Central Europe Chemistry

You hold in your hands a special issue of Nachrichten aus der Chemie, the monthly magazine for members of the Gesellschaft Deutscher Chemiker (GDCh), the German Chemical Society. In this issue we focus on Central Europe, with contributions authored by colleagues from Hungary, Slovenia and Slovakia. It is being distributed to the members of the GDCh and the Austrian Chemical Society (GÖCH) as well as to the members of the chemical societies in the Czech and Slovak Republics, Slovenia and Hungary. It thus reaches almost 40,000 chemists. With this special publication we want to emphasise and celebrate the importance of the relationship between the GDCh and the chemical community in Germany and our counterparts in your countries. As members of ChemPubSoc Europe and through our bilateral lectureships with a number of chemical societies, we already cooperate in many ways with Central European chemical societies, for example on scientific publications. On the personal level, too, there is considerable scientific collaboration and exchanges of scientists and students. But there is always room for more: the chemical societies should act as active partners and as catalysts to step up the work we do together. Another important platform for collaboration, one in which your societies are important partners for the GDCh, is Euchems, the European Association for Chemical and Molecular Sciences. We are particularly pleased, therefore, to include in this special issue an interview with the Euchems President Elect, Ulrich Schubert. Living as he does in Vienna, he is an apt representative of Central Europe. He outlines the priorities for his presidency, which will commence at the next Euchems General Assembly in Belgrade in October this year.
I hope that this publication helps to further strengthen the ties between our societies and to sharpen our joint European focus. Enjoy your reading!
Wolfram Koch, Executive Director of the German Chemical Society
 This year chemistry has a major opportunity to display its skills — and not only to our educated partners, students, employees, colleagues and interested opinion makers. No: this year we are targeting people who have to believe us either because they did not have the opportunity to study or because their education was weak in natural sciences. This year we are out to communicate in a language that the public understands. They will only listen, and they will only be convinced, if the scientific community's messages are clear and concise. But we can succeed in this only if we reach a level of common understanding beyond our traditional professional struggle for scientific precision, with its unemotional, intellectual striving for the best and most accurate results. Our expertise in technical and logical discriminatory analysis is only one side of the coin. We also need the understanding and empathy of and for non-academics who are sometimes misled by interests.
Until now, we have been rather isolated within the national boundaries of our regionally diversified Europe. Still, over the last ten years a wonderful dynamic process has taken hold. Parallel with the political unification of Europe, fledgling networks within the scientific community have been able to intensify their exchange of information and ideas. This appears perfectly normal to today's students. To the older generation, however, it is a boon — a gift they never anticipated. So we will celebrate chemistry and its role in modern life during our Chemistry Days in Linz, Austria, this year and join the Euchems congress in Prague in the Czech Republic in 2012. This issue of Nachrichten aus der Chemie will serve as an advance ambassador.
Wolfgang Buchberger, Head of the Organising Committee of the 14th Austrian Chemistry Days


II Our new world
W. Koch, W. Buchberger
III “Solidarity is a necessity” C. Remenyi
Interview with Ulrich Schubert, president elect of the Euchems.
Photos: Aamon, Christian Delbert, Alexander Raths, FomaA (all <a href="https://Fotolia.com" target="_blank">Fotolia.com</a>); BASF (2x); Ernst Guggolz
A chemical Engineer's View of the Red Mud Disaster J. Szépvölgyi
What chemists can learn from the
mud disaster in Hungary last autumn.
 VIII Thaumasite: Its Relevance to Sulp hate Corrosin in Concrete M. Drabik
Thaumasite sulphate attack consti tutes a real danger.
  XI 4th Euchems Che mistry Congress Prague
Invitation and Preview.
  XII Micro- and Mesoporous Materials: On the way to applications V. Kauèiè
Materials for environment protection, and health care.

Artikel

Our New World

Porous materials with pore diameters of a few tenths of a nanometre (microporous materials) and with pore diameters between a few nanometres and a few tens of nanometres (mesoporous materials) have a very wide range of applications. Their particularly important properties are large surface areas, adsorption capacities, and shape selectivity for molecules. A well-known and immensely exploited class of microporous materials are zeolites. These are aluminosilicate materials built of AlO4 and SiO4 tetrahedra, which are connected through common oxygen vertices into many different porous structures.<xref rid="bib1" ref-type="ref">1</xref> Zeolites are extensively used as catalysts in oil and gas refinement, because they contain catalytically active acid sites due to the aluminium within their frameworks.
Over the past two decades researchers have attempted to improve the efficiency of zeolites in order to extend their range of applications and to tailor their properties for specific applications. These attempts included the modification of zeolites with small amounts of (transition-) metal ions to generate redox sites within them<xref rid="bib2" ref-type="ref">2</xref> and the preparation of zeolites in the form of nano-sized particles to increase their surface areas.<xref rid="bib3" ref-type="ref">3</xref> Intensive research in the field of porous materials also led to the development of silicate mesoporous materials<xref rid="bib4" ref-type="ref">4</xref>,<xref rid="bib5" ref-type="ref">5</xref> and of porous materials with hybrid inorganic-organic composition.<xref rid="bib6" ref-type="ref">6</xref>


