Characteristics of Bi-based glass powders with various glass transition temperatures prepared by spray pyrolysis

Spherical shape, submicron, and non-aggregated bismuth-based glass powders were prepared. Glass powders with low glass transition temperature melted the silver powders at firing temperatures of as low as 400 °C. After firing at 400 °C, the specific resistances of the silver conducting films obtained from glass powders with glass transition temperatures of 498 and 373 °C were 21.6 and 5.8 μΩ cm, respectively. After firing at 450 and 500 °C, the specific resistances of the silver conducting films obtained from glass powders with glass transition temperature of 425 °C were the lowest, i.e., 3.0 and 3.1 μΩ cm, respectively.     

Size-controlled Bi-based glass powders prepared by spray pyrolysis as inorganic additives for silver electrode

Bi-based glass powders as additive for silver conducting pastes were prepared by spray pyrolysis. The glass powders formed from the spray solution with low concentration of 0.025 M had bimodal size distribution with nanometer and submicron sizes. However, glass powders with spherical shape and narrow size distribution were prepared from the spray solutions with concentrations of 0.05 and 0.5 M. The mean size of the glass powders increased from 0.34 to 0.7 μm when the concentrations of the spray solutions changed from 0.05 to 0.5 M. The glass transition temperature of the glass powders with the mean size of 0.34 and 0.70 μm were 382 and 396 °C, respectively. The glass layers fired at 450 °C had clean surfaces irrespective of the mean size of the glass powders. Silver conducting films were formed by melting of the silver powders irrespective of the mean sizes of the glass powders at firing temperatures between 400 and 500 °C. The specific resistances of the silver conducting films change from 3.13 to 4.03 μΩ cm according to the mean size of the glass powders at a firing temperature of 500 °C.     

Characteristics of Ag powders coated with Pb-based glass material prepared by spray pyrolysis under various gas environments

Ag powders coated with Pb-based glass material for Si solar cell application are directly prepared by spray pyrolysis in various gas environments. Pb-based glass is successfully formed in the composite powders irrespective of gas environment. The composite powders have bimodal size distributions of nanometer and submicron sizes. However, the number of nano-sized powders decreases when the reducing gas was used as the carrier gas. The silver-conducting films fired at 700 and 800 °C have dense structures without pores irrespective of the gas environment in the preparation of the composite powders. Glass materials are uniformly segregated between micron-sized silver grains. The conducting film formed from the composite powders prepared under 20% H₂/Ar atmosphere have sheet resistance of 7.8, 6.8, 5.1 and 5.9 mΩ/sq at firing temperatures of 500, 600, 700 and 800 °C, respectively.     

Synthesis of spherical shape borate-based bioactive glass powders prepared by ultrasonic spray pyrolysis

Spherical shape borate-based bioactive glass powders with fine size were directly prepared by high temperature spray pyrolysis. The powders prepared at temperatures between 1200 and 1400 °C had mixed phase with small amounts of fine crystal and an amorphous rich phase. Glass powders with amorphous phase were prepared at a temperature of 1500 °C. The mean size of the glass powders prepared by spray pyrolysis was 0.76 μm. The glass powders prepared at a temperature of 1200 °C had two distinct exothermic peaks (T_c1 and T_c2) at temperatures of 588 and 695 °C indicating crystallization. The glass transition temperature (T_g) of the powders prepared at a temperature of 1200 °C was 480 °C. Phase-separated crystalline phases with spherical shape were observed from the surface of the pellet sintered at a temperature of 550 °C. Crystallization of the pellet was completely occurred at temperatures of 750 and 800 °C. The pellets sintered at temperatures below 700 °C had single crystalline phase of CaNa₃B₅O₁₀. The pellet sintered at a temperature of 800 °C had two crystalline phases of CaNa₃B₅O₁₀ and CaB₂O₄.     

