Step Sintering Process Research Articles

Fluorine-substituted HA reinforced with zircon as a novel nano-biocomposite ceramic: Preparation and characterization

Abstract This work began with preparing hydroxyapatite from bovine bones and continued with doping fluorine into hydroxyapatite matrix to produce fluorine-doped hydroxyapatite in optimum conditions. At the end a fluorine hydroxyapatite–zircon nanocomposite ceramic with good bioactivity and good chemical stability was synthesized through a mechano-chemical route and subsequent two step sintering process. The ability of apatite formation on the produced nanocomposite samples, as a yardstick for evaluation of the bioactivity, was estimated by using simulated body fluid. According to the results obtained, after soaking the nanocomposite samples in the fluid solution, the pH value was increased during the first week of experiments. Furthermore, the concentration of the Ca ions at the end of the second week in the fluid solution was dependent on the Si – OH nucleation sites on the surface of nanocomposite.

Enhanced capacitance supercapacitor electrodes from porous carbons with high mesoporous volume

The electrochemical properties of porous carbons used as supercapacitor electrodes are largely determined by the pore size and its distribution. Here, we report that high–mesopore–volume nanocarbons (HMC) produced by one–step sintering process considerably improve the capacitive behavior by providing the desired highly accessible surfaces. The symmetric supercapacitors based on the HMC materials show high gravimetric capacitances of ∼180 and ∼215Fg−1 and also high volumetric capacitances in organic and ionic liquid electrolytes. High mesoporous volume ratio of HMC sample (∼76%) facilitates fast ionic transport while preserving good electronic conductivity and thus delivers both high energy and power density. This simple, cost–effective and scalable preparation technique and excellent capacitive behavior of HMC samples encourage their practical application.

MPB Phase Transition and Microstructure of (1 – x)PMN–xPZT Activated by 0.05BZN Ceramics

The relaxor ferroelectric materials can be found in morphotropic phase boundary (MPB) existing between tetragonal and cubic phase. Since the MPB shifts to other phases by adding ceramics composition. [(1 – x)Pb(Mg1/3 Nb2/3)O3–x Pb(Zr0.52Ti0.48)O3] were doped by 0.05Ba(Zn1/3 Nb2/3)O3 when x = 0.4, 0.3, and 0.2 ceramics, which prepared by using a two–step sintering process. The MPB transitions were studied by the use of XRD. The samples, at x = 0.4, were in MPB and then gradually shifted to cubic phase at x = 0.2. The microstructure of samples fracture found that the largest grain size of 4.51 μm for x = 0.2. This study using TEM technique which demonstrated a crystalline morphology with the largest crystal size about 1.293 μm at x = 0.3. These results also revealed that not only the ferroelectric phase shifted to relaxor behavior with decreasing PZT contents in PMN–PZT system but also activated by BZN, which led to the presence of the relaxor behavior.

Processing of Injection Moulded of Synthesized HAp by Single Step Wick-Debinding and Sintering

The present study was conducted to investigate the possibility of merging the wick-debinding and sintering of injection-molded ceramic parts into a single-step operation. In this study, the synthesized hydroxyapatite (HAp) feedstock prepared was injection moulded according to ASTM standard C1424-10 to produce green specimens. The green specimens were then debound and sintered through a single step wick-debinding and sintering process by using alumina powder as an embedment agent. The principle of this method is that it carried out at a temperature where the binder is melt, allowing it to flow out of the specimens into pores in the contacting of substrate. Once, the binder is successfully removed from the specimens, sintering process is took place to bond the particle together leading to densification of sintered specimens. From the results, it shows that the binders were successfully removed from the green specimens by capillary suction of the molten binder and single phase of HAp was presented at the sintering temperature of 1000°C.

Understanding the Oxygen Reduction Activity of Composite Catalysts Based on Carbon and Calcium-Doped Lanthanum Cobalt Manganese Oxide

