Oxalic acid electrolytes

Electrically produced anodic coatings from chromic, sulfuric, or oxalic acid electrolytes are more dense and less porous. Their corrosion resistance is improved by hot-waler sealing, which is even more effective with the inclusion of dichromale. 

First, anodic films of 30 pm thickness were formed on aluminium foils (99.99%) in oxalic acid electrolyte at a constant current density of 15 mA/cm by anodizing into the opened windows made with the use of photolithography (Fig. la-d). Subsequently, the fabricated samples presented in Fig. Id were divided into two groups. 

Figure 3. PL spectra measured from dichromatic luminescent image (a) blue area of porous anodic alumina film of 30 pm thickness after anodizing in oxalic acid electrolyte (b) red area of a porous anodic alumina film of 20 pm thickness after anodizing in orthophosphoric acid electrolyte, followed by immersion in europium nitrate and subsequent heat treatment at 200 °C for 30 min.

Europium and PAA luminescences from the second group of specimens, subjected to sequential anodizing in two electrolytes (Fig. Ig) were excited efficiently with 337 nm light (Fig. 3). The PL spectrum measured from the area of aluminium films anodized initially in oxalic acid electrolyte into open windows (Fig. ld,e) reveals mainly strong blue luminescence band of PAA (Fig. 3a). Significantly, red emission from this area of the sample is not observed. At the same time, the PL spectrum measured from the area of... 

Other electrolytes have been tested. Saccharin sodium hydrate was recently proposed by Bazzaoui et al. [91], as well as saccharin added to oxalic acid as supporting electrolyte [92]. In this latter case an improvement with respect to the oxalic acid electrolyte was attributed to a reinforcement of the barrier effect of the passive layer. Less usual ways have been explored with ionic liquids as media for electropolymerization. Formation of highly conducting PPy on iron in l-butyl-3-methylimidazolium hexafluorophosphate was reported [93] however, it does not seem promising because such solvents are expensive and also because adhesion to the metal is poor. 

The anodized coating consists of two major components the nonporous barrier layer adjoining the metal and a porous layer extending from the barrier layer to the outer portion of the film. Sulfuric, chromic, and oxalic acid electrolytes form both barrier and porous layers while boric acid electrolytes produce only barrier films. 

Fig. 20. DSC-TGA data for HA PAA prepared using oxalic acid electrolyte and showing evolved gas Mass Spectrometry data for CO2.

Fukuda Y. (1974), Role of oxalate ion in the formation of oxide film on aluminum in oxalic acid electrolyte , Nippon Kagaku Kaishi, 10, 1868-75. 

Kanagaraj D., Raj V, Vincent S., Rrasannakumar B, Senthilkumar A. and Venkatakrishna S. (2001), Rulse anodizing of AAllOO aluminium alloy in oxalic acid electrolyte . Bull. Electrochem., 17, 285-88. 

Other workers have shown that the use of specific dopants to assist in rapid deposition or metal passivation of active metals can help in this regard. For example, oxalic acid electrolytes have been used to facilitate electrodeposition of PPy on Al. ... 

For some applications, especially in the area of corrosion protection, electropolymerization of polyaniline onto active substrate is of interest. Lacroix and co-workers achieved this by first coating mild steel with a very thin PPy layer and then electrocoating polyaniline on top of this. Others have electrodeposited polyaniline-PPy composites on aluminum or steeP surfaces using oxalic acid electrolytes. A number of ring-substituted anilines have also been directly electrodeposited on active iron substrates using an oxalic acid electrolyte. To create novel nanostructures, polyanilines have been recently deposited on aligned carbon nanotubes or into the interstitial spaces of inverse opals to create novel ordered 3-D networks (Figure 4.2). Molecular templates (such as cyclodextrin) have also been added to electrode surfaces to facilitate electrodeposition of nanostructures. ... 

Anodic alumina films with polyaniline and Ti02 nanoparticle-enriched regions on their surface were electrochemically synthesised on an AA3105 aluminium alloy in oxalic acid electrolyte containing dissolved aniline and dispersed nanoparticles. The resultant coatings comprised a porous anodic alumina film of about 2.7 pm thickness, with an outer hybrid polyaniline/TiOz layer of several tens of nanometres thickness. 

The process is one of electrolytic reduction and the apparatus is similar to that shown in Fig. 77, p. 144. It consists of a small porous cell (8 cm. x 2 cm. diam.) surrounded by a narrow beaher (ii cm. X 6 cm. diam.). The oxalic acid, mixed w lth too c.f. 10 per cent sulphuric acid (titrated against standard baryl.a solution] forms the cathode liquid and is placed in Iht beakei. The porous cell is filled with the same strength of siilphuiic acid and foims the anode liquid. The electrodes ara made from 01 dinary clean sheet lead. The anode consists of i thiu strip projecting about two inches from the cell and tliu... 

EbuUioscopic method, 37 Electrolytic reduction, oxalic acid, 102 nitrobenzene, 144, 145 Eosin, 187 Epichlorhydrin, in Estimation of carbon and hydrogen, 4 halogens, 22 nitrogen, 13 sulphur, 28 Ether, 59... 

Films produced in oxalic acid contain smaller amounts (about 3%) of the electrolyte and only traces of chromium are found in chromic acid films. Sealed films show the electron diffraction pattern of the monohydrate, bohmite. 

They extracted values of the pre-exponential factor and of W in Eq. (49) for two electrolytes (sulfuric and oxalic acids) at different concentrations, A being in a reasonable range and W exhibiting remarkable constancy (0.847 and 0.751 for sulfuric acid and oxalic acid, respectively). It should be noted, however, that the model contained many adjustable parameters. 

Figure 34. Cell size in porous oxides versus anode potential for different electrolytes A, oxalic acid , phosphoric acid O, glycolic acid 3, tartaric acid.224...

This system was subsequently investigated by Christensen et at. (1990) also using in situ FTIR, who observed identical product features (see Figure 3.48). In order first to compare directly the IR spectrum of oxalate generated in situ, the authors took advantage of the surface reactivity of Pt and the poor diffusion of species to and from the thin layer. Thus, a solution of oxalic acid in the electrolyte was placed in the spectroelectrochemical cell, the potential of the platinum working electrode stepped to successively lower values and spectra taken at each step. The spectra were all normalised to the reference spectrum collected at the base potential of 0 V vs. SCE. As a result of the deprotonation of adventitious water ... 

A patent by BASF describes the direct reduction of oxalic acid to glyoxylic acid with no added electrolyte... 

In the pure state, a potential electrolyte such as oxalic acid (HOOCCOOH) consists of uncharged molecules. A true electrolyte such as NaCl in the pure state consists of two separate ions, Na and CP. The proton is a bare nucleus it has no electrons. It is chemically unstable as an isolated entity because of its affinity for electrons. As a result, the proton reacts with the free electron pair of oxygen in the H2O molecule. 

Ghem. xxxi. 161, 1902) obtained 8 = 095 mm. from measurements on the rate of the electrolytic oxidation of oxalic acid. Fischer (Elektrochemie, p. 60) obtained the following values from data on the limiting current densities in the precipitation of copper at a rotating cathode ... 

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