Electrophoretic deposition is shown to be a useful coating method for the deposition of metal, oxide, and carbide coats on metal or graphite. The timecurrent-voltage relationship on the rate of deposition is discussed, and factors important to preparation of suitable plating suspensions and to the formation of adherent deposits, with and without binders, are described. The method has been applied to the plating of coats of B, Dy, Zr, Au, Nb, Mo, W, Re, Nb~Sn, ZrH2, ThC, UC, NpC, PuC, (ZrU)C, UWC~, UO~, UMoC~, Ta~O~, and both W-UO2 and Mo-UO~ composites.The phenomenon of electrophoresis has been observed and investigated for at least 150 years, but only very limited use has been made of electrophoresis as a method of applying coatings to materials. Yet electrophoresis offers a very general and useful method of coating conducting materials such as metals and graphite with a wide variety of conductors and nonconductors.The stability of a plating suspension has been explained in terms of an electrical layer (1-10). Various theories on the formation of an adherent deposit have been advanced (11-16); however, this feature of electrodeposition is the least understood and the most difficult to control. This paper describes ways of preparing stable plating suspensions, and lists the important parameters for plating by electrophoretic deposition. Experimental ProcedureSelection and purification of the suspension medium.--Polar organic liquids are most commonly used as suspension media for electrophoretic deposition since stable suspensions can be formed in these liquids, and the low electrical conductivity of these liquids minimizes electrolysis of the liquid and attendant gassing at the electrodes. The liquids used in this investigation were isopropyl alcohol (IPA) and nitromethane. These were selected on the basis of their proved utility as suspension media as shown by the important applications of electrophoretic deposition developed by Reichard et al. (17).The IPA (Bakers Analyzed Reagent Grade) was untreated before use. The nitromethane (Eastman Kodak's No. 189) was dried by shaking for a few minutes with calcium sulfate (Drierite) and was then filtered through a "fine" fritted glass filter before use. The drying procedure also appeared to remove ionic impurities from the nitromethane.Comminution o] powders.--The suspensions used for electrophoretic deposition usually had a particle size ranging from 1-20~. This range of particle size was chosen because colloidal size particles gave low plating rates, and particles coarser than 25~ led to uneven deposits. The optimum size was found to be about 6t~, and grinding times were selected to give a large fraction of the powder close to this size.All powders were comminuted by jar milling in IPA. The niobium suspensions were prepared by milling --325 mesh Fansteel Metallurgical Corporation niobium for 8 to 12 hr with steel balls and jars. Suspensions of other materials were milled for 1 to 1O hr in Teflon or polyethylene containers with tungsten rods or tungsten carbide balls....
P)] -K~( B u F ) = 0 (10)LVhen the expression for (BuF) obtained from equation 10 is substituted in (9), the rate equation in terms of the experimental variables is dPid2 = KI(Pm -P ) + Upon integration of equation 11 and rearrangement of terms, equation 3 is obtained. If it is assumed that the contribution of reaction (4) to the total rate of reaction is negligibly small, equation 2 is obtained upon integration of equation 11 and rearrangement of terms. This would indicate that reactions ( 5 ) and (6) are the principal reactions in the mechanism, while reaction (4) becomes more important as the reaction is greatly accelerated, as, for example, in experiments 5, 6, 20-23 and 38.Since P o and the "steady state" concentration of catalyst are not accurately known, values of the rate constants in equation 11 cannot be calculated from the present data.Mechanisms involving isobutylene, carbonium ions or free radicals as intermediates in reaction (5) cannot explain the initial kinetic effects in experiments 7, 8 and 33. In addition, mechanisms involving ions or free radicals involve too high an energy of activation, as shown by Pearlson and S i m o n~.~The results of the present work indicate that a simple step by step mechanism cannot explain the experimental facts, but that a hydrogen or proton transfer is involved. This, despite the fact that the reaction under study is probably one of the very simplest of the organic chemical reactions of the condensation type, points out the necessity for a more critical examination of other reactions for which mechanisms have been proposed.Acknowledgments.-We express our appreciation to the Allied Chemical and Dye Corporation for financial aid during part of the time this research was in progress. Thanks are due Dr. R. UT. Taft, Jr., for his helpful suggestions concerning the interpretation of the data. AND bIELVIN L. RENQUIST Heat capacity measurements between 80 and 300°K. have been made upon the following seven compounds: n-heptyl alcohol, cetyl alcohol, furfuryl alcohol, cyclopentanol, n-butyraldehyde, n-heptaldehyde and methyl ethyl ketone. From these calorimetric data the corresponding molal entropies a t 298 16°K. have been derived and in turn, with the aid of suitable enthalpy values, the free energies of formation have been computed for all the compounds, save the heptaldehyde.The present measurements were made during the decade starting with 1940 and available facilities did not provide temperatures below the boiling point of liquid nitrogen. However, extrapolation of entropies below SO'K. introduces uncertainties of the order of one unit, or less, in the molal entropy of any of these compounds, corresponding to a maximum of about 300 cal. in the resulting free energy value. This latter figure is equivalent to an uncertainty of merely 0.01270 in the heat of combustion of cetyl alcohol and about 0.049yc in that of furfuryl alcohol. Thus the accuracy of the enthalpy data is generally the limiting factor in evaluating the molal free energies of such organic compounds.Mater...
Values, with uncertainties of about 0.03 percent, are here presented for the heats of combustion of polythene and polyisobutylene. The results for polythene indicate that this polymer is crystalline at least to the extent of about 50 percent at 25°C. The results for polyisobutylene are abnormally high and can be explained on the basis of a steric interference effect within the molecules of this liquid polymer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.