Effect of precursor types on the characteristics of the Pb-based glass powders prepared by spray pyrolysis

Lead (Pb)-based glass powders with a spherical shape and submicron size were directly prepared by spray pyrolysis using spray solutions with various types of Pb and silicon (Si) components. The glass powders formed by the spray solution with Pb chloride and tetraethyl orthosilicate (TEOS) precursors had a broad X-ray diffraction (XRD) peak at around 28° with small crystalline peaks. The powders had an impurity peak caused by chlorine in the EDX spectrum. However, the glass powder formed from the spray solutions that contained Pb nitrate and Pb acetate precursors had an amorphous phase, irrespective of the type of Si precursor. The dielectric layers formed from the glass powders obtained from the spray solutions with Pb nitrate and Pb acetate had a dense structure and high transmittance above 85%, irrespective of the type of Si precursor components. In contrast, the dielectric layer formed from the glass powders prepared from the spray solution with Pb chloride and TEOS had large voids in the layer and had low transmittance below 50% under the visible range.     

Firing characteristics of size-controlled silver-glass composite powders prepared by spray pyrolysis

Size-controlled spherical silver-glass composite powders were directly prepared by using spray pyrolysis. The mean sizes of the composite powders changed from 0.34 to 0.78 μm when the concentration of the spray solution was changed from 0.05 to 2 M. The firing characteristics of composite powders formed from the spray solutions with a glass content equal to 3 wt.% of the silver component were affected by the mean sizes of the powders. Silver-conducting films formed from large-sized composite powders had a denser structure than those formed from small-sized composite powders. Further, silver-conducting films formed from composite powders with a mean size of 0.78 μm had specific resistances of 3 and 2 μΩ cm at firing temperatures of 450 and 500 °C. However, silver-conducting films formed from composite powders with a mean size of 0.34 μm had specific resistances of 8.2 and 6.9 μΩ cm at firing temperatures of 450 and 500 °C.     

Characteristics of BaNd2Ti5O14 powders directly prepared by high-temperature spray pyrolysis

BaNd₂Ti₅O₁₄ powders were directly prepared by high-temperature spray pyrolysis. The powders prepared at temperatures of 1300 and 1500 °C exhibited a pure BaNd₂Ti₅O₁₄ phase. The powders prepared at 1300 °C were spherical in shape. However, the powders prepared at 1500 °C showed non-spherical shapes. The BaNd₂Ti₅O₁₄ powders had a composition similar to that of the spray solution. The mean sizes of the BaNd₂Ti₅O₁₄ powders increased from 0.23 to 0.60 μm when the concentration of the spray solution was increased from 0.01 to 0.2 M. At a sintering temperature of 1100 °C, bridge-like structures were formed between the powders. Pellets sintered at 1300 °C exhibited a dense structure comprising rod-like crystals.     

火焰喷雾热解法制备纳米晶镁铝尖晶石粉

以硝酸镁和硝酸铝(均为分析纯)混合物(其中Mg与Al的摩尔比为1∶2)为溶质,不同体积比的蒸馏水和乙醇为溶剂(其体积比分别为3∶2,1∶1,2∶3),制备成Mg2 浓度分别为0.1 mol.L-1、0.3 mol.L-1和0.5 mol.L-1的前驱物溶液,置于密闭容器内,分别在不同的容器压力(0.1 MPa,0.2 MPa,0.3 MPa,0.4 MPa)下用火焰喷雾热解法合成纳米晶镁铝尖晶石,借助XRD、SEM和激光粒度分析仪研究了乙醇和水的体积比、溶液浓度和容器压力对合成镁铝尖晶石粉的产量和形貌的影响。研究结果表明:合成粉末的颗粒尺寸和晶粒尺寸都随乙醇和水比值的减小而增加,其晶粒尺寸随前驱物溶液浓度的增加先减小后增大,随容器压力的变化很小,但随着压力的增加,合成粉末的团聚体增多、增大,产量明显增大。综合考虑认为,本试验的最佳合成条件是前驱物溶液中Mg2 浓度0.3 mol.L-1,乙醇和水的体积比3∶2,容器压力0.3 MPa,此时得到的合成尖晶石粉末几乎都为球形,但粒度分布范围较宽。     

