Appearance Of Crystalline Phase Research Articles

Calcium Phosphate Coating Prepared by Microarc Oxidation Affects hTERT Expression, Molecular Presentation, and Cytokine Secretion in Tumor-Derived Jurkat T Cells.

Calcium phosphate (CaP) materials are among the best bone graft substitutes, but their use in the repair of damaged bone in tumor patients is still unclear. The human Jurkat T lymphoblast leukemia-derived cell line (Jurkat T cells) was exposed in vitro to a titanium (Ti) substrate (10 × 10 × 1 mm3) with a bilateral rough (average roughness index (Ra) = 2–5 μm) CaP coating applied via the microarc oxidation (MAO) technique, and the morphofunctional response of the cells was studied. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscope (EDX) analyses showed voltage-dependent (150–300 V) growth of structural (Ra index, mass, and thickness) and morphological surface and volume elements, a low Ca/PaT ratio (0.3–0.6), and the appearance of crystalline phases of CaHPO4 (monetite) and β-Ca2P2O7 (calcium pyrophosphate). Cell and molecular reactions in 2-day and 14-day cultures differed strongly and correlated with the Ra values. There was significant upregulation of hTERT expression (1.7-fold), IL-17 secretion, the presentation of the activation antigens CD25 (by 2.7%) and CD95 (by 5.15%) on CD4+ cells, and 1.5–2-fold increased cell apoptosis and necrosis after two days of culture. Hyperactivation-dependent death of CD4+ cells triggered by the surface roughness of the CaP coating was proposed. Conversely, a 3.2-fold downregulation in hTERT expression increased the percentages of CD4+ cells and their CD95+ subset (by 15.5% and 22.9%, respectively) and inhibited the secretion of 17 of 27 test cytokines/chemokines without a reduction in Jurkat T cell survival after 14 days of coculture. Thereafter, cell hypoergy and the selection of an hTERT-independent viable CD4+ subset of tumor cells were proposed. The possible role of negative zeta potentials and Ca2+ as effectors of CaP roughness was discussed. The continuous (2–14 days) 1.5–6-fold reductions in the secretion of vascular endothelial growth factor (VEGF) by tumor cells correlated with the Ra values of microarc CaP-coated Ti substrates seems to limit surgical stress-induced metastasis of lymphoid malignancies.

On the Glass Structure of the Bi2O3–SiO2–GeO2 System

Wide- and small-angle X-ray scattering is used to study the structure of the single-phase glass of the Bi2O3–GeO2 system and three-component Bi2O3–GeO2–SiO2 system in three sections with the GeO2/SiO2 molar ratios of 3, 1, and 1/3. The Bi2O3 content is changed from 20 to 50 mol % in the first two sections; and from 10 to 50 mol %, in the third one. Based on the data of wide-angle X-ray scattering, it can be concluded that structural groupings containing BiO3 triangles and SiO2 and GeO4 tetrahedra connected with them are formed in the glass of the studied triple system due to the chemical reactions of Bi2O3, SiO2, and GeO2. When the Bi2O3 content is increased the structural groupings are combined and local areas with three-dimensional structure are formed. As a result, each BiO3 triangle is connected with three tetrahedra, and each tetrahedron is connected with four triangles. It is established that the initial stages of the appearance of crystalline phases during the cooling of the melts are observed in the glass containing not less than 40 mol % of Bi2O3.

Effect of controlled crystallization on polaronic transport in phosphate‐based glass‐ceramics

AbstractThe effect of induced crystallization on changes in electrical transport of two types of glass‐ceramics, pure polaron conductive 40Fe2O3‐60P2O5 (F40) (mol%) and predominantly polaronic 5Li2O‐5ZnO‐40P2O5‐50WO3 (Li‐50W) (mol%) was investigated. F40 glass‐ceramics produced at low heat‐treatment temperatures contain single‐phase Fe3(P2O7)2 whereas at higher temperatures two more phases Fe4(P2O7)3 and Fe(PO3)3 are formed. Structural modifications strongly depend on the crystallization temperature and time. The appearance of crystalline phases studied by Mössbauer spectroscopy exhibits changes in Fe2+/Fetot ratio in crystalline/glassy phases. The detailed analysis of different iron sites allows their correlation with changes in electrical conductivity as crystallization progresses. Depending on the course of crystallization, the contribution of each phase to the overall conductivity is determined by the frequency dependence of Zʺ(ω) and Mʺ(ω). DC conductivity shows a sharp decrease as Fe3(P2O7)2 phase appears and consequently glass matrix remains impoverished in Fe2+‐Fe3+ pairs. In the multiphase systems prepared at higher crystallization temperatures, the overall electrical conductivity increases although the continuous grain boundaries along different crystalline grains play a limiting factor. In contrast, the slight conductivity change in Li‐50W glass‐ceramics upon crystallization is a result of remaining W5+‐W6+ pairs in the residual glassy phase. Independence of electrical transport on Li+ ions confirms predominantly polaronic transport in Li‐50W glass‐ceramics.

