Induction Time Of Crystallization Research Articles

Beef tallow/high oleic sunflower oil shortenings produced by chemical interesterification optimized by response surface methodology (RSM): Effect of processing conditions on physical properties

AbstractResponse surface methodology (RSM) was used to obtain two shortenings (IEA and IEB) by chemical interesterification (CI) of beef tallow (BT) and high oleic sunflower oil (HOSFO) with melting points of 35.5°C and 38.5°C, higher OOO and SOO contents, and lower PPP, SOS, POS, and POP percentages than BT. The maximum percentage of HOSFO in the formulations and the optimum time, temperature, and catalyst concentrations to achieve the desired physicochemical properties for the shortenings were determined from the model. The shortenings were characterized, and the effects of processing and storage conditions were explored. HPLC/MS analysis showed that the mono and di‐unsaturated triacylglycerols (TAGs) had unsaturated fatty acids at the sn‐2 position. The changes in chemical composition due to the interesterification process were mostly differences in percentages more than in the type of TAGs present. IEA and IEB showed profiles of solid fat content versus temperature and G' values similar to those reported for soft and firm margarine, respectively. Under static cooling conditions, for BT, BA, BB, and IEB, the α‐form was the main polymorph, whereas the β′‐tendency increased with increasing temperature and slow cooling rate. IEA crystallized in the β′‐form between 20 and 32°C. Under dynamic cooling conditions, nucleation was impeded at fast cooling rate and promoted at slow rate as evidenced by induction times of crystallization. Interesterification decreased the MP, increased the β′ tendency that lasted at least 8 months at 25°C, and improved the nutritional value of shortening making them suitable as trans‐fat alternatives.

Cystine Renal Calculi: New Aspects Related to Their Formation and Development.

Background: Crystallization experiments of renal-calculi-forming compounds (calcium oxalate, calcium phosphates, uric acid) are normally performed by monitoring these processes during periods of time similar to the residence of urine inside the kidney. Nevertheless, cystine requires high supersaturation for its crystallization, and most experiments last for longer periods. It must be considered that at high supersaturation, the inhibitors of crystalline development have poor effects. Methods: The induction time of crystallization (ti) of cystine in experimental conditions similar to those of the formation of cystine renal calculi and the effect of different cystine-binding thiol agents was determined through turbidimetric measurements. We also studied the macro- and microstructure of 30 cystine kidney stones through stereoscopic microscopy and scanning electron microscopy. Results: Under the studied conditions, the ti in absence of crystallization inhibitors was 15 min, and the presence of 9 mM of penicillamine, tiopronin, or N-acetylcysteine totally inhibited crystallization, as their effects relate to the formation of complexes with cystine, although N-acetylcysteine also delayed cystine crystalline development and modified cystine crystal morphology. Cystine stones have traditionally been classified as smooth and rough. The study of their structure shows that all of them begin their formation from a few crystals that generate a compact radial structure. Their subsequent growth, depending on the renal cavity where they are located, gives rise to the rough structure in the form of large blocks of cystine crystals or the smooth structure with small crystals. Conclusions: To prevent the development of cystine renal stones, the formation of small crystals must be avoided by reducing urinary cystine supersaturation, with N-acetylcysteine being the most effective among the studied cystine-binding thiol agents. Also, the removal of cystine crystals through increased water intake and physical activity can be a very important preventive measure.

