Reduction Of Sintering Temperature Research Articles

Lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3-Y2O3 ceramics with large piezoelectric coefficient obtained by low-temperature sintering

Lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3-xwt.%Y2O3 (BCZT-xY) piezoelectric ceramics have been synthesized using solid-state reaction technique and the effects of Y2O3 addition on the phase structure and piezoelectric properties of the ceramics have been studied. The results reveal that the addition of Y2O3 significantly improves the sinterability of BCZT ceramics, resulting in a reduction of sintering temperature from 1,540 to 1,350 °C, and an increase of the Curie temperature T C from 85 to 95 °C. X-ray diffraction data shows that Y2O3 diffuses into the lattice of BCZT-xY ceramics and a pure perovskite phase forms in the ceramics. Scanning electron microscopy images indicate that a small amount of Y2O3 addition affects the microstructure, obviously. Main piezoelectric parameters of these ceramics are optimized around x = 0.06 wt % with a large piezoelectric coefficient (d 33 = 560 pC/N), a high planar electromechanical coefficient (k p = 53 %) and a low dissipation factor (tan δ = 0.9 %) at 1 kHz. The results indicate that the BCZT-xY ceramics are promising lead-free materials for practical applications.

Influence of ball milling on sintering behavior and electrical properties of (Li,Na,K)NbO3 lead-free piezoceramics

Volatilization of alkali elements during sintering process is one of the major factors influencing the processing stability of lead-free (Na,K)NbO3 (KNN) piezoceramics. With a purpose to reduce sintering temperature by refining particle sizes, an extensive ball-milling step was intentionally introduced to the fabrication process of KNN-based ceramics with a nominal composition of Li0.058(Na0.52K0.48)0.942NbO3 by a solid-state powder synthesis and normal sintering method. It was revealed that prolonging the period for milling calcined powders before sintering process significantly reduced the particle sizes and hence sintering temperature. As a result, sintering at a reduced temperature of 1,025 °C resulted in a highly dense material with good piezoelectric and ferroelectric properties with converse piezoelectric coefficient d* 33 and remnant polarization P r reaching 266 pm/V and 15.7 μC/cm2, respectively. This study provided a facile and effective method to enhance the piezoelectric properties in KNN-based ceramics with an optimized composition by reducing the particle sizes.

Effect of P-Zn-La-Si-Al-N-Mg-Yb Oxides Additives on Sintering and Microwave Dielectric Behaviors of Nd(Co1/2Ti1/2)O3 Ceramics

The microstructure and dielectric properties of the complex perovskite Nd(Col/2Ti1/2)03ceramics with 60P2O5-15ZnO-5La2O3-5Al2O3-5N2O-5MgO-5Yb2O3glass additions from 1-2 wt% were prepared with the conventional solid-state route have been investigated. The resultant microwave dielectric properties were analyzed based upon the densification, the X-ray diffraction patterns and the microstructures of the ceramics. Doping with 60P2O5-15ZnO-5La2O3-5Al2O3- 5N2O-5MgO-5Yb2O3glass (up to 2 wt%) can effectively promote the densification of Nd(Co1/2Ti1/2)O3ceramics at low sintering temperature. A distinct sintering temperature reduction (100-200°C) can be achieved by adding 60P2O5-15ZnO-5La2O3-5Al2O3-5N2O-5MgO-5Yb2O3glass to the Nd(Co1/2Ti1/2)O3ceramics. The correlation between the microstructures and the microwave dielectric properties was also examined. The Nd(Co1/2Ti1/2)O3ceramics with 60P2O5-15ZnO-5La2O3- 5Al2O3-5N2O-5MgO-5Yb2O3glass additions can find applications in microwave devices requiring low sintering temperature.

Microwave assisted hydrothermal synthesis of engineered cerium oxide nanopowders

Cerium oxide nanopowders have been prepared via microwave assisted hydrothermal technique in the presence of different amounts of poly vinyl pyrrolidone (PVP). The prepared nanopowders were characterized using XRD, TEM and SAED. The results showed that the particle size of the ceria nanopowders was decreased with the increase of PVP amount. The prepared ceria has nanocrystalline cubic fluorite structure with high purity. The influence of PVP content on the densification behavior of CeO 2 was investigated by means of dilatometer and scanning electron microscopy (SEM). It was found that the increase of PVP amount reduced sintering temperature. The cold-pressed powders can be sintered to full density at temperatures starting from 1070 °C in just 10 min.

