Preparation and Microstructural,Structural,Optical and Electro-Optical Properties of La Doped Pmn-Pt Transparent Ceramics

Transparent relaxor ferroelectric ceramics of the system lanthanum modified lead magnesium niobate have been investigated for a variety of electro-optic properties could make these materials alternatives to (Pb,La)(Zr,Ti)O3. However, a study that relates the properties in function stoichiometric formula, it has not been analyzed heretofore. Therefore, in this work the effect of A-site substitution of La+3 in the characterization microstructural, structural, optical and electro-optical on (1-x)[Pb(1-3/2y)Lay(Mg1/3Nb2/3)O3]-xPbTiO3 and (1-z)[(1-x)Pb(Mg1/3Nb2/3)O3+xPbTiO3]+zLa2O3 has been performed. It was observed that the properties according to the stoichiometric formula and the PT had a maximum whose behavior was related to the addition of lanthanum in each stoichiometries.

Synthesis of Polycrystalline Nd∶YAG Nanopowders Used for Sintering Transparent Ceramics via Gel Combustion

Polycrystalline nano-sized neodymium doped yttrium aluminum garnet (Nd∶Y3Al5O12, Nd∶YAG) powders were synthesized via a gel combustion method using nitrates and citric acid as starting materials. The evolution of phase composition and micro-structure of the powders were characterized by X-ray powder diffraction, thermogravimetry/differential thermal analysis and scanning electron microscopy. Well-crystallized Nd∶YAG nano-sized powders could be obtained at 950 ℃ for 2 h. The resultant powders are well dispersed, have a relatively narrow size distribution with an average particle size of approximately 50 nm, and show excellent sinterability. These powders can be densified to 99.2% of the theoretical density by HP sintering at 1700 ℃ for 3 h under 20 MPa nitrogen pressure.

Microwave Assisted Sintering and Photoluminescence Properties of BaaSi6OleNe：Eu^2＋ Green Phosphors

Eu^2＋-doped Ba3Si6012N2 green phosphors were prepared by microwave assisted sintering method at 1275℃ for 4 h, while the counterparts using conventional solid-state reaction method were synthesized at temperature higher than 1300℃ and for to 10 h. Microwave assisted sintering could reduce the activation energy and enhance the diffu- sion rate, thus greatly improved the sintering. Moreover, the influence of Si3N4 content on phase formation, morphol- ogy, absorption, and quantum efficiency, and photoluminescence properties of phosphors were studied. As a result, the Ba3Si6OI2N2：Eu^2＋ samples sintered by microwave assisted sintering method have a higher phase purity and photo- luminescence intensity under ultraviolet excitation as compared with samples sintered in the conventional tube furnace The proposed method is a potential preparation method for the oxynitride phosphors with strong photoluminescence and high phase purity.

Use of fly and bottom ashes from a thermoelectrical plant in the synthesis of geopolymers:Evaluation of reaction efficiency

The use of by-products as raw materials in the manufacturing of industrial products has risen in the last years because of environmental considerations.One example is the use of coal ashes from thermalelectrical plants in the production of geopolymer–a green cement made by mixing aluminosilicate with alkaline activator.In this study,fly and bottom ashes from a thermal-electrical unit were used as sources of aluminosilicate in the synthesis of geopolymers.A mixture of sodium hydroxide(10 mol/L)and sodium silicate(SiO_(2)/Na_(2)O ratio of 2.2)was used as the alkaline activator.The type(fly or bottom ash)and content of the ash were the variables in the synthesis.The ashes were characterized by X-ray fluorescence(XRF),X-ray diffraction(DRX),particle size distribution(PSD),specific surface area(BET),and thermal analysis(DTA/TGA).The ash-based geopolymer samples were measured to obtain their compressive strength after curing.The evolution of the geopolymerization process was also assessed based on final alkali concentration measurements.The results show that it is possible to obtain geopolymers using coal ashes as raw materials with high solid content.The compressive strength for the bottom ash geopolymer after 90 days of curing is 35 MPa.The low concentration of unreacted alkalis after curing(1.5×10^(-3)e 3.5×10^(-3)M)corresponds to high efficiency of the geopolymerization reaction.

Evaluation on Properties of CaO-BaO-B_2O_3-Al_2O_3-SiO_2 Glass-Ceramic Sealants for Intermediate Temperature Solid Oxide Fuel Cells

To develop suitable sealants for intermediate temperature solid oxide fuel cells （IT-SOFC）, glass-ceramics based on the CaO-BaO-B203-AI203-Si02 system were studied. Coefficient of thermal expansion （CTE）, glass transition temperature （Tg） and dilatometric softening point temperature （Td） of specimens were determined by means of dilatometer analysis and crystallization temperature was measured by differential thermal analysis （DTA）. Also, crystallization behavior during prolonged heat-treatment and microstructure properties were studied by means of X-ray diffraction （XRD） and scanning electron microscopy （SEM）, respectively. Electrical properties were measured at different temperatures, and the results showed a high resistance （〉104 Ω） at the SOFC operation temperature （600-800 ℃）. Moreover, mechanical properties of heat-treated specimens （1, 10, 30, 50 h） were measured, Microstructure investigation revealed a well-adhered bonding between the sealant glass-ceramic electrolyte and glass.

