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1.
In the present study, LSGM (La0.8Sr0.2Ga0.8Mg0.2O2.8) powder has been synthesized using precipitation route followed by hydrothermal treatment. Quantitative phase analyses of different powders, have been done by Rietveld analyses of the XRD data and they reveal formation of single phase orthorhombic LSGM at 1400 °C, 8 h. Morphology of the calcined powder and microstructure of the sintered pellets are observed by transmission electron microscope (TEM) and scanning electron microscope (SEM), respectively. Thermal analysis has been carried out to find out the thermal expansion co-efficient. Successive electrical characterization of the 99% dense sintered pellet has been done by impedance spectroscopic analysis. The diffused semicircles observed in the Nyquist plots have been simulated as (RQ)(RQ) circuit and the total ionic conductivity obtained is found to be the highest for LSGM synthesized by similar routes.  相似文献   

2.
《Ceramics International》2016,42(13):14956-14962
SrxCa1−xAlSiN3: Eu2+ phosphors were prepared by using the high temperature solid state reaction in a 1.1 Mpa N2 atmosphere. The phase structures, photoluminescence (PL) properties, and chromaticity properties of the phosphors affected by Sr/Ca Substitution have been investigated in detail. With increasing Sr content (x value), the crystal grain became bigger and the average grain size increased from 5 µm to 10 µm. PL emission bands of SrxCa1−xAlSiN3: Eu2+ showed a blue-shift from 660 (x=0) to 617 nm (x=0.8), the shoulder of the excitation spectra around 550 nm showed a slightly blue-shift and decay lifetime shortened from 776.96 (x=0.2) to 642.35 ns (x=0.8). Both the emission and excitation intensity of peak position increased with Sr content increased. The ideal white light with high CRI (Ra>88) can be obtained by mixing the SrxCa1−xAlSiN3: Eu2+ phosphors and commercial green phosphors with appropriate proportion of the components.  相似文献   

3.
《Ceramics International》2007,33(6):1105-1109
Stoichiometric and monophasic Ba1−xSrxTiO3 (x = 0.3) nanopowders were successfully prepared by the citric acid gel method using barium nitrate, strontium nitrate and tetra-n-butyl titanate as Ba, Sr, Ti sources and citric acid as complexing reagent. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), infrared (IR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the thermal decomposition behavior, the crystallization process and the particle size and morphology of the calcined powders. The results indicated that single-phase and well-crystallized Ba1−xSrxTiO3 (x = 0.3) nanopowders with particle size around 80 nm could be obtained after calcining the dried gel at 950 °C for 2 h.  相似文献   

4.
In this work, a continuous hydrothermal synthesis method in supercritical water was applied to environmentally benign production of Ca1−xSrxTiO3 (x = 0.0–1.0) solid-solution nanoparticles as key materials in conducting, electric, magnetic, and photocatalytic fields. A T-type micromixer (330 μm id) was introduced for rapid heating of stating solutions of Ca(NO3)2, Sr(NO3)2, and TiO2 sol using turbulent flow mixing with preheated NaOH aqueous solution and also for exact control of reaction temperature. At 673 K and 30 MPa for 5.0 s mean residence time, Ca1−xSrxTiO3 solid-solution nanoparticles having crystallite diameters of around 20 nm with monomodal diameter distributions were obtained without byproducts and production of CaTiO3 and SrTiO3 separately over the whole composition range. Effects of NaOH molality, Ca and Sr compositions in the starting solutions, and mean residence time on the reaction were examined. The results showed that TiO2 sol dissolution and Ca1−xSrxTiO3 precipitation were almost finished within 0.25 s mean residence time, and after that Ostwald ripening proceeded.  相似文献   

