Protective Silica Coatings on Zinc-Sulfide-Based Phosphor Particles

A spray drying approach was used to apply 15-nm-thick SiO₂ continuous coatings onto ZnS:Ag phosphor particles. A prehydrolyzed TEOS dip coating formula was used as the SiO₂ precursor. The phosphor was mixed together with the precursor then atomized without allowing gelation to occur until the droplets containing the particles were in flight. The coating gelled and dried while falling through a graded heat zone. The dried coated particles were captured in a cyclone separator and heat-treated to further densify the SiO₂ coating. The coatings protected the phosphors while in service in field emission display (FED) devices.     

Effect of Polyelectrolyte Dispersants on the Preparation of Silica-Coated Zinc Oxide Particles in Aqueous Media

Sodium silicate was utilized to obtain a SiO₂ coating on ZnO particles to prevent a photocatalytic reaction between ZnO and phenol. During the coating process, pH control is important to avoid dissolution of the ZnO as well as to obtain a good dispersion. Two kinds of polyelectrolyte dispersants were used to control the surface charge of the ZnO particles in aqueous media. As a result, poly(ethylenimine) (PEI) shifted the isoelectric point of ZnO from pH 9 to pH 10, whereas poly(ammonium acrylate) (PAA) made the surface charge of ZnO negative between pH 6 and pH 11. The change in the ZnO surface charge produced by adding polyelectrolyte dispersants makes it possible to obtain uniform silica–coated ZnO particle in aqueous media. UV–irradiation experiments showed that PEI, which can make the surface charge opposite to that of SiO₂, is more effective in obtaining a thick silica coating on ZnO.     

Physical properties of Al-doped ZnO films deposited on nonwoven substrates by radio frequence magnetron sputtering

In this study, the polyethylene terephthalate (PET) spunbonded nonwoven materials were used as substrates for creating electro-optical functional nanostructures on the fiber surfaces. A magnetron sputter coating was used to deposit Al-doped ZnO (AZO) films onto the nonwovens. The influences of the deposition time on the structural, optical, and electrical properties of AZO films were investigated. Atomic force microscopy (AFM) was employed to examine the topography of the fibers. The AFM observation revealed a significant difference in the morphology of the fibers before and after the AZO sputter coating. The examination by UV–visible spectrophotometer analysis showed that the nonwovens deposited with transparent nanostructure AZO films had better UV absorption, and an average transmittance was approximately 50% in the visible light wavelength region. The surface conductivity of the materials was analyzed using a four-probe meter, and it was found that electrical resistance was significantly decreased as the sputtering time increased.     

Fabrication and characterization of silicon wire solar cells having ZnO nanorod antireflection coating on Al-doped ZnO seed layer

In this study, we have fabricated and characterized the silicon [Si] wire solar cells with conformal ZnO nanorod antireflection coating [ARC] grown on a Al-doped ZnO [AZO] seed layer. Vertically aligned Si wire arrays were fabricated by electrochemical etching and, the p-n junction was prepared by spin-on dopant diffusion method. Hydrothermal growth of the ZnO nanorods was followed by AZO film deposition on high aspect ratio Si microwire arrays by atomic layer deposition [ALD]. The introduction of an ALD-deposited AZO film on Si wire arrays not only helps to create the ZnO nanorod arrays, but also has a strong impact on the reduction of surface recombination. The reflectance spectra show that ZnO nanorods were used as an efficient ARC to enhance light absorption by multiple scattering. Also, from the current-voltage results, we found that the combination of the AZO film and ZnO nanorods on Si wire solar cells leads to an increased power conversion efficiency by more than 27% compared to the cells without it.     

Microstructure of Varistors Prepared with Zinc Oxide Nanoparticles Coated with Bi2O3

Zinc oxide (ZnO) nanoparticles coated with 1–5 wt% Bi₂O₃ were prepared by precipitating a Bi(NO₃)₃ solution onto a ZnO precursor. Transmission electron microscopy showed that a homogeneous Bi₂O₃ layer coated the surface of the ZnO nanoparticles and that the ZnO particle size was ∼30–50 nm. Scanning electron microscopy showed that ZnO grains sintered at 1150°C were homogeneous in size and surrounded by a uniform Bi₂O₃ layer. When the ZnO grains were surrounded fully by Bi₂O₃ liquid phases, further increases in the ZnO grain size were not affected by the Bi₂O₃ content. This predesigned ZnO nanoparticle structure was shown to promote homogeneous ZnO grains with perfect crystal growth.     

