Properties Of Zinc Oxide Powders Research Articles

The effect of high-temperature nanoparticle-based modification on the structure of zinc oxide powders

The authors have studied the effect of solid-state nanoparticle-based modification on the structure of zinc oxide powders. To carry out the experiment, seven types of nanoparticles of various oxides were applied. The modification was performed by heating the powder mixtures in the air at 650°C for 2 hours. The concentration of nanopowders was 10 wt.%, the average grain size of nanoparticles varied from 10 to 80 nm. It was established that high-temperature nanoparticle-based modification does not lead to significant structural changes and cannot affect the properties of zinc oxide powder. While modifying zinc oxide powders, an increase in photo- and radiation stability can occur primarily because of mechanisms associated with the deposition of nanoparticles on the surface of the micropowder. Due to structural changes, certain types of nanoparticles (e.g., alumina in the sample under investigation) can make a rather insignificant contribution to the stability of optical properties when exposed to radiation.

Control over the Surface Properties of Zinc Oxide Powders via Combining Mechanical, Electron Beam, and Thermal Processing.

The surface properties of zinc oxide powders prepared using mechanical activation, electron beam irradiation, and vacuum annealing, as well using combinations of these types of treatments, were studied using X-ray photoelectron spectroscopy. The structure of the obtained materials was studied by an X-ray diffraction technique and by scanning electron microscopy. We found that over five hours of grinding in an attritor, the size of nanocrystals decreases from 37 to 21 nm, and microdeformations increase from 0.3% to 0.6%. It was also found that a five-hour grinding treatment promoted formation of vacancies in the zinc sublattice at the surface and diffusion of Zn2+ cations into the bulk of the material. Irradiation of commercial zinc oxide powders with an electron beam with an energy of 0.9 MeV and a dose of 1 MGy induced breaking of Zn–O bonds, diffusion of interstitial zinc ions into the bulk, and oxygen atom escape from regular positions into the gas phase. A combined treatment of five hours of grinding and electron beam irradiation promoted accumulation of interstitial zinc ions at the surface of the material. Annealing of both initial and mechanically activated ZnO powders at temperatures up to 400 °C did not lead to a significant change in the properties of the samples. Upon exceeding the 400 °C annealing temperature the X-ray photoelectron spectra show almost identical atomic composition of the two types of materials, which is related to diffusion of interstitial zinc ions from the bulk of the material to the surface.

Research of structural properties of zinc oxide nanopowders obtained by high-energy mechanical milling (attritor) using Raman spectroscopy

In the paper the evolution characteristics of structural properties of zinc oxide powders produced by mechanical milling in a high-energy attritor using Raman spectroscopy are studied. Milling time was 1, 3 and 5 h. It is found that the main spectral change observed in the Raman spectra of the samples, is a monotonic intensity increase of E1(LO)x mode associated with increasing concentrations of defects in the material.

Optical properties of zinc oxide powders modified by nanoparticles ZrO2, Al2O3, TiO2, SiO2, CeO2 and Y2O3 with various concentrations

This study carried out on the diffuse reflective spectra of zinc oxide modified by Al2O3, ZrO2, SiO2, CeO2, TiO2 and Y2O3 nanoparticles. It was established that during the modification are formed the solid solutions between zinc oxide and nanopowder as Al2ZnO4, ZrZnO3, Zn2SiO4, CexZn(1−х)Оy, Zn2TiO4, YxZn(1−x)Oy. The diffuse reflection spectra of the modified powders are changed in the UV and visible range with a maximum at 395 nm. This band is determined by the intrinsic point defects in the crystal lattice of ZnO as interstitial zinc ions and zinc vacancy. In the IR region also recorded changes due to the absorption of OH-groups adsorbed on the surface modified zinc oxide.

