Grain Growth (grain + growth)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Grain Growth

  • abnormal grain growth
  • anisotropic grain growth

  • Terms modified by Grain Growth

  • grain growth behavior
  • grain growth method

  • Selected Abstracts


    Competitive Abnormal Grain Growth between Allotropic Phases in Nanocrystalline Nickel

    ADVANCED MATERIALS, Issue 10 2010
    L. N. Brewer
    Electron backscatter diffraction-generated phase map showing the distribution of the abnormally grown grains for both the face centered cubic (red) and hexagonal close packed (blue) phases. Annealing condition was 17,h at 548,K. [source]


    Heat Shock Protein in Developing Grains in Relation to Thermotolerance for Grain Growth in Wheat

    JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 1 2010
    P. Sharma-Natu
    Abstract Wheat (Triticum aestivum L.) cvs DL 153-2 and HD 2285 (relatively tolerant), HD 2329 and WH 542 (relatively susceptible), were grown under normal (27 November) and late (28 December) sown conditions. In another experiment, these cultivars were grown under normal sowing and at anthesis stage, they were transferred to control (C) and heated (H) open top chambers (OTCs). Under late sowing, wheat cultivars were exposed to a mean maximum temperature of up to 3.6 C higher than normal sowing and in H-OTCs, mean maximum temperature was 3.2 C higher than C-OTCs during grain growth period. Heat susceptibility index (S) for grain growth and grain yield was determined at maturity in both the experiments. The level of heat shock protein (HSP 18) in the developing grains was determined in C- and H-OTC grown plants and in normal and late sown plants by Western blot analysis. The moderately high temperature exposure increased the accumulation of HSP 18 in the developing grains. The relatively tolerant cultivars, as also revealed from S, showed a greater increase in HSP 18 compared with susceptible types in response to moderate heat stress. An association of HSP 18 with thermotolerance for grain growth in wheat was indicated. [source]


    Allocation of Photosynthates and Grain Growth of Two Wheat Cultivars with Different Potential Grain Growth in Response to Pre- and Post-anthesis Shading

    JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 5 2003
    Z. Wang
    Abstract Grain yield in wheat is dependent on photosynthate production and allocation. Light intensity is one of the main factors affecting photosynthate production and allocation, and grain yield. This study was conducted to determine whether cultivars varying in grain number per spike and grain weight respond differently to pre-anthesis shading (PRE) and post-anthesis shading (POST), and to characterize the responses in production and allocation of photosynthate, yield and yield components, and spike traits. Both PRE and POST caused a decrease in both dry matter (DM) accumulation and allocation to grain. Cultivar Lumai 22, which has a large spike and large grains, was more sensitive to either PRE or POST. PRE reduced photosynthate production and partitioning to the spike in Lumai 22 at anthesis. In contrast, PRE had little influence on these parameters in the small-spike, small-grain cultivar Yannong 15. POST reduced the partitioning to the grain, especially in Lumai 22, for which marked reductions in biomass and grain yield were found for both the PRE and POST treatments. Changes in yield components attributable to shading varied with cultivars. The number of spikes m,2 was not affected by either PRE or POST. Lumai 22 was more seriously affected by shading than Yannong 15 in terms of grain number per spike and weight per grain. The decreases in grain number or weight per spikelet in both the PRE and POST treatments took place mainly in the upper and basal spikelets, especially in Lumai 22. We concluded that the adaptability of the small-spike, small-grain cultivar Yannong 15 to either PRE or POST was much greater than that of the large-spike, large-grain cultivar Lumai 22 in terms of many characteristics closely related to grain yield. Hence, we suggest that, in areas where low light intensity often occurs, the small-spike, small-grain cultivar would be more likely to produce high, stable grain yields. [source]


    Superplasticity of a Fine-Grained TZ3Y Material Involving Dynamic Grain Growth and Dislocation Motion

