Showing papers on "Devitrification published in 2001"
TL;DR: In this article, the authors summarized the current status of research in the field of nanocrystallization of metallic glasses especially highlighting the influence of glass composition and conditions of devitrification process on size, morphology and composition of crystallization products.
Abstract: The paper summarizes briefly the current status of research in the field of nanocrystallization of metallic glasses especially highlighting the influence of glass composition and conditions of devitrification process on size, morphology and composition of crystallization products. Conventional crystallization creates a nanocrystalline structure only in glasses with particular compositions. Any metallic glass, decomposing in a primary crystallization process, can be converted into partially nanocrystalline material using non-conventional methods of heat treatment, e.g. high-temperature or low-temperature nanocrystallization. Temperature of devitrification process influences sizes and compositions of crystallization products for any volume fraction of crystalline phase. The change of crystallites sizes can change their morphologies. The change of a crystallite composition usually affects the lattice parameter but also can result in a change of crystallographic structure of the same phase or in formation of another phase. Composition of primary crystallites is dependent on temperature as well as on time of devitrification process. The lower the annealing temperature and the shorter the annealing time (smaller crystallites) the more the crystallites composition differs from the equilibrium state.
218 citations
Patent•
06 Apr 2001TL;DR: In this article, the devitrification barrier coating is formed from silicon nitride, which can be deposited on the vitreous component using chemical vapor deposition (CVD), and the outer surface is covered at least in part by a devitification barrier layer.
Abstract: A chemical vapor deposition apparatus comprises a reaction chamber and one or more vitreous components having an outer surface that is covered at least in part by a devitrification barrier layer. In some arrangements, the one or more vitrious components can include a thermocouple. In a preferred arrangement, the devitrification barrier coating is formed from silicon nitride, which can be deposited on the vitreous component using chemical vapor deposition (CVD).
127 citations
TL;DR: In this paper, temperature-modulated differential scanning calorimetry measurements allow the online study of heat capacity changes during isothermal crystallization of polycarbonate and poly(3-hydroxybutyrate) polymers.
Abstract: The relaxation strength at the glass transition shows significant deviations from a two-phase model for semicrystalline polymers. The introduction of a rigid amorphous fraction (RAF), which is noncrystalline but does not participate in the glass transition, allows a description of the relaxation behavior. The question arises when does this amorphous material vitrify. Temperature-modulated differential scanning calorimetry measurements allow the online study of heat capacity changes during isothermal crystallization. For bisphenol-A polycarbonate (PC) and poly(3-hydroxybutyrate) (PHB) at reasonably high modulation frequencies (10 mHz), no contribution from reversing melting to the measured heat capacity was detected at the crystallization temperature; therefore, changes in the baseline heat capacity can be studied. The amount of RAF obtained at the crystallization temperature was compared with that obtained from the step in heat capacity at the glass transition at lower temperatures. No changes in the amount of the RAF occur in the temperature range between crystallization and the glass transition. Consequently, the rigid amorphous material is totally established during the isothermal crystallization of PC and PHB. The reason for the vitrification of the RAF is the immobilization of cooperative motions owing to the fixation of parts of the molecules in the crystallites, which is favorable at the fold surfaces. In this way, crystallization in PC and PHB limits itself by vitrifying the crystallizable material next to the growing crystals. On heating, devitrification of the RAF occurs when the crystals, which were formed last, melt in the temperature range of the lowest endotherm.
120 citations
TL;DR: In this article, a reduction of inhomogeneous linewidth by a factor of 2 is observed between glass and glass-ceramic on different transitions resulting in an increase of the maximum cross-sections.
109 citations
Abstract: Structural models of alkali tellurite glasses, (M2O)x(TeO2)l-x with M = Li, Na, K are presented. The glass structure was studied with neutron and X-ray diffraction, and, in the case of sodium, NMR. Real-space models of the glass structure were built using the reverse Monte Carlo algorithm. The distribution of polyhedral types as a function of alkaline ion type and composition is derived. It is concluded that the broad distribution of polyhedral species, as compared to that found in crystalline tellurites of similar composition, is responsible for the marked resistance to devitrification shown by these glasses.
