电解金属沉积物的粘附

A study of the conditions which determine the adherence  of one metal electrolytically deposited upon another is an interesting and promising field of research from the scientific standpoint, as well as of importance from the technical standpoint. It is not the purpose of this paper to present instructions as to how adherent deposits may be attained, but rather to  call attention to some of the problems which are worthy of  scientific investigation and the solution of which will have a  bearing upon practical applications,  The value of an electro-deposited metal is determined by its  degree of adherence to the surface upon which it is deposited,  and upon the physical conditions or structures that the molecules  assume during the process of deposition.  The adherence is governed by various factors, some of  which are well understood and others of which offer promising  lines for research. The metal surface which is to receive the  deposit should have, in the greatest degree, that property which  Wesley has defined as (( next to godliness )). The surface should  be clean ; not only apparently, but actually free from all foreign  materials. Surfaces which may pass inspection of the eye, may  not meet the tests of the electroplating tank, and appearances  alone are here, as in many other cases, frequently deceptive.  Everything on the metal surface, whether it be visible oxide,  grease and scale, or invisible and transparent layers of oil,  hydroxides, or other chemical compounds, and even films of gas,  may be considered as dirt in accordance with that definition  which defines it as " matter in the wrong place )). The cleaning  of the surface is an operation requiring the utmost care of the  operator, and the work thereby involved constitutes the largest  item of expense in the operation of an electroplating plant.

The methods of preparing the surface may be, for convenience, divided into the mechanical, physical, chemical and electrolytic methods. The mechanical means include grinding,  scouring, and the use of abrasives and sand blast. The physical  methods include burning, and dissolving by means of. solvents,  such as gasoline, alcohol, and the like. The chemical methods  make use of the acids, alkalies, cyanides, and various other  materials which act che‘mically upon the materials to be removed, making them sduble or changing the nature of them  in such a manner that they may be readily removed by mechanical means.  Disadvantages which are attendant upon chemical methods  in common use are due to the deleterious action of the acids upon  the metal to be plated, to the penetration of the acid into the  pores of the metal with the consequent difficulty of complete removal, and to the liberation of hydrogen and other gases which  may be absorbed by the metal. The acid dip which is almost  invariably used where steel is to be plated upon, in some instances affects the physical property of the steel to such an extent that certain grades of steel sheet and wire cannot be plated.  The finest grades of steel wire are so seriously affected by the  chemical treatment, commonly deemed necessary in preparation  for plating, that its strength and elasticity are greatly reduced.  To just what this (( rotting ” is due is perhaps not definitely  known. It cannot be ascribed entirely to the removal of a thin  layer of the surface metal, or to the penetration of the acid into  the metal, and the absorption of hydrogen is assumed by some to  be the cause of the deterioration.