Guest Editorial
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Don Baudrand, Don Baudrand Consulting, e-mail:donwb@tscnet.com
Editorial
“NEW DEVELOPMENTS IN PLATING” is a talk I gave April 1, 1989 at the “AESF Golden
West Regional " conference.
Many of the items were known and used at the time of the writing; some were not
yet started commercially. Let’s see were we stand today.
Introduction
New developments can be triggered by many different events. For example:
Products are developed to fill a specific need such as protection of a
particular metal or alloy; or to form a hard surface on a softer material; or to
color a surface and many more triggers. Products and/or processes may be
developed to respond to a safety or environmental consideration or a government
regulation, which may cause traditional products to become obsolete, outlawed or
no longer useful. Then there are the accidental discoveries made when
researchers are looking for something else. This paper deals with a few new
developments. (I don’t know all of them, nor do I have time or paper to discuss
all that I do know. I hope the ones I have chosen will spark some interest.) I
consider new developments to be a look into the future. (November 8, 2005,
compared with April I, 1989, 16 and ¾ years later)
Chrome Replacement
The EPA’s Final Report #PB 85—115905, “Health Assessment Document For Chromium,”
documented that hexavalent chromium has been shown to cause mutations by causing
problems with DNA(1): “Therefore, long known as a material that can cause or
contribute or contribute to dermatitis, breathing problems and cancer, is also a
possible cause of birth defects.”
It is not difficult to predict that the reduction or elimination of hexavalent
chrome plating and conversion coatings is in sight.
How can chrome plating be replaced or reduced in use? Several possible
substitutes are now available with no doubt more to come as the pressure mounts
to remove hexavalent from plating shops.
Trivalent chrome plating is gaining popularity for decorative chrome plating,
and or hard chrome applications.
Electroless nickel can offer applications in many areas where hard chrome is now
used Electroless nickel can be hardened to give a good wear surface. It can be
plated Bright to produce a reflective surface.
Electroless nickel has already served to replace hard chrome in many
applications. For example plated drills and taps, rolls for printing, rolls and
guides for moving materials such as in textile production, bearings and
journals, and so on. The characteristics of electroless nickel deposits from
certain nickel phosphorus and nickel boron solutions are similar to hard chrome
in wear, abrasion, coefficient of surface friction and abrasion resistance, and
electroless nickel is superior to chromium in many corrosive environments.
Also contending as chrome replacements are plasma spray and detonation spray
processes. Many materials, including hard metals, stainless steel, and even
ceramics can be deposited this way. Ion implantation is another contender, along
with laser surface modifications.
Cadmium plating is disappearing. The toxicity of cadmium and the difficulty in
waste treating the effluents to meet the new standards have caused people to try
to find substitute materials. MIL-Std-186D “Protective Finishes for Army Missile
Systems” states, “4.16 Cadmium plating shall be restricted to essential
applications only.” “Use zinc plating, tin plating or aluminum coating instead
Tin plating is not likely to be satisfactory since it is not very protective,
However, some tin-containing alloys may be suitable. Zinc, zinc-nickel and
aluminum be ion vapor deposition have been used to replace cadmium in some
applications. New, better alloys are needed to completely fill the need. Boeing
has a patented zinc-nickel process for license that claims equivalent or better
corrosion protection to that of cadmium. Because of the low couple to aluminum,
electroless nickels are used for some cadmium replacement.
Zinc from the newest technology: non-cyanide alkaline plating solutions is
finding wide application. Its superior covering and throwing power, low cost and
ease of waste treatment along with ease of control makes it a likely candidate
to replace most cyanide zinc solutions. The newer acid chloride zinc processes
afford good protection and bright decorative deposits.
Pulse plating is opening doors to better plate distribution for some metal
deposits. But more importantly, pulse-plating devices can allow alloys to be
plated that would not produce satisfactory deposits using D.C. plating. Examples
are: Au-Fe, Cr-Fe, Ni-Fe, Co-Ni-Fe, Cr-Fe-Ni, Fe-Ni-Ti, etc.(2) Further, control
of the structure of the deposits is possible. For example, “super-lattice”
alloys can be produced and ductile amorphous alloys can also be produced. This
is an area of the leading edge of plating technology.
Metals and alloys of these metals that have been reported using pulse plating
are: germanium, Indium, Lanthanum, Lithium, Magnesium, manganese, Molybdenum,
Ruthenium, Antimony, Selenium, Tellurium (3&4), Titanium, Thallium, Zinc and
Zirconium.
EMI Shielding, although not new, is becoming essential to electronic devices.
Plated (electroless copper and electroless nickel) offer many advantages. All
types of electronic device containers must have shielding properties. Plated
ceramic micro-spheres to include in resins used to coat non-conductors, provide
excellent shielding properties. Electroless nickel provides shielding, but by
its self may not be conductive enough for low contact resistance. A thin gold
layer over EN-P or nickel- boron offer solutions to these problems.
Electronic connector makers are exploring and producing, on a small scale,
plastic connectors plated with about 1 mil of electroless nickel. This emerging
technology is expected to grow. The advantage is in its corrosion resistance.
Co-depositing solid materials with electroplating and electroless plating is
moving into new territory. For example, codeposited fluorescent pigments that
color-plated copper, zinc, nickel and EN have been reported. Codeposited
polymers such as PTFE and others import low surface friction properties.
Waste treatment of plating and processing solutions is of great importance now
and increasingly so in the future. Process chemicals that are easier or less
expensive to treat will find a place in our industry.
Toxic materials are of concern in terms of the safely and well being of plating
personnel as well as concern for the high cost of the liability they represent.
There is a trend toward the use of non-toxic or less toxic chemicals.
References:
1. E. C. Groshart, SurFin’88, Los Angeles L-6 June 1988
2. Metal Finishing, Vol.87, No. 1., Page 45, Jan 1989
3. “Electrodeposition of Tellurium from sulfate Eletrolyte in an Ultrasonic
field,” R.H. Hadgrove, KR Rasulor, Elektrokhimiya 8(12), 1843-5
4. “Effect of electrolysis Conditions on the Properties of Tellurium
Electroplate from Hydrochloric acid Baths” VM Bigelis, GN Kim, LV Navalikhin, M
Kalanov, OA Abrarov. Elektrokhimiya 18(11), 1458-61.