Phase stability, low temperature cofiring and microwave dielectric properties of BaTi5O11 ceramics with BaCu(B2O5) addition

The effects of BaCu(B2O5) (BCB) additions on the sintering temperature, microstructure and microwave dielectric properties of BaTi5O11 modified with 1.0 wt% CuO (BTC) ceramic have been investigated using X-ray diffraction, scanning electron microscopy and dielectric measurement. The BTC ceramic shows a high sintering temperature (~1,100 °C) and good microwave dielectric properties as Q × f = 44,530 GHz, er = 40.5, τf = 39 ppm/°C. The addition of BCB to BTC effectively reduced the sintering temperature from 1,100 to 925 °C. The reduced sintering temperature was attributed to the BCB liquid phase. The BTC ceramic doped with 4 wt% BCB has a good microwave dielectric properties with Q × f = 25,502 GHz, er = 37.4, τf = 33.1 ppm/°C. The chemical compatibility of silver electrodes and low-fired samples has also been investigated.

Densification and properties of superhard B6O materials with cobalt additions

Abstract The search for suitable additives for boron suboxide (B6O) materials which could improve densification, reduce sintering temperature and tailor the microstructure has been productive. B6O materials doped with 0–5 vol% cobalt addition were sintered at temperatures up to 1850 °C and pressure of 50 MPa for 20 min. Relationships between the formed phases, microstructures and mechanical properties of the sintered materials were investigated as a function of sintering conditions and added cobalt content. The hardness of the sintered B6O materials increases with sintering temperature, while the fracture toughness increases with increasing cobalt content and reduces with increasing sintering temperature.

Preparation of Boron Suboxide Nanoparticles and Their Processing

Crystalline boron suboxide B 6 O particles with size in the range of 1.5 µm – 2 µm and crystallite size in the range of 32 nm – 40 nm were prepared by calcination at 1400 °C for one or two hours of precursors obtained by mixing X-ray amorphous boron with water solution of B 2 O 3 followed by evaporation and drying. Decrease of molar ratio B/B 2 O 3 from 16 to 14 in the precursor mixture reduced nonstoichiometry of prepared B 6 O although simultaneously it increased admixture of B 2 O 3 . Particulate composites of B 6 O with TiN or Ni nanoparticles were prepared by mechanical mixing. The spark plasma sintering process intensified the densification of prepared boron suboxide nanoparticles at 1900 °C and allowed manufacturing of fully dense bodies (98 %) during five minutes. Additives of TiN or Ni nanoparticles reduced sintering temperature to 1700 °C and their promoted formation of Ti or Ni borides. DOI: http://dx.doi.org/10.5755/j01.ms.18.1.1345

Lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3–CeO2 ceramics with high piezoelectric coefficient obtained by low-temperature sintering

Lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3–x%CeO2(BCZT–xCe) piezoelectric ceramics have been prepared by the traditional ceramic process and the effects of CeO2 addition on their phase structure and piezoelectric properties have been studied. The addition of CeO2 significantly improves the sinterability of BCZT ceramics which results in a reduction of sintering temperature from 1540°C to 1350°C without sacrificing the high piezoelectric properties. X-ray diffraction data show that CeO2 diffuses into the lattice of BCZT and a pure perovskite phase is formed. SEM images indicate that a small addition of CeO2 greatly affects the microstructure. Main piezoelectric parameters are optimized at around x=0.04wt% with a high piezoelectric coefficient (d33=600pC/N), a planar electromechanical coefficient (kp=51%), a high dielectric constant (ɛr=4843) and a low dissipation factor (tanδ=0.012) at 1kHz, which indicates that the BCZT–xCe ceramics are promising for lead-free practical applications.

Reducing sintering temperature of yttria stabilized zirconia through addition of lithium nitrate and alumina

Reducing sintering temperature of yttria stabilized zirconia (YSZ) has been achieved through doping with alumina and lithium nitrate at levels below 1mol%. Sintering experiments of pure and doped samples have been conducted with the same profile using an optical dilatometer. All samples exhibited anisotropic sintering over a wide range of temperatures but final shrinkage values were comparable in axial and radial directions. Sintering temperature has been reduced by as much as 110°C. We believe that the reduction in sintering temperatures is due to viscous flow in the first stage sintering. Bimetallic doping (mixture of alumina and lithium nitrate doping) is more effective in reducing sintering temperature than single doping possibly due to better distribution of doping material throughout the matrix material. Separate sintering experiments for 5h have been conducted at 1250°C and 1170°C on doped 8mol% and 3mol% YSZ, respectively, and have shown that near full density (∼96%) is reachable.

