Sintering Temperature (sintering + temperature)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Sintering Temperature

  • lower sintering temperature


  • Selected Abstracts


    Lightweight Porcelain Stoneware by Engineered CeO2 Addition,

    ADVANCED ENGINEERING MATERIALS, Issue 1-2 2010
    Enrico Bernardo
    The use of porcelain stoneware in innovative applications such as the covering of internal walls or the manufacturing of ventilated facades may be limited by its relatively high density. In this paper, we discuss the achievement of a reduction in density of about 30%, coupled to a limited water absorption (about 2%), by the addition of CeO2 to the raw materials. This additive provides some porosity due to the evolution of oxygen, in turn caused by the high temperature reduction to Ce2O3. This gas formation depends both on sintering temperature, holding time, and is obviously affected by the concentration of additive. Two different processing strategies were found to match the density and water absorption requirements for the application of stoneware tiles. One involved the the control of the CeO2 content together with processing at high temperature for a limited holding time; the other one corresponded to the fabrication of a graded material, comprising a highly porous core (produced using a high content of CeO2) sandwiched between two external compact surface layers. [source]


    Multi-walled Carbon Nanotube-Reinforced Hydroxyapatite Layers on Ti6Al4V Medical Implants by Electrophoretic Deposition (EPD),

    ADVANCED ENGINEERING MATERIALS, Issue 1-2 2008
    C. Kaya
    Sol-gel synthesised nano-size hydroxyapatite (HA) powders were dispersed in water-based suspensions with the addition of multi-walled carbon nanotubes. Ti6Al4V medical alloys were coated with monolithic and carbon nanotube-reinforced HA using electrophoretic deposition (EPD) in an attempt to control deposit structure and thickness. It was shown that the sintering temperature of the deposited HA layers was significantly lowered by the use of sinter active nano-powders. Moreover the addition of carbon nanotubes increased the bonding strength of the EPD-formed layers to the metallic substrate. The cost-effective EPD technique used in the present work has high industrial potential for coating metallic medical implants with composite bioactive layers. [source]


    Optimisation and Evaluation of La0.6Sr0.4CoO3,,,, Cathode for Intermediate Temperature Solid Oxide Fuel Cells

    FUEL CELLS, Issue 5 2009
    Youkun Tao
    Abstract In this work, La0.6Sr0.4CoO3,,,,/Ce1,,xGdxO2,,,, (LSC/GDC) composite cathodes are investigated for SOFC application at intermediate temperatures, especially below 700,C. The symmetrical cells are prepared by spraying LSC/GDC composite cathodes on a GDC tape, and the lowest polarisation resistance (Rp) of 0.11,,,cm2 at 700,C is obtained for the cathode containing 30,wt.-% GDC. For the application on YSZ electrolyte, symmetrical LSC cathodes are fabricated on a YSZ tape coated on a GDC interlayer. The impact of the sintering temperature on the microstructure and electrochemical properties is investigated. The optimum temperature is determined to be 950,C; the corresponding Rp of 0.24,,,cm2 at 600,C and 0.06,,,cm2 at 700,C are achieved, respectively. An YSZ-based anode-supported solid oxide fuel cell is fabricated by employing LSC/GDC composite cathode sintered at 950,C. The cell with an active electrode area of 4,,4,cm2 exhibits the maximum power density of 0.42,W,cm,2 at 650,C and 0.54,W,cm,2 at 700,C. More than 300,h operating at 650,C is carried out for an estimate of performance and degradation of a single cell. Despite a decline at the beginning, the stable performance during the later term suggests a potential application. [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]


    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]


    Near Zero Shrinkage of an Low-Temperature Co-Fired Ceramic Package by Constrained Sintering Using Screen Printed Alumina Paste

    INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2010
    Sang Myoung Lee
    Conventional free sintering of low-temperature co-firing ceramic (LTCC) technology has several merits such as sintering temperature below 1000C that enables co-firing with electrode materials of silver or copper metal and multilayer structure formation. But due to the free sintering process, large shrinkage occurs. To fabricate electronic devices and components with near zero shrinkage within x, y directions constrained sintering (CS) technology is required. In this study a constrained sintering paste (CSP) utilizing alumina powder, which has a higher sintering temperature than LTCC powders, was fabricated for CS technology. The effect of CSP formulated using alumina powder on shrinkage was studied according to variation in paste composition. As a result ceramic package structure with a cavity was fabricated with shrinkage control of 0.028%, which is far smaller than the current CS technology shrinkage of approximately 0.1%. [source]


