Recrystallization Conditions Research Articles

Crystal Habits of Itraconazole Microcrystals: Unusual Isomorphic Intergrowths Induced via Tuning Recrystallization Conditions.

The external appearance of a crystal of active pharmaceutical ingredient (API), usually referred to as a crystal habit, has a substantial impact on the API's physicochemical and physiochemical properties and, subsequently, its pharmaceutical performance. In this work, we investigate the role of different parameters of antisolvent crystallization impacting on the itraconazole (ITR) crystal habit and how this crystal habit manipulation, including crystal intergrowth, can affect crystal interactions with water molecules. Three distinct isomorphic crystal habits of ITR, a twinned blade-shaped (CHtw), a plate-shaped (CHpl), and a flat sheet-shaped with dendritic ends (CHsh), were obtained by controlling crystallization conditions. A liquid-liquid crystalline phase separation was observed as an intermediate stage preceding crystal growth. The March-Dollase parameter was used as a quantitative description of the preferred orientation, where CHsh exhibited the highest preferred orientation. The three crystal habits were evaluated for their wettability and water vapor distribution, at 37 °C, using the Young-Nelson fitting model. CHtw crystals sorbed a statistically significantly higher amount of water than CHpl and CHsh, which was attributed to the presence of crystal defects due to the twinning boundary. On the other hand, the amount of water adsorbed on the surface of CHpl and CHsh crystals was comparable and it was about twice that adsorbed on CHtw crystals. This was related to the abundance of hydrophilic chemical functionalities on the (010) facet of CHpl and CHsh as supported by the full interaction map carried out using Mercury software. This study expands investigations of the impact of crystal habit manipulation on API's functional properties beyond the well-known solubility improvement approaches.

Selective recrystallization of metastable polymorph of melt acetaminophen by using tempering operation

In organic melt crystallization, the control of polymorphism is important because of the bioavailability enhancement. In this present study, the methods for stable production of Acetaminophen (ACM) metastable polymorph are investigated in the tempering operation. The purpose is to obtain the operating guidelines for tempering operation for selective manufacturing technique of the polymorphic form. As the results, metastable form II was obtained with sufficient reproducibility under the condition of recrystallization during reheating stage. The operating conditions for crystallization of ACM metastable polymorph were determined by defining four requirements. The operating guidelines for production method of ACM metastable polymorph were proposed.

A strategy for total recovery of residue from terephthalic acid production process

Terephthalic acid is generally produced via oxidation of p-xylene. In this process, a large quantity of residue is produced containing cobalt, manganese, and bromine catalysts as well as by-products such as benzoic acid. Our purpose is to totally recover this residue. Extraction by water has been used as an efficient method to recover catalyst from this residue. In this study, the best condition for extraction was obtained at water/residue dilution ratio of 6 : 1, extraction temperature of 45°C and extraction time of 40 min. Efficiency of catalyst recovery was 92 wt % at these conditions. The catalyst containing extracted solution can be reused in the oxidation process after being concentrated by an evaporator. The benzoic acid content of the residue is also recovered by recrystallization. The best condition for recrystallization was achieved at water/residue dilution ratio of 4: 1 and dissolution and crystallization temperatures of 95 and 25°C, respectively. Recovery efficiency and purity of benzoic acid were 85 and 97 wt %, respectively, at these conditions. The recovered benzoic acid can be used in many applications. Once catalysts and benzoic acid were recovered from residue, whatever remained was terephthalic acid which was recovered by up to 98 wt % with a purity of 95% and can be recycled to the purity unit.

