Big Crystals Research Articles

THE SOLIDIFICATION MICROSTRUCTURE OF BIOMEDICAL TITANIUM ALLOYS UNDER THE CENTRIFUGAL FORCE

Two biomedical alloys, Ti -39 Nb -5.1 Ta -7.1 Zr ( TNTZ1 ) and Ti -35.3 Nb -5.1 Ta -7.1 Zr ( TNTZ2 ) were melted using LZ5 type centrifugal equipment for casting titanium. The solidification microstructures of TNTZ1 and TNTZ2 alloys cast in graphite crucible without centrifugal force are mostly big arborescent crystal with dispersed porosity in it. After pouring into a graphite mould under centrifugal force, the lower part of ingot showed mostly arborescent crystals with few equiaxed crystals, while the upper part of ingot is basically spherical equiaxed crystals. The solidification defects, such as dispersed pores were very difficult to find. Nb is supposed to refine the arborescent crystals. X-ray diffraction (XRD) analysis showed Ti -phase and Nb -phase existing in the above two alloys. The content of Ti was found relatively low in crystal interior and relatively high in crystal boundary. The content of Nb/Zr was uniform in whole microstructure.

Growth of big single crystals of Sr2YRu1-xCuxO6 from high temperature solutions

Single crystals of Sr2YRu1-xCuxO6 (x = 0 - 0.4) have been grown from PbO-PbF2 based solutions in the temperature range 1150 – 1350°C. A silicon carbide heating element furnace (with a recrystallized alumina tube lining) in a vertical configuration was used to grow the crystals in platinum crucibles. Conditions for the stable growth of big crystals have been investigated. The morphology of the crystals containing Cu was found to change from octahedral to cube octahedral as the growth temperature is increased from 1150 to 1350°C. Crystals measuring up to 4.5 mm across and 2.5 mm thick have been grown from 1250°C. The incorporation of Cu into the crystals was ascertained by EDS and x-ray diffraction analysis. A diamagnetic transition which increased in magnitude and temperature with x was observed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Why are clay minerals small?

The most abundant silicates formed under the Earth’s ‘normal’ surface conditions, i.e. clay minerals, are always of small grain size. Under the same conditions, other mineral species such as carbonates, sulphates and oxides may form much bigger crystals. The reason why phyllosilicates formed in soils or in weathered rocks are always of small grain size is not related to the low-temperature-pressure conditions but rather to particular aspects of their crystal structure. Many recently published works describe the order-disorder cation distribution in the tetrahedral and octahedral sheets and the crystal defects in the layer stacks. Related to the Periodic Bond Chains (PBCs) theory, these data suggest that the size and the shape of clay crystallites could depend on the amount of crystal defects in the three axes of symmetry [100], [110] and [110]. The accumulation of crystal defects poisons the crystal growth along one, two or three PBCs. Then, nucleation becomes less energy-consuming than crystal growth and favours the formation of numerous smaller crystals rather than fewer bigger ones.

Organic-inorganic interaction and the growth mechanism of hydroxyapatite crystals in gelatin matrices between 37 and 80 °C

The crystal development of hydroxyapatite[HAp] phase in gelatin[GEL] matrices was investigated in the temperature range 37 to 80 degrees C by using X-ray diffraction, scanning electron microscopy(SEM), thermoanalytical measurement(DT/TGA), Fourier-Transformed Infra-Red(FT-IR) spectroscopy, and transmission electron microscopy(TEM) with electron diffraction(ED). It was found that during the coprecipitation of apatite phase in GEL matrices and the next aging process the crystallites were formed and developed through the two reaction mechanisms of organic-inorganic interaction between apatite phase and GEL molecules, and thermodynamic reaction for the crystal growing. The analytical evidences showed that there was a definite competition between these two mechanisms with the reaction temperature. Below 50 degrees C the crystal development of HAp was greatly suppressed by the existence of the GEL molecules, indicating the heterogeneous nucleation by the supposed number of carboxyl groups in GEL. Above 50 degrees C the effective organic components as a template for the heterogeneous nucleation of apatite crystallites were greatly degraded and so more amount of inorganic ions could be favorably accredited on the preexisting crystallites in virtue of the limited nucleation chance, finally resulting in the crystal growth. At higher temperature pretty big HAp crystals were developed with the depletion of the organics to be bound with crystallites in the slurry solution. Presumably it is believed that the poisoning of the functional groups in GEL molecules was vigorously occurred in the phosphoric acid environment above approximately 50 degrees C.

