Crystallization Experiments Research Articles

Trace element partitioning in zoned clinopyroxene as a proxy for undercooling: Experimental constraints from trachybasaltic magmas

Sector-zoned clinopyroxene records kinetic effects imposed by variable degrees of magma undercooling, ΔT, and can be utilised to track the dynamics of magmatic systems. The partitioning of trace elements into sectors grown in different crystallographic orientations can be used as a proxy for ΔT. However, an experimental assessment of the relationship between trace element zoning and ΔT has been lacking to date. Here we present trace element data from a series of undercooling crystallisation experiments on a primitive trachybasalt from Mt. Etna (Italy), at conditions of crustal storage (400 MPa, NNO + 2), and ΔT ranging from 23 to 173 °C. Changes in ΔT were modulated by varying both resting and liquidus temperatures, the latter via the melt-H2O content of the experiments. The resting temperature was retained for 24 h to ensure the attainment of near-equilibrium conditions.High-resolution elemental mapping reveals the distribution of trace elements in individual clinopyroxene zones. Increasing ΔT drives a shift from polyhedral morphologies with Al-rich prism and Al-poor hourglass sectors (ΔT = 23–25 °C), to skeletal (ΔT = 75–123 °C) and dendritic (ΔT = 132–173 °C) crystals with Al-rich skeletons and Al-poor overgrowths. Aluminium-rich zones have higher concentrations of rare earth elements (REE) and high field strength elements (HFSE) than Al-poor zones across all investigated ΔT conditions, and overall, Al, REE and HFSE contents increase with ΔT. This indicates that tetrahedral aluminium (TAl) and associated charge-balancing mechanisms govern the incorporation of REE and HFSE within clinopyroxene. Lattice strain parameters for REE in the M2 site indicate the incorporation of light relative to heavy REE in clinopyroxene is controlled by competing effects between the strain-free partition coefficient, D0, and the optimum cation radius, r0. Critically, the middle and heavy REE switch from incompatible to compatible with increasing ΔT. Used to model fractional crystallisation, our data demonstrate that fractionation of clinopyroxene at low ΔT controls pre-eruptive melt evolution. Importantly, this indicates crystallisation of clinopyroxene in the deep portions of Mt. Etna’s plumbing system is not rapid and is unlikely to result in the early formation of dendrites.We develop a parameterisation of ΔT based on REE partitioning between experimental clinopyroxene and coexisting melt, which can be applied to sector-zoned augite crystallising from mafic alkaline magmas, to reconstruct dynamic processes and thermal pathways during magma transport and storage. Applied to sector-zoned clinopyroxene microphenocrysts and groundmass microcrysts from the 1974 eccentric eruption at Mt. Etna, our parameterisation tracks an increase in ΔT with magma ascent and eruption, following recharge of Cr-rich mafic magma at depth. Sector-zoned clinopyroxene can track ΔT variations leading to volcanism at Mt. Etna and could be applied to quantify magma dynamics in other active volcanoes.

Insight into differentiation in alkalic systems: Nephelinite-carbonate-water experiments aimed at Ol Doinyo Lengai carbonatite genesis

Ol Doinyo Lengai (ODL, Tanzania, East African Rift) is the only known volcano currently erupting carbonatite on Earth with 30 yr. cycles alternating between quiescent carbonatite effusion and explosive, compositionally-zoned silicate eruptions. We performed isothermal crystallization and thermal gradient experiments involving ODL nephelinite, Na2CO3 and H2O to understand magmatic differentiation in this system using SEM-EDS x-ray analysis, x-ray tomography, SIMS and LA-ICPMS to characterize samples. Isothermal crystallization experiments document that hydrous liquids coexist with nepheline+feldspar; as peralkalinity increases, temperatures decrease. Presence of Na2CO3 increases the solubility of water in the liquid. Experiments placing nephelinite with H2O+ Na2CO3 in a 1,000–350°C thermal gradient show that rapid reaction occurs, resulting in virtually melt-free mineral aggregates having mineral layering reflecting systematic differentiation throughout the capsule. Both types of experiments argue that a continuous interconnected melt exists over a large temperature range in alkalic magmatic systems allowing for differentiation in a reactive mush zone process. Liquid compositions change from carbonate-water bearing nephelinites at high temperature down to hydrous carbonate silicate liquids at <400°C. We propose a model for ODL eruption behavior: 1) nephelinite magmas pond and build a sill complex downward with time; 2) hydrous carbonate melts form in the mush and buoyantly rise, ultimately erupting as natrocarbonatites observed; 3) H2O contents build up in melt at the bottom of the sill complex, eventually leading to water vapor saturation and explosive silicate eruptions. The model accounts for eruption cycling and the unusual compositional zoning of ODL silicate tephras.

