Primary Crystallization Products Research Articles

Exploring Carbamazepine Polymorph Crystal Growth in Water by Enhanced Sampling Simulations.

In this work, the polymorphism of the active pharmaceutical ingredient carbamazepine (CBZ) was investigated by using molecular dynamics simulations with an enhanced sampling scheme. A single molecule of CBZ attaching to flat surfaces of different polymorphs was used as a model for secondary nucleation in water. A novel approach was developed to compute the free energy profile characterizing the adsorption of molecules with orientation aligned with the crystal structure of the surface. The distribution of states that showed alignment was used to rescale the adsorption free energy to include only the contribution that is consistent with crystal growth. The resulting free energy surfaces showed favorable thermodynamics for the most stable form, Form III and the second most stable form, Form I. The primary crystallization product, a dihydrate, was found to be less favorable, implying a nonclassical crystallization pathway. We suggest that a major contribution determining the energetics is the hydrophobicity of the surface. This thermodynamic ranking provides valuable information about the molecular pathways of polymorph growth and will further contribute to the understanding of the crystallization process of CBZ, which is imperative since polymorph formation can alter the physical properties of a drug significantly.

BATCH COMPOSITION INFLUENCE ON SINTERING AND CRYSTALLIZATION PROCESSES OF CORDIERITE GLASSES OBTAINED BY THERMAL PLASMA MELTING

This article focuses on the production of glasses and glass-ceramic materials with a cordierite (2MgO∙2Al2O3∙5SiO2) composition. The processes of crystallization and sintering of cordierite glasses, which are based on natural raw materials, pure oxides and pre-synthesized cordierite, have been investigated. It has been determined that cordierite glasses produced via plasma melting exhibit high structural defects attributed to rapid heating and cooling rates. The relaxation of microstresses in the glasses takes place within the temperature range of 480 – 490 °C. Glasses based on synthesized cordierite exhibit a crystallization temperature of 930 – 1020 °C, depending on the presence and type of nucleating agents. This is approximately 20 – 50 °C lower compared to glasses based on component mixtures. The primary crystallization product of studied glasses at 900 °C is the high-quartz solid solution with formula MgO∙Al2O3∙3SiO2, which is dissociate above 1000 °C with the formation of cordierite. The addition of 5% ZrO2 to the batch increases the viscosity of softened glasses and their crystallization temperature, resulting in increased activity of glass powders in the sintering processes due to the higher impact of liquid-phase sintering on the general densification process of glass-ceramics. This allows for the production of glass-ceramics with open porosity of 2 – 4% at 1300 – 1350 °C. The addition of 5% TiO2 to the batch reduces the glass crystallization temperature. However it does not significantly effect on the cordierite glass-ceramics sintering processes. For citation: Sharafeev S.M., Shekhovtsov V.V., Zvyagina E.E. Batch composition influence on sintering and crystallization processes of cordierite glasses obtained by thermal plasma melting. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 7. P. 80-87. DOI: 10.6060/ivkkt.20246707.7032.

Genesis of megaspherulites in El Viejo Rhyolitic Coulee (Pleistocene), Southern Puna, Argentina

