Experimental Investigation and Thermodynamic Modeling of Influence of Nickel and Titanium Content on the Structure and Selected Properties of Tin Bronzes

Investigations are conducted in order to maintain or to improve the selected properties of the group of foundry copper-tin alloys with nickel and titanium additions, at a limited fraction of the critical (deficit) element such as tin. The crystallisation process, as well as changes of the microstructure and selected mechanical properties of the CuSn8 alloy—occurring due to introducing alloying additions—were analysed. Investigations of the macro and microstructure were performed using optical and scanning electron microscopy. Based on the thermal analysis and thermodynamic modelling using the CALPHAD (CALculations of PHAse Diagrams) method, the crystallisation process was analysed. The identification of phases was performed by XRD (X-ray diffraction). In addition, such parameters as tensile strength-UTS, elongation-A and hardness-HBS were tested. Under the influence of the introduced titanium, the columnar crystals are reduced due to the crystallisation of the alloy at the walls of the mould. Precipitations (intermetallic phases) crystallize first (primary). The intermetallic phases associated with the presence of the alloying elements nickel and titanium are located in the interdendritic regions. In tin bronzes with titanium additions, hardness (HBS) increases, tensile strength (UTS) negligibly decreases, while elongation (A) significantly decreases. In the case of CuSnNi bronze, the addition of 0.2 wt.% Ti increases the hardness and increases ultimate tensile strength (UTS), while reducing the elongation (A). Higher Ti additions increase HBS, slightly decrease the tensile strength, and significantly reduce the elongation.

Flow cell to study crystallisation processes in-situ using terahertz time-domain spectroscopy

A versatile setup based on terahertz time-domain spectroscopy was developed to monitor the process of crystallisation and characterise the structure of the crystals as well as the dynamics of the solvent in situ. The setup can be used to investigate crystallisation processes over a wide range of temperature, either under static conditions or during continuous flow. An attached optical imaging probe can be used to monitor the process in parallel to the terahertz spectroscopy investigation. The implementation of terahertz spectroscopy offers a great opportunity to investigate the dielectric relaxation dynamics of the solvent and the vibrational modes characteristic for the crystalline phases simultaneously. The details of the crystallisation setup are demonstrated at the example of the crystallisation process of magnesium sulphate heptahydrate from its aqueous phase.

Population Balance and CFD Simulation of Particle Aggregation and Growth in a Continuous Confined Jet Mixer for Hydrothermal Synthesis of Nanocrystals

Population balance and computational fluid dynamics models are built and integrated to carry out a simulation study of the reactive crystallisation process in a confined jet mixer (CJM) for the continuous flow synthesis of TiO2 nanoparticles at a supercritical water condition. In the population balance model, the crystal growth in size is modelled as being due to combined nanocrystal aggregation as well as surface growth. A free molecular model is used to predict the particle aggregation. The performance of the combined aggregation and surface growth models is compared with models that only consider surface growth as the only mechanism for particle size enlargement. It was found that the combined model gives a more accurate prediction of particle size distribution.

Ultrasonic Time-of-Flight Computed Tomography for Investigation of Batch Crystallisation Processes

Crystallisation is a crucial step in many industrial processes. Many sensors are being investigated for monitoring such processes to enhance the efficiency of them. Ultrasound techniques have been used for particle sizing characterization of liquid suspensions, in crystallisation process. An ultrasound tomography system with an array of ultrasound sensors can provide spatial information inside the process when compared to single-measurement systems. In this study, the batch crystallisation experiments have been conducted in a lab-scale reactor in calcium carbonate crystallisation. Real-time ultrasound tomographic imaging is done via a contactless ultrasound tomography sensor array. The effect of the injection rate and the stirring speed was considered as two control parameters in these crystallisation functions. Transmission mode ultrasound tomography comprises 32 piezoelectric transducers with central frequency of 40 kHz has been used. The process-based experimental investigation shows the capability of the proposed ultrasound tomography system for crystallisation process monitoring. Information on process dynamics, as well as process malfunction, can be obtained via the ultrasound tomography system.

Cationic surfactant–directed structural control of NaCl crystals from evaporating sessile droplets

We report morphological regulation of NaCl (sodium chloride) crystals through the evaporative crystallisation process of microdroplets containing a cationic surfactant CTAB (cetyltrimethylammonium bromide). Various fascinating evaporative salt morphologies are observed...

Crystallised chitosan + Vitamin-E Coated Drug-Eluting Stents to Prevent Restenosis and Stent Associated Infections

Drug-Eluting Stents (DES) was developed to reduce re-endothelialisation and thrombosis. Chitosan due to its biocompatible and biodegradable property, it is used in drug delivery and wound healing applications. Chitosan-Vitamin E (alpha-tocopherol) coated stents were prepared by seeding and crystallisation process. Drug release profile, anti-bacterial activity and biocompatibility were analysed. FESEM analysis of the coated stent evidenced the homogenous coating of the drug-polymer mixture does not provide any surface space on the stent for the bacterial adhesion. Maximum bacterial reduction percentage was observed for biofilm-producing Staphylococcus aureus (96.6±1.04%). Escherichia coli and Pseudomonas aeruginosa showed bacterial reduction percentage of 93.3±2.51% and 93.6±2.08% respectively. Release profiles of crystalline chitosan from the coated stents indicated that the rate of chitosan release was sustained and constant with the release time. Chitosan coated stent samples showed significant biocompatibility indicated by the cell viability percentage of 96.6±1.04% when compared with the control samples (99.1±0.76%). To conclude, the drug-releasing phenomenon aided by the vitamin was correlated with its ability to prevent the formation of restenosis in atherosclerosis cases.

Crystallisation of REE carbonates from aqueous solutions

<p>Low temperature aqueous synthesis of Rare Earth Element (REE) carbonates show extensive variability in the resulting minerals. Precipitated mineral phases and crystallisation rates vary depending, in part, on the REE used. Indeed, much of the work to date on REE aqueous geochemistry focuses on the individual behaviour of discrete REEs. </p><p><br>We present a low temperature aqueous geochemical investigation of REE carbonate crystallisation pathways, which takes into consideration the influence of multiple REEs in solution. This serves to mimic more realistic conditions that are found in natural geological settings propitious to REE mineralisation. Our experiments focus on the behaviour of La, Ce, Nd, Dy carbonates at 30<sup>o</sup>C.</p><p><br>Concordant with previous studies, our results suggest that the crystallisation process of REE carbonates begins with the formation of an amorphous phase that transitions into a crystalline phase after a lag time that depends on the element and the proportions in the mixture. </p><p><br>This lag time is REE specific and is shorter for lighter REE compared to their heavier counterparts. In particular, the presence of another REE in the system affects the crystallisation timings and the morphology of the resulting crystals. For example, samples of mixed La/Nd carbonates begin their phase transition at lag times in between that of the two end-members (i.e. La and Nd) carbonate compositions. Furthermore, we find that the resulting growth rates and crystal habits are unique to the ratio of the REE mixture, with the underlying ionic potential of the mixture linked to the growth rates. In addition, observations throughout the crystallisation process also show that growth begins with flocculation of nanoparticles followed by crystal growth via Ostwald ripening.</p><p><br>REEs are sought after due to their unique properties and are integral to modern technologies such as lasers, catalytic converters, batteries, electro-magnets and wind turbines. Considering how the crystallisation behaviour with REE mixtures differs from that of discrete REE in solution, this work gives insights into the fundamental chemistry of REEs in aqueous solutions - relevant for studies of REE mineralisation and materials processing. </p>