    A Novel Temperature-Compensated Microwave Dielectric (1,x)(Mg0.95Ni0.05)TiO3,xCa0.6La0.8/3TiO3 Ceramics System

    INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2009
    Chun-Hsu Shen
    The microstructure and microwave dielectric properties of a (1,x)(Mg0.95Ni0.05)TiO3,xCa0.6La0.8/3TiO3 ceramics system have been investigated. The system was prepared using a conventional solid-state ceramic route. In order to produce a temperature-stable material, Ca0.6La0.8/3TiO3 was added for a near-zero temperature coefficient (,f). With partial replacement of Mg2+ by Ni2+, the dielectric properties of the (1,x)(Mg0.95Ni0.05)TiO3,xCa0.6La0.8/3TiO3 ceramics can be promoted. The microwave dielectric properties are strongly correlated with the sintering temperature and the composition. An excellent Q f value of 118,000 GHz can be obtained for the system with x=0.9 at 1325C. For practical application, a dielectric constant (,r) of 24.61, a Q f value of 102,000 GHz, and a temperature coefficient of resonant frequency (,f) of ,3.6 ppm/C for 0.85(Mg0.95Ni0.05)TiO3,0.15Ca0.6La0.8/3TiO3 at 1325C are proposed. A parallel-coupled line band-pass filter is designed and simulated using the proposed dielectric to study its performance. [source]


    Tape Casting and Dielectric Properties of Zn2Te3O8 -Based Ceramics with an Ultra-Low Sintering Temperature

    INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2009
    Johanna Honkamo
    The suitability of dielectric ceramics made of zinc tellurate (Zn2Te3O8) and titanium dioxide (TiO2) with an ultra-low sintering temperature (650C) for tape casting and thus for the multimodule technique with Al electrodes was investigated. The properties of the tape before and after sintering as well as the amount of organic additives for the casting process and a thermal analysis of the tape up to 1000C are reported. In addition, electrodes on a multilayer module made on stacked tapes were prepared using Al paste and postfiring, followed by relative permittivity and loss tangent measurements to verify the electrical performance of the whole structure. The dielectric properties of the stacked module without any electrodes were also measured. The results show that the composition is well suited for the tape process but extra care should be taken especially with the proper sintering temperature for optimized electrical performance. [source]


    Microstructure Control of Sintered Porous Yttria-Stabilized Zirconia as a Durable Thermal Shielding Material

    INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2009
    Kazuya Sasaki
    The microstructure of a thermal shielding material affects its thermal conductivity and mechanical property. In this study, the effects of the sintering temperature and the polymethyl methacrylate powder as a pore-former on the microstructure of a sintered porous yttria-stabilized zirconia (YSZ), which is used as a durable thermal shielding material, were investigated. It became clear that the microstructure of the sintered YSZ could be controlled by the particle size and the amount of the pore-former and the sintering temperature. The effect of the yttria amount in the YSZ on the microstructure was also clarified. [source]


    A comparative study of single-line and Rietveld strain,size evaluation procedures using MgO ceramics

    JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2002
    Suminar Pratapa
    Strain,size evaluations from diffraction line broadening for MgO ceramic materials have been compared using single-line integral-breadth and Rietveld procedures with the Voigt function. Diffraction data were measured by Bragg,Brentano X-ray diffractometry (XRD), without incident beam monochromatization, and neutron diffractometry (ND) to encompass near-surface and bulk effects, respectively. The specimens consisted of sets of MgO ceramics and MgO,Y2O3 ceramic composites sintered over a range of temperatures. An MgO ceramic sintered at 1723,K for 2,h exhibited slightly less XRD broadening than the standard LaB6 NIST 660 SRM, and was therefore selected to make instrument profile corrections for both XRD and ND data. It was found for both data types that: (a) sintering initially relieves residual strain present in the MgO powder used to sinter the ceramics and also promotes grain growth; (b) residual strain of the MgO ceramic minimizes as the sintering temperature increases, and then increases with further rise in the sintering temperature, presumably as a result of intragranular interactions associated with grain growth; and (c) introduction of the second phase (Y2O3) increases strain and inhibits crystal growth. The single-line and Rietveld methods gave similar strain values from both the XRD and ND data within the limits of experimental error, but there were substantial differences between the single-line and Rietveld size estimates determined with the XRD and ND data. [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]


    Fe2O3 on Ce-, Ca-, or Mg-stabilized ZrO2 as oxygen carrier for chemical-looping combustion using NiO as additive