Crystallization of Calcium Carbonate: Modeling Thermodynamic Equilibrium, Pathway, Nucleation, Growth, Agglomeration, and Dissolution Kinetics with the Presence of Mg2+, Ba2+, and Sr2+

Calcium carbonate (CaCO3) crystallization is a complex operation due to the diverse thermodynamic and kinetic factors involved during the particle formation of vaterite, aragonite, and calcite. This article involves the experimental and computational study of CaCO3 crystallization in the presence of Mg2+, Ba2+, and Sr2+. Crystallization experiments were performed varying the Mg2+, Ba2+, and Sr2+ concentration, monitored by dynamic light scattering, scanning electron microscopy, and X-ray diffractometry techniques. The crystallization model includes the thermodynamic equilibrium, pathway, and kinetic rates associated with a populational balance. It was obtained that the Mg2+ inhibited vaterite nucleation and accelerated its transformation to calcite. The Ba2+ and Sr2+ ions accelerate both calcite growth and vaterite-calcite transformation rates. All external ions produced an increase in crystal size and a decrease in the total crystalline mass, albeit in different proportions. Simulation results with the developed model presented a good agreement with experimental data with an error of 12% per variable. Thus, the proposed model framework may be helpful for the evaluation of the calcium carbonate crystallization process as a practical tool to provide insight into the extensively experimentally studied effects of external ions on CaCO3 crystal populations.

Studies on two phenoxo-bridged homopolynuclear Cu(II) bis(salamo) type complexes based on theoretical calculations and fluorescence properties

The dinuclear Cu(II) complex [Cu2(HL)Br2(MeOH)]·MeOH (1) and the tetranuclear Cu(II) complex [Cu4(L)2](ClO4)2·2EtOH (2), based on a new bis(salamo) type ligand H3L, have been successfully self-assembled and structurally characterized by X-ray single crystal diffraction experiments. In complex 1, the partially deprotonated ligand unit (HL)2– is coordinated with the Cu(II) ions. It is noteworthy that two bromine ions and one methanol molecule with balanced charges are involved in the coordination. Both central coordination Cu(II) ions are five-coordinated. Finally, complex 1 can form a two-dimensional planar network structure and a one-dimensional chain-like structure through intermolecular hydrogen bonds and CH π interactions, respectively. Meanwhile, complex 2 has a centrosymmetric structure with two phenolic oxygen atoms bridging two molecules of metallized ligand [Cu2(L)] units, where Cu1 is five-coordinated and Cu2 is four-coordinated. Thus, complex 2 forms a three-dimensional superamolecular network structure and a one-dimensional chain-like structure through intermolecular hydrogen bonds and π–π stacking interactions, respectively. The energy gaps between the HOMO and LUMO orbitals of complexes 1 and 2 were investigated by DFT calculations, indicating that the complexes are stable. The interaction sites of the ligand with the Cu2+ ions were examined by ESP investigation, and the results are consistent with the crystal structure. The weak intermolecular interaction forces of complexes 1 and 2 were explored by Hirshfeld surfaces and IRI analyses. The luminescent properties of complexes 1 and 2 were illustrated by fluorescence spectroscopy research.