5.
Nano-powders of La0.6Sr0.4CoO3?x (LSC) and Sm0.5Sr0.5CoO3?x (SSC) compositions, which are being investigated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) with La(Sr)Ga(Mg)O3?x (LSGM) as the electrolyte, were synthesized by low-temperature sol–gel method using metal nitrates and citric acid. Thermal decomposition of the citrate gels was followed by simultaneous DSC/TGA methods. Development of phases in the gels, on heat treatments at various temperatures, was monitored by X-ray diffraction. Sol–gel powders calcined at 550–1000 °C consisted of a number of phases. Single perovskite phase La0.6Sr0.4CoO3?x or Sm0.5Sr0.5CoO3?x powders were obtained at 1200 °C and 1300 °C, respectively. Morphological analysis of the powders calcined at various temperatures was done by scanning electron microscopy. The average crystallite size of the powders was ~15 nm after 700 °C calcinations and slowly increased to 70–100 nm after heat treatments at 1300–1400 °C.  相似文献   

6.
Marble dust (200 μm size), air and water polluting waste, generated by the marble cutting industries has been used as cheap source of lime for hydrothermal solidification of clay–quartz mixtures at different saturated steam pressure (0.525–1.225 MPa). Marble dust was calcined at two different temperatures (900 and 1000 °C) and then added to the clay–quartz mixture, with clay/(clay + quartz) ratio 0.9, at two different amounts. The hydrothermally solidified samples were characterized by bulk density, apparent porosity, flexural strength, porosimetric study, phase and microstructural analysis and the results were compared against similarly treated chemical grade CaCO3 containing compositions. Tobermorite [Ca5(Si6O18H2)·4H2O] and hydrogarnet [Ca3Al2(SiO4)(OH)8] were the major phases formed in the treated samples, which are responsible for the strength development. Microstructural study supports the generation of these hydrated phases. Porosimetric study reveals that higher exposed area of the chemical grade CaCO3 containing composition results higher extent of hydrothermal reaction and higher strength. Though marble dust containing compositions showed relatively lower strength values, the combined properties of the hydrated products are suitable as new building material where such mesopore containing products with inherent micron range pore size distribution are important parameters.  相似文献   

7.
《Ceramics International》2016,42(5):6263-6272
Hydroxyapatite (HA) [Ca10(PO4)6(OH)2] is a bioactive ceramic with excellent osteoconductive properties. This characteristic helps HA to be integrated into the bone without provoking an immune reaction, thus making it a useful biocompatible material for load bearing bone implant. In this study, nanohydroxyapatite (NHA) was synthesised using a precipitation method assisted with ultrasonication. The process parameters such as ultrasonic time (t) (10–30 min), ultrasonic amplitude (A) (50–70%), solution temperature (T) (50–90 °C), and solution pH (7–9) were varied on the basis of single factor and their effects on NHA synthesis was investigated. Besides that, the effect of calcination on the NHA powder morphology was also studied by varying the calcination time (2, 4 and 6 h) and temperature (400, 800 and 1200 °C). The characterisations of the synthesised NHA powder were conducted using thermogravimetric analysis (TGA), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), transmission electron microscope (TEM), zeta-sizer and Fourier transform infrared spectroscopy (FTIR). It was found that nano-sized HA particles can be produced at optimum set of process parameters of t=25 min, T=90 °C, A=65%, and pH=8. Results revealed that the thermal stability, morphology and crystallinity of the NHA powder was further improved by calcinating the powder at optimum temperature and time of 800 °C and 2 h, respectively.  相似文献   

8.
《Ceramics International》2017,43(15):12018-12025
Nanoscale forsterite (Mg2SiO4) has recently been proposed for bone tissue engineering application. Due to the special role of strontium (Sr) in bone remodeling, the stimulation of bone formation and reduction in bone resorption, the modification of forsterite by doping with Sr is expected to increase bioactivity and biocompatibility. The aim of this study was to incorporate Sr (0, 0.05, 0.1, 0.2 and 0.4 at%) into forsterite using sol-gel method and to investigate the effect of Sr content on the phase composition, in vitro apatite-formation ability as well as osteoblast-like MG63 viability. Results demonstrated that while forsterite was the main phase of all Sr-doped forsterite nanopowders, Sr2MgSi2O7, MgO and MgSiO3 were present as the minor phases depending on the Sr content. Moreover, the presence of Sr atom influenced the crystallite and particle size as well as lattice parameters of the forsterite powder, while did not significantly change the morphology of particles. Noticeably, the incorporation of Sr up to 0.2 at% enhanced the average crystallite size (from 25.3 nm to 45.9 nm) and particle size (31.0 ± 3.9 nm to 62.9 ± 11.8 nm) of pure forsterite powder. Additionally, according to the Rietveld refinement, the incorporation of Sr up to 0.2 at% increased the lattice parameters of forsterite more than 0.1%, depending on the Sr content. In vitro bioactivity assessment in simulated body fluid (SBF) revealed while all Sr-forsterite samples possessed greater bioactivity than pure forsterite nanopowder, the incorporation of 0.1 at% Sr revealed improved bioactivity compared to other Sr-forsterite samples. However, according to MTT assay, while all forsterite-based ceramics significantly improved the cell proliferation compared to tissue culture plate (TCP) and forsterite nanopowder, Sr-forsterite nanopowders consisting of 0.05–0.1 at% Sr revealed a considerably promoted cell proliferation. In conclusion, Sr-forsterite nanopowder could be a promising candidate for bone tissue engineering and reconstruction of bone defects such as osteoporosis.  相似文献   