<h2>Catalysts</h2>
Catalysts are important to the chemical industry and environmental remediation because they can very effectively convert one chemical to another. Our recent work is focused on the development of supported catalysts, more precisely, on the development of materials that consist of porous silicate supports and catalytic components based on transition metals. The catalytic components are included either as nanoparticles of metal oxides or as metal-modified zeolitic nanoparticles. Preparation of catalytic components in the form of nanoparticles enhances the efficiency of catalysts, because it enlarges the surfaces of particles and thus increases the accessibility to catalytic sites. To avoid agglomeration of nanoparticles, it is favourable to stabilise them into/onto a support, e.g., to deposit or incorporate them into mesoporous materials.
We developed the synthesis route for the incorporation of isolated transition-metal ions (Ti, Mn, Fe) into zeolitic particles (Silicalite-1, ZSM-5, BETA) of typical dimensions of up to 100 nm. In order to understand how to prepare such nanoparticles most efficiently, detailed studies of zeolite formation and growth were carried out using spectroscopic and microscopic techniques.<xref rid="bib7" ref-type="ref">7</xref> Knowledge of the preparation of functionalised zeolitic seeds has allowed us to develop hierarchical porous structures, that is, microporous/mesoporous composite materials. For example, we organised microporous zeolitic seeds containing isolated Ti centres into mesoporous silicate structures with a hexagonal cubic mesopore arrangement (TiBeta/MCM-41, TiBeta/MCM-48, TiBeta/SBA-15).<xref rid="bib8" ref-type="ref">8</xref>—<xref rid="bib10" ref-type="ref">10</xref> These composite solids enabled the diffusion of larger molecules through their mesopores than did pure microporous zeolitic materials. The composites were also thermally more stable than pure mesoporous materials and were not prone to transition-metal leaching. This means that the materials could be readily recovered following catalytic reactions.
More recently we have started to use mesoporous supports for the immobilisation of metal oxides. We have homogeneously distributed MnOx nanoparticles onto a new mesostructured silicate support with textural porosity, KIL-2.<xref rid="bib11" ref-type="ref">11</xref> The material is a potential catalyst for environmentally friendly applications due to its convenient structural characteristics (porosity, distribution and accessibility of nanoparticles), hydrothermal stability, and its non-toxicity and cost-effectiveness. Ordered (SBA-15) and disordered (KIL-2) mesoporous silicate supports were used also for the immobilisation of TiO2 nanoparticles. TiO2 supported on SBA-15 and KIL-2 showed high photocatalytic activity towards the degradation of volatile organic compounds such as isopropanol and toluene.


<h2>Natural zeolites for wastewater treatment</h2>
We come even closer to the topic of environmental protection by investigating the potential of natural zeolitic tuffs for the removal of toxic metals from wastewater and drinking water. Natural zeolites have attracted interest because of their availability and non-toxicity, as well as by their robustness and high selectivity. In collaboration with the groups from Zagreb and Belgrade we performed detailed structural and kinetic studies of unmodified and metal-loaded zeolitic tuffs from two deposits (Vranjska Banja, Serbia, and Donje Jesenje, Croatia) in order to determine the sorption behaviour of selected zeolites for zinc, copper, manganese, nickel, chromium and arsenic.<xref rid="bib12" ref-type="ref">12</xref>—<xref rid="bib15" ref-type="ref">15</xref> The studies showed that the higher content of zeolite clinoptilolite in zeolitic tuff from Serbia (more than 70 %, vs. 50 % for Croatian tuff) resulted in its better sorption performance for selected metals. The pre-treatment of zeolites with Na+ significantly enhanced the uptake of all metal cations, while pre-treatment with Fe3+, which resulted in stable iron-oxo-species on the zeolite surface, enabled the sorption of anions. Spectroscopic and microscopic analyses (XAS, XPS, SEM, TEM) showed that metal concentrations in all samples decreased from the surfaces towards the subsurface region of crystallites suggesting that metal atoms first accumulate on the surfaces of crystallites. Metals arrange in the pores as cations coordinated with framework oxygen atoms or some water molecules (e. g. Cu2+ and Zn2+) or in the form of larger poly-oxo-complexes (e. g. Cr3+). Anionic species form smaller oxo-complexes, which are attached to the iron cations on the surface of the clinoptilolite. Post-treatment of the samples with HCl, NaCl or NH4Cl solutions revealed irreversible sorption of chromium and arsenic and mostly reversible sorption of zinc and copper.


<h2>Hydrogen storage materials</h2>
Hydrogen is foreseen as an efficient and clean energy carrier and has already been widely tested as an alternative to fossil fuels. One of the main obstacles toward the commercialisation of hydrogen technology is safe storage of H2 under moderate conditions. One family of promising materials for hydrogen storage applications is the metal-organic framework (MOF) materials,<xref rid="bib16" ref-type="ref">16</xref> which are crystalline materials composed of metal units linked through organic linkers with strong covalent bonds to form three-dimensional porous structures with exceptional adsorptive properties. At low temperatures (77 K) they already meet the 2010 U.S. Department of Energy targets for H2 storage capacity (gravimetric and volumetric storage capacity of 6 wt.% and 45 g H2/L, respectively), but at ambient conditions their storage capacities are still low.<xref rid="bib17" ref-type="ref">17</xref>
We focused our research mostly on MOF materials based on light and/or non-toxic metal atoms, such as magnesium, calcium, titanium, iron, and zinc. We developed four new 3-dimensional metal-organic open-framework materials: two zinc-based 1,3,5-benzenetricarboxylates, a magnesium succinate and a calcium pimelate. We coped with the structures of new materials by using either a CCD single-crystal diffractometer or a synchrotron facility (Soleil, Paris, France). In collaboration with the Institute Lavoisier, University of Versailles, we attempted to enhance the interaction between H2 molecules and MOF materials and thus to increase H2 storage capacity at ambient temperatures by modification of the selected MOF materials via post-synthetic or in-situ introduction of functional groups. Iron terephthalate (FeIII(bdc)OH or MIL53(Fe)) was modified by CF3, titanium terephthalate (Ti8O8(OH)4(bdc)6 or MIL125(Ti)) was modified by NH2 group, and zirconium terephthalate (Zr6O6(OH)4(bdc)6 or UiO-66(Zr)) by NH2 and CF3 groups. We discovered that modification of the organic linker caused an increase of H2 storage capacity only in the case of MIL53(Fe). Another attempted method for increasing storage capacity for H2 is to introduce charged metal species onto the pore surface. Mg2+, Ni2+ and Li+ are introduced into highly porous iron terephthalate and trimesate (MIL-101(Fe) and MIL-100(Fe)) through anionic functional groups. Determination of H2 storage capacities of these modified MOF materials is in progress.