Investigation on The Effect of Low Frequency Ultrasound on The Crystallization of a Pharmaceutical Compound L+ Ascorbic Acid

One of the most crucial processes in the chemical processing industry is crystallization, which has the major challenge of producing solid products with the required purity and properties. The standard crystallization methods have various processing limitations; hence, research into alternative methods like ultrasonic-assisted crystallization has been at the forefront. The present work investigates the application of low-frequency ultrasound irradiation (40 kHz) for improving the cooling crystallization of ascorbic acid. The impact of ultrasonic irradiation on crystal size, shape, and induction time has been studied, and a comparison with the conventional method has been made. The standing time had a minor effect on particle size on average, while the initial temperature had a far more significant impact. Photographic analysis using image-analysis software indicated that when ultrasound was applied to the saturated solutions, the resulting crystals were smaller and more uniform in size and shape. The resultant crystal grows predominantly in a single direction, resembling thin prisms. The use of ultrasound was also shown to reduce the induction time significantly. This ultrasonic impact is stronger at lower initial temperatures. Indeed, the smallest induction time of 300 s was obtained for sonicated solutions at an initial temperature of 65°C and ultrasonic power of 250 w. When different levels of ultrasonic power dissipation were tested, it was established that the time required for the first nuclei to appear decreased as the power increased. There was, nevertheless, a marginal impact on average crystal size.

Sulfate Doping Promotes Agglomeration of Calcium Fluoride Crystals.

Calcium salt precipitation is an effective solution to wastewater fluoride pollution. The purity and precipitation efficiency of calcium fluoride is critical for its removal and recovery. This study aimed to reveal the role of coexisting sulfates in the precipitation of calcium fluoride. A low sulfate concentration promoted calcium fluoride precipitation. The size of calcium fluoride-aggregated particle clusters increased from 750 to 2000 nm when the molar ratio of sulfate to fluoride was increased from 0 to 3:100. Sulfate doped in the calcium fluoride crystals neutralized the positive charge of the calcium fluoride. Online atomic force microscopy measurements showed that sulfate reduced the repulsive force between calcium fluoride crystals and increased the adhesion force from 1.62 to 2.46 nN, promoting the agglomeration of calcium fluoride crystals. Sulfate improved the precipitation efficiency of calcium fluoride by promoting agglomeration; however, the purity of calcium fluoride was reduced by doping. Sulfate reduced the induction time of calcium fluoride crystallization and improved the nucleation rate of calcium fluoride. Sulfate should be retained to improve the precipitation of calcium fluoride and to avoid its loss from the effluents. However, it is necessary to separate sulfate from fluoride to obtain high-purity calcium fluoride. Therefore, sulfate concentration regulation in high-fluoride wastewater is key to achieving the efficient removal and recovery of fluoride ions.

Surfactant-assisted crystallization of lysozyme and its mechanism

Surfactants were used to assist in the crystallization of lysozyme. Three types of surfactants with different structures (sodium dodecyl sulfate, cetyltrimethylammonium bromide, or betaine hydrochloride [BH]) were used. The study indicated that three surfactants were all capable of shortening the crystallization induction time of lysozyme, with BH inducing the shortest crystallization induction time (t = 1 min) and the largest crystal size (37 μm). The molecular interactions among each of the three surfactants aforementioned and lysozyme were also investigated by simulations. It was found that hydrogen bonding dominantly acted between the carboxyl structure of the surfactant BH and the lysozyme, which produced the most favorable conformation for the self-assembly of lysozyme (promote lysozyme orderly aggregation and shorten the crystallization induction time). On this basis, the mechanism of surfactant-promoted lysozyme crystallization was proposed.

Investigations on melamine-based uric acid kidney stone formation and its prevention by inhibitors.

Melamine (Mel) as a milk powder adulterant came to light in September 2008, when a kidney stone disease (KSD) outbreak struck China. The mechanism of the formation of Mel-associated uric acid (UA) stones is relatively unknown. Therefore, in the present study, Mel's influence was explored at comparatively higher and lower concentrations in artificial urine. The parameter optimization performed when the Mel concentration in artificial urine was low, which revealed that higher pH values and lower UA concentration considerably delayed the induction of UA crystallization. When Mel concentration was increased relative to UA concentration, the induction time of UA crystallization decreased dramatically. At the highest concentration of Mel investigated (at UA-Mel molar ratio 1:1), PXRD analysis and SEM revealed a change in crystalline structure of the samples. Based on FTIR analysis, it was determined that UA-Mel interactions are essentially physical, because no new characteristic bands developed. Two inhibitors, namely tri-potassium citrate (TPC) and 3, 7-dimethylxanthine (DMX), were investigated for their inhibitory action on UA crystallization in the presence of Mel. DMX was observed to be more promising than TPC in delaying the induction of crystallisation and hence inhibiting crystal formation.

