Lead corrosion

Lead corrosion (also known as lead corrosion ) is a process of lead corrosion that begins on the surface of endangered objects with the formation of light gray crusts, then leads to the sharp crust edges being rounded off as they deteriorate and finally ends with pitting with cavern formation and ever more profound destruction.

In the air, lead turns gray as a result of the oxidation process. In this form of lead (II) oxide (PbO) and lead hydroxide (Pb (OH) ₂ ). The latter reacts with the carbon dioxide in the air and forms basic lead (II) carbonate Pb (OH) ₂  · 2 PbCO ₃ , which protects the metal below from further corrosion.

With chlorine, lead reacts to form lead (II) chloride, with sulfur to lead (II) sulfide:

${\displaystyle \mathrm {Pb+Cl_{2}\longrightarrow PbCl_{2};\ \Delta H=-359\ {\frac {kJ}{mol}}} }$

${\displaystyle \mathrm {Pb+S\longrightarrow PbS;\ \Delta H=-94\ {\frac {kJ}{mol}}} }$

Under the influence of phosphoric acid , hydrofluoric acid , sulfuric acid and hydrochloric acid , a thin protective coating is formed from the salts formed on the surface of metal objects, which mainly consist of lead.

Examples

Corroded pipes of the organ of St. Kiliani (Höxter)

Lead feeding can both historic preservation areas (historic organ pipes , stained glass windows z) as well. B. in mechanical engineering ( lead slide bearings ) represent a massive problem.

Lead corrosion has caused immense damage to the pipework of various historically significant organs. Today it is assumed that this lead corrosion is mainly due to acids, for example acetic acid in oak, which is often used in organ building. Studies have shown that lead alloys with three or more percent tin are particularly well protected against lead corrosion.

Church buildings have been better insulated and sealed since the end of the 20th century. As a result, the indoor air is exchanged less often, which leads to permanently increased air humidity in the interior. Together with the acetic acid evaporating from oak wood, the increased air humidity effectively accelerates lead corrosion. A layer of lime was previously used as a preservation. Experiments are being made with a bath in sulfuric acid.

In the past, lead corrosion was also a problem with letter metal . In earlier times, lead was one of the most important and most widely used metals.

Web links

• Frank Grotelüschen : Decay of historical organs - lead corrosion and church mold , Deutschlandfunk - “ Science in focus ” from June 11, 2017

• Carolin Haller: Saving historical organ instruments: Measures against corrosion on lead pipes. Leibniz Institute for Material-Oriented Technologies. In: Internet presence. Informationsdienst Wissenschaft eV -idw-, November 30, 2018, accessed on December 2, 2018 . 

Individual evidence

1. ↑ Quoted from: Julia Voigt, Mila Schrader: Bauhistorisches Lexikon: building materials, construction methods, architectural details . Edition Elsewhere. ISBN 3-931824-29-2 .
2. ↑ ^{a b} Lead corrosion - when writings turn to dust. Archived from the original on June 9, 2012 ; Retrieved May 17, 2012 . 
3. ↑ "Collapse", EU investigation into lead corrosion. Archived from the original on December 31, 2013 ; accessed on December 31, 2013 . 
4. ↑ The COLLAPSE project Corrosion of organ pipes - causes and recommandations. Archived from the original on December 31, 2013 ; accessed on December 31, 2013 . 
5. ↑ https://www.deutschlandfunk.de/historische-orgeln-schutz-fuer-alte-metallpfeifen.676.de.html?dram:article_id=434611
6. ^ Römpp Chemielexikon, Volume 1, page 449, 9th edition 1989