Lead-free (Ba0.7Ca0.3)TiO3-Ba(Zr0.2Ti0.8)O3-xwt %CuO ceramics with high piezoelectric coefficient by low-temperature sintering

Lead-free (Ba0.7Ca0.3)TiO3-Ba(Zr0.2Ti0.8)O3-xwt %CuO(BCZT-xCu) piezoelectric ceramics have been fabricated by the solid-state reaction process and the effects of CuO addition on the phase structure and piezoelectric properties of the ceramics have been studied. Our results reveal that the addition of CuO significantly improves the sinterability of BCZT ceramics which results in a reduction of sintering temperature from 1,540 to 1,350 °C without sacrificing the high piezoelectric properties. X-ray diffraction (XRD) data shows that CuO diffuses into the lattice of BCZT-xCu ceramics and a pure perovskite phase forms in the ceramic. SEM images indicate that a small amount of CuO addition affects the microstructure, obviously. Main piezoelectric parameters of these ceramics are optimized around x = 0.04 wt % with a high piezoelectric coefficient (d33 = 510 pC/N), a planar electromechanical coefficient kp of 45%, a high dielectric constant (er = 3,762) and a low dissipation factor (tanδ = 1.05%) at 1 kHz. The results indicate that the BCZT-xCu ceramics are promising lead-free practical applications.

Effect of B<sub>2</sub>O<sub>3</sub> on Microwave Dielectric Properties of Ca[(Li<sub>1/3</sub>Nb<sub>2/3</sub>)<sub>0.92</sub>Zr<sub>0.08</sub>]O<sub>3−δ</sub>−0.05TiO<sub>2</sub> Ceramics

The effects of B2O3 on the sinter ability and microwave dielectric properties of Ca [(Li1/3Nb2/3)0.92Zr0.08]O3−δ−0.05TiO2 (CLNZ−0.05TiO2) ceramics were investigated. B2O3 doping can effectively reduce sintering temperature by 150~200 °C. The temperature coefficient of resonator frequency τf increased with an increase of B2O3 content and sintering temperature. When B2O3 of 2.5 wt % were added, the optimum microwave dielectric properties: εr =34.2, Qf =15680GHz and τf = − 4.7×10−6/°C were obtained at the sintering temperature of 950 °C.

Fabrication of (Nd0.01LaXY0.99−X)2O3 Nanoparticles and Transparent Ceramics by Combustion Synthesis

Y2O3 acts as the matrix material when doped with different content of La2O3 for reducing sintering temperature and refining grains. The (Nd(0.01)La(x)Y(0.99-x))2O3 nanoparticles and transparent ceramics are fabricated by a combustion synthesis. The powder feature is characterized by TEM. The microstructure, mechanical properties and transmittance of the samples are examined by SEM, HV-1000 hardness tester and fluorescence analyzer respectively. The results show that the (Nd(0.01)La(x)Y(0.99-x))2O3 nanoparticles are homogeneous in size and nearly spherical with average diameter in the range of 40-60 nm. There are no other phases except the Y2O3 cubic phase in the (Nd(0.01)La(x)Y(0.99-x))2O3 nanoparticles. The grains of the samples significantly reduce with increasing La2O3 content. The hardness and fracture toughness increase rapidly first and then gradually tend to plateau with increasing La2O3 content. The transmittance of sample also increases gradually with increasing La2O3, the largest transmittance exceeds 77% when the La2O3 content is x = 0.12.

인공경량골재의 EAF dust 첨가에 따른 초경량화에 관한 연구

제철공업에서 부산물로 발생되는 EAF(Electric Arc Furnace) dust는 유해한 철분 성분을 다량 함유하고 있어 환경파괴를 일으킬 위험이 있는 지정폐기물이다. EAF dust의 자원화를 위하여 석탄화력 발전소에서 발생되는 바닥재와 준설토에 EAF dust를 첨가하여 세라믹 다공체의 제조 가능성을 연구하였다. 또한 등유는 비교적 저온에서 발포기구에 작용하는 탄소(C)의 효과를 보기위해 첨가하였다. 혼합은 건식 공정으로 했으며, 소결 방법은 <TEX>$1050^{\circ}C$</TEX>부터 <TEX>$1200^{\circ}C$</TEX>까지 <TEX>$50^{\circ}C$</TEX> 간격으로 10분간 직화소성 하였다. 소결된 시편의 비중, 흡수율 및 미세구조를 관찰한 결과, EAF dust는 시편 내의 발포 현상을 용이하게 하여 초경량 다공체 골재를 얻을 수 있었다. <TEX>$1150{\sim}1200^{\circ}C$</TEX>의 소결온도에서 10 wt% EAF dust를 첨가한 인공경량골재는 비중 1.0 g/<TEX>$cm^3$</TEX> 이하의 초경량 인공 경량 골재를 만드는 것이 가능할 것으로 판단되었다. EAF dust from steel industry used as primary materials for the production of lightweight aggregates. Fe compounds in EAF dust plays an important role in the bloating reaction. This study was conducted to evaluate the feasibility of using bottom ash and dredged soil from coal power plant and EAF dust. The effect of different raw material compositions and sintering temperatures on the lightweight aggregate properties were evaluated. The characteristic of thermal bloating of bottom ash and dredged soil were mainly influenced by ferrous materials. The specific gravity of aggregate was decreased with the addition of EAF dust and kerosene was reduced sintering temperature on the bloating formation. Lightweight aggregate containing 10% EAF dust having apparent density under 1.0 g/<TEX>$cm^3$</TEX> were produced at <TEX>$1150{\sim}1200^{\circ}C$</TEX>.