Water-Controlled Crystallization of CaCO3, SrCO3, and MnCO3 from Amorphous Precursors

Calcium carbonate is the most abundant biomineral, whose amorphous form is stabilized in nature by a variety of organic additives and water. It is used to manipulate the morphology of new materials and to make strong inorganic/organic hybrid materials. However, the crystallization pathways (e.g., nucleation and growth, two-step nucleation pathways involving disordered, amorphous, or dense liquid states preceding the appearance of crystalline phases) remain often unclear. We have synthesized three amorphous carbonates, CaCO3 (ACC), SrCO3 (ASC), and MnCO3 (AMnC), that do not require any stabilization by additives to study their crystallization kinetics and mechanisms in the presence of water. The evolution of the carbonate concentration during crystallization was monitored potentiometrically with a pH electrode. The crystallization of ASC proceeds extremely fast, whereas the transformation of AMnC is relatively slow. ACC is an intermediate case between these extremes. The kinetic data were interpreted by a ...

Electrical transport in iron phosphate glass-ceramics

In this study, the effect of crystallization on electrical transport in iron phosphate glass with composition 40Fe2O3-60P2O5 (mol%) was investigated. This type of glasses exhibits the electronic conduction which is described by polaronic conduction mechanism. Induced and controlled heat-treatment of 40Fe2O3-60P2O5 glass leads to partially and almost fully crystallized glass-ceramics. The influence of heat-treatment temperature on structural changes, the appearance of crystalline phases, their interactions and influence on electrical transport were studied in details.Depending on heat-treatment temperature various phases, such as Fe3(P2O7)2, Fe4(P2O7)3 and Fe(PO3)3, embedded in glass matrix, were confirmed by powder X-ray diffraction (XRPD) and Raman spectroscopy (RS), whereas thermally induced microstructural changes were evaluated by high-resolution transmission electron microscopy (HR-TEM).Impact of the structural changes on the electrical properties was explored by means of impedance spectroscopy (IS) in wide frequency and temperature range. DC conductivity decreases in the first stage of the crystallization process and achieves its minimum. With further increase of the heat-treatment temperature, the electrical conductivity rises as a result of an enhanced crystallinity. IS results show the evolution of crystallization and formation of crystalline phases in glassy matrix. Correlation between the shape of the spectra and the nature of the electrical transport was confirmed. Different electrical processes have been identified by detail analysis and contribution of each crystalline phase, glass matrix and grain boundaries to total resistance/conductivity is determined by complex impedance plots by means of equivalent circuit modeling.

Near-infrared luminescent barium gallium-germanate glasses and glass-ceramics doped with bismuth

A series of barium gallium-germanate glasses (84-х) GeO2–14BaO–2Ga2O3–x Bi2O3 (х=0; 0,1; 1; 3; 5mol%) was synthesized by crucible technology. It was revealed that the appearance of a BaGe4O9 crystalline phase took place after additional thermal treatment of the glass samples. The structural and optical properties of the glasses and glass-ceramics were studied. It was shown that the spectral shapes and the peak positions of the absorption, luminescence and excitation bands strongly depend on the type of materials. In particular, the absorption band peaked at 480 and 660nm is characteristic for the glass samples whereas in the absorption spectrum of the glass-ceramic two bands at 480nm and 560nm were observed. Moreover, with the appearance of a crystalline phase, the luminescence peak shifts towards shorter wavelengths, while its intensity increases. The possible states of Bi ions in the BaGe4O9 crystalline phase were calculated using a molecular cluster model. The obtained results indicate that an incorporated in the crystalline phase Bi+ ion could be considered as a possible near IR luminescence source.

Tuning crystallization pathways through sequence engineering of biomimetic polymers.