Crystalline domains in rhyolitic domes and coulees are commonly characterized by spherulites and lithophysae. Spherulites typically range from microscopic to a few centimeters in diameter. Larger spherulites, termed “megaspherulites,” are rare but have been reported in the USA and Mexico. The uncommon nature of such structures supports the need for a study to explore the factors and special conditions that allow them to reach such a large size. In the Southern Puna of Argentina, El Viejo Coulee includes megaspherulites up to 4 m in diameter. We present observations from field work, petrography, scanning electron microscopy, bulk geochemistry, and Fourier transform infrared spectroscopy. The megaspherulites occur in obsidian lenses that differ in phenocryst content and composition from the foliated coherent facies that forms the rest of the coulee. The obsidian lacks vesicles and microlites and is unaltered. The megaspherulites comprise growth cones consisting of micropoikilitic texture where quartz encloses potassium feldspar. The growth cones are separated by interconal areas composed of lithophysae. We propose that the megaspherulites were formed above the glass transition temperature (Tg) and are the product of primary crystallization of rhyolitic melt. The exceptionally large size of the megaspherulites implies high diffusion rates which are favored by temperatures above Tg during crystallization. The large size also suggests scarcity of nucleation sites, which is consistent with the megaspherulites being hosted by unaltered microlite- and vesicle-free glass. The position of the obsidian lens at the base of the coulee may have played a critical role in maintaining the temperature above the Tg long enough to allow the crystallization of the megaspherulites. These conditions also favored crystallization in the most advanced stage where micropoikilitic texture replaced the fans of crystal fibers typical of spherulites. Crystallization of anhydrous quartz and feldspar in the growth cones led to the concentration of volatiles in the melt in the interconal areas, resulting in volatile exsolution and formation of vesicles that became nucleation sites for lithophysae. The study advances our understanding of some of the special processes that are involved in the cooling and solidification of rhyolitic magmas. Fundamentally, we find that the position of the obsidian at the base of the coulee was critically important because this position favored maintenance of the temperature above the Tg which, in turn, favored high diffusion rates. Also, the scarcity of nucleation sites in the obsidian melt allowed only a small number of spherulites to nucleate; those that nucleated therefore grew very large. The meter-scale megaspherulites may have taken ~ 55 years to create.

Influencing the crystallization of Fe80Nb10B10 metallic glass by ball milling

Melt-spun amorphous Fe80Nb10B10 ribbons were subjected to ball milling for different periods. The results show that ball milling not only induces the formation of nano-crystalline α-Fe during milling, but also drastically changes the crystallization behavior of the residual amorphous phase. In contrast to the as-spun ribbon, which crystallizes during heating through the formation of the metastable Nb5Fe33B10 phase and subsequent decomposition into stable α-Fe and a small fraction of Fe2B and NbFeB, ball milling progressively suppresses the formation of Nb5Fe33B10 as primary crystallization product and promotes the formation of α-Fe at low temperatures. The ball-milled nano-crystalline/amorphous powders have a saturation magnetization 2.5–3 times higher than the as-quenched amorphous ribbon along with Curie temperature increase by about 70 K with respect to the parent as-spun material. The structure and related magnetic properties of the milled material do not significantly change in the bulk samples synthesized by powder consolidation at temperatures up to ∼900 K, which indicates that the stable nature of α-Fe makes this nano-crystalline/amorphous composite material potentially suitable for a wide range of high temperature applications.

Glass-Forming Ability and Early Crystallization Kinetics of Novel Cu-Zr-Al-Co Bulk Metallic Glasses

In recent years, CuZr-based bulk metallic glass (BMG) composites ductilized by a shape memory B2 CuZr phase have attracted great attention owing to their outstanding mechanical properties. However, the B2 CuZr phase for most CuZr-based glass-forming compositions is only stable at very high temperatures, leading to the uncontrollable formation of B2 crystals during quenching. In this work, by introducing Co (i.e., 4, 5, and 6 at. %) and 10 at. % Al into CuZr-based alloys, the relatively good glass-forming ability (GFA) of CuZr-based alloys still can be achieved. Meanwhile, the B2 phase can be successfully stabilized to lower temperatures than the final temperatures of crystallization upon heating CuZr-based BMGs. Unlike previous reported CuZr-based BMGs, the primary crystallization products upon heating are mainly B2 CuZr crystals but not CuZr2 and Cu10Zr7 crystals. Furthermore, the primary precipitates during solidification are still dominated by B2 crystals, whose percolation threshold is detected to lie between 10 ± 2 vol. % and 31 ± 2 vol. %. The crystallization kinetics underlying the precipitation of B2 crystals was also investigated. Our results show that the present glass-forming composites are promising candidates for the fabrication of ductile CuZr-based BMG composites.

