous earth, charcoals, graphite, carbon black, alumina gel particles, alumina particles, glass particles, glss fibers, asbestos, powder of 6 anorthite, calcium sulphate, fluorspar, zeolite, acid clay and pumice stone.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Silicon Compounds (AREA)
• Glass Compositions (AREA)

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Citations (2)

• 1967
  • 1967-12-21 GB GB58118/67A patent/GB1202879A/en not_active Expired
  • 1967-12-22 DE DE1621132A patent/DE1621132C3/de not_active Expired
  • 1967-12-26 US US693093A patent/US3470073A/en not_active Expired - Lifetime
  • 1967-12-29 FR FR1549879D patent/FR1549879A/fr not_active Expired
  • 1967-12-29 CH CH1832867A patent/CH485862A/fr not_active IP Right Cessation

Patent Citations (2)

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