Reduction Of Sintering Temperature Research Articles

A feasibility study of W-Cu composites production by high pressure compression of tungsten powder

For manufacturing a heavy duty W-Cu composite, a porous tungsten skeleton is required; which later can be filled by molten copper via infiltration technique. The compression force usually up to 200 MPa can be provided by cold isostatic press (CIP) and the temperatures used for sintering the green compacts are more 2000 °C. However, in this research, high pressure within the range of 200 to 663 MPa was used to produce high density green specimens (60-80%) by CIP while sintering was carried out at a moderate temperature of 1550 °C. The tungsten skeletons were infiltrated with molten copper at 1300 °C. The reduction of sintering temperature from over 2000 °C to 1550 °C for a highly densified W-skeleton not only resulted into a successful production of W-Cu composites but also the obtained physical and mechanical properties of these composites are comparable to those obtained for lower compaction pressures and sintering temperature higher than 2000 °C.

Microwave dielectric properties and compatibility with silver of low-fired Ba5Nb4O15 ceramics by BaCu(B2O5) addition

The influence of BaCu(B2O5) (BCB) addition on the sintering temperature and microwave dielectric properties of Ba5Nb4O15 ceramics has been investigated. The addition of small amount of BCB can effectively lower the sintering temperature of Ba5Nb4O15 ceramics from 1400 to 875 °C and induce no obvious degradation of the microwave dielectric properties. The reduced sintering temperature was attributed to the BCB liquid phase. Typically, the 1.5 wt% BCB-added Ba5Nb4O15 ceramic sintered at 875 °C for 2 h exhibited good microwave dielectric properties of Q × f = 28,655 GHz, εr = 40.2, and τf = 60 ppm/°C. The dielectric ceramic demonstrated stability against the reaction with the Ag electrode, which suggests that the ceramics could be applied in multilayer microwave devices requiring low sintering temperatures.

Microstructure and interfacial reactions between B6O and (Ni, Co) couples

The search for suitable additives for boron suboxide (B6O) materials which could improve densification, reduce sintering temperature and tailor the microstructure has been of great importance. In an earlier study it was shown that transition metal borides qualify as sintering aids for B6O, but partial segregations of the boride secondary phases were found. In this work, efforts have been made to understand the chemical interaction between the B6O and boride phase. A reaction couple of sintered B6O, nickel and green compact B6O were assembled and heat-treated at 1850 8C for 20 min. XRD and SEM examinations of the reaction zone show the formation of nickel boride, diffusing into the B6O matrix and a substantial grain growth of B6O at the interface. # 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Facile preparation of TiO2 nanostructures by direct annealing of the Ti foil

TiO2 nanostructures have been fabricated by direct annealing of the Ti foil with Pd catalyst. The Pd catalysts play an important role in reducing sintering temperature for the synthesis of TiO2 nanostructures. The morphologies can be varied between the nanowires (NWs) and nanobelts (NBs) by adjusting the amount of Pd and annealing temperature. It shows that the vapor liquid solid and vapor solid may be the most suitable mechanism for the TiO2 nanostructure growth. Experimental results suggest that this method is an effective, simple and inexpensive route for the preparation of TiO2 nanostructures with high quality and high yield.

Characterization and Energy Storage Density of BaTiO<sub>3</sub> - Ba(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub> Ceramics

The energy storage density of (1-x) BaTiO3 – x Ba(Mg1/3Nb2/3)O3 (x = 0, 0.1, 0.2, 0.3) ceramics was investigated. The microstructure of samples was characterized by scanning electron microscopy (SEM). The energy storage density was calculated from the P-E hysteresis loops measured at room temperature. Experimental results show that the energy storage density of 0.9 BaTiO3 – 0.1 Ba(Mg1/3Nb2/3)O3 ceramics is highest among all compositions. At 15.8kV/mm electric field, the energy storage density of the sample can reach up to 1.07J/cm3, which is about 1.5 times higher than pure BaTiO3. The improvement of the energy density can be due to two factors: one is the improved breakdown strength caused by the optimized microstructure, the other is the decreased remnant polarization. This result indicates that bulk 0.9 BaTiO3 – 0.1 Ba(Mg1/3Nb2/3)O3 ceramic has advantages compared with pure BaTiO3 ceramic for energy storage applications, and with further improvements in microstructure and reduction of sintering temperature, could be a good candidate for energy storage capacitors.

