Gypsum was used as a building material in antiquity and is still widely used as a binder in plaster, drywall, and spackling paste. Known as dihydrate in construction chemistry, gypsum is a water-containing calcium sulfate (CaSO4. 2 H2O).
In various calcination processes, some of the water of crystallization is removed, resulting in calcined gypsum, or hemihydrate (CaSO4. 0.5 H2O). When this material comes into contact with water, it reabsorbs it and sets up. The structure and exact water content of hemihydrate have remained a matter of speculation.
Michael F. Bräu (BASF Construction Chemicals GmbH) and Horst Weiss (BASF SE) have now brought this speculation to an end: by using single-crystal structural analyses they were able to solve the structure, generate a structural model, and support it with computer calculations. As reported in the journal Angewandte Chemie, hemihydrate does indeed contain exactly one half of a water molecule per structural unit—tightly bound to the calcium sulfate framework.
Hemihydrate is the most heavily produced inorganic compound worldwide, so its structure and water content are of great interest, both economically and scientifically. The first structural model of this compound was proposed in 1933, and it still holds today. Since then, there have been a number of refined models, which do a good job of reproducing the fundamental calcium sulfate scaffold. However, there has always been disagreement about whether the water molecules also adopt a defined arrangement and if so, what it looks like.
Answering such questions requires structural analyses based on X-ray diffraction experiments carried out on single crystals of the right size and quality. The atoms of a crystal deflect incoming X-rays; the resulting characteristic diffraction pattern makes it possible to calculate the positions of the individual atoms in the crystal. However, this has been very difficult to achieve in the case of gypsum crystals. Bräu and Weiss have now been successful. By using various tricks they were able to interpret the diffraction pattern and to use their computer calculations to consolidate the data into a plausible structural model. The alignments of the individual water molecules and their distances from each other prove that there are no interactions between them; they are bound only to the calcium sulfate framework. They are packed in so tightly that no further water molecules can enter into the channels of the basic structure. Variations of the crystal with a proportion of water molecules above 0.5 per formula unit thus seem to be very unlikely.
Author: Michael F. Bräu, BASF Construction Chemicals GmbH, Trostberg (Germany), mailto:firstname.lastname@example.org
Title: How Much Water Does Calcined Gypsum Contain?
Angewandte Chemie International Edition 2009, 48, No. 19, 3520–3524, doi: 10.1002/anie.200900726
Michael F. Bräu | Angewandte Chemie
Bolstering fat cells offers potential new leukemia treatment
17.10.2017 | McMaster University
Ocean atmosphere rife with microbes
17.10.2017 | King Abdullah University of Science & Technology (KAUST)
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
17.10.2017 | Life Sciences
17.10.2017 | Life Sciences
17.10.2017 | Earth Sciences