Immersion silver

For simplicity a cell consisting of two identical electrodes of silver immersed in silver nitrate solution will be considered first (Fig. 1.20a), i.e. Agi/AgNOj/Ag,. On open circuit each electrode will be at equilibrium, and the rate of transfer of silver ions from the metal lattice to the solution and from the solution to the metal lattice will be equal, i.e. the electrodes will be in a state of dynamic equilibrium. The rate of charge transfer, which may be regarded as either the rate of transfer of silver cations (positive charge) in one direction, or the transfer of electrons (negative charge) in the opposite direction, in an electrochemical reaction is the current I, so that for the equilibrium at electrode I... 

Such silver can be rather difficult to clean without abrasives (which wear away the metal). The following is a simple electrochemical means of cleaning the silver immerse the tarnished silver in a saucer of electrolyte, such as salt solution or vinegar, and wrap it in a piece of aluminium foil. Within a few minutes the silver is cleaner and bright, whereas the aluminium has lost some of its shininess. 

The potential of oxygen over platinum responded nicely to changes in oxygen pressure according to the Nernst expression (5). The reference electrode was silver immersed in 0 1M silver nitrate in the fused alkali nitrates, the mixture being contained in a thin glass envelope. To test the effect of changes in oxide ion concentration on the potential, a source of pure alkali oxide was needed. It is also ulti-... 

Reversible metallic electrodes immersed in solutions of varying concentrations of their salts are termed electrodes of the first kind. Reversible electrodes of the second kind are metallic electrodes immersed in a saturated solution of a sparingly soluble salt, whose solubility is determined by the concentration of a soluble salt with the same anion. Metallic silver immersed in KCl solution saturated with AgCl is an electrode of the second kind. The concentration of the Ag ions in the solution is determined by the concentration of the Cl ions, i.e. of the KCl. In a galvanic cell made up of two such electrodes, the current... 

The effect of time of the silver immersion plating on the SERS signal for meso- and macro-PS is demonstrated in Fig. 2. 

Antitamish and preflux Immersion silver Immersion tin Electroless palladium (Pd)... 

Immersion silver Immersion silver is relatively benign to the solder mask, and few, if any, issues are known as of the writing of this book. 

There are a number of other surface finishes used in the industry, such as Electroless Nickel Electroless Palladium Immersion Gold (NiPdAu), Immersion Silver, Immersion Gold, Immersion Tin, OSP and Electrolytic Nickel Gold. There are reliability and process trade offs with each surface finish. That is why it is recommended that strain/strain rate characterization and thermal cycling be performed for each set of surface finish before it is selected for the specific end-use conditions in which it will be used. The industry test methods used to evaluate different surface finishes are outlined in detail in the next chapter. 

No-clean solder pastes can solder most popular metal finishes adequately due to improvements in the activator packages. Gold over nickel, bare copper with organic surface preservatives, silver immersion, tin plates, and hot-air leveled boards are popular, while component terminations such as tin, tin/lead, silver, silver palladium, and nickel are used. Solder pastes can be designed to solder specific surfaces and maintain the non-corrosive and electrical resistance required to qualify them as no-clean pastes. 

When soldered, SAC alloys will wet the metallization at substantially reduced rates when compared to 63/37. Solderability is impacted by the speed of wetting and the degree of spread. Pure tin finishes are the most suitable to solder with SAC alloys. Bare copper OSP usually gives the poorest results, especially on assemblies that have seen a previous thermal process. Silver immersion and Ni-Au finishes give values between tin and copper, and are common lead-free choices. 

The surface finishes selected were Immersion Silver, Immersion Tin, two HASL (lead-free) and four Organic Surface Protections (OSPs). Four solder alloys were planned for testing, but two were eliminated due to cost, leaving SACX and Sn/Cu/Ni. Five fluxes were evaluated, two of which were chosen because they were commonly used in other experiments. 

HASL OSP Immersion silver Immersion tin Electroless Ni/Pd Ni/immersion Ag (ENIG) Ni/Pd + Au flash... 

Flux Rinses Immersion silver Immersion tin Pd catalyst Pd catalyst Pd catalyst... 

Finally, other tests to control jet fuel corrosivity towards certain metals (copper and silver) are used in aviation. The corrosion test known as the copper strip (NF M 07-015) is conducted by immersion in a thermostatic bath at 100°C, under 7 bar pressure for two hours. The coloration should not exceed level 1 (light yellow) on a scale of reference. There is also the silver strip corrosion test (IP 227) required by British specifications (e.g., Rolls Royce) in conjunction with the use of special materials. The value obtained should be less than 1 after immersion at 50°C for four hours. 