Energy storage is essential for large-scale integration of renewable energy such as solar and wind into electricity generation. Fuel cells and metal-air batteries are promising technologies for grid-scale energy storage owing to their high energy densities and environmental compatibility. However, it is well known that the slow kinetics of the oxygen reduction reaction (ORR) at the cathode limits the efficiency of these fuel cells and metal-air batteries. Among transition metal oxides calcium-doped lanthanum cobalt oxide is one of the promising catalyst for ORR because of the ability of these materials to support oxygen evolution and oxygen reduction reactions [1]. In previous work, we demonstrated that in transition metal oxide–carbon composites catalysts, carbon is the primary electrocatalyst for the two electron electro-reduction of oxygen to hydrogen peroxide and the transition metal oxide decomposes the hydroperoxide to generate additional oxygen [2]. Therefore we have aimed at understanding the role of mixed metal oxides on decomposition of hydrogen peroxide. Manganese-substituted compounds of the formula La0.6Ca0.4Co1-xMnxO3 compound with x value = 0.0, 0.1, 0.3, 0.5, 0.7 and 0.9 were synthesized by the sol-gel method using citrate route. As previously described [3], a two-step sintering method was employed for the synthesis of these compounds. In the first step the material subjected to controlled combustion at 120-170 oC, then the material was collected, ground and heat-treated in a second step sintering process at 700o C for 2 hours. The ability of transition metal oxide to decompose peroxide was studied using a ring disk (coated glassy carbon) electrode, and also by direct measurement of decomposition rate of peroxide, and by steady state polarization studies of oxidation and reduction of hydrogen peroxide. The ORR activity mass-normalized kinetic current at -100 mV (vs. reference Hg/HgO 20% potassium hydroxide) and the percentage of H2O2 at the ring for various values of manganese content are shown in Figure 1. The poster presentation will discuss these results. Fig. 1 Mass normalized kinetic current for oxygen reduction reaction on La0.6Ca0.4Co1-xMnxO3 compounds at -100 mV (vs. Hg/HgO 20 % KOH) and percentage of H2O2 at the ring in 1 M KOH solution for various fractions of manganese. Acknowledgement The work presented here was funded by ARPA-E Grids Program (DE-AR0000136), the University of Southern California and the Loker Hydrocarbon Research Institute.

Optimization of FeSe superconductors with the high-energy ball milling aided sintering process

FeSe Superconducting bulks with high superconducting phase ratio were prepared with high energy ball milling (HEBM) aided sintering process. During the HEBM process, the solid solution of Fe–Se (Fe(Se)SS) can be successfully obtained, which not only assured the atomic uniformity of precursor powders, but greatly shortened the diffusion distance between Fe and Se atoms. Therefore tetragonal β-FeSe superconducting phase can be formed directly with one step sintering process and the formation of hexagonal δ-FeSe non-superconducting phase can be avoided. The influences of Fe/Se ratio and sintering temperature on the phase transition process and the superconducting properties were systematically studied. The change of Fe/Se ratio showed great influences on both the superconducting volume and critical temperature of final bulks. By increasing the sintering temperature to 700 °C, FeSe bulk with higher texture, better crystallization and optimized chemical composition was achieved. The FeSe superconducting bulk with the critical temperature Tc(onset) of 9.0 K was obtained with the Fe/Se ratio of 1.20, HEBM time of 6 h, and sintering temperature of 700 °C.

Effect of agglomeration and calcination temperature on the mechanical properties of yttria stabilized zirconia (YSZ)

Effect of azeotropic distillation after co-precipitation process of powder synthesis on powders morphology and mechanical properties of yttria stabilized zirconia was studied. The formation of hard or soft agglomerates during drying or calcination of co-precipitated powder can easily be prevented through azeotropic distillation. The powder prepared by direct co-precipitation and azeotropic treatment after co-precipitation process was calcined at different temperatures and was characterized through X-ray diffraction, transmission electron microscope and BET surface area measurement. The calcined powders were compacted uniaxially and sintered in two step sintering process. Sintered, polished and thermally etched samples were observed under scanning electron microscope. Vickers hardness and indentation fracture toughness were estimated. It is observed that reasonably higher density with better hardness and fracture toughness can be achieved for azeotroped samples in same sintering condition. Azeotropic treatment increases the surface area almost three times which helps to achieve better sintering. Pin on disc wear tests against alumina disc at 20N and 50N loads up to 3000m distance were carried out. The wear depth and coefficient of friction for both the material were compared.

Two step sintering process and metal grid design optimization for highly efficient ITO free organic photovoltaics

The need for inexpensive alternative to indium doped tin oxide (ITO) transparent electrodes is imminent for cost-efficient solution processed optoelectronic applications. ITO-free transparent electrodes can be based on inkjet-printed Silver (Ag) nanoparticles grids embedded into PEDOT:PSS buffer layers. We present an in-depth investigation of the morphological evolution of the inkjet printed Ag nanopartricle sintering process combined with an ultimate control of the printed grid design requirements for efficient ITO-free organic photovoltaics (OPVs). We report on glass/ITO-free P3HT:PC60BM and Si-PCPDTBT:PC70BM based OPVs with power conversion efficiency of 2.8% and 4.9% respectively. These devices exhibited minimal losses when compared to reference ITO-based OPVs.

