Effective Sintering Aid Research Articles

Effect of Bi2O3 on the electrochemical performance of LaBaCo2O5+δ cathode for intermediate-temperature solid oxide fuel cells

The LaBaCo2O5+δ−x wt.% Bi2O3 (LBCO-xBi2O3, x=10, 20, 30, and 40) were prepared as composite cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs) via the conventional mechanical mixing method. The effect of Bi2O3 on polarization resistance, overpotential, and long-term stability of the LBCO cathode was investigated. An effective sintering aid for LBCO cathode, Bi2O3 not only lowers its sintering temperature by ~200°C, but also improves the electrochemical performance within the intermediate temperature range of 600–800°C. Electrochemical impedance spectroscopy measurements showed that the addition of 20wt% Bi2O3 to LBCO exhibited the lowest area-specific resistance of 0.020Ωcm2 at 800°C in air, which was about a seventh of that of the LBCO cathode at the same condition. At a current density of 0.2Acm−2, the cathodic overpotential of LBCO-20Bi2O3 was about 12.6mV at 700°C, while the corresponding value for LBCO was 51.0mV. Compared to B2O3–Bi2O3–PbO frit, the addition of Bi2O3 significantly improved the long-term stability of cathode. Therefore, LBCO-20Bi2O3 can be a promising cathode for IT-SOFCs.

Effect of sintering aid (CoO) on transport properties of nanocrystalline Gd doped ceria (GDC) materials prepared by co-precipitation method

Abstract Electrical and dielectric properties of the nanocrystalline GDC materials co-doped with CoO (by deposition precipitation method) were studied in the temperature range of 150–600 °C. CoO co-doped samples show higher grain interior conductivity than that of GDC. Dielectric loss tangent (tan δ) shows the presence of defect associates such as ( Co - V o ¨ - Co ) and ( Co - V o ¨ ) in co-doped samples in addition to the defects ( Gd - V o ¨ - Gd ) and ( Gd - V o ¨ ) that are present in GDC system. Dynamic parameters such as migration energy and association energy of oxygen vacancies do not vary significantly with co-doping CoO in the GDC materials. With higher content of CoO, excess of Co2+ in the grain boundary regions leads to trapping of vacancies and/or depletion of vacancies in the space charge region. Therefore grain boundary activation energy increases and grain boundary conductivity decreases with CoO content above 1 mol%, at lower temperatures. In the temperature range of 150–600 °C overall conductivities in CoO co-doped samples increase two to three times than that of GDC material.

Effect of alumina on the properties of ceria and scandia co-doped zirconia for electrolyte-supported SOFC

Abstract The properties of ceria and scandia co-doped zirconia electrolytes with different alumina additions were investigated. Microstructure analysis revealed that alumina was an effective sintering aid for ceria and scandia co-doped zirconia. Small addition (

Low-Temperature Sintering of Barium Calcium Zirconium Titanate Lead-Free Piezoelectric Ceramics

The need for lead-free piezoceramics has caused a renewal of interest in BaTiO₃-based systems. Recently, it was found that ceramics in the (Ba,Ca)(Zr,Ti)O₃ system have properties comparable to those of Pb(Zr,Ti)O₃. However, these ceramics require rather high sintering temperatures of 1450-1550℃. In this work, the effect of TiO₂ and CuO addition on the sintering behavior, microstructure, dielectric and piezoelectric properties of (Ba 0.85 Ca 0.15 )(Zr0.1Ti 0.9 )O₃ (BCTZ) ceramics will be discussed. BCTZ ceramics were prepared by the mixed oxide route and 1 ㏖ % of TiO₂ or CuO was added. Undoped and doped ceramics were sintered at 1350℃ for 1-5 h. CuO was found to be a very effective sintering aid, with samples sintered for 1 h at 1350℃ having a bulk density of 95% theoretical density; however the piezoelectric properties were greatly reduced, probably due to the small grain size.

Mechanical properties' improvement of a tricalcium phosphate scaffold with poly-l-lactic acid in selective laser sintering

To improve the mechanical properties of a scaffold fabricated via selective laser sintering (SLS), a small amount (0.5–3 wt%) of poly-l-lactic acid (PLLA) is added to the β-tricalcium phosphate (β-TCP) powder. The fracture toughness of the scaffold prepared with the mixture powder containing 1 wt% PLLA increases by 18.18% and the compressive strength increases by 4.45% compared to the scaffold prepared from the β-TCP powder. The strengthening and toughening is related to the enhancement of β-TCP sintering characteristics via introducing a transient liquid phase in SLS. Moreover, the microcracks caused by the volume expansion due to the β–α phase transformation of TCP are reduced because of the PLLA inhibition function on the phase transformation. However, PLLA additive above 1 wt% would lead to a PLLA residue which will decrease the mechanical properties. The experimental results show that PLLA is an effective sintering aid to improve the mechanical properties of a TCP scaffold.

Preparation of doped BaZrO3 and BaCeO3 from nanopowders

To lower the calcining and sintering temperatures of 16 at% Y-doped BaZrO3 (BYZ), Gd-doped BaCeO3 (BGC) and Smdoped BaCeO3 (BSC), nanopowders of BaCO3 and either (i) yttria stabilized zirconia, (ii) Gd2O3 and CeO2 or (iii) Sm2O3 and CeO2, were used as starting materials, respectively. BYZ powders were prepared by two mixing methods (i.e. ball milling and magnetic stirring), followed by calcination at 1050–1250 °C, while BSC and BGC powders were prepared by ball milling and calcined at 1050 °C. The results reveal that the ball milling and magnetic stirring methods yield similar results for BYZ powder preparation. By adding 1 wt% ZnO nanopowder, the average relative densities of BYZ pellets were increased from ∼70% to ∼96% at the sintering temperatures of 1300 °C. Thus, with the utilization of nanopowders and ZnO as a sintering aid, the calcining and sintering temperatures were lowered to 1050 °C and 1300 °C, respectively, while still attaining the relative bulk densities of both BYZ and BGC higher than 95.7%. However, since the relative bulk density of BSC reached only 93% even sintered at 1400 °C, ZnO was not an effective sintering aid for the BSC fabrication.

Effects of sintering aids on the densification of Mo–Si–B alloys

The effects of seven sintering aids (0.5 at.% Ni, Co, Fe, Cr, Zr, Nb, and Pd) on the densification of Mo–Si–B alloys of six different compositions (Mo, Mo–0.2Si, Mo–0.2Si–0.02B, Mo–2.5Si–2.5B, Mo–7Si–5B, and Mo–8.9Si–7.7B at.%) are systematically investigated. It was found that Ni, Co, and Fe are effective in enhancing densification of Mo–Si–B alloys, and Ni is the most effective sintering aid. This study supports a previously proposed hypothesis that activated sintering results from enhanced mass transport in the sintering-aid-induced quasi-liquid intergranular films (a type of grain boundary complexion). The relative effectiveness of these sintering aids can be rationalized by analyzing several key thermodynamic parameters that control the stability of premelting-like grain boundary complexions. Future studies are needed to develop interfacial thermodynamic models and methods for computing “grain boundary complexion (phase) diagrams” for multicomponent systems, which can be a useful component for the “Materials Genome” project that will enable better predictions of the activated sintering and other materials phenomena.

Effect of Sintering Aids on the Stress Evolution of Constrained Sintered Gadolinium-Doped Ceria Films

The in situ stress evolution of constrained Ce0.9Gd0.1O1.95 (CGO) porous thick films containing no sintering aids, 3 mol% lithium, or 3 mol% cobalt were measured from 25-1040C in air. The addition of 3 mol% lithium facilitated relaxation of the 1040C constrained sintering stress, and raised the sintered film relative density from 59 ± 5% (for pure CGO) to 85 ± 5%. In contrast, the addition of 3 mol% cobalt did not facilitate relaxation of the 1040C constrained sintering stress, and only raised the sintered film relative density to 64 ± 5%. This is surprising because both lithium and cobalt at the 3 mol% doping level are effective unconstrained CGO sintering aids (reducing the sintering temperature from ~1400C to ~800C and ~1000C, respectively). These results are consistent with cobalt enhancing solid-state diffusion and lithium inducing liquid phase sintering. Anomalous, low-temperature tensile stresses were also observed for films of all three compositions.