Effect of Cu on the magnetism of Zn1－xFexO DMS

Diluted magnetic semiconductor Zn1-xFexO and Zn1-xFexO:Cu crystals were synthesized by hydrothermal method with 3molL-1 KOH as mineralizer, with 35% fill factor, under the reaction temperature of 430℃ for 24h. When Zn(OH)2 doped with FeCl2·6H2O was used as precursor, different shapes of Fe doped ZnO crystals were synthesized, of which the atomic percentage of Fe in the bigger crystals were 0.49%—0.52%. The magnetization of the crystals lowered with increasing temperature, a superconducting quantum interference device (SQUID) was used for measuring magnetism. Compared with Zn1-xFexO crystals the magnetization of Zn1-xFexO:Cu crystals doped with Cu increased obviously in the high temperature region, and at room temperature they were ferromagnetic.

The Lyophilization of Dispersed Systems: Influence of Freezing Process, Freezing time, Freezing Temperature and RBCs Concentration on RBCs Hemolysis

ABSTRACTIn this work, we studied the influence of different parameters controlling cooling stage on biological dispersed system injury. The human red blood cell (RBCs) was chosen as work model. The study examined the influence of two freezing processes on RBCs hemolysis, one process producing big crystals, the other producing small crystals. Using both processes, we examined the effect of freezing temperature, freezing time, and RBCs concentration on injuries to RBCs. Freezing damage was assessed by the hematocrite measure before freezing and after thawing. The process producing a small number of big ice crystals (Pa) seems—in relation to the one producing a large number of small ice crystals (Pb)—to be less traumatic for the RBC, although the two are not statistically different. Freezing temperature and freezing time influence the preservation of RBCs. At 0 and −20°C there were high preservation and total hemolysis, respectively. At −5°C and −10°C, the RBC hemolysis depends on freezing temperature and freezing time. The RBCs hemolysis rates increases when freezing time increases and when freezing temperature decreases. The rates of RBCs preserved decreases with RBCs concentration some with either the freezing process used (Pa or Pb). More, an accentuation of the difference between the two used freezing processes on RBCs hemolysis was retrieved. The analysis of the conductivity evolution within the RBCs suspension frozen showed that the destruction of the RBCs is had essentially to the solution effects. When the crystallization eutectic takes place, the RBCs are already completely destroyed.

Tribological investigations of diamond–metal grinding pads

New grinding pads have been developed as composite materials consisting of synthetic diamonds embedded in a metallic matrix of bronze. The wear resistance of the pad material and its abrasive action was determined in reciprocating sliding tests with a corundum ball acting on the polishing sheets with water in the contact. Tests with 5000 and 50,000 cycles have been carried out. The material removal is not the same on the pad and the corundum ball. High abrasion was found on the corundum ball for big size diamond crystals and a sufficient amount of diamonds in the pad, whereas a fine diamond grain size shows higher wear of the pad. These fine-grained pads are suitable for fine polishing of sapphire plane surfaces down to a roughness R a of less than 40 nm.

Array of HgI2 detectors on the HL-1M Tokamak

An array of seven HgI2 detectors, which are suitable for detecting the time and space evolution of the x-ray radiation flux and energy spectrum in the range between 15–150 keV relevant to suprathermal electron and runaway electrons was installed on the HL-1M Tokamak (R0=1.02 m, a=0.26 m, BT=3.5 T, IP=350 kA, ne=3–6×1013 cm−3, Te=0.8–1.5 keV). Our iodine mercury (HgI2) semiconductor detectors possess the properties of low noise level, high detection efficiency, high counting rate, high energy resolution, and working at room temperature. Every detector is a high quality, high purity detector cut out of a big size HgI2 crystal. A new type of multichannel energy spectrometer with a high speed acquisition system was developed. Therefore, the spatial and temporal distribution of the x-ray energy spectrum induced by thermal and superthermal electrons can be observed.

Crystallization in Partially Amorphous Ni<SUB>50</SUB>Ti<SUB>32</SUB>Hf<SUB>18</SUB> Melt Spun Ribbon