SADeepcry: a deep learning framework for protein crystallization propensity prediction using self-attention and auto-encoder networks

The X-ray diffraction (XRD) technique based on crystallography is the main experimental method to analyze the three-dimensional structure of proteins. The production process of protein crystals on which the XRD technique relies has undergone multiple experimental steps, which requires a lot of manpower and material resources. In addition, studies have shown that not all proteins can form crystals under experimental conditions, and the success rate of the final crystallization of proteins is only <10%. Although some protein crystallization predictors have been developed, not many tools capable of predicting multi-stage protein crystallization propensity are available and the accuracy of these tools is not satisfactory. In this paper, we propose a novel deep learning framework, named SADeepcry, for predicting protein crystallization propensity. The framework can be used to estimate the three steps (protein material production, purification and crystallization) in protein crystallization experiments and the success rate of the final protein crystallization. SADeepcry uses the optimized self-attention and auto-encoder modules to extract sequence, structure and physicochemical features from the proteins. Compared with other state-of-the-art protein crystallization propensity prediction models, SADeepcry can obtain more complex global spatial long-distance dependence of protein sequence information. Our computational results show that SADeepcry has increased Matthews correlation coefficient and area under the curve, by 100.3% and 13.4%, respectively, over the DCFCrystal method on the benchmark dataset. The codes of SADeepcry are available at https://github.com/zhc940702/SADeepcry.

Element migration and phase distribution characteristics during crystallization of rare earth phase in rare earth slag

The crystallization experiment of molten rare earth (RE) slag under different cooling rates was carried out. The characteristics of element migration and phase distribution during RE phase crystallization were studied by using different equipment. The experimental results show that there are two RE phases in the RE slag, namely (Ca, Ce, La)5(SiO4)6F and (Ca,Ce,La,Mg)3(Ti,Al,Nb)2O7. During the cooling crystallization process of molten RE slag, Ca and P elements in the RE phase of (Ca,Ce,La)5(SiO4)6F migrate from inside to outside, and finally gather at the outer edge of the phase to form phase Ca3(PO4)2. The RE phase (Ca,Ce,La)5(SiO4)6F is distributed inside the furnace-cooled slag, and the RE phase (Ca,Ce,La,Mg)3(Ti,Al,Nb)2O7 is distributed in the surface layer of the furnace-cooled slag. And based on the phase distribution characteristics, the central hollowing method is proposed to realize the preliminary enrichment of valuable elements Ti, Nb and RE in RE slag.

Partial pressure of Cd in equilibrium with stochiometric melt and solid of (Cd0.8Zn0.2)Te between 300 °C and 1250 °C for melt growth

The partial pressures over Cd0.8Zn0.2Te solid and melt were measured by the optical absorption technique on five optical cells loaded with four homogenized samples and one with as-grown crystal. From the measured partials pressures, the three-phase loops with five solidus and four liquidus points were established together with the Cd partial pressure over the melts. A series of crystal growth experiments by directional solidification of Cd0.8Zn0.2Te with controlled Cd overpressure, provided by Cd reservoir temperatures from 750 to 935 °C, were conducted. From the Te precipitates content observed by the IR micrographs, the correlation between the Cd reservoir temperature and the Cd0.8Zn0.2Te melt temperature, which resulted in the lowest precipitate density, was established. From the calculated masses of the elements in the vapor phase, the compositions of the condensed phases for each set of partial pressure data were derived. The correlation between the temperature of the Cd reservoir and the temperature of a stoichiometric Cd0.8Zn0.2Te sample, such that the equilibrium Cd overpressure is coexisted, have been established for the Cd0.8Zn0.2Te melt and the solid between 300 and 1250 °C. Using this information, the temperatures of the Cd reservoir and the Cd0.8Zn0.2Te sample can be programed during the melt growth to process intrinsic/stochiometric crystals. Additionally, the correlation on the equilibrium Cd overpressure environment for the Cd0.8Zn0.2Te solid can also be employed for the heat treatment of post-growth annealing to adjust the composition of the grown crystals toward stoichiometry.