Reduction of Sintering Temperature of Porous Tungsten Skeleton Used for Production of W-Cu Composites by Ultra High Compaction Pressure of Tungsten Powder

Production of tungsten-copper composites includes compaction and sintering of tungsten powder, then infiltration of copper melt within the tungsten skeleton. Sintering of tungsten compacts usually requires a temperature range of 1800 to 2200°C. This means, this process not only needs advanced heating equipments and high expenses but also may cause formation of defects such as structural heterogeneities, cracks and distortions. In this research the required sintering temperature was reduced to 1500°C by increasing compaction pressure. Also the relation between compaction pressure applied through a cold isostatic press (CIP), and green density of the compacted tungsten powder was established. In addition, the effect of various pressures on densification of tungsten compacts during sintering at moderate temperature, i.e. 1500°C was studied, and the optimum structure for infiltration was chosen. Then by infiltrating Cu melt into the optimized W-skeleton, composites of W-Cu having a density of 17.2 gr/cm3 were produced. This method of production provides an innovative technique for obtaining a desired density of infiltrable skeleton, sinterable at a lower temperature than the temperatures used for the conventionally packed W-compacts without introducing structural inhomogeneities during sintering. Study of some characteristics of the optimized composite produced by the above technique satisfied the requirements for production of W-Cu composites having all the specifications given for these types of composites produced at higher temperatures than 1500°C.

Low‐Temperature Sintering and Properties of 0.98PZT–0.02SKN Ceramics with LiBiO2 and CuO Addition

The low‐temperature sintering behavior of Pb(Zr0.53, Ti0.47)O3–Sr(K0.25, Nb0.75)O3 (PZT–SKN) piezoelectric ceramics with LiBiO2 and CuO addition has been investigated. The addition of 6 wt% LiBiO2 or 1 wt% LiBiO2+1 wt% CuO promotes the sinterability of 0.98PZT–0.02SKN ceramics owing to the generation of a liquid phase, resulting in a reduction of sintering temperature by about 300°–350°C. The microstructure, dielectric, and piezoelectric properties of flux‐sintered ceramics were examined and compared with materials conventionally sintered at 1250°C. PZT–SKN ceramics with 1 wt% LiBiO2+1 wt% CuO addition were sintered to high density at 900°C for 1 h. The resulting samples exhibited a high‐field d33 piezoelectric coefficient of 415 pm/V with a Curie temperature Tc of around 351°C, dielectric constant ɛr of 1235, and planar coupling factor kp of 0.54. The reduced sintering temperature and short soaking time, together with the favorable dielectric and piezoelectric properties of the fluxed PZT–SKN ceramics, demonstrate the potential opportunity of integration with low‐temperature cofired ceramic materials and low‐fire electrode materials for the multilayer piezoelectric transducer application.

Dielectric properties of low-temperature sintered Ba0.6Sr0.4TiO3 derived from citrate method

Superfine and uniform Ba0.6Sr0.4TiO3 powder with average particle size of 56 nm was derived from citrate method at calcining temperature of 550 °C. The desired morphological feature of the powder was found to be effective in reducing sintering temperature of the ceramic specimens. Sintering at 1260 °C produced ceramic specimen with a fine-grained (about 0.5 μn) microstructure and reasonable densification around 95% of the theoretical density. The dielectric properties of the ceramic specimen were investigated in terms of dielectric thermal spectrum, polarization versus electric-field relation and dielectric nonlinearity under bias electric-field. The ceramic specimen exhibited a dielectric constant (ϵr) of 3530 and a dielectric loss (tan δ) of 0.47% at 10 kHz and zero bias field together with a tunability of 39.3% at 10 kHz and 20 kV/cm. Moreover, the dielectric nonlinearity was detected to be sensitive to the field history. This sensitivity was tentatively explained with respect to the existence of polar nano-regions (PNRs) superimposed on macroscopically paraelectric background of the ceramic matrix.

