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Struvite (MgNH4PO4·6H2O) is a mineral first identified in 1845. It is being tested for several reasons: (1) it is a problem in liquid wastewater treatment plants; (2) on the other hand, it is recovered from these wastewaters for its phosphorus, magnesium and nitrogen; (3) is the main component of microbial-induced urinary stones. We have recently shown that struvite is ferroelectric and piezoelectric. In this paper, we present the first experimental evidence of the pyroelectric nature of struvite. Using a single-diffusion gel growth technique, we grew struvite crystals as flat, parallel plates. We performed measurements of pyroelectric currents on struvite of this shape, using it as a dielectric of a plate capacitor. The occurrence of pyroelectric effects in struvite was investigated by measuring depolarization currents as a function of temperature. This technique allows the disclosure of ferroelectric/pyroelectric transitions as well as the reconstruction of the ferroelectric loop. We found that the value of the pyroelectric coefficient p attains a maximum of 22 × 10−6 C m−2 K−1 slightly below room temperature, going down to p ≅ 10 × 10−6 C m−2 K−1 at room temperature. This value is comparable to values for other minerals. For example, the pyroelectric polarization coefficient of tourmaline, the mineral for which the pyroelectric effect was first discovered, is 4 × 10−6 C m−2 K−1. This value is 2.5 times lower than that measured for struvite, illustrating struvite's fairly strong pyroelectricity. [ABSTRACT FROM AUTHOR]

The research presented in the paper concerns the elastic properties of struvite. The article combines theoretical and experimental research. Experimental studies were carried out on struvite single crystals grown in sodium metasilicate gel by single diffusion. This unique method leads to obtaining crystals of sufficiently large size to conduct, for the first time, experimental measurement of elastic properties of monocrystalline struvite. Using the nanoindentation method, the Ez = 29.1 ± 0.7 GPa value of the component of Young's modulus was determined for a struvite single crystal. In addition, the elastic constants C11, C22, and C33 were determined using micro-Brillouin spectroscopy. Theoretical calculations of the abovementioned properties have been carried out by employing density functional theory methods. Scaling of the theoretical elastic constants leads to obtaining good agreement with the experimental values. Values of the Ex and Ey components of the Young's modulus, not available from the experimental nanoindentation technique, have been determined theoretically as 23 GPa and 27 GPa, respectively. Differences in the values of elastic components and Young's modulus components are related to the layered crystal structure of struvite and directional character of the hydrogen-bonding pattern. [ABSTRACT FROM AUTHOR]

Al-TiB2in situ composites are important class of structural materials where the TiB2 particles are grown in situ within the aluminum matrix. The true morphology of the in situ grown TiB2 particles is not clear as particles with different morphologies are reported in the literature. The present work reports the three-dimensional morphologies and habits of in situ grown TiB2 particles in aluminum-based composites by the halide slat method. TiB2 particles were grown in molten aluminum by the reaction of two fluoride salts; K2TiF6 and KBF4. The TiB2 particles exhibited truncated hexagonal pyramid morphology. It was found that the pyramidal planes are morphologically more important and the crystal is bounded by the fast-growing faces. The habit (predominant facet plane) and growth morphology of the crystals was analyzed through the kinetic-geometric model. The ratio of the relative growth rates of different forms was calculated. The pyramidal form can increase its size by growing faster than the adjacent faces, whereas the basal and prism forms decrease in size if they grow faster than the adjacent faces. We show that depending on the interfacial angle geometry, a given face may or may not enlarge, and the face needs not always constrain the crystal with the slowest growth rate. Both the theoretical analysis and the experiments demonstrate the particles to have hexagonal pyramidal morphology. Finally, the present work explains how past observations suggesting the TiB2 particles to have hexagonal, elongated hexagonal, rectangular, and cubic habits are due to the two-dimensional sections of the truncated hexagonal pyramid. [ABSTRACT FROM AUTHOR]

The influence of (-)-epicatechin, a component of green tea, on the nucleation and growth of struvite crystals, the main component of infectious urinary stones, is studied. The struvite crystallization process was performed in the solution of artificial urine, and the activity of urease-bacterial enzyme was simulated in a chemical way. The effect of the tested substance on the crystallization processes was monitored by spectrophotometric measurements and microscopic observations. The results obtained show that, in the presence of (-)-epicatechin, struvite nucleation occurs faster when compared with the control test. This means that its nucleation is shifted toward lower pH values. It has been also found that the presence of the tested substance can lead to an increase in the mass of struvite formed in artificial urine. The experimental results are explained on the basis of theoretical chemical speciation analysis of chemical complexes formed in artificial urine. This chemical speciation analysis demonstrates that the observed effects are caused by the influence of (-)-epicatechin on the formation of mainly the MgCit- complex and also the MgHCit and MgC2O4 complexes. [ABSTRACT FROM AUTHOR]