The isokinetic behavior in diffusion controlled growth processes

The isokinetic behaviour of crystallization processes controlled by diffusion is analysed under both isothermal and continuous cooling/heating conditions. The kinetic function is computed employing an approximate expression for the so called exponential integral. Diffusion controlled 3D growth of homogeneously nucleating crystalline grains is an isokinetic reaction if the nucleation and diffusion activation energies are identical. In the non isokinetic range, the kinetic functions in both continuous heating and isothermal transformations are the same except for a factor which depends on the nucleation and diffusion activation energies ratio. This development is applied to the crystallization of AgGeSe glasses. The primary crystallization kinetic of glasses with compositions (Ge25Se75)100−y Agy (with y = 10, 15, 20 and 25 at. %) was studied in a previous work using differential scanning calorimetry and X-ray diffraction. The analysis is grounded on the Kolmogorov-Johnson-Mehl-Avrami model generalized to account for the compositional changes of the parent phase, responsible for the decreasing of both the nucleation frequency and the growth rate of the primary grains. The kinetic study of the crystallization process from continuous heating calorimetric data has been performed applying the master curve method. The primary crystallization product is the ternary phase γ-Ag8GeSe6. The values of apparent activation energy Ea, obtained are in the range: 2.0 eV/at < Ea < 2.6 eV/at. A model of diffusion controlled 3D growth with decreasing homogeneous nucleation and soft impingement has been developed that reproduces the rate of transformation obtained experimentally for the studied alloys.

Sm–Nd systematics of lunar ferroan anorthositic suite rocks: Constraints on lunar crust formation

We have measured Sm–Nd systematics, including the short-lived 146Sm–142Nd chronometer, in lunar ferroan anorthositic suite (FAS) whole rocks (15415, 62236, 62255, 65315, 60025). At least some members of the suite are thought to be primary crystallization products formed by plagioclase flotation during crystallization of the lunar magma ocean (LMO). Most of these samples, except 62236, have not been exposed to galactic cosmic rays for a long period and thus require minimal correction to their 142Nd isotope composition. These samples all have measured deficits in 142Nd relative to the JNdi-1 terrestrial standard in the range −45 to −21ppm. The range is −45 to −15ppm once the 62236 142Nd/144Nd ratio is corrected from neutron-capture effects. Analyzed FAS samples do not define a single isochron in either 146Sm–142Nd or 147Sm–143Nd systematics, suggesting that they either do not have the same crystallization age, come from different sources, or have suffered isotopic disturbance. Because the age is not known for some samples, we explore the implications of their initial isotopic compositions for crystallization ages in the first 400Ma of solar system history, a timing interval that covers all the ages determined for the ferroan anorthositic suite whole rocks as well as different estimates for the crystallization of the LMO. 62255 has the largest deficit in initial 142Nd and does not appear to have followed the same differentiation path as the other FAS samples. The large deficit in 142Nd of FAN 62255 may suggest a crystallization age around 60–125Ma after the beginning of solar system accretion. This result provides essential information about the age of the giant impact forming the Moon. The initial Nd isotopic compositions of FAS samples can be matched either with a bulk-Moon with chondritic Sm/Nd ratio but enstatite-chondrite-like initial 142Nd/144Nd (e.g. 10ppm below modern terrestrial), or a bulk-Moon with superchondritic Sm/Nd ratio and initial 142Nd/144Nd similar to ordinary chondrites.

Ductile Co–Nb–B bulk metallic glass with ultrahigh strength

A ternary Co61Nb8B31 bulk metallic glass with plasticity of 5% and yield strength of 5200MPa was fabricated. It is shown that the primary crystallization product of the Co61Nb8B31 glass is the vertex- and edge-sharing Co2Nb type phase. The enhanced plastic strain is consistent with the observed multiple shear bands that can redistribute the internal shear stress. The appreciable plastic strain favors the formation of metallic bonding network-like structure and holds high Poisson's ratio.