102 citations
Journal Article•
TL;DR: In this paper, an amorphous gas atomized powder was consolidated by warm extrusion and the onsets of the glass transition and crystallization temperatures of this extruded material were observed at slightly higher and lower temperatures than those of the starting powders.
Abstract: Cu47Ti34Zr11Ni8 amorphous gas atomized powders were consolidated by warm extrusion. After consolidation near 723 K using an extrusion ratio of 5, the material retains between 88% and 98% of the amorphous structure found in the gas atomized powder. The onsets of the glass transition and crystallization temperatures of this extruded material are observed respectively at slightly higher and lower temperatures than those of the starting powders. These temperature shifts are attributed to a composition change in the remaining amorphous phase during partial devitrification throughout the extrusion process. Powders extruded at the same temperature, but using higher extrusion ratios of 9 and 13, exhibit substantial devitrification during the consolidation process yet still deform homogeneously.
73 citations
TL;DR: The changes occurring during the heating of a borosilicate glass have been investigated by differential thermal analysis, dilatometric analysis and thermomechanical analysis as discussed by the authors, and a value of 290 kJmol −1 was obtained for the activation energy for viscous flow, where the precipitation of cristobalite was identified by X-ray diffraction.
69 citations
TL;DR: The kinetics, microstructural changes, and crystal structure development for crystallization of amorphous, quenched, mullite composition glass (3Al 2 O 3 ·2SiO 2 ) were studied between 900 and 1400°C as discussed by the authors.
Abstract: The kinetics, microstructural changes, and crystal structure development for crystallization of amorphous, quenched, mullite composition glass (3Al 2 O 3 ·2SiO 2 ) were studied between 900 and 1400°C. The phenomena observed were characterized using non-isothermal differential scanning calorimetry (DSC), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), powder X-ray diffraction (XRD, with both a standard laboratory diffractometer, as well as with synchrotron radiation), and Rietveld analysis. Crystallization of amorphous mullite was observed to occur in two steps. The activation energy for crystallization was 892 kJ/mol for the first step and 1333 kJ/mol for the second step. From the amorphous state, the first phase(s) to crystallize were alumina-rich, pseudotetragonal mullite (∼70 mol% Al 2 O 3 ). These crystals were highly strained and contained numerous nanometer scale inclusions. With increasing temperature, the crystals were observed to incorporate increasing amounts of SiO 2 , and approach the equilibrium orthorhombic structure. By 1400°C the pseudotetragonal to orthorhombic transition was complete, the strain was eliminated, most of the inclusions had been assimilated, there was ∼67% reduction in grain size, and the crystals had attained the composition of the initial, bulk glass (∼60 mol% Al 2 O 3 ).
66 citations
09 Aug 2001
TL;DR: In this article, phase transitions of freeze-dried persimmon in a large range of moisture content were determined by differential scanning calorimetry (DSC), where samples were conditioned by adsorption at various water activities (aw=0.11 −0.90) at 25°C.
Abstract: Phase transitions of freeze-dried persimmon in a large range of moisture content were determined by differential scanning calorimetry (DSC). In order to study this transitions at low and intermediate moisture content domains, samples were conditioned by adsorption at various water activities (aw=0.11–0.90) at 25°C. For the high moisture content region, samples were obtained by water addition. At aw≤0.75 two glass transitions were visible, with Tg decreasing with increasing water activity due to water plasticizing effect. The first Tg is due to the matrix formed by sugars and water. The second one, less visible and less plasticized by water, is probably due to macromolecules of the fruit pulp. At aw between 0.80 and 0.90 a devitrification peak appeared after Tg and before Tm. At this moisture content range, the Gordon–Taylor model represented satisfactorily the matrix glass transition curve. At the higher moisture content range (aw>0.90), the more visible phenomenon was the ice melting. Tg appeared less visible because the enthalpy change involved in glass transition is practically negligible in comparison with the latent heat of melting. In the high moisture content domain Tg remained practically constant around Tg′ (−56.6°C).