Effect of ultrasonic-induced selenium crystallization behavior during selenium reduction

In this work, the crystallization process of selenium was accelerated by ultrasonic wave. The effects of ultrasonic waves and conventional conditions of selenium crystallization were compared to understand the effects of different conditions on crystallization, including ultrasonic time, ultrasonic power, reduction temperature, and H2SeO3 concentration. The mechanism of ultrasound affecting selenium crystallization was also investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results showed that ultrasonic time, ultrasonic power, and reduction temperature significantly influenced the crystallization process and morphology of selenium. Ultrasonic time had a large effect on the completeness (all products have been crystallized) and integrity of the crystallization of the products. Meanwhile, ultrasonic power and reduction temperature had no effect on the completeness of crystallization. However, it had a significant effect on the morphology and integrity of the crystallized products, and different morphologies of the nano-selenium materials could be obtained by changing the ultrasonic parameters. Both primary and secondary nucleation are important in the process of ultrasound-accelerated selenium crystallization. The cavitation effect and mechanical fluctuant effects generated by ultrasound could reduce the crystallization induction time and accelerate the primary nucleation rate. The high-speed micro-jet formed in the rupture of the cavitation bubble generated is the most important reason to influence the secondary nucleation of the system.

Supersaturation maintenance of carvedilol and chlorthalidone by cyclodextrin derivatives: Pronounced crystallization inhibition ability of methylated cyclodextrin

Cyclodextrin (CD) is used to solubilize poorly water-soluble drugs by inclusion complex formation. In this study, we investigated the effect of CD derivatives on stabilizing the supersaturation by inhibiting the crystallization of two poorly water-soluble drugs, carvedilol (CVD) and chlorthalidone (CLT). The phase solubility test showed that β-CD and γ-CD derivatives enhanced the solubility of CVD to a greater extent, whereas the solubility of CLT was enhanced more by β-CD derivatives. The solubilization efficacy of CD derivatives was dependent on the size fitness between the drug molecule and the CD cavity. In the drug crystallization induction time measurement, the same initial drug supersaturation ratio (S) was employed in all the CD solutions, and the methylated CD derivatives greatly outperformed unmethylated CD derivatives in stabilizing the supersaturation of both CVD and CLT. The crystallization inhibition strength of CD derivatives was strongly affected by the CD derivative substituent. Moreover, the calculated logarithm of octanol/water partition coefficients (log P) of CD derivatives showed a good correlation with drug crystallization inhibition ability. Thus, the high hydrophobicity of methylated CD plays an essential role in inhibiting crystallization. These findings can provide a valuable guide for selecting appropriate stabilizing agents for drug-supersaturation formulations.

Novel Barite Crystallization and Inhibition Model Based on Surface Adsorption

Summary Inorganic mineral crystallization is a critical process for numerous industrial and geoengineering processes, including oil and gas production and transportation, geothermal energy exploitation, membrane filtration, cooling tower, heat exchanger, to mention a few. Its unexpected formation can cause significant engineering, economic, and safety issues. Scale inhibitors have been widely used in various geoengineering projects as one of the most efficient and economic methods for mineral scale control. However, after decades of research, the inhibition mechanisms still remain unknown. This study applied a newly developed mechanistic mineral crystallization and inhibition model to barite, one of the most difficult mineral scales to be remediated. This new model assumes that inhibitors prolong the crystallization induction time by adsorbing onto the nucleus surface following a Langmuir-type adsorption isotherm and increasing the surface tension. The new model accurately predicts the barite crystallization induction time without or with 10 commonly used scale inhibitors. More importantly, the adsorption affinity constants (i.e., KL) fitted with the new model from the barite crystallization induction time matched well with those fitted from the direct inhibitor adsorption testing and from measuring barite crystal growth rate changes due to various inhibitors. A good correlation was also observed between the KL values of various inhibitors with barite from this study and those with other minerals (i.e., hydroxyapatite and calcite) from the literature. Such good agreements and correlations validated the adsorption mechanism adopted in the new mechanistic model. This study will deepen the understanding of mineral crystallization and inhibition mechanisms and improve scale management in various industrial and geoengineering processes.

