High Crystal Growth Rate Research Articles

Removal of magnesium and aluminum from wet phosphoric acid by ralstonite precipitation: Thermodynamic and performance analysis, mechanistic studies and precipitate characterization

The purification of wet-process phosphoric acid has always posed a challenge for both academic and industrial researchers. In order to address this issue, a treatment unit was developed to mitigate magnesium and aluminum impurities from industrial semi-aqueous wet process phosphoric acid (SWPPA) (39.4 wt% P2O5) through ralstonite precipitation using Na+/F− as the precipitator (F− provided by HF). Thermodynamic analysis, DFT calculation and separation experiments results were used to investigate the impact of sodium sources properties on impurities removal rates and H3PO4 yield. Additionally, the effects of reaction temperature, reaction time, precipitating agent dosage, and aging time on precipitation efficiency were also examined. The results show that the ability of sodium source to ionize Na+ and react with H3PO4 and HF plays a crucial role in determining the impurity removal performance of magnesium and aluminum. The precipitants NaCl and Na2CO3 exhibit the highest removal rates for magnesium and aluminum, which is attributed to the easy ionization of Na+ ions. In comparison to Na2CO3, the higher H3PO4 yield with NaCl as precipitator can be achieved due to its lower nucleation rate and higher crystal growth rate in the phosphoric acid system. NaCl and HF as precipitants effectively reduces the concentrations of magnesium and aluminum in the untreated SWPPA solution from 23.47 g MgO/kg P2O5 to 3.29 g MgO/kg P2O5, 48.98 g Al2O3/kg P2O5 to 15.54 g Al2O3/kg P2O5. The removal rates for magnesium and aluminum are found to be 85.98% and 68.27%, respectively, with minimal residue of Na+/F−.

Effects of Assisting Solvents on Purification Efficiency in the Layer Melt Crystallization of Glycerol.

The efficiency of layer melt crystallization for the selective separation of glycerol from a glycerol-diethylene glycol mixture containing 4 wt % of diethylene glycol was evaluated using solvent-free and solvent-aided approaches. The effect of 1-butanol and the binary solvent of 1-butanol and acetone with a total molar composition of 25 mol % on the crystal growth kinetics and the purity of the final product was studied at different undercooling degrees and crystallization yields. The melting point temperature of the mixtures was predicted by using the modified UNIFAC Dortmund model. The addition of both a single and binary solvents significantly increased the crystal growth rate and purity of the final product compared to crystallization from the solvent-free mixture. Additionally, higher crystal growth rates and product purity were observed in the binary solvent system compared to those in the single solvent system at the same degree of undercooling. The second stage of solvent-aided crystallization resulted in glycerol with a purity above 99.5 wt %, depending on the type of solvent used and the rate of crystal growth.

Molecular dynamics simulation of seeded crystal growth in glass

The mechanism of non-congruent growth of a crystal from glass has been sought using molecular dynamics simulations. Specifically, as a model of this process, the growth of a lithium niobate (LiNbO 3 ) crystal seed sandwiched between two lithium niobosilicate (LNS) glass slabs has been simulated as a function of time and temperature. The growth of pre-existing crystal is strongly affected by the orientation of crystal seed, temperature, and the SiO 2 concentration in the surrounding LNS glass matrix. The orientation of LiNbO 3 seed surface that has inherently larger interplanar distance results in a relatively slower crystal growth. The addition of SiO 2 to LNS system significantly decreases the crystal growth, which primarily occurs in the region devoid of Si. The suppressive effect of SiO 2 on growth rate can be traced to the existence of defect complex comprising of Si substituted at the Nb site and a nearby Nb vacancy. • Crystal growth is observed in interfacial structures containing lithium niobosilicate glasses and lithium niobate crystals. • Crystal orientation with large interplanar space results in high crystal growth rate. • High SiO 2 content suppresses the formation of ordered structures. • [Si Nb -V Nb ] defect complex exists in LiNbO 3 crystal at low SiO 2 concentration.