Modeling of Flow Stress and Grain Size Based on Z Parameter and Material Constants of Al-5.2Mg-0.6Mn Alloy during Hot Deformation

The flow stress curves of Al-5.2Mg-0.6Mn alloy were tested by isothermal compression method with Gleeble-1500 thermal simulator at the temperatures of 300, 350, 400, 450 and 500°C with strain rate of 0.001, 0.01, 0.1 and 1s-1, respectively. The morphologies of grains deformed were analyzed by TEM. Four material constants including structural factor (A), stress exponential (n), stress multiplier (α) and average activation energy (Q) of the alloy were calculated by linear regression processing. The models of flow stress (σ) and grain size (d) based on Zener-Hollomon parameter (Z) and the constants were established. The results show that the values of A, n, α, Q of the alloy were equal to 3.058×109s-1, 3.314, 0.0184 mm2N-1, 160.94 kJmol-1 respectively, and the models of flow stress and average sub-grains size can be described as σ=54.31ln {(0.327×10-9Z)0.302 +[(0.327×10-9Z)0.604+1]0.5} and d=(0.045lnZ-0.675)-1, respectively. The flow stress appreciably reduced but average grain size increased with decreasing Z value. The conditions of dynamic recrystallization occurring for the alloy were the temperature above or equal to 350°C and lnZ below or equal to 24.47.

Constitutive modeling and prediction of hot deformation flow stress under dynamic recrystallization conditions

Simple modeling approaches based on the Hollomon equation, the Johnson–Cook equation, and the Arrhenius constitutive equation with strain-dependent material’s constants were used for modeling and prediction of flow stress for the single-peak dynamic recrystallization (DRX) flow curves of a stainless steel alloy. It was shown that the representation of a master normalized stress–normalized strain flow curve by simple constitutive analysis is successful in modeling of high temperature flow curves, in which the coupled effect of temperature and strain rate in the form of the Zener–Hollomon parameter is considered through incorporation of the peak stress and the peak strain into the formula. Moreover, the Johnson–Cook equation failed to appropriately predict the hot flow stress, which was ascribed to its inability in representation of both strain hardening and work softening stages and also to its completely uncoupled nature, i.e. dealing separately with the strain, strain rate, and temperature effects. It was also shown that the change in the microstructure of the material at a given strain for different deformation conditions during high-temperature deformation is responsible for the failure of the conventional strain compensation approach that is based on the Arrhenius equation. Subsequently, a simplified approach was proposed, in which by correct implementation of the hyperbolic sine law, significantly better consistency with the experiments were obtained. Moreover, good prediction abilities were achieved by implementation of a proposed physically-based approach for strain compensation, which accounts for the dependence of Young’s modulus and the self-diffusion coefficient on temperature and sets the theoretical values in Garofalo’s type constitutive equation based on the operating deformation mechanism. It was concluded that for flow stress modeling by the strain compensation techniques, the deformation activation energy should not be considered as a function of strain.

Surface treatment of the window layer in CdS/CdTe solar cells

CdS films are used as window layers in CdS/CdTe solar cells, and an annealing process is required to promote grain growth and recrystallization in them. However, when annealing is performed in an air atmosphere, oxides such as CdO and CdSO4 form on parts of the layer’s surface, which reduces the shunt resistance and the fill factor and results in poor device performance. In this study, we annealed the CdS film in a CdCl2 atmosphere instead of air. Then, CdCl2 annealing and air annealing were compared by investigating the structural and the electrical properties of the CdS window layers. Our results reveal that the CdCl2 annealing protects the CdS film from oxidation and provides good recrystallization conditions. We also found that this CdCl2 annealing enhance the device’s performance. In particular, considerably higher shunt resistance and conversion efficiency were obtained for the CdCl2-annealed device compared with the air-annealed device.

Critical Condition of Dynamic Recrystallization of Mid-Ti Contained in Q345B

the one pass compression test of Mid-Ti Contained in Q345B was achieved by using the Gleeble-1500 thermal simulation experiment machine. The true stress-strain curve was studied under the deformation temperature was between 1000 to 1150°C and the strain rate was from 0.01 to 0.3 s-1. And then, based on Sellars model, the function relationships between critical strain (εc), strain rate (ε) and deformation temperature (T) of dynamic recrystallization of the Mid-Ti Contained in Q345B were reached:εc=2.588×10-3Z0.12,Z=εexp (439583/8.314T).

Polymorph control of luminescence properties in molecular crystals of a platinum and organoarsenic complex and formation of stable one-dimensional nanochannel.

