Looking Back - The 24th William Blum Lecture
This article is a re-publication of the 24th William Blum Lecture, presented at the 70th AES Annual Convention in Indianapolis, Indiana, on June 27, 1983. A career retrospective of Mr. Pearlstein’s works, the lecture covered work on electroless plating, chromate conversion coatings, double-layer phenomena and dealing with cyanide wastes.
Recipient of the 1982 William Blum
AES Scientific Achievement Award
Editor’s Note: Originally published as Plating & Surface Finishing, 70 (10) 42-16 (1983 and 70 (11), 36-41 (1983), this article is a re-publication of the 24th William Blum Lecture, presented at the 70th AES Annual Convention, SUR/FIN 1983, in Indianapolis, Indiana on June 27, 1983. Originally published in two parts, the lecture was a career retrospective of Mr. Pearlstein’s works. The first part covered work on electroless plating, chromate conversion coatings and double-layer phenomena. The second was devoted to work on dealing with cyanide wastes. A printable PDF version of the complete lecture is available by clicking HERE.
I am honored to have been selected as recipient of the AES Scientific Achievement Award and am most pleased to be able to participate in honoring the memory of Dr. William Blum, whom I was privileged to have known quite well; he was indeed a "giant" in advancing the science and technology of electroplating.
I cannot let this opportunity pass without acknowledging that whatever I've been able to accomplish in my career is in large measure owed to my dear wife, Roslyn, for her constant understanding, support and kindness, during the past 27 years. I also wish to thank the AES Philadelphia Branch for the friendships and support and would like to express my gratitude for having had the privilege and pleasure of working with the highly talented AES headquarters staff and society members around the country in association with the AES Education Committee, Intensive Training Course, CEF program, etc.
As the title of this paper implies, I am taking this opportunity to look back over some of my past projects related to plating and surface finishing, not to rehash the old studies, but to focus on some sidelights and highlights of the investigations - some hitherto unpublished in the open literature - that may be of interest.
I can trace my introduction to plating to about 1953 when investigating processes for metallizing plastic dipoles of proximity fuses. I had been intrigued by Brenner's electroless deposition process1 and found that PdCl2 solutions could be used to activate nonconductors for initiating electroless nickel deposition. It seems very mundane now but one of the thrills of my life was observing a piece of white polystyrene initiate gas bubble formation and miraculously become coated with a metallic nickel deposit. Adsorption of a catalytically active species was accomplished by immersion in a warm PdCl2/HCl solution at pH about 4.3, the Tyndall effect indicated presence of a colloid. Unfortunately, this solution had a relatively short useful life, as palladium salt, presumably hydroxide, would soon precipitate out. Certain agents such as gelatin were helpful in temporarily retarding this effect. Immersion in a SnCl2 solution prior to immersion in an acidic PdCl2 bath was a more effective means of activating nonconductors for electroless deposition.2 However, the Shipley colloidal Pd activator3 proved most suitable for commercial use, particularly in the printed circuit industry. Virtually any nonconductor that did not dissolve in the electroless bath could be successfully activated for electroless deposition. An exception was a material identified as "mica-filled phenolic," which resisted all efforts at activation even when visible palladium films were produced on the surface. Apparently, this material contained a potent catalytic poison that prevented successful deposition. Though the phenomenon was not investigated further, it indicated the possibility of preventing deposition where unwanted (e.g., on racks) by incorporating catalytic poisons.
My primary responsibility at that time was the development of a practical process for "electrolytic grinding" of tungsten carbide machine tools. It may be of interest to note that the almost unbelievable current density of more than 450 A/in.2* was obtained at about 6 V, owing to rapid movement of electrolyte and close proximity of tungsten carbide anode and periphery of a rotating copper wheel cathode; a single layer of diamonds bonded to the copper wheel separated the anode and cathode. This work was very interesting and led to a rapid and highly cost-effective process for producing carbide form tools,4 but I was drawn by the mystique of electroless deposition and kept returning to it when I could find an excuse to do so.
My work with electroless finishing dealt with nickel alloys, copper alloys, silver, cobalt and palladium, among other metals. The following discussion presents some of the highlights.
Electroless plating baths were modified to enable the deposition of ternary and quaternary alloy deposits in order to increase the variety of chemical, physical and mechanical properties that could be utilized for particular applications.5 Autocatalytically deposited alloys such as Ni-W-P and Ni-Re-P are potentially useful for applications where higher temperature or greater chemical resistance is required than can be obtained from conventional Ni-P deposits. Mallory6 has developed numerous interesting and potentially useful polyalloys. I feel that electroless alloy deposits have not yet been fully developed and exploited.
What follows is a summary of some unpublished work on electroless copper alloys using a primitive bath: 69 g/L Rochelle Salt (tetrahydrate) + 20 g/L NaOH + 13.8 g/L CuSO4 + other metal salts. In addition, 40 mL of 36% HCHO (containing 12.5% methanol as preservative) was added per liter of the above bath. See Table 1 for details and remarks.
It is noteworthy that the addition of chromate had a strong stabilizing effect on the bath yet increased the deposition rate significantly. Electroless copper and alloys readily deposited on clean steel, but the presence of chromate in the bath prevented any deposition on steel, probably by passivation; deposition was not inhibited on palladium-activated surfaces. Perhaps this phenomenon could be utilized to achieve selective deposition. The electroless copper-cobalt alloy was strongly adherent to steel, was lighter in color than would have been expected from the cobalt content, and was considerably more tarnish resistant than normal copper deposits. Cadmium is normally considered a catalytic poison in electroless plating baths but exhibited no such characteristics in the electroless copper bath; deposits contained as much as 18.2% cadmium, as shown in Table 1. Additions of a bath stabilizer such as 2-mercaptobenzothiazole (MBT)7 to the electroless copper alloy baths tended to decrease the concentration of the alloying element in deposits, except for cadmium, which was increased. A bath containing 10 g/L CdCl2 and 12 mg/L MBT produced brassy-appearing deposits containing more than 29% Cd. An electroless copper bath based on DMAB reducing agent was developed that produced adherent strike deposits on steel and could be codeposited with 10% tin.8
Table 1 - Electroless copper alloys.