Controlling the Polymorphic Outcome of 2,6-Dimethoxybenzoic Acid Crystallization Using Additives

In this study, 2,6-dimethoxybenzoic acid (2,6MeOBA) was used as a model substance to investigate the use of additives to control the polymorphic outcome of crystallization. 2,6MeOBA exists as three polymorphs. Two of the 2,6MeOBA polymorphs, I and III, obtained in most of the crystallization experiments, were characterized by thermal analysis, and their relative thermodynamic stability was determined. Forms I and III are enantiotropically related, where form III is the high-temperature form. Pure form II was very difficult to obtain. Crystallization of 2,6MeOBA was explored under different conditions by performing evaporation and cooling crystallization from different solvents. Surfactants, polymers, and different molecular compounds with diverse possibilities for the formation of intermolecular interactions were tested as additives. The additives facilitating the crystallization of the metastable forms were additionally studied under different crystallization conditions. The effect of additives polyethylene glycol (PEG) and hydroxypropyl cellulose (HPC) on the thermodynamic stability and solvent-mediated phase transition (SMPT) kinetics was evaluated. HPC and PEG showed the potential to favor the formation of form III in crystallization from water.

One-dimensional diffuse scattering of 1,3-di(tert-butyl)cyclopentadienyl pentaphosphaferrocene modelled with closed-form expressions

1,3-di(tert-butyl)cyclopentadienyl pentaphosphaferrocene (Cp′′FeP5) crystallizes as polytypes, where adjacent layers are related by either a c- or an n-glide reflection. In the simplest possible polytypes only one kind of glide reflections is realized, leading to overall Pca21 or Pna21 symmetry respectively. Crystals isolated from the same crystallization experiment feature a varying degree of stacking disorder. One-dimensional diffuse scattering of a crystal with particularly strong disorder was modelled with closed-form expressions derived from a growth model. A range of interaction of s = 2 was necessary to satisfactorily describe the observed diffraction intensities. The crystal can be described as a disordered analogue of an allotwin, that is an intergrowth of the Pca21 or Pna21 polytypes with a distinct preference for the former.

Supramolecular porous frameworks of two Ni(II) coordination polymers with varying structures, porosities, and magnetic properties

Based on a simple benzimidazole derivative and nickel nitrate, two nickel(II) based supramolecular three-dimensional (3D) porous solids, namely {[Ni(Hbic)2(OH2)2]·H2O}n (1) and {[Ni(Hbic)2(OH2)]·2CH3OH}n (2) (H2bic = 1H-benzimidazole-5-carboxylic acid), were synthesized and characterized. Single crystal X-ray diffraction experiments revealed that compound 1 is a 1D coordination polymer with a linear chain structure while 2 is a 2D metal–organic framework (MOF) with a honeycomb network structure. Interestingly, the coordination chains in 1 and layers in 2 can form stable supramolecular 3D porous frameworks sustained by hydrogen bonding interactions and intermolecular π–π interactions. The distinct permanent porosity of the frameworks was established by N2 adsorption experiments. The Ni2+ centers in the two frameworks locate in two different distorted octahedral coordination environments, which lead to the varying crystal color with the effect of diverse supramolecular packing of the crystal structures. Magnetic investigation revealed that the frameworks exhibit significant easy-axis magnetic anisotropy with the zero-field splitting parameter D = -27.8 and −16.5 cm−1 for 1 and 2, respectively. However, no field-induced slow magnetic relaxation behaviors can be detected for 1 and 2. The foregoing results highlight that simple organic molecule can be used for the preparation of supramolecular magnetic frameworks with permanent porosity and coordination polymers-based supramolecular porous frameworks can act as a platform for tunable porosity and magnetic properties.