Low-temperature sintering of BaTiO3 with Mn-Si-O glass

In order to reduce sintering temperature and prevent adverse dielectric effects, pure BaTiO3 powder with the addition of Mn-Si-O glass was sintered in the temperature range of 1175–1300°C. Microstructural observation showed that BaTiO3 grains of the sintered samples only grew from the initial 400 nm to an average of 430 nm between 1175–1275°C for 1 h, or sintered at 1250°C as long as 27 h. Abnormal BaTiO3 grains are not found in the sintered samples. The microstructure and phase analysis showed that the dielectric properties, tetragonality, and grain growth of BaTiO3 are closely controlled by the formation of the liquid phase, newly formed Ba2TiSi2O8 grains, and Mn solid solution in BaTiO3 grains.

Superior sinterability of nano-crystalline gadolinium doped ceria powders synthesized by co-precipitation method

Reduced sintering temperature of doped ceria can greatly simplify the fabrication process of solid oxide fuel cells (SOFCs) by utilizing the co-firing of all cell components with a single step. In the present study, nano-crystalline gadolinium doped ceria (GDC) powders of high sinterability at lower sintering temperature has been synthesized by co-precipitation at room temperature. The successful synthesis of nano-crystalline GDC was confirmed by XRD, TEM and Raman spectroscopy analysis. Dilatometry studies showed that GDC prepared by this method can be fully densified (97% relative density) at a sintering temperature of 950 °C which is fairly lower than ever before. It has also been found that the sintered samples have a higher ionic conductivity of 1.64 × 10 −2 S cm −1 at 600 °C which is suitable for the intermediate temperature SOFC application.

Enhanced dielectric properties and sinterability of CaCu 3Ti 4O 12 ceramics by Sr 2+ doping

CaCu 3Ti 4O 12 ceramics substituted by Sr 2+ for Ca 2+ were prepared by the solid state reaction method. It was found that Sr 2+ substitution increased the lattice constant of CaCu 3Ti 4O 12 in a consistent manner. The dielectric properties, sinterability, and microstructures of the Ca 1− x Sr x Cu 3Ti 4O 12 ceramics were investigated. Large enhancement of dielectric properties (increase in dielectric constants and decrease in dielectric losses) was observed in the Ca 1− x Sr x Cu 3Ti 4O 12 ceramics at x=0.2 within the frequency range between 0.2 and 20 kHz. It was found that the doping of Sr 2+ greatly improved the sinterability of Ca 1− x Sr x Cu 3Ti 4O 12 ceramics by largely reducing sintering temperature and promoting densification and grain growth during sintering.

The microwave properties of Li doped 0.7(Ba,Sr)TiO 3–0.3MgO thick film interdigital capacitors on the alumina substrates

The crystalline and electrical properties of Li doped 0.7(Ba,Sr)TiO 3–0.3MgO thick film interdigital capacitors have been investigated. Screen printing method was employed to fabricate Li doped 0.7(Ba,Sr)TiO 3–0.3MgO thick films on the alumina substrates. (Ba,Sr)TiO 3 materials have high dielectric permittivity (>500 @ 1 MHz) and low loss tangent (0.01 @ 1 MHz) in the epitaxial thin film form. To improve dielectric properties and reduce sintering temperature, MgO and Li were added, respectively. 10 μm thick films were screen printed on the alumina substrates and then interdigital capacitors with seven fingers of 200 μm finger gap were patterned with Ag electrode. Current–voltage characteristics were analyzed with elevated temperature range. Up to 50 °C, the thick films showed positive temperature coefficient of resistivity (d ρ/d T) of 6.11 × 10 8 Ω cm/°C, then film showed negative temperature coefficient of resistivity (d ρ/d T) of −1.74 × 10 8 Ω cm/°C. From the microwave measurement, the relative dielectric permittivity of Li doped 0.7(Ba,Sr)TiO 3–0.3MgO thick films interdigital capacitors were between 313 at 1 GHz and 265 at 7 GHz.