Competition effect of solid-state stretching induced orientation and phase separation on stereocomplex crystallization of PLLA/PDLA during annealing

Benefiting from its superior thermal and mechanical properties, the stereocomplex crystal (SC) of PLLA/PDLA is catching increasing interest. In this work, a systematic investigation was performed to reveal the effect of solid-state stretching on the formation of SC during annealing. Results show that as the stretching temperature was close to the glass transition temperature (Ts = 60 °C), the polymer chains orientation was increased gradually with draw ratio (λ). As a result, the crystallization induction time (t0) was shortened, the growth rate (Gr) of SC was enlarged, and the crystallinity of SC (XSC) was elevated as a result of orientation-induced crystallization. Whereas, the saturation of t0, Gr, and XSC appeared quickly when λ reached 2.7, although the orientation of polymer chains continued to increase. The reason is that in addition to orientation, strong phase separation between PLLA and PDLA was also triggered therein. The phase separation prohibited greatly the crystallization of SC due to a long time would be needed for PLLA or PDLA chains to diffuse to a distance close enough to activate the hydrogen-bonding interaction, which is the prerequisite of SC crystallization. When the stretching temperature was elevated to 75 °C, the phase separation became much weaker. So XSC was higher compared to that of the blend stretched at 60 °C to the same λ. Moreover, in the annealing temperature from 180 °C–190 °C, t0 was much smaller for the blend stretched at 75 °C since the crystallization of SC in this temperature range is a diffusion-controlled process.

Structured lipids produced from palm-olein oil by interesterification: A controllable lipase-catalyzed approach in a solvent-free system

Palm olein (POL) was modified by enzymatic interesterification with different degrees of acyl migration in a solvent-free packed bed reactor. The fatty acid and acylglycerol composition, isomer content, thermodynamic behavior, and relationship between crystal polymorphism, solid fat content (SFC), crystal microstructure, and texture before and after modification were studied. We found that the increase in sn-2 saturation interesterification was not only due to the generated tripalmitin (PPP) but also caused by acyl migration, and the SFC profiles were changed accordingly. The emergence of high melting point acylglycerols was an important factor accelerating the crystallization rate, further shortening the crystallization induction time, leading to the formation of large crystal spherulites, thereby reducing the hardness. The transformation from the β' to the β form occurred during post-hardening during storage. The isomer content also affected the physicochemical properties of the modified POL.

Gypsum scale formation and inhibition kinetics with implications in membrane system