The mononuclear diiodoplatinum(II) complex (trans-PtI2(cis-DHDAMe)2), where cis-DHDAMe = cis-1,4-dihydro-1,4-dimethyl-2,3,5,6-tetrakis(methoxycarbonyl)-1,4-diarsinine, forms three different crystalline polymorphs that can be either concomitantly or separately obtained on varying the recrystallization conditions. Cubic red crystals (α-phase) and red-orange needles (β-phase) exhibit solid-state red emissions at room temperature. Cubic red crystals of the γ-phase show no solid-state emission at room temperature. All crystalline structures were confirmed by X-ray crystallography. Room-temperature strongly luminescent crystals (α-phase) (λem = 657 nm, Φ = 0.52) have a triclinic P1 (No. 2) structure and no voids in the crystal structure. Red-orange needle-shaped crystals of the β-phase exhibit moderate red luminescence (λem = 695 nm, Φ = 0.09) at room temperature and have a trigonal, R3 (No. 148), structure. In the needlelike crystals of the β-phase, stable hexagonal arrays of nanoporous channels, 5.0 Å in diameter, are formed. Room-temperature nonluminescent crystals (γ-phase) have an orthorhombic, Pbca (No. 61), structure with a void volume that is 4.9% of the total crystal volume. After heating the α-phase crystals at 150 °C for 2 min, a powder XRD pattern different from the original crystal is obtained, and its solid-state emission at room temperature decreased. After heating the β-phase crystals at 150 °C for 2 min, the emission wavelength and the quantum yield of the solid-state emission at room temperature and the powder XRD pattern are the same as those of the α-phase after heating at 150 °C. A crystal-to-crystal transition triggered by the thermal stimulus produces a different stable polymorph of the mononuclear diiodoplatinum(II) complex. The one-dimensional nanoporous crystals encapsulated iodine without distorting the crystal packing.

Effects of Hydrogen on the Critical Conditions for Dynamic Recrystallization of Titanium Alloy During Hot Deformation

Hot deformation tests were performed to study the flow behavior and microstructural evolution of a Ti600 titanium alloy with different hydrogen contents. The effects of hydrogen on the critical conditions for the initiation of dynamic recrystallization (DRX) were investigated. The DRX kinetics models of hydrogenated Ti600 alloy were developed, and the DRX volume fractions were quantified under different deformation conditions. The results indicate that the addition of proper hydrogen (no greater than 0.3 pct) benefits the decrease of both the critical stress and critical strain for the initiation of DRX. The critical stress and critical strain are dependent linearly on the peak stress and the strain to peak stress, respectively. The strain range from the initiation to the completion of DRX increases gradually with hydrogen in the hydrogen range of 0 to 0.3 pct, and a slightly decreased strain range is observed at the hydrogen content of 0.5 pct relative to that of 0.3 pct. The addition of large amounts of hydrogen (0.3 pct or greater) in Ti600 alloy induces incomplete DRX during hot deformation.

Silver nanoparticles in isotactic polypropylene (iPP). Part I. Silver nanoparticles as metallic nucleating agents for B-iPP polymorph

Isotactic polypropylene (iPP) nanocomposites containing 0.1, 0.2, 0.4 and 0.6 wt % of silver nanoparticles (nAg) were prepared by melt compounding in a one-screw extruder. Selected samples were isothermally recrystallized at different temperatures 50, 75, 100, 125, 130 and 135 °C, and under non-isothermal conditions. The size of the silver particles dispersed in the iPP matrix were estimated by ultraviolet/visible spectroscopy (UV-VIS). The effects of nAg additions on the structure of the iPP were studied by wide angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC) techniques. The results clearly indicate that the addition of nAg induces the formation of the -iPP polymorph. It is shown that the relative amount of the form in the recrystallized nanocomposites depends on both the concentration of silver nanoparticles and thermal conditions of recrystallization.