A partially amorphous Ni50Ti32Hf18 melt spun ribbon has been characterized by means of calorimetry, X-ray diffraction and transmission electron microscopy, showing that the amorphous regions are mostly concentrated in the wheel side as a consequence of a higher cooling rate during the fast solidification (i.e. higher solidification rate). Special emphasis has been given to the crystallization process of the amorphous regions, studying the evolution of the microstructure and the martensitic transformation. Although several crystallization procedures have been carried out by thermal treatments, either slightly under or over the crystallization temperature measured by DSC, TC, the final microstructure and calorimetric behavior of the fully crystalline samples does not depend on the applied temperature. The fully crystalline samples contain regions with small crystallites produced during the thermal treatment (showing that the crystal nucleation energy is rather low for this alloy) together with the large crystals originated during the melt-spinning. At room temperature (RT), both types of crystals are in martensitic state. The new crystallized regions with small grain size show notably lower transformation temperatures and higher hysteresis in comparison to the big crystals already existing before the crystallization treatments. However, an additional mechanism, apart from the crystal size, affects the transformation temperatures, likely related to the presence of more defects (mainly grain boundaries) in the crystallites created by thermal treatments. These defects could act as nucleation sites for the martensite and increase the transformation temperatures with respect to the as cast spherical crystallites of similar sizes.

Effect of deposition parameters on different stages of diamond deposition in HFCVD technique

The effect of applied bias and system pressure on different stages in the deposition process occurring during diamond deposition on mirror polished Si single crystal substrates in the HFCVD technique has been investigated. For characterization of the deposit, Fourier Transform Infrared Spectroscopy and Laser Raman spectroscopy have been used as the primary techniques while X-ray diffraction and scanning electron microscopy served as supplementary techniques. The findings are that the use of an overall low system pressure ∼1.3 mbar and application of an appropriate bias to the substrate during the initial stages facilitates the growth of highly oriented cubic silicon carbide film on mirror polished Si single crystal substrates under conditions conventionally used to grow diamond in HFCVD technique. A critical pressure ‘regime’ ∼26 mbar has been found to exist during the growth stage for the concurrent growth of SiC and diamond such that only SiC grows below this pressure and diamond starts growing at or above this value. It is suggested that around this transition region, SiC gets partly converted to nanocrystalline diamond structured carbon, which then grows into bigger crystals under appropriate growth conditions.

Synthesis of small crystal polycrystalline mordenite membrane

Mordenite membrane was prepared on α-Al 2O 3 tube by in situ hydrothermal synthesis with tetraethylammonium bromide (TEABr) as template agent. By the application of aging process of the parent solution, the size of mordenite crystals could be remarkably reduced from 20–30 (without aging) to 4–5 μm. The small crystal mordenite membrane had higher performance of pure gas permeation than big crystal mordenite membrane. The ideal selectivity of H 2/N 2 was 9.80, much higher than 3.82 of big crystals mordenite membrane. The membrane displayed high water-permselective performance in pervaporation (PV) test toward water/organic liquid mixtures. The highest separation factors achieved toward water/methanol, water/ethanol, water/ n-propanol and water/ i-propanol were 2600 ( X W=50%, T=323 K), 5500 ( X W=50%, T=343 K), 6000 ( X W=15%, T=343 K) and 6800 ( X W=50%, T=343 K), respectively.

Growth and characterization of methyl- p-hydroxybenzoate ( p-MHB): a non-linear optical material

Methyl p-hydroxybenzoate ( p-MHB) single crystals were grown from solvents like methanol and acetone using slow cooling technique. Solubility studies were made using these solvents at various temperatures. Metastable zone-width studies have been carried out. Powder X-ray diffraction study has been carried out and the lattice parameters were calculated. Various functional groups present in the grown material have been identified using FTIR spectra. Proton NMR spectrum was recorded and the presence of hydrogen atoms in the molecule was confirmed. The transparency of crystal was tested using UV–visible spectrophotometer. The crystal is also tested for the mechanical strength using Vicker's hardness tester. Growth parameters were optimized and big crystals were grown.

Evolution of bulk composition, mineralogy, strain style and fluid flow during an HT–LP metamorphic event: sillimanite zone of the Catalan Coastal Ranges Variscan basement, NE Iberia