1,5-Dimethyltetrazole as a ligand in energetic 3d5 to 3d10-metal coordination compounds

During the last decade, energetic coordination compounds gained considerable attention due to the simple adjustments in their physicochemical properties. By combining different metal cations, energetic anions, and ligands, those compounds can be adapted for their intended use. This study used 1,5-dimethyltetrazole (3) as a highly endothermic, easily accessible, and insensitive ligand. It is a structural isomer to 1-ethyl-5H-tetrazole (1-ETZ), which was recently described as a suitable ligand. 1,5-Dimethyltetrazole was synthesized using two different methods: (1) reaction of acetone with azido (trimethyl) silane and (2) reaction of acetoxime benzenesulfonate with sodium azide. Subsequently, 1,5-dimethyltetrazole was reacted with the perchlorate salts of different 3d metals (e.g., Mn, Fe, Co, Ni, Cu, Zn) to obtain new energetic coordination compounds (ECCs). In addition, copper (II) complexes with 2,4,6-trinitro-phenolate anions were synthesized. The resultant complexes were investigated through low-temperature, single crystal diffraction experiments complemented by elemental analysis, infrared spectroscopy, and differential thermal analysis. Moreover, sensitivities towards impact and friction were investigated. In this study, all ECCs exhibited impact sensitivities between 2 and 10 ​J, friction sensitivities between 128 and 360 ​N, and thermal stabilities of up to 360 ​°C.

Active and passive defects in tetragonal tungsten bronze relaxor ferroelectrics

Tetragonal tungsten bronze (TTB) based oxides constitute a large family of dielectric materials which are known to exhibit complex distortions producing incommensurately modulated superstructures as well as significant local deviations from their average symmetry. The local deviations produce diffuse scattering in diffraction experiments. The structure as well as the charge dynamics of these materials are anticipated to be sensitive to defects, such as cation or oxygen vacancies. In this work, in an effort to understand how the structural and charge dynamical properties respond to these two types of vacancy defects, we have performed measurements of dielectric susceptibilities and single crystal diffraction experiments of two types of TTB materials with both ‘filled’ (Ba2NdFeNb4O15 and Ba2PrFeNb4O15) and ‘unfilled’ (Sr0.5Ba0.5Nb2O6) cation sublattices. We also perform these measurements before and after oxygen annealing, which alters the oxygen vacancy concentrations. Surprisingly, we find that many of the diffuse scattering features that are present in the unfilled structure are also present in the filled structure, suggesting that the random fields and disorder that are characteristic of the unfilled structure are not responsible for many of the local structural features that are reflected in the diffuse scattering. Oxygen annealing clearly affected both color and dielectric properties, consistent with a diminishment of the oxygen vacancy concentration, but had little effect on observed diffuse patterns.

Experimental Constraints on the H2O-Saturated Plagioclase Liquidus and the Storage Depth of the Izu-Oshima 1986B Basaltic Andesite Melt

High-temperature melting and crystallization experiments were carried out at pressures from 1 atm to 196 MPa and under H2O-saturated conditions on the basaltic andesite melt of the Izu-Oshima 1986B eruption (i.e., the BM melt), using a 1-atmosphere fO2-controlled furnace and an internally heated pressure vessel. These data were used to constrain the H2O-saturated plagioclase liquidus (HSPL) of the melt. The fO2 conditions were controlled by a mixed H2-CO2 gas at the Ni-NiO (NNO) buffer for the 1 atm experiments, but were not controlled for the high-pressure experiments. Plagioclase is the liquidus phase at 1 atm, whereas early saturation of Fe-Ti oxide above the plagioclase liquidus occurred in the high-pressure experiments due to the elevated fO2 conditions. The HSPL temperature decreases from 1172 ± 8°C to 1030 ± 20°C as the pressure increases from 1 atm to 196 MPa. A combination of previously proposed models for the plagioclase liquidus and melt H2O-solubility can predict the experimentally determined HSPL temperatures, even if oxidation-induced magnetite crystallization occurs. Using these models and the previously reported pre-eruptive temperature of ∼1100 ± 30°C, we estimate the pre-eruptive pressure conditions of the BM melt to be 42-32+48 MPa, which corresponds to depths of 1.9-1.4+1.9 km. The estimated depth is consistent with that of the shallow active dikes previously identified from geophysical studies, suggesting that the BM melt was derived from a small, shallow magma chamber formed in the shallow dike region.