Effect of Sintering Aids on the Stress Evolution of Constrained Sintered Gadolinium-Doped Ceria Films

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Processing and characterization of CoO and Sm2O3 codoped ceria solid solution electrolyte

A series of ceria-based solid solution electrolytes, CoO and Sm2O3 codoped ceria Ce0.8Sm0.2−xCoxO2−δ (denoted as CSO for x=0 and CSCx for x=0.01–0.09), are synthesized via a carbonate co-precipitate method. The phase composition of the precursor is determined by XRD, EA and TG/DSC. The oxidation valence of Co in the samples calcined at different temperatures is probed by XPS and determined to be in +2 valence state at the temperature >1000°C. The sintering investigation demonstrates that the addition of Co promotes densification to occur at lower temperatures with a uniform grain growth. Impedance spectroscopy measurements indicate an improvement in the grain and the grain boundary conductivities for the samples with appropriate Co/Sm ratio. The optimal amount of Co additive is proved to be 7mol%. It shows that CSC0.07 exhibits higher conductivity (σt=0.0538Scm−1 at 600°C) and lower activation energy (Ea=0.567eV) compared with CSO and other CSCx. The results suggest that cobalt oxide could be used not only as an effective sintering aid but as a favorable dopant to ceria as well.

Decrease of sintering temperature by CuO doping of the 0.8Pb(Mg1/3Nb2/3)O3‐0.2PbTiO3 ceramics prepared by reaction‐sintering method

AbstractCuO‐doped 0.8Pb(Mg1/3Nb2/3)O3‐0.2PbTiO3 (0.8PMN‐0.2PT) ceramics were prepared by the reaction‐sintering method. X‐ray diffraction (XRD) measurement, scanning electron microscopy (SEM) observation and density measurement confirmed that the CuO‐doped 0.8PMN‐0.2PT ceramics prepared by the reaction‐sintering method with the addition of up to 5 mol% CuO and sintered over a wide sintering temperature range exhibit pure rhombohedral perovskite structure, rather homogeneous micromorphology and high relative density. As compared to the undoped 0.8PMN‐0.2PT ceramics prepared by the same method, CuO proves to be an effective sintering aid, which can greatly decrease the sintering temperature of the 0.8PMN‐0.2PT ceramics prepared by the reaction‐sintering method, where high relative density can be obtained and the electrical properties are not deteriorated or improved of the synthesized 0.8PMN‐0.2PT ceramics. The CuO doping content and sintering temperature exert great influences on the crystal structure, density and electrical properties of the 0.8PMN‐0.2PT ceramics prepared by the reaction‐sintering method.

Sintering mechanism for high-density NZP ceramics

We have studied the shrinkage kinetics and mechanism of NaZr2(PO4)3 containing inorganic additives. The sintering of NaZr2(PO4)3 containing ZnO microadditives is shown to follow a liquid-phase mechanism. Effective sintering aids include oxides of metals in the oxidation states 2+ and 3+ that are capable of reacting with sodium zirconium phosphate to form solid solutions. Ceramics having a relative density of 96–99% and isostructural with NaZr2(PO4)3 can be prepared by adding 0.75–2.0 wt % ZnO as a sintering aid capable of influencing the structure of grain boundaries in ceramic materials, pressing green bodies at 200–300 MPa, and sintering them at 1000–1100°C for 7–15 h.

