New inorganic coatings for cement-bound material surfaces with rare earths as hydrophobic agents

• Applicants: Professor Dr. Michael U. Kumke; Dr. Peter Thissen
• Subject Area: Construction Material Sciences, Chemistry, Building Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 555171095

The overall goal of the project is to produce novel inorganic coatings for cement-bound materials. Cementitious materials are the most significant due to their advantages in terms of raw material availability, processing, usability, material properties, durability and price. On the other hand, there is the large amount of CO2 in the production of cement. The coatings are intended to significantly increase the service life of the materials. In return, this would lead to savings in cement use and thus help reduce global CO2 emissions. Silicone resins are used as standard coatings in construction chemistry. These contain siloxane/polysiloxane bonds (Si-O-Si) for crosslinking with the mineral material surfaces and organic groups (-CH3) as carriers of hydrophobicity. However, long-term studies have shown that, despite their high binding energy, the siloxane bonds cannot withstand the chemical attack of water. The main reason for this is their high polarity. The organic groups cannot withstand long-term chemical attacks and are slowly broken down in the form of CO2. Another disadvantage of organic groups is that they represent a potential food source for the biofouling microorganisms. In addition, organic coatings often suffer from a low penetration depth into the building material to be protected. Our idea is to formulate a completely inorganic coating (without carbon). The opportunity arose because we were able to shift the hydrophobic carrier into a rare earth oxide. Rare earth oxides (such as Eu2O3) have an electronic structure in which the 4f orbitals are shielded from interactions with the environment by the full octet of electrons in the 5s2p6 outer shell. Consequently, these atoms would be less likely to exchange electrons and would not form a hydrogen bond with the water molecules at the interface. The aim of the project will be to anchor the hydrophobic carrier in the material with ligands so that it is not washed out again. All components used must be biologically harmless in the long term. First, samples are made for this. By using model surfaces, the use of materials can be greatly reduced. In addition, calcium silicate hydrate phases grown on silicon single crystals are ideally reproducible and can be used in surface science methods. Attempts will then be made to transfer the process to real cement-bound material surfaces.

• DFG Programme: Research Grants