Electroplating surface preparation

Decoration Difficult to paint and metallise/electroplate. Surface preparation very important. 

Titanium and titaniiim alloys can be difficult to plate because sm face oxides can prevent good adhesion of the plating with the titanium substrate. Carefiil surface preparation is therefore essential. The type of property improvements (c.g., wear resistance, lubridty, corrosion resistance) varies with the different plating processes, which generally include electrodeposition methods (electroplating). 

Electroplating generally refers to the method of bath electrodeposition, where the part to be plated is made an electrode (the cathode) in an electrochemical cell. ASTM B 481 describes three separate processes for surface preparation and electroplating of titanium and titanium alloys (ASTM B 481, Standard Practice for Preparation of Titanium and Titanium Alloys, The American Society for Ibsting... 

In the metaiiization process, a layer of metal is deposited on plastic films using severai different methods, ranging from vapor deposition to electroplating. When preparing surfaces for adhesion, one must consider the surface differences between the type of Aim substrates, the potential variations of film characteristics within different substrate families, variations with use of the same substrate between vacuum metailizing chambers, and any possible variations within an end-use application, even when using identical films. 

In electroless deposition, the substrate, prepared in the same manner as in electroplating (qv), is immersed in a solution containing the desired film components (see Electroless plating). The solutions generally used contain soluble nickel salts, hypophosphite, and organic compounds, and plating occurs by a spontaneous reduction of the metal ions by the hypophosphite at the substrate surface, which is presumed to catalyze the oxidation—reduction reaction. 

Surfaces. Essentially any electrically conductive surface can be electroplated, although special techniques may be required to make the surface electrically conductive. Many techniques ate used to metalline nonconductive surfaces. These are weU-covered ia the Hterature (3) and can range from coating with metallic-loaded paints or reduced-silver spray, to autocatalytic processes on tin—palladium activated surfaces or vapor-deposited metals. Preparation steps must be optimized and closely controlled for each substrate being electroplated. 

Poor preparation of the substrate can result in loss of adhesion, pitting, roughness, lower corrosion resistance, smears, and stains. Because electroplating takes place at the exact molecular surface of a work, it is important that the substrate surface be absolutely clean and receptive to the plating. In the effort to get the substrate into this condition, several separate steps may be required, and it is in these cleaning steps that most of the problems associated with plating arise. 

Using impedance data of TBN+ adsorption and back-integration,259,588 a more reliable value of <7 0 was found for a pc-Cu electrode574,576 (Table 11). Therefore, differences between the various EffM) values are caused by the different chemical states and surface structures of pc-Cu electrodes prepared by different methods (electrochemical or chemical polishing, mechanical cutting). Naumov etal,585 have observed these differences in the pzc of electroplated Cu films prepared in different ways. 

The major use of sodium cyanamide is in the production of sodium cyanide, a compound that is used extensively in preparing solutions for the electroplating of metals. Another use for NaCN is in extraction processes employed to separate gold and silver from ores as a result of their forming complexes with CN . Sodium cyanide, an extremely toxic compound, is also used in the process known as case-hardening of steel. In this process, the object to be hardened is heated and allowed to react with the cyanide to form a layer of metal carbide on the surface. 

Phosphoric acid is used in many ways that include foods and beverages. It is also used in cleaning metal surfaces, electroplating, fertilizer production, preparing flame-proofing compounds, and other processes in the chemical industry, making it one of the most important of the chemicals of commerce. 

Surface characterization is of vital importance in electroplating processes. First there is the preparation of the surface to receive the plating and the need to know the surface s suitability to receive and its condition after the completion of plating. Then there is the in situ characterization during plating, which is the subject of Chapter 14. 

Smooth platinum, lead dioxide and graphite are anode materials commonly used in electrooxidation processes. All show large overpotentials for oxygen evolution in aqueous solution. Platinum coated titanium is available as an alternative to sheet platinum metal. Stable surfaces of lead dioxide are prepared by electrolytic oxidation of sheet lead in dilute sulphuric acid and can be used in the presence of sulphuric acid as electrolyte. Lead dioxide may also be electroplated onto titanium anodes from lead(Il) nitrate solution to form a non-porous layer which can then be used in other electrolyte solutions [21],... 

Surfaces of finely divided nickel also promote the formation of aniline. A practical route to tlie preparation of electrodes coaled with a finely divided metal involves electroplating nickel onto a cathode from a solution containing a suspension of finely divided Raney nickel (Ni 50% A1 50%) or Devarda copper alloy (Cu 50% A1 45% Zn 5%), Some alloy particles stick to the cathode surface which is then activated by leaching out the aluminium using hot aqueous sodium hydroxide... 

Nickel phosphate is used in coating steel and in treatment of metal surfaces. It also is used to prepare the pigment, nickel yellow for oil and water colors. The compound is used in electroplating also. 

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