Characterization of free carbon in the as-thermolyzed Si-B-C-N ceramic from a polyorganoborosilazane precursor

Polyorganoborosilazane((B[C_(2)H_(4)-Si(CH_(3))NH]_(3))n)was synthesized via monomer route from a single-source precursor and thermolyzed at 1300℃in argon atmosphere.The as-thermolyzed Si-B-C-N ceramic was characterized using X-ray diffraction(XRD)and Raman spectroscopy.The crystallization behavior of silicon carbide in the as-thermolyzed amorphous Si-B-C-N matrix was understood by XRD studies,and the crystallite size calculated using Scherrer equation was found to increase from 2 nm to 8 nm with increase in dwelling time.Concomitantly,Raman spectroscopy was used to characterize the free carbon present in the as-thermolyzed ceramic.The peak positions,intensities and full width at half maximum(FWHM)of D and G bands in the Raman spectra were used to study and understand the structural disorder of the free carbon.The G peak shift towards 1600 cm-1 indicated the decrease in cluster size of the free carbon.The cluster diameter of the free carbon calculated using TK(Tuinstra and Koenl)equation was found to decrease from 6.2 nm to 5.4 nm with increase in dwelling time,indicating increase in structural disorder.

Synthesis and spectral properties of Nd-doped glass-ceramics in SiO_2-CaO-MgO system prepared by sol-gel method

SiO2-CaO-MgO glass and glass-ceramic powder doped with Nd3＋ were synthesized with sol-gel method. Tetraethylorthosilicate （TEOS）, Ca（NO3）2？4H2O, Mg（NO3）2？6H2O, Nd（NO3）3？6H2O, ethanol, distilled water, and HNO3 were used as starting materials. The synthesized powder’s properties were examined with simultaneous thermal analysis （STA）, X-ray diffraction （XRD）, photoluminescence （PL） and scanning electron microscopy （SEM） analysis. The STA curves showed that the softening point and crystallization temperatures were shifted to higher temperatures with increasing dopant content. Regarding XRD patterns of glass samples, Nd was found to act as an intermediate oxide in glass matrix. The XRD patterns of glass-ceramic samples indicated that bredigite and akermanite crystallized in the glass matrix after heat treating at 900 oC. The fluorescence spectra showed that glass-ceramics emitted much stronger irradiation than glasses with the same dopant content. The SEM images illustrated uniform and homogeneous distribution of applied oxides in glass and glass-ceramic compositions.

Ferrimagnetic ceramic adsorbents for cleanup of H_2S from exhaust gases

Adsorbents that exhibit magnetic properties in addition to other required process-relevant characteristics open up new perspectives for the dry reduction and/or elimination of HES and other sulfur compounds from exhaust gases. These adsorbents eliminate the sulfur compounds from exhaust gases by virtue of their coatings and their magnetic property which makes it possible the use of magnetically assisted and stabilized fluidization in an externally applied magnetic field. In the present paper, the feasibility of the sorptive function of porous ceramic ferrimagnetic beads is ensured by sol-gel coating of zinc oxide without the formation of Zn-Fe-oxides and without considerable decrease of available pore volume. The results of material characterization by SEM, Auger electron spectroscopy, X-ray and mercury-porosity measurements and the loading capacity of a HES/N2 model gas are presented and discussed. The resulting HES loading of the functionalized adsorbent beads is more than 10 times larger than that of the starting material. @ 2007 Chinese Society of Particuolo^v and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V.

Facile synthesis of Ca-SiAlON:Eu^(2+) phosphor by the microwave sintering method and its photoluminescence properties

Pure Ca-SiAlON:Eu2+ was synthesized by microwave sintering method at a relatively low temperature of 1550℃.Photoluminescence intensity of the resultant phosphor was higher than those of the samples synthesized by conventional gas-pressure sintering technique at 1750℃.When it was excited at 450 nm,the as-prepared yellow Ca-SiAlON:Eu2+ sample had an external quantum efficiency of 42%,comparable to the sample synthesized at 1750℃ under 0.5 MPaN2 gas pressure by the GPS method reported in reference.The experimental results demonstrated that the microwave sintering method was also an interesting approach for synthesizing nitride phosphors,which promises lower firing temperature than those by carbothermal reduction and nitridation (CRN) methods,higher heating rate and shorter duration time compared with those by gas-pressure sintering.

Flexible highly-effective energy harvester via crystallographic and computational control of nanointerfacial morphotropic piezoelectric thin film

Controlling the properties of piezoelectric thin films is a key aspect for designing highly efficient flexible electromechanical devices. In this stud）~ the crystallographic phenomena of PbZr1-xTixO3 （PZT） thin films caused by distinguished interfacial effects are deeply investigated by overlooking views, including not only an experimental demonstration but also ab initio modeling. The polymorphic phase balance and crystallinity, as well as the crystal orientation of PZT thin films at the morphotropic phase boundary （MPB）, can be stably modulated using interfacial crystal structures. Here, interactions with MgO stabilize the PZT crystallographic system well and induce the texturing influences, while the PZT film remains quasi-stable on a conventional A1203 wafer. On the basis of this fundamental understanding, a high-output flexible energy harvester is developed using the controlled-PZT system, which shows significantly higher performance than the unmodified PZT generator. The voltage, current, and power densities are improved by 556%, 503%, and 822%, respectively, in comparison with the previous flexional single-crystalline piezoelectric device. Finally, the improved flexible generator is applied to harvest tiny vibrational energy from a real traffic system, and it is used to operate a commercial electronic unit. These results clearly indicate that atomic-scale designs can produce significant impacts on macroscopic applications.