Copper and alloys pdf

Two heritage copper-alloy types of special interest were identified that contain elemental values outside the range of the core set of Since not all laboratories will require calibra- tions with extended ranges to accommodate these unusual alloy types, supplementary sets were specified to augment the core set if desired.

The Nickel Supplementary Set contains three additional standards and the Arsenic Supplementary Set contains two additional standards.

This was done to aid in the assessment of calibration errors associated with absorption, enhancement and other matrix effects. For instance, similar levels of arsenic were included in standards with widely varying levels of lead.

Specifically, similar arsenic concentrations of 0. Specifically, similar silver concentrations of 0. Distribution of concentrations For most of the elements represented in the CHARM Set, the distribution of specified values was weighted towards zero, with the lowest values near to expected detection limits and increasing roughly exponentially to the expected maximum value.

For the analysis of heritage copper alloys, the authors felt that this potential difficulty at the highest range of concentrations was outweighed by the benefit of added precision near the detection limit.

Forcing the average value of the distribution towards zero helps to deliver smaller uncertainties for values close to the detection limits Ellison et al. This improvement occurs because the error of pre- diction for a regression is minimized at the centroid of the regression x , y Burgess Weighting the elemental distributions towards zero should also help in the determination of robust and reliable detection limits. MBH routinely lists each of the certifying laboratories on its certificates, along with a complete table of analytical methods and results for each element.

Between eight and 15 independent laboratories determine the concen- tration of each element within any given CRM, using a combination of inductively coupled plasma — atomic emission spectrometry ICP—AES , flame atomic absorption spectrometry FAAS and wet chemical methods.

Robust uncertainty values are generated from the raw analytical results, in combination with the results of a separate homogeneity evaluation con- ducted at MBH using optical emission spectrometry OES. In all, eight new CRMs were specified, cast and certified as part of the core set of The cast discs should also more closely resemble the heritage alloys in their metallographic structure than HIPped discs.

The certified reference materials CRMs in this set were made by melting various recipes of commercial metals and master alloys, as follows. Each charge was melted in an open-air induction furnace, and cast into a sequence of multiple chill moulds.

The casting process was completed within 30 s, to minimize compositional variation. The moulds were laid on to a heavyweight steel sheet to promote rapid solidification, and thus minimize segregation. Processing and testing of the castings were carried out in accordance with the requirements of ISO Guides 30—35, which cover the preparation and use of reference materials ISO , a,b, , , Thus, in principle, this set should remain available well into the future.

The only limitation on this may be with regard to the Arsenic Supplementary Set. The RMs in this set were produced many years ago and current health and safety concerns may preclude their replication in the future. The certified elemental concentrations for all elements in these CRMs are given in Figure 2. The final distribution of concentrations by elements is represented in Figure 3. The certified elemental concentrations for all elements in the supplementary sets are given in Figure 4.

Although every effort was made to produce a final product that matched the initial specifications, a certain amount of variation in the results was to be expected. As a result, the new castings were produced one or two at a time and preliminary characterization of the batch was done by OES.

Any deviations from the intended concentrations in the material were taken into account and the specifications for subsequent castings were adjusted as necessary to maintain an optimal distribution of concentrations for each element. The production of high-arsenic alloys presents health and safety concerns.

This raises concerns that arsenic vapour could escape the melt, lowering the final concentration and possibly endangering the health of the foundry workers.

Experience has shown that all the arsenic added to a melt in this manner has stayed within the solidified metal. However, this experience has only applied to low resultant As levels, below 0.

Preparation of the new alloys for the CHARM Set involved adding As at incrementally higher levels, to test As retention without putting safety at risk. The maximum final concentration attempted was 0. Paul Getty Trust, Archaeometry 57, 5 — A. Values given in parentheses are not certified. The overall range of the set is also given on the right. All values are shown in weight per cent. Aluminium was included in the specifications for the set for two primary reasons. First, it is present in some modern alloys, and given vacuum or helium purge conditions, it should be detectable by XRF.

Second, aluminium also serves to stabilize iron in molten copper alloys. The author team had expressed interest in having iron values up to 1. The overall range of the core set plus the supplemental sets is also given on the right.

However, the authors believe that these standards represent a major step forward in the production of accurate and reliable calibrations for XRF analysis of heritage copper alloys and also towards increasing the number of elements that can routinely be analysed. Furthermore, the authors hope that the Copper CHARM Set will be used by a wide range of museum-, art- and archaeology-oriented scientists and conservators to dramatically improve the inter-laboratory reproducibility of their results.

Such improvement should have a significant impact on research in the field, allowing greater data sharing between laboratories and fostering growth in collaborative research.

A planned follow-up round robin, based on the methodology used in Heginbotham et al. That meeting, sponsored by Robert H. Smith and the Center for Advanced Study in the Visual Arts, focused on these issues, particularly as they relate to the analysis of Renaissance bronze sculpture.

Moderated by Nicholas Penny, then Senior Curator of Sculpture, and Shelley Sturman, Head of the Object Conservation Department, the participants agreed that the ability to compare data would be valuable, but enumerated a host of problems and obstacles to be overcome before meaningful inter-laboratory comparisons could be made. This study is a direct product of that meeting. Funding for this project was provided by The J. Smith and the Smith Family Foundation for their support, counsel and assistance.

Asmus, B. Barwick, V. Bourgarit, D. Burgess, C. Chase, W. Craddock, P. La Niece and P. Craddock , —27, Butterworth-Heinemann, Oxford. Lang and P. Craddock , —7, British Museum, London. Craddock , —92, British Museum, London. De Vries, J. Grieken and A. Markowicz , —, Marcel Dekker, New York. Ellison, S. Fabian, H. Gerhartz, Y. Yamamoto, F. Campbell, R. Pfefferkorn, J. Rounsaville and F.

Ullmann , —, VCH, Weinheim. Glinsman, L. Heginbotham, A. Mardikian, C. Chemello, C. Watters and P. Ingelbrecht, C. ISO, , Guide Calibration in analytical chemistry and use of certified reference materials, International Organization for Standardization, Geneva. ISO, a, Guide Reference materials—Contents of certificates and labels, International Organization for Standardization, Geneva. ISO, b, Guide Uses of certified reference materials, International Organization for Standardization, Geneva.

Reference materials—General and statistical principles for certification, International Organization for Standardization, Geneva. Revision of definitions for reference material and certified reference material, International Organization for Standardization, Geneva. General requirements for the competence of reference material producers, International Organization for Standardization, Geneva.

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