The role of glass composition in the 3D laser fabrication of lithium niobate single crystal in lithium niobosilicate glass

Spatially selective growth of lithium niobate (LiNbO3) crystals deep within lithium niobosilicate (LNS) glass can be achieved via femtosecond laser irradiation, wherein these crystals could serve as optical elements in photonic integrated circuits. In practice, it is challenging to achieve continuous, single-crystal growth of LiNbO3 within LNS glass. This work reports on progress in overcoming this challenge by exploring how the formation of single-crystal LiNbO3 is influenced by the incongruent composition of the glass matrix. An investigation of the parameter space of glass composition ((100 – x) LiNbO3 – x SiO2 for x = 22, 26, 30, and 34), laser scanning speed, and laser power leads to the observation of several growth modes: continuous growth at an optimal speed, segmented growth below it, and polycrystalline growth above it. For certain glass compositions, a balance of long incubation time and high crystal growth rate results in the ability to grow indefinitely long (∼cm) single crystal lines at the optimal scanning speed. Guidance for predicting which glass compositions are most suitable for single crystal growth based on the LNS composition diagram is provided.

Study on the mechanism of enlarged spherulite diameter for aliphatic polyester ionomers

Aliphatic polyesters with repeated chemical cycle performance are the promising candidate to eliminate environment pollution evoked by the petroleum-based plastics. The incorporation of ionic group can improve the strength, thermal resistance and melt viscosity of polyesters and promote them to utilize at high performance film or foam. Interestingly, these semi-crystalline ionomers achieve significant enlarged spherulite diameter (Du) when the content of ionic group is 0.58 mol%. To explore the unexpected phenomenon, poly(ethylene succinate) and poly(decamethylene succinate) phosphorus-containing ionomers (PESIs-K and PDSIs-K) with 0.58–1.91 mol% ionic group containing phosphorus (PCIG) were prepared by condensation polymerization of ethylene glycol (or 1, 10-decamethylene glycol), succinic acid and phosphorous ion monomers (DHPPO-K), respectively. The effects of PCIG content and types of diols on the chemical structures, thermal behavior, crystallization, and rheological behavior of samples were characterized by FTIR, NMR, DSC, POM, XRD, SAXS, DMA and rotational rheometer, respectively. Strikingly, the t1/2 of PESI1-K decreased from 7.0 to 2.9 min, while its Du increased from 103 to 171 μm. The reasons were that PESI1-K with moderate heterogeneous nucleation sites and melt viscosity guaranteed it to achieve high crystal growth rate, and enough growth time and space for each grain. Moreover, the incorporation of electrostatic interactions by ionic clusters facilitated the crystalline grains to cumulate in large spherulites without collapse. However, due to the improved flexibility, the relaxation time of PDS and its ionomers were much lower than those of PES and PESIs-K, while their self-nucleation capacity increased, which decreased the Du. Summarily, the effects of PCIG on crystallization behaviors were elaborated in detail and the improved Du mechanism of ionomers was proposed.

Continuous Cooling Crystallization in a Coiled Flow Inverter Crystallizer Technology—Design, Characterization, and Hurdles

Continuous small-scale production is currently of utmost interest for fine chemicals and pharmaceuticals. For this purpose, equipment and process concepts in consideration of the hurdles for solids handling are required to transfer conventional batch processing to continuous operation. Based on empirical equations, pressure loss constraints, and an expandable modular system, a coiled flow inverter (CFI) crystallizer with an inner diameter of 1.6 mm was designed. It was characterized concerning its residence time behavior, tested for operation with seed crystals or an ultrasonic seed crystal unit, and evaluated for different purging mechanisms for stable operation. The residence time behavior in the CFI corresponds to ideal plug flow behavior. Crystal growth using seed crystals was demonstrated in the CFI for two amino acids. For fewer seed crystals, higher crystal growth rates were determined, while at the same time, secondary nucleation was observed. Feasibility for the interconnection of a sonicated seeding crystal unit could be shown. However, the hurdles are also identified and discussed. Prophylactic flushing combined with a photosensor for distinguishing between solvent and suspension phase can lead to stable and resource-efficient operation. The small-scale CFI technology was investigated in detail, and the limits and opportunities of the technology are presented here.