Doped ceria powders prepared by spray pyrolysis for gas sensing applications

In the present study, ceria powder with and without gadolinium (Gd) or zirconium (Zr) dopants were synthesized by a spray pyrolysis (SP) process. The resulting powders (undoped CeO₂, Gd-doped ceria and Zr-doped ceria) were first mixed with organic binders, screen printed on alumina substrates, and then heat treated at 1200 °C for 2 h in air. Experimental results showed that the as-pyrolyzed powders were nanocrystalline and spherical in shape with uneven surfaces. After heat treatment, the powder coatings showed a 3-D network structure with interconnected pores exhibiting a high surface area. The electrical conductivity of CeO₂ was increased by the dope of Zr. The increasing rate of conductivity of ZDC (Zr-doped ceria) with decreasing oxygen pressure was also higher than that of undoped CeO₂. The CeO₂ and ZDC exhibited an n-type semiconductance in all the oxygen pressure regions, showing promise as candidates for sensor applications. The GDC (Gd-doped ceria) revealed a p-type and an n-type semiconductance in high- and low-oxygen pressure regions, respectively. The sensor applications of GDC are thus limited. Meanwhile, the ZDC exhibited a shorter response time due to its smaller grain size, showing a better oxygen sensing behavior.     

Characteristics of samaria-doped ceria nanoparticles prepared by spray pyrolysis

Samaria-doped ceria (SDC) nanoparticles were prepared by spray pyrolysis. The means sizes of the samaria-doped ceria nanoparticles were controlled from 21 to 150 nm by changing the calcination temperatures between 700 and 1200 °C. The pellets formed from the SDC particles calcined at temperatures between 700 and 1000 °C had similar grain sizes between 0.75 and 0.82 μm. However, pellet formed from the SDC particles calcined at a temperature of 1200 °C had large grain size of 1.22 μm. The pellet formed from the SDC particles calcined at a temperature of 1000 °C had slightly smaller resistance of grain-boundary than those of the pellets formed from the SDC particles calcined at temperatures between 700 and 900 °C. However, the pellet formed from the SDC particles calcined at a temperature of 1200 °C had low resistance of grain-boundary. The pellet formed from the SDC particles calcined at a temperature of 1200 °C had conductivity of 44.65 × 10^?3 S cm^?1 at a measuring temperature of 700 °C that more twice than those of the pellets formed from the SDC calcined below 1000 °C.     

Characteristics of Ag-doped BaTiO3 nanopowders prepared by spray pyrolysis

Pure and Ag-doped BaTiO₃ nanopowders were prepared by spray pyrolysis. Precursor powders, prepared from a spray solution with citric acid and ethylenediaminetetraacetic acid (EDTA) as chelating agents, had large, hollow particles irrespective of Ag doping. Both pure and Ag-doped powders had partially aggregated particles after post-treatment at 900 °C that could be easily milled to nanoparticles. The mean sizes of the pure and Ag-doped BaTiO₃ particles were 75 and 91 nm, respectively. The Ag-doped particles were mainly of cubic BaTiO₃ crystal structure, with small Ag phases observed. High-density BaTiO₃ pellets were formed by sintering the powders at the low temperature of 1000 °C. The silver was uniformly distributed in a tetragonal BaTiO₃ phase without phase separation in the doped pellet. The dielectric constants of the pellets formed from the pure and Ag-doped BaTiO₃ powders were 1826 and 2400, respectively.     

Nano-sized LiNi0.5Mn1.5O4 cathode powders with good electrochemical properties prepared by high temperature flame spray pyrolysis

LiNi_0.5Mn_1.5O₄ cathode powders with a mean particle size of 140 nm are prepared by high-temperature flame spray pyrolysis. Li/LiNi_0.5Mn_1.5O₄ cells show two plateaus at approximately 4.1 and 4.7 V during discharge, irrespective of any excess of the lithium component in the spray solution, although the 4.1 V plateau decreases when the spray solution contained 20% excess lithium. The discharge capacity of the powder prepared from a spray solution with 20% excess lithium decreases from 133 to 126 mAh g^?1 by the 50th cycle at a current density of 0.1 C, which is a capacity retention of 95%.     