Effect of Sr on Sm-doped ceria electrolyte

The effect of Sr addition (0–10 mol%) on the densification, crystal structure, ionic conductivity, thermal expansion, and flexural strength of Ce 0.8Sm 0.2O 1.9 (SDC) was studied. Sr addition promotes densification and reduces sintering temperature by ∼100 °C. X-ray diffraction analysis showed that all the samples exhibit a fluorite structure. Impedance spectroscopy measurements indicated that SDC incorporated with an appropriate ratio of Sr (4–10 mol%) has higher ionic conductivity and lower activation energy compared with those of SDC. As the added amount of Sr increases by up to 6 mol% (0.94SDC-0.06Sr), the sample attains the highest ionic conductivity, about 30% higher than that of SDC at 700 °C. Moreover, flexural strength increases with Sr content, with the addition of 10 mol% Sr increasing the flexural strength of SDC from 97 to 160 MPa. In addition, thermal expansion is linear for all the samples. The addition of Sr does not appreciably change thermal expansion coefficient.

Sintering and Electrical Properties of Ce&lt;sub&gt;0.8&lt;/sub&gt;Sm&lt;sub&gt;0.2&lt;/sub&gt;O&lt;sub&gt;1.9&lt;/sub&gt; Solid Electrolyte Modified by Addition of MnO&lt;sub&gt;2&lt;/sub&gt;

The effect of MnO2 addition (0–2.0 mol%) on the densification, crystal structure, and ionic conductivity of Ce0.8Sm0.2O1.9 (SDC) was studied. The addition of MnO2 promotes densification, reducing sintering temperature by ~150°C. X-ray diffraction analysis showed that all the samples exhibit a fluorite structure. Impedance spectroscopy measurements indicated that SDC with appropriate ratio of MnO2 addition has higher ionic conductivity and lower activation energy compared with that of SDC. As the addition amount of Mn increases up to 1.0 mol% [(Ce0.8Sm0.2O1.9)0.99+(MnO2)0.01], the sample attains the highest ionic conductivity, about 35% higher than that of SDC at 600°C. In addition, Mn addition has little effect on bulk conductivity, but a marked influence on grain boundary behavior is observed.

Effect of B2O3 Additions and Sintering Temperature on the Microwave Dielectric Properties of 0.7La(Mg0.5Sn0.5)O3–0.3(Sr0.8Ca0.2)3Ti2O7 Ceramics

The microwave dielectric properties of 0.7La(Mg0.5Sn0.5)O3–0.3(Sr0.8Ca0.2)3Ti2O7 ceramics were investigated for application in mobile communication. A sintering temperature reduction of about 150°C was obtained by using B2O3 as sintering aid. The X-ray diffraction patterns of the 0.7La(Mg0.5Sn0.5)O3–0.3(Sr0.8Ca0.2)3Ti2O7 ceramics exhibited no significant variation of phase with extent of B2O3 addition and sintering temperatures. The dielectric constant, quality factor, and temperature coefficient of resonant frequency of 0.7La(Mg0.5Sn0.5)O3–0.3(Sr0.8Ca0.2)3Ti2O7 ceramics doped with 0.50 wt% B2O3 addition sintered at 1400°C for 4 h are 30.0, 28,800 GHz, and 0 ppm/ OC, respectively.

Effect of Fe 2O 3 on Sm-doped ceria system solid electrolyte for IT-SOFCs

The effect of Fe 2O 3 addition (0–2.5 mol%) on the densification, crystal structure, ionic conductivity, and aging behavior of Ce 0.8Sm 0.2O 1.9 (SDC) was studied. The addition of Fe 2O 3 promotes densification, reducing sintering temperature by ∼100–150 °C. X-ray diffraction showed that these materials exhibit a fluorite structure; a second phase of Fe 2O 3 is identified when Fe 2O 3 content was ≥1.5 mol%. Impedance spectroscopy measurements indicated that SDC with 0.25 mol% Fe 2O 3 has the highest conductivity, about 10% higher than that of SDC at 700 °C. Conversely, a reduction in conductivity is observed in all samples after aging in air at 800 °C for 120 h. Because of the harmful effect of aging, conductivity rapidly decreases as Fe 2O 3 content in the samples exceeded 0.25 mol%. However, SDC with 0.25 mol% Fe 2O 3 shows the same magnitude of decrease in conductivity compared with that of SDC after aging. This indicates that SDC with 0.25 mol% Fe 2O 3 continues to present the best conductivity even after high-temperature aging.