G. Giovannelli

An investigation into the electrodeposition of Au-Cu-matrix particulate composites

The electrodeposition of AuCu/B4C composites from alkaline baths containing free cyanide is described. The electrochemical behaviour of the bath and the metallographic and crystalline structures of the electrodeposited alloys were studied with and without addition of particles. Electrochemical instabilities were observed and their bearing on the structure of both pure matrix and composite electrodeposits is shown and elucidated. The electrochemical and structural conclusions on the AuCu/B4C system are thought to be general for alloy-matrix composite plating with nonconductive particles.

Crystallographic structure of gold films electrodeposited at low current densities

In this paper we report on the electrodeposition of Au from dicyanoaurate electrolytes at low current densities. If electrodeposition is carried out at current densities lower than 0.25 mA cm−2 a new hexagonal crystalline structure can be observed. This structure is generally codeposited with fcc Au. The new structure dominates for short deposition times. This structure is stabilised by the addition to the bath of metal ions giving rise to UPD behaviour on Au, such as Cu2+ and Tl+. This structure was tentatively assigned to the space group 184 (p6cc). This structure can be explained in terms of the incorporation of extraneous, probably cyanide-related, material. This interpretation is also supported by in situ Raman spectroscopy and by XPS analyses showing that the bulk deposits contain C, N and K. The electrochemical behaviour of the electrodeposition system was studied by cyclic voltammetry. Cyanoaurate baths display a significant cathodic passivation. This phenomenon is reduced by the addition of Cu2+ or Tl+. Voltammograms of baths containing these additives show clear UPD features but no stripping peaks. This behaviour is suggestive of an assisted Au electrodeposition mechanism. Tl is deposited at UPD and oxidatively desorbed by Au(I). Cu is codeposited at UPD with Au forming an alloy.

Electrodeposition of Au-Sn alloys from acid Au(III) baths

A bath for the electrodeposition of white gold alloys of interest for the electroforming of hollow jewellery is proposed and investigated. The system was an acidic Au(III)–Sn(IV) bath for the electrodeposition of Au–Sn alloys. The electrochemical investigations were based on cyclic voltammetry, linear-sweep voltammetry, galvanostatic electrodeposition experiments and in situ Raman spectroscopy. The electrode kinetics of alloy formation were elucidated by stripping voltammetry. The effects of cathodically adsorbed CN− were studied by in situ Raman spectroscopy. Electrodeposited foils were studied from the crystallographic, compositional and morphological points of view. Codeposition of Au and Sn gives rise to a single phase of approximately equiatomic composition over a current density interval of 10 to 40 mA cm−2. This orthorhombic phase is structurally the same as the ζ′ phase of the equilibrium Au–Sn system, but its stoichiometry and lattice parameters are different. The equilibrium two-phase δ, ζ′ structure can be obtained by heat-treatment.

Hydrogen incorporation and embrittlement of electroformed Au, Cu and Au–Cu

Abstract Electroformed Au, Cu, Au–Cu layers and composites display severe brittleness in both as plated and heat treated conditions. This phenomenon has not been considered in the literature previously. In this paper we show the relevant embrittling phenomenology and explain it with the incorporation of hydrogen produced in electrochemical side reactions occurring during the formation of the metallic deposits. Our conclusions were drawn on the basis of the following experiments: (i) electrochemical measurements—proving the effect of bath composition on the hydrogen evolution side reaction—(ii) hydrogen removal tests—hot extraction and high vacuum treatments—(iii) mass spectrometric identification of released gases, (iv) SEM observations of micrometric voids, (v) SAXS measurements of nanometric voids and (vi) SEM fractography of heat treated samples. Hydrogen removal by a high vacuum room temperature treatment is proposed.

An investigation into the electrodeposition of AuCu-matrix particulate composites. Part II : Baths not containing free cyanide

In this paper we report on the electrodeposition of AuCu/B4C composites from acid baths with gold cyanocomplexes and no free cyanide. The electrochemical behaviour of the bath and the metallographic and crystalline structures of the electrodeposited alloys were studied with and without addition of particles. Electrochemical instabilities were previously observed for free-cyanide baths and their bearing on the structure of both pure matrix and composite electrodeposits were elucidated. No instabilities were observed in the alloy deposition from the acid baths containing complexed cyanide: compositionally and structurally homogeneous microstructures were obtained both with and without particle embedding.