9.
Silicon carbide (SiC) layers were deposited on silica (SiO2) glass powder by rotary chemical vapor deposition (RCVD) to form SiO2 glass (core)/SiC (shell) powder; this powder was consolidated by spark plasma sintering (SPS). SiO2 glass powder with a particle size of 250 nm was coated with 5–10-nm-thick SiC layers. The resultant SiO2 glass (core)/SiC (shell) powder was consolidated to form a nano-grain SiO2 glass composite at a relative density above 90% by SPS in the sintering temperature range of 1573–1823 K. The Vickers hardness and fracture toughness of the SiO2 glass composite at 1723 K were found to be 14.2 GPa and 5.4 MPa m1/2, respectively.  相似文献   

10.
《Ceramics International》2017,43(15):11786-11791
Hollow Microspheres of SiO2-TiO2 photocatalysts whose walls are made up of mesoporous cellular foams were synthesized with the aid of hexane as a swelling agent and P123 as a pore template by an emulsion templating method. Pore structure of materials and crystal phase of titanium oxide was tailored by hydrothermal and calcination temperature during synthesis of samples. The samples were characterized with field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), N2 adsorption–desorption experiments, X-ray photoelectron spectroscopy (XPS) and X ray diffraction (XRD) techniques. The effect of pore structure and titania phase on photoactivity were evaluated by methylene blue (MB) degradation test under UV light as well. Results showed that hydrothermal temperature during synthesis process has a significant effect on pore and window sizes of mesostructured cellular foam. Interestingly, for the sample hydrothermally treated at higher temperature (130 °C), anatase to rutile transformation was avoided after calcination treatment as high as 800 °C. The highest photocatalytic activity was detected from the sample hydrothermally treated at 130 °C and calcined at 800 °C for which the highest degree of crystallinity and anatase phase as well as enhanced pore connectivity was obtained.  相似文献   

11.
《Ceramics International》2007,33(6):1125-1128
Cadmium tungstate (CdWO4) nanorods were successfully synthesized via a hydrothermal process and characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and photoluminescent spectra techniques (PL). A pure monoclinic phase of well-crystallized CdWO4 nanorods, with lengths of 250–400 nm and widths of 30–60 nm, could be readily synthesized at as low temperature as 70 °C.The CdWO4 nanorods showed a PL emissions peak at 435 nm.  相似文献   

12.
The solid solutions in the systems of Ca-Cd HAp [Ca10−xCdxHAp (x = 0–10)], Ca-Sr HAp [Ca10−xSrxHAp (x = 0–10)] and Ca-Pb HAp [Ca10−xPbxHAp (x = 0–10)], were successfully synthesized at 200 °C for 12 h under hydrothermal conditions. The site of the metal ions in the solid solutions was analyzed by the Rietveld method. The results of the Rietveld analysis indicated that the metal ions of Pb2+, Sr2+, and Cd2+ all preferentially occupied M (2) sites in the apatite structure. The preferential occupancy of the metal ions in M (2) sites were explained mainly by their ionic radius and electronegativity.  相似文献   

