Aging artificial

Precipitation Heat Treatment. The supersaturated solution produced by the quench from the solution temperature is unstable, and the alloys tend to approach equiUbrium by precipitation of solute. Because the activation energies required to form equiUbrium precipitate phases are higher than those to form metastable phases, the soHd solution decomposes to form G-P zones at room temperature (natural aging). Metastable precursors to the equihbrium phases are formed at the temperatures employed for commercial precipitation heat treatments (artificial aging). 

Koch-vergiitung, /. Metal.) artificial aging, -wasser, n. boiling water, -zeit, /. period of boiling or cooking, -zucker, m. brown sugar powdered sugar. 

Artificial aging. This provides hardening by precipitation of constituents from the solid solution. 

F. Sitek, 11th Conference of the Danube Countries on Natural and Artificial Aging of Plastics, Dubrovnik (Yugoslavia), October 1978. 

G.A. van der Doelen, J.J. Boon, Artificial ageing of varnish triterpenoids in solution, Journal of Photochemistry and Photobiology A Chemistry, 134, 45 57 (2000). 

Figure 3.11 DTMS total ion currents of (a) fresh dammar resin and dammar after (b) 1 week or (c) 2 weeks of artificial ageing. Reproduced from J. Photochem. Photobiol., A, 134, 13, Copyright 2000, with permission from Elsevier...

D. Scalarone, J. van der Horst, J. J. Boon and O. Chiantore, Direct temperature mass spectro metric detection of volatile terpenoids and natural terpenoid polymers in fresh and artificially aged resins, J. Mass Spectrom., 38, 607 617 (2003). 

In this study, only compounds with saturated ketone groups were found to be strongly oxidised after artificial ageing with simulated window-filtered daylight [39]. Compounds... 

The resin composition was indeed found to influence the ageing processes in mastic, the polymer fraction was shown to reduce the oxidation of triterpenoids (Figure 5.8). This was found for both natural ageing [33, 36] and artificial ageing. Because the polymer, a polymyrcene, contains many double bonds that can easily be oxidised [42], it might act as a radical stabiliser. The mastic samples shown in Figure 5.8 were obtained from three aliquots of the same mastic solution, the polymer part of the first aliquot was removed and added to the third. 

Figure 5.8 GALDI mass spectra of mastic with variable amounts of polymer, artificially aged for 880 h (36] (a) without polymer (b) normal mastic and (c) with added polymer. Oxidation and decomposition is enhanced with lower amounts of polymer, thus the mastic polymer retards oxidation of the triterpenoids...

L. Carlyle, N.E. Binnie, G. Van der Doelen, J. Boon, B. McLean, and A. Ruggles, Traditional Painting Varnishes Project Preliminary Report on Natural and Artificial Aging and a Note on the Preparation of Cross sections, in Postprints of Firms, Material Aesthetik Geschichte, International Kolloquium, AdR, Braunschweig, 1998, pp. 110 127. 

Lipids are generally identified in paint samples by evaluating characteristic ratio values of FA amounts and comparing them with naturally or artificially aged reference paint layers. Molar or weight contents are obtained after quantification based on calibration curves. 

A recent study on artificially aged paint layers highlighted the possible decrease of P/S ratio with ageing, due to the preferential loss of palmitic acid with respect to stearic acid, under the influence of the concentration of pigments [38]. 

This phenomenon has been investigated [27] by artificially ageing beeswax. It was hypothesized that the loss of alkanes was due either to the fact that the wax was heated during use or to its sublimation over the centuries under particular environmental conditions. Figure 7.2 summarizes the chemical mechanisms involved in beeswax degradation [27]. 

The chromatogram in Figure 7.6 shows a typical profile of an aged drying oil. It was obtained in the analysis of a reference layer of linseed oil on glass pertaining to the reference paint material collection of Opificio delle Pietre Dure (Florence, Italy), artificially aged by irradiation with a mercury lamp at 365 nm for 21 days, at a temperature of 20 °C and 80% relative humidity [9]. 

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