<h2>Materials for heat storage</h2>
Development of new heat-storage systems is extremely important for broader solar-energy and waste-heat utilisation for domestic and industrial use. Efficient low-cost heat storage is particularly important when there is a gap between when a renewable energy or waste heat is available and when the energy or heat is required (e. g., solar energy is available in summer and needs to be stored until winter).<xref rid="bib18" ref-type="ref">18</xref>
Another class of promising materials for heat storage is adsorbents, among which microporous and mesoporous materials with a broad surface area play an especially important role. The utilisation of water adsorbents for heat storage is schematically explained in Figure 3. The heat collected and stored in an adsorbent during summer could be, upon adsorption by water molecules, released and used during winter.
In our group we study the interdependency of the structure of novel microporous and mesoporous materials and their energy storage abilities (energy density, thermal power, transport properties, and the temperature levels for charging and discharging). Using the knowledge obtained, we then also try to improve microporous and mesoporous storage materials. For example, we have prepared and optimised a very promising microporous aluminophosphate adsorbent. Its performance, which combines the water uptake mechanism, the heat of adsorption, and hydrothermal stability, is the best so far among the aluminophosphates for water-sorption-based heat storage applications and also for heat transformation in heat pumping systems.


<h2>Drug-delivery systems</h2>
Drug-delivery systems based on mesoporous silicates have recently attracted considerable attention, because they could enable controlled release of drugs. This means that by using such drug-delivery systems in combination with proper endogenic or exogenic physical or chemical stimuli, drugs could be released in a given part of the human body within a given time period in sufficient concentrations.<xref rid="bib19" ref-type="ref">19</xref> In our group we are studying incorporation and release of indomethacin as a model drug to and from two carriers, SBA-15 and MCM-41. Both have well-defined hexagonal pore systems, but the diameters of the pores within them are different. The diameter of pores in SBA-15 is about 9 nm, while the diameter of pores in MCM-41 is approximately 3.5 nm. Indomethacin is an anti-inflammatory drug that is especially interesting as a model drug substance because it can crystallise in several different forms.
Our study particularly focuses on the physical state of the drug within mesopores with different diameters. We are investigating how this state depends on the concentration of the drug within the pores and how it influences drug release. We are also studying the influence of the functionalisation of the silicate walls on drug incorporation and release. Detailed description requires inspection by XRD, NMR, thermal (TG and DSC) analysis, nitrogen adsorption and helium picnometry.
Initial results show very interesting and unexpected effects due to the confining of a drug within mesopores: incorporation of indomethacin proceeds differently in pores with different diameters. In SBA-15, when the amount of the incorporated drug is small, the drug forms a thin layer on the pore wall. When the amount is increased, particles extending throughout the entire pore diameter begin to grow. In MCM-41, on the other hand, particles form even at small amounts of the incorporated drug. The two porous systems also direct or favour formation of two different forms of indomethacin. SBA-15 directs the formation of indomethain alpha, while MCM-41 directs the formation of indomethacin gama.


<h2>Characterization</h2>
Characterization of the materials prepared in our laboratory is an extremely important part of our research. It allows us to understand the structure and function of the materials. We combine diffraction techniques with microscopy and with spectroscopic methods probing the local short-range arrangements of constituents. In the past years we have installed (or gained access to) valuable equipment such as three X-ray powder diffractometers (Siemens D5000, PANalytical X'Pert PRO, and PANalytical X'Pert PRO HTK), microscopes SEM (Zeiss SupraTM 3VP), TEM (200-kV field-emission gun microscope JEOL JEM 2100), and AFM (Agilent 5500), NMR spectrometer (600 MHz Varian NMR systems with several MAS probeheads), gas adsorption analyzer (Micromeritics, ASAP), system for thermal analysis (SDT 2960), and synchrotron facilities for X-ray absorption spectroscopy (DESY in Hamburg, Elettra in Trieste).
Emanuela Žunkoviè, Tomaž Èendak, Tadeja Birsa Èeliè, Darja Mauèec, Tina Ukmar, Mojca Rangus, Saša Cecowski, Matjaž Mazaj, Gregor Mali, Alenka Ristiè, Nataša Zabukovec Logar, Nataša Novak Tušar, Roman Gabrovšek, Venèeslav Kauèiè are authors of this article. Venčeslav Kaučič is a head of the Laboratory for Inorganic Chemistry and Technology at the National Institute of Chemistry in Ljubljana and since 1992 professor of Inorganic Chemistry at the University of Ljubljana. His current research interests include synthesis and characterisation of porous solids (micro- and mesoporous materials, their composites and metal-organic frameworks), with the emphasis on the use and development of crystallographic methods. He is currently the president of the Slovenian Chemical Society and the president of the Science Council of the Slovenian Science Foundation.