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2010
    Guillaume Bernard-Granger
    Superplastic deformation of a fully dense TZ3Y material, having a starting grain size around 135,145 nm and depleted of any amorphous phase at grain boundaries, has been investigated using compressive creep tests in air in the temperature range of 1100,1300C and the real stress range of 50,100 MPa. The key parameters of the creep law have been determined by performing temperature changes at a fixed stress and stress jumps at a fixed temperature. From such experiments, an average value for the apparent stress exponent of around 3 is obtained when the applied stress varied from 50 to 100 MPa and the temperature was kept constant in the range of 1100,1300C. The apparent activation energy of the mechanism controlling the creep deformation is evaluated at 57775 kJ/mol in the temperature range of 1200,1300C, for a real stress of 70 MPa. The values of the apparent grain size exponent can be calculated from the initial grain size in the as-sintered samples and the grain size in the crept samples. In all cases, it was determined to be around 2. Observation of the microstructure of the crept samples, using scanning electron microscopy, reveals grain growth but does not show any significant elongation of the elemental grains. Transmission electron microscopy of a sample crept under 100 MPa at 1300C reveals clear intragranular dislocation activity. This dislocation activity seems to be mainly confined in folds emitted at triple points. Because the creep parameters (experimental and calculated using a simple geometric model) and the microstructure observed are in good agreement, we propose that the creep mechanism involved is grain boundary sliding accommodated by dynamic grain growth and the formation of triple-point folds. [source]


    Electrical Properties of Textured Potassium Strontium Niobate (KSr2Nb5O15) Ceramics Fabricated by Reactive Templated Grain Growth

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2008
    Sedat Alkoy
    Highly [001] textured KSr2Nb5O15 (KSN) ceramics were fabricated by templated grain growth using acicular KSN template particles (5,15 wt%) and reactive matrix of SrNb2O6 and KNbO3. Excess Nb2O5 (1,1.5 wt%) was added as a liquid former. Increasing sintering temperature and time resulted in increased texture with a maximum texture fraction of 0.98. Dielectric, ferroelectric, and piezoelectric measurements indicate anisotropic properties that are close to single crystal values in the textured ceramics with the highest Pr,18 ,C/cm2, Ps,25 ,C/cm2, and d33=65 pC/N obtained in the c -axis direction. [source]


    Preparation of a Highly Conductive Al2O3/TiN Interlayer Nanocomposite through Selective Matrix Grain Growth

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006
    Xihai Jin
    An electroconductive TiN/Al2O3 nanocomposite was prepared by a selective matrix grain growth method, using a powder mixture of submicrosized ,-Al2O3, nanosized ,-Al2O3, and TiN nanoparticles synthesized through an in situ nitridation process. During sintering, a self-concentration of TiN nanoparticles at the matrix grain boundary occurred, as a result of the selective growth of large ,-Al2O3 matrix grains. Under suitable sintering conditions, a typical interlayer nanostructure with a continuous nanosized TiN interlayer was formed along the Al2O3 matrix grain boundary, and the electroconducting behavior of the material was significantly improved. Twelve volume percent TiN/Al2O3 nanocomposite with such an interlayer nanostructure showed an unprecedentedly low resistivity of 8 10,3,cm, which was more than two orders lower than the TiN/Al2O3 nanocomposite without such an interlayer nanostructure. [source]


    Effect of Li2O and PbO Additions on Abnormal Grain Growth in the Pb(Mg1/3Nb2/3)O3,35 mol% PbTiO3 System

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2004
    John Gerard Fisher
    Abnormal grain growth in Pb(Mg1/3Nb2/3)O3,35 mol% PbTiO3 (PMN-35PT) ceramics doped with Li2O and PbO has been investigated. Replacing the PbO dopant with up to 2 mol% Li2O caused an increase in the number of abnormal grains. For the composition containing 2 mol% Li2O and 6 mol% PbO, the amount of abnormal grain growth decreased with increasing sintering temperature. Single crystals of ,6 mm 6 mm 2 mm thickness were grown from the 2 mol% Li2O, 6 mol% PbO-containing composition via the templated grain growth method. Grain growth behavior with temperature is explained in terms of the effect of Li2O on interface-reaction-controlled grain growth and the critical driving force. [source]


    Effect of Yttria and Yttrium-Aluminum Garnet on Densification and Grain Growth of Alumina At 1200,1300C