Glass forming ability, thermal stability, crystallization and magnetic properties of [(Fe,Co,Ni)0.75Si0.05B0.20]95Nb4Zr1 metallic glasses

The variation in the glass forming ability, thermal stability, crystallization and magnetic properties of [(Fe60Co40−xNix)0.75Si0.05B0.20]95Nb4Zr1 metallic glasses with x=0 and 10at.% has been studied. The addition of Ni enhances the extension of the supercooled liquid region. Different criteria for the prediction of glass forming ability have been used leading to different conclusions due to the different parameter's dependence. However, it was experimentally observed that upon copper mold casting the Ni-free master alloy allows preparation of fully amorphous rods with the largest diameter. The structural evolution upon crystallization has been monitored using X-ray diffraction and Mössbauer spectroscopy. The results show the precipitation of the metastable Fe23B6-type phase as the primary crystallization product. The kinetic analysis using the Master Curve method leads to a value of the activation energy Ea=494kJ/mol and indicates a homogeneous nucleation and diffusion-controlled growth transformation. Further heating shows the formation of different Fe environments that give rise to stable phases in the fully crystalline samples. The magnetic properties as Curie temperature and saturation polarization are affected by the partial substitution of Ni but no significant effect was observed on the coercivity values.

Effects of quasicrystal formation on the crystallization of (Ti36.1Zr33.2Ni5.8Be24.9)100−xCux (x = 5, 7, 9, 11, 13, 15, 17) metallic glasses

The crystallization behaviors of the (Ti36.1Zr33.2Ni5.8Be24.9)100−xCux (x = 5, 7, 9, 11, 13, 15, 17; at. %) metallic glasses are investigated under both the continuous heating and isothermal conditions by the differential scanning calorimetry. Quasicrystals are found in the crystallization products under both conditions by X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy. The evolution of the primary crystallization products of these alloys is discussed in detail. The effects of the increasing distortion energy of the icosahedral short-range order with the increasing Cu content in the(Ti36.1Zr33.2Ni5.8Be24.9)100−xCux (x = 5, 7, 9, 11, 13, 15, 17) alloys are found to be responsible for the evolution of the crystallization products. The isothermal crystallization kinetics deviates from the Johnson-Mehl-Avrami-Kolmogoroff (JMAK) model. A modified JMAK model with an impingement parameter is found to be suitable for the isothermal crystallization kinetics of the current alloys. The effects of quasicrystal formation on the crystallization kinetics are disscussed in detail. And it is found that the isothermal crystallization kinetics are influenced by both of the “soft impingement” effect and the formation of the quasicrystals.

Chromite symplectites in Mg-suite troctolite 76535 as evidence for infiltration metasomatism of a lunar layered intrusion