Dielectric properties of nano-sized Ba0.7Sr0.3TiO3 powders prepared by spray pyrolysis

Nano-sized Ba_0.7Sr_0.3TiO₃ powders are prepared by post-treatment of the precursor powders with hollow and thin wall structure at temperatures between 900 and 1100 °C. Ethylenediaminetetraacetic acid and citric acid improve the hollowness of the precursor powders prepared by spray pyrolysis. The mean sizes of the powders post-treated at temperatures of 900, 1000 and 1100 °C are 42, 51 and 66 nm, respectively. The densities of the Ba_0.7Sr_0.3TiO₃ pellets obtained from the powders post-treated at 900, 1000 and 1100 °C are each 5.36, 5.55 and 5.38 g cm^?3 at a sintering temperature of 1300 °C. The pellet obtained from the powders post-treated at 1000 °C has higher maximum dielectric constant than those obtained from the powders post-treated at 900 and 1100 °C.     

Preparation of nanometer AlN powders by combining spray pyrolysis with carbothermal reduction and nitridation

Nanometer AlN powders were prepared by combining spray pyrolysis with carbothermal reduction and nitridation (CRN). The aluminum oxide/carbon composite powders prepared by spray pyrolysis from a sucrose spray solution were several microns in size, with hollow and porous structures. Precursor powder with 67 wt% carbon content was transformed into phase-pure AlN powder by CRN at temperatures above 1,400 °C. The hollow-structured AlN powder was ground to 20 nm mean size by simple milling.     

Characteristics of Y3Al5O12:Ce phosphor powders prepared by spray pyrolysis from ethylenediaminetetraacetic acid solution

Nanometer and submicron-sized YAG:Ce phosphor powders were prepared by spray pyrolysis from the spray solutions with ethylenediaminetetraacetic acid (EDTA). The precursor powders with hollow and thin wall structure turned to the fine-sized YAG:Ce phosphor powders after post-treatment at high temperatures of 1400 and 1500 °C. The mean size of the phosphor powders post-treated at a temperature of 1500 °C was 0.72 μm. The white LEDs formed from the YAG:Ce phosphor powders post-treated at 1400 and 1500 °C showed (0.2781, 0.2871) and (0.2731, 0.2795) on the CIE chromaticity diagram, and about 78.20 and 79.04 of Ra. The luminous efficiency of the white LED formed from the commercial YAG:Ce phosphor powders was 84.36 lm/W. However, the luminous efficiencies of the white LEDs formed from the YAG:Ce phosphor powders post-treated at 1400 and 1500 °C were 47.74 and 76.64 lm/W.     

Nano-sized Ag–BaTiO3 composite powders with various amount of Ag prepared by spray pyrolysis

The preparation of precursors of BaTiO₃ nanopowders with various amounts of Ag by spray pyrolysis is reported. The precursor powders obtained with hollow and thin-wall particles are composed of uniformly dispersed Ba, Ti, and Ag components. After post-treatment and a simple milling process, the precursor powders, irrespective of the amount of Ag, are transformed into Ag–BaTiO₃ composite nanoparticles. The mean particle size of the Ag (10 mol%)–BaTiO₃ powders is 142 nm. BaTiO₃ pellets containing Ag exhibit dense structures even at a low sintering temperature of 1000 °C. BaTiO₃ pellets with 10 mol% Ag show the highest dielectric constant of 2950, as opposed to the pure BaTiO₃ pellets (without Ag), whose dielectric constant is 1827.     

