H. Neil McMurray

Latent Fingerprint Detection Using a Scanning Kelvin Microprobe

Electrochemical interactions between latent human fingerprints and metal surfaces in ambient air are investigated using a scanning Kelvin microprobe. Inorganic salts present in sweat deposited at fingerprint ridges locally depassivate the metal surface producing a Volta potential decrease of greater than 200 mV. Volta potential patterns may persist for months and prints may be visualized by potential mapping, even when overcoated with a polymer layer. Because the Volta potential differences are produced by involatile salts they persist when the organic components of the fingerprint residue have been volatilized by heating to 600 degrees C.

Anion-exchange inhibition of filiform corrosion on organic coated AA2024-T3 aluminum alloy by hydrotalcite-like pigments

Novel anion-exchange anticorrosion pigments consisting of nitrate, carbonate, and chromate exchanged hydrotalcite (HT) are shown to effectively inhibit the propagation of filiform corrosion (FFC) on organic coated AA2024-T3 aluminum alloy. The HT-pigments are dispersed in polyvinyl butyral (PVB) coatings applied to the AA2024-T3 surface. Following FFC initiation by application of aqueous HCl to a penetrative coating defect, the time-dependent extent of coating delamination is determined both optically and by means of repeated in situ scanning using a scanning Kelvin probe apparatus. All HT-pigments are shown to profoundly reduce rates of coating delamination by comparison to unpigmented samples. However, inhibitor efficiency is dependent upon the exchangeable anion and increases in the order

Inhibition of Filiform Corrosion on Polymer Coated AA2024-T3 by Hydrotalcite-Like Pigments Incorporating Organic Anions

Benzotriazolate, ethyl xanthate, and oxalate anion-exchanged hydrotalcite (HT) pigments are evaluated with respect to their ability to inhibit filiform corrosion (FFC) on organic coated AA2024-T3 aluminum alloy. FollowingFFC initiation by application of aqueous HCl to a penetrative coating defect, the time-dependent extent of coating delamination was determined both optically and by repeated in situ measurements performed using a scanning Kelvin probe (SKP). Inhibitor efficiency is shown to increase in the order ethyl xanthate « oxalate < benzotriazolate. Benzotriazolate is also shown to interact specifically with the alloy surface, depressing Volta potential values by up to 0.4 V.

Novel thick-film pH sensors based on ruthenium dioxide-glass composites

Abstract Potentiometric pH electrodes are described, which consist of 30 μm films of a ruthenium dioxide-glass composite, prepared by sintering mixtures of powdered lead borosilicate glass and ruthenium dioxide hydrate onto Pyrex substrates at 900 °C. Electrical contact is made either at a point remote from the solution-contacting portion of the electrode or via a platinum wire contact immediately underlying the active area. Composite electrodes with an RuO 2 :lead borosilicate glass ratio of 1:1 show a near-Nernstian dependence of potential upon pH in aqueous buffer between pH 2 and 12, a maximum hysteresis of 30 mV and a response time of approximately 90 s. Response rates appear to be limited by the diffusion of protons through the porous composite and decrease with decreasing RuO 2 :glass ratio. The composite electrodes are completely indifferent to changes in the concentration of dissolved oxygen, but show a small response to chloride ions. Changes in electrode characteristics with aging are reported, of which the most significant is a −65 mV drift in E 0 .

Oxygen quenching of tris(2,2′-bipyridine) ruthenium(II) complexes in thin organic films

Abstract A study is presented of the quenching, by oxygen, of the luminescence of tris(2,2′-bipyridine) ruthenium(II) complexes immobilized in thin, transparent, polymer-based films. The film media consist of a water-insoluble linear polymer plasticized with a trialkylphosphate ester, in which the complex ruthenium cations are solubilized by ion pairing with organophilic anions such as tetraphenylborate. Luminescence lifetimes were studied in relation oxygen concentration in a gas stream contiguous with the film medium, film thickness and concentration of the metal complex within the film medium. It is shown that the microheterogeneous environment of the luminescent complex, which has recently been implicated in the non-linear quenching responses of polymer-immobilized, transition metal complex oxygen sensors, may arise simply as a consequence of the limited solubility of the complex in the film medium. When solubility is limited, the partial precipitation of the complex results in a colloidal of luminescent particles which exhibit non- uniform susceptibilities to quenching by oxygen. Good solubility, and therefore linear quenching characteristics, are promoted by methyl substitution of the bipyridyl ligand and by use of a plasticizer (tributylphosphate) with marked cation solvating powers.