Influence of annealing on the scintillation properties of zinc oxide powders and ceramics

It was shown that annealing ZnO and ZnO:Ga initial powders and ceramics in different atmospheres significantly changes the characteristics of the studied samples. Two main luminescence bands of different origins were observed in powders at 540 nm and 580 nm. Annealing either in vacuum or in Ar:H2 atmosphere increased intensity of green luminescence with peak at 540 nm whereas annealing in air enhanced a luminescence band with peak at 580 nm in the powders. Corresponding changes in luminescence kinetic properties were observed. Annealing of the ceramics in vacuum and air did not affect the luminescence properties, while annealing them in Ar:H2 atmosphere increased green luminescence intensity of undoped ceramics and excitonic luminescence intensity of doped ones. Comparison of the X-ray, gamma-ray and cathode-ray excited luminescence lead to conclusion that the enhancement of luminescence intensity took place in surface layer of about 100 μm thickness.

Characterization of Nano-sized ZnO Electrodes with Curcumin-derived Natural Dye Extract for DSSC Application

Zinc oxide (ZnO) powder was first prepared by hydrothermal synthesis at low temperature. X-ray diffraction (XRD) investigation was carried out to examine the structural properties of ZnO powder. ZnO colloidal solution was deposited onto ITO/glass by rolling. After air drying, annealing in O2, atmospheric ambient was performed at 300 C and 400 C for 1 h. As the surface treatment, sintered ZnO film was immersed in 0.1 M HCl, washed with DIW and dried at room temperature. The Curcumin, a yellow-orange dye found in turmeric root, was used as a photosensitizer and was carefully prepared to avoid colour fading. Next, the ZnO film was dipped in dye solution for 15 h. High performance carbon counter electrode was prepared and used as a counter electrode. Two glass slides were offset and two binder clips were used to hold the electrodes together. Photovoltaic response of ZnO cell was measured and it was expected to utilize the DSSC application. The conversion efficiency of DSSC at 400oC (0.129%) was found to be larger than that of the cell at 300oC (0.117%).

Some Properties of Zinc Oxide Powder

Some Properties of Zinc Oxide Powder

Optical reflectance of aluminum-doped zinc oxide powders

Changes in the electronic properties of zinc oxide powders doped with aluminum were related to the optical reflectance characteristics. ZnO powders doped as a solid solution, having from 0.035 to 1.00 mol % Al, were characterized. Diffuse optical reflectance was measured over near-ultraviolet and visible wavelengths from 340 to 700 nm. Diffuse infrared reflectance was used to characterize the free-electron density in each powder. Free-electron densities ranged from 2.5×1014 cm−3 for undoped ZnO to 3.5×1017 cm−3 for the 1.00-mol % Al powder. The Al-doped powders showed significant resistance to color center formation, whereas the undoped powder did not. The suppression of the optical absorption at approximately 400 nm in the Al-doped powder may be related to the suppression of a band state to localized defect state charge transfer.

Controlled microstructural properties of zinc oxide powder formed by the thermal decomposition of zinc hydroxynitrate

A detailed analysis of the microstructural properties, i.e., microdistortion, size and shape of crystallite, of zinc oxide produced by thermal decomposition of zinc hydroxynitrate Zn 3(OH) 4(NO 3) 2 is presented. The physico-chemical parameters of the reaction, such as the heating rate, mean decomposition rate, sample mass and residual pressure, are important in determining the microstructure of the ZnO produced. Under the experimental conditions used, the shape of the crystallites is cylindrical on average. By modifying the parameters it is possible to modulate the crystallite sizes and also their anisotropic form factor over a limited range. The influence of the residual pressure is prominent in the formation of reticular microdistortions. Strain-free ZnO, of interest in diffraction line-broadening analysis, can be prepared only in small quantities under vacuum, the upper limit for the precursor mass being about 25 mg.

Optical properties of zinc oxide powders

Optical properties of zinc oxide powders

Barrier Properties in Electrophotographic Zinc Oxide

A number of factors are known to influence greatly the photoelectrical and the electrophotographical properties of zinc oxide powder. Some of them, such as the degree of zinc excess and the state-species and amount-of chemisorbed oxygen, are in most cases uncontrollable, in the sense that they are almost determined at the time of manufacturing, unless some drastic treatment is imposