Sintering

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Sintering

  • laser sintering
  • plasma sintering
  • pressureless sintering
  • selective laser sintering
  • spark plasma sintering

  • Terms modified by Sintering

  • sintering additive
  • sintering aid
  • sintering condition
  • sintering method
  • sintering parameter
  • sintering process
  • sintering shrinkage
  • sintering stress
  • sintering technique
  • sintering temperature
  • sintering time

  • Selected Abstracts


    Preparation of Titanium Foams by Slip Casting of Particle Stabilized Emulsions,

    ADVANCED ENGINEERING MATERIALS, Issue 8 2009
    Bram Neirinck
    Bulk titanium foams were prepared by emulsion templating during slip casting. The emulsion template was stabilized using partially hydrophobized titanium particles while the continuous phase consisted of a titanium hydride powder suspension. Sintering was performed in inert atmosphere. The use of titanium hydride resulted in lower sintering temperatures and denser, stronger struts. Both homogeneous foams with high compressive strength and structures with a gradient in pore size were obtained. [source]


    Size Effect on Properties of Varistors Made From Zinc Oxide Nanoparticles Through Low Temperature Spark Plasma Sintering

    ADVANCED FUNCTIONAL MATERIALS, Issue 11 2009
    Lna Saint Macary
    Abstract Conditions for the elaboration of nanostructured varistors by spark plasma sintering (SPS) are investigated, using 8-nm zinc oxide nanoparticles synthesized following an organometallic approach. A binary system constituted of zinc oxide and bismuth oxide nanoparticles is used for this purpose. It is synthesized at room temperature in an organic solution through the hydrolysis of dicyclohexylzinc and bismuth acetate precursors. Sintering of this material is performed by SPS at various temperatures and dwell times. The determination of the microstructure and the chemical composition of the as-prepared ceramics are based on scanning electron microscopy and X-ray diffraction analysis. The nonlinear electrical characteristics are evidenced by current,voltage measurements. The breakdown voltage of these nanostructured varistors strongly depends on grain sizes. The results show that nanostructured varistors are obtained by SPS at sintering temperatures ranging from 550 to 600,C. [source]


    Comparative study of aromatization selectivity during N-heptane reforming on sintered Pt/Al2O3 and Pt-Re/Al2O3 catalysts

    JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2008
    Alfred A Susu
    Abstract BACKGROUND: The metal dispersed over a support can be present as small crystallites with sizes less than 5 nm. The smaller crystallites favour aromatization while larger crystallites favour cracking/hydrogenolysis. Sintering results in the agglomerization of smaller metal crystallites. Correlation of size with aromatization selectivity was investigated. RESULTS: The primary products of n-heptane reforming on fresh Pt were methane, toluene, and benzene, while on fresh Pt-Re, the only product was methane. Both catalysts exhibited enhanced aromatization selectivity at different oxygen sintering temperatures. The reaction products ranged from only toluene at 500 C sintering temperature to methane at a sintering temperature of 650 C with no reaction at 800 C for the Pt/Al2O3 catalyst. On Pt-Re/Al2O3 catalyst, methane was the sole product at a sintering temperature of 500 C while only toluene was produced at a sintering temperature of 800 C. CONCLUSION: This is the first time that sintering has been used to facilitate aromatization of supported Pt and Pt-Re catalysts. A superior selectivity behaviour associated with bi-metallic Pt catalysts is established. It was found that no reaction occurred on Pt catalyst after sintering at 800 C whereas sintering Pt-Re at 800 C promoted aromatization solely to toluene. Copyright 2008 Society of Chemical Industry [source]


    Sintering of Transparent Yttria Ceramics in Oxygen Atmosphere

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010
    Yihua Huang
    A novel method is reported for the preparation of transparent polycrystalline yttria ceramics in oxygen atmosphere. Zirconia and other additives were added to control the grain growth. Pores can be eliminated clearly at a temperature <1650C with the grain size around 1 ,m. The grain growth kinetics and the mechanisms controlling grain growth were studied. Sintering in oxygen atmosphere is beneficial for making samples with a big size at low cost and avoiding the posttreatment of samples sintered in vacuum or hydrogen atmosphere. [source]


    Sintering and Microwave Dielectric Properties of the LiNb0.63Ti0.4625O3 Ceramics with the B2O3,SiO2 Liquid-Phase Additives

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009
    Yanping Long
    The effect of B2O3,SiO2 liquid-phase additives on the sintering, microstructure, and microwave dielectric properties of LiNb0.63Ti0.4625O3 ceramics was investigated. It was found that the sintering temperature could be lowered easily, and the densification and dielectric properties of LiNb0.63Ti0.4625O3 ceramics could be greatly improved by adding a small amount of B2O3,SiO2 solution additives. No secondary phase was observed for the ceramics with B2O3,SiO2 additives. With the addition of 0.10 wt% B2O3,SiO2, the ceramics sintered at 900C showed favorable microwave dielectric properties with ,r=71.7, Qf=4950 GHz, and ,f=,2.1 ppm/C. The energy dispersive spectra analysis showed an excellent co-firing interfacial behavior between the LiNb0.63Ti0.4625O3 ceramic and the Ag electrode. It indicated that LiNb0.63Ti0.4625O3 ceramics with B2O3,SiO2 solution additives have a number of potential applications on passive integrated devices based on the low-temperature co-fired ceramics technology. [source]


    Pressureless Densification of Zirconium Diboride with Boron Carbide Additions

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2006
    S. C. Zhang
    Zirconium diboride (ZrB2) was densified (>98% relative density) at temperatures as low as 1850C by pressureless sintering. Sintering was activated by removing oxide impurities (B2O3 and ZrO2) from particle surfaces. Boron oxide had a high vapor pressure and was removed during heating under a mild vacuum (,150 mTorr). Zirconia was more persistent and had to be removed by chemical reaction. Both WC and B4C were evaluated as additives to facilitate the removal of ZrO2. Reactions were proposed based on thermodynamic analysis and then confirmed by X-ray diffraction analysis of reacted powder mixtures. After the preliminary powder studies, densification was studied using either as-received ZrB2 (surface area ,1 m2/g) or attrition-milled ZrB2 (surface area ,7.5 m2/g) with WC and/or B4C as a sintering aid. ZrB2 containing only WC could be sintered to ,95% relative density in 4 h at 2050C under vacuum. In contrast, the addition of B4C allowed for sintering to >98% relative density in 1 h at 1850C under vacuum. [source]


    Sintering of Lead Titanate Using a Spark-Plasma-Sintering Technique

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2004
    Kazuyuki Kakegawa
    Lead titanate (PbTiO3) is difficult to sinter without additives, even when a spark-plasma-sintering technique is applied. The high tetragonality, c/a, of PbTiO3 causes destructive strain after sintering. We found that a sintered body of PbTiO3 could be obtained, when the PbO/TiO2 value was <0.9. However, decreasing the ratio did not increase the bulk density; rather, it caused a decrease in the grain size. The mechanical strain that resulted from the phase change from cubic, at the sintering temperature, to tetragonal, at room temperature after the sintering, was released by the decrease in the grain size. [source]


    Sintering of AlN Using CaO-Al2O3 as a Sintering Additive: Chemistry and Microstructural Development

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2002
    Eirik Hagen
    The densification of aluminum nitride using Ca12Al14O33 as a sintering aid has been studied with emphasis on the effect of using coarse or fine powder, the amount of sintering aid, the sintering temperature, and embedding. Both crystalline and amorphous grain boundary phases were observed. Significant weight losses were observed for coarse-grained samples, and if suitable embedding was not used. Porous and coarse-grained ceramics with high contiguity and minor amounts of secondary phases were obtained by enhanced evaporation while dense ceramics were obtained limiting the evaporation. High weight losses in the graphite environment resulted in formation of a dense AlN surface layer. [source]