Secondary magnesite formation from forsterite under CO2 sequestration conditions via coupled heterogeneous nucleation and crystal growth

Flow-only and coupled flow-diffusion experiments at 95 °C and 100 bars pCO2 carried out in micro-capillary tubes packed with forsterite mineral grains were used to constrain a coupled classical heterogeneous nucleation and crystal growth reactive transport model describing the formation of secondary magnesite. The study made use of a novel experimental setup in which one capillary tube for flow is connected via a three-way tee to a perpendicular capillary tube sealed at the distal end in which only molecular diffusion is allowed to occur—an experimental analogue of a single fracture-rock matrix system. While the high flux of CO2 bearing fluids and their low pH did not result in the formation of secondary carbonates in the flow-dominated channels, as much as 2.7% magnesite formed in a diffusion-controlled capillary tube sample after 300 hours of reaction. The precipitation of secondary magnesite was not uniformly distributed, however, but showed a distinctive peak shaped pattern along the sample reacted as quantified by RAMAN spectroscopic analysis. About 50% of the total magnesite precipitation formed within a narrow interval of a few millimeters close to the middle of the 3 cm diffusion sample. To simulate the behavior of the diffusion–reaction column, and in particular the pronounced mm scale peak at approximately 1.8 cm, an interfacial free energy of approximately 70 mJ·m−2 combined with a relatively high crystal growth rate for secondary magnesite was required. In agreement with the observations based on RAMAN spectroscopy, the simulations suggest that more than 50% of Mg2+ dissolved from the primary forsterite precipitated as secondary magnesite. The magnesite precipitation at the central peak position in the diffusion sample showed such rapid growth that it created a local minimum in pore fluids Mg2+ concentration close to the peak, creating a “nucleation shadow” that focused continued growth there as nearby regions had no nucleation seeds available for crystal growth. Continued crystal growth on the initial magnesite band acted to further increase the reactive surface area at this point, thus enhancing the spatially focused crystal growth rate and creating a positive feedback leading to pattern formation. This highlights the potentially critical role of an initial nucleation event in controlling mineral precipitation patterns in subsurface porous media, patterns that may determine how the pore structure subsequently evolves physically and chemically over time due to reactive flow and transport.

Potential Efficient Separation of Oil from Bilgewater and Kitchen Wastewater by Fractional Freezing Process

Oily wastewater discharge to water bodies can have many negative consequences, especially on the marine ecological environment. Although there are numerous techniques for treating oily wastewater, this paper aims to introduce and evaluate the potential of the fractional freezing (FF) process as a new oil–water separation technique to overcome the several weaknesses found in the conventional oil–water separation methods. FF separates two liquid compounds based on their freezing point difference. In this study, two oily wastewater samples were used: oily bilgewater and oily kitchen wastewater. The effects of coolant temperature, freezing time, and stirring rate on the FF process efficiency were studied, and the significance of the data was supported by statistical analysis. The results show that a low coolant temperature is essential for allowing crystal nucleation formation and inducing crystal growth for an efficient separation process. However, the higher crystal growth rate that occurs at an even lower temperature might entrap the impurities inside the growing crystal. Consequently, continuing the crystallization for a longer time may yield a less efficient separation process. Furthermore, a too high stirring rate will rupture the solid formation, hence reducing the process efficiency. The final values of oil/grease and free fatty acids (FFA) obtained after the FF process of both samples were found to comply with the standard permitted by the International Maritime Organization (IMO) and Palm Oil Refiners Association of Malaysia (PORAM). Moreover, the p-values obtained for both of the above-mentioned samples were below 0.05 for all experiments. It can be concluded that this method has the potential to separate oil from the oily bilgewater and kitchen wastewater.