Despite the very low chromium concentrations in its cumulus olivine (∼140ppm), lunar troctolite 76535 contains large amounts of Cr sporadically, but highly concentrated, in symplectite assemblages consisting of Mg–Al-chromite and two pyroxenes. Previously proposed symplectite formation mechanisms include crystallization of trapped interstitial melt, diffusion of Cr from cumulus olivine, and/or remobilization of cumulus chromite grains. These mechanisms would imply that the highly Cr-depleted nature of Mg-suite parental magmas and their source materials inferred from cumulus olivine may be illusory. We have conducted a detailed petrologic and textural study of symplectites, as well as chromite veins, intercumulus assemblages, olivine-hosted melt inclusions and clinopyroxene-troilite veins in 76535 with the goals of constraining the origin of the symplectites, and the degree of Cr-depletion in Mg-suite magmas relative to other lunar basalts. Orthopyroxene and clinopyroxene in melt inclusions are depleted in Cr relative to their symplectite counterparts, averaging 900 and 1200ppm vs. 7400 and 8100ppm Cr2O3, respectively. Olivine in contact with symplectite assemblages may exhibit a diffusion profile of Cr going into olivine, whereas olivine boundaries away from symplectites show no diffusion profile. There is also a distinct lack of primary chromite as inclusions in cumulus phases and melt inclusions. Multiple textural observations, melt inclusion chemistry, and modeling of chromite–olivine equilibrium rule out previously proposed symplectite formation mechanisms, and strongly suggest that chromite was not a primary crystallization product of the 76535 parental magma. Accordingly, the post-cumulus addition of Cr and Fe is required to produce the symplectites. After considering multiple models, the addition of Cr and Fe to 76535 via infiltration metasomatism by an exogenous chromite-saturated melt is the model most consistent with multiple textural and geochemical observations. Failure of models that call upon Cr diffusion out of olivine grains imply that the observed Cr-depleted nature of olivine observed in many Mg-suite lithologies is a primary feature of the Cr-depleted nature of the Mg-suite parental magmas and their source materials. This substantial depletion of Cr in the magma relative to mare basalt magmas still requires a satisfactory explanation in order to be consistent with Mg-suite petrogenetic models and currently accepted bulk-Moon compositions. Additionally, if the intimate interaction of migrating melts with early lunar crustal lithologies was a widespread phenomenon after LMO solidification, it provides another mechanism by which to reset or delay closure of radiogenic isotopic systems and explain the Mg-suite-ferroan anorthosite age overlap.

High temperature x ray diffraction determination of the body-centered-cubic–face-centered-cubic transformation temperature in (Fe70Ni30)88Zr7B4Cu1 nanocomposites

In situ high-temperature x ray diffraction and magnetization measurements were performed on a melt-spun (Fe70Ni30)88Zr7B4Cu1 amorphous alloy to follow its structural evolution. At 728 K, a bcc-FeNi phase was observed as the primary crystallization product followed by transformation to an fcc phase ∼773 K. During cooling to room temperature, the fcc-to-bcc transformation was not observed, and the metastable fcc-NiFe phase was retained at room temperature.

Correlation between supercooled liquid region and crystallization behavior with alloy composition of La-Al-Cu metallic glasses

Bulk metallic glasses (BMGs) with large supercooled liquid region are promising materials for superplastic forming. In this paper, we demonstrate a microstructure-based strategy to pinpoint the composition with the largest supercooled liquid region in La86−xAl14Cux (x=16 at%–20 at%) metallic glass system. By monitoring the changes in crystallization behavior of the glassy alloys with composition to search for the alloys exhibiting eutectic crystallization, the glassy alloys with the largest supercooled liquid region in the given alloy system can be found. The metallic glasses with Cu contents of 16 at%–19 at% exhibited two crystallization peaks, and the primary crystallization product was identified to be α-La by means of DSC, XRD and TEM. The increase in Cu content resulted in the decay of the primary crystallization peak and the increase in onset temperature of crystallization, leading to the enlargement of supercooled liquid region. By further suppressing the α-La primary crystallization with increasing Cu content up to 20 at%, the eutectic crystallization of α-La and LaCu13 through one crystallization reaction occurred upon heating, where the largest supercooled liquid region of 65 K for La66Al14Cu20 glassy alloy was located. This study indicats that, in a given glassy alloy system, a larger supercooled liquid region can be achieved by optimizing the alloy compositions to suppress the primary crystallization.