Effect of tribologically-induced changes in surface termination of silicon-containing diamond-like carbon coatings on the resistance to biomolecule adsorption

Silicon-containing diamond-like carbon (DLC) is a class of thin-film materials with excellent mechanical properties, high thermal stability, and good tribological performance over a wide range of environmental conditions. While non-alloyed/non-doped DLCs also exhibit good biocompatibility and bioinertness, our understanding of the effect of silicon in DLCs on biomolecules/DLC interactions is still elusive. Here, we evaluated the structural, mechanical, and tribological properties of Si-containing DLC coatings with silicon content fraction of 11% and 16%. Tribological tests, performed by sliding a stainless steel pin on the coatings in water, indicated a low friction response (steady-state coefficient of friction <0.11), while quartz crystal microbalance experiments indicated no adsorption of a model biomolecule, namely adenosine triphosphate (ATP), on Si-containing DLCs. Near-edge X-ray absorption fine structure spectromicroscopy analyses performed after tribological experiments provided evidence for an increase in the fraction of silanol surface terminal groups formed in the worn region upon sliding in water without any significant sp3-to-sp2 rehybridization of carbon atoms. The fraction of surface hydroxyl groups in the worn region increases with the silicon content in Si-containing DLC, which leads to a decrease in friction. This tribologically-induced change in surface termination did not lead to the adsorption of ATP upon incubation of tribotested samples in ATP solutions for several hours. These findings open the path for the use of Si-containing DLC in applications requiring good tribological properties in aqueous solution and an excellent resistance to biomolecule surface adsorption that is maintained even after tribologically-induced variations in surface termination.

Uncovering the role of impurity sugars on the crystallization of d-tagatose crystal: Experiments and molecular dynamics simulations

Impurity sugars produced in upstream process of functional sugars are significantly impacting the product quality. In this work, the effect of congeners (d-maltose (d-MAL), d-fructose (d-FRU), d-glucose (d-GLU)) on primary and secondary nucleation of d-tagatose (d-TAG) crystals was investigated. The impurity sugars showed an inhibition on primary nucleation of d-TAG crystals, while a promotion on the secondary nucleation of d-TAG. Interestingly, the impact of impurity sugars on d-TAG crystal growth was similar to that on primary nucleation. The diffusion ability, hydrogen bonding forming ability, interaction energy of d-TAG crystal surfaces and impurity sugars were evaluated by molecular dynamics (MD) simulations to reveal the nucleation and growth behavior. Based on the above findings, we designed the d-TAG crystallization experiments, and obtained d-TAG crystals with uniform particle size distribution and regular morphology. This study helps to understand the influence of impurity sugars on crystallization, guiding the industrial manufacturing of functional sugars.

Cryo-EM structures of wild-type and E138K/M184I mutant HIV-1 RT/DNA complexed with inhibitors doravirine and rilpivirine

Structures trapping a variety of functional and conformational states of HIV-1 reverse transcriptase (RT) have been determined by X-ray crystallography. These structures have played important roles in explaining the mechanisms of catalysis, inhibition, and drug resistance and in driving drug design. However, structures of several desired complexes of RT could not be obtained even after many crystallization or crystal soaking experiments. The ternary complexes of doravirine and rilpivirine with RT/DNA are such examples. Structural study of HIV-1 RT by single-particle cryo-electron microscopy (cryo-EM) has been challenging due to the enzyme's relatively smaller size and higher flexibility. We optimized a protocol for rapid structure determination of RT complexes by cryo-EM and determined six structures of wild-type and E138K/M184I mutant RT/DNA in complexes with the nonnucleoside inhibitors rilpivirine, doravirine, and nevirapine. RT/DNA/rilpivirine and RT/DNA/doravirine complexes have structural differences between them and differ from the typical conformation of nonnucleoside RT inhibitor (NNRTI)-bound RT/double-stranded DNA (dsDNA), RT/RNA-DNA, and RT/dsRNA complexes; the primer grip in RT/DNA/doravirine and the YMDD motif in RT/DNA/rilpivirine have large shifts. The DNA primer 3'-end in the doravirine-bound structure is positioned at the active site, but the complex is in a nonproductive state. In the mutant RT/DNA/rilpivirine structure, I184 is stacked with the DNA such that their relative positioning can influence rilpivirine in the pocket. Simultaneously, E138K mutation opens the NNRTI-binding pocket entrance, potentially contributing to a faster rate of rilpivirine dissociation by E138K/M184I mutant RT, as reported by an earlier kinetic study. These structural differences have implications for understanding molecular mechanisms of drug resistance and for drug design.