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Micro‐ and Mesoporous Materials: On the way to Applications

Red mud is the by-product of the Bayer-processing of bauxites, one of the oldest large-scale industries in the world. In 1892 Karl Joseph Bayer, an Austrian chemist, applied for a patent on the digestion of bauxite, an aluminium-containing ore, by means of a concentrated sodium hydroxide solution employed at elevated temperature and pressure, which enables dissolution of the aluminium content and its separation from other bauxite components. From the caustic solution the dissolved aluminium hydroxide can be precipitated by dilution. Then the hydroxide is subjected to calcinations to form alumina, from which metallic aluminium is produced by electrolysis. The other metallic components of bauxite, such as iron, titanium, and rare earth metals, are not dissolved during digestion, so that they form a residue, which in turn is disposed of using various amounts of caustic solution. Nowadays about 90 % of bauxite is processed using the Bayer technology.
The caustic mud containing the bauxite residue is termed “red mud”. It consists of two main components, the caustic solution and the bauxite residue. Its characteristic red colour is due to its high iron content. The creation and disposal of red mud are a problem throughout the world. Over the course of 93 years, from the beginning of alumina production in 1892 until 1985, some 109 tons of bauxite residue were disposed of worldwide. This quantity then doubled in the next 15 years. The deposited bauxite residue amounts to about 3·109 tons in the world now, with an annual accumulation rate of about 120·106 tons.
The red mud leaving the Bayer processing plant in the Ajka refinery consists of 30 % bauxite residue and 70 % sodium hydroxide solution with a pH of 12 — 13. This mud has a density of about 1.5 g·cm—3, and its rheological properties are close to those of pure water. In environmental terms, the high alkalinity spells a special danger; the direct environmental impacts and serious health consequences of the disaster in Ajka are mainly attributed to the caustic ”flood”. Environmental loading due to the sedimentation of bauxite residue must not to be overlooked either, however.
There have been intensive investigations of the composition, physical and chemical properties of bauxite residue just before and after the Ajka disaster. The dissolution of different components along with their health and environmental impacts were widely studied: for several reasons, there was a diversity of results. It is important that these discrepancies and the facultative paradoxes involved be exposed through careful consideration of all important aspects, including sampling and the conditions under which the analyses were performed.
It is often asked how much sloppy slurry, in what composition, escaped from Chamber 10, and how it could spread over a territory of some 10 km2. These questions have still not been entirely answered, and further investigation by specialists in the field is required. Nevertheless, the available information does permit some conclusions. According to conservative estimates, caustic slurry of about 1.3 million m3 spilled out from the chamber. The solid content of the slurry was 7 to 8 %; that is, with a density of 1.15 — 1.2 g·cm—3 with a viscosity of 0.01 Pa·s it was less concentrated than the red mud from Ajka refinery. The force and velocity of the caustic flood is believed to be due to the high level of solution within the chamber and the very rapid breaking of the dam, so that a vast amount of low-density liquor rushed through a relatively narrow opening. Two items on the aerial photo of the dam (Figure 1) are particularly worthy of note. The first is the sharply vertical surface of the fracture, which indicates an instantaneous rupture of the dam. The second is the upper part of the fracture surface, which is white and thus was not in contact with red mud. From this we know that the dam broke from the bottom up. To summarise: in this case we can assume a very rapid breaking of the dam from the bottom up, with the thin slurry flowing through the opening with great force.


<h2>Red mud disposal</h2>
The harmful effects of the red mud flood were closely connected to disposal practices in Ajka. Some of the causes were, first, the low solid content and high alkalinity of the thin slurry. For a long time, not only in Ajka but in other alumina refineries all over the world, a caustic slurry of about 30 — 35% solid content from bauxite digestion was pumped into land-based ponds without neutralisation or thickening. This practice, called “lagooning” (Figure 3a), is the simplest and cheapest land-based disposal method, though the riskiest in environmental terms. As with all disposal methods, lagooning has both advantages and disadvantages. Advantages are:
<list list-type="order">
<list-item>
</list-item></list>it has the lowest capital costs of all land-based disposal methods;

<list-item>
it does not require additional thickening or filtration;
</list-item>
<list-item>
the dust potential is minimised;
</list-item>
<list-item>
there is no return of impurities to the Bayer technology.
</list-item>

Disadvantages are:
<list list-type="order">
<list-item>
</list-item></list>it requires substantial areas of land for disposal;

<list-item>
significant financial resources need to be allocated for long term closure and rehabilitation;
</list-item>
<list-item>
there is a loss of sodium hydroxide and alumina with entrained solution.
</list-item>

If the red mud is not neutralised before disposal further problems are encountered, such as:
<list list-type="order">
<list-item>
</list-item></list>a strongly caustic, poorly compacted mud in the pond overlaid with a highly alkaline solution;

<list-item>
a range of safety and environmental hazards;
</list-item>
<list-item>
the significant amount of engineering required for safe operation and to lower the chances of disaster;
</list-item>
<list-item>
the difficulty of closing and rehabilitating the disposal site due to the huge amount of caustic liquor that would need to be removed.
</list-item>