61 citations
TL;DR: A new model which couples membrane-limited water transport equations, classical nucleation theory, and diffusion-limited crystal growth theory was used to explore the role of cell dehydration in devitrification of human keratinocytes frozen in the presence of glycerol, showing that the rate of intracellular nucleation was less sensitive to cell dehydration than was the crystal growth rate.
52 citations
TL;DR: In this article, two precursor-derived SiCN ceramic monoliths were performed employing different liquid polymers, which were obtained by ammonolysis of functionalized chlorosilanes, and transmission electron microscopy was conducted in order to study the devitrification/thermal stability of the corresponding bulk SiCN glasses.
Abstract: Processing of two precursor-derived SiCN ceramic monoliths was performed employing different liquid polymers, which were obtained by ammonolysis of functionalized chlorosilanes. Preparation of monolithic samples was performed by mixing liquid polysilazane with cross-linked SiCN-powder particles, derived from the same precursors by heat treatment at 300 °C, and subsequent annealing upon pyrolysis at temperatures exceeding 1000 °C to initiate crystallization. Characterization of the polymer-derived ceramics was performed after pyrolysis at 1000 °C and, in particular, after annealing at temperatures ranging from 1400 to 1540 °C. Transmission electron microscopy was conducted in order to study the devitrification/thermal stability of the corresponding bulk SiCN glasses. Depending on the functionalities of the SiCN precursor and the processing conditions, different microstructures were obtained. The material prepared from precursor A showed crystallization of large α-Si3N4 grains within the overall homogeneous amorphous bulk material after exposure at 1540 °C for 6 h in nitrogen atmosphere. In contrast, the ceramic monoliths derived from SiCN precursor B remained completely amorphous, with no indication of local nucleation or crystallization. It is thought that devitrification of these polymer-derived glasses is promoted by local rearrangements of the glass network within the amorphous bulk. In addition, the role of the excess free carbon, commonly present in polymer-derived SiCN ceramics,on the thermal stability is discussed. Copyright © 2001 John Wiley & Sons, Ltd.
TL;DR: In this paper, the Ries impact glass is found within the suevite, the breccia that forms the uppermost layers of the ejecta blanket around the crater, and the glass is considered to represent quenched melts produced as a result of the impact.
TL;DR: In this paper, 3Al 2 O 3 ·2SiO 2 ) coatings were found to start out as a nanocrystalline layer, which is an intimate mixture of γ-Al 2O 3 nanocrystites imbedded in a vitreous silica-rich matrix at the substrate/coating interface.
Abstract: Dense, uniform and crack-free mullite (3Al 2 O 3 ·2SiO 2 ) coatings were deposited on SiC by chemical vapor deposition. The coatings were compositionally graded, with the Al/Si ratio increasing towards the outer surface of the coatings for improved corrosion resistance. The coatings were found to start out as a nanocrystalline layer, which is an intimate mixture of γ-Al 2 O 3 nanocrystallites imbedded in a vitreous silica-rich matrix at the substrate/coating interface. Mullite grains nucleated when the surface composition of the growing coating was in a narrow range close to that of stoichiometric mullite. The phase transformations occurring in these coatings during high-temperature anneals in the range 1100–1400 °C were studied. These phase transformations, which include a tetragonal-to-orthorhombic transformation, mullitization and devitrification of silica in the nanocrystalline layer, and α-alumina precipitation and twinning of the alumina-rich mullite, are discussed in light of the adhesion and corrosion resistance of the coatings.
TL;DR: In this paper, the authors report on the synthesis of bulk nanostructured (Zr/Ti)-Cu-Al-Ni alloys through devitrification of cast bulk glassyspecimens, and presents results for their mechanical properties at room and elevated temperatures.
TL;DR: In this paper, it was found that the first stage of the devitrification process is related to the precipitation of fine particles of an icosahedral phase from about 3 to 7 nm in size.
Abstract: Structure changes in Zr–Ti–Ni–Cu metallic glass on heating have been studied by x-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. It has been found that the first stage of the devitrification process is related to the precipitation of fine particles of an icosahedral phase from about 3 to 7 nm in size. Direct evidence of the formation of the icosahedral phase has been obtained using nanobeam diffraction in transmission electron microscopy.