    AICHE JOURNAL, Issue 8 2010
    Magnus Rydn
    Abstract Oxygen-carrier particles for chemical-looping combustion have been manufactured by freeze granulation. The particles consisted of 60 wt % Fe2O3 as active phase and 40 wt % stabilized ZrO2 as support material. Ce, Ca, or Mg was used to stabilize the ZrO2. The hardness and porosity of the particles were altered by varying the sintering temperature. The oxygen carriers were examined by redox experiments in a batch fluidized-bed reactor at 800,950C, using CH4 as fuel. The experiments showed good reactivity between the particles and CH4. NiO was used as an additive and was found to reduce the fraction of unconverted CH4 with up to 80%. The combustion efficiency was 95.9% at best and was achieved using 57 kg oxygen carrier per MW fuel. Most produced oxygen carriers appear to have been decently stable, but using Ca as stabilizer resulting in uneven results. Further, particles sintered at high temperatures had a tendency to defluidize. 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]


    Sintering Temperature Dependence of Thermoelectric Performance and Crystal Phase of Calcium Cobalt Oxides

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010
    Masahiro Tahashi
    Polycrystalline samples were synthesized by a conventional solid-state reaction. As starting materials, Co3O4 and Ca(OH)2 were mixed in a molar ratio of Ca:Co=3:4 and sintered at 1073,1373 K. The compound phases and thermoelectric properties of the resulting products were dependent on the sintering temperature. X-ray diffraction analysis showed that the Ca3Co4O9 compound was stable up to 1193 K and that Ca3Co2O6 was formed at 1273 K. At 1373 K, the sample decomposed into cobalt oxide and calcium oxide. A maximum power factor of about 100 ,W/(K2m) at 873 K was obtained for the Ca3Co4O9 phase sintered at 1193 K. [source]


    Effect of Applied Stress on IR transmission of Spark Plasma-Sintered Alumina

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010
    Dibyendu Chakravarty
    The effect of applied stress on IR transmittance of nanocrystalline alumina prepared by spark plasma sintering was evaluated. Transparent alumina with maximum transmittance >80% was obtained over the entire mid-IR wavelength range of 3,5 ,m by applying a high stress of 275 MPa at 1150C using specially designed high-strength compound dies. The transmittance observed was similar to previous reports at identical wavelengths, but at a lower sintering temperature. The transparent samples have an average grain size of 0.3 ,m and a hardness of 23 GPa. At lower stresses and sintering temperatures, transmittance reduced drastically due to remnant pores in the matrix as observed from the microstructural analysis. The effect of porosity was found to be critical in developing transparency as even a marginal decrease in porosity led to substantial increase in transmittance. [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]


    Bi2O3,MoO3 Binary System: An Alternative Ultralow Sintering Temperature Microwave Dielectric

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009
    Di Zhou
    Preparation, phase composition, microwave dielectric properties, and chemical compatibility with silver and aluminum electrodes were investigated on a series of single-phase compounds in the Bi2O3,MoO3 binary system. All materials have ultralow sintering temperatures <820C. Eight different xBi2O3,(1,x)MoO3 compounds between 0.2,x,0.875 were fabricated and the associated microwave dielectric properties were studied. The ,-Bi2Mo2O9 single phase has a positive temperature coefficient of resonant frequency (TCF) about +31 ppm/C, with a permittivity ,r=38 and Qf=12 500 GHz at 300 K and at a frequency of 6.3 GHz. The ,-Bi2Mo3O12 and ,-Bi2MoO6 compounds both have negative temperature coefficient values of TCF,,215 and ,,114 ppm/C, with permittivities of ,r=19 and 31, Qf=21 800 and 16 700 GHz at 300 K measured at resonant frequencies of 7.6 and 6.4 GHz, respectively. Through sintering the Bi2O3,2.2MoO3 at 620C for 2 h, a composite dielectric containing both , and , phase can be obtained with a near-zero temperature coefficient of frequency TCF=,13 ppm/C and a relative dielectric constant ,r=35, and a large Qf,12 000 GHz is also observed. Owing to the frequent difficulty of thermochemical interactions between low sintering temperature materials and the electrode materials during the cofiring, preliminary investigations are made to determine any major interactions with possible candidate electrode metals, Ag and Al. From the above results, the low sintering temperature, good microwave dielectric properties, chemical compatibility with Al metal electrode, nontoxicity and price advantage of the Bi2O3,MoO3 binary system, all indicate the potential for a new material system with ultralow temperature cofiring for multilayer devices application. [source]