Some of the disadvantages can be eliminated by employing mineral acids to neutralise the slurry prior to discharge.
Under favourable geological conditions the disposal site can be developed in natural caves or hollows. If the site does not provide these, artificial ponds should be constructed with thorough consideration of all important technological and environmental factors. With Chamber 10 in Ajka, there were doubts regarding even this. The pond, whether natural or man-made, should be lined with a water impervious material to minimise infiltration of liquor into the underlying soil and ground water. The most suitable lining is a single layer of compacted clay, but other options such as polymers or geo-membranes can also be used.
The other land-based disposal method is dry disposal (Figure 3b). In this case the residue from the mud washing is filtered to form a dry cake of &gt;60% solid content. The material on the filter is also washed with water or steam to regain the soda and to decrease the alkalinity of the residue. The bauxite residue of increased solid content is transported to disposal by trucks.
Advantages of dry disposal include:
<list list-type="order">
<list-item>
</list-item></list>smaller area of land required for storage;

<list-item>
less complicated engineering structures and a lower risk of material discharge;
</list-item>
<list-item>
soda and alumina recycled into the Bayer process;
</list-item>
<list-item>
reduced environmental hazard;
</list-item>
<list-item>
facilitation of further processing of bauxite residue;
</list-item>
<list-item>
less complicated closure and rehabilitation.
</list-item>

The disadvantages of this method are that:
<list list-type="order">
<list-item>
</list-item></list>it requires sufficient land area for storage;

<list-item>
significant capital investment is needed for long-term closure and rehabilitation;
</list-item>
<list-item>
specially constructed high capacity filters are needed;
</list-item>
<list-item>
the recycled caustic solution may induce technical problems in the Bayer technology;
</list-item>
<list-item>
there is a chance of dust lift-off from the surface of the dry stack.
</list-item>

Recently, with environmental aspects gaining more attention, the regulations on disposal are becoming stricter. Thus, disposal practice is moving towards dry disposal worldwide. The biggest alumina refineries mainly use dry disposal methods. Even in the Ajka refinery dry bauxite residue is stored from February 28, 2011 beginnigly. There will be fewer soda and alumina losses, the risk of a disaster like that of October 4, 2010, will be minimised, and the negative environmental impacts of alumina production will decrease as well.


<h2>The residue as secondary raw material</h2>
In addition to deposition, the bauxite residue can be utilised as a secondary raw material (cf. Table). It contains valuable metals, such as iron, titanium, vanadium and rare metals in different concentrations. Extensive research and development on transforming bauxite residue into valuable products has been conducted in various countries, including Hungary, has taken two main directions:
The first involves utilisation of the bauxite residue itself as a material with special physical and chemical properties, or, alternatively, to separate the constituents of the bauxite residue and transform each into value-added products.
The second option, based on technical references and our extensive research on Hungarian bauxite residues, involves the many technical possibilities for selecting and processing the components of red mud. The solutions may differ significantly in volume and in technical and economic terms. We can say with certainty, however, that complex processing aiming at transformation of all components of red mud into valuable products may be feasible in technical, environmental and economic terms at one and the same time.


<h2>What we have learned</h2>
 We have learned much from the red mud disaster in Ajka — a long list of legal, technical, environmental, human, social and other lessons. Let us name just two: first, human and environmental aspects can never be made secondary to economic or any other considerations; second, during operations involving such safety hazards as a red mud pond, we must take precautions against any worst-case scenario, and the facility should be designed, constructed and operated with this aspect always in mind.
Jαnos Szépvölgyi is director of the Institute of Materials and Environmental Chemistry of the Hungarian Academy of Sciences.

A Chemical Engineer's View of the Red Mud Disaster

The destruction of concrete and mortar in environments rich in sulphates and carbonates is termed sulphate attack: in terms of topical chemical changes, it is attributed to thaumasite<xref rid="bib1" ref-type="ref">1</xref> added to ettringite. The scope of sulphate ingress (as opposed to durability) into concrete has been recorded based on a decrease of flexural strength, changes in length, and observation. Phase changes studies have confirmed beyond doubt the relevance and role of thaumasite and thaumasite sulphate attack (TSA) to concrete, but the latter must not be overestimated. Thus, the amount of thaumasite in destructed concrete bodies, as well as quantification of the TSA portion of overall deterioration caused by sulphate attack on construction material, remain the subjects of ongoing discussion in the research and technology of concrete and mortar.
 The first step in damage to concrete and mortar and the constructions based on them is observable in the formation of ettringite and conjugated mass and volume changes leading to cracks, which enable water to access the original material. Repeated (cyclical) wetting and drying increase both the permeability of the material and the probability of reactions of atmospheric CO2 with sulphates and the C-S-H phase of the original material to form a. o. thaumasite — CS·Cs·Cc·H15.<xref rid="bib1" ref-type="ref">1</xref>—<xref rid="bib3" ref-type="ref">3</xref> One of the preconditions for TSAs on concrete construction materials is relatively low environmental temperatures (below 15o C). The presence of thaumasite, and thus the development of TSAs on concrete, have been confirmed by X-ray phase analysis, thermal analysis and electron microscopies.