Journal Article•
TL;DR: In this article, an algorithm with no adjustable parameters is presented to simulate the kinetics of concurrent sintering and crystallisation of monodispersed and polydispersed glass particles.
Abstract: We review and discuss an algorithm with no adjustable parameters to simulate the kinetics of concurrent sintering and crystallisation of monodispersed and polydispersed glass particles. The algorithm is based on the two classical sintering models of Frenkel and Mackenzie-Shuttleworth, the JMAK crystallisation theory and on our own model for polydispersed particle sintering. The input parameters are: particle size distribution (v r ), surface tension (γ), viscosity (η), number of nucleation sites (N s ) and crystal growth velocity (U). We test the algorithm at a variety of annealing temperatures using experimental data and densification rates for two powdered glasses-polydispersed alumino-borosilicate glass, which is stable against devitrification, and monodispersed cordierite glass which easily crystallises. We show that the algorithm provides a powerful simulation tool for predicting the sintering conditions of real glass powders, for any size distribution and temperature, thus minimising the number of time consuming experiments.
TL;DR: In this article, several melt-spun ribbons of different compositions in the Al-rich corner of the Al−Ni-Sm ternary system were analyzed by means of X-ray diffraction (XRD) and differential scanning calorimetry (DSC) in order to determine their thermal stability and to understand the nanocrystallisation process.
Abstract: Several melt-spun ribbons of different compositions in the Al-rich corner of the Al–Ni–Sm ternary system were analysed by means of X-ray diffraction (XRD) and differential scanning calorimetry (DSC) in order to determine their thermal stability and to understand the nanocrystallisation process. Out of all the compositions analysed, only three were found to be completely amorphous, whereas the others were partially crystallised. The activation energies of the α-Al nanocrystallisation were evaluated using the Kissinger method. Isothermal DSC scans revealed the existence of quenched-in nuclei in the more unstable amorphous alloys. These quenched-in nuclei are probably due to the melt-spinning process and the crystalline structure after devitrification is strongly dependent on them.
TL;DR: X-ray absorption fine structure (XAFS), x-ray diffraction, and differential thermal analysis have been combined to investigate the structure of ultrafine amorphous Ni{sub 70}B{sub 30} alloy during the crystallization process as mentioned in this paper.
Abstract: X-ray-absorption fine structure (XAFS), x-ray diffraction, and differential thermal analysis have been combined to investigate the structure of ultrafine amorphous Ni{sub 70}B{sub 30} alloy during the crystallization process. The XAFS results demonstrate that a fcc-like nanocrystalline Ni phase with a medium-range order is formed at 573 K where the first exothermic process is observed. We confirmed that the metastable intermediate states consist of the two phases, i.e., nanocrystalline Ni and crystalline Ni{sub 3}B alloy. The results support the Riveiro {close_quote}s scenario [J. Magn. Magn. Mater. 188, 153 (1998)] for the devitrification of NiB alloy, in that crystalline phases of Ni{sub 3}B and Ni-rich NiB alloy are formed as the intermediate states. Based on the complementary information obtained by the three techniques, we present a simple mechanism of crystallization process for the ultrafine amorphous Ni{sub 70}B{sub 30} alloy.
TL;DR: In this paper, the incorporation of Al, Mg, Ca, Fe, and alkaline elements into the glass structure is discussed from the perspective of glass-chemical experience with obsidian glasses from the point of view of glass technology.
31 May 2001-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors investigated heterogeneous nucleation of α-Al and other phases in an Al 70 Ni 13 Si 17 (in at%) alloy, using a novel metallic glass technique.
