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174 results on '"Eggert, Gerhard"'

4. Sustainable and Beneficial: Pollutant Absorption and Relative Humidity Control in Display Cases by Saturated Salt Solutions.

Author

Eggert, Gerhard, Brieger, Oliver, Marschibois, My Sa, Becker, Daniel, Bur, Christian, Siebel, Katja Franziska, and Grieb, Heiner

Subjects
*METAL oxide semiconductors, *SOLUTION (Chemistry), *ENVIRONMENTAL engineering, *HUMIDITY control, *GAS detectors
Abstract

In the light of sustainability, the nearly forgotten control of relative humidity (RH) in display cases with saturated salt solutions is re-evaluated. Spilling and creeping of salts can be avoided. By choosing magnesium nitrate or potassium carbonate, the temperature dependence of the RH and the emission of harmful gases are negligible. Measurements with metal oxide semiconductor (MOS) gas sensors showed such solutions to be excellent absorbers for corrosive pollutants such as acids and aldehydes, especially the alkaline potassium carbonate (hitherto not used in museums). The practical application of such solutions in display cases is currently being tested in a community science project in a number of museums. This will result in improved guidelines for conservators and it is hoped, in a revival of this passive, failsafe, low-carbon footprint technique. [ABSTRACT FROM AUTHOR]

Published
2024
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26. Crystal Structure, Polymorphism, and Anisotropic Thermal Expansion of $α-Ca(CH_{3}COO)_{2}$

Author

Bette, Sebastian, Eggert, Gerhard, Emmerling, Sebastian, Etter, Martin, Schleid, Thomas, and Dinnebier, Robert E.

Subjects
ddc:540
Abstract

Crystal growth & design 20(8), 5346 - 5355 (2020). doi:10.1021/acs.cgd.0c00563, Dehydration of calcium acetate monohydrate (Ca(CH$_3$COO)$_2$·H$_2$O) by heating to 300 °C leads to the formation of anhydrous $α$-Ca(CH$_3$COO)$_2$. During heating and cooling cycles, high- and low-temperature forms of $α$-Ca(CH$_3$COO)$_2$ were discovered. The reversible first-order phase transformation between the two forms occurs in a temperature range between 150 and 170 °C. The crystal structures were solved from laboratory powder X-ray diffraction (PXRD) data. The low temperature form of $α$-calcium acetate (LT-$α$-Ca(CH$_3$COO)$_2$) crystallizes at room temperature in a primitive triclinic unit cell with space group $P1$ with lattice parameters of $a$ = 8.7168(3) Å, $b$ = 12.6408(3) Å, $c$ = 12.3084(3) Å, $α$ = 117.4363(17)°, $β$ = 77.827(2)°, $γ$ = 115.053(2)°, and a unit cell volume of 1090.23(6) Å$^3$. High-temperature $α$-calcium acetate (HT-$α$-Ca(CH$_3$COO)$_2$) crystallizes at 300 °C in a rhombohedral unit cell with space group $R^-3$, lattice parameters of $a$ = 21.1030(5) Å, $c$ = 8.7965(2) Å, and a unit cell volume of 3392.58(17) Å$^3$. In both crystal structures, edge sharing polyhedra of calcium cations and acetate anions that coordinate in both a mono- and bidentate way build up channel-like motifs. During the phase transition, the coordination mode of a bridging acetate anion changes from monodentate to bidentate, and the elliptical channels of the low temperature form become circular. This leads to both negative and positive thermal expansion along different principal axes in the crystal structure of LT-$α$-Ca(CH$_3$COO)$_2$ and to an overall considerably big volumetric thermal expansion., Published by ACS Publ., Washington, DC

Published
2020
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27. Patricia Phillips (Hrsg.), The Archaeologist and the Laboratory

Author

Eggert, Gerhard

Abstract

Rezension zu: Patricia Phillips (Hrsg.), The Archaeologist and the Laboratory. Council for British Archaeology Research Report 58, London 1985. 70 Seiten mit 25 Abbildungen im Text und 55 Farbfotos auf Mikrofiche., Bonner Jahrbücher, Bd. 189.1989: Bonner Jahrbücher

Published
2019
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30. Karl Herold, Konservierung von archäologischen Bodenfunden

Author

Eggert, Gerhard

Abstract

Rezension zu: Karl Herold, Konservierung von archäologischen Bodenfunden. Metall, Keramik, Glas. Österreichische Akademie der Wissenschaften, Philosophisch-Historische Klasse, Sitzungsbericht 565. Verlag der Österreichischen Akademie der Wissenschaften, Wien 1990. 236 Seiten, 42 Farbtafeln., Bonner Jahrbücher, Bd. 192.1992(1993): Bonner Jahrbücher

Published
2019
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35. Korrosion von national wertvollen Kulturgütern aus Glas und Metall durch anthropogene Carbonyl-Schadgase im Innenraum