Water desalination using membrane technology is one of the main technologies to resolve water pollution and scarcity issues. In the membrane treatment process, mineral scale deposition and fouling is a severe challenge that can lead to filtration efficiency decrease, permeate quality compromise, and even membrane damage. Multiple methods have been developed to resolve this problem, such as scale inhibitor addition, product recovery ratio adjustment, periodic membrane surface flushing. The performance of these methods largely depends on the ability to accurately predict the kinetics of mineral scale deposition and fouling with or without inhibitors. Gypsum is one of the most common and troublesome inorganic mineral scales in membrane systems, however, no mechanistic model is available to accurately predict the induction time of gypsum crystallization and inhibition. In this study, a new gypsum crystallization and inhibition model based on the classical nucleation theory and a Langmuir type adsorption isotherm has been developed. Through this model, it is believed that gypsum nucleation may gradually transit from homogeneous to heterogeneous nucleation when the gypsum saturation index (SI) decreases. Such transition is represented by a gradual decrease of surface tension at smaller SI values. This model assumes that the adsorption of inhibitors onto the gypsum nucleus can increase the nucleus superficial surface tension and prolong the induction time. Using the new model, this study accurately predicted the gypsum crystallization induction times with or without nine commonly used scale inhibitors over wide ranges of temperature (25–90 °C), SI (0.04–0.96), and background NaCl concentration (0–6 mol/L). The fitted affinity constants between scale inhibitors and gypsum show a good correlation with those between the same inhibitors and barite, indicating a similar inhibition mechanism via adsorption. Furthermore, by incorporating this model with the two-phase mineral deposition model our group developed previously, this study accurately predicts the gypsum deposition time on the membrane material surfaces reported in the literature. We believe that the model developed in this study can not only accurately predict the gypsum crystallization induction time with or without scale inhibitors, elucidate the gypsum crystallization and inhibition mechanisms, but also optimize the mineral scale control in the membrane filtration system.

Caffeine metastable zone width and induction time in anti-solvent crystallization

In this study, the anti-solvent approach was used to investigate caffeine's induction time and metastable zone width (MSZW). Chloroform is used as a solvent, and carbon tetrachloride is used as an anti-solvent. Initially, caffeine solubility data is gathered in the chloroform/carbon tetrachloride mixture at various chloroform mass fractions. Caffeine solutions with various concentrations were then created to determine the MSZW. The anti-solvent (carbon tetrachloride) was injected into the solution to achieve supersaturation. The metastable zone limit was obtained by adding the anti-solvent at a constant rate and using turbidity changes in the system. The time of induction in various supersaturations was also investigated. In this section, various concentrations of solutions were created. Then, the system was instantly supersaturated with an anti-solvent. The period between the addition of the anti-solvent and the change in the turbidity of the solution was known as the induction time. The visual technique is compared to the use of an online turbidimeter before starting induction time measurements, and it is shown that the induction times obtained with the online turbidimeter are shorter and more accurate. Additionally, the induction time was investigated by various supersaturations, and it was discovered that as the supersaturation approaches the metastable zone border, the induction time decreases. Furthermore, in the same supersaturations, the influence of mixing on induction time was explored, and it was revealed that the higher the stirring speed, the shorter the induction time. Finally, the interfacial energy of solid–liquid phase was calculated for two systems with different initial chloroform mass fractions. It was shown that a reduction in polarity of medium increases the interfacial energy.

Crystallization of citicoline sodium by anti-solvent assisted with ultrasound

Citicoline sodium tend to agglomerate during the crystallization process which can't be well solved by changing some conventional crystallization conditions. To solve this problem, an ultrasonic-assisted crystallization method was developed in this paper. The effects of ultrasound on the crystal metastable zone widths (MSZWs), induction time, crystal habit, and particle size distribution (PSD) were studied experimentally. The dynamic method was used to determine the solubility of Citicoline sodium in ethanol–water binary mixed solvents. The induction time and the MSZWs were measured under ultrasound and silent conditions. Moreover, the crystallization process was optimized using ultrasonic-assisted anti-solvent crystallization method. The influence of ultrasound on crystal habit during the crystallization process could be observed by optical microscope. Ultrasound optimized products can be characterized by scanning electron microscope (SEM), laser particle size analyzer, X-ray powder diffraction and infrared spectroscopy. The experimental results showed that the MSZWs and the induction time could be reduced by the application of ultrasonic irradiation. The agglomeration and crystal habit of Citicoline sodium could be improved by optimizing the crystallization process with ultrasound. After optimization, the mass yield was increased to 95 %, the median particle size DV (50) was about 10 μm and the PSD was narrower.