Determining the Conditions for Dynamic Recrystallization in Hot Deformation of C–Mn–V Steels and the Effects of Cr and Mo Additions

The refinement of microstructure and its homogeneity during controlled hot strip rolling is primarily achieved by controlling the austenite recrystallization before its transformation during accelerated cooling. The paper describes the methodology to determine the deformation conditions favorable for dynamic recrystallization (DRX). Using this methodology it becomes possible to delineate the conditions for postdeformation static and metadynamic recrystallization as well. The work is based on viscoplastic power law formalism applied to steady state flow within wide range of deformation temperatures and strain rates. Two equations of the same form but with different coefficients can be used depending on whether the steady state flow is controlled by dynamic recovery (DRV) or DRX. The transition from DRV- to DRX at the corresponding value of Zener-Hollomon parameter Zt can be viewed as the demarcation between static and metadynamic recrystallization occurring after deformation. The approach is illustrated using low carbon Mn–V steel. Alloying with Cr and especially with Mo suppresses DRX and MDRX as manifested by increasing Zt.

AVALIAÇÃO DAS PROPRIEDADES MICROESTRUTURAIS E MECÂNICAS DAS LIGAS Ti-35Nb-7Zr E Ti-41,1Nb-7,1Zr PARA APLICAÇÃO BIOMÉDICA

The aim of this work was to achieve Ti-β alloys without considerable toxic elements (Al and V) with lower elastic moduli to improve the mechanical compatibility with the bone (17 GPa-35 GPa) [1,2]. Ti-35Nb-7Zr and Ti-41,1Nb-7,1Zr alloys were produced in fusion by arc melting under argon atmosphere. The ingots, with the initial diameter of 18 mm were submitted to solution heat treatment, cool rotary forging and recrystallization treatment until 6 mm of diameter. The microstructural analyses were performed using Optical Microscopy, X-ray diffraction and hardness. The mechanical characterization was evaluated through uniaxial tensile tests. The results showed that properties are dependent on the compositions studied. Microstructure results indicated that both alloys are Ti-β. Ti-35Nb-7Zr in β-solution treated condition posses the lowest value of hardness (157 HV). Vickers hardness values for alloys within 35Nb and 41,1Nb, in the recrystallization condition were very close 161 and 169 HV, respectively. The Ti-35Nb-7Zr alloy presented the lowest elastic modulus (54 GPa) and the highest ductility, based on reduction of area and elongation without change tensile strength

The Effect of Secondary Metalworking Processes on Susceptibility of Aircraft to Catastrophic Failures and Prevention Methods

Abstract The causes of plane crashes, stemming from the subcritical growth of fatigue cracks, are examined. It is found that the crashes occurred mainly because of the negligence of the defects arising in the course of secondary metalworking processes. It is shown that it is possible to prevent such damage, i.e. voids, wedge cracks, grain boundary cracks, adiabatic shear bands and flow localization, through the use of processing maps indicating the ranges in which the above defects arise and the ranges in which safe deformation mechanisms, such as deformation in dynamic recrystallization conditions, superplasticity, globularization and dynamic recovery, occur. Thanks to the use of such maps the processes can be optimized by selecting proper deformation rates and forming temperatures.

Determination of Critical Conditions for Initiation of Dynamic Recrystallization by New Method

ABSTRACTBased on the stress versus strain relation for materials at high temperatures, a new method to determine critical conditions for initial dynamic recrystallization (DRX) was proposed by analyzing the stress versus strain curve in a double natural logarithm coordinates (Ln–Ln plot) directly. The critical conditions of initial DRX of a low carbon steel were determined by the new method and the resultant values were compared with those determined by previous methods. The results show that the normalized strains are 0.6491, 0.7026, and 0.7055, respectively, by using the corresponding curves and all of the values fall in the range of 0.6–0.85 proposed by Sellars. The normalized stress and strain determined by using the strain hardening rate versus stress curve have a good agreement with those determined by using the stress versus strain curve in an Ln–Ln plot.

Helical Nanostructure of Achiral Silver p-Tolylacetylide Molecules

Silver p-tolylacetylide is an achiral molecule; however, its nanostructure has been found to consist of twisted nanoribbons. The twisted ribbon is a helicoid that combines translation and perpendicular rotation along the ribbon axis. A helix, a typical chiral structure, can be created by the aggregation of achiral molecules, and the recrystallization conditions control the twist of the nanoribbons. Therefore, the recrystallization controls the chirality.