An investigation into microstructure and particle distribution of Ni–P/diamond composite thin films

The present paper deals with a theoretical and experimental study of the co‐deposition of spheroidal particles in a metal matrix deposited by autocatalytic chemical deposition (ACD). The 3‐D particle size distribution — as measured by image analysis of SEM micrographs of metallographic cross‐sections — is related to the size distribution of the starting powder — as measured by photon autocorrelation spectroscopy — through a simple analytical model. The application of the model to the co‐deposition of diamond particles in an ACD Ni–P (9 wt.% P) amorphous matrix led to a correct prediction of average volume of embedded particles (V¯), coverage factor (CF) and number of co‐deposited particles per unit volume of deposit (NV).

Mechanical Properties of ACD and ECD Particulate Metal-Matrix Composite Thin Films

Some mechanical and tribological properties of ACD Ni-P/diamond and ECD Au/boron carbide composite thin films are measured and discussed. Preparation methods are briefly described. Hardness, Youngs modulus and Milmans plasticity parameter are evaluated by diamond-pyramid indentation methods; sliding-wear behaviour is tested by means of the pin-on-disk technique. The application of the correlations for indentation testing are treated statistically in view of a quantitative use. The variations in mechanical properties induced by the dispersion of ceramic particles and quantitatively correlated with the structural characteristics of the composite films.

Study on levellers for Cu electrodeposition from acidic sulphate solution: an in situ spectroelectrochemical approach

Abstract This paper deals with a study of the adsorption behaviour of three molecules which can be employed as levellers in Cu electrochemical plating from acidic sulphate solutions: 4cyanopyridine (4CP), 3-diethylamino-7-(4-dimethylaminophenylazo)-5-phenylphenazinium chloride (Janus Green B, JGB) and a benzyl-phenyl modified polyethyleneimine (BPPEI). This investigation was carried out by in situ surface enhanced Raman spectroscopy (SERS) during electroplating and by in situ electroreflectance spectroscopy (ERS) on electrodeposited Cu layers. Variations of SERS effect with potential and potentiostatic polarisation time were studied. Cathodic reactivity of JGB and BPPEI was highlighted by the analysis of spectral changes as a function of applied potential and by time resolved spectroscopy. The formation of surface electronic states related to the formation of chemisorption bonds between the levellers and the Cu electrode was revealed by ERS.

An in situ Raman investigation of organic species incorporated in cu layers electrodeposited from PEG-containing acidic sulphate and cyanoalkaline electrolytes

SUMMARY In situ surface Raman spectroscopy was used to detect organic species embedded in Cu electrodeposits obtained from cyanoalkaline and acidic sulphate solutions containing polyethylene glycol (PEG). These measurements rely on the release of the organic species at the surface of the electrode during controlled corrosion in pure acidic aqueous solutions and on the development of surface-enhancing morphological elements in the course of the anodic dissolution. After an induction period, well defined vibrational bands appear, assigned to vinyl and hydroxyl groups that can result from cleavage reactions of the PEG chain. This technique is shown to be robust and to exhibit negligible dependence on details of the corrosion process (either galvanostatic of potentiostatic) or of the environment (0.5 M H2SO4 or HCl).

Electrodeposition of Au–Sn alloys from alkaline baths

A bath for the electrodeposition of white gold alloys of interest for the electroforming of hollow jewellery is proposed. The investigated system is an alkaline KAu(CN)2 bath for the electrodeposition of Au–Sn alloys. The electrochemical investigations are based on cyclic voltammetry and electrodeposition experiments. Electrodeposited foils were studied from the crystallographic, compositional and morphological points of view. Co-deposition of Au and Sn gives rise to the formation of a series of intermetallic phases, which can be detected by X-ray diffraction and anodic stripping. Deposits are typically polyphasic; the phase composition generally does not correspond to the equilibrium one. Chemical compositions ranging from high-Au to high-Sn can be obtained by galvanostatic deposition at suitable current densities.