    Sintering and Microstructure Modification of Mullite/Zirconia Composites Derived from Silica-Coated Alumina Powders

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2001
    Viktor Yaroshenko
    This paper addresses the densification and microstructure development during firing of mullite/zirconia composites made from silica-coated-alumina (SCA) microcomposite powders. Densification occurs in two stages: in the presence of a silica,alumina mixture and after conversion to mullite. The first stage of densification occurs through transient viscous phase sintering (TVS). This is best promoted by rapid heating, which delays the crystallization of silica to higher temperatures. A further sintering stage is observed following mullitization. The introduction of seeds promotes solid-state sintering, most probably due to refinement of the mullite matrix. For seed concentrations up to about 1% the sintering kinetics depend on seed concentration. This suggests that nucleation still remains the rate-controlling mullitization step. Above this concentration the reaction becomes growth controlled. Introduction of seeds also promotes direct mullitization without transient zircon formation that was observed in a previous study of the same process without seeding. Seeding also promotes the development of elongated grains by way of a solid-state recrystallization process. [source]


    Sintering Behavior of Nanocrystalline Zirconia Doped with Alumina Prepared by Chemical Vapor Synthesis

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000
    Vladimir V. Srdi
    Powders of nanocrystalline zirconia doped with 3,30 mol% alumina have been synthesized using chemical vapor synthesis (CVS). Dense or mesoporous ceramics of small and narrowly distributed grain and pore sizes in the nanometer range are obtained via pressureless vacuum sintering. The microstructural development of the doped samples is strongly dependent on the alumina content. Sintering of zirconia samples with 3 and 5 mol% alumina at temperatures of 1000C for 1 h results in fully dense, transparent ceramics with grain sizes of 40,45 nm and homogeneous microstructures. [source]


    Sintering of Partially Stabilized Zirconia by Microwave Heating Using ZnO,MnO2,Al2O3 Plates in a Domestic Microwave Oven

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000
    Satoru Fujitsu
    Partially stabilized zirconia (PSZ) powders were fully densified by microwave heating using a domestic microwave oven. Pressed powder compacts of PSZ were sandwiched between two ZnO,MnO2,Al2O3 ceramic plates and put into the microwave oven. In the first step, PSZ green pellets were heated by self-heating of ZnO,MnO2,Al2O3 ceramics (1000C). In the second step, the heated PSZ pellets absorbed microwave energy and self-heated up to a higher temperature (1250C), leading to densification. The density of PSZ obtained by heating in the microwave oven for 16 min was 5.7 g/cm3, which was approximately equal to the density of bodies sintered at 1300C for 4 h or 1400C for 16 min by the conventional method. The average grain size of the sample obtained by this method was larger than the average grain size of samples sintered by the conventional method with a similar heating process. [source]


    Ink-Jet Printing of Metallic Nanoparticles and Microemulsions

    MACROMOLECULAR RAPID COMMUNICATIONS, Issue 4 2005
    Alexander Kamyshny
    Abstract Summary: Two types of ink-jet inks are presented: ink containing an aqueous dispersion of silver nanoparticles and an oil-in-water microemulsion-based ink. The metallic ink contains nanoparticles of silver, which are formed in the presence of an ionic polymeric stabilizer. Sintering of the printed image obtained with the use of such silver-based inks at temperatures as low as 300,C results in formation of patterns possessing noticeable conductivity. The microemulsion inks are based on a thermodynamically stable microemulsion, in which the dispersed oil phase is a volatile solvent containing a water-insoluble colorant. After contact of the jetted ink droplets with a substrate, nanodroplets of the microemulsion are converted into nanoparticles of the solubilized colorant. In some cases, it was found that the evaporation of microemulsion ink droplets leads to formation of rings composed of ordered nanoparticles. Scheme of ink-jet printing of an oil-in-water microemulsion followed by conversion of the nanodroplets into nanoparticles, caused by quick evaporation of the solvent within the microemulsion droplets. Therefore, the ink behaves as a dye-based ink prior to printing, but after printing it behaves like a pigment-based ink. [source]


    Sintering of porous silicon

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003
    G. Mller
    Abstract In this paper we study the dynamics of pore coarsening in porous silicon during annealing. We model the sintering of pores with two-dimensional and three-dimensional simulations. We compare our simulations with transmission and scanning electron micrographs of experimentally annealed porous silicon samples. Simulations and experiments yield lognormally distributed pore sizes. The quantitative agreement between simulation and experiment shows that minimization of the inner surface energy is the driving force for morphological changes in PS during annealing. Surface diffusion is the dominant mechanism in the reorganization of Si-atoms in PS. [source]


    Growth and characterization of magneto-optical YFeO3 crystals

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2007
    Hui Shen
    Abstract The floating zone growth of magneto-optical crystal YFeO3 has been investigated. The polycrystalline feed rod was prepared by a pressure of 250MPa and sintering at about 1500C. A crack- free YFeO3 single crystal has been successfully grown. The crystal preferred to crystallize along <100> direction with about 10 deviation. The X-ray rocking curve of the crystal has a FWHM of 24 arcsec, confirming the high crystal quality of the sample. The (100) plane was etched by hot phosphoric acid and the dislocation density was about 104/cm2. A thin outer layer with Y2O3 -rich composition was found at the periphery of as-grown crystals, which was attributed to the Fe2O3 evaporation during growth. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Mechanical activation of precursors for nanocrystalline materials

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2003
    H. Heegn
    Abstract Nanostructured materials win big scientific interest and increasingly economic meaning through their specific exceptional properties. Precursors that were compacted by pressing and sintering are normally used preparation of materials. In present work, the influence of mechanical activation by grinding on the structure as well as on compacting and sintering behavior of oxides from magnesium, aluminium and silicon has been investigated. Starting materials for each metal oxide differ in microstructure, dispersity, and porosity. The influence of mechanical activation on the destruction of crystalline structure to nanocrystalline, as well as to the amorphous stage and the compaction of powders with nano-particles, as well as structures with nanoscale pores have been compared. The possibilities of the consolidation of nanostructured materials were investigated. The mechanical activation took place in a disc vibration mill. The mechanical activated materials as well as their pressing and their sintering products were characterized by density, particle-sizedistribution, specific surface, pore-structure, microstructure, and crystallite size by X-ray powder diffraction (XRD). The mechanical activation of the model-substances led, in most cases, to an improvement of the compaction properties; thus, this improvement can be achieved with subsequent sintering densities up to 98% of the theoretical density. From these experiments, generalizations transferable to other materials can be made. [source]


    Rheological behavior of crystallizing palm oil

    EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 10 2006
    Veerle De Graef
    Abstract The static isothermal crystallization of palm oil was studied by oscillatory rheology. The phase angle, complex modulus, storage modulus and loss modulus were followed as a function of the crystallization time. Various crystallization temperatures were applied, and the results obtained by oscillatory rheology were compared with crystallization data obtained by more classical techniques like differential scanning calorimetry (DSC) and pulsed nuclear magnetic resonance (pNMR). It was shown that oscillatory rheology is a valuable complementary method to DSC and pNMR to evaluate primary crystallization. Like DSC and pNMR, oscillatory rheology is capable of differentiating whether crystallization occurs in a two-stage or a single-stage process. In addition, oscillatory measurements also allow the evaluation of aggregation, network formation and post-hardening events like sintering and thus provide information on the crystal network and the final macroscopic properties of the crystallized sample. [source]