On the anisotropic scratching behavior of single crystalline copper at nanoscale

Anisotropic material behavior raises some difficulties in characterizing and predicting the wear response of crystalline materials. A systematic set of nano-scratch crystal plasticity finite element simulations and experiments is performed to study the effect of crystal orientation and scratching direction on the wear resistance of single crystalline copper. Our results show that the scratching profile and wear volume are significantly influenced by the crystallographic orientation and scratching direction, suggesting a considerable anisotropy in the scratch response of crystalline copper. Quantifying the wear volume using Archard’s wear law shows that this anisotropy results in an orientation and scratching direction dependent wear coefficient. Alternatively, it is shown that a unique wear coefficient can be obtained for crystalline materials when one uses the scratching hardness in Archard’s wear law. This new finding may help to unify discrepant experimental and numerical wear observations and to advance physics-based wear laws without empirical coefficients.

Understanding the Inconsistencies in the Literature for the CO2 Reduction Reaction on Polycrystalline Copper

As the desire to for carbon neutral processes increases with the prominence of global warming, the electrochemical reduction of carbon dioxide has the ability to not only reduce atmospheric CO2 levels, but also produce value added chemicals such as CO, C2H4, and CHOOH using renewable energy. Polycrystalline copper is a popular electrocatalyst for the CO2 reduction reaction (CO2RR) as it is the only pure metal catalyst to reduce CO2 to products that require more than two electrons, at reasonable faradaic efficiencies [1]. This has led to the development of many novel copper-based catalysts, such as oxide derived copper, copper nanoneedles and copper nanospheres to enhance the activity and selectivity of the CO2RR [2-5]. Often when developing these unique catalysts, polycrystalline copper will be used as a reference material to show how the new material is more active and has better selectivity [2-5]. However, the literature shows substantial inconsistencies for the selectivity of the CO2RR on polycrystalline copper (under identical conditions), which brings into question the reliability of the results on the more complicated materials. For example, on polycrystalline copper, Mistry et al. reported a faradaic efficiency for methane and ethylene of 43% and 31%, respectively, at -1 V vs RHE in CO2 saturated 0.1 M KHCO3 solution [6], whereas Hori et al. reported a faradaic efficiency of 0% for both methane and ethylene under identical conditions [7].Here, we show that the discrepancy is likely not due to a single factor alone, but it is made up of several contributing factors. These include surface pre-treatments of the polycrystalline copper [7, 8] (such as sanding, mechanical polishing, electropolishing and etching), natural variation in the crystal orientation on the copper surface [9-11], and the way that iR compensation is applied and subsequently corrected for post-experiment. It was found that the faradaic efficiency for methane and ethylene could increase by up to 140% and 124%, respectively, over a 0.035 V range, which if iR compensation is not correctly adjusted for post experiment, could lead to significant errors in the reported results. We also show that the solution resistance can change by 51% over a 6 hour period of electrolysis, requiring the solution resistance to be regularly measured throughout the experiment to be able to correctly adjust the potential post experiment. Single crystal CO2RR experiments have also shown differences between the mechanism for reducing CO on a Cu(111) surface, compared to a Cu(100) surface, which leads to different activities and selectivities [12]. Interestingly, we show electron backscatter diffraction (EBSD) measurements for different pieces of the same polycrystalline copper that have different crystal orientation distributions.

Seccm-IRM: A New Tool for Quantitative in Situ Studies of Crystal Growth

Scanning electrochemical cell microscopy (SECCM) is a versatile scanning probe imaging technique that allows for simultaneous elucidation of structure activity relationships at the nanoscale in defined electrolyte volumes and provides high resolution (nm length scale) information on the topography of surfaces and interfaces1. Since its inception in 2010 SECCM has improved understanding of model systems such as graphene, graphite, carbon nanotubes, nanoparticles and conductive diamond and provided electrochemists with a tool for true single entity measurements. Electrodeposition of microscale thin films has previously been reported2 but not of crystalline species, which is the focus of this work.SECCM can also be used as a tool for the precise delivery of nano to microscale solution droplets to surfaces. By using optically transparent yet conductive substrates (such as indium tin oxide (ITO), gold or graphene ) we can couple SECCM to highly surface-sensitive imaging modes such as interference reflectance microscopy (IRM)3 or traditional brightfield microscopy, allowing the evaporation and consequent precipitation of solutes to be monitored. The SECCM apparatus allows the deposition of large arrays, under well-defined conditions (deposition time, surface potential), with each droplet representing an individual and independent crystallisation experiment and provides statistical data based on single particle level. The emergence of precipitates within these arrays is tracked to investigate the effect of additives and also surface potential on crystallisation.SECCM can use capacitative response to examine minimally ionised systems, non-aqueous solvents etc allowing organic crystals to be studied. This work focuses on the precipitation of two such model organic systems: l-cystine and 5-methyl-2-[(2-nitrophenyl)amino]thiophene-3-carbonitrile (ROY). l-Cystine is of biological relevance due to its role in the formation of kidney stone’s which are resistant to traditional therapies4. The need therefore arises for l-cystine crystallisation inhibitors making it a prime candidate for testing additive screening procedures. ROY is investigated as a model system5 to identify the merits of SECCM-IRM as a polymorph screen method. We show how sensitive precipitation is to substrate, applied potential and solvent system. References Ebejer, N.; Güell, A. G.; Lai, S. C. S.; McKelvey, K.; Snowden, M. E.; Unwin, P. R., Scanning Electrochemical Cell Microscopy: A Versatile Technique for Nanoscale Electrochemistry and Functional Imaging. Annual Review of Analytical Chemistry 2013, 6 (1), 329-351. Aaronson, B. D. B.; Garoz-Ruiz, J.; Byers, J. C.; Colina, A.; Unwin, P. R., Electrodeposition and Screening of Photoelectrochemical Activity in Conjugated Polymers Using Scanning Electrochemical Cell Microscopy. Langmuir 2015, 31 (46), 12814-12822. Valavanis, D.; Ciocci, P.; Gabriel; Morris, P.; Lemineur, J.-F.; McPherson, I. J.; Kanoufi, F.; Unwin, P. R., Hybrid scanning electrochemical cell microscopy-interference reflection microscopy (SECCM-IRM): tracking phase formation on surfaces in small volumes. Faraday Discussions 2022. Rimer, J. D.; An, Z.; Zhu, Z.; Lee, M. H.; Goldfarb, D. S.; Wesson, J. A.; Ward, M. D., Crystal Growth Inhibitors for the Prevention of l -Cystine Kidney Stones Through Molecular Design. Science 2010, 330 (6002), 337-341. Lévesque, A.; Maris, T.; Wuest, J. D., ROY Reclaims Its Crown: New Ways To Increase Polymorphic Diversity. Journal of the American Chemical Society 2020, 142 (27), 11873-11883.

Predictive control of particlesize distribution of crystallization process using deep learning based image analysis

AbstractThe challenges to regulate the particle‐size distribution (PSD) stem from on‐line measurement of the full distribution and the distributed nature of crystallization process. In this article, a novel nonlinear model predictive control method of PSD for crystallization process is proposed. Radial basis function neural network is adopted to approximate the PSD such that the population balance model with distributed nature can be transformed into the ordinary differential equation (ODE) models. Data driven nonlinear prediction model of the crystallization process is then constructed from the input and output data and further be used in the proposed nonlinear model predictive control algorithm. A deep learning based image analysis technology is developed for online measurement of the PSD. The proposed PSD control method is experimentally implemented on a jacketed batch crystallizer. The results of crystallization experiments demonstrate the effectiveness of the proposed control method.