Distinct impacts of natural organic matter and colloidal particles on gypsum crystallization

Gypsum scaling via crystallization is a major obstacle limiting the applications of membrane-based technologies and heat exchangers in engineered systems. Herein, we perform the first comparative investigation on the impacts of natural organic matter (Suwannee River humic acid, SRHA) and colloidal particles on the gypsum crystallization process in terms of induction time and crystal morphology. Results show that the presence of SRHA significantly increases the induction time of gypsum crystallization. Specifically, at a solution saturation index of 4.92, the induction time increases 6.5-fold in the presence of 6 mg/L SRHA, compared to the case without SRHA. SRHA also alters the morphology of the formed calcium sulfate crystals, resulting in a polygon-like shape, differing from the characteristic needle-like shape of gypsum in the absence of additives. These changes in crystal morphology are attributed to the adsorption of SRHA on the gypsum crystal surface, blocking the active sites for gypsum growth. In contrast, in the presence of colloidal particles, the observed induction time of gypsum crystallization either decreases or increases, depending on the competitive interplay between the enhancement effect in the nucleation step and the inhibition effect in the subsequent crystal growth step. Furthermore, the formed gypsum crystals in the presence of colloidal particles exhibit a needle-like morphology similar to the crystals formed in the absence of any additives. Our study provides fundamental understanding of gypsum crystallization in feedwaters containing natural organic matter and colloidal particles, highlighting the importance of feedwater composition in gypsum scaling.

Characterization and Crystal Nucleation Kinetics of a New Metastable Polymorph of Piracetam in Alcoholic Solvents.

A new polymorph of the drug active pharmaceutical ingredient piracetam (Form VI) has been discovered and characterized by X-ray powder diffraction (PXRD), solid-state Raman, attenuated total reflectance infrared spectroscopy, and differential scanning calorimetry. The PXRD diffractogram of Form VI shows a distinct peak at 24.2° (2θ) that distinguishes it from the previously known polymorphs and solvates. Form VI is metastable with respect to the previously known polymorphs Form II and Form III; in ethanol solution at 288 K, Form VI transforms into Form II within 15 min, while in isopropanol solution Form VI is kinetically stable for at least 6 h. A total of 1200 crystal nucleation induction time experiments of piracetam in ethanol and isopropanol solutions have been conducted, in sets of 40–80 repeat experiments carried out at different temperatures and solute concentrations. Each solution nucleated as a single polymorph, and each set of repeat experiments resulted in different proportions of Form II, Form III, and Form VI, with Form VI dominating at low nucleation temperatures and Form II at higher nucleation temperatures. The induction time data for Form VI at 288 K have been evaluated within the framework of the classical nucleation theory. At equal driving force, nucleation of Form VI is less obstructed in ethanol than in isopropanol, as captured by a lower interfacial energy and higher pre-exponential factor in ethanol. The proportion of Form VI obtained at a comparable driving force increases in the order ethanol < isopropanol.

Effect of stabilization and fatty acids chain length on the crystallization behavior of interesterified blends during storage

In this work, we studied the influence of fatty acid chain length and crystallization temperature on the crystallization behavior during the storage of binary blends modified by chemical interesterification. The blends were produced with soybean oil and fully hydrogenated oils from palm kernel, palm, soybean, microalgae, and crambe, evaluated separately, at a ratio of 50:50 (% w/w). The blends were crystallized by two crystalline stabilization methods. In method I, the samples were maintained at 25 °C for 24 h before the analyses. In method II, the samples were maintained at 5 °C for 24 h, followed by crystalline stabilization at 25 °C for 24 h before the analyses. The interesterification reaction caused considerable changes in the TAGs profile with increasing asymmetric TAGs. These TAGs changes promoted an increase in the crystallization induction time, a decrease in the maximum solids content, and changes in crystals morphology. The increase in the FAs chain length promoted the increased nucleation rate that influenced morphology crystals. Method II promoted a reduction in the medium diameter of crystals and the appearance of the β phase with storage time. For crystallization carried out at higher temperatures (method I), we observed that β’ was favored. Unusual polymorphic transitions were observed with storage time in samples with higher tristearin content. We identified clear correlations between the predominance of β’ phase in the interesterified blends and TAGs of S2U and SU2-type. In addition, the blends with a more diverse range of fatty acids concerning chain size also showed the β’ polymorph. β polymorph, on the other hand, was associated with symmetric TAGs, S3 and U3, and CN-54 type TAG. In this study, we used the Rietveld method to quantify the polymorphs and amorphous content in the blends before and after the randomization reaction. This approach allowed a deeper understanding of the crystalline behavior in the blends, which would be difficult to achieve by performing only a visual analysis of the X-ray diffractograms.