Preparation of Transparent Conductive (ZnO)mIn2O3 Fine Powder by Gel-Combustion Reaction

A fine powder of (ZnO) _m In₂O₃ ( m =3, 4) was obtained by the self-combustion reaction, under firing at a furnace temperature of 350°C in a nitrogen atmosphere, of a gel prepared from a mixed zinc and indium nitrate aqueous solution peptized with citric acid. A (ZnO)₃In₂O₃ single-phase product was obtained when citric acid was substituted by glycine, because the combustion temperature of glycine mixture is >1260°C. The highest electrical conductivity, 0.2 S cm⁻¹, was obtained in a tin-substituted, transparent conducting (ZnO) _m In₂O₃ product, where m =3 and 4.     

Influences of ZnO on the Properties of SrZr0.9Y0.1O2.95 Protonic Conductor

The effects of ZnO additive on the microstructure, phase formation, and electrical conduction of yttrium-doped strontium zirconate were investigated. The sintering temperature of SrZr_0.9Y_0.1O_2.95 can be lowered to 1350°C by addition of ZnO. The electrical conduction is found to be strongly correlated with the ZnO contents. When the ZnO content is <5 mol%, the electrical conductivity increased with an increase in the ZnO contents. Electromotive force measurements under fuel cell conditions indicated a pure ionic conduction over this range of ZnO contents. However, it had a detrimental effect on the electrical conduction when the ZnO content was more than 6 mol%. The main reason for this is discussed according to the defect chemistry and microstructure.     

Photocatalytic Silver Recovery Using ZnO Nanopowders Synthesized by Modified Glycine-Nitrate Process

Zinc oxide (ZnO) powders were synthesized by the modified glycine-nitrate process (MGNP) with various oxidants and fuels. Single-phase ZnO powders were easily obtained regardless of oxidants and fuels. The particle size and shape of ZnO powders were dependent on the types of fuels. The ZnO powder synthesized using Zn(OH)₂ and glycine as an oxidant and a fuel, at a fuel/oxidant ratio of 0.8, showed the best powder characteristics, such as an average grain size of 30 nm and the specific surface area of 120 m²/g. The removal of silver ions from the waste-development solution was tried to confirm photocatalytic activities of the synthesized ZnO powder. The silver ions were completely removed within 15 min. This silver recovery rate is three times higher than that of commercial state-of-the-art TiO₂. The photoluminescence (PL) measurement also showed the PL intensity at ultraviolet (UV) of the synthesized ZnO powder is almost three times higher than that of commercial state-of-the-art TiO₂. The synthesized ZnO nanopowder absorbed more UV than any other powders, including commercial state-of-the-art TiO₂ and ZnO powders. This means the high UV absorption efficiency leads to the generation of more electrons that are involved in the reduction of silver ions.     

ZnO:Al包覆CaSiO3:(Pb,Mn)荧光粉

利用溶液中的共沉淀反应制备了CaSiO3:(Pb,Mn)红色光致荧光粉.以Zn(NO3)2·6H2O和AlCl3·6H2O为原料,借助CO(NH2)2水解反应,用化学均相共沉淀法和热处理工艺在荧光粉表面包覆一层ZnO:Al透明导电薄膜.对包覆前后的样品进行了X射线衍射结构分析、光致荧光分析、透射电镜形貌观察及电阻测量.结果显示:包覆后荧光粉的电导率显著提高,但光致荧光峰的位置和强度无明显变化.综合考虑包覆对荧光粉电阻率和荧光性质的影响,优化包覆条件和热处理条件为:n(Zn)/n(Ca)=10%,n(Al)/n(Zn)=5%,75℃水解1 5 h;包覆后的样品在500℃热处理45 min.     

Property approach of Si based ZnO films under thermal shock

ZnO and Al-doped ZnO (AZO) films were deposited on p-Si(100) wafers using magnetron sputtering, the effect of thermal shock on Si based films and its interface were evaluated by various characterization methods such as in-situ nanoscratch, atomic force microscope (AFM), X-ray diffraction (XRD), fourier transform infrared (FTIR) spectra and ultraviolet–visible diffuse reflectance spectroscopy (UV-DRS). The results show the adhesion strength of Si/ZnO interface is relatively stable under thermal shock, the surface grains of Si coated ZnO form dense clusters then refine them. XRD and FTIR show Si based films exhibit (002) orientation with good structural stability related to Zn–O bond, the interfacial reactions of Si based films could experience strong interaction through Si, Zn and O atoms located at Si/ZnO interface during thermal shock. Moreover, some comparatively prominent peaks are observed by UV-DRS, which caused by Si interacted with ZnO, the AZO films deposited on quartz glass substrates illustrate the optical properties are obviously influenced and degraded after thermal shock.     