Initial Preparation and Characterization of Single Step Fabricated Intermediate Temperature Solid Oxide Fuel Cells (IT‐SOFC)

AbstractIn this study, facile tape casting process has been successfully carried out to fabricate an unit anode supported intermediate temperature solid oxide fuel cell (IT‐SOFC) with four different layers: a composite cathode which is a mix of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF48) and Gd0.1Ce0.9O1.9 (GDC10), GDC10 as thin electrolyte layer, NiO‐GDC10 without pore former as thin anode functional layer (AFL), and anode support layer of NiO‐GDC10 with carbon pore former. The multi‐layer was sintered once to produce an unit planar cell. An OCV of 1.002 V at 500 °C, and maximum power density of 466 mW cm–2 at 648 °C are obtained. These results indicate negligible leakage of fuel through electrolyte. Furthermore scanning electron microscope (SEM) revealed crack free dense electrolyte. The single step sintering process gives an unit planar cell, which exhibits good performance without use of sintering aids, co‐pressing, and lamination of green tape.

Copper Indium Gallium Selenide (CIGS) Photovoltaic Devices Made Using Multistep Selenization of Nanocrystal Films

The power conversion efficiency of photovoltaic devices made with ink-deposited Cu(InxGa1-x)Se2 (CIGS) nanocrystal layers can be enhanced by sintering the nanocrystals with a high temperature selenization process. This process, however, can be challenging to control. Here, we report that ink deposition followed by annealing under inert gas and then selenization can provide better control over CIGS nanocrystal sintering and yield generally improved device efficiency. Annealing under argon at 525 °C removes organic ligands and diffuses sodium from the underlying soda lime glass into the Mo back contact to improve the rate and quality of nanocrystal sintering during selenization at 500 °C. Shorter selenization time alleviates excessive MoSe2 formation at the Mo back contact that leads to film delamination, which in turn enables multiple cycles of nanocrystal deposition and selenization to create thicker, more uniform absorber films. Devices with power conversion efficiency greater than 7% are fabricated using the multiple step nanocrystal deposition and sintering process.

Dual Carbon Coating Used in the Preparation of LiFePO<sub>4</sub>/C Cathode Material

The LiFePO4/C cathode material was synthesized by two–step addition of dual carbon sources method based on the in situ polymerization method combining with two–step sintering process. In this study, the structure and morphology have been studied systematically by X–ray diffraction (XRD) and scanning electron microscope (SEM).The electrochemical performances have been shown by the charge/discharge capacity, rate property, cycle performance. It was evidenced that the two–step addition of dual carbon sources had remarkable advantages, including the more complete coating carbon, and the improvement in the electrochemical performance of LiFePO4/C.

One-step sintering process of gadolinia-doped ceria interlayer–scandia-stabilized zirconia electrolyte for anode supported microtubular solid oxide fuel cells

A microtubular solid oxide fuel cell (SOFC) consisting of Gd-doped CeO 2 (GDC) interlayer–Sc stabilized zirconia (ScSZ) electrolyte has been prepared on an anode supported tube using one step sintering process at 1350 °C. The cell performance under high fuel utilization condition, with H 2 flow rate as low as 4.3 mL min −1 per 1 cm 2 electrode area is evaluated. The one-step sintering process results in an improvement of open circuit voltage but an increase of ohmic resistance due to possible high resistive layer and voids observed between GDC and ScSZ layers. The performance of the cell shows power densities of 0.35–0.57 W cm −2 with corresponding energy efficiencies of 45–20% (LHV), respectively, at 700 °C. Impedance analyses at different voltages have shown that the overpotential due to gas transport is dominant in the low current density region.

Dielectric Characteristics and Tunability of Barium Zirconium Titanate Ceramics Prepared by Two-Step Sintering Method

Barium zirconium titanate ceramics with a composition of BaZr0.07Ti0.93O3 were synthesized using a modified two step sintering process and the dielectric and mechanical properties of the ceramics were investigated. The modified sintering helped to improve the sinterability of the samples resulting in a high ceramic density. Improvements in the dielectric constant, dielectric tunability and hardness values were also observed. The enhancements in dielectric and mechanical properties were directly related to the improvement in densification of the samples.

Fabrication and Characterizations of YSZ Electrolyte Films for SOFC

Yttria stabilized zirconia (YSZ) has been widely used as electrolyte in solid oxide fuel cell (SOFC). The effect of fabrication process on the properties of YSZ electrolyte thick film is discussed in the paper. With YSZ nano-powders of about 20-60nm as raw material, YSZ green adobe was fabricated by tape calendering process. Three-step sintering process was performed firstly holding at 1000°C for 2h, then raising to 1300~1400°C, then decreasing to 1200~1300°C within 30 minutes, and finally calcining at 1200~1300°C for 5~20 hrs. Dense YSZs with relative density of 96-99% are obtained; the grain size of YSZ was reduced to 0.5-3µm. During the process of grain growth, there are both grain boundary diffusion and grain boundary migration. The feasibility of densification without grain growth relies on the suppression of grain boundary migration while keeping grain boundary diffusion active at a temperature as low as 1200~1300°C. Whereas the electric conductivities of the YSZs are even higher than that obtained in conventional single step sintering process. The process is applied to the anode-supported SOFCs co-fired at 1250~1300°C, and the cathode-supported SOFCs co-fired at 1200~1250°C.