    Spark Plasma Sintered Silicon Nitride Ceramics with High Thermal Conductivity Using MgSiN2 as Additives

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2009
    Gui-hua Peng
    Silicon nitride ceramics were prepared by spark plasma sintering (SPS) at temperatures of 1450,1600C for 3,12 min, using ,-Si3N4 powders as raw materials and MgSiN2 as sintering additives. Almost full density of the sample was achieved after sintering at 1450C for 6 min, while there was about 80 wt%,-Si3N4 phase left in the sintered material. ,-Si3N4 was completely transformed to ,-Si3N4 after sintering at 1500C for 12 min. The thermal conductivity of sintered materials increased with increasing sintering temperature or holding time. Thermal conductivity of 100 W(mK),1 was achieved after sintering at 1600C for 12 min. The results imply that SPS is an effective and fast method to fabricate ,-Si3N4 ceramics with high thermal conductivity when appropriate additives are used. [source]


    Pressureless Rapid Sintering of UO2 Assisted by High-frequency Induction Heating Process

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008
    Jae Ho Yang
    Heat generation of uranium dioxide (UO2) powder and its pressureless rapid sintering behaviors have been studied using a high-frequency induction heating apparatus. The porous graphite housing has been used to prevent heat loss and to preheat the uranium oxides, simultaneously. At an elevated temperature, UO2 powder generated extra heat by itself. The synergism of individual heat generation between the graphite and UO2 powder could effectively heat the UO2 to the sintering temperature of 1700C. Using this process, densification behavior of cylindrical and disk-type UO2 green pellets according to the heating rate and grain structure of sintered UO2 pellets were investigated. Rapid sintering caused a large crack around the circumference of the sintered pellet. The formation of cracks could be avoided when the heating rate or sample dimension are properly reduced. A dense and crack-free UO2 pellet with a relative density of up to 96% was produced within 5 min of the process time. The induction heat sintering process can be a potential candidate for the rapid fabrication of ceramics and composites. [source]


    Oxidation Kinetics and Mechanisms of Hot-Pressed TiB2,MoSi2 Composites

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008
    Golla Brahma Raju
    The densification of titanium diboride (TiB2) at lower sintering temperature requires the use of sinter-aid. However, from the high temperature application point of view, it is important to assess whether the presence of sinter-aid degrades the material properties, including the oxidation resistance. In the present work, the isothermal oxidation behavior of TiB2 - x wt% MoSi2 (x=0, 2.5, and 10) composites was carried out using thermogravimetric analyzer in order to study the effect of MoSi2 content on the oxidation kinetics of TiB2 at 1200C for a duration of 12 h. The oxidized surface of monolithic TiB2 composed of highly textured rod-like rutile (TiO2) crystals. In contrast, the oxide scales on TiB2,MoSi2 materials consist of a thin layer of SiO2 along with TiO2. Interestingly, the analysis of the continuous measurements of the weight gain reveals parabolic rate law of oxidation for all the investigated ceramics. However, the oxidation kinetics is slower for the TiB2 -10 wt% MoSi2, probably due to the presence of SiO2 in the oxide scale. [source]


    Low-Loss Microwave Dielectrics in the (Mg1,xZnx)2TiO4 Ceramics

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008
    Cheng-Liang Huang
    The microwave dielectric properties and the microstructures of (Mg1,xZnx)2TiO4 ceramics prepared by the conventional solid-state route were investigated. Lattice parameters were also measured for samples with different x. As x increased from 0 to 0.05, the Qf of the specimen can be promoted from 150 000 GHz to a maximum 275 300 GHz. It also showed a remarkable lowering in the sintering temperature (,100C). Ilmenite-structured (Mg0.95Zn0.05)TiO3 was detected as a second phase. The coexistence of the second phase, however, is not harmful to the dielectric properties of the specimen because it possesses compatible ones. A fine combination of microwave dielectric properties (,r,15.48, Qf,275 300 GHz, ,f,,34 ppm/C) was obtained for (Mg0.95Zn0.05)2TiO4 specimen sintered at 1330C for 4 h. It is proposed as a very promising dielectric material for low-loss microwave and millimeter wave applications. [source]


    Enhancing Electrical Properties in NBT,KBT Lead-Free Piezoelectric Ceramics by Optimizing Sintering Temperature