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2004
    Michael K. Cinibulk
    Densification and grain growth of alumina were studied with yttria or yttrium-aluminum garnet (YAG) additives at the relatively low temperatures of 1200,1300C. Yttria doping was found to inhibit densification and grain growth of alumina at 1200C and, depending on dopant level, had a lesser effect at 1300C. At 1200C, yttria inhibits densification more than it hinders grain growth. The rate of grain growth increases faster with temperature than the rate of densification. Alumina-YAG particulate composites were difficult to sinter, yielding relative densities of only 65% and 72% after 100 h at 1200 and 1300C, respectively. Pure YAG compacts exhibited essentially no densification for times up to 100 h at 1300C. [source]


    {111} Twin Formation and Abnormal Grain Growth in Barium Strontium Titanate

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2003
    Byoung-Ki Lee
    Two series of experiments were performed to study the experimental conditions for the formation of {111} twins and related microstructures in barium strontium titanate ((Ba, Sr)TiO3). In the first series, the phase equilibria in the BaTiO3,SrTiO3,TiO2 system were determined. XRD and WDS analysis, done in the BaTiO3 -rich region, of 45(Ba,Sr)TiO3,10TiO2 samples annealed at 1250C for 200 h in air showed that (Ba,Sr)TiO3 was in equilibrium with Ba6Ti17O40 (B6T17) and Ba4Ti13O30 phases with strontium solubility (Sr/(Ba + Sr)) of ,0.02 and 0.20, respectively. In the second series the microstructures of samples consisting of a mixture of (Ba,Sr)TiO3 and 2.0 mol% TiO2, were observed after sintering at 1250C for 100 h in air. {111} twins formed only in the samples with faceted B6T17 second phase particles, similar to the case of BaTiO3. In these samples, abnormal grain growth occurred in the presence of the {111} twins. In contrast, no {111} twins formed and no abnormal grain growth occurred in the samples containing second phase particles other than B6T17. With an increased substitution of strontium for barium, the aspect ratio of abnormal grains containing {111} twin lamellae was reduced. This result was attributed to a reduction in the relative stability of the {111} planes with the strontium substitution. [source]


    Grain Growth of ,-SiAlON in the Calcium-Doped System

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2002
    Ya-Wen Li
    Two calcium-doped ,-SiAlON compositions (Ca0.6Si10.2Al1.8,O0.6N15.4 and Ca1.8Si6.6Al5.4O1.8N14.2) were prepared by hot pressing at 1600 and 1500C, respectively, for complete phase transformation from ,-Si3N4 to ,-SiAlON. Both samples were subsequently fired at different temperatures for different periods of time to study the grain growth of ,-SiAlON. Elongated ,-SiAlON grains were developed in both samples at high temperatures. The kinetics of grain growth was investigated based on the variations in length and width of the ,-SiAlON grains under different sintering conditions. Different growth rates were found between the length and width directions of the ,-SiAlON crystals, resulting in anisotropic grain growth in the microstructural development. [source]


    Grain Growth and Twin Formation in 0.74PMN0.26PT

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2002
    Jay S. Wallace
    The mechanisms controlling normal and exaggerated grain growth in lead magnesium niobate,lead titanate (PMN,PT) ceramics have been investigated by varying the PbO-based liquid-phase volume fraction from 0.03 to 0.6 and sintering temperature from 900 to 1100C. There is a transition in matrix grain growth rate and matrix grain shape with liquid fraction; samples with liquid volume fractions less than ,0.15 show relatively small equiaxed grains resulting from grain-to-grain impingement. Samples with higher liquid fractions show significantly larger, facetted, cube-shaped grains, whose size is independent of liquid fraction, indicating that a surface nucleation rate mechanism controls growth in this regime. Exaggerated grains were found in the high liquid fraction samples. Electron backscatter diffraction showed that all of the exaggerated grains contained 60,111, twins but none of the normal matrix grains contained twins. The reentrant angles in the twinned grains give them a growth advantage over untwinned grains, resulting in a population of exaggerated grains. [source]


    Abnormal Grain Growth in Alumina with Anorthite Liquid and the Effect of MgO Addition