Solidification behavior, glass forming ability and thermal characteristics of soft magnetic Fe–Co–B–Si–Nb–Cu bulk amorphous alloys

The effect of varying Cu content on the bulk glass forming ability (GFA) of (Fe 0.36Co 0.36B 0.192Si 0.048Nb 0.04) 100−XCu X alloys ( X = 0, 0.5, 0.75 and 1.0) is revealed by investigating the thermal behaviors and phase competitions upon solidification. The changes in GFA are interpreted in terms of suppression of consecutive solidification reactions via microstructural and thermal features. Instead of the type of the primary crystallization product originating from the prevalent atomic order in the glass or supercooled liquid, precipitation of faceted binary and higher-order pro-eutectic compounds such as (Fe,Co) 2B and (Fe,Co)NbB from the alloy melt and resulting skewed eutectic coupled zone are correlated with the observed GFA. With the employed centrifugal casting method, the (Fe 0.36Co 0.36B 0.192Si 0.048Nb 0.04) 99.25Cu 0.75 alloy shows the largest critical thickness of 3 mm and the best soft magnetic properties such as 1.58 T saturation magnetization intensity and 11.7 A/m coercivity after annealing.

Ab initiotheoretical study of magnetization and phase stability of the(Fe,Co,Ni)23B6and(Fe,Co,Ni)23Zr6structures ofCr23C6andMn23Th6prototypes

We present an ab initio theoretical investigation of the magnetization and phase stability of two different complex cubic structures of prototype Cr23C6 and Mn23Th6, with an emphasis on the Fe,Co,Ni23B6 and Fe,Co,Ni23Zr6 compositions. These phases have recently been observed as secondary or even primary crystallization products of Fe,Co,Ni-Zr-B and related metallic glasses that have been studied for applications as soft magnets with nanocrystalline grain size. We first demonstrate the validity of the theoretical technique employed through a detailed comparison between the predictions of the calculations for the Co-Zr binary system and the experimentally stable phases. We then investigate the magnetization and stability of the binary phases. While the Fe-based binary Fe23Zr6 and Fe23B6 phases are expected to have the highest magnetization, the Co-based binary Co23Zr6 and Co23B6 structures are predicted to be the most stable of each prototype. The Co23Zr6 structure is the only binary 23:6 structure predicted to be a stable phase for the Fe,Co,Ni23B6 and Fe,Co,Ni23Zr6 systems investigated here. Small additions of Zr atoms to the Fe,Co,Ni23B6 phases tend to substitutionally occupy the 8c Wykoff site and stabilize these structures. In contrast, small additions of B to the Fe,Co,Ni23Zr6 phases have a much weaker site preference and tend to destabilize these structures. As a result, Fe,Co,Ni23B6 structures are stabilized in Fe,Co,Ni-Zr-B systems relative to the binary Fe,Co,Ni23B6 systems while the Fe,Co,Ni23Zr6 phases are not. The results presented in this work are in good qualitative agreement with experimental observations of the compositional modifications tending to promote formation of the 23:6 phases in Fe-Co-Zr-B and related metallic glasses.

Geochronology of zircon megacrysts from nepheline-bearing gneisses as constraints on tectonic setting: implications for resetting of the U-Pb and Lu-Hf isotopic systems

Nepheline-bearing gneisses from the 75 km2 Tambani body in the Mozambique Belt of southern Malawi, are miaskitic biotite-nepheline monzodiorites, reflecting an absence of K-feldspar, alkali amphiboles or pyroxenes, and contain euhedral zircon megacrysts up to 5 cm across. The zircons contain U = 1–1,860 ppm, Th = 0–2,170 ppm and Y = 400–1,100 ppm, and very low concentrations of all other measured trace elements except Hf (HfO2 = 0.53–0.92 wt. %). Cathodoluminescence images reveal oscillatory sector growth zoning and no evidence for xenocrystic cores, indicating that the zircons represent primary magmatic crystallization products that have survived amphibolite grade metamorphism. U-Pb isotopic analyses (by TIMS) yield an upper intercept age of 730 ± 4 Ma (MSWD = 1.7), which we interpret as the time of magmatic crystallization of the zircons. This is coincident with 11 SHRIMP spot analyses, which yield a mean age of 729 ± 7 Ma (MSWD = 0.37). Metamorphism, at 522 ± 17 Ma as suggested by monazite, caused partial Pb-loss during local recrystallization of zircon. Lu-Hf isotopic data for three whole-rock samples of nepheline-bearing gneiss are collinear with those for zircon megacrysts, and correspond to an age of 584 ± 17 Ma (MSWD = 0.37. We interpret the Lu-Hf array to represent a mixing line defined by the Hf isotopic signature of primary zircon and that of the rock-forming minerals reset during metamorphic (re-)crystallization; hence the 584 Ma age is likely geologically meaningless. Given the well-defined association of nepheline syenites (and phonolitic volcanic equivalents) with continental rifting, we suggest that the Tambani body represents a magmatic product formed at 730 Ma during the break-up of the Rodinia supercontinent. The 522 Ma age is akin to other Pan-African metamorphic ages that record collisional suturing events during the final assembly of Gondwana. Zircon-bearing nepheline gneisses thus preserve a record of intra-continental rifting and of continental collision in southern Malawi.

