Crystal Growth In Glasses Research Articles

Indomethacin: Effect of Diffusionless Crystal Growth on Thermal Stability during Long-Term Storage.

Differential scanning calorimetry and Raman spectroscopy were used to study the nonisothermal and isothermal crystallization behavior of amorphous indomethacin powders (with particle sizes ranging from 50 to 1000 µm) and their dependence on long-term storage conditions, either 0-100 days stored freely at laboratory ambient temperatures and humidity or placed in a desiccator at 10 °C. Whereas the γ-form polymorph always dominated, the accelerated formation of the α-form was observed in situations of heightened mobility (higher temperature and heating rate), increased amounts of mechanically induced defects, and prolonged free-surface nucleation. A complex crystallization behavior with two separated crystal growth modes (originating from either the mechanical defects or the free surface) was identified both isothermally and nonisothermally. The diffusionless glass-crystal (GC) crystal growth was found to proceed during the long-term storage at 10 °C and zero humidity, at the rate of ~100 µm of the γ-form surface crystalline layer being formed in 100 days. Storage at the laboratory temperature (still below the glass transition temperature) and humidity led only to a negligible/nondetectable GC growth for the fine indomethacin powders (particle size below ~150 µm), indicating a marked suppression of GC growth by the high density of mechanical defects under these conditions. The freely stored bulk material with no mechanical damage and a smooth surface exhibited zero traces of GC growth (as confirmed by microscopy) after >150 days of storage. The accuracy of the kinetic predictions of the indomethacin crystallization behavior was rather poor due to the combined influences of the mechanical defects, competing nucleation, and crystal growth processes of the two polymorphic phases as well as the GC growth complex dependence on the storage conditions within the vicinity of the glass transition temperature. Performing paired isothermal and nonisothermal kinetic measurements is thus highly recommended in macroscopic crystallization studies of drugs with similarly complicated crystal growth behaviors.

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.

ON THE POSSIBILITY OF OBTAINING EFFECTIVE PHOSPHORIC FERTILIZERS AS A RESULT OF INTERACTION OF PHOSPHORITE-CONTAINING WASTE WITH ACTIVATED GLAUCONITE SANDS

The aim of the study is to synthesize technical glass ceramics containing magnesium oxide and fluoride in boroaluminosilicate systems. As a result of the work, the range of compositions was determined, in which it is possible to obtain transparent sitalls with the required physicochemical characteristics. The optimal ratio of oxides for the synthesis of the initial glass has established, and the temperature ranges of nucleation and growth of crystals in glass for the formation of a cordierite crystalline phase have been determined. The processes of crystallization of glasses of cordierite composition, containing B2O3, have studied by a one-stage mode of heat treatment of glasses at 1000-1200 oC. The sequence of crystallization of phases in glasses and their effect on the properties of glass-crystalline materials of the system (MgO•Al2O3)-B2O3-SiO2, the compositions were in the region of metastable segregation of the system along the section of 2MgOꞏ2Al2O3∙5SiO2-2(MgO∙Al2O3)5B2O3, were determined

Laser patterning and growth mechanism of orientation designed crystals in oxide glasses: A review

There has been a great progress in the spatially selected patterning of crystals with a single crystal-like architecture by continuous wave (CW) and femtosecond (fs) pulsed laser irradiations in oxide glasses. Highly oriented crystals with different morphologies such as straight/bending/spiral lines and two-dimensional planar shapes are patterned using heat-driven type CW laser irradiations with a scanning mode. The features of the laser patterning of nonlinear optical crystals with birefringence such as β-BaB2O4, LaBGeO5, LiNbO3, and BaAlBO3F2 are focused, and the origin and mechanism of the c-axis orientation along the laser scanning direction are discussed from the viewpoints of surface energy and interfacial free energy between crystal and surrounding glassy phase. The homo-epitaxial crystal growth in the laser patterning of crystal lines and the rotation of crystal axes in ferroelastic β′-Gd2(MoO4)3 are demonstrated as unique features of the laser-induced crystallization. The laser-induced crystallization provides a new insight and more deep understanding for the nucleation and crystal growth in glasses and proposes a new crystal growth science and engineering in solid-state materials.