Metamorphic rocks in the Osor complex (Guilleries massif, NE Iberian Peninsula) show the following structural and compositional features: strong differentiation into quartz-rich gneissic semipelitic and quartz-absent, mica-rich schistose bands, higher density of igneous (both basic and leucogranitic) and quartz veins in the schistose domains and strong strain partitioning in the pelitic bands. Garnet is present in both kinds of lithologies, showing also differential textural and chemical features interpreted to be dependent on bulk composition, deformation and fluid interaction histories. Textures, mineral composition and thermobarometry suggest the operation of concurrent mechanical, mass transfer and thermal phenomena such as: (1) variations in strain style, (2) fluid infiltration, (3) magmatic injection and (4) HT–LP metamorphic and metasomatic episodes. The following sequence of events is suggested: initially the cooling of syntectonic high- T basic quartz diorite sheets promoted high strain rates, low d P/d T thermobaric evolution, incipient anatexis in the pelitic bands and devolatilization through a pervasive to vein-channelized prograde fluid flow. The prograde flow enhanced an ongoing compositional tectono-metamorphic differentiation and produced metasomatism through depletion of the Osor rocks in alkalis and calcium. Later injection and cooling of peraluminous leucogranitoid sheets, preferentially along pelitic bands, increased the ratio of magmatic/metamorphic components in the fluids and strongly enriched them in alkalis producing a second metasomatic episode. During crystallization of quartz and leucogranitoid veins, the pelitic bands were strongly enriched back again in alkalis, promoting the blastesis of big crystals of post-peak muscovite and albite as well as the retrogression of garnet. The metasomatic mica-rich levels must have been the preferred locus for development of a new deformation style dominated by shear band fabrics in metapelites and related to a release of the gravitational instability originated previously due to crustal thickening. The increasing decompressional component of the retrograde P– T path also suggests that this style of deformation was prevalent during, if not responsible for, a phase of exhumation of the metamorphic complex. It is suggested that similar patterns of thermomechanical and mass transfer phenomena could well be a fundamental characteristic common to all HT–LP metamorphic belts.

Crystallization of ladderlike polyphenylsilsesquioxane (PPSQ)/isotactic polystyrene (i-PS) blends

The crystals of polyphenylsilsesquioxane (PPSQ) and isotactic polystyrene (i-PS) blends prepared from their toluene solutions had been studied by optical polarized microscope and DSC. Some big bright regular parallelogram-like single crystals from PPSQ with coarse surface are observed (PPSQ≥90%) and no regular crystals could be formed (PPSQ≤70%), however, at PPSQ≤10%, this blend formed irregular continuous crystals from i-PS similar with pure i-PS. Crystallinity of rich-i-PS phase in the blend is higher than the corresponding percent of i-PS (i-PS≥30%) while its crystallinity is less than the percent of i-PS (i-PS≤10%). Effect of miscibility and solvent on their crystallization has also been discussed.

Sintering polymer nano-crystals at high pressure

Semicrystalline polymers, such as polyethylene (PE), polyethylene terephthalate (PET) can crystallize in solvent and molten state. Folded-chain crystals with thickness about 10–20 nm are commonly obtained. These folded-chain crystals contain much more defects in the bulk and surface. They are metastable in thermodynamics for their small size in chain-axis direction and folded-chain surface. These problems hinder us to investigate some structures and properties about polymer crystals [1]. After Wunderlich reported that PE extended-chain crystals with thickness up to 3 μm could be formed under high pressure [2], many polymers have been investigated at high pressure. Extended-chain crystals of some polymers, such as polyamide (PA) [3–5], PET [6, 7] and PVDF [8, 9], were obtained through high-pressure crystallization. Because extended-chain crystals have few folded-chain conformation and their thickness is up to several micron meters. These extended-chain crystals are stable in thermodynamics. Up to know, the thickness of reported largest extended-chain crystals is up to 40 μm [10], but the crystallization time was much longer (200 h). This suggests that some new methods should be introduced to grow larger polymer crystals, which are the basis for investigation and application about the structures and properties of polymer crystals. Sintering is a method commonly used in ceramic. Some big crystals are usually formed during sintering. This is induced by abnormal grain growth [11]. The phenomena should be prevented because a few big crystals will destroy the mechanism properties of ceramic. But this method perhaps can be introduced in the growth of polymer crystals. In this work, sintering method was employed to PET nano crystals. Scanning electron microscopy revealed that PET extended-chain crystals with thickness up to 70 μm were formed only sintered for 6 h. This suggested that sintering is a promise method for the growth of large polymer crystals. An un-oriented commercial PET was used as the original material (Yanshan Petrol. Chem. Co. China). The molecular weight, calculated from molecular weight, was about 18 000. The starting material was firstly heated to 568 K for 10 min at normal pressure, and quickly cooled down to 473 K, then the sample was kept at the conditions for 48 h. This process was termed as pre-crystallization. The crystallized PET sample was broken into small granulates (about 0.5 mm) for hydrolysis. The weight ratio of water and PET sample was