Tin(IV) Oxide Coating of Aluminum Borate Whiskers and Alumina Particles by Chemical Vapor Deposition

Aluminum borate whiskers of 0.5–1.0 μ diameter and alumina particles of 10–20 μ diameter were coated with SnO₂ by the reaction of SnCl₄–H₂O–N₂ gas mixtures in a rotary kiln reactor. Prior to coating, the whiskers were slightly etched to ensure adhesion between the SnO₂ layer and the whisker surface. The whiskers were coated at 100°C for 1 h, and then at 300°C for 2 h. This procedure was effective for covering the entire whisker surface with a uniform SnO₂ layer. Precoating was not necessary for the alumina particles. A compressed disk of the coated whiskers had an electrical conductivity of 30–40 S/m.     

Chemical Precipitation Synthesis and Optical Properties of ZnO/SiO2 Nanocomposites

SiO₂ nanowires, made from natural chrysotile, were used to synthesize zinc oxide (ZnO)/SiO₂ composites by chemical precipitation. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy, and Fourier transform infrared. Their optical properties were studied by a ultraviolet-vis spectrophotometer and a fluorescence spectrophotometer. Structural analysis revealed that the crystal size of ZnO crystallites is <20 nm, and the leached SiO₂ nanowires were amorphous. TEM analysis showed that the size of ZnO particles in SZ8 was mainly in the range from 15 to 20 nm and dispersed uniformly on the surface of SiO₂ nanowires. The photoluminescence spectra showed that ZnO/SiO₂ composites have stronger emitting intensity at the blue–green band than pure ZnO synthesized under the same reaction conditions. Therefore, the composites will be of great interest in the application of luminescence material. The as-prepared ZnO/SiO₂ composites can be used as photocatalysts for waste water treatment because they separate much more easily away from solution.     

碱土铝酸盐蓄光型发光材料的后处理研究

采用胶体包覆和表面成膜包覆相结合的方法,对碱土铝酸盐蓄光型发光材料进行包覆后处理研究。分析了包覆后处理对材料表面结构变化、发光性能及应用性能的影响。研究表明:经过包覆后处理的发光材料在水中浸泡时,发光材料对水能保持稳定,水相的pH值和电导率保持基本稳定;而未经包覆后处理的发光材料在水中分解,其水相的pH值和电导率上升很快。经过包覆处理的SrAl_2O_4:Eu,Re(Re为稀土元素)(PLO)在水中浸泡720 h后能保持80％的初始亮度,未经处理的发光材料则失去发光性能。包覆后处理能在发光材料表面形成了一层连续的比较致密的保护层,有效地减少外界对发光材料的影响,而且可以修复发光材料颗粒原有的裂纹等缺陷。包覆处理后能有效提高发光材料的应用性能,如耐水性、分散性及耐高温性能,更能适应不同的应用领域。     

Effects of Seed Layer Characteristics on the Synthesis of ZnO Nanowires

Single crystalline zinc oxide (ZnO) nanowires were synthesized on sputter-deposited ZnO seed layers via hydrothermal reactions in an equimolar (20 mM) aqueous solutions of Zn(NO₃)₂·6H₂O and C₆H₁₂N₄ at 90°C. The sputter-deposited ZnO seed layers were prepared to exhibit different crystalline structures in order to examine their effects on the growth of ZnO nanowires. It was found that the nanowire diameter depends on the size of the (002) grains of the seed layer. This is attributed to the epitaxially growth of the nanowires from the columnar grains of the seed layer which is shown by the TEM analysis.     

Nanofibrillated cellulose in wood coatings: Dispersion and stabilization of ZnO as UV absorber

The effect of nanofibrillated cellulose (NFC) on the dispersion and stabilization of zinc oxide (ZnO) nanoparticles in waterborne wood coatings was examined. Different coating compositions with and without NFC at varying concentrations of unstabilized, powdery or stabilized ZnO were produced. Properties of free coating films prepared via bar coating and wood specimens coated by brush with the coating compositions were evaluated. This included the effects of NFC and ZnO on the coating appearance, film formation, distribution of ZnO in the coatings, tensile properties and UV absorbing properties of free films and the effects of artificial weathering on the coated wood specimens. We showed that NFC significantly improved the distribution of the unstabilized ZnO in the coatings and prevented sedimentation of ZnO. NFC also improved film formation and inhibited crack formation during curing and weathering for more brittle binder materials. NFC had a pronounced matting effect but did not influence the coating colour. Colour stability of coated wood specimens during weathering was affected by the ZnO content, but needs further improvement. The results show that the biopolymer NFC is suitable to stabilize ZnO in coatings for wood, which could be of interest for other applications, as well.     

