Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where David J. Vaughan is active.

Publication


Featured researches published by David J. Vaughan.


Physics and Chemistry of Minerals | 1981

Pyrite, marcasite, and arsenopyrite type minerals: Crystal chemical and structural principles

John A. Tossell; David J. Vaughan; Jeremy K. Burdett

Quantitative molecular orbital (MO) calculations and qualitative perturbational MO arguments are used to interpret the spectra and structure of transition metal dichalcogenides and related compounds. Competition between pyrite (FeS2), marcasite (FeS2) and loellingite (FeAs2) structure types is explained in terms of the number of electrons occupying a set of MOs obtained from the mixing of dianion (A2) orbitals and metal (M) dσ orbitals. Direct metal-metal d orbital interaction is argued to be small. Attention is focused upon the M - A - M angles which differ substantially among the three structure types as a consequence of varying numbers of electrons in orbitals which closely resemble the pπ* orbitals of the dianions. Variations in M - A and A - A distances can also be understood in terms of the occupations of this set of MOs. Disulfide valence region photo-emission spectra are interpreted in terms of calculations on MS6 and S6 molecular clusters. M3d orbitals are found to progressively approach the S3p orbitals with increasing atomic number of M from Fe to Ni. For CuS2 comparison of calculation and experiment supports an approximate electron configuration of Cu+1 S2−1.


Physics and Chemistry of Minerals | 1983

Electronic structures of sulfide minerals — Theory and experiment

David J. Vaughan; John A. Tossell

The sulfide minerals exhibit a rich diversity in sturctural chemistry and in electrical, magnetic and other physical properties. Models based on molecular orbital theory and incorporating some elements of band theory can be developed to describe the diverse valence electron behavior in these minerals. Qualitative models can be proposed on the basis of observed properties, and the models can be tested and refined using experimental data from X-ray emission and X-ray photoelectron spectroscopy and quantum mechanical calculations performed on cluster units which form the basic building blocks of the crystals.This approach to chemical bonding in sulfide minerals is illustrated for binary non-transition metal sulfides (ZnS, CdS, HgS, PbS), binary transition metal sulfides (FeS2, CoS2, NiS2, CuS2 ZnS2) and more complex sulfides (CuFeS2, Cu2S, Ag2S, CuS, Co3S4, CuCo2S4, Fe3S4). The relationship between qualitative and quantitative theories is reviewed with reference to the pyrite-marcasite-arsenopyrite-loellingite series of minerals. Application of the models to understanding structure-determining principles, relative stabilities, solid solution limits and properties such as color, reflectance and hardness are discussed.


Physics and Chemistry of Minerals | 1988

Investigation into the nature of copper and silver sites in argentian tetrahedrites using EXAFS spectroscopy

John M. Charnock; C. David Garner; R. A. D. Pattrick; David J. Vaughan

Synchrotron radiation has been used to collect Cu K-edge and Ag K-edge EXAFS from several tetrahedrite, (Cu,Ag)10(Zn,Fe,Cu)2Sb4S13, minerals. The results have been used to investigate the coordination environment of the Ag and Cu, and to determine which sites in the structure are occupied by silver atoms when they replace copper. The Ag EXAFS spectrum of a sample with high silver content reveals an interaction between silver and antimony which may explain the anomalous decrease in unit cell size found in natural tetrahedrites when the silver content increases beyond four atoms per unit formula.


Archive | 1984

Electronic Structures of Sulfides and Leaching Behavior

David J. Vaughan

The electronic structures of major sulfide minerals (pyrite, chalcopyrite, covellite, chalcocite, sphalerite, galena) are best understood in terms of models based on molecular orbital theory and incorporating elements of band theory. Such models may be developed from molecular orbital cluster calculations (using the SCF-Xα scattered wave method, for example) and tested and refined by comparison with the results of spectroscopic studies, particularly those employing X-ray emission and X-ray photoelectron spectroscopies. The models provide a basis for understanding the crystal chemistry and physical properties of the minerals, including their electrical behavior, and potentially can be developed to gain a fuller understanding of the surface properties of the minerals. Application of these ideas in understanding and predicting leaching behavior will be discussed with particular emphasis OIL the sulfides of copper and iron.


Physics and Chemistry of Minerals | 1986

Interpretation of the Auger electron spectra (AES) of sulfide minerals

David J. Vaughan; John A. Tossell

Auger electron spectra (AES) of sulfides are interpreted using published photoelectron spectra, sulfurKβ X-ray emission spectra (XES) and Multiple ScatteringXα calculations on metal-sulfide molecular clusters and using newly measured spectra for ZnS, Cu2S and MoS2. For compounds without appreciable metald-sulfur 3p interactions, only one sulfur LVV peak or a closely spaced doublet is observed. For those with substantial metald-sulfur 3p interactions additional peaks occur, with peaks at lower electron kinetic energy arising from ejection of electrons from orbitals more tightly bound than theS3p, and those with higher kinetic energy arising from electrons in less tightly bound orbitals. Thus, for many sulfide minerals, the sulfur LVV Auger Spectrum is essentially a self-convolution of the valence band density of states weighted by the amount of S3p character, and can be predicted from a knowledge of the sulfurKβ X-ray emission spectra and the X-ray photoelectron spectra.


Materials Research Bulletin | 1979

Phase equilibria in the copper-cobalt-sulfur system

James R. Craig; David J. Vaughan; John B. Higgins

Abstract Phase equilibria in the copper-cobalt-sulfur system have been determined by means of silica tube techniques between 400° and 900°C. Throughout this interval the Cu2−xS solid solution containing up to 11 wt % Co, coexists with cobalt sulfides (CoS2, Co3S4, Co1−xS, Co9S8, Co4S3). Co3S4 accepts up to 20.5 wt % copper and CoS2 up to 12 wt % copper into solid solution. The increase in unit cell dimensions of Co3S4 and CoS2 when copper substitutes for cobalt has also been determined.


Archive | 1984

Sulfide Mineralogy: A Review with Special Reference to Phases of Interest in Hydrometallurgy

David J. Vaughan

The sulfide minerals, most particularly those containing iron, copper, nickel, cobalt, lead and zinc, are reviewed in terms of current knowledge of their crystal structures, compositional variations and physical properties. Problems concerning both structural transformations in sulfides and sulfide stoichiometry are considered. Sulfide minerals in ore deposits commonly occur in assemblages which are composed of limited groups of coexisting phases and which show characteristic mineral intergrowth textures. Such occurrences of natural sulfides are reviewed in the light of data available on the thermochemistry and phase relations in sulfide systems.


Archive | 1978

Mineral chemistry of metal sulfides

David J. Vaughan; James R. Craig


Archive | 1988

Resources of the earth

James R. Craig; David J. Vaughan; Brian J. Skinner


Canadian Mineralogist | 1987

Electronic structure and the chemical reactivity of the surface of galena

John A. Tossell; David J. Vaughan

Collaboration


Dive into the David J. Vaughan's collaboration.

Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar

Stephen Boult

University of Manchester

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Researchain Logo
Decentralizing Knowledge