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2002
    Chan Woo Park
    Abnormal grain growth (AGG) in alumina with anorthite liquid has been observed with varying anorthite and MgO contents, at 1620C. When only anorthite is added to form a liquid matrix, the grain,liquid interfaces have either flat or hill-and-valley shapes indicating atomically flat (singular) structures. The large grains grow at accelerated rates to produce AGG structures with large grains elongated along their basal planes. This is consistent with the slow growth at low driving forces and accelerated growth above a critical driving force predicted by the two-dimensional nucleation theory of surface steps. With increasing temperature, the AGG rate increases. The number density of the abnormally large grains increases with increasing anorthite content. The addition of MgO causes some grain,liquid interfaces to become curved and hence atomically rough. The grains also become nearly equiaxed. With increasing MgO content the number density of the abnormally large grains increases until the grain growth resembles normal growth. This result is qualitatively consistent with the decreasing surface step free energy associated with partial interface roughening transition. [source]


    Microstructure in Silicon Nitride Containing ,-Phase Seeding: III, Grain Growth and Coalescence

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2001
    Horng-Hwa Lu
    The mechanical properties of Si3N4 materials depend mainly on the microstructure, which originates during the densification process. The microscopic evidence indicates that ,-Si3N4 seeds incorporated in the starting powders play an important role in microstructural development, especially in the heterogeneous grain growth of ,-Si3N4 grains during sintering. The growth of ,-grains is initiated from the ,-seeds, resulting in a core/shell microstructure. The presence of Moir fringes and dislocations is attributed to misfit strain and compositional differences between the core and the shell. Coalescence can occur at the final stage of sintering. [source]


    Templated Grain Growth of Barium Titanate Single Crystals

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2000
    Paul W. Rehrig
    BaTiO3 single crystals were grown via templated grain growth (TGG), which is a process in which a single-crystal "template" is placed in contact with a sintered polycrystalline matrix and then heated to migrate the single-crystal boundary into the matrix. Millimeter-sized, stoichiometric single crystals of BaTiO3 were produced by heating polycrystalline matrix with a relative density of 97% and a Ba/Ti ratio of <1.00, which was bonded to a BaTiO3 single crystal, at temperatures above the eutectic temperature. Growth rates of 590,790, 180,350, and 42,59 ,m/h were observed for {111}-, {100}-, and {110}-oriented single-crystal templates, respectively. Lower-surface-energy facets were formed for {111}- and {100}-oriented templates, whereas {110} crystals maintained a {110} growth front, which indicated that this plane orientation was the lowest-energy surface in this system. SrTiO3 also was shown to be a suitable substrate for TGG of BaTiO3. [source]


    Growth and characterization of Nd, Yb , yttrium oxide nanopowders obtained by sol-gel method

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2007
    A. Rzepka
    Abstract Nanopowders of Y2O3 pure, doped and codoped by Nd3+, Yb3+ were obtained by sol-gel method. Solution with ethylene glycol was choosed as the proper solution where crystallites of powder with Nd and Yb dopants had the same size. Finally the one-phased compounds of Y2O3 doped 0.5 at% Nd and 1, 2 or 4 at% Yb were obtained. Grain growth and their morphology were investigated in various temperature and time of heating. The changes of crystallite sizes and lattice constants in relation to the heating time and temperature for the composition Y2O3 doped 0.5 at% Nd and 2 at% Yb are presented. Y2O3 containing 0,5 at% of Nd exhibits intense luminescence bands centered at 920 nm, 1100 nm and 1360 nm whereas a single band at about 1020 nm appears in samples co-doped with neodymium and ytterbium. Luminescence spectra recorded did not depend on the sample preparation procedure and size of grains. OH impurity affects critically the relaxation dynamics of luminescent ion in nanopowders. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Hot Isostatic Pressing of Transparent Nd:YAG Ceramics

