Kinetics Of Crystallization Process Research Articles

Cryoprotective Effect of Pectin Tanacetan from Tanacetum vulgare L.

We researched the ability of tanacetan pectin from inflorescences of common tansy Tanacetum vulgare L. to change the osmolarity and freezing point of water in solutions of cryoprotectants: glycerol-3.5%, dimethyl sulfoxide (DMSO)-10%, dimethylacetamide-10% (DMAC), and 1.2-propanediol (1.2-PD)-10%, as well as the effect of solutions of tanacetan (0.2%, 0.4%) on the kinetics of crystallization processes and the nature of crystal formation. We used a combination of protector and pectin that we tested earlier, which provided effective protection for human leukocytes and platelets, as well as bovine spermatozoa, at temperatures below freezing (-20°C and -80°C). It has been established that tanacetan slows down the process of water freezing in glycerol, but not in DMSO, DMAC, and 1.2-PD, promotes deeper supercooling of the medium, and affects the morphological structure of ice. The addition of pectin to the cryosolution increases the activity of the main cryoprotectant glycerol even at its low concentrations. The combination of glycerol and tanacetan can be effective in freezing biological materials, which is confirmed by the preservation of leukocytes at -20°C and -80°C for 7 days, platelets at -80°C for 30 days, and spermatozoa at -80°C within 1 day. A comprehensive analysis of the chemical, physicochemical, and cryoprotective properties of tanacetan indicates the prospect of using pectin in the cryopreservation of biological objects at temperatures of electric freezers.

Kinetics of crystallization mechanisms in poly(3-hexylthiophene) and poly(9,9-dihexylfluorene-alt-2,5-didodecyloxybenzene) conjugated polymers

Conjugated polymers are perceived as promising materials for emerging applications in energy and environment. Kinetics of crystallization processes in conjugated polymers may not only model the processes but also helps in revealing their mechanisms. This paper gives an account of the kinetic investigation on crystallization processes in two known conjugated polymers, poly(3-hexylthiophene) (P3HT) and poly(9,9-dihexylfluorene-alt-2,5-didodecyloxybenzene) (PF6OC12) under non-isothermal conditions by employing the advanced polymer crystallization kinetics approach. Kinetic study suggests that both P3HT and PF6OC12 crystallize by following fairly single-step nucleation and diffusion phenomena. In addition, the diffusion activation energies of P3HT and PF6OC12 obtained are compared and conform to the universal activation energy value of the segmental jump during the diffusion processes in polymers. Nevertheless, while PF6OC12 pursues two-dimensional (2D) growth of spherulites, P3HT on the other hand, follows a rather complex crystallization mechanism. It is noteworthy that the glass transition temperatures of both the conjugated polymers are more or less the same. The obtained kinetic parameters are interpreted in terms of their plausible physical meanings. A thermodynamic expression to determine the transition entropy of polymer crystallization is also derived and discussed.

Influence of Ti Doping on the Properties of Ge-Sb-Te Thin Films for Phase Change Memory

The influence of Ti doping on the resistivity, activation energy of conductivity, energy band gap, Urbach energy, crystallization temperature, heat effect and crystallization kinetic parameters in Ge2Sb2Te5 thin films for phase change memory was investigated. It was shown that introduction of Ti influences on the thermal properties, and kinetics of crystallization process. Results of analyzes showed that Ti doping affects crystallization time, and probability of spontaneous crystallization at room temperature, which must be taken into consideration at designing PCM cells with Ti electrodes.

Crystallization of zirconia doped basalt fibers

Crystallization of basalt fibers containing 0–7wt% ZrO2 was studied. Fibers were drawn from basalt glasses and annealed in air at different temperatures. Phase composition of obtained samples was determined by XRD. Kinetics of crystallization processes was investigated by DSC. Kinetic models and parameters were estimated for crystallization of spinel-like phase, pyroxene and plagioclase using model-free analysis. It was found that doping of fibers with 1–3wt% ZrO2 increased Arrhenius parameters of aluminosilicate crystallization. When the zirconia content was 5–7wt% the crystallization mechanism significantly changed. This phenomenon resulted in increasing of fiber thermal stability.

Nanocrystalline LaMnO3 preparation and kinetics of crystallization process

Precursor of nanocrystalline LaMnO3 was synthesized by solid-state reaction at low heat using La(NO3)3·6H2O, MnSO4·H2O, and Na2CO3·10H2O as raw materials. XRD analysis showed that precursor was a mixture containing orthorhombic La2(CO3)3·8H2O and rhombohedral MnCO3. When the precursor was calcined at 800°C for 2h, pure phase LaMnO3 with rhombohedral structure was obtained. Magnetic characterization indicated that rhombohedral LaMnO3 behaved weak magnetic properties. The thermal process of the precursor experienced four steps, which involved the dehydration of crystallization water at first, and then decomposition of manganese carbonate into MnO2, and decomposition of La2(CO3)3 and MnO2 together into La2O2CO3 and Mn2O3, and lastly reaction of monoclinic La2O2CO3 with Mn2O3 and formation of rhombohedral LaMnO3. Based on the Kissinger equation, the value of the activation energy associated with the formation of rhombohedral LaMnO3 was determined to be 260kJmol−1. The value of the Avrami exponent, n, was equal to 1.68, which suggested that crystallization process of LaMnO3 was the random nucleation and growth of nuclei reaction.

