A.J. Arvia

The formation of anodic layers on annealed copper surfaces in phosphate-containing solutions at different pH

Resume The electrochemical behaviour of Cu in different phosphate buffers is studied through electrochemical techniques combined with scanning electron microscopy and energy dispersive X-ray analysis. At pH 6.0 and 8.0 the onset of passivation is due to the anodic formation of a basic Cu(II) phosphate, whereas at pH 11.5 the passivating layer corresponds to a duplex Cu(I) oxide-Cu(II) oxide layer. The potentiostatic anodic current transients can be reproduced by a model involving the initial growth of a thin anodic layer and the simultaneous electrodissolution of Cu. The electrodissolution of passivated Cu takes place through the passivating layer. This reaction contributes to the thickening of the outer part of the passivating layer.

Spectroscopic investigations of C3 primary alcohols on platinum electrodes in acid solutions.: Part I. n-propanol

Abstract The electrochemical behavior of n-propanol (n-PrOH) on polycrystalline Pt in acid solutions was investigated using in situ Fourier transform infrared spectroscopy (FTIRS) and on line differential electrochemical mass spectrometry (DEMS). The main products of n-PrOH oxidation are CO2, propanal and propionic acid. Different types of adsorbates with one, two or three C atoms were detected. Ethane and propane are produced from n-PrOH adsorbates during potential cycling in the H-adatom potential region. An increase in the quantity of adsorbed CO was observed after hydrogenation of n-PrOH adsorbates.

Electroreactivity of isopropanol on platinum in acids studied by DEMS and FTIRS

Abstract The reactivity of isopropanol on polycrystalline Pt in acid solutions was investigated using in-situ Fourier transform IR spectroscopy (FTIRS) and on-line differential electrochemical mass spectrometry (DEMS). The electro-oxidation products are acetone and CO2; the former is observed when isopropanol is present in the bulk of the solution, and the latter is produced from strongly adsorbed species. Both bulk and adsorbed isopropanol electro-reduction yield propane. HD exchange is observed during propane formation when the reaction takes place in a D2O + DClO4 solution. This observation suggests the formation of adsorbates bonded to the surface through the Cα atom of the isopropanol molecule. FTIR spectra of adsorbed species show the presence of CH3 and COH groups. The most probable adsorbate structures are (CH3CCH3)Pt, (CH3CHCH3)Pt and (CH3COHCH3)Pt, presumably accompanied by (CH3COCH3)Pt.

The reactivity of primary C3-alcohols on gold electrodes in acid media. A comparative study based on dems data

Abstract The reaction products of propargyl alcohol (Pa), allyl alcohol (AA) and n-propanol (n-PrOH) at different applied potentials have been investigated on Au electrodes in 0.5 M H2SO4. On line mass spectrometry (DEMS) reveals that CO2 and acrolein are formed from bulk AA electro-oxidation. PA electro-oxidation produces CO2 and propargyl aldehyde, and electroreduction yields propyne, propylene and AA. No strongly bound intermediates for AA were detected. PA forms adsorbates which give CO2 and a C3 hydrocarbon during electro-oxidation and electroreduction, respectively. No electrochemical activity could be detected for n-PrOH on Au.

THE KINETICS OF PITTING CORROSION OF COPPER IN ALKALINE SOLUTIONS CONTAINING SODIUM PERCHLORATE

Abstract-The plttmg corrosion of Cu has been mvestlgated m 0 1 M NaCIO,, 8-l 1 pH range, through voltammetry and potentlostatlc transient techniques complemented unth scanning electron nucroscopy observations Phenomenolognzal relatlonshlps between breakdown potential, density of pits, spatial pit chstnbutlon, pH and applied potential have been established Results are Interpreted m terms of a nucleation and growth mechanism under two different kinetic controls The transition m the rate controlling process depends on the extent of the plttmg process The spahal chstnbutlon of pits suggests the random nature of pit nucleation on the Cu surface Key words copper, copper corrosion, pitting corrosion, perchlorate solutions, pit dlstrlbutlon 1. INTRODUCTION The electrochemical behavlour of copper m alkaline aqueous solutions IS rather complex because a number of different processes take place m various well-defined potential ranges, their charactenstlcs bemg dependent on the solution composltlon and the physical treatment of the metal[l-61 In general, the anodization of Cu m alkaline solutions produces several Cu oxides and hydroxides as well as Cu(1) and Cu(I1) soluble species, depending on the pH of the solution The onset of passivity on Cu has been related to the formation of an anodlc layer compns- mg a duplex layer[l, 51 which consists of an inner Cu,O layer and an outer CuO layer Depending on the nature of the anions prevalhng m the solution, msoluble Cu salts can preclpltate upon the passive layer, sometimes bemg also capable of blocking the growth of pits at the Cu surface[6] Conversely, the formation of Cu salts favours a more extensive attack of Cu leading to pitting corrosion A recent comparative electrochemical study of the behavlour of Cu m alkaline solutions containing either NaClO, or NaHCO, + Na, CO3 [6] showed that under certain applied potential condltlons and solution pH, ClO; ions can produce Cu pitting For those solutions the extent of Cu pitting depends on S, the solublhty of the correspondmg Cu salt, namely, NaClO, solutions being more aggressive than NaHCO, + Na,CO, solutions For Cu(ClO,),, S 13 mol 1-l and for Cu basic carbonates, S 1 10m5 mol 1-j at 25”C[7,8] The present work reports new results related to the mltlatlon of Cu pitting m perchlorate-contammg solutions by employmg two types of specimen,