<h2>Thaumasite: composition and basic structural features</h2>
Thaumasite rarely occurs as a natural mineral, an alteration product of limestone. The chemical formulae [Ca3Si(OH)6·12 H2O](SO4)(CO3) or CaSiO3·CaCO3· ·CaSO4·15 H2O show the composition and basic structural features of thaumasite: the short-hand cement chemistry notation CS·Cs·Cc·H15 is widely used (also in this text). Although it is generally assumed that a solid solution series between thaumasite and ettringite exists, both substances crystallize within different space groups. A possible discontinuity has been identified and is characterised by a gap in the a-dimension of the solid solution phases,<xref rid="bib4" ref-type="ref">4</xref> while details of the crystal structure of thaumasite were reported much earlier.<xref rid="bib5" ref-type="ref">5</xref> A series of thermal decomposition studies of thaumasite are to be found in the literature.<xref rid="bib6" ref-type="ref">6</xref>—<xref rid="bib10" ref-type="ref">10</xref> The basic outputs may be summarised as part of the data on the decomposition of mineral thaumasite<xref rid="bib5" ref-type="ref">5</xref>—<xref rid="bib8" ref-type="ref">8</xref>, as may proposals of the methodology of thermo-analytical and microstructural investigations of thaumasite as a form of sulphate attack in concrete.<xref rid="bib8" ref-type="ref">8</xref>—<xref rid="bib12" ref-type="ref">12</xref>
Until the end of the 1990s, the destruction of concrete and mortar by sulphate attack was attributed to the formation of two minerals: ettringite (C6As3H32) and gypsum (CsH2).<xref rid="bib1" ref-type="ref">1</xref>—<xref rid="bib3" ref-type="ref">3</xref>,<xref rid="bib12" ref-type="ref">12</xref>,<xref rid="bib13" ref-type="ref">13</xref> This form of destruction is accompanied by a local increase in volume and by the consumption of aluminium within the cement, both obviously in limited quantity in ordinary concrete. The thaumasite form of sulphate attack on concrete and in mortar — TSA — requires a source of sulphate and also of carbonate.<xref rid="bib1" ref-type="ref">1</xref>,<xref rid="bib2" ref-type="ref">2</xref> It tends to form at low temperatures — typically about 4 — 10 oC. Thaumasite results from a reaction by the strength-forming C-S-H phases to sulphate ions or a sulphate-containing compound in the presence of a source of carbonate and water (moisture). Sulphate can be derived from a variety of sources: groundwater or mineral salts are common examples. Carbonate is present in atmospheric CO2 or in limestone present within the concrete or mortar. Although the calcium silicate hydrate in concrete provides most of the strength of concrete, it also becomes a reagent of thaumasite formation. Thus the affected system suffers extreme weakening: concrete severely affected by thaumasite formation can easily be broken with the fingers and the coarse aggregate extracted.
We have earlier reported our findings of the presence and contents of thaumasite in a selection of buildings from several regions in Slovakia that possibly display the characteristics and effects of TSA.<xref rid="bib3" ref-type="ref">3</xref>,<xref rid="bib14" ref-type="ref">14</xref> Our laboratory has also studied and analysed thaumasite formation and TSA itself on model systems using an aggressive attack methodology: a cooled (5 ± 2o C) MgSO4 (1.5 % by mass) and Na2SO4 (5 % by mass) solution, the volume of the solution is 10 times that of the test sample. These extremely aggressive environmental testing conditions were chosen to achieve in a relatively short time data that would take much longer to compile under service conditions.
Changes in X-ray phase analysis, electron microscopy, flexural strength and length were measured and evaluated using routine methodologies. Phase compositions of probes were determined by means of X-ray data (difractometer Philips PW 2235, CuKa radiation), simultaneous thermal analysis (sdt 2960 — T.A. Instruments, TGA &amp; DTA), and electron microscopy (electron microscope Zeiss EVO 40 with the microanalyzer Bruker axs). An assessment of the scope of deterioration was also achieved by visual observation and by standardised measuring of changes in flexural strength and length, and by evaluating the evolution of these over a given period.