High solids loading ceramic colloidal dispersions in UV curable media via comb-polyelectrolyte surfactants

Ceramic articles and ceramic/polymer composites with complex 3d shapes can be produced by rapid prototyping techniques such as stereolithography of ceramic dispersions in UV curable resins. Nanometer and submicrometer ceramic particles are advantageous for high resolution microstructures, surface quality and reduced sintering temperatures. Frequently, special surfactants are needed to maximize solids loading while maintaining suitable rheological properties for stereolithography applications (viscosity <5 Pa s, 30 1/s). We present here a general scheme for relatively high loading/low viscosity dispersions of nanometer and submicrometer particles in UV curable resins using comb-polyelectrolyte surfactants. In the present approach, adsorption is favorably carried out in aqueous media and the dry particles with adsorbed surfactant are transferred to the organic media through centrifugation, washing, drying and dry milling. The method is demonstrated for Al 2O 3, ZnO and mixed Al 2O 3/ZnO colloidal dispersions. Dispersions containing >48 vol% particles suitable for stereolithography have been achieved. Dispersions containing 36 vol% particles are predicted to have viscosities in the range suitable for direct inkjet printing applications at 75 °C. The particle stabilization and transfer schemes, rheological behavior and UV curing characteristics are presented.

A Chemical Route to BiNbO4 Ceramics

The liquid phase sintering of fine BiNbO4 powders allows to obtain dense ceramics with excellent microwave dielectric properties (ɛ=44–46; Q×f=16,500–21,600 GHz) at T≥700°C. The thermal decomposition of freeze‐dried precursors results in the crystallization of a metastable β′‐BiNbO4 polymorph that transforms into a stable orthorhombic α‐modification at T≥700°C. The dependence of sinterability on the powder synthesis temperature shows the maximum at 600°C, corresponding to the formation of crystalline BiNbO4 powders with a grain size 80–100 nm. Sintering temperature reduction to 700°C prevents the deterioration of silver contacts during co‐firing with BiNbO4 ceramics. In situ scanning electron microscopy observation of the morphological evolution during sintering shows that the intense shrinkage soon after the appearance of a CuO–V2O5 eutectics‐based liquid phase is accompanied by complete transformation of the ensemble of primary BiNbO4 particles.

Microwave Dielectric Properties of ZnO-2TiO2-Nb2O5 Ceramics with BaCu (B2O5) Addition

The influence of BaCu(B2O5) (BCB) addition on the sintering temperature and microwave dielectric properties of ZnO-2TiO2-Nb2O5 (ZTN) ceramic has been investigated using dilatometry, x-ray diffraction, scanning electron microscopy, and microwave dielectric measurements. A small amount of BCB addition to ZTN can lower the sintering temperature from 1100°C to 900°C. The reduced sintering temperature was attributed to the formation of the BCB liquid phase. The ZTN ceramics containing 3.0 wt.% BCB sintered at 900°C for 2 h have good microwave dielectric properties of Q × f = 19,002 GHz (at 6.48 GHz), e r = 45.8 and τ f = 23.2 ppm/°C, which suggests that the ceramics can be applied in multilayer microwave devices, provided that Ag compatibility exists.

The properties of YSZ electrolyte sintering at 1300 °C

The properties of yttria stabilized zirconia(YSZ) related to the sintering process were discussed. YSZ nano-powders about 40–100 nm as raw material, the sub-micrometer grain sizes such as 0.4–3 μm in YSZ were gotten by sintering process at 1300 °C, which was performed at 1000 °C for 2 h, then raised the temperature at the rate of 50 °C/h to 1400 °C, then decreased directly to 1300 °C in 30 minutes, finally at 1300 °C for 5–20 hours. The ratio of bigger grain size becomes larger as the holding time increasing at 1300 °C. The grains less than 1 μm are about 50%, eg, 43.2%, 52.2% and 51.1% related to 1300 °C holding 5 hours, 8 hours and 10 hours, respectively. As YSZ grain size became small, the electrical conductivities did not decrease, even increased, about 0.20 s/cm at 1000 °C. The reduced sintering temperature and time were benefited to co-fire with the electrodes in electrode-supported SOFCs.