Understanding of crystallization behaviors in laser 3D printing of bulk metallic glasses

In 3D printing of bulk metallic glasses (BMGs) by selective laser melting (SLM), partial crystallization normally occurs in heat-affected zones (HAZs), which significantly deteriorates the properties of 3D-printed BMGs. To understand which factor dominates amorphous-to-crystalline conversion of 3D-printed BMGs, two representative BMG alloys with different glass forming ability (GFA), i.e., Zr55Cu30Ni5Al10 (named as Zr55 with high GFA) and Zr60.14Cu22.31Fe4.85Al9.7Ag3 (named as ZrAg with low GFA), were selected for SLM 3D printing, and their crystallization behaviors were comparatively studied. It is revealed that the 3D-printed ZrAg BMG with low GFA always possessed a higher amorphous phase content than the Zr55 BMG with a high GFA under different laser energy inputs. Thermal analysis and TEM observations revealed that crystal growth rate is the crucial factor for the resistance against amorphous-to-crystalline conversion in 3D-printed BMGs, as the ZrAg system exhibited much lower crystal growth rate although it has a lower GFA. The different crystal growth behavior of the two BMGs is associated with their different crystallization mechanisms: ZrAg BMG follows the mode of primary-type crystallization with multiple phases formation, leading to a low crystal growth rate, while Zr55 BMG follows the mode of polymorphous-type crystallization, which is characterized with formation of a simple crystalline phase, thus leading to a high crystal growth rate. The present work sheds light on the understanding of crystallization mechanism in 3D-printed BMGs and provides a guide for selection or design of BMG compositions for 3D printing.

Impact of cathode loss on plasma characteristics, microstructures and properties of 7YSZ coatings in PS-PVD

The slight changes in geometry and mass of the cathode of O3CP plasma torch during service life caused the variety of arc motion between the cathode and anode. The voltage appeared to rise first and then fall. In this experiment, the impact of cathode loss on plasma characteristics, microstructures and properties of 7YSZ coatings was investigated. Optical emission spectroscopy (OES) was used to characterize the plasma jet characteristics such as plasma temperature and electron number density. It is found that vapor deposition is the main deposition mechanism, and the microstructures of the coatings are mainly affected by the supersaturation and subcooling of the vapor phase, which determine the nucleation and growth of crystals. At the middle of cathode service life, the plasma temperature and electron number density are the highest and the powder is completely evaporated. High crystal growth rates and surface diffusion lead to large columnar crystals with large grain size. The best thermal shock resistance. The thermal shock resistance is the best in this case. When the cathode is in the beginning and end of service life, there are columnar grains with small size produced and many solid particles in the gaps due to diffusion difficulties generated by low temperature. Shadowing enhances to manufacture fine grains and few branches. The presence of solid particles prevents the release of thermal stress and reduces thermal shock resistance of coatings. Fine grains prevent cracks propagation to improve the bonding strength of coatings.

Manufacture and characterization of two distinct quasi-polymorphs of empagliflozin

Abstract We investigated the polymorphic behaviors of empagliflozin (EMP), an SGLT2 inhibitor focusing on the preparation and characterization of its two distinct quasi-polymorphs combined with in-line monitoring of crystallization processes. EMP has only been reported as a single polymorph without pseudo-polymorphs so far. In this study, two differentiable crystal forms, the needle-shaped ‘Form I’ and platy-shaped ‘Form P’, were reproducibly created using an anti-solvent approach. Although the two forms of EMP yielded the same results in many of these analyses, they could be differentiated by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), and microscopy. Based on a detailed analysis of DSC thermograms, a small but obvious transition was detected during the melting of crystalline EMP at 152–157 °C. This transition, which occurred at a low activation energy, was identified as a polymorphic transformation from Form P to Form I. The anti-solvent crystallization process was monitored by in-line NIR absorbance measurements and interpreted using principal component analysis (PCA). The crystal form was dependent on the crystallization solvent. Two different solvent/anti-solvent pairs (ethanol-water and ethanol-hexane) yielded substantially different PCA results, indicating distinct pathways to the creation of each crystal form. Rapid nucleation and high crystal growth rate was achieved by crystallization under Scheme P, which also exhibited fluctuation in its PC score plot. This was associated with reversible polymorphic selection between the two crystal forms during the crystallization of EMP.

