C14 or $35 tagged thiourea were used to follow the uptake of C and S into the electroless nickel deposit and to determine adsorption curves for thiourea on nickel and cobalt. Enhancement of the rate of deposition is observed for cobalt but not for nickel. A Raney nickel type of mechanism and an electron transfer mechanism are proposed to explain the results.The effect of thiourea and other sulfur-containing compounds on the rate of the electroless deposition process for acid nickel has previously been described (1, 2). Radiochemical studies of this process utilizing sulfur and carbon tagged thiourea have also been reported (3). None of this previous work has dealt with the effect of thiourea on the electroless deposition of nickel or cobalt from alkaline media. The purpose of the present paper is to broaden these studies into the alkaline region for cobalt and nickel and also to report the results of studies utilizing sulfur and car-_~ bon tagged thiourea in this type of deposition system. EExperimental "e The following systems were studied (i) NiC12.6H20, "~ 30 g/l; NH4C1, 50 g/l; NaH2PO2.H20, 20 g/l; Na cit-~" rate.2H20, 100 g/1. (it) CoC12-6H~O, 30 g/l; NH4C1, 50 g/l; NaH2PO2.HaO, 20 g/l; Na citrate-2H20, 100 g/1. The pH of the system was adjusted to the desired levels with NH4OH.The temperature of the plating systems was maintained at 85 ~ • 2~ by means of an electric heating mantle. The substrates used in this investigation were 1 x 89 in. nickel strips. These substrates were sensitized by previously described techniques (4). Deposits were made at 1-hr periods; agitation of the system was accomplished by mechanical stirring. Measurements of p H were carried out for all experiments using high temperature glass and calomel electrodes.In each experiment the desired amount of C 14 or S 85 thiourea was added to the system. The activity of the solution during deposition and the activity of deposited samples were determined using previously de-36 scribed techniques (3). All nickel substrates were weighed prior to and following deposition to determine the weight of the deposit. All results are re-32 ported as the average of several experimental runs. Results 28The effect of thiourea concentration on the rate of nickel and cobalt deposition from alkaline systems is 24 shown in Fig. 1. Previous work in acid systems has shown a gradual increase in the rate of nickel depo-% -20 sition up to a concentration of about 0.5 rag/liter of thiourea (2). Thiourea concentrations greater than 0.5 rag/liter result in a gradual decrease in the rate L6 until at 1.4 mg/liter, the rate goes to 0. Figure 1 shows that for the electroless deposition of nickel from an alkaline medium, the rate steadily decreases until about 1 mg/liter of thiourea, where there is a very rapid decrease to 0. There is no enhancement of the plating rate due to the addition of thiourea in the 8 alkaline electroless deposition of nickel. The addition of thiourea to an alkaline cobalt electroless system as 4 also seen in Fig. 1 leads to a rate maximum at about 0....

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The effect of thiourea on the electroless nickel deposition reaction has been studied by the use of sulfur‐35 and carbon‐14 labeled thiourea. The amount of sulfur in the deposit was found to be much greater than the amount of carbon, thereby indicating cleavage. The effect of thiourea on the rate of nickel deposition has been shown to be due to two different mechanisms depending on the thiourea concentration. It is proposed that the catalytic substrate acts as a Raney nickel‐type surface. Kinetics studies have been carried out correlating the rate of sulfur inclusion in the deposit with rate of nickel deposition. Mechanisms have been postulated to explain the observed results.

Small quantities of certain addition agents will prevent the codeposition of tungsten with iron, nickel, or cobalt. Data are presented comparing addition agent concentration with the amount of tungsten in a nickel-tungsten codeposit. Polarographic data indicate that addition agents which prevent tungsten codeposition are capable of being adsorbed at a Hg cathode and form complexes with the codepositing metal ion. These complexes are more readily reduced than is the original codepositing species. The cathode potential of the deposition process is lowered to a more positive potential by the addition agent. Structural studies show that the deposit does not consist of alternate layers of tungsten and codeposited metal as is required by the catalytic reduction mechanism. It is shown that the addition agent effect can be explained by a mechanism of codeposition involving complex formation.Many claims have been made for the deposition of pure tungsten from aqueous tungstate solution (1-3). Subsequent investigation of these processes has shown that the deposits always contain iron, nickel, or cobalt (codepositing metal ion) (4), and that deposition ceases when these impurities are exhausted from the plating solution. When no such impurities are present in the plating solution, oxides of tungsten may be deposited at the cathode; however, under these conditions reduction of tungstate to tungsten has not been observed.Many baths have been developed for the codeposition of tungsten with iron, nickel, or cobalt. The most successful of these are the complex ammoniacal baths which have been developed by Brenner (5) and by Holt (6). Brenner's baths allow the codeposition of sound Ni-W deposits containing 20% tungsten. Iron-tungsten deposits containing 50% tungsten can be plated from such baths. Two mechanisms have been proposed to explain the codeposition process. These are the catalytic reduction mechanism and the complex formation mechanism.The catalytic reduction mechanism proposes that laminations observed in the codeposits are alternate layers of tungsten and the codeposited metal (iron, nickel, or cobalt) (7). The codeposited metal acts as a catalytic surface on which, in the presence of hydrogen, the tungstate anion is reduced chemically and electrochemically to metallic tungsten. When a layer of tungsten has covered this catalytic surface, the deposition ceases and the formation of a fresh layer of catalytic codeposited metal begins.The complex formation mechanism describes the codeposition as taking place from some complex of tungstate and the codepositing metal ion (7). The function of the codepositing metal ion is to provide a reducible tungstate complex. The major disadvantage of the complex formation mechanism is that no complex of tungstate with ions of iron, nickel, or cobalt has been observed.The effect of addition agents on tungsten codepo-1 Present address: Minneapolis-Honeywell Regulator Company, Research Center, Hopkins, Minnesota.sition and data indicating that the codeposits are solid solutions are discusse...

Means of preparing Co-P electrodeposits having a wide range of magnetic properties are discussed. X-ray diffraction data, electron micrographs, and Bitter patterns are presented. An explanation of the origin of the high coercivity is presented. Low flux density of the material is described, and a possible explanation is presented.