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2009
    Sang-Ho Lee
    This paper demonstrates that fine-grained (2,3 ,m), transparent Nd:YAG can be achieved at SiO2 doping levels as low as 0.02 wt% by the sinter plus hot isostatic pressing (HIP) approach. Fine grain size is assured by sintering to 98% density, in order to limit grain growth, followed by HIP. Unlike dry-pressed samples, tape-cast samples were free of large, agglomerate-related pores after sintering, and thus high transparency (i.e., >80% transmission at 1064 nm) could be achieved by HIP at <1750C along with lower silica levels, thereby avoiding conditions shown to cause exaggerated grain growth. Grain growth was substantially limited at lower SiO2 levels because silica is soluble in the YAG lattice up to ,0.02,0.1 wt% at 1750C, thus allowing sintering and grain growth to occur by solid-state diffusional processes. In contrast, liquid phase enhanced densification and grain growth occur at ,0.08,0.14 wt% SiO2, especially at higher temperatures, because the SiO2 solubility limit is exceeded. [source]


    Microstructure Development in Unsupported Thin Films

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002
    Brian P. Gorman
    To better understand the role of the substrate in the microstructural evolution of thin films, unsupported nanocrystalline yttrium-stabilized zirconia (ZrO2:16%Y or YSZ) films were examined as a function of temperature and annealing time. Grain growth, texturing, and pinhole formation were measured using transmission electron microscopy (TEM) and electron diffraction. Films were produced and subsequently annealed on metallic grids using a previously developed technique that results in near full density films at low annealing temperatures. Microstructural evolution in these films was unique compared with constrained films. Grains were found to spheroidize much more readily, ultimately resulting in the formation of porosity and pinholes. Grain growth was found to stagnate at a size particular to each annealing temperature, presumably due to the effects of Zener pinning. It is proposed that the lack of substrate strain and confinement effects allows for the dominance of surface energetics with respect to microstructural evolution. [source]


    Microwave Hybrid Post-Heat Treatment of Reaction Sintered Alumina/Lanthanum Hexaaluminate Composite Ceramics,

    ADVANCED ENGINEERING MATERIALS, Issue 3 2010
    Zahra Negahdari
    One of the main problems in development of in situ reaction sintered alumina/lanthanum hexaaluminate composite ceramics is achievement of simultaneous densification and in situ formation of lanthanum hexaaluminate (LHA) platelets inside the matrix. Microwave hybrid post-sintering was investigated as a method to enhance the solid-state reaction of LHA formation and the densification of composite ceramics with 2.8,80 vol% LHA. Comparison of the conventionally and microwave assisted sintered alumina/lanthanum hexaaluminate composite ceramics revealed that utilization of microwave heating in second stage of sintering could enhance the solid-state reaction, the densification, and the anisotropic grain growth of the LHA platelets in ceramics containing more than 20 vol% LHA and for heat treatment at 1500,C. [source]


    Oriented Grain Growth Analyses With In Situ Annealing Experiments Using High Energy Synchrotron Radiation

    ADVANCED ENGINEERING MATERIALS, Issue 3 2010
    Caterina Elisabetta Tommaseo
    The development of the recrystallization and annealing textures of Al,Mn alloys with 0.4, 0.7 and 1,wt.-% manganese is analyzed using specific techniques that allow the detection of changes in grain orientation during in situ annealing. In order to investigate the evolution of texture components during annealing, highly rolled samples were annealed from room temperature to 500,C at a constant heating rate. The advantage of in situ annealing experiments using synchrotron radiation is the detection of grain orientations over time, which allows observation of the development of the recrystallization and annealing textures in a sample. In fact, the recrystallization and annealing textures in the Al,0.4Mn are characterized by an interruption in the detection of most of the grain orientations between 380 and 425,C and by competition between the cube {001}<100>, {011}<1-33>, {011}<0-11> and rotated-cube {001}<110> grain orientations, where the latter is detected until the end of the experiment. In the Al,0.7Mn sample a competition between the cube {001}<100>, {011}<100>, and rotated cube {001}<110>, {011}<0,11> grain orientations is observed. In the sample with the highest manganese concentration (1,wt.-%) an unhindered grain growth of all possible grain orientations with a high amount of the {011}<0-11> grain orientation is observed. The evolution of the resulting local textures is discussed in terms of preferentially oriented grain growth depending on the temperature and manganese concentration. [source]