How Do Ice Crystals Grow inside Quasiliquid Layers?

A microscopic understanding of crystal-melt interfaces, inseparably involved in the dynamics of crystallization, is a long-standing challenge in condensed matter physics. Here, using an advanced optical microscopy, we directly visualize growing interfaces between ice basal faces and quasiliquid layers (QLLs) during ice crystal growth. This system serves as a model for studying the molecular incorporation process of the crystal growth from a supercooled melt (the so-called melt growth), often hidden by inevitable latent heat diffusion and/or the extremely high crystal growth rate. We reveal that the growth of basal faces inside QLLs proceeds layer by layer via two-dimensional nucleation of monomolecular islands. We also find that the lateral growth rate of the islands is well described by the Wilson-Frenkel law, taking into account the slowing down of the dynamics of water molecules interfaced with ice. These results clearly indicate that, after averaging surface molecular fluctuations, the layer by layer stacking still survives even at the topmost layer on basal faces, which supports the kink-step-terrace picture even for the melt growth.

Metallogenesis of the Totoral LCT rare-element pegmatite district, San Luis, Argentina: A review

The Totoral Pegmatite District (TPD) is the southernmost rare-element LCT pegmatite field of the Pampean Pegmatite Province. The TPD produced intermittently in the last 60 years Ta-Nb ore minerals, spodumene, beryl and ceramic raw materials. It is located in the southern part of the Eastern Pampean Range of San Luis province. It was developed during the late stage of accretion of the Famatina terrane to the West Gondwana in the Lower Paleozoic (≈450 Ma). The parental S-type leucogranites and rare-element pegmatites of REL-Li subclass form three groups aligned NNE. The leucogranites were originated by muscovite (±incipient biotite) dehydration melting of preferably metapelites (±metagreywackes) of the Pringles Metamorphic Complex (PMC). The resultant bimodal suite of S-type muscovite-tourmaline and muscovite-biotite leucogranites show major, trace elements, and Pb-Ba ratios compatible with both low-T and higher-T collisional leucogranites. These leucogranites were emplaced after regional metamorphism in the upper part of the mica schists unit of PMC at 640–725 °C and ≈400–500 MPa, and they fractionated to their associated pegmatites as is supported by the spatial association, similar age and fractionation trends of leucogranites and pegmatites. The regional integrated pegmatite zoning shows the sequence: leucogranite, pegmatitic leucogranite, barren-transitional to beryl-type, beryl-columbite-phosphate subtype, albite-spodumene type, complex-type spodumene-subtype and albite type rare-elements pegmatites. This zonation follows a path towards decreasing pressure of emplacement. The crystallization of pegmatites was triggered by the rapid undercooling provoked by the thermal contrast due to the fast forced emplacement in the hosting mica schists and the H2O and fluxes content of the melts that produced nucleation delay and high crystal growth rate of the minerals. The Li-bearing pegmatites have genetic links with the higher-T leucogranites. The emplacement of the pegmatites was facilitated by a shear zone, and they show synkinematic ductile-state deformation ascribed to the late stage of the Famatina terrane accretion. Later on, most of them were tectonically affected in brittle state by the diastrophism attributed to the westward accretion of the Cuyania terrane.

Sulphate partitioning into calcite: Experimental verification of pH control and application to seasonality in speleothems