Abstract: Heterogeneous nucleation of α-Al and other phases was investigated in an Al 70 Ni 13 Si 17 (in at.%) alloy, using a novel metallic glass technique. The glass was formed by melt spinning and its devitrification/crystallisation behaviour during isothermal and anisothermal anneals was investigated using differential scanning calorimetry and X-ray diffractometry. The results obtained indicated suitability of the above alloy system for the nucleation study. TiB 2 grain refiner particles were subsequently added to the melt and the melt-spun ribbons produced were examined using transmission electron microscopy. No α-Al nucleation was detected on the boride particles, while it was systematically observed on hexagonal dendrites present in the glassy matrix, which suggests that Si poisoning of the borides is occurring. The high Si content appears to suppress the formation of Al 3 Ti layers on the surface of TiB 2 particles, thus reducing their potency to nucleate α-Al.
TL;DR: Time-resolved devitrification studies of Ti 34− x Cu 47 Zr 11 Ni 8 Si x metallic glasses were performed using a recently developed high temperature furnace in a Debye-Scherrer geometry as discussed by the authors.
Abstract: Time-resolved devitrification studies of Ti 34− x Cu 47 Zr 11 Ni 8 Si x metallic glasses were performed using a recently developed high temperature furnace in a Debye–Scherrer geometry. Samples included powders produced by high pressure gas atomization and surface coatings deposited by air plasma spraying. Synchrotron radiation at the Advanced Photon Source at Argonne National Laboratory was used to follow the devitrification of samples during heating at 40 K min −1 between 623 and 1073 K. The crystallization behavior observed with structural diffraction data compare well with results from thermal analysis using differential scanning calorimetery. At 1073 K, these amorphous alloys evolve to a four phase microstructure which includes phases that appear to be closely related to Cu 51 Zr 14 , CuTi and Cu 2 TiZr.
Patent•
06 Sep 2001
TL;DR: In this article, a high rigidity glass-ceramic substrate is provided, which contains, as a predominant crystal phase or phases, at least one crystal phase selected from the group consisting of enstatite (MgSiO 3 ), enStatite solid solution (MgsSiO3 solid solution), magnesium titanate (mgTi 2 O) and Magnesium titanate solid solution(MgTi2 O 5 solid solution) and has excellent melting property of a base glass.
Abstract: A high rigidity glass-ceramic substrate is provided which contains, as a predominant crystal phase or phases, at least one crystal phase selected from the group consisting of enstatite (MgSiO 3 ), enstatite solid solution (MgSiO 3 solid solution), magnesium titanate (MgTi 2 O) and magnesium titanate solid solution (MgTi 2 O 5 solid solution), has fine crystal grains (preferably globular crystal grains) of precipitated crystal phases, has excellent melting property of a base glass, high resistivity to devitrification, easiness in polishing, excellent smoothness in the surface after polishing and has high Young's modulus capable of coping with a high speed rotation.
TL;DR: In this paper, temperature-modulated DSC (TMDSC) measurements at reasonably high frequencies allow for the determination of base-line heat capacity for bisphenol-A polycarbonate (PC).
Abstract: Temperature-modulated DSC (TMDSC) measurements at reasonably high frequencies allow for the determination of base-line heat capacity. In this particular case vitrification and devitrification of the rigid amorphous fraction (RAF) can be directly observed. 0.01 Hz seems to be a reasonably high frequency for bisphenol-A polycarbonate (PC). The RAF of PC is established during isothermal crystallization. Devitrification of the RAF seems to be related to the lowest endotherm. For PC the melting of small crystals between the lamellae is expected to yield the lowest endotherm.
TL;DR: In this article, the effect of the second phase on the thermal stability and on the mechanical properties at room temperature as well as at temperatures around the glass-transition temperature, Tg, was discussed with respect to their properties.
Abstract: Bulk nanostructured composite materials can be obtained by partial devitrification of slowly cooled bulk glass-forming multicomponent metallic glasses or by blending a glassy matrix alloy with insoluble second-phase particles by solid state processing. Their properties are discussed with respect to the effect of the second phases on the thermal stability and on the mechanical properties at room temperature as well as at temperatures around the glass-transition temperature, Tg. Microhardness measurements at room temperature reveal a substantial increase in the hardness of the composites because of the uniform distribution of nanoscale particles in the glassy matrix. Also, there is a significant increase in yield strength with increasing volume fraction of particles. At elevated temperatures around T g volume fractions of up to 40 vol.-% of nanoscaled particles yield no significant change in strength as compared with the particle-free material, but the deformation behavior of the composites is mainly controlled by the Newtonian viscous flow of the glassy matrix phase. This easy-flow behavior opens a promising route for shaping complex parts of bulk nanostructured composites derived from metallic glasses at moderate temperatures and high strain rates.