    Neutron Reflectometry: A Tool to Investigate Diffusion Processes in Solids on the Nanometer Scale,

    ADVANCED ENGINEERING MATERIALS, Issue 6 2009
    Harald Schmidt
    Abstract The investigation of self-diffusion for the characterization of kinetic process in solids is one of the most fundamental tasks in materials science. We present the method of neutron reflectometry (NR), which allows the detection of extremely short diffusion lengths in the order of 1,nm and below at corresponding low self-diffusivities between 10,25 and 10,20,m2 s,1. Such a combination of values cannot be achieved by conventional methods of diffusivity determination, like the radiotracer method, secondary ion mass spectrometry, quasielastic neutron scattering, or nuclear magnetic resonance. Using our method, the extensive characterization of materials which are in a non-equilibrium state, like amorphous or nanocrystalline solids becomes possible. Due to the small experimentally accessible diffusion length microstructural changes (grain growth and crystallization) taking place simultaneously during the actual diffusion experiment can be avoided. For diffusion experiments with NR isotope multilayers are necessary, which are chemical homogeneous but isotope modulated films. We illustrate the basic aspects and potential of this technique using model systems of different classes of materials: single crystalline germanium, amorphous silicon nitride, and nanocrystalline iron. [source]


    Effects of Zirconium Additions on the Microstructure of As-Cast and Aged AZ91 Magnesium Alloy

    ADVANCED ENGINEERING MATERIALS, Issue 3 2009
    Farhoud Kabirian
    The effects of Zr addition on the microstructure of AZ91 alloy were investigated under as-cast and isothermally aged conditions. The microstructures contained a eutectic , -Mg17Al12 phase together with fine Al,Zr intermetallic compounds. These intermetallic compounds inhibited grain growth during the 420,C isothermal aging of Zr-containing alloys. Microstructural changes caused by Zr additions were most probably due to the consumption of Al by Zr, and redistribution of Al during solidification of dendrites. [source]


    Microstructures and Mechanical Properties of Hot-Pressed ZrB2 -Based Ceramics from Synthesized ZrB2 and ZrB2 -ZrC Powders,

    ADVANCED ENGINEERING MATERIALS, Issue 3 2009
    Wei-Ming Guo
    The influence of ZrC on the microstructure and mechanical properties of ZrB2 -SiC ceramics was investigated. SEM observation showed that the presence of ZrC greatly inhibited the grain growth of ZrB2 and SiC phases. With the introduction of ZrC, the Vickers' hardness, fracture toughness, and bending strength of the sintered ceramics increased significantly. [source]


    Diffusion in Nanocrystalline Metals and Alloys,A Status Report,

    ADVANCED ENGINEERING MATERIALS, Issue 5 2003
    R. Wrschum
    Abstract Diffusion is a key property determining the suitability of nanocrystalline materials for use in numerous applications, and it is crucial to the assessment of the extent to which the interfaces in nanocrystalline samples differ from conventional grain boundaries. The present article offers an overview of diffusion in nanocrystalline metals and alloys. Emphasis is placed on the interfacial characteristics that affect diffusion in nanocrystalline materials, such as structural relaxation, grain growth, porosity, and the specific type of interface. In addition, the influence of intergranular amorphous phases and intergranular melting on diffusion is addressed, and the atomistic simulation of GB structures and diffusion is briefly summarized. On the basis of the available diffusion data, the diffusion-mediated processes of deformation and induced magnetic anisotropy are discussed. [source]


    Time,Temperature,Transformation (TTT) Diagrams for Crystallization of Metal Oxide Thin Films

    ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
    Jennifer L. M. Rupp
    Abstract Time,temperature,transformation (TTT) diagrams are proposed for the crystallization of amorphous metal oxide thin films and their specific characteristics are discussed in comparison to glass-based materials, such as glass-ceramics and metallic glasses. The films crystallize from amorphous to full crystallinity in the solid state. As an example the crystallization kinetics for a single-phase metal oxide, ceria, and its gadolinia solid solutions are reported made by the precipitation thin-film method spray pyrolysis. The crystallization of an amorphous metal oxide thin film generally follows the Lijschitz,Sletow,Wagner (LSW) Ostwald ripening theory: Below the percolation threshold of 20 vol% single grains crystallize in the amorphous phase and low crystallization rates are measured. In this state no impact of solute on crystallization is measurable. Once the grains form primary clusters above the threshold the solute slows down crystallization (and grain growth) thus shifting the TTT curves of the doped ceria films to longer times and higher temperatures in comparison to undoped ceria. Current views on crystallization of metal oxide thin films, the impact of solute dragging, and primary TTT diagrams are discussed. Finally, examples on how to use these TTT diagrams for better thermokinetic engineering of metal oxide thin films for MEMS are given, for example, for micro-Solid Oxide Fuel Cells and resistive sensors. In these examples the electrical properties depend on the degree of crystallinity and, thereby, on the TTT conditions. [source]


    Crystallization and Grain Growth Kinetics for Precipitation-Based Ceramics: A Case Study on Amorphous Ceria Thin Films from Spray Pyrolysis

    ADVANCED FUNCTIONAL MATERIALS, Issue 17 2009
    Jennifer L. M. Rupp
    Abstract The introductory part reviews the impact of thin film fabrication, precipitation versus vacuum-based methods, on the initial defect state of the material and microstructure evolution to amorphous, biphasic amorphous-nanocrystalline, and fully nanocrystalline metal oxides. In this study, general rules for the kinetics of nucleation, crystallization, and grain growth of a pure single-phase metal oxide thin film made by a precipitation-based technique from a precursor with one single organic solvent are discussed. For this a complete case study on the isothermal and non-isothermal microstructure evolution of dense amorphous ceria thin films fabricated by spray pyrolysis is conducted. A general model is established and comparison of these thin film microstructure evolution to kinetics of classical glass-ceramics or metallic glasses is presented. Knowledge on thermal microstructure evolution of originally amorphous precipitation-based metal oxide thin films allows for their introduction and distinctive microstructure engineering in devices-based on microelectromechanical (MEMS) technology such as solar cells, capacitors, sensors, micro-solid oxide fuel cells, or oxygen separation membranes on Si-chips. [source]


    The preservation of seismic anisotropy in the Earth's mantle during diffusion creep

    GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2009
    J. Wheeler
    SUMMARY Seismic anisotropy in the Earth, particularly in the mantle, is commonly interpreted as the result of solid-state deformation by dislocation creep that induces a lattice preferred orientation (LPO). Diffusion creep operates where stress levels are lower and/or grain sizes smaller. It is often assumed that diffusion creep induces grain rotations that eventually destroy any existing LPO. A new numerical test of this assumption shows that it is not necessarily the case: diffusion creep will create some relative grain rotations, but rotation rates decrease through time. Hence, when microstructural change due to diffusion creep dominates that due to grain growth, defined here as ,type P' behaviour (the converse being ,type O' behaviour), the model indicates that LPO will be weakened but preserved (for a variety of strain paths including both pure and simple shear). One measure of anisotropy is the proportional difference in shear wave velocities for different polarization vectors (AVs). A model olivine microstructure with equant grains and initial maximum AVs of 10.0 percent has this value reduced to 6.7 per cent when ,rotational steady state' is attained. Other models with different initial maximum AVs values exhibit final maximum AVs values more than half the initial values. If the grains are initially elongate by a factor of 2, maximum AVs is reduced just slightly, to 8.5 per cent. Thus, when grain growth plays a subordinate role to the deformation, diffusion creep weakens seismic anisotropy by a factor of less than 2 (using maximum AVs as a measure and olivine as an example). Consequently, the link between seismic anisotropy and deformation mechanism in the mantle requires reappraisal: regions with LPO may comprise material which once deformed by dislocation creep, but is now deforming by diffusion creep in a rotational steady state. [source]


    Textured Microstructure and Dielectric Properties Relationship of BaNd2Ti5O14 Thick Films Prepared by Electrophoretic Deposition