Carbonate-associated sulphate (CAS) is a useful carrier of palaeoenvironmental information throughout the geologic record, particularly through its stable isotope composition. However, a paucity of experimental data restricts quantitative understanding of sulphate incorporation into carbonates, and consequently CAS concentrations and their diagenetic modifications are rarely interpreted. However, in the case of calcite speleothems, the remarkably high-resolution CAS records which are obtainable via modern microanalytical techniques represent a potentially invaluable source of palaeoenvironmental information. Here, we describe the results of controlled experiments of sulphate co-precipitation with calcite in freshwater solutions where pH, saturation state, and sulphate concentration were varied independently of each other. Solution pH is confirmed as the principal control on sulphate incorporation into calcite. The relative efficiency of incorporation was calculated as a partition coefficient DSO4 = (mSO4/mCO3)solid/(mSO4/mCO3)solution. High crystal growth rates (driven by either pH or saturation state) encouraged higher values of DSO4 because of an increasing concentration of defect sites on crystal surfaces. At low growth rates, DSO4 was reduced due to an inferred competition between sulphate and bicarbonate at the calcite surface. These experimental results are applied to understand the incorporation of sulphate into speleothem calcite. The experimentally determined pH-dependence suggests that strong seasonal variations in cave air PCO2 could account for annual cycles in sulphate concentration observed in stalagmites. Our new experimentally determined values of DSO4 were compared with DSO4 values calculated from speleothem-drip water monitoring from two caves within the Austrian and Italian Alps. At Obir cave, Austria, DSO4 (×105) varies between 11.1 (winter) and 9.0 (summer) and the corresponding figures for Ernesto cave, Italy, are 15.4 (winter) and 14.9 (summer). These values approximate predicted DSO4 values based on our chamber experiments containing both low (2 ppm) and high (20 ppm) sulphate concentrations. Our experimental values of DSO4 obtained at crystal growth rates typical of stalagmites, closely match those observed in other cave sites from around the world. This validates the universality of the controls behind DSO4 and will enhance the use of speleothem CAS as a palaeoenvironmental proxy.

Accelerated crystallization of high molar mass poly(l/d-lactic acid) by blending with low molar mass poly(l-lactic acid)

The crystallization kinetics of poly(l/d-lactic acid) (PLLA) with a molar mass of around 120 kDa and containing 4% of d-isomers is sizably improved by blending with low amount (<10 m%) of a PLLA of high stereoregularity, made of pure l-isomer, and molar mass of 4 kDa. Blends of the two PLLA’s are prepared by solution mixing. The blends are homogeneous in the melt and display a single, composition-dependent glass transition. Increasing concentration of the highly stereo-regular low-molar mass component in the blends results in an earlier onset of crystallization and a higher crystal growth rate. The blend composition affects the crystal polymorphism of PLLA, as increasing content of the highly stereoregular and low molar mass polymer favors growth of α-crystals at lower temperatures than typically observed in unmodified PLLA. It is suggested that the short PLLA molecules of the low-molar mass component start to crystallize at higher temperature than the long molecules of the high-molar mass component, acting as crystal nuclei for the subsequent crystal growth that involves both species.

Impact of Crystal Structure and Polymer Excipients on the Melt Crystallization Kinetics of Itraconazole Polymorphs

The crystal structure of itraconazole (ITZ) Form II has been determined by single-crystal X-ray diffraction, and the effects of crystal structure and two polymer excipients, Kollidone VA64 (PVPVA64) and hydroxypropylmethyl cellulose acetate succinate (HPMCAS), on the melt crystallization kinetics of ITZ Forms I and II have been investigated. Form II structure is characterized by a unit cell similar to that of Form I, but with a different orientation of the dichlorophenyl groups. Form II displays a considerably higher crystal growth rate than Form I, which cannot be explicated by their difference in crystal density alone. Both polymers at 20% (w/w) significantly retard the crystallization of Forms I and II without altering the crystal structure of either polymorph. Crystallization kinetic analysis by the two-dimensional surface nucleation model suggests that the polymers inhibit the crystallization of ITZ from amorphous dispersions by reducing the molecular mobility in the molten state as well as augmentin...