Author

Eggert, Gerhard

Subjects
Conservation science
Abstract

Glas-induzierte Metallkorrosion auf Museums-Exponaten (GIMME) tritt auf, wenn instabile historische Gläser durch Reaktion mit Luftfeuchtigkeit alkalische Oberflächenfilme ausbilden und diese in Kontakt zu Metall geraten. Eine modellhafte Durchmusterung von 800 einschlägigen Objekten aus der national bedeutenden Sammlung des Deutschen Bergbaumuseums Bochum (DBM) bestätigte, dass größenordnungsmäßig 10 % von GIMME betroffen sind. Das bisher übersehene GIMME-Phänomen ist also gar nicht selten, wenn man gezielt danach sucht, sondern tritt vielmehr regelmäßig auf. Als bisher unberücksichtigte neue Objektgruppen mit direktem Glas-Metall-Kontakt wurden gläserne Röhrenlibellen an Vermessungsinstrumenten und elektrische Glühlampen identifiziert. Wegen der nunmehr nachgewiesenen Häufigkeit ist die GIMME-Forschung für alle größeren Museen mit gemischter Sammlung relevant. Die Untersuchung von Korrosionsproben aus dem DBM und aus 18 weiteren Sammlungen in 7 Ländern mit Ramanmikroskopie bestätigten die Dominanz von Formiaten. Anders als auf Glas selbst und bei Korrosion von Bronzen in der Außenatmosphäre trat Sulfat (aus Schwefeldioxid) nicht bei GIMME auf. Als neue Korrosionsprodukte konnten durch Auswertung von Röntgenbeugungs-messungen die Strukturen eines basischen Kalium-Bleicarbonats (Kalium aus Pottascheglas) und eines basischen Zink-Kupferformiats (auf Messing) vollständig aufgeklärt werden. Weitere auftretende unbekannte Verbindungen ließen sich charakterisieren (Metallkationen, Anionen.

Published
2019
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40. The enigmatic 'battery of Baghdad.' (scientific theories on the ancient uses of a 2,000 year old finding)

Author

Eggert, Gerhard

Subjects
Antiquities -- Usage, Evidence, Scientific -- Evaluation -- Usage, Power supply (Electronics) -- Materials -- Evaluation -- Usage, Science and technology, Evaluation, Usage, Materials
Abstract

This 2,000-year-old find is considered by some scientists to be an electrical power source. Did it really work? 'Nothing is impossible,' it is said. This at least holds true for [...]

Published
1996

41. Ancient aluminum? Flexible glass?: looking for the real heart of a legend

Author

Eggert, Gerhard

Subjects
Legends -- Criticism and interpretation, Science and technology, Criticism and interpretation
Abstract

This incredible story is still being repeated and amplified even after almost 2,000 years. Is there any basis for it? What accounts for its longevity? The story has hardly been [...]

Published
1995

42. The formation of formates: 3a review of metal formates on heritage objects.

Author

Eggert, Gerhard and Fischer, Andrea

Subjects
FORMATES, METALS, COPPER alloys, POLLUTANTS, GLASS recycling, WOOD products, BIOACTIVE glasses, ANTIFOULING paint
Abstract

Metal formates sometimes occur as degradation products on heritage objects due to the use of wood products or other sources of formic acid and formaldehyde. They are often related to alkaline surfaces which transform formaldehyde directly into formate. The dominant role of formate on alkaline surfaces, for example in glass-induced metal corrosion (GIM) or calcium carbonate degradation, was explored in the Stuttgart research on rare heritage corrosion products. This review discusses these findings together with those from the literature: ocurrences of sodium and potassium formate on glass, calcium formate and calcium acetate-formate phases on calcareous materials, magnesium formate on Sorel cement and dolomitic sandstone, lead formate on metal and pigments, cadmium formate on coated objects, as well as various copper and zinc formates on copper alloys. In the latter cases, formates dominate as glass-induced metal corrosion products. The formation of formates constitutes irreversible damage, degrading the material of heritage objects. Therefore, preventive conservation needs to remove all sources of carbonyl pollutants in order to avoid such corrosion. [ABSTRACT FROM AUTHOR]

Published
2021
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47. When Glass and Metal Corrode Together, VI: Chalconatronite.

Author

Fischer, Andrea, Eggert, Gerhard, and Stelzner, Jörg

Subjects
*COPPER alloys, *FORMALDEHYDE, *GLASS, *CHRISTMAS trees, *SODIUM carbonate, *METALS
Abstract

Chalconatronite, Na2[Cu(CO3)]2·3H2O, is formed as a corrosion product when copper alloys are exposed to sodium carbonate solutions in the air. This also happens when metals come into contact with corroding soda glass which forms alkaline surface films in reaction with humidity from clean air. More often, substantial amounts of formaldehyde are present indoors which react to formate via the Cannizzarro reaction and accumulate over time in the films. Twenty cases of chalconatronite (including two mentioned in the literature) are reported as occurring on heritage objects with glass in contact with copper alloys: Baroque reliquaries with set glass gems, enamel on metal (sixteenth century and a modern replica of intentionally unstable composition), Christmas tree glass baubles with wires, glass buttons with metal shanks, a glass figure with a wire support, miners' lamps, and a glass framed daguerreotype. These confirmed identifications might help conservators in investigating similar cases to shed more light on the formation conditions. [ABSTRACT FROM AUTHOR]

Published
2020
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