    Low Temperature Fabrication of ,-TCP,PCL Nanocomposites for Bone Implants,

    ADVANCED ENGINEERING MATERIALS, Issue 8 2010
    Michael Bernstein
    Abstract A method to fabricate strong bioresorbable calcium phosphate,polymer nanocomposites with low polymer content without exposing the material to excessively high-processing temperatures is reported. Dense ,-TCP-based nanocomposites containing 5 or 15,vol% of uniformly distributed polycaprolactone (PCL) polymer were obtained by mixing ,-TCP nanopowder with PCL dissolved in chloroform followed by room temperature consolidation at the high pressure of 2.5,GPa (cold sintering). The composites had an attractive combination of compressive strength and ductility, and their dissolution behavior was similar to that of pure cold sintered ,-TCP. The immersion of ,-TCP,PCL composites in simulated body fluid (SBF) yielded in vitro deposition of a bone-like apatite layer suggesting the ability of these materials to bind to native bone tissue upon implantation. [source]


    Oxidation Resistance of Multilayer SiC for Space Vehicle Thermal Protection Systems,

    ADVANCED ENGINEERING MATERIALS, Issue 7 2010
    Claudia Milena Vega Bolivar
    The oxidation resistances of different kinds of SiC-based laminates are compared. The materials under investigation are produced by tape casting of green ceramic sheets, followed by stacking of the sheets in a multilayer structure and laminate consolidation by de-binding and sintering. Three kinds of specimens are tested: multilayer SiC with fully dense layers, multilayer SiC integrating porous layers and multilayer composites made by stacking SiC/Cf composite layers. Two kinds of chopped carbon fibres (polyamide coated and uncoated) are used for the manufacture of the composite sheets. The oxidation behaviour is investigated by simultaneous TGA,DTA,MS analysis. Specimens are also submitted to a long-term oxidation treatment (30,h at 1,600,C in flowing air) and their microstructure and mechanical behaviour compared before and after oxidation. This assessment shows that the integration of porous or composite layers in the multilayer architecture does not worsen the oxidation resistance. In every case the formation of a surface passivating layer prevents major degradation phenomena, so that only small changes in the mechanical features are found after oxidation. [source]


    Processing of Carbon Nanofiber Reinforced ZrB2 Matrix Composites for Aerospace Applications,

    ADVANCED ENGINEERING MATERIALS, Issue 7 2010
    Jorge Barcena
    Ceramic matrix composites (CMCs) based on zirconium diboride (ZrB2) reinforced by vapor grown carbon nanofibers are a potential constituent of reusable thermal protection systems. A manufacturing procedure was devised that involved the fabrication of thin films by tape casting to obtain a layer that could be integrated into a more complex system. Higher thermal conductivities and improved toughness can be expected for nanofiber additions, as compared to the matrix alone. Consolidation by hot-pressing was more effective than pressureless sintering, in terms of the final relative density and flatness of specimens. Examination of microstructures showed that few carbon nanofibers were present in the matrix after consolidation by sintering, which was attributed to a reaction between the nanofibers and zirconium oxide present on the surface of the ZrB2 powder. As a solution, oxygen impurities from the boride powders were removed by reduction with carbon coatings derived from phenolic resin. The deleterious reaction was avoided, but residual carbon remained at the grain boundaries, likely from decomposition of the binder. The use of an alternative binder (PMMA vs. PVB) will be used in future studies to reduce the residual carbon content. Further, consolidation by Spark Plasma Sintering (SPS) will be explored to further reduce the reaction of surface oxides with the nanofibers. Finally, characterization of the microstructure at the nanometric level and further determination of the mechanical and thermal properties will be conducted as part of future studies. [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]


    Microstructure and Compression Strength of Novel TRIP-Steel/Mg-PSZ Composites,

    ADVANCED ENGINEERING MATERIALS, Issue 12 2009
    Horst Biermann
    Abstract Novel composites on basis of austenitic stainless TRIP-steel as matrix with reinforcements of Mg-PSZ are presented. Compact rods were produced by cold isostatic pressing and sintering, square honeycomb samples by the ceramic extrusion technique. The samples are characterized by optical and scanning electron microscopy before and after deformation, showing the microstructure and the deformation- induced martensite formation. The mechanical properties of samples with 5,vol% zirconia are superior compared to zirconia-free samples and composites with higher zirconia contents in terms of bending and compression tests. The honeycomb samples exhibit extraordinary high specific energy absorption in compression. [source]