Mixed oxides obtained from Co and Mn containing layered double hydroxides: Preparation, characterization, and catalytic properties

Co–Mn–Al layered double hydroxides (LDHs) with various Co:Mn:Al molar ratios (4:2:0, 4:1.5:0.5, 4:1:1, 4:0.5:1.5, and 4:0:2) were prepared and characterized. Magnesium containing LDHs Co–Mg–Mn (2:2:2), Co–Mg–Mn–Al (2:2:1:1), and Co–Mg–Al (2:2:2) were also studied. Thermal decomposition of prepared LDHs and formation of related mixed oxides were studied using high-temperature X-ray powder diffraction and thermal analysis. The thermal decomposition of Mg-free LDHs starts by their partial dehydration accompanied by shrinkage of the lattice parameter c from ca. 0.76 to 0.66 nm. The dehydration temperature of the Co–Mn–Al LDHs decreases with increasing Mn content from 180 °C in Co–Al sample to 120 °C in sample with Co:Mn:Al molar ratio of 4:1.5:0.5. A subsequent step is a complete decomposition of the layered structure to nanocrystalline spinel, the complete dehydration, and finally decarbonation of the mixed oxide phase. Spinel-type oxides were the primary crystallization products. Mg-containing primary spinels had practically empty tetrahedral cationic sites. A dramatic increase of the spinel cell size upon heating and analysis by Raman spectroscopy revealed a segregation of Co-rich spinel in Co–Mn and Co–Mn–Al specimens. In calcination products obtained at 500 °C, the spinel mean coherence length was 5–10 nm, and the total content of the X-ray diffraction crystalline portion was 50–90%. These calcination products were tested as catalysts in the total oxidation of ethanol and decomposition of N 2O. The catalytic activity in ethanol combustion was enhanced by increasing (Co+Mn) content while an optimum content of reducible components was necessary for high activity in N 2O decomposition, where the highest conversions were found for calcined Co–Mn–Al sample with Co:Mn:Al molar ratio of 4:1:1.

Magmatic processes and mixing origin of andesite: Miocene Karama?ara volcanics, Central Anatolia, Turkey