13.
This study investigates the production of highly reactive dicalcium silicate Ca2SiO4 (C2S).To that end, binders were synthesised by annealing of alpha-dicalcium silicate hydrate (α-C2SH) between 400 and 800 °C. Two different heating sequences were tested. The phase compositions were determined by means of XRD. Depending on the annealing temperature and the heating conditions the cementitious materials consist of an X-ray-amorphous content as well as x-Ca2SiO4 (x-C2S) and γ-Ca2SiO4 (γ-C2S). The hydration kinetics of some selected binders were investigated by means of isothermal calorimetry. The specific reactivity of the phases produced by means of annealing was determined during the first 40 h of hydration by use of XRD and TGA.The resulting binders show the highest reactivity when low annealing temperatures (< 500 °C) were used. After 72 h, degrees of hydration of about 89% are achieved. The most reactive component is the X-ray-amorphous content, followed by x-C2S.  相似文献   

14.
A two-step doping strategy was applied to the synthesis of La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM1020) powder by a gel combustion method. The Mg-doped LaGaO3 powder was prepared in the first step, and Sr incorporation in the Mg-doped LaGaO3 powder was done in the second step to obtain the final LSGM1020 powder. The two-step procedure is effective in preparing higher purity powders than the traditional one-step procedure. Rietveld refinement of X-ray powder diffraction (XRD) patterns shows that incorporation of Mg in LaGaO3 in the first step enlarges the LaGaO3 lattice: this facilitates the incorporation of Sr in the second doping step and thus high purity powder is obtained. Relatively phase pure LSGM1020 powder with only 3.1% of LaSrGaO4 was obtained after calcination at 1300 °C for 5 h. Therefore, the two-step doping strategy is an effective procedure for the preparation of LSGM powders with high Sr- and Mg-doping levels.  相似文献   

15.
In the present study, the effect of SiC addition on properties of basalt base glass–ceramic coating was investigated. SiC reinforced glass–ceramic coating was realized by atmospheric air plasma spray coating technique on AISI 1040 steel pre-coated with Ni + 5 wt.%Al bond coat. Composite powder mixture consisted of 10%, 20% and 30% SiC by weight were used for coating treatment. Controlled heat treatment for crystallization was realized on pre-coated samples in argon atmosphere at 800 °C, 900 °C and 1000 °C which determined by differential thermal analysis for 1–4 h in order to obtain to the glass–ceramic structure. Microstructural examination showed that the coating performed by plasma spray coating treatment and crystallized was crack free, homogeneous in macro-scale and good bonded. The hardness of the coated samples changed between 666 ± 27 and 873 ± 32 HV0.01 depending on SiC addition and crystallization temperature. The more the SiC addition and the higher the treatment temperature, the harder the basalt base SiC reinforced glass–ceramic coating became. X-ray diffraction analysis showed that the coatings include augeite [(CaFeMg)–SiO3], diopside [Ca(Mg0.15Fe0.85)(SiO3)2], albite [(Na,Ca)Al(Si,Al)3O8], andesine [Na0.499Ca0.492(Al1.488Si2.506O8] and moissanite (SiC) phases. EDX analyses support the X-ray diffraction analysis.  相似文献   

16.
《Ceramics International》2017,43(12):9117-9123
In this work, a series of Eu2+-doped (Ca1−xSrx)8MgLu(PO4)7 and Eu2+/Mn2+-codoped Ca6.5Sr1.5MgLu(PO4)7 phosphors were prepared via the combustion-assisted solid-state reaction process. XRD patterns and Rietveld refinements were used to verify the incorporations of Sr into Ca8MgLu(PO4)7:Eu2+. Upon the same excitation wavelength of 380 nm, the emission peaks of Eu2+-doped (Ca1−xSrx)8MgLu(PO4)7 (0≤x≤1) phosphors red-shifted from 453 to 519 nm with increasing Sr/Ca ratio. The red-shift of the Eu2+ emission with increasing Sr/Ca ratio was ascribed to the change of Eu2+ emission at different lattice sites. With variation of the Mn2+ content, the emission color of Eu2+/Mn2+ codoped Ca6.5Sr1.5MgLu(PO4)7 phosphors exhibited the luminescence tunable from greenish blue to white and eventually to red. The energy transfer from Eu2+ to Mn2+ in Ca6.5Sr1.5MgLu(PO4)7 host matrix was demonstrated to be of a resonant type via a dipole- dipole mechanism with the critical distance of ∼16.7 Å. By the Sr substitution for Ca and properly tuning by the relative composition change of Eu2+/Mn2+, chromaticity coordinates of (0.329, 0.326) can be reached at near UV light excitation. The combination of host composition design and energy transfer may provide a novel strategy to obtain white light and tunable luminescence.  相似文献   