    Creating Aligned, Elongated Pores in Titanium Foams by Swaging of Preforms with Ductile Space-Holder,

    ADVANCED ENGINEERING MATERIALS, Issue 1-2 2009
    Yasumasa Chino
    Preforms of titanium powders containing a naphthalene-based space-holder phase are swaged. The elongated space-holder particles are sublimated and the preform is sintered, resulting in titanium foams with 49,65% porosity consisting of: a) small equiaxed pores from incomplete powder sintering and b) larger, elongated pores replicating the space-holder, which are aligned along the swaging direction. The foam carbon content (0.39,wt%) is below the value for severe titanium embrittlement. [source]


    Fatigue of Metal Hollow Spheres Structures,

    ADVANCED ENGINEERING MATERIALS, Issue 3 2008
    O. Caty
    Fatigue properties of three kinds of hollow metal spheres structures were determined in compression/compression. These results were completed with a fatigue damage process study by ex-situ X-ray tomography and a finite element simulation using tomographic 3D images. All these data permitted to understand the chronology of damage in the structure. The difference in behaviour of the three kinds of materials is mainly explained by the process root used (brazing and sintering) and by the nature of the constitutive material. [source]


    Microstructure and Properties of Pressureless Sintered HfB2 -Based Composites with Additions of ZrB2 or HfC,

    ADVANCED ENGINEERING MATERIALS, Issue 10 2007
    L. Silvestroni
    Ternary HfB2 -ZrB2 and HfB2 -HfC composites (see figure) with 20,vol.-% MoSi2 were produced from commercial powder and densified through pressureless sintering. Dense materials with fine microstructures were obtained at 1900,1950,C. Flexural strength at 1500,C confirmed the excellent stability of the composites at high temperature. [source]


    Process Shrinkage and Accuracy during Indirect Laser Sintering of Aluminium,

    ADVANCED ENGINEERING MATERIALS, Issue 4 2006
    B. Sercombe
    In this paper we have investigated the shrinkage and accuracy of indirect selective laser sintered aluminium. The majority of the ,1.2-1.4% linear shrinkage occurs during the infiltration of the skeleton structure. By optimising scale and offset parameters during selective laser sintering of the preforms, accuracy similar to that of casting processes can be achieved. [source]


    Size Effect on Properties of Varistors Made From Zinc Oxide Nanoparticles Through Low Temperature Spark Plasma Sintering

    ADVANCED FUNCTIONAL MATERIALS, Issue 11 2009
    Lna Saint Macary
    Abstract Conditions for the elaboration of nanostructured varistors by spark plasma sintering (SPS) are investigated, using 8-nm zinc oxide nanoparticles synthesized following an organometallic approach. A binary system constituted of zinc oxide and bismuth oxide nanoparticles is used for this purpose. It is synthesized at room temperature in an organic solution through the hydrolysis of dicyclohexylzinc and bismuth acetate precursors. Sintering of this material is performed by SPS at various temperatures and dwell times. The determination of the microstructure and the chemical composition of the as-prepared ceramics are based on scanning electron microscopy and X-ray diffraction analysis. The nonlinear electrical characteristics are evidenced by current,voltage measurements. The breakdown voltage of these nanostructured varistors strongly depends on grain sizes. The results show that nanostructured varistors are obtained by SPS at sintering temperatures ranging from 550 to 600,C. [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]


    Microwave Flash Sintering of Inkjet-Printed Silver Tracks on Polymer Substrates

    ADVANCED MATERIALS, Issue 47 2009
    Jolke Perelaer
    Microwave flash sintering of inkjet printed colloidal silver dispersions on thin polymer substrates was studied as a function of the antenna area and initial resistance. The presence of conductive antennae promotes nanoparticle sintering in pre-dried ink lines (see figure). For dried nanoparticle inks connected to antennae, sintering times of 1 s are sufficient to obtain pronounced nanoparticle sintering and conductivities between 10 and 34% compared to bulk silver. [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]