    ADVANCED FUNCTIONAL MATERIALS, Issue 7 2009
    Zhi Fu
    Abstract An alternative approach to tailor the temperature coefficient of permittivity (TC,r) of high Q dielectric BaO,Re2O3,TiO2 (Re: rare earth elements) thick films is presented. 10- to 80-m-thick BaNd2Ti5O14 (BNT) films are fabricated by electrophoretic deposition on Pt foils under different processing conditions. Observed anisotropic grain growth is facilitated by constrained sintering. The increase of the sintering temperature increases markedly the aspect ratio of the grains, decreases the dielectric permittivity and TC,r changes from ,114 to +12,ppm C,1. By controlling the sintering temperature, near-zero TC,r, high Q thick films can be fabricated with 45,<,,r,<,70. These findings are of technological relevance since they demonstrate that control of substrate constraint and sintering conditions can be used to control grain anisotropy and thus microwave properties of the BaO,Re2O3,TiO2. The thick films facilitate scaling to small device sizes for high frequency operation. Similar observations are expected in other microwave systems thus opening further technological opportunities. [source]


    Nanoparticle Coating for Advanced Optical, Mechanical and Rheological Properties,

    ADVANCED FUNCTIONAL MATERIALS, Issue 16 2007
    F. Hakim
    Abstract Primary titania nanoparticles were coated with ultrathin alumina films using Atomic Layer Deposition (ALD). The deposited films were highly uniform and conformal with an average growth rate of 0.2,nm per coating cycle. The alumina films eliminated the surface photocatalytic activity of titania nanoparticles, while maintained their original extinction efficiency of ultraviolet light. Deposited films provided a physical barrier that effectively prevented the titania surface from oxidizing organic material whereas conserving its bulk optical properties. Parts fabricated from coated powders by pressureless sintering had a 13,% increase in surface hardness over parts similarly fabricated from uncoated particles. Owing to its homogeneous distribution, the secondary alumina phase suppressed excessive grain growth. Alumina films completely reacted during sintering to form aluminum titanate composites, as verified by XRD. Coated particles showed a pseudoplastic behavior at low shear rates due to modified colloidal forces. This behavior became similar to the Newtonian flow of uncoated nanoparticle slurries as the shear rate increased. Suspensions of coated particles also showed a decreased viscosity relative to the viscosity of uncoated particle suspensions. [source]


    A Screening Design Approach for the Understanding of Spark Plasma Sintering Parameters: A Case of Translucent Polycrystalline Undoped Alumina

    INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2010
    Yann Aman
    An experimental screening design was used to evaluate the effects of spark plasma sintering (SPS) parameters such as heating rate, sintering temperature, dwell duration, and green-shaping processing on the relative density, grain size, and the optical properties of polycrystalline alumina (PCA). It is shown that heating rate and sintering temperature are the most critical factors for the densification of PCA during SPS. Green-shaping processing could prevent grain growth at low SPS sintering temperatures. No predominant SPS parameters are observed on the optical properties. Hence, the optical properties of PCA are controlled by microstructural evolution during the SPS process. [source]


    Heat Shock Protein in Developing Grains in Relation to Thermotolerance for Grain Growth in Wheat

    JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 1 2010
    P. Sharma-Natu
    Abstract Wheat (Triticum aestivum L.) cvs DL 153-2 and HD 2285 (relatively tolerant), HD 2329 and WH 542 (relatively susceptible), were grown under normal (27 November) and late (28 December) sown conditions. In another experiment, these cultivars were grown under normal sowing and at anthesis stage, they were transferred to control (C) and heated (H) open top chambers (OTCs). Under late sowing, wheat cultivars were exposed to a mean maximum temperature of up to 3.6 C higher than normal sowing and in H-OTCs, mean maximum temperature was 3.2 C higher than C-OTCs during grain growth period. Heat susceptibility index (S) for grain growth and grain yield was determined at maturity in both the experiments. The level of heat shock protein (HSP 18) in the developing grains was determined in C- and H-OTC grown plants and in normal and late sown plants by Western blot analysis. The moderately high temperature exposure increased the accumulation of HSP 18 in the developing grains. The relatively tolerant cultivars, as also revealed from S, showed a greater increase in HSP 18 compared with susceptible types in response to moderate heat stress. An association of HSP 18 with thermotolerance for grain growth in wheat was indicated. [source]