TL;DR: In this paper, the devitrification in screen printed and annealed films made with borosilicate glass particles with the composition PbO-SiO 2 -B 2 O 3 =65:25:10 % wt.
TL;DR: In this article, the density of brownish spots formed on the surface of silica glass through the reaction with silicon melt is studied using three types of glass, that are made from natural quartz powder, synthetic silica powder, and Al-doped synthetic silicas powder.
Abstract: The density of brownish spots formed on the surface of silica glass through the reaction with silicon melt is studied using three types of silica glass, that are made from natural quartz powder, synthetic silica powder, and Al-doped synthetic silica powder. The density of the brownish spots was higher in natural quartz glass (NQG) than in synthetic silica glass (SSG) and in Al-doped synthetic silica glass (ASG). The result is consistent with that of the devitrification of silica glass observed in the interior of the bulk glass after a heat treatment. Aluminum and calcium are detected as aggregates in the devitrification spots of NQG. It is noted that ASG, containing a comparable concentration of well-dispersed aluminum, shows a significantly lower density of brownish spots and internal devitrification spots than NQG. Thus, it is considered that the formation of the brownish spots originates from the devitrification of silica glass caused by aggregates of impurities.
TL;DR: In this paper, a spinodal decomposition of a fluorozirconate glass was studied by means of X-ray diffraction, Raman measurements after different time of heat treatment.
Abstract: The main families of zirconium based fluoride glasses have been shown to undergo an heterogeneous nucleation process forming a BaF 2 –ZrF 4 crystal phase. Here, a new fluorozirconate glass, with composition (mol%) 68.6ZrF 4 ,18.4LaF 3 ,5AlF 3 ,5GaF 3 ,3ErF 3 , undergoing a spinodal decomposition is presented. The devitrification process of this glass is studied by means of X-ray diffraction, Raman measurements after different time of heat treatment. Spatial fluctuations of composition are measured by X-ray microanalysis before the observation of any crystallisation trace. The final morphology of the separated phases, observed on the micrographs, shows a mainly crystalline connected glass-ceramic. The instability against decomposition of this composition has been attributed to the lack of glass-modifier and divalent ion in the starting melt.
TL;DR: In this paper, the InYBSNZnGa glass has a good stability exemplified by the value of the stability factors: T x − T g =108 K, S =4.1 K, and T g ≥309 °C.
TL;DR: In this paper, composites materials formed by CuO, Ag, and Ag+CuO clusters embedded in SiO 2 xerogels were prepared and the prepared samples were annealed in air at different temperatures.
Abstract: Composites materials formed by CuO, Ag, and Ag + CuO clusters embedded in SiO 2 xerogels were prepared. The prepared samples were annealed in air at different temperatures. By using IR absorption and X-Ray diffraction (XRD) the sample structure was studied. It was found that the embedded species and the heat treatments modify strongly the SiO 2 structure. The appropriate metal inclusions can lead to a relative low temperature form of cristobalite and quartz.
TL;DR: In this paper, the results of Mossbauer and X-ray diffraction (XRD) investigations of nanocrystalline alloys containing 0, 2, 4, 6 and 8 at.
Abstract: New composite soft magnetic alloys in the compositional series Fe73.5−xAlxSi13.5B9Cu1Mo3 were recently obtained by partial thermal devitrification of amorphous ribbons. We report the results of Mossbauer and X-ray diffraction (XRD) investigations of nanocrystalline alloys containing 0, 2, 4, 6 and 8 at.% Al, following annealing at 560°C for 1 h. The results indicate that most of the Si and Al are located in the cubic-DO3Fe(Si,Al) crystallites, after the primary crystallization is achieved.