Sintering Behavior of the β"-Alumina Solid Electrolyte for Battery Applications

The β″-alumina solid electrolyte proposed for the application in the electric vehicle battery system was prepared via a liquid phase sintering method. The main aim of the study is to reduce sintering temperature which is normally required as high as 1700oC. The MgO-stabilized Naβ″-alumina with the composition Na1-xMg2xAl5-xO8 where x = 0.125 was prepared. The mixture of Na2CO3, MgO and γ -Al2O3 were produced and well-mixed by wet ball milling method. Then, calcination was performed at 1200oC for 10 h. Calcined β″-alumina was then added with a sintering aid, CuO, at several concentrations prior to forming by a dry pressing technique. The green pellets were then sintered at different temperatures with constant dwell time for 4 h. Phase identification on calcined powders indicate that β″-alumina present as a mojor phase co-existed with tiny proportion of β′-alumina. Co-existence of these two phases is commonly found for this particular system. Phase checking for sintered samples with CuO additive show no phase change but concentration ratio of the β′-alumina seem to increase with increasing sintering temperature and mol% of the CuO. Sintering at 1550oC, the higher densification is clearly observed for ceramic with higher CuO content, i.e. 5 and 10 mol%. Layered-structure of the β″-alumina can be clearly seen from the SEM micrographs. The SEM results also show that higher CuO content promoted a higher grain development and produced less porosity. Dc conductivity values of the samples with CuO adding are reasonable high comparing to that of without CuO adding. This study has been show that β″-alumina produced by liquid phase sintering here is considerably appropriate to the application in the battery of electric vehicles.

Low temperature sintering and microwave dielectric properties of Ba3Ti5Nb6O28 ceramics with BaCu(B2O5) additions

Abstract The effects of BaCu(B2O5) (BCB) additions on the sintering temperature and microwave dielectric properties of Ba3Ti5Nb6O28 ceramic have been investigated using dilatometer, X-ray diffraction, scanning electron microscopy and dielectric measurement. The pure Ba3Ti5Nb6O28 ceramic shows a high sintering temperature (∼1250 °C) and good microwave dielectric properties as Q × f of 11,400 GHz, ɛr of 37.0, τf of −8 ppm °C−1. It was found that the addition of BCB to Ba3Ti5Nb6O28 could lower the sintering temperature from 1250 to 925 °C. The reduced sintering temperature was attributed to the BCB liquid phase. The addition of BCB also enhanced the microwave dielectric properties to Q × f of 19,191 GHz, ɛr of 38.2, τf of 12 ppm °C−1.

Effect of CuO additives on sintering and dielectric behaviors of CeO 2 ceramics

The effects of CuO addition (1 and 2 wt%) on microstructures and microwave dielectric properties of CeO 2 ceramics with CuO additions have been investigated. It is found that CeO 2 ceramics can be sintered at 1490 °C due to the liquid phase effect of CuO addition. At 1580 °C, CeO 2 ceramics with 1 wt% CuO addition possesses a dielectric constant ( ɛ r) of 21.7, a Q × f value of 50,000 (at 9GHz) and a temperature coefficient of resonant frequency ( τ f ) of −59 ppm/°C. A large sintering temperature reduction (about 200 °C) can be achieved by adding CuO to the CeO 2 ceramics. The CuO–added CeO 2 ceramics can find applications in microwave devices.

Electrically Conductive Adhesives for Electronic Packaging and Assembly Applications

Some recent advances in materials, structures and properties that affect the mechanical and electrical characteristics and reliability performance of electrically conductive adhesives (ECAs) are discussed. This is done in the context of electronic packaging and assembly applications. Micro-silver-filled epoxy ECAs (with an average silver particle size of 5 μm) modified by addition of a conducting polymer, low melting point (LMP) alloys, or nanoparticles (average particle size of 80 nm) are described and compared with respect to volume resistivity, tensile strength and adhesion to copper. To understand the conduction and sintering behaviors of the various ECA formulations, SEM, optical microscopy and X-ray photoelectron spectroscopy (XPS) are used to investigate the micro-structure and chemical nature of the cured ECAs. Volume resistivity of the specially formulated adhesives is in the range of 10–4 to 10–6 Ohm cm. Adhesives formulated with a conducting polymer exhibit the greatest tensile strength with copper when compared to the other formulations investigated. The conducting polymer-modified ECA exhibited electrical conductivity on the order of that achieved with conventional ECAs. Hence, good electrical performance is achieved concurrent with superior mechanical properties. It was found that with increasing curing temperature, the volume resistivity of all ECAs decreased. This is attributed to sintering of metal particles at higher temperatures. Incorporation of nanoparticles reduces sintering temperature. Sintering of ECAs with micrometer-scale silver particles was further evaluated using high temperature/pressure lamination. A continuous metallic network resulted when the lamination temperature was greater than 300°C. Electrical stability of ECA joints with aluminum was evaluated by stress testing in an environment of elevated temperature and humidity. A thin layer of silane-based coupling agent on the aluminum surfaces retards the degradation of the electrical properties of the joint. In general, proper preparation of the metal surface to which an ECA is mated is critical for maintaining both electrical and mechanical performances.