Photocatalytic La4Ti3O12 nanoparticles fabricated by liquid-feed flame spray pyrolysis

Hexagonal plate-like nanoparticles (NPs) of the layered perovskite La₄Ti₃O₁₂ were fabricated using liquid-feed flame spray pyrolysis (LF-FSP) followed by subsequent heat-treatments. Their photocatalytic activity was evaluated using decolorization of methyl orange solutions under Uv irradiation. LF-FSP combusts metalloorganic precursor aerosols to produce mixtures of cubic simple perovskite (ABO₃) phase and lanthanum oxycarbonate (La₂O_4·846C_0.846) phase with very low agglomeration and average particle sizes (APSs) of 23 nm (as-produced NPs). Rietveld refinement of synchrotron XRD powder patterns verified that the simple perovskite in the as-produced NPs is LaTiO₃ (originally cubic Pm-3m-type space group) and heat-treating gives NPs of the trigonal layered perovskite La₄Ti₃O₁₂ (R-3-type space group). La₄Ti₃O₁₂ NPs heat-treated at 1100 °C/3-6h/air exhibits hexagonal plate-like morphology and high crystallinity offering enhanced photocatalytic degradation of methyl orange solutions compared to the as-produced NPs. The LF-FSP approach to obtaining layered perovskite La₄Ti₃O₁₂ NPs provides a simple route to photocatalytic materials in reasonable quantities.     

Growth behavior of nanosized ceria powders prepared by coprecipitation routes

Nanosized ceria (CeO₂) powders were obtained by coprecipitation routes of cerium nitrate hexahydrate [Ce(NO₃)₃·6H₂O]. The growth behavior of the nanosized CeO₂ powders was investigated by X-ray diffraction, transmission electron microscopy and selected area electron diffraction. The XRD results showed that the dried precursor powders contained a single crystalline phase of CeO₂, and only a single phase of CeO₂ appeared when the dried precursor powders were calcined at different temperatures for various durations. Moreover, the crystallite size of CeO₂ increased on increasing the calcination temperature and duration. The kinetics equation of the nanosized CeO₂ powders grown between 673 and 1273 K for various durations is described as     

Fine-sized BaMgAl10O17:Eu phosphor powders prepared by spray pyrolysis from the spray solution with BaF2 flux

Fine-sized BaMgAl₁₀O₁₇:Eu²⁺ phosphor powders with plate-like morphology were prepared by spray pyrolysis process. The effects of ratio of BaF₂ and Ba(NO₃)₂ used as the source materials of Ba component on the morphological and optical properties of the BaMgAl₁₀O₁₇:Eu²⁺ phosphor powders were investigated. BaF₂ was used as the flux material as well as the source material of Ba component. The phosphor powders prepared from the spray solution with the same mole concentrations of BaF₂ and Ba(NO₃)₂ had fine size, plate-like morphology and narrow size distribution. The addition of BaF₂ as the source material of Ba component increased the photoluminescence intensities of the phosphor powders. The phosphor powders prepared from the spray solution with the ratios of BaF₂ and Ba(NO₃)₂ larger than 1 had the similar photoluminescence intensities to that of the commercial product.     

Characteristics and pozzolanic reactivity of glass powders

This paper deals with the morphology, fineness and pozzolanic activity of four glass powders: one (GP-fine) from the screening of crushed waste glasses, one (GP-dust) from a dust collector for the glass crushing process and two (GP-4000 and GP-6000) from further grinding of the powder from the dust collector in a ball mill. GP-fine and GP-dust consist mainly of large flaky particles, while GP-4000 and GP-6000 consist mainly of small angular particles. The finenesses of these glass powders are measured by particle size distribution and Blaine fineness method. For a similar particle size distribution, ground glass powder has a higher Blaine specific surface area than Portland cement due to the angular morphology of glass particles. Finely ground glass powders exhibited very high pozzolanic activity. The finer the glass powder is, the higher its pozzolanic reactivity is. An increase in curing temperature accelerates the activation of pozzolanic reactivity of both glass powder and coal fly ash in terms of strength development rate. Mortar cube strength results (ASTM C109) indicated that curing temperature has a greater influence on the glass powder than on fly ash. The rapid mortar bar expansion test (ASTM C1260) results indicate that the replacement of Portland cement with ground glass powder also reduces the expansion due to alkali-aggregate reactions, although it is not as effective as coal fly ash.