News & Scientific Highlights
Refined diagnosis of the “concrete disease”
When bridges, dam walls and other structures made of concrete (cement and aggregates such as sand/gravel) are marked by map-like cracks after a few decades, the diagnosis is ASR (alkali-silica Reaction), in popular science terms also called “concrete disease or concrete cancer”. The ASR-induced microscale crack initiation can hardly be modelled, mainly due to our limited knowledge of the structure and property of the ASR products. Using X-ray absorption micro-spectroscopy at the PHOENIX beamline of the Swiss Light Source (SLS) allowed a refined diagnosis of ASR products by providing new insights into the crystallinity and structure of ASR products with micro-scale resolution.
Tuning the magnesium content in magnesium rich-calcites
Magnesium rich calcites are important functional biominerals. For example, they can be found in protective shells or eye lenses. Natural organism provide a surprisingly high degree of control on the amount of magnesium incorporation into calcites by yet not well understood mechanisms. Understanding such control mechanism is important when designing bio inspired functional materials. Here we systematically explore the impact of thermodynamic parameters on the degree of magnesium incorporation into calcite. In particular, we identify the thermodynamic conditions, where very high magnesium rich calcites (50% Mg/50% Ca) forms under ambient conditions of temperature and pressure. This is an important finding for geochemistry: Very high magnesium rich calcite is believed to be the precursor for dolomite. Despite its frequent occurrence in nature, its unknown formation pathway remains one of the big mysteries in geochemistry.
Aerosol-based synthesis of pure and stable amorphous calcium carbonate
Calcium carbonates are key materials to biomineralization, they are frequently used in industrial applications and also for carbon capture technologies. Finally, they serve as an important model system to test novel nucleation theories. Calcium carbonate crystalizes in a multi-step process, where amorphous calcium carbonate (ACC) is the most important precursor in the crystallization process. Existing synthesis protocols generate ACC of different stability and purity. To improve our mechanistic understanding of carbonate crystallization, reactivity and polymorph formation, the reproducible synthesis of clean and stable ACC is an important, and yet unresolved step. Here we use the fast reaction of CO2 with calcium hydroxide in airborne aerosols to reproducibly create pure and stable ACC, which may serve as a well-defined starting material for further chemical processing.
Study of Graphite Cycling in Sulfide Solid Electrolytes
Nowadays, most of the commercial Li-ion batteries employ graphite as the active material in negative electrodes. In the race for the next-generation Li-ion batteries, tremendous research efforts in academia and industry are carried out to replace the current flammable liquid electrolyte with a solid electrolyte, which could improve both, the batteries safety and energy density. Our study investigates two different sulfide-based solid electrolytes, 0.75Li2S-0.25P2S5 (LPS) and 0.3LiI-0.7(0.75Li2S-0.25P2S5), in combination with graphite and discloses the stability of the graphite-solid electrolyte interface. Optimizing the electrode morphology is the key to enhance the rate capability of all-solid-state cells. Using the special tender X-ray range allows chemical characterization of sulfur, phosphor and iodine.
HERCULES school 2019 at SLS
In the week of April 1-5 PSI welcomes 20 PhD students and postdocs taking part in the European HERCULES 2019 school on Neutron and Synchrotron Radiation. They will attend lectures and perform two days of practical courses at several beam lines of the Swiss Light Source.
Investigation of anionic redox activities in organic-based electrode for Li-ion batteries
To date the electrochemical activity of battery materials was always relying in the oxidation/reduction of cationic redox (change of oxidation state of transition metals generally). However, recently, it was established in new cathode materials (so call Li-rich cathode) that the oxygen from the crystal lattice might also play the role of anionic redox center leading to enhance then the specific charge of battery materials.
Von Hamos spectrometer for tender energies open to users
A new compact von Hamos spectrometer for tender x-rays (current energy range 2.25-4.5 keV), is now available for emission spectroscopy. This spectrometer allows analyzing the energetic composition of fluorescent light from the sample. It provides research opportunities for emission spectroscopy, and RIXS on the K (P-Sc), L (Zr-Cs) and M (Ir-Fr) absorption edges.
Amorphous CaCO3: Influence of the Formation Time on Its Degree of Hydration and Stability
Carbonate minerals serve as reservoir for CO2 in the global CO2 cycle, as biomineral in animal skeletons and shells of marine animals, and are used in carbon capturing techniques. Moreover, they serve as an important model system in crystallization studies, and have important commercial applications, for example as fillers. Researchers from EPFL and PSI developed a new methodology to study the crystallization of CaCO3 that offers both high temporal and spatial resolution, which is the key challenge in elucidating early stages of crystallization. Using X-ray absorption spectroscopy and other techniques it could be demonstrated that the degree of hydration of amorphous CaCO3 increases during its growth. As a result of the increasing degree of hydration, the stability of the resulting amorphous particles against solid-state crystallization decreases.
The negative charge density in Al-O monolayers on SiO2 surfaces
Single atomic layers of aluminum oxide embedded in SiO2 thin films, play an important role for the design of carrier-selective passivating contacts for high efficiency silicon based photovoltaic applications. Researchers from the Australian National University (ANU, Canberra, Australia), the Karlsruhe Institute of Technology (IT, Karlsruhe, Germany) and PSI have used synchrotron radiation to reveal the bonding configuration and local atomic surrounding of the Al-atoms in such surface oxide layers. The results corroborates theoretical calculations and contribute to a new model to explain the origin of the negative fixed charge in the Al-O/SiO2 stack, which has promising properties for a carrier-selective passivating contact for future silicon solar cells.