Study of microstructure and dielectric properties of PMN–PZT ceramics via a mixed powder method including sol–gel precursor

An attempt to synthesize pyrochlore free ( x)PMN–(1 − x)PZT ceramics (where x is 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1) by a mixed powder method was made. In this work, a sol–gel prepared PZT powder was mixed with the mixture of milled PbO, MgO and Nb 2O 5, and sintered in a two step sintering process. The produced samples with high PZT content showed low densities due to the low compaction ratio of PZT powder. The dielectric properties of PZT-rich and PMN-rich materials were high (with dielectric constant of about 19,000 and 33,000 for PZT-rich and PMN-rich ceramics, respectively) while the other samples exhibited low dielectric properties. Also, the effect of combining PMN with PZT on Curie temperature was studied.

Fabrication of YAG Transparent Ceramics by Two Step Sintering Process

Well dispersed yttrium aluminum garnet (YAG) nanopowders with mean particle size of about 50nm synthesized by modified co-precipitation method were used to sinter YAG transparent ceramics with 0.5wt% TEOS as sintering additive by two step sintering process. The samples were first heated to a higher temperature ranging from 1700 ◦ C to 1800 ◦ C, then cooled down to a lower temperature ranging from 1500 ◦ C to 1600 ◦ C, and held at the lower temperature for 10h. Grain-boundary migration is suppressed and grain-boundary diffusion is promoted during the two step sintering process. When the two step sintering temperatures are 1800 ◦ C and 1550 ◦ C, the microstructure of YAG is homogeneous with average grain size of 6µm without abnormal grain growth and the transmittance of the specimen is 72.0%.

Realization of high-energy density polycrystalline piezoelectric ceramics

This letter reports a high energy density piezoelectric material in the system given as: Pb[(Zr0.52Ti0.48)O3]1−x[(Zn1∕3Nb2∕3)O3]x+yMnCO3, where x=0.1 and y varies from 0.5to0.9wt%. A piezoelectric material with high energy density is characterized by a high product of piezoelectric voltage constant (g) and piezoelectric strain constant (d). The condition for obtaining large magnitude of g constant was derived to be as ∣d∣=εn, where ε is the permittivity of the material and n is constant having lower bound of 0.5. It was found that for all practical polycrystalline piezoelectric ceramic materials the magnitude of n lies in the range of 1.1–1.30 and as the magnitude of n decreases towards unity a giant enhancement in the magnitude of g was obtained. A two step sintering process was developed to optimize a polycrystalline ceramic composition with low magnitude of n. For the optimized composition the value of g33 and d33 was found to be 55.56×10−3m2∕C and 291×10−12C∕N, respectively, yielding the magnitude product d33∙g33 as ∼16168×10−15m2∕N which is significantly higher than the reported values in literature. The magnitude of n for this composition was calculated to be 1.151. This material is extremely promising for immediate applications in the sensing and energy harvesting.

High Oxide Ion Conductivity in Mg‐Doped La10Si6O27 with Apatite‐Type Structure.

AbstractFor Abstract see ChemInform Abstract in Full Text.

High Oxide Ion Conductivity in Mg-Doped La10Si6O27 with Apatite-type Structure

Abstract Structure and ionic conductivity of Mg-doped La10Si6O27 was investigated on dense ceramic samples prepared from sol–gel derived powders using two step sintering process. The conductivity was increased by the doping (from 22 to 30–39 mS cm−1 at 800 °C) because of expansion of the apatite lattice.

Microstructure Development during Sintering in Polycrystalline MgO⋅1.5Al<sub>2</sub>O<sub>3</sub> Spinel

Fine Al-rich spinel MgO⋅1.5Al2O3 powder was synthesized by hydrolysis of mixed alkoxides. High sinterability of powder allowed to obtain relative density higher than 95% at temperature as low as 1300°C by pressureless sintering in air. Samples sintered at temperature of 1100°-1500°C had quite heterogeneous microstructure owing to precipitation of large corundum particles ( 1400°C). However, homogeneous microstructure with fine grains could be obtained by a two step sintering process in which spinel grain growth at high temperature was inhibited by corundum particles momentarily retained above solvus temperature. Precipitation behavior during sintering was compared with that during annealing, and the precipitation mechanism was discussed.