Oxidation-accelerated crystallization of (GeS2)y(Sb2S3)1-y chalcogenide glasses

Influence of oxygen presence on the crystallization behavior of (GeS2)y(Sb2S3)1-y glasses (for y up to 0.3) was studied by differential scanning calorimetry, X-ray diffraction analysis and infrared microscopy - the study was performed in dependence on particle size. The oxygen was found to significantly accelerate crystallization from mechanically induced defects for the (GeS2)0.1(Sb2S3)0.9 composition and to sustain the intensity of crystal formation in case of the (GeS2)0.2(Sb2S3)0.8 and (GeS2)0.3(Sb2S3)0.7 compositions. On the other hand, presence of oxygen influenced neither the morphology of the crystallites, nor the actual crystallization model-free and model-based kinetics. Direct microscopic observation confirmed strict surface crystallization for all studied composition. Compositional evolutions of the viscosity data and microscopically determined crystal growth rate curves have shown that it is the exceptionally high crystal growth rate and crystallization tendency (compared to the minor-to-moderate contribution of viscosity itself) that are responsible for the significant influenceability of the (GeS2)0.1(Sb2S3)0.9 crystallization by the presence of oxygen.

Control of heat transfer in continuous-feeding Czochralski-silicon crystal growth with a water-cooled jacket

The continuous-feeding Czochralski method is an effective method to reduce the cost of single crystal silicon. By promoting the crystal growth rate, the cost can be reduced further. However, more latent heat will be released at the melt-crystal interface under a high crystal growth rate. In this study, a water-cooled jacket was applied to enhance the heat transfer at the melt-crystal interface. Quasi-steady-state numerical calculation was employed to investigate the impact of the water-cooled jacket on the heat transfer at the melt-crystal interface. Latent heat released during the crystal growth process at the melt-crystal interface and absorbed during feedstock melting at the feeding zone was modeled in the simulations. The results show that, by using the water-cooled jacket, heat transfer in the growing crystal is enhanced significantly. Melt-crystal interface deflection and thermal stress increase simultaneously due to the increase of radial temperature at the melt-crystal interface. With a modified heat shield design, heat transfer at the melt-crystal interface is well controlled. The crystal growth rate can be increased by 20%.

Kinetics of calcium oxalate crystal formation in urine.

It is routinely observed that persons with increased urinary stone risk factors do not necessarily form uroliths. Furthermore, stone formers can present with urinalyses that do not reflect the clinical picture. We explain this discrepancy by differences in crystallization kinetics. In 1162 urines, crystallization of Ca-oxalate was induced according to the BONN-Risk-Index (BRI) method. The urine's relative light transmissivity (RLT) was recorded from 100% at start of titration to 95% due to nuclei formation and crystal growth. From the RLT changes, a measure of the thermodynamic inhibition threshold of crystal formation (BRI) and of crystal growth kinetics is derived ("turbidity slope" after crystallization onset). On average, subjects presenting with a low inhibition threshold, i.e., high BRI, also present significantly higher crystal growth rates compared with subjects in lower BRI classes. Only subjects in the highest BRI class show a lower growth rate than expected, probably due to a depletion of supersaturation by massive initial nucleation. With increasing thermodynamic risk of crystal formation (i.e., increasing BRI) due to an imbalance between inhibitors and promoters of crystal formation, an increase in the imbalance between inhibitors and promoters of crystal growth (i.e., increasing growth rate) is observed. Both lead to an increased urolith formation risk. Healthy subjects with increased BRI are an exception to this trend: their urine is thermodynamically prone to form stones, but they show a kinetic inhibition preventing nuclei from significant growth.

Effect of Growth Rate and Wafering on Residual Stress of Diamond Wire Sawn Silicon Wafers

The mechanical integrity of photovoltaic (PV) silicon wafers is critical to avoid failure during solar cell manufacturing. Residual stress present in wafers affects mechanical integrity. Residual stresses are generated during solidification of ingots and during the wafering or wire sawing process used to produce silicon wafers. In this paper, the residual maximum shear stress in diamond wire sawn photovoltaic multi-crystalline silicon wafers corresponding to different crystal growth rates and their pre-and post-etched conditions are analyzed. The full-field residual stress distributions in the wafers are measured using near infra-red transmission birefringence polariscopy. Results show that wafers corresponding to the high crystal growth rate are characterized by larger residual maximum shear stress. As the growth rate increases to two times the standard growth rate, the average residual stress increases by 43%. The increase in residual stress in the high growth rate wafers is attributed to the interaction of abrasives with more grain boundaries present in these wafers. Etching results in lower residual stress for all growth rates and ingot locations.