Electron microscopy study of tubular crystals (BiS)1+δ(NbS2)n

Big crystals (mm-sized) with anomalous tubular morphology were synthesised in the Bi–Nb–S system. Their structural study by electron microscopy and related techniques revealed that they can be described as misfit layer structures, a type of composite modulated structures. The misfit monolayer ≈BiNbS3 and bilayer ≈BiNb2S5 phases appear as well in the preparation but with lamellar morphology as it is typical for these kind of compounds. They consist of periodical intergrowth of pseudotetragonal layers BiS (Q) with pseudohexagonal layers NbS2 (H). ≈BiNbS3 has a stacking sequence …Q,H,Q,H,… and ≈BiNb2S5 has a stacking sequence …Q,H,H,Q,H,H,…Backscattered electron imaging, wavelength dispersive X-ray spectroscopy and transmission electron microscopy of transversal cross-sections of single tubular crystals showed that these crystals present a strong compositional and inter-laminar stacking disorder along the tube radius. This disorder is suggested to be the cause for the original wrapping of the layers that gives rise to the tubes. Besides the disordered areas, some ordered slabs have been found with stacking sequences corresponding to binary 3R–NbS2 (≈6Å), ≈BiNb2S5 (≈17.4Å) (which dominate in the crystal) and to a new related phase ≈BiNb4S9 with a stacking sequence …Q,H,H,H,H,Q,H,H,H,H,… and a periodicity of ≈29.2Å.

Mechanical activation of the synthesis reaction of BaTiO 3 from a mixture of BaCO 3 and TiO 2 powders

The influence of long term milling in an attritor of a mixture of BaCO 3 and TiO 2 powders on the reaction synthesis of BaTiO 3 was studied. Thermal analysis (TG and DTA) of the unmilled and milled powders and X-ray diffraction of powders calcined at different temperatures were undertaken. Milling does not change the reaction sequence between BaCO 3 and TiO 2. BaTiO 3 and Ba 2TiO 4 are produced in both kinds of powders. However, milling reduces the formation temperature and accelerates the formation rate of these two phases. The production of final BaTiO 3 is incomplete in the milled powder, probably because of the formation of big crystals of Ba 2TiO 4. As a consequence, the milled powder contains large amounts of Ba 2TiO 4 after calcination at 1200°C. Milling produces allotropic transformations in TiO 2 from anatase phase, to α-PbO 2-like phase and finally to rutile structure.

98/03829 Comments on the evaluation of valve regulated lead-acid batteries (VRLA) under deep cycling regimes

The performance of the self-discharged gel cell has been studied in this work. Although the gel valve-regulated lead–acid (VRLA) batteries were shelved for nearly 3 years, the active mass structure of the positive plate, its resistance and the corrosion layer of the grid are not much affected. On the negative plate, the potential of hydrogen evolution in gel cell is more negative than that in AGM cell. So its self-discharge rate is slower. However, there is still slight accumulation of big PbSO4 crystals. It makes the resistance and overpotential of the self-discharged negative plate increase. But it is not enough to limit the capacity of the gel batteries, which is susceptible to the electrolyte amount. And the capacity of the long self-discharged gel cell can be completely restored by recharging.

Effect of Nucleation Rate on Heteroepitaxial Diamond Growth on Si (100) via Electron-Emission-Enhanced Nucleation by Hot Filament Chemical Vapor Deposition

Diamond nucleation and heteroepitaxial diamond film growth on Si (1000) were studied by scanning electron microscopy find Raman spectra. The diamond nucleation process was performed by electron emission using hot filament chemical vapor deposition. The nucleation density was found to be up to 10 11 cm -2 . Highly oriented epitaxial growth of diamond by this method was achieved on mirror-polished silicon substrate. Experimental results showed that the nucleation rate has a significant effect on heteroepitaxial diamond films on virgin silicon surface. Low and high nucleation rates led to some discrete big diamond crystals and polycrystalline diamond films, whereas, with an appropriate nucleation rate, the epitaxial growth of diamond on an untreated silicon substrate can be accomplished.

DSC study of honey granulation stored at various temperatures

Non pasteurized, liquid and transparent honey containing very few and fine crystals was stored at 20, 10, 4 and −20°C. The crystal growth was analysed by differential scanning calorimetry (DSC) and by measuring the absorbance intensity at 660 nm over a 6 mth period. In honey stored at 20°C coarse crystals were formed with melting temperatures (Tm) between 45 and 65°C, whereas honey stored at −20°C granulated as a finely-grained, fondant-like honey, with Tm between 25 and 45°C. In honeys stored at 10 and 4°C big and small crystals were produced having intermediate characteristics when compared with honeys stored at 20 and −20°C. The rates of honey granulation were calculated from Δ H values at the four temperatures. A linear relationship was found between the enthalpy of melting (Δ H) and the absorbance at 660 nm. The activation energy for the melting of coarse crystals was also determined with DSC.