Effects of dissolved organic matter on phosphorus recovery via hydroxyapatite crystallization: New insights based on induction time

Recovery of phosphorus from sewage can help establish a new phosphorus cycle and hydroxyapatite (HAP) crystallization is a promising way. HAP crystallization is an amorphous calcium phosphate (ACP) mediated process, and its induction time reflects the rate of HAP nucleation, and seriously affects the efficiency of phosphorus recovery. In this study, the effects of different types of dissolved organic matter (DOM) on the induction time and phosphorus recovery performance of ACP-mediated HAP phosphorus recovery were studied, and the mechanism was analyzed by X-Ray Diffraction, Fourier transform infrared spectroscopy, and scanning electron micrograph with energy dispersive spectrometry. The results show that DOM greatly prolongs the induction time of ACP-mediated HAP crystallization and leads to an increase in the yield of microcrystals, thus leading to a decrease in phosphorus recovery efficiency. DOM inhibits ACP-mediated HAP crystallization by complexing lattice ions and occupying active growth sites on the crystal surface. Pre-removal of DOM can not only improve the speed and efficiency of phosphorus recovery by the HAP crystallization process but also improve product quality.

Crystallization Propensity of Amorphous Pharmaceuticals: Kinetics and Thermodynamics.

Four model compounds, nifedipine, indomethacin, felodipine, and ketoconazole, all with nearly identical glass transition temperatures, were chosen to study the effects of thermodynamics and molecular mobility on their crystallization propensities. The time and temperature dependence of the crystallization induction time of each compound was determined by differential scanning calorimetry (DSC) and enabled the generation of their time-temperature-transformation (TTT) diagrams. The relaxation times (τα) were measured by dielectric spectroscopy, and the Gibbs free energy (ΔG) and entropy (ΔS) difference between the crystalline and amorphous states were obtained by DSC. The temperature dependence of the crystallization induction time (τ0(T)) is a function of the thermodynamic activation barrier and the frequency of "attempted jumps" (1/τα(T)) to overcome the barrier. Even though the four model compounds exhibited very similar molecular mobility (relaxation time) over a wide range of temperatures, their crystallization propensities were very different. The observed difference in crystallization propensity was explained in terms of the difference in the thermodynamic barrier, and it is correlated to the empirical relation (TΔS3)/ΔG2.

Effect of aeration operation on crystallization induction time of melt with the difficulty of nucleation

Quality control of the crystalline materials obtained from melts with the difficulty of nucleation is challenging. When nucleation is enhanced in such melts, the quality distribution is improved. Herein, the aeration method, which enhances nucleation in solution systems, was employed in a melt to investigate the aeration effect on nucleation in a melt and the effect of the crystallization conditions with aeration on the induction time τind. Experimental results show that aeration enabled nucleation in a melt under supercooling conditions, where nucleation could not occur without aeration. Furthermore, τind depended on the operating conditions with aeration (initial supercooling, aeration period, and atmospheric temperature). The crystal size in the obtained solid phase decreased as the atmospheric temperature decreased. These results suggest that the desired nucleation timing and crystal size can be obtained by manipulating the crystallizer and aeration conditions. Thus, aeration is promising for improving the quality distributions in crystalline materials.