The Miocene Karamağara volcanics (KMV) crop out in the Saraykent region (Yozgat) of Central Anatolia. The KMV include four principal magmatic components based on their petrography and compositional features: basaltic andesites (KMB); enclaves (KME); andesites (KMA); and dacites (KMD). Rounded and ellipsoidal enclaves occur in the andesites, ranging in diameter from a few millimetres to ten centimetres. A non-cognate origin for the enclaves is suggested due to their mineralogical dissimilarity to the enclosing andesites. The enclaves range in composition from basaltic andesite to andesite. Major and trace element data and primitive mantle-normalized rare-earth element (REE) patterns of the KMV exhibit the effects of fractional crystallization on the evolution of the KME which are the product of mantle-derived magma. The KMA contain a wide variety of phenocrysts, including plagioclase, clinopyroxene, orthopyroxene, hornblende and opaque minerals. Comparison of textures indicates that many of the hornblende phenocrysts within the KMA were derived from basaltic andesites (KMB) and are not primary crystallization products of the KMA. Evidence of disequilibrium in the hybrid andesite includes the presence of reacted hornblendes, clinopyroxene mantled by orthopyroxene and vice versa, and sieve-texture and inclusion zones within plagioclase. The KMV exhibit a complex history, including fractional crystallization, magma mixing and mingling processes between mantle and crust-derived melts. Textural and geochemical characteristics of the enclaves and their hosts require that mantle-derived basic magma intruded the deep continental crust followed by fractional crystallization and generation of silicic melts from the continental material. Hybridization between basic and silicic melts subsequently occurred in a shallow magma chamber. Modelling of major element geochemistry suggests that the hybrid andesite represents a 62:38 mix of dacite and basaltic andesite. The implication of this process is that calc-alkaline intermediate volcanic rocks in the Saraykent region represent hybrids resulting from mixing between basic magma derived from the mantle and silicic magma derived from the continental crust. Copyright © 2005 John Wiley & Sons, Ltd.

Mössbauer Spectroscopy in Study of Thermally Induced Crystallization of Amorphous Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Nanoparticles

Fe Mossbauer spectroscopy is demonstrated as an effective tool in the identification, magnetic and structural characterization of iron(III) oxides formed by thermally induced oxidative decomposition of FeC 2O4·2H 2O and by the secondary crystallization of amorphous Fe 2O3 nanopowder. AFM measurements revealed that the primary amorphous nanoparticles are between 1 and 3 nm, in accordance with the large surface area of 250 m 2 /g as determined by BET analysis. The temperature depended Mossbauer measurements of amorphous Fe 2O3 showed the magnetic transition temperature lower than 70 K with the sharp evolution of the spectral lines between 53 and 76 K as typical for ultrafine and strongly interacted particles. As the primary crystallization product at low temperatures, γ-Fe 2O3 (maghemite) was identified by XRD. The broad distribution of magnetic fields in Mossbauer spectra illustrates the broad size distribution of maghemite nanoparticles. The thermally stable α-Fe 2O3 (hematite) can be produced by the direct crystallization of amorphous phase at higher temperatures or by the structural transformation of the primarily formed maghemite at lower temperatures. Particles of hematite formed at 200 °C reveal the Morin transition temperature suppressed below 20 K corresponding to the size about 20 nm.

Nanocrystalline microstructures in Fe93-xZr7Bx alloys

The crystallization behaviour of amorphous Fe93 − x Zr7B x (x = 3, 6, 12 at.%) alloys, the microstructures of the primary crystallization products of stable and metastable phases and the subsequent transformations, have been studied using a combination of differential scanning calorimetry, differential thermal analysis, X-ray diffraction and transmission electron microscopy, including microdiffraction. It has been found that, for x = 3 and 6 at.%, the sole product of primary crystallization is the bcc α-Fe phase and the average grain sizes of the crystalline phase were 14 nm and 12 nm for the two alloys, respectively. However, when x = 12 at.%, primary crystallization results in more than one crystalline phase, and a metastable phase with the cubic “Fe12Si2ZrB” structure is the major crystallization product after the primary crystallization reaction, accompanied by the α-Fe phase. The average grain size of this metastable phase was 35 nm for the alloy heated to 883 K at 20 K/min. Isothermal heat treatments at 873 K and 973 K confirm that after being heated for 240 h, this metastable phase transforms into equilibrium phases: bcc α-Fe, hcp ZrB2 and probably hcp Fe2Zr. The apparent activation energies for the primary crystallization reaction during continuous heating for these three alloys are 4.4 ± 0.2 eV, 3.5 ± 0.2 eV and 6.9 ± 0.3 eV, respectively.