17.
The aim of this work was to prepare hydroxyapatite (HA) pieces, by the gelcasting method, with appropriate mechanical properties for using as bone implants. The mechanical properties of the obtained pieces were evaluated. The influence of the solid content on the rheological behaviour of the slurries and, in turn, on the mechanical properties, was investigated. Pieces were prepared by using slurries containing 55 and 60 vol.% of an HA calcined at 1200 °C and 47 vol.% of HA calcined at 1100 °C. HA powders calcined at lower temperature than 1100 °C were not suitable for producing concentrated slurries. The raw and calcined HA were characterised by XRD, FTIR, X-ray fluorescence and elemental analysis. The pieces sintered at different temperatures and times were characterised by XRD, and the sintering treatment applied to the specimens for mechanical testing (1300 °C for 24 h) was selected taking into account the phases present after sintering.The mechanical properties of the green bodies were higher than obtained by other methods and the ones of the final pieces were comparable to those obtained by other techniques. The results indicated that slurries with a solid content higher than a limit value (for which limited contraction occurs) must be used and that the rheological properties of the slurries play an important role in the mechanical properties of the resulting pieces.  相似文献   

18.
《Ceramics International》2015,41(8):9521-9526
The influence of sintering temperature on the microwave dielectric properties and microstructure of the (1−y)Zn2SnO4yCa0.8Sr0.2TiO3 ceramic system were investigated with a view to their application in microwave devices. A (1−y)Zn2SnO4yCa0.8Sr0.2TiO3 ceramic system was prepared by the conventional solid-state method. The X-ray diffraction patterns of the 0.85Zn2SnO4–0.15Ca0.8Sr0.2TiO3 ceramic system did not significantly vary with sintering temperature. A dielectric constant of 9.6, a quality factor (Q×f) of 15,900 GHz, and a temperature coefficient of resonant frequency of −4 ppm/°C were obtained when the 0.85Zn2SnO4–0.15Ca0.8Sr0.2TiO3 ceramic system was sintered at 1175 °C for 4 h.  相似文献   

19.
The composites of 0.99La0.7(CaxSr1?x)0.3MnO3/0.01CuZnFe4O4 (LCSMO/CZF) (x = 0, 0.1, 0.2, 0.3, 0.5, 0.7 and 1) were fabricated by conventional solid state reaction method, and their electrical transport and magnetoresistance (MR) properties were investigated by physical property measurement system (PPMS). The result of X-ray diffraction (XRD) and scanning electronic microscopy (SEM) indicated that no new phase appeared in the composites except LCSMO and CZF phases. CZF is mainly distributed at the grain boundaries and surfaces of the matrix. The resistivity of all the composites was measured in the range 100–350 K at 0 T, 0.5 T and 1 T magnetic field. Room temperature MR peak appears for the composites x = 0.03. The observed variation of MR with varying Ca and Sr concentration has been qualitatively.  相似文献   

20.
Transparent lutetium titanate (Lu2Ti2O7) bodies were fabricated by spark plasma sintering using Lu2O3 and TiO2 powders calcined from 700 °C to 1200 °C. No solid-state reaction was identified after calcination at 700 °C, whereas single-phase Lu2Ti2O7 powder was prepared at 1100 and 1200 °C. The calcination at 700 °C promoted densification at the early stages of sintering, whereas residual pores at grain boundaries resulted in Lu2Ti2O7 bodies with low transparency. Low-density and opaque Lu2Ti2O7 bodies formed owing to the coarsening of the powder calcined at 1200 °C. The Lu2Ti2O7 body sintered using the powder calcined at the moderate temperature of 1100 °C had a density of 99.5% with the highest transmittances of 41% and 74% at wavelengths of 550 nm and 2000 nm, respectively.  相似文献   

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