Effect of MoO 3 concentration on sintering and electrical properties of SiO 2-containing neodymium-doped ceria electrolytes

The effects of MoO 3 concentration on the sintering and electrical properties of Ce 0.8Nd 0.2O 1.9 + 500 ppm SiO 2 (NDCSi) and (Ce 0.8Nd 0.2O 1.9) 1 − x (MoO 3) x + 500 ppm SiO 2 ( x = 0.01, 0.02, 0.03, 0.04, 0.05, NDCSi + 1MoO 3, NDCSi + 2MoO 3, NDCSi + 3MoO 3, NDCSi + 4MoO 3, NDCSi + 5MoO 3) prepared through a modified sol–gel method were systematically investigated. The structures and ionic conductivities were characterized by XRD, FE-SEM and EIS. The results indicated a sharp increase in densification and conductivity for the system of NDCSi containing small amount of MoO 3. It shows that NDCSi + 3MoO 3 exhibited much higher relative density (RD = 96%), higher conductivity ( σ t = 1.25 × 10 −2 S cm −1 at 600 °C) and lower activation energy ( E a = 0.81 eV) compared with NDCSi and the other MoO 3 doped-NDCSi samples. Furthermore, MoO 3 could be used as an effective sintering aid and a grain boundary scavenger for NDCSi system. And we obtained the optimal amount of the MoO 3 is 3 mol%.

Microstructure and microwave dielectric properties of ZnO-B2O3 added (Ca0.254Li0.19Sm0.14)TiO3 ceramics

The effects of ZnO-B2O3 (ZB2) on the sintering behavior and microwave dielectric properties of (Ca0.254Li0.19Sm0.14)TiO3 ceramics were investigated. The densities of the specimens reached the maximum value by adding 3 wt.% ZB2 and then decreased. The sintering temperature of the specimens was lowered from 1300 to 1100°C without degradation of the microwave dielectric properties. The (Ca0.254Li0.19Sm0.14)-TiO3 + 3 wt.% ZB2 sintered at 1100°C for 3 h showed good microwave dielectric properties, ɛ r = 108.2, Q f = 6545 GHz, and τ f = 6.5 ppm/°C, respectively, indicating that ZB2 was an effective sintering aid to improve the densification and microwave dielectric properties of (Ca0.254Li0.19Sm0.14)TiO3 ceramics.

Influence of CuO and B2O3 on sintering and dielectric properties of tungsten bronze type microwave ceramics: a case study in Ba4Nd9.3Ti18O54

The effect of CuO and B2O3 co-doping on the sintering behavior, microstructure and microwave dielectric properties of tungsten bronze type Ba4Nd9.3Ti18O54 (BNT) ceramics has been investigated by means of a traditional solid-state mixed oxide route. On the one hand, it was indicated that the mixture of CuO and B2O3 is an effective sintering aid for BNT matrix compositions owing to the existence of a low-temperature eutectic reaction. On the other hand, it was found that the addition of CuO and B2O3 has an obvious effect on microwave dielectric properties of BNT ceramics, depending on the amount of sintering aids, the sample density and microstructure. The liquid phases from sintering aids can promote densification, but simultaneously induce grain growth which tends to decrease the sintering driving force. BNT ceramics doped with 3 wt% CuO–B2O3 mixture can be well sintered at 950°C for 4 h and still exhibit relatively good microwave dielectric properties.

Cost-effective solid-state reactive sintering method for high conductivity proton conducting yttrium-doped barium zirconium ceramics

Using cost-effective precursors of BaCO 3, ZrO 2, and Y 2O 3, proton conducting ceramic pellets of BaZr 0.8Y 0.2O 3 − δ (BZY20) were successfully fabricated with the help of a range of sintering aids including LiF, NiO, Al 2O 3, and SnO 2. This simple and cost-effective solid-state reactive sintering (SSRS) method involved only a single high-temperature sintering step. The effect of various experimental conditions on the crystal structure, relative density, morphology, and total conductivity of the as-prepared BZY20 ceramic pellets were investigated in detail. Tunable experimental parameters included the type of sintering aid, the amount of aid, and the sintering temperature. NiO was determined to be the most effective sintering aid investigated. Under optimized conditions using 1–2 wt.% NiO as a sintering aid, dense BZY20 ceramic pellets (> 95% relative density) with grain sizes as large as 5 μm were successfully prepared at a relatively low sintering temperature of 1400 °C. In comparison, most alternative sintering techniques for BZY require temperatures in excess of 1700 °C. Total conductivities as high as 2.2 × 10 − 2 and 3.3 × 10 − 2 S cm − 1 were obtained from the resulting pellets at 600 °C under dry- and wet-argon atmospheres respectively. These are among the highest values reported for BZY20, highlighting the potential of the NiO-modified reactive sintering approach to provide a simple, cost-effective, reduced-temperature route to achieve dense, large-grained parts for protonic-ceramic applications.