Two-step nucleation pathways in which disordered, amorphous, or dense liquid states precede the appearance of crystalline phases have been reported for a wide range of materials, but the dynamics of such pathways are poorly understood. Moreover, whether these pathways are general features of crystallizing systems or a consequence of system-specific structural details that select for direct versus two-step processes is unknown. Using atomic force microscopy to directly observe crystallization of sequence-defined polymers, we show that crystallization pathways are indeed sequence dependent. When a short hydrophobic region is added to a sequence that directly forms crystalline particles, crystallization instead follows a two-step pathway that begins with the creation of disordered clusters of 10-20 molecules and is characterized by highly non-linear crystallization kinetics in which clusters transform into ordered structures that then enter the growth phase. The results shed new light on non-classical crystallization mechanisms and have implications for the design of self-assembling polymersystems.

Influence of heat treatment on the mechanical properties, corrosion behavior, and biocompatibility of Zr56Al16Co28 bulk metallic glass

This paper reports the influence of heat treatment on the mechanical properties, corrosion behavior and biocompatibility of Zr56Al16Co28 bulk metallic glass (BMG) investigated by dynamic mechanical analysis (DMA), electrochemical analysis in vitro hemocompatibility and in vivo experiments. Zr56Al16Co28 alloys with amorphous, semi-crystalline and fully crystallized microstructures were obtained by thermal treatment of as-cast Zr56Al16Co28 BMG below or above glass transition temperature (Tg). The modulus slightly decreased with increasing temperature below Tg whereas the modulus dramatically increased treated above Tg due to the appearance of crystalline phase. The passivation potential did not change for samples heat-treated below Tg but decreased significantly above Tg, which indicated that Zr56Al16Co28 BMG possessed better corrosion resistance than crystallized Zr56Al16Co28 alloys. Zr56Al16Co28 alloys showed good hemolytic resistance regardless of the microstructural condition and presented lower hemolytic rate than their crystallized counterparts. In vivo test revealed that as-cast Zr56Al16Co28 BMG presented similar biocompatibility to the structurally relaxed BMG and better biocompatibility than the crystallized counterparts. Mice implanted with Zr56Al16Co28 BMGs showed lower degree of inflammatory infiltration response compared to mice implanted with the crystallized counterparts. The results showed that the properties of as-cast Zr56Al16Co28 BMG were generally comparable to its structurally relaxed counterpart and superior to the crystalline samples.

The effect of zirconia polymorphs on the structure and catalytic properties of V 2O 5/ZrO 2 catalysts

The effect of zirconia polymorphs on the activity and selectivity of V 2O 5/ZrO 2 for the alkylation of phenol with methanol has been investigated. Relatively pure monoclinic zirconia (m-ZrO 2) and tetragonal zirconia (t-ZrO 2) were prepared. A series of vanadium oxide supported on m- and t-ZrO 2 with varying vanadium oxide content from 2.5 to 15 wt% were prepared by wet impregnation method. The catalysts were characterized by X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (UV-DRS), temperature-programmed reduction of H 2 (TPR), temperature-programmed desorption (TPD) of NH 3, specific surface area and pore size distribution measurements. The XRD results suggest that highly dispersed or amorphous state of vanadium oxide is present at lower loadings. X-ray diffraction patterns also indicate the presence of crystalline V 2O 5 phase from 7.5 wt% of V 2O 5 on m-ZrO 2 support and there is no indication for the formation of V 2O 5 crystalline phase up to 15 wt% of V 2O 5 on t-ZrO 2 support. The UV–vis diffuse reflectance spectra indicate the existence of isolated and clusterized tetrahedral (Td) V 5+ species at lower loadings in all catalysts. The temperature-programmed reduction of H 2 shows a single reduction peak corresponding to V 5+ to V 3+ in all the samples. TPD of ammonia suggests that surface acid density of m-ZrO 2 phase is found to be more than t-ZrO 2 phase. Acidity of the supported catalysts is increased with increase in V 2O 5 loading up to monolayer formation and decreased with the appearance of crystalline phase of V 2O 5. At monolayer coverage, V 2O 5/m-ZrO 2 is fourfold more active than V 2O 5/t-ZrO 2 for alkylation of phenol at 673 K. Selectively C-alkylated products were formed on all the catalysts. A linear correlation is observed between catalytic activity and surface acidity of catalysts.

