Metals provenance studies

Recent reviews (11-12) make it unnecessary to do more than draw attention to some salient points of lead isotope archaeology. For many years, comparative lead isotope studies of ancient metals and ores from the appropriate ore deposits have been in the forefront of metal provenance studies in archaeology (13-15). The earliest lead isotope studies by Brill (17-18) and... 

As LA-MC-ICP-MS becomes more accessible, provenance studies may begin to combine elemental and isotopic characterization. Some time ago, Stos-Gale [114] suggested that metal provenance studies could be based on combined lead isotope and trace element analyses, and the same kind of combined approach would seem desirable in the case of turquoise as well as other, seldom analyzed materials such as ceramic glazes. Cooper et al. [115] combined trace element and LA-MC-ICP-MS lead isotope analysis of native copper from North America, but found that the lead isotopes were of little use in source discrimination. 

Trace-element analysis of metals can give indications of the geographic provenance of the material. Both emission spectroscopy (84) and activation analysis (85) have been used for this purpose. Another tool in provenance studies is the measurement of relative abundances of the lead isotopes (86,87). This technique is not restricted to metals, but can be used on any material that contains lead. Finally, for an object cast around a ceramic core, a sample of the core material can be used for thermoluminescence dating. 

The approach employed for the preparation of nortriquinacene derivatives was based upon ring contraction of the a-diazocarbonyl derivative and subsequent degradation of the epimeric carboxyl derivatives (Scheme 67).393 All attempts to deprotonate hydrocarbon 445 have proven unsuccessful. Metal reduction studies on 444 and the related chlorides also failed to provide evidence for formation of a stabilized carbanion. Calculations agree with the absence of significant homoconjugation in 429. For example, this species is predicted to have a pyramidal rather than a trigonal anionic carbon.393 In addition, exo-methylene derivatives of nortri-... 

Seven years ago we started the first systematic research program on the application of the lead isotope techniques to provenance studies in archaeology. Particular stress was placed on the sources of metals in the Mediterranean Bronze Age. For the first 2 years we worked mostly on the sources of lead and silver in Bronze Age Greece, Cyprus, and Egypt (32-36). In 1982, we pioneered the application of the lead isotope method for prove-nancing copper-based artifacts (15, 37-38). 

This methodology enjoys the merits of other approaches and exhibits several additional advantages 1) it has proven applicable to a wide range of transition metal and main group oxides 2) the metal precursors studied so far are readily available, being either alkoxide or halide complexes 3) in many cases, syntheses can be run in alcoholic solvents in essentially nonhydrolytic conditions, which aids in controlling hydrolysis and condensation rates 4) the critical micelle concentrations required for polyethylene-oxide-polypropylene-oxide di- and triblock copolymers are usually much lower than the concentrations needed for ionic surfactants and 5) because of the neutral, nonaqueous conditions used in these preparations, control of pH is not required, and the surfactant can be removed from the mesostructured material by calcination or milder solvent extraction methods with nonpolar solvents. 

The lack of a well-defined specular direction for polycrystalline metal samples decreases the signal levels by 10 —10, and restricts the symmetry information on adsorbates, but many studies using these substrates have proven useful for identifying adsorbates. Charging, beam broadening, and the high probability for excitation of phonon modes of the substrate relative to modes of the adsorbate make it more difficult to carry out adsorption studies on nonmetallic materials. But, this has been done previously for a number of metal oxides and compounds, and also semicon-... 

From the early work of Taylor [63T01] connecting dislocation behavior to observed viscoplastic shock-compression response, numerous studies have attempted to relate conventional dislocation dynamics models to experimental observations. Theory and observations consistently require unusually large numbers of mobile dislocations. Although qualitatively descriptive, progress to date on dislocation models has not proven to provide quantitative descriptions to the observations in metals. 

A greater hindrance for paleoclimate studies, however, is that the traditional method required reduction in an all metal vacuum line at high temperature (in externally-heated nickel reaction vessels) with bromine pentafluoride (BrFs), a highly reactive gas (Clayton and Mayeda 1963). Handling this material in anything other than a dedicated geochemistry laboratory has proven extremely difficult and dangerous (Chivas 1984). 

The investigations on boundary lubrication used to focus on the friction elements made of metallic materials, and of steel in particular. This is, of course, due to the fact that a great majority of machines are built from metal and steel, but it is also because the hydrocarbon-based oils have been proven to be an extraordinarily good lubricant for metal surfaces. Unfortunately, the conventional oils are not so effective to lubricate the components made of other materials, like ceramics, rubbers, silicon, etc., so that the study on new types of lubricants suitable for such materials has attracted great attention in recent years. 

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