Processing and microstructure characterization of liquid-phase-sintered, α-SiC matrix composites

Abstract Dense silicon carbide (SiC)-based ceramics were obtained by hot-pressing using BaAl 2 Si 2 O 8 (BAS) as an additive. The results showed that BAS could serve as an effective liquid sintering aid to promote densification and facilitate the growth of SiC grains. The relative densities, flexural strength and fracture toughness of the composites increase with increasing the BAS content. The flexural strength and fracture toughness of 40 wt%BAS/SiC composite could reach 510 MPa and 7.0 MPa m 1/2 , respectively, The main toughening mechanisms are crack deflection, crack bridging and SiC grain pullout. The complete crystallization of BAS is beneficial to the high temperature mechanical properties and the obtained 40 wt%BAS/SiC composite could maintain the room strength up to 1200 °C.

Properties of Barium Stannate Titanate with Boron Oxide Addition

In this study, barium stannate titanate ceramics with an addition of boron oxide were synthesized via a solid-state sintering method. The effect of sintering aid on electrical and mechanical properties of barium stannate titanate ceramics was investigated. It was found that, the ceramic with 2 wt% boron oxide showed the lowest porosity and the highest dielectric constant of ~ 13700 at room temperature. In addition, an increase in the boron oxide content was observed to enhance the hardness of the ceramics. These results may be helpful in the multilayer capacitor applications.

Effect of sintering aid on microwave dielectric properties of Mg(Zr0.05Ti0.95)O3 ceramics

Abstract The effects of B 2 O 3 addition on the sintering behavior, microstructure, and the microwave dielectric properties of Mg(Zr 0.05 Ti 0.95 )O 3 (MZrT) ceramics have been investigated. The results of X-ray diffraction (XRD) indicate the presence of six crystalline phases, Mg(Zr 0.05 Ti 0.95 )O 3 , Mg 0.25 Zr 0.38 Ti 0.38 O 1.75 , Mg 2 TiO 4 , MgTi 2 O 5 , TiO 2 , and (Mg,Ti) 2 (BO 3 )O, in the sintered ceramics, depending on the amount of B 2 O 3 added. It was found that the firing temperature required to make the Mg(Zr 0.05 Ti 0.95 )O 3 ceramics dense is lowered by increasing the B 2 O 3 content. The τ f value of the Mg(Zr 0.05 Ti 0.95 )O 3 with B 2 O 3 glass was also improved dramatically. Addition of 1.5 wt% B 2 O 3 glass lowers the sintering temperature of Mg(Zr 0.05 Ti 0.95 )O 3 from 1420 to 1270 °C, with relatively high Q × f = 108,000 (GHz), ɛ r of 17.6, and of low τ f = −2 ppm/°C.

Effective Sintering Aids of Boric Frit and Lithium Salts for Low-Temperature Sintering of Dielectric Ceramics

The sintering temperature of the dielectric ceramics had been lowered more than 300°C with 1.5 ∼ 6wt% combination additives of boric frit and lithium salts in present work. The combined effect of the additives of boric frit and lithium salts could be applied on different structures, such as a perovskite structure (SrTiO 3 ,CaZrO 3 ), a new tungsten bronze-type structure (Ba 4.5 Nd 9 Ti 18 O 54 ) and other structures (Ba 2 Ti 3 Nb 4 O 18 , Ba 3 Ti 4 Nb 4 O 21 ). Low loss (tanδ ∼10−4) dielectrics with a variety of dielectric constant (30∼300) were obtained in the systems of Ba-Ti-Nb-O, Sr-Ti-O, Ca-Zr-O and Ba-Nd-Ti-O with the boric frit and lithium salts sintered at 900∼1000°C.