Compositional effects on mechanical properties, viscosity, and crystallization of (Li2O, B2O3, MgO)-Al2O3-SiO2 glasses

Compositional effects on mechanical properties, viscosity, crystallization and crystallization kinetics of MgO-Al2O3-SiO2 based high-strength (HS) glass and glass fibers were examined in detail by varying (Li2O + B2O3)/MgO ratio (LB/M). A set of complementary techniques was applied to the crystallization studies, including differential scanning calorimetry (DSC), powder x-ray diffraction (XRD), scanning electron microscopy equipped with energy dispersive spectrometer (SEM/EDS). Phase identification and crystal morphology survey were made. Crystallization kinetics of the HS glass fibers under various thermal conditions was studied in detail to elucidate plausible crystallization mechanisms in relationships to LB/M. Our study showed that the combined, high concentration of Li2O and B2O3, at the expense of MgO, i.e., higher LB/M, suppressed crystal growth in glass. From the DSC studies, exothermic peaks came from formation of β-quartz (s.s.) below 900°Cand subsequent transformation into cordierite greater than 1000 °C according to XRD analysis of the heat-treated samples. For crystallization under the non-isothermal conditions, Kissinger and Matusita & Sakka methods were applied to elucidate glass crystallization mechanism(s). In addition, the HS glass fibers were shown to have 29% higher tensile strength and 15% higher modulus than E-Glass fibers commercially used for a wide range of composite applications.

Study on crystallization behaviors of As–Se–Bi chalcogenide glasses

AbstractThe crystallization behaviors of As–Se–Bi chalcogenide glasses were investigated by differential scanning calorimetry (DSC) and X‐ray diffraction (XRD). Three models were used to study the glass transition behavior and the activation energy. Results showed thermal stability of glass against crystallization decreased with Bi addition in As–Se–Bi system. The mechanism of crystal growth in glasses was also studied by the Avrami exponent n. For B0, B2.5, and B5, n values are 3.12, 1.59, and 2.21 (low temperature) and 4.61 (high temperature), respectively. The thermal stability of glass is in good agreement with glass network structure. It was found that glass network structures closely associated with the Bi content and As/Se ratio were studied by X‐ray diffraction and Raman spectroscopy. And the different ratios lead to the change in Bi2Se3 crystalline orientation.

Nucleation and Crystal Growth in Laser-Patterned Lines in Glasses

Laser-induced crystallization is a new method for the design and control of the crystallization of glasses and opens a new door in the study of nucleation and crystal growth in glasses. Nonlinear optical Sm-doped -BaB2O4 (-BBO) crystal lines were patterned by continuous wave Yb:YVO4 fiber laser (wavelength 1080 nm) in 8Sm2O3-42BaO-50B2O3 glass as an example, and nucleation and crystal growth behaviors in the laser-patterned bending and crossing lines were examined. It was confirmed that the growth of c-axis oriented -BBO crystals follows along the laser scanning direction even if laser scanning direction changes. The model of self-organized homo-epitaxial crystal growth was demonstrated for the orientation of -BBO crystals at the crossing point of two lines, in which the first crystal line at the crossing point acts as nucleation site for the second crystal line. This study proposes a new crystal growth technology.

Multilayer aberration correction for depth-independent three-dimensional crystal growth in glass by femtosecond laser heating

Focused femtosecond lasers are known for their ability to modify transparent materials well below the surface with 3D selectivity, but spherical aberration causes degraded focal intensity and undesirable absorption conditions as focal depth increases. To eliminate such effects we have implemented an aberration correction procedure that accounts for multiple refracting layers in order to crystallize LaBGeO5 glass inside a temperature-controlled microscope stage via irradiation through a silica glass window. The correction, applied by a spatial light modulator, was effective at removing the focal depth-dependent degradation and achieving consistent heating conditions at different depths, an important consideration for patterning single-crystal architecture in 3D. Additional effects are noted, which produce a range of crystal cross-section shapes and varying degrees of partial crystallization of the melt.

Glass-Crystal Growth Mode for Testosterone Propionate

The recently discovered glass-crystal (GC) growth mode in some glass-forming liquids is characterized by strong and abrupt growth rate enhancement just in the vicinity of the glass transition temperature. GC growth previously has been observed in only 10 compounds. The data on testosterone propionate presented here indicate the fastest GC growth acceleration observed to date. Moreover, testosterone propionate is the first compound to show a helically twisted morphology concomitant with GC growth. It has been previously stated that an aryl ring is a prerequisite of GC growth, but testosterone propionate obviates that claim.

Does Crystal Density Control Fast Surface Crystal Growth in Glasses? A Study with Polymorphs

As organic liquids are cooled to become glasses, crystal growth at the free surface can be substantially faster than in the interior, a phenomenon uncommon for other materials and for which different explanations exist. We have measured the surface and bulk growth rates of three polymorphs in carbamazepine glasses. Crystal density has no controlling effect on the extent to which surface crystal growth is enhanced over bulk crystal growth, in contradiction to models that relate fast surface crystal growth to the release of crystallization-induced tension.