Microstructural and Thermoelectric Characteristics of Zinc Oxide-Based Thermoelectric Materials Fabricated Using a Spark Plasma Sintering Process

M-doped zinc oxide (ZnO) (M=Al and/or Ni) thermoelectric materials were fully densified at a temperature lower than 1000°C using a spark plasma sintering technique and their microstructural evolution and thermoelectric characteristics were investigated. The addition of Al₂O₃ reduced the surface evaporation of pure ZnO and suppressed grain growth by the formation of a secondary phase. The addition of NiO promoted the formation of a solid solution with the ZnO crystal structure and caused severe grain growth. The co-addition of Al₂O₃ and NiO produced a homogeneous microstructure with a good grain boundary distribution. The microstructural characteristics induced by the co-addition of Al₂O₃ and NiO have a major role in increasing the electrical conductivity and decreasing the thermal conductivity, resulting from an increase in carrier concentration and the phonon scattering effect, respectively, and therefore improving the thermoelectric properties. The ZnO specimen, which was sintered at 1000°C with the co-addition of Al₂O₃ and NiO, exhibited a ZT value of 0.6 × 10⁻³ K⁻¹, electrical conductivity of 1.7 × 10⁻⁴Ω⁻¹·m⁻¹, the thermal conductivity of 5.16 W·(m·K)⁻¹, and Seebeck coefficient of −425.4 μV/K at 900°C. The ZT value obtained respects the 30% increase compared with the previously reported value, 0.4 × 10⁻³ K⁻¹, in the literature.     

Polymorphism and Hydration of Tricalcium Silicate Doped With ZnO

Up to 4.7% ZnO can be incorporated into the crystalline lattice of C₃S. Five allotropic forms (i.e. T_I, T_II, M_I, M_II, and R) can be stabilized at room temperature, depending on the amount of ZnO. When heated to high temperature, the C₃S-ZnO solid solution decomposes and ZnO escapes from the crystalline lattice. The hydration and strength development of C₃S are altered by ZnO doping.     

Stability of Metal Oxide Doped ZnO in Molten Alkali Carbonates

The decomposition of Cr-doped ZnO and Zr-doped ZnO in Li₂CO₃/K₂CO₃ melts at 923 K under a humidified 30% CO₂/air atmosphere was found to occur by different routes, with the relevant equilibrium solubilities in the carbonate melt mitigating the decomposition path. Chromium–doped ZnO undergoes Cr depletion resulting from dissolution of the doped material followed by reprecipitation of a Cr-depleted ZnO; the Cr remains dissolved as highly soluble chromate. This reaction progresses until Cr equilibrium solubility is met. Zirconium-doped ZnO shows preferential ZnO solubility, with reprecipitation of ZrO₂ and Li₂ZrO₃.     

Electrodeposition of flexible stainless steel mesh supported ZnO nanorod arrays with enhanced photocatalytic performance

Large scale well oriented ZnO nanorod arrays (ZNRAs) were electrodeposited on flexible stainless steel mesh (SSM) substrate pre-treated by Al doped ZnO (AZO) seed layers. The effects of substrate pre-treatment conditions such as Al doping and spin coating times of the colloid on the morphology characteristics and photocatalytic properties of as-prepared ZNRAs were systematically studied. The results showed that by introducing Al into ZnO colloid solution, well aligned ZNRAs with relatively higher specific surface area (higher growth density and smaller rod diameter) could be obtained on the premodified SSM substrate. In addition, increasing spin coating times of AZO colloid solution would decrease the average diameter of ZNRAs. Under the optimum preparing conditions, the formed flexible SSM supported ZNRAs exihibited enhanced photocatalytic performance of 93.42% and remarkable photocatalytic stability under the UV-lamp for degradation of Rhodamine B.     

Nanoscale Coating of Silicon and Manganese on Ferrimagnetic Yttrium Iron Garnets

A uniform microstructure of Gd-substituted yttrium iron garnet (Y₂Gd₁Fe₅O₁₂) was obtained with additives of Si and Mn using a sol-gel coating process. Tetraethyl orthosilicate (TEOS) and manganese acetate were used as Si and Mn sources for the sol-gel coating procedure, respectively. TEM/EDS analysis confirmed the presence of a relatively uniform nanoscale coating of Si and Mn around each particle. High density and uniform microstructure were obtained after sintering at 1400°C in O₂ atmosphere. The density and grain size of the specimens depended on Mn content. The results were compared with materials fabricated without additives incorporated by the sol-gel coating procedure.