Surface recrystallization of a gamma-TiAl alloy induced by shot peening and subsequent annealing treatments

Fine-grained recrystallization microstructure induced by shot peening and subsequent annealing treatment was achieved in the surface of Ti–48Al–2Cr–2Nb alloy. Annealing treatment at 900°C for 6–12h and the lamellar orientation angle of close to 45° are the most favorable conditions for recrystallization. The rotation, dissolution and invasion of the lamellae fragments into the adjacent normal lamellae under the driving force of residual deformation energy with phase boundary bulging mechanism is considered to be the most possible microscopic approach of the recrystallization.

Blooming of Irganox 3114® antioxidant onto a medical grade elastomer. Impact of the recrystallization conditions on the antioxidant polymorphism, on the film wettability and on the antioxidant leachability

Studying the blooming and recrystallization of additives onto the surface of polymer medical devices is of a great interest because it can affect the biocompatibility of the material. The polymorphism of a phenolic antioxidant (Irganox 3114(®)) used as an additive in medical devices and pharmaceutical packaging was studied: two different polymorphs were characterized by differential scanning measurements, FTIR and X-ray diffraction analyses. Then, the behavior of the additive in medical grade polyurethane films was described: a recrystallization into the stable polymorphic form was observed onto the polymer surface after annealing at different temperatures. The morphology observed depends not only on the additive/polymer ratio but also on the whole amount of additive in the polymer film. Depending on the recrystallization morphology, the wettability with water could be lowered and the leachability of the additives into aqueous media could be favored.

Controlling grain boundary character distribution of high-temperature B2 phase in Ti–Ni–Fe alloy

A method is proposed for controlling the grain boundary character distribution of high-temperature B2 phase in Ti–Ni–Fe alloys. The method utilizes the lattice correspondence between the deformation twins in B19′ martensite and the residual planar defects in the B2 parent phase. The optimal conditions for recrystallization and additional annealing of the tensile-deformed specimen with residual strain of about 20% were determined to be 873 K for 0.9 ks and 773 K for 3.6 ks, respectively. In the specimen annealed under these optimal conditions, over 90% of grain boundaries were coincidence boundaries with Σ ≤ 27. In particular, 33% of the grain boundaries were low-angle boundaries, that is, Σ1 boundaries. The atomic structures of the Σ9 coincidence grain boundaries and the Σ1 low-angle boundaries were observed by high-angle annular dark field scanning transmission electron microscopy. The atomic structure of these boundaries was explained well by theoretical predictions.

Effects of solvents and crystallization conditions on the polymorphic behaviors and dissolution rates of valsartan

For the quality evaluation of raw materials, the influence of various types of solvents on the polymorphic crystallization behaviors and dissolution rates of two sources of valsartan (VAL) from China and India was investigated. Samples were prepared by recrystallization from water or organic solvents, such as acetonitrile, acetone and ethanol, using methods with and without heating. Recrystallization behaviors were characterized by differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD). Scanning electron microscopy (SEM) was also used to observe the morphology of samples. The dissolution rate of recrystallized samples in water was evaluated and compared to the original VAL sample. There were significant differences in morphology, crystal structure and dissolution rate among the samples recrystallized using organic solvents. VAL was transformed into another polymorphic form by the solvents and recrystallization conditions. These physical properties of VAL also differed between the two sources of VAL. Thus, the physicochemical differences of raw materials should be carefully considered in early dosage formulation approaches.

Constitutive Relationship and Critical Condition for Dynamic Recrystallization of Inconel 625 during Hot Deformation

Hot compression tests of the commercial Inconel 625 were performed in the temperature range of 950 - 1200 °C and strain rate range of 0.01 - 10 s-1. The constitutive relationship and the critical condition for dynamic recrystallization of Inconel 625 were established. The influence of strain on the flow stress was investigated by considering the effect of the strain on material constants. It was found that a five-order polynomial was suitable to represent the influence of the strain. The stress-strain curves obtained by the proposed constitutive equation showed a good agreement with experimental results. It can be used for the analysis problem of hot forming processes.The critical condition for dynamic recrystallization was obtained by using strain hardening rate. The critical strain increased with temperature decreasing and strain rate increasing. The critical condition for dynamic recrystallization can be expressed as .