Diffusion-controlled and diffusionless crystal growth in liquid o-terphenyl near its glass transition temperature

o-terphenyl is one of the organic liquids in which a fast mode of crystal growth is activated near the glass transition temperature T(g) and continues deep in the glassy state. This growth mode, termed glass-crystal (GC), is not limited by molecular diffusion in the bulk liquid, in contrast to the diffusion-controlled growth at higher temperatures. The GC mode has been previously described as abruptly emerging near T(g) and having a constant growth rate at a fixed temperature, two features important for testing its various explanations. We report here that the GC mode already exists in the equilibrium liquid of o-terphenyl up to 1.15T(g) (T(g)=246 K) in the form of loose, fast-growing fibers and that its growth rate is constant at T(g)+2 K, but decreases by 30% in 10 h at T(g)-13 K, during which time the glass' fictive temperature decreases by 6 K. The slow down of GC growth becomes less noticeable over time so that fast growth is still observable after long annealing. The fiber growth, similar to the fully activated GC growth that yields compact spherulites, is also not limited by bulk diffusion. Crystal growth in the GC mode has a comparable activation energy as liquid desorption but a much faster rate, properties in common with polymorphic conversions. The time dependence of GC growth is not readily explained by the effect of physical aging on the thermodynamic driving force of crystallization, the liquid desorption, the primary structural relaxation, or a secondary relaxation. The secondary dielectric relaxation observed by dielectric spectroscopy in glassy o-terphenyl disappears too quickly for its molecular motions to be responsible for GC growth.

Crystallization near Glass Transition: Transition from Diffusion-Controlled to Diffusionless Crystal Growth Studied with Seven Polymorphs

A remarkable property of certain glass-forming liquids is that a fast mode of crystal growth is activated near the glass transition temperature Tg and continues in the glassy state. This growth mode, termed GC (glass-crystal), is so fast that it is not limited by molecular diffusion in the bulk liquid. We have studied the GC mode by growing seven polymorphs from the liquid of ROY, currently the top system for the number of coexisting polymorphs of known structures. Some polymorphs did not show GC growth, while others did, with the latter having higher density and more isotropic molecular packing. The polymorphs not showing GC growth grew as compact spherulites at all temperatures; their growth rates near Tg decreased smoothly with falling temperature. The polymorphs showing GC growth changed growth morphologies with temperature, from faceted single crystals near the melting points, to fiber-like crystals near Tg, and to compact spherulites in the GC mode; in the GC mode, they grew at rates 3-4 orders of magnitude faster with activation energies 2-fold smaller than the polymorphs not showing GC growth. The GC mode had rates and activation energies similar to those of a polymorphic transformation observed near Tg. The GC mode was disrupted by the onset of the liquid's structural relaxation but could persist well above Tg (up to 1.15 Tg) in the form of fast-growing fibers. We consider various explanations for the GC mode and suggest that it is solid-state transformation enabled by local molecular motions native to the glassy state and disrupted by the liquid's structural relaxation (the alpha process).

Diffusionless Crystal Growth from Glass Has Precursor in Equilibrium Liquid

A remarkable property of certain glass-forming liquids is that a fast mode of crystal growth is suddenly activated near the glass transition temperature, Tg, and continues in the glassy state. This mode of growth, termed GC (glass-crystal), is so fast that it is not limited by molecular diffusion in the bulk liquid. We have studied the GC growth by growing multiple crystal polymorphs from the liquid of ROY, currently the top system for the number of coexisting polymorphs of known structures. We observed a new feature of GC growth that conflicts with its current description in the literature. We found that the GC mode is not truly a new growth mode suddenly appearing near Tg but one already existing in the equilibrium liquid up to approximately 1.15 Tg, in the form of fast-growing fibers. This finding is relevant to testing different explanations for GC growth and favors the view that GC growth is enabled by molecular motions that are native to the glass but still persist in the viscous liquid.

The role of stress development and relaxation on crystal growth in glass

The role of internal stresses energy is usually neglected when crystallization kinetics is considered. The common argument is that stress is relaxing too fast to affect the process. In this article we develop a generalized formalism to describe steady-state growth kinetics in viscoelastic media. The residual stress energy results from interplay between the rate of stress development (due to the propagation of a crystal throughout the matrix) and rate of stress dissipation (due to relaxation of the viscous matrix). The degree to which the stress energy can relax depends on the ratio of τc/τr the characteristic time for crystal growth, τc, and the relaxation time, τr. The present results challenge the widespread fallacy that internal stresses relax too fast to affect crystal growth. Our model explains the often observed lack of agreement between the theoretical predictions (without taking into account the stresses energy development) and experimental data.