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2008
    Ya-Ru Zhang
    Conventional sintering of (Na1,xKx)0.5Bi0.5TiO3 (abbreviated as NKBTx, x=18,22 mol%) lead-free piezoelectric ceramics was investigated to clarify the optimal sintering temperature for densification and electrical properties. Both sintered density and electrical properties were sensitive to sintering temperature; particularly, the piezoelectric properties deteriorated when the ceramics were sintered above the optimum temperature. The NKBT20 and NKBT22 ceramics synthesized at 1110,1170C showed a phase transition from tetragonal to rhombohedral symmetry, which was similar to the morphotropic phase boundary (MPB). Because of such MPB-like behavior, the highest piezoelectric constant (d33) of about 192 pC/N with a high electromechanical coupling factor (kp) of about 32% were obtained in the NKBT22 ceramics sintered at 1150C. [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]


    Thermodynamic Studies on the AlN Sintering Powders Treated With Phosphate Species

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007
    Susana Maria Olhero
    The processing of aluminum nitride (AlN) ceramics in aqueous media requires the use of a surface layer to protect the surface of the particles against hydrolysis. This surface layer might influence the densification, affecting the reactions between AlN and sintering additives. The present paper describes a thermodynamic and experimental approach to evaluate the effects of a phosphate-based protecting surface layer on the densification of AlN in the presence of YF3,CaF2 as sintering aids, and to predict the densification behavior during sintering using thermodynamic assessments. Based on thermodynamic calculations and the measured weight loss of the samples during heating to sintering temperature, the chemical reactions occurring during firing were proposed. The proposed reactions were related to the experimental results as well as the final properties of the AlN samples, namely, thermal conductivity, microstructure, secondary phases, and density. [source]


    Sintering Behavior of Gehlenite.

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2007
    Macro-/Mesoporous Gehlenite, Mechanical, Microstructure, Part I: Self-Forming, Physical Properties, Pore-Forming Mechanism
    A novel kind of pore self-forming macro-/mesoporous gehlenite (2CaOAl2O3SiO2) ceramic (abbreviated C2AS) having a highest porosity of 80% corresponding to a volume expansion of 134% during sintering has been developed. The pore self-forming ability, microstructure, mechanical, and thermal physical properties of the porous ceramic are related to the sintering temperature. The gehlenite ceramic shows a very good pore self-forming ability over a very wide range of temperature from 900 to 1450C. No vesicant is required and no hydrothermal treatment is needed, as is generally the case for other kinds of porous ceramics or glasses. The pore self-forming ability of the C2AS porous ceramic can be attributed to the escape of the adsorbed water vapor during the sintering process, due to automatic hydration of the fine, amorphous, flakey-shaped starting C2AS powder particles synthesized by the organic steric entrapment (PVA) method, as well as to their fine, porous microstructure. The pores of the ceramics can be either open or closed, and the average pore size ranges from 0.6 to 1.1 ,m, corresponding to a porosity of 75%,80%, respectively. The porous ceramic can preserve nanometer-sized (26,50 nm) crystallites up to 1000C. Sintered or thermally treated under different conditions, the porous ceramics exhibit relatively high flexural strengths ranging from 9.1 to 15.4 MPa, with a standard deviation of 0.3 and 4.2 MPa, respectively. Thermal properties of the porous ceramic up to 1000C, including thermal expansion coefficient, thermal diffusivity, specific heat, and thermal conductivity, were investigated, and the stability of the porous ceramic in boiling water was also studied. [source]


    Synthesis, Physical, and Mechanical Properties of Bulk Zr3Al3C5 Ceramic

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2007
    Lingfeng He
    An in situ reactive hot-pressing process using zirconium (zirconium hydride), aluminum, and graphite as staring materials and Si and Y2O3 as additives was used to synthesize bulk Zr3Al3C5 ceramics. This method demonstrates the advantages of easy synthesis, lower sintering temperature, high purity and density, and improved mechanical properties of synthesized Zr3Al3C5. Its electrical and thermal properties were measured. Compared with ZrC, Zr3Al3C5 has a relatively low hardness (Vickers hardness of 12.5 GPa), comparable stiffness (Young's modulus of 374 GPa), but superior strength (flexural strength of 488 GPa) and toughness (fracture toughness of 4.68 MPam1/2). In addition, the stiffness decreases slowly with increasing temperature and at 1600C remains 78% of that at ambient temperature, indicating that Zr3Al3C5 is a potential high-temperature structural ceramic. [source]