Effect of the ionic aggregation on the crystallisation behavior of poly(ethylene) part of ionomer

The influence of ionic interaction on the melt-crystallization behavior of the ethylene ionomer was studied using modulated DSC (MDSCTM), wide angle X-ray scattering (XRD) and hot stage microscopy. The kinetics of the crystallization process of the ionomer was evaluated using isothermal differential scanning calorimetry (iso-DSC). Wide-angle X-ray scattering was used to examine the d spacing of poly(ethylene) part. The crystallinity of the poly(ethylene) part of ionomer measured from XRD is found to be 24%, which is comparable to that obtained from MDSCTM. Small-angle X-ray scattering (SAXS) results show that the clusters and multiplets exist in the ionomer, and the cluster is about 127Ĺ. The kinetics of crystallization process obtained using Avrami equation shows that the crystallization process is fundamentally similar to poly(ethylene) as it goes through nucleation and propagation stages of the crystals. However, the morphology of the crystal appears to be different and influenced by clusters (platelike and/or needle-shaped) as evident from Avrami constant. This is different from the poly(ethylene) (which is spherulitic in nature) due to polar cluster and hydrophobic PE melt interaction.

Kinetics of crystallization processes in some glass ceramic products

The paper presents the kinetic study of the crystallization processes which take place in basalt glasses containing variable amount of nucleation agent (CaF2, 310%). The activation energies have been calculated using Kissinger's equation and verified with the Ozawa-Flynn-Wall equation. In this order, the DTA curves have been registered with different heating rates, between 4 and 20 degrees/min. A correlation equation between the activation energy and the amount of nucleation agent (% of CaF2) was established. By X-ray diffraction it was proved that the crystalline phase formed in the crystallization process represents a pyroxenic solid solution, Ca(Mg,Fe)SiO3.

Testing Method for the Johnson–Mehl–Avrami Equation in Kinetic Analysis of Crystallization Processes

The kinetics of crystallization processes in solids are usually described by the Johnson–Mehl–Avrami equation. One of the most popular methods to test the applicability of this equation is based on a double logarithmic plot of fraction crystallized (α). However, such plot is not very sensitive to small changes in α, and its reliability is rather limited. A simple and convenient testing method based on rate data (dα/dt) is proposed. The method can be applied to virtually any type of kinetic data obtained under isothermal or nonisothermal conditions.

Kinetics of crystallization processes in AlYNiCo studied by electrical resistivity

Al 90Y 5Ni 1Co 4 amorphous and partially crystalline alloys were investigated by means of differential scanning calorimetry, direct current four probe method and X-ray diffraction. The process of crystallization of particles of the order of 10 nm (nanocrystallization) was induced by decreasing the rate of the quenching process from 54 to 39 rev/s or by annealing amorphous samples. The resistivity versus temperature isochronal relation for both groups of alloys was interpreted assuming diffusion controlled growth and zero nucleation rate. The effect of yttrium on the decrease of the growth rate was assumed to be a transformation mechanism leading to nano-size crystalline phase formation.

The role of X on the properties of FeXBSi metallic glasses

The kinetics of crystallization processes in a series of metallic glasses, Fe 78X 2B 16Si 4, with X as one of the elements of groups IV–VIII in the periodic table, have been studied using differential scanning calorimetry, and the behaviors of the kinetic parameters are described. A novel method of analysis, suggested by the kinetic equations, entails partitioning the total heat of crystallization into separable heats of crystallization of the constituent phases. This technique has been used to show that the various additive elements X may be classified into groups according to the affinity of X for the elements in the parent FeBSi ternary metallic glass.

Crystallization of metal-oxide glasses in Bi-Sr-Ca-Cu-O systems.

A crystallization study has been carried out for rapidly solidified Bi-Sr-Ca-Cu-O glasses with nominal compositions ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{x}}$, ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{3}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{\mathrm{x}}$, and ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{4}$${\mathrm{Cu}}_{5}$${\mathrm{O}}_{\mathrm{x}}$. A temperature-time-transformation diagram for the glass with nominal composition ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{x}}$ has been constructed, within which crystalline superconducting and nonsuperconducting phase regions are identified. Eutectic and primary crystallization have been found to occur during the annealing process in these metal oxides. Glass transition temperature ${T}_{g}$ values, superconducting transition temperature values of crystallized products, and microstructural changes are measured and analyzed by differential thermal analysis, electrical resistivity, and magnetization shielding, x-ray diffraction, and scanning electron microscopy experiments. Also discussed are thermodynamics and kinetics of crystallization processes and the formation of the 110-K superconducting phase.

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.