Nucleation and crystal growth in water containing soda–lime–silica glasses

The nucleation and crystal growth in glasses of composition close to Na 2O·2CaO·3SiO 2 were investigated. The steady state nucleation rate, the time lag of nucleation and also the crystal growth rate were measured as a function of the temperature for three glasses with different water content, introduced by bubbling steam through the liquids. It was shown that an increase in the water content results in the following: a decrease of the time lag of nucleation, a shift of the temperature for the maximum nucleation rate to lower temperatures, accompanied by an increase of nucleation rate values, and an increase of crystal growth rate. The analysis of the nucleation rate was performed in the framework of the classical theory of nucleation in condensed systems. In doing it the time lag of nucleation was used to estimate the kinetic barrier to nucleation. We conclude that at temperatures higher than the glass transition temperature the water content does not affect the thermodynamic barrier of nucleation but results in a decrease of the kinetic barrier.

Bulk nucleation and crystal growth in calcium tetra and digermanate glasses

Calcium tetragermanate and calcium digermanate glasses were prepared and studied with the aid of differential thermal analysis, X-ray diffraction and FTIR spectroscopy. The molar ratio of GeO 6 GeO 4 groups increases with the CaO GeO 2 molar ratio. A two steps crystallisation process was found: initially microcrystals are formed that at higher temperatures are transformed in well shaped crystals. An unidentified phase crystallises in both glasses. CaGe 2O 5 crystals also grow in calcium digermanate glass. The influence of the specific surface area of the glass sample and of a heat treatment of nucleation was pointed out. The activation energy for crystal growth in each glass was evaluated by a non isothermal method.

Kinetics of crystallization processes in glass forming melts

A survey is given of experimental results concerning the kinetics of nucleation and the mechanism of crystal growth in glass forming systems. The main aim of the review is, however, to correlate the kinetics of overall crystallization processes in glass forming melts with structural changes taking place in the initial melt during crystallization. Detailed investigations of the kinetics of overall crystallization summarized here for a number of phosphate and silicate melts, indicate that even in relatively simple glass forming melts crystallization is in fact connected with considerable molecular (e.g. anionic) reconstructions. It is shown that the kinetics of nucleation in glass forming melts can be described in terms of the more general, transient formulation of the classical theory of phase formation. Experimental evidence on the mode of crystal growth in glass forming melts is summarized, attention being concentrated on data obtained at low undercoolings. The conditions for the predominant manifestation of the basic mechanisms of crystal growth (normal, spiral and via surface nucleation) are considered, accounting for the structure of the initial melts and the state of the crystal/melt interface.

The mechanism of crystal growth in glass forming systems

A critical survey on experimental results on the mode of growth in simple glass forming melts is given, attention being mainly concentrated to data obtained at small undercoolings. Dissolution rates, change of interfacial conditions at constant undercooling as well as detailed structural determinations are considered as experimental evidences, complementary to a thorough analysis of growth-temperature dependences. For network glass formers (SiO 2, GeO 2, P 2O 5, Na 2B 4O 7) with melt structures, similar to those of the corresponding crystals, the normal mode of growth is typical. For a number of simple glass forming substances in which the crystallization is connected with a process of molecular reconstruction (NaPO 3, LiPO 3), spiral growth could be proved. Dislocation-free crystals of high entropy of melting glass forming substances (Na 2S 2O 3 · 5 H 2O, thymol) are obtained after prolonged annealing and growth in thin bored capillaries. Two-dimensional growth is verified for the resulting perfect crystals.

The initiation of crystal growth in glasses

SummaryThe application of classical nucleation theory to the initiation of crystal growth in glasses is discussed. Its application to experimental results obtained for the rate of nucleation in three types of glass, one showing nucleation separately from crystal growth, another showing simultaneous nucleation and growth, and the third showing crystal growth after metastable liquid/liquid phase separation, is then described. Recent work on the kinetics of unmixing in glasses is outlined. The influence of so-called ‘nucleating agents’ in the glasses described appears to be exerted through changes in the anionic structure.

Crystal growth in glass

Summary Information from the growth of crystals in a liquid might help to extend our knowledge of the liquid state. Glass is a convenient material for this, since the rates of reaction are generally slow and can be studied over a very wide range of conditions, though the necessarily high temperatures lead to experimental problems. This article reviews the techniques used and compares some of the results with theoretical predictions.