EXAFS Study of Annealing Effects on Mg<sub>65</sub>Cu<sub>25</sub>Gd<sub>10</sub> Metallic Glass

The effect of heat treatment on mechanical prosperities of Mg65Cu25Gd10 glass has been studied in this paper. The thermal stability and the structure of as-spun and heat treated Mg65Cu25Gd10 alloys were examined by differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). The compression tests were performed using a computer controlled tensile test machine. Extended X-ray absorption fine structure (EXAFS) was applied to study the structural changes of Mg65Cu25Gd10 glass during annealing. Results showed that the decline of mechanical properties for Mg65Cu25Gd10 glass after annealing was closely related to the changes in local environment of Cu atoms and appearance of crystalline phases, and not the Gd local structure.

Effect of structural evolution and surface morphological changes on the electrochemical response of an FeNbAlMnCuSiB alloy

The electrochemical response of a soft magnetic FeNbAlMnCuSiB alloy was studied through different stages of devitrification. The structural evolution including appearance of a nanocrystalline phase and intermetallics, and accompanying surface topographical changes were studied and correlated to the electrochemical behavior of this alloy. The electrochemical behavior was not directly related to changes in surface roughness but it was very responsive to the structural changes, particularly to the formation of the nanocrystalline phase and to the precipitation of Fe7Nb6 phase. There was a progressive passivation breakdown with the appearance of crystalline phases on annealing.

Hydrogen bonded molecular assemblies in crystals and gels of chiral bis(amino alcohol) oxalamides

The research of supramolecular organisation of organic molecules into nano-or micro-dimensional assemblies is of high relevance for design of new materials for versatile applications and for understanding of the organisation of matter in general. Macroscopic manifestation of self-aggregation can result in ordered gels which include entraped solvent molecules. It is recognised that gelation is based on self � assembly of gelators in solution, leading to supramolecular arrays of specific non-covalent interactions: hydrogen bonds, van der Waals interactions and metal coordination. It is a chalenge to predict gelation on the basis of the constitutional and conformational characteristics of an organic molecule and the properties of the liquid to be gelled. Recently we have shown that chiral bis(amino acid) oxalamides represent a rare group of gelators capable to gel water and various lipophilic organic solvents (Makarevic et al., Chem. Eur. J. 2001, 7, 3328), whereas our new results are related to chiral bis(leucinol)oxalamides exhibiting gelating properties. The crystal structures of both, SS- and rac-bis(leucinol)oxalamide reveal two-dimensional hydrogen bonded networks through oxalamide and alcohol functionalities. X-ray powder diffraction was used to identify an appearance of crystalline phases in gels and xerogels of enantiomeric and racemic samples. In all cases the monoclinic crystalline phase identical to the crystals of SS-enantiomer was found. The high gelating properties of racemic compound might be related by van der Waals interactions between enantiomeric fibres of oposite chirality, whereas molecular organisation in fibres is governed by hydrogen bonds.

Effect of the heat treatment on the morphology and sorption ability to metal ions of metallurgical slag

The effect of the phase composition of metallurgical slag on its ability to adsorb copper ions from aqueous solutions has been investigated. Granulated slag samples, mainly amorphous, have been pre-heated at 400, 600, 800 and 1000°C, then cooled slowly in the absence of moisture. Above 600°C crystallisation of a mineral gehlenite of the melilite group and of calcium silicates of the Ca2SiO4 structure type begins. The appearance of crystalline phases facilitates exchange and adsorption and the amount of copper adsorbed per a gram slag increasing about 2–4 times. The important role of the crystalline phases in the slag permits the synthesis of new materials adsorbing heavy metal ions on the basis of controlled liquid slag crystallization.

The Role of Impurities in the Crystallization of Ball-Milled Amorphous Alloys

Melt spun amorphous Fe 83 B 17 ribbons were pulverized in a planetary ball mill. Two parallel sets of experiment were made, where the material of the vial made the only difference in the experimental conditions. In the first kind of experiments tungsten carbide balls and vials were used, while in the second series the tungsten carbide balls were put in chrome steel vials. This way the effect of impurities on the mechanically induced crystallization could be studied and distinguished from other possible effects. Changes of the amorphous phase and the appearance of crystalline phases were followed by Mossbauer spectroscopy and DSC measurements. The results indicate that contamination from the milling tools causes a shift of the chemical composition of the milled amorphous material. In the case of steel milling tools the appearance of bcc nuclei initiate crystallization during milling. Instead of this bcc structure, a modified amorphous phase with a broader hyperfine field distribution - attributed to the significant amount of dissolved tungsten-- is observed when the amorphous alloy is milled with tungsten carbide balls and vials.. The differences detected under experimental conditions where only the material of the vial was different confirm that the specific impurities introduced in the milling process play a decisive role in the crystallization of amorphous alloys under ball-milling conditions.