A typical Ag/AgCl electrode is shown in figure 11.9 and consists of a silver wire, the end of which is coated with a thin film of AgCl. The wire is immersed in a solution that contains the desired concentration of KCl and that is saturated with AgCl. A porous plug serves as the salt bridge. The shorthand notation for the cell is... 

Bronze disease necessitates immediate action to halt the process and remove the cause. For a long time, stabilization was sought by removal of the cuprous chloride by immersing the object in a solution of sodium sesquicarbonate. This process was, however, extremely time-consuming, frequentiy unsuccesshil, and often the cause of unpleasant discolorations of the patina. Objects affected by bronze disease are mostiy treated by immersion in, or surface appHcation of, 1 H-henzotriazole [95-14-7] C H N, a corrosion inhibitor for copper. A localized treatment is the excavation of cuprous chloride from the affected area until bare metal is obtained, followed by appHcation of moist, freshly precipitated silver oxide which serves to stabilize the chloride by formation of silver chloride. Subsequent storage in very dry conditions is generally recommended to prevent recurrence. 

This conversion is normally accompHshed by immersion, but spraying, swabbing, bmshing, and electrolytic methods are also employed (178) (see Metal SURFACE treatments). The metals that benefit from chromium surface conversion are aluminum, cadmium, copper, magnesium, silver, and 2inc. Zinc is the largest consumer of chromium conversion baths, and more formulations are developed for 2inc than for any other metal. 

The ideal electroless solution deposits metal only on an immersed article, never as a film on the sides of the tank or as a fine powder. Room temperature electroless nickel baths closely approach this ideal electroless copper plating is beginning to approach this stabiHty when carefully controUed. Any metal that can be electroplated can theoretically also be deposited by electroless plating. Only a few metals, ie, nickel, copper, gold, palladium, and silver, are used on any significant commercial scale. 

Tsai then applied thick films of the polyamic acid of PMDA and 4-BDAF to polished silver substrates and thermally imidized the films. The substrates were immersed into liquid nitrogen, causing the films to delaminate and XPS was used to examine the polyimide and silver fracture surfaces (see Fig. 33). The C(ls) spectra of the silver fracture surface were very similar to those of neat polyamic acid, indicating that imidization was inhibited by interaction of the polyamic acid with the silver substrate. This was evident from the observation of two peaks near... 

A piece of pure metallic sodium about half the size of a pea is dropped into 0-5 c.c. of the oil in a dry test tube, and heated until all chemical action has ceased. The test tube and contents are immersed whilst still hot in 10 c.c. of distilled water in a porcelain dish. The solution is. filtered, acidulated with nitric acid, and silver nitrate solution added. Any turbidity or opalescence indicates the presence of chlorine compounds. 

Figure 3.6-1 The electrochemical window of 76-24 mol % [BMMIM][(CF3S02)2N]/Li [(Cp3S02)2N] binary melt at a) a platinum working electrode (solid line), and b) a glassy carbon working electrode (dashed line). Electrochemical window set at a threshold of 0.1 mA cm. The reference electrode was a silver wire immersed in 0.01 m AgBp4 in [EMIM][BF4] in a compartment separated by a Vicor frit, and the counter-electrode was a graphite rod.

In the previous example of an electrolytic cell the two electrodes were immersed in the same solution of silver nitrate, and the system was therefore thermodynamically at equilibrium. However, if the activities of Ag at the electrodes differ, the system is unstable, and charge transfer will occur in a direction that tends to equalise the activities, and equilibrium is achieved only when they are equal. 

Fig. 10.41 Silver/silver chloride half-cell (Admirally patiern). The elecirode is immersed in a chloride-containing solution which diffuses through the porous pot and thus comes into contact...

Chemical reduction is used extensively nowadays for the deposition of nickel or copper as the first stage in the electroplating of plastics. The most widely used plastic as a basis for electroplating is acrylonitrile-butadiene-styrene co-polymer (ABS). Immersion of the plastic in a chromic acid-sulphuric acid mixture causes the butadiene particles to be attacked and oxidised, whilst making the material hydrophilic at the same time. The activation process which follows is necessary to enable the subsequent electroless nickel or copper to be deposited, since this will only take place in the presence of certain catalytic metals (especially silver and palladium), which are adsorbed on to the surface of the plastic. The adsorbed metallic film is produced by a prior immersion in a stannous chloride solution, which reduces the palladium or silver ions to the metallic state. The solutions mostly employed are acid palladium chloride or ammoniacal silver nitrate. The etched plastic can also be immersed first in acidified palladium chloride and then in an alkylamine borane, which likewise form metallic palladium catalytic nuclei. Colloidal copper catalysts are of some interest, as they are cheaper and are also claimed to promote better coverage of electroless copper. 

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