<h2>Investigating thaumasite</h2>
The methodology developed<xref rid="bib9" ref-type="ref">9</xref> and used for the indication of thaumasite based on thermo-analytical data depends on analysis of step 1 of the thermal decomposition of thaumasite (cf. eq. 1) exerting characteristic (a) stoichiometry and (b) DTA endoeffect, both taking place from 108 to 128 oC. The mole fraction xth of thaumasite in the inspected sample is straightforwardly expressed (cf. eq. 2) as the ratio of the value of TG mass loss — ΔmI(exp) of probe at the above temperature interval and the value of mass loss from proposed stoichiometry during this step of decomposition — ΔmI(st) = 37.6%. Both the occurrence of the DTA endoeffect between 108 and 128 oC and the value of TG mass loss that are characteristic of step 1 of the thermal decomposition of thaumasite enable an evaluation of the content of thaumasite present in the sample down to as little as 0.1%. Figure 1 illustrates the decomposition (dehydroxylation) of thaumasite as evidenced by the DTA effect (108.7 oC) and thus by relevant TG mass loss (ΔmI(exp)), while the values of ΔmI(exp) had already been widely used for calculation of the content of thaumasite both in the model system and in construction materials in several parts of Slovakia that were inspected for evidence of TSA.
CaSiO3·CaCO3·CaSO4·15 H2O →
→ CaSiO3·CaCO3·CaSO4·2 H2O  + 13 H2O (eq.1)
 xth = ΔmI(exp)/ 37.60 (eq. 2)
The content of thaumasite investigated using the complex methodology above, both in the materials under aggressive attack and in local construction materials, is compared and referred to as an indicator of the evidence and effects of TSA. The reference materials exert values of TG mass losses of 1% to 10% for the temperature interval 110°-130o C; the mol fraction of thaumasite 0.027 &lt; xth &lt; 0.266 was calculated using the eq. 2. The values close to the upper part of the interval of our data were presented<xref rid="bib8" ref-type="ref">8</xref> for samples stored under extreme conditions (UK weather conditions, accessibility of earth sulphates, sulphides and carbonates). A comparison of the relevant values of mol percentages of thaumasite in local construction materials in Slovakia with a possible manifestation and effects of TSA (0.011 &lt; xth &lt; 0.035)<xref rid="bib14" ref-type="ref">14</xref> shows that the content of thaumasite in samples taken from six months to two years following the model aggressive attack attains to and exceeds the level of thaumasite content displayed by construction materials after 30 to 70 years of service under Slovakian weather conditions. Additional studies (i.e., on the improvement of sulphate resistance of concretes, not reported here) have showed that TSA may be delayed if slag or fly ash are used either in the form of blended cements or as a latently hydraulic additive directly applied to the raw mix concrete.
The latest results and studies<xref rid="bib13" ref-type="ref">13</xref>,<xref rid="bib15" ref-type="ref">15</xref> indicate that thaumasite formation is always preceded by expansion and cracking of the sample due to ettringite formation. It has been observed that thaumasite can form within the C-S-H phase, consuming the available carbonate and sulphate, and, given the very slow kinetics of thaumasite formation, is probably facilitated by the opening of the structure due to ettringite-induced cracking. The specific conditions for the formation of thaumasite were also derived by means of thermodynamic calculations and experimental investigations of a laboratory specimen.<xref rid="bib11" ref-type="ref">11</xref>,<xref rid="bib12" ref-type="ref">12</xref> The studies also confirmed that the formation of thaumasite can be prevented through the use of moderate sulphate concentrations, if during the production of concrete a sufficient quantity of pozolanic or latent-hydraulic materials is added. When these materials are admixed, calcium hydroxide is consumed, and the calcium silicon relationship in the C-S-H phases is consequently reduced. These calcium-poor C-S-H phases are more chemically resistant to the formation of thaumasite than are the usual calcium-rich C-S-H phases. If the attack takes place in the presence of the mineral gypsum (and not via sulphate ions), all of the binding agents examined prove to be equally susceptible to damage through the formation of thaumasite. In this case physical resistance should be increased in order to avoid the formation of thaumasite.
Finally, knowledge of phase composition, the formation mechanism and specific formation conditions is completed by microstructural studies (Figure 2, and Lit.<xref rid="bib11" ref-type="ref">11</xref>—<xref rid="bib13" ref-type="ref">13</xref>). Basically, most of the content of monosulphate- and monocarbonate AFm phases is mixed with C-S-H. The transformation to ettringite in the presence of C-S-H leads to the development of expansion stress and the formation of cracks in cement paste and on interfaces with filler particles. Aside from the accessibility of phases, the former mechanism is a necessary precondition for phase changes for the formation of thaumasite in cracks and interfaces, as our experiments have shown. At the same time, a loss of cohesion is observed, i.e., a decrease in strength, the ultimate phenomenon being the destruction of surface material.


<h2>Concluding remarks</h2>
Research on TSA and thaumasite (including our results) shows that thaumasite sulphate attack constitutes a real danger, especially under severe environmental conditions and as a follow-up to delayed ettringite formation. Prevention is effective to a limited extent only.
The time period after which TSA may exert negative effects upon the parameters of concrete under ambient climatic and environmental conditions should not be overestimated. As in the example, the amount of thaumasite, and thus the extent of deterioration after decades of service of construction material under ambient conditions, is usually much less than the level achieved during testing of model systems over two years under extremely aggressive environmental conditions.
Milan Drábik is a senior scientist in the Ceramics Department of the Institute of Inorganic Chemistry, Slovak Academy of Sciences, Bratislava and associate professor in the Department of Inorganic Chemistry, Faculty of Natural Sciences, Comenius University, Bratislava. <a href="mailto:drabik@fns.uniba.sk">drabik@fns.uniba.sk</a>


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–</li><li>14 M. Drábik, Sv. Balkovic, V. Živica: Thaumasite in concretes vs. thaumasite in autoclaved aerated concretes (in Slovak); In: Proc. of ”Maltoviny 2010”, 15 — 22, (VUT Brno, ISBN 978—80—214—4204—7, 2010).</li><li>15 
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Thaumasite: Its Relevance to Sulphate Corrosion in Concrete

Ulrich Schubert, Professor of Inorganic Chemistry at the Materials Chemistry Institute of the Vienna University of Technology, is Euchems president elect. Nachrichten aus der Chemie asked him about his priorities and aims.


Nachrichten aus der Chemie: In a few months you will be president of Euchems: Is this a pleasure or a burden?
Ulrich Schubert: It will probably end up as a mixture of both. But it was gratifying and a great honour to be asked to be a candidate in the first place, and then actually to be chosen. Will the office end up being burdensome? The word burden has a bad aftertaste and I don't believe I could ever feel that way about this position. But the amount of work that is coming my way has already become clear in the few months since the election: in that short time my e-mail has tripled.
Nachrichten: What are the issues topping your agenda?
Schubert: The first priority is to represent Euchems interests vis-à-vis European institutions and authorities, as well as European and international partner organisations. For example, deliberations for the eighth European Framework Research Programme have already begun, and Euchems wants to play a key role in them.
Nachrichten: And what will be priority number two?
Schubert: The second most important assignment for Euchems is networking. In my view, a network of young chemists is especially important. We senior academics already have our networks, but among our juniors there is room for improvement. The very active European Young Chemists Network, EYCN, needs our full support.
Nachrichten: Is there a third construction site?
Schubert: Yes. The lines of communication from Euchems via the national member societies to their individual members and back are in urgent need of upgrading. It's a typical umbrella-organisation predicament. The average member of each national chemistry association knows far too little about the benefits they're getting from Euchems.