Effect of Li2CO3 addition on the dielectric and piezoelectric responses in the low-temperature sintered 0.5PZN–0.5PZT systems

Low-temperature sintering of 0.5Pb(Zn1∕3Nb2∕3)O3–0.5Pb(Zr0.47Ti0.53)O3 ceramics (0.5PZN–0.5PZT) was investigated using Li2CO3 as sintering aids. The addition of Li2CO3 significantly improved the sinterability of 0.5PZN–0.5PZT ceramics, resulting in a reduction of sintering temperature from 1100to950°C. Moreover, the effect of Li2CO3 addition on the dielectric and piezoelectric responses in 0.5PZN–0.5PZT systems was systematically studied in this work. The analysis of x-ray diffraction patterns and scanning electron microscopy indicated that the solubility limit of Li ions in perovskite structures was near 0.5wt% in Li2CO3 form. Below the solubility limit, Li+ ions entered the six-fold coordinated B sites of oxygenic octahedral center and enhanced the compositional fluctuation in nanoscale, resulting in the increase of the degree of diffuseness γ. While at high doping level above the solubility limit, γ decreased subsequently, which was attributed to the formation of pyrochlore phase. Raman analysis on the B-site cation order correlates well with the dielectric measurement results. The large improvements in the piezoelectric properties such as the coupling factor and piezoelectric constant were also observed for doped specimens. Optimized parameters, such as d33=278pC∕N, kp=0.50, and εmax=8800, were achieved by doping 0.5wt% Li2CO3 in low-temperature sintered 0.5PZN–0.5PZT systems, which shows great promise as practical materials for multilayered piezoelectric device applications. The observed improvement in the electric properties can be attributed to the grain size effect. After doping, the clamping effect caused by oxygen vacancies and grain boundary phases on domain wall motion was largely reduced due to the increase of grain size; therefore, a significant reduced coercive field and an increased remanent polarization were observed in doped 0.5PZN–0.5PZT systems.

A study in the mechanical milling of alumina powder

The mechanical milling of alumina in order to reduce grain sizes to ≤100 nm has been proposed as a means of reducing sintering temperatures and improving pressureless sintered density, particularly as a means of allowing co-firing with metallic components for biomedical implants. There is a persistent problem with contamination from the milling media, usually hardened steel which can be only partially alleviated by acid leaching. We have explored the use of alternative milling media with a view to reducing the levels of contamination. Alumina powders were milled with hardened steel, tungsten carbide, alumina and zirconia milling media under identical conditions of ball mass:powder mass ratio 10:1 and target milling times of 32 h. All of the milling media were found to cause unacceptable levels of contamination. Zirconia media gave the lowest contamination (3–4%) and in some circumstances, the addition of a small amount of zirconia may lead to increased toughness without loss of bio-compatibility.

Probation on Abrasion of Ceramic Cutting Tools

Abrasion of ceramic based and ceramic coated cutting tools is the highlighted problem, but little progress has been made. A detailed study of carbides, nitrides, borides, oxides, whiskers or metal additives of small amount and a variety of anti-wear mechanism was given so that the wear resistance of ceramic matrix tool can be greatly improved. A variety of abrasion of ceramic coated cutting tools was also studied, such as adhesive abrasion resistance, grinding abrasion resistance, fretting abrasion resistance, fatigue abrasion resistance, corrosion abrasion resistance, hot crack abrasion resistance, diffusion abrasion resistance and phase change abrasion resistance, etc. For example, with the increase of metal content in metal carbide ceramic coating, its hardness decreases; and coating hardness is different when coated with different coating technique, and its abrasion performance is also related to shape, size, distribution and post-processing of laser remelting. Abrasion extent, key factors, abrasion mechanism and applied range were also described. It is noticed that addition of rare earth oxides can improve strength, toughness, density, microstructure, phase composition of ceramic cutting tools and reduce sintering temperature.