Infrared investigation of barite and gypsum crystallization: Evidence for an amorphous to crystalline transition

Infrared was used to monitor the progression of barite (BaSO4) and gypsum (CaSO4·2H2O) crystallization. It was found that barite crystallized with broad infrared peaks that narrowed over time. This was accentuated when an inhibitor was added. The infrared of gypsum in the early stages showed a phase that was clearly different to either bassinite or gypsum. It is hypothesised that in the absence of inhibitors, the rate-determining step for barite crystallization is the transformation from a disordered solid to a crystalline solid as little water was observed to be present during this process when inhibitors are not present. All of these findings are consistent with a non-classical model of crystallization where disordered solids eventually rearrange to a crystalline solid if not inhibited. It also suggests that water may be key to determining the “lifetime” of the disordered clusters

On a diffusion model with absorption and production

We discuss the structure of radial solutions of some superlinear elliptic equations which model diffusion phenomena when both absorption and production are present. We focus our attention on solutions defined in R (regular) or in R \ {0} (singular) which are infinitesimal at infinity, discussing also their asymptotic behavior. The phenomena we find are present only if absorption and production coexist, i.e., if the reaction term changes sign. Our results are then generalized to include the case where Hardy potentials are considered

Controlling crystal growth with modifiers

Modifying crystal growth processes using additives is a well established approach to solvingproblems in many processes. Nature also makes extensive use of crystalline inorganicstructures modified by soluble and insoluble organic materials. This Highlight discusses someof the recent and interesting developments in this area, with an emphasis on the control ofcrystal growth rates, covering both inhibitors and the lesser known promoters of crystalgrowth. Hybrid materials resulting from the incorporation of modifiers into crystallinestructures are also discussed, with an emphasis on non-classical crystallisation mechanisms,involving the oriented attachment of nanoparticles

Multilingual search for cultural heritage archives via combining multiple translation resources

The linguistic features of material in Cultural Heritage (CH) archives may be in various languages requiring a facility for effective multilingual search. The specialised language often associated with CH content introduces problems for automatic translation to support search applications. The MultiMatch project is focused on enabling users to interact with CH content across different media types and languages. We present results from a MultiMatch study exploring various translation techniques for the CH domain. Our experiments examine translation techniques for the English language CLEF 2006 Cross-Language Speech Retrieval (CL-SR) task using Spanish, French and German queries. Results compare effectiveness of our query translation against a monolingual baseline and show improvement when combining a domain-specific translation lexicon with a standard machine translation system

Using absorbance as a measure of turbidity in highly caustic solutions

This note shows that the dissolution of kaolin and its subsequent re-crystallization as DSP can be monitored using a simple UV–vis method that measures the turbidity of the system. The method is shown to be accurate, reproducible and sensitive. The dissolution of kaolin can be accurately determined by way of a solids calibration curve and this is supported by simultaneous measurements of the dissolved silicate by an inductively coupled plasma (ICP) technique. Additionally, turbidity is often used to measure induction times of nucleation thus the method can monitor dissolution and nucleation simultaneously. It must be remembered, however, that turbidity will show different behaviour to ICP when phenomena such as settling and aggregation occur thus these processes must be considered when interpreting data. Finally, the size limit of the turbidimetric technique must be determined as this, too, can influence the interpretation of data

Rod-shaped barium sulfate particles from a completely inorganic system

Rod-shaped barium sulfate particles can be formed from purely inorganic systems at 75 1C and theseparticles are single crystals elongated in the c-axis. This c-axis growth promotion relative to the othercrystal faces is absent when the cation impurities are absent suggesting a specific interaction of thecations with the growing crystal. Attempts have been made to determine the cause of this c-axisgrowth promotion, but no one mechanism appears to adequately explain this effect and it may be dueto a combination of different impacts. The same cations do not induce rod-shaped particles at 25 1C,thus suggesting an important role of kinetics in the crystallization of these particles. Finally, previousreports suggesting that the formation of rod-like particles is due to the presence of an organic additivemay be incorrect as sufficient sodium ions may have been present to give these particles even in their absence

Tetrazoles: calcium oxalate crystal growth modifiers

Molecules containing tetrazole substituents have become of interest due to their being bioisosteres of carboxylic acids and like their carboxylate counterparts, tetrazolate anions have been able to affect the crystal growth of barium sulphate and calcium carbonate. In this proof of principle study, we show that this behaviour also extends to calcium oxalate and therefore opens the possibility of using tetrazole-based additives for investigating mineralization processes of human pathological relevance

Aspartic acid as a crystal growth catalyst

Ion desolvation is an important kinetic step in the growth of divalent ionic crystals - a category that encompasses numerous materials relevant to biomineralization. It has recently been shown for one such divalent ionic crystal that the rate-limiting desolvation of the cation can be assisted by the anion and that this process can be surface specific. Here we show that even a simple biological molecule, such as aspartic acid, can have a measurable catalytic effect on barite crystal growth and that this effect is related to the lowering of the activation barrier for cation desolvation. We therefore suggest that growth rate enhancement on specific faces through catalysis of the cation desolvation step may be a viable mechanism for the positive control of biomineralization

Investigating vaterite phase stabilisation by a tetrazole molecule during calcium carbonate crystallisation

Tetrazole compounds have recently been found to impact on crystal morphology but in a manner different from that of carboxylate molecules. One such molecule was found to stabilise vaterite and this was investigated by assessing the impact of systematic changes on its structure. It was found that both the tetrazole and the formyl functionalities were required for vaterite stabilisation. The mechanism of stabilisation appears to be via inhibition of vaterite dissolution

Crystallization of jarosite in the presence of amino acids

Jarosite was formed in the presence of five amino acids at two pHs, namely 1.75 and 2.9, to determine what impact amino acids have on its formation. It was found that at the lower pH glycine was the most potent in terms of morphological and yield impacts. XRD analysis showed that incorporation of the amino acid occurs at this low pH for glycine and proline. Dynamic light scattering studies showed that glycine impacts significantly on the jarosite nucleation rate while proline and alanine do not. At the higher pH all of the amino acids had much less impact on morphology or yield. At pH 3 the solids were found to be a 3-phase system consisting of goethite, schwertmannite and jarosite. In this case, alanine appeared to stabilise the presence of schwertmannite more than the other amino acids