<h2>How chemists benefit from Euchems</h2>
Nachrichten: And what does the individual chemist gain from membership? 
Schubert: Well, first I'd have to name the big Euchems conferences like those in Nuremberg, Turin and Budapest, because of their high visibility. Another example are networking possibilities through our divisions and working groups. But there are low-profile benefits, too, such as the lobbying at European institutions by our policy manager in Brussels, where we now have a permanent office. It is also worthwhile reading the Euchems Newsletter and the Euchems Brussels News Updates, both of which are on the Internet at <ext-link ext-link-type="uri"><a href="https://www.euchems.org" target="_blank">www.euchems.org</a></ext-link>.
Nachrichten: But is yet another lobbying organisation actually needed in Brussels? There's already, for instance, Euro-Chemistry, an association of a number of national research organisations. And then there's Cefic, the European Chemical Industry Council — an influential player.
Schubert: You are right about Cefic: it carries much more weight in policy-making than we will ever have, in terms of financial resources alone. But it acts on behalf of other interests too. To put it as succinctly as possible: Cefic speaks for the chemical industry; Euchems for the chemists — as human individuals. Of course their interests overlap to a certain extent and are complementary to those of Euchems. Other associations and organisations such as the European Cooperation in Science and Technology (Cost) and the European Science Foundation (ESF) are not specifically chemically oriented. The same is partially true for Euro-Chemistry. This is a recently founded grouping of a few research organisations centred around the French CNRS. Their objectives are not clear, and it is not clear how these multi-disciplinary organisations could represent chemistry.
Nachrichten: What does lobbying in Brussels actually accomplish anyway?
Schubert: I would not take the word lobbying too literally. It is more of a joint effort to raise awareness about chemistry. An example is the promotion of European research by the European Research Council (ERC), which puts chemistry in a very good light. Still, one thing is a pity: though there are two evaluation panels concerned with chemical applications, neither refers explicitly to chemistry in its title. Here we chemists are ourselves at fault. We are often far too reticent. We should stress that in many fields of research it is chemistry that provides the intellectual leadership. That doesn't mean we should distance ourselves from the other disciplines, but adopting the role of a mere utility for the life sciences or for materials research is a fundamental error. Chemistry has a better standing generally than chemists themselves believe. Many go on insisting that chemistry has an image problem. That may have been true twenty years ago, but today every decision-maker is fully aware that chemistry is a motor for innovation.


<h2>Financial structure needs to be changed</h2>
Nachrichten: Should Euchems do more to raise its profile politically?
Schubert: Basically, yes. We ought to define issues where chemistry is central or could assume a leading role. But Euchems is not a wealthy organisation. If we want Euchems to take on more pan-European functions, we will have to change its present financial structure.
Nachrichten: What changes are needed?
Schubert: Presently the contribution per member of national chemical societies for Euchems membership comes to about two euros — give or take ten per cent. For large organisations like the German Chemical Society this is relatively little, but for some small societies, for example in Eastern Europe, even that much hurts. So simply raising membership fees proportionately is not an option.
Nachrichten: What other solutions do you have in mind?
Schubert: One possibility could be stronger involvement on the part of the chemical industry. We certainly don't want to leave any chemical society — neither a national organisation nor Euchems — depending on drip-feeding by the chemical industry, though the chemical industry in fact benefits substantially from the work of the chemical societies. An alternative would be to discuss whether Euchems should open its doors to other types of members apart from national chemical societies, such as institutional members.
Nachrichten: Would you welcome stronger networking by the various chemical sectors at European level under the umbrella of Euchems?
Schubert: Networking and joining forces is a must in Europe, because of its federal structure. This is true for political Europe as well as for chemistry in Europe. Euchems is the ideal platform for such networking. Europe's chemistry must speak with one voice, and this is only possible if the various players coordinate their activities. Any fragmentation will have a negative impact.
Nachrichten: In concrete terms, what can be done?
Schubert: Let's take the international year of chemistry: many activities, publications and posters developed by the large societies can easily be adapted by the smaller ones. It would be very good if Euchems could act as a catalyst for cooperation among the societies. Also interesting would be for societies to join forces themselves and hold regional conferences. The big European Euchems conference has become an established event — next year the fourth one takes place in Prague.
Nachrichten: Has the biennial Euchems Conference got off to a good start in your opinion?
Schubert: The first three conferences were very successful, with attendance at around 2500: the conferences weren't planned to be much larger than that. Mammoth meetings like the ACS conferences are fragmented into countless sub-conferences. That is no model for us. Still, the last Euchems conference in Nuremberg did bring one problem to light, namely, the greatly disproportionate number of chemists attending from the host country. I am not worried about Prague. That conference will draw plenty of international guests because of its convenient central location and its wealth of tourist attractions. But what will happen when the conference venue is a very small or somewhat remote country? The large societies are needed here: they must see that such conferences find the same acceptance the others do. Solidarity among the individual societies is a necessity.
Nachrichten: You have both a German and an Austrian passport, and you live and work in Vienna, in the heart of Europe. Is Europe more to you than an administrative unit?
Schubert: I belong to a generation that grew up while Europe was growing together. When I was in school, the Franco-German Treaty of Friendship was of the greatest importance. Later it was my privilege to experience at first hand the end of the Cold War and the Eastern Europeans' liberation from Communism. I firmly believe that the countries of this continent are friends who must cooperate. The chemical societies reflect this beautifully. Perhaps it's easier for us scientists to leave national partisanship behind. I've seen this in my own group, which is very international — nothing unusual in Austria: During the Balkan conflict, a Serb and an Albanian from Kosovo did their PhD work in my group. This did not cause any problems. And hopefully both not only experienced chemistry but also other positive sides of human relationships.

“Solidarity is a necessity”

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