    Cation Ordering and Dielectric Characteristics in Barium Zinc Niobate

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2007
    Chun-Te Lee
    Barium zinc niobate (Ba(Zn1/3Nb2/3)O3) (BZN) complex perovskite has been reported to have special microwave dielectric properties with close relation of its ordered structure. This study investigated the effect of calcination on the evolution of ordered structure and on quality factor with Raman spectroscopy, X-ray diffractometry, and transmission electron microscopy. The results revealed that single calcination at a lower temperature inhibited the growth of the ordered domain during sintering. In contrast, the 1:2-ordered domain in double-calcined BZN powder grew significantly with a higher sintering temperature and a longer soaking time. It is attributed that double calcination caused a higher degree of 1:2 ordering and better homogeneity. At the same time, the quality factor of the sintered ceramic body was highly promoted when using double-calcined powder. A close relation of the quality factor with the size of ordered domain, the degree of 1:2 ordering, and the relative density of BZN ceramics was presented. [source]


    Conversion of Bamboo to Biomorphic Composites Containing Silica and Silicon Carbide Nanowires

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2007
    Teresa L. Y. Cheung
    Luk Bamboo had been converted into biomorphic composites containing high-purity cristobalite-SiO2 and ,-silicon carbide (SiC) nanowires after sintering at 1200 and 1400C, respectively. The fabrication process was simple, in which no catalyst was needed and the sintering temperature was low. The procedure included pyrolysis of biotemplates, infiltration of a Si-containing reactant, and sintering. Both the SiO2 and SiC nanowires were grown by a two-stage growth mechanism, in which the impurities from raw bamboo acted as catalysts. We successfully demonstrated that inexpensive Luk bamboo could provide a breakthrough, cost-effective, and eco-friendly route for self-assembling one-dimensional nano-structures in highly porous biomorphic materials. [source]


    Sintering Behavior and Dielectric Properties of Bi3NbO7 Ceramics Prepared by Mixed Oxides and High-Energy Ball-Milling Methods

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2007
    Di Zhou
    The sintering behavior and dielectric properties of Bi3NbO7 ceramics prepared by the high-energy ball milling (HEM) method and conventional mixed oxides method with V2O5 addition were investigated. All the samples were sintered between 840 and 960C. For the ceramics prepared by the mixed oxides method, the pure tetragonal Bi3NbO7 phase formed without any cubic phase. With changing sintering temperature, the dielectric constant ,r lies between 79 and 92, while the Qf values are between 300 and 640 GHz. The samples sintered at 870C have the best microwave dielectric properties with ,r=79, Qf=640 GHz, and the temperature coefficients of resonant frequency ,f between 0 and ,20 ppm/C. For the ceramics prepared by the HEM, a pure cubic phase was obtained. The ,r changes between 78 and 80 and Qf were between 200 and 290 GHz. [source]


    Normal Sintering of (K,Na)NbO3 -Based Ceramics: Influence of Sintering Temperature on Densification, Microstructure, and Electrical Properties

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2006
    Yuhua Zhen
    Normal sintering of Li-doped and Li/Ta-codoped potassium sodium niobate (KNbO3,NaNbO3, KNN)-based ceramics was investigated to clarify the optimal sintering condition for densification, microstructure, and electrical properties. It was found that density increased greatly within a narrow temperature range but tended to decrease when the sintering temperature slightly exceeded the optimal one, accompanied by the appearance of abnormal grain growth, which was considered to be due to the intensified volatilization of alkali metal oxides. Piezoelectric and dielectric properties also showed a similar relationship between the density and sintering temperature, but the highest piezoelectric strain coefficients were obtained at the temperatures lower than that for the highest density, because both densification and composition affect the electrical properties. The highest d33 value of 206 pC/N was obtained for the Li- and Ta-codoped KNN ceramics prepared at 1090C. [source]


    Transmission Electron Microscopy Microstructure of 0.95(Na0.5K0.5)NbO3,0.05BaTiO3 Ceramics

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2006
    Hwack Joo Lee
    Microstructural characterizations using transmission electron microscopy on 0.95(Na0.5K0.5)NbO3,0.05BaTiO3 ceramics sintered at 1030,1150C for 2 h were carried out. The liquid phase was found at the triple junction of the grains in all specimens and abnormal grain growth occurred in the presence of the liquid phase. Abnormally grown grains whose shapes were cuboidal were well developed. Anisotropically faceted amorphous liquid phase pockets were observed inside the grain in a specimen sintered at 1060C for 2 h. The interface between the grain and the liquid matrix was flat and some were identified to be {100} planes of the grains. A certain amount of liquid at the sintering temperature of 1060C enhanced the abnormal grain growth and contributed to the improvement of the piezoelectric properties. [source]