DEMS and in-situ FTIR investigations of C3 primary alcohols on platinum electrodes in acid solutions.: Part II. Allyl alcohol

Abstract On-line mass spectroscopy (DEMS) and in-situ Fourier transform IR spectroscope (FTIRS) have been employed to study the electro-oxidation and the electroreduction products of allyl alcohol on Pt electrodes in acids. The electroreduction products were propanol and a mixture of propylene, propane and ethane. The main oxidation products were CO 2 and acrolein. Results are interpreted and possible mechanisms are suggested with the participation of adsorbates having different chain lengths and structures.

A mechanistic approach to the electroformation of anodic layers on copper and their electroreduction in aqueous solutions containing NaHCO3 and Na2CO3

The electrochemical behaviour of Cu in solutions containing Na2CO3 + NaHCO3 (8.8 < pH < 11.1) has been studied using potentiodynamic and poteniostatic techniques complemented by Scanning Electron Microscopy. The initial stages of the anodic layer formation involve the electroformation of a thin inner Cu2O layer followed by the growth of a CuO/Cu(OH)2CuCO3 complex outer layer. Soluble (Cu(II) species were detected in the entire anodization potential range. Kinetic models devised for phase change electrochemical processes have been applied to explain the characteristics of anodic and cathodic current transients.

Spectroscopic investigations of C3-primary alcohols on platinum electrodes in acid solutions.: Part III. Propargyl alcohol

Abstract Electro-oxidation and electroreduction of propargyl alcohol (PA) on Pt electrodes in acid solutions was studied using differential electrochemical mass spectrometry and in-situ Fourier transform IR spectroscopy. The main electro-oxidation product is CO 2 . Only very small amounts of propargyl aldehyde are detected at high potentials. Electroreduction of PA yields mainly propane, propylene, propanol, allyl alcohol and small amounts of propyne and ethane. Hydrogenation of the strongly adsorbed residues of PA produces hydrocarbons but not alcohols.

Multiple adsorbate interactions between reduced CO2 adsorbates and either allyl alcohol or propargyl alcohol residues on platinum in 0.5 M sulphuric acid

Abstract The interaction of propargyl alcohol and allyl alcohol with a platinum (Pt) electrode modified by the presence of reduced CO 2 adsorbates (r-CO 2 ) is studied through voltammetry and potentiostatic current transients by using a flow cell technique. The interaction between each alcohol and r-CO 2 is promoted at three constant potentials corresponding to different degrees of Pt surface coverage by H-atoms. For both alcohols the anodic stripping peaks and the charge balance are interpreted in terms of the formation of composed adsorbates. Based upon the probable r-CO 2 structure and H-bonding interactions between r-CO 2 and the alcohol molecules or their adsorbed residues, average alcohol residues/r-CO 2 molecular ratios are estimated.

Electrochemical kinetics and growth modes of silver deposits on polyfaceted platinum spherical electrodes

Abstract The Ag electrodeposition on Pt spherical substrates was investigated over a wide range of experimental conditions to establish a correlation between the kinetics of the process and the different growth modes of the Ag overlayer. At E d ≊ E rev , the electrodeposition of the first Ag layer obeys a combined adsorption-desorption and nucleation and 2-D growth process under diffusion control. At E d E rev , the formation of the 2-D Ag layer proceeds through an adsorption mechanism, whereas the formation of the 3-D Ag layer fits a progressive nucleation and 3-D growth mechanism under diffusion control. Finally, when E d E φ , a potential threshold related to Ag dendritic growth, the kinetics of the reaction apparently obeys a progressive nucleation and 1-D growth. This process is triggered at edges and corners of large Ag crystals. Dendritic growth takes place outside the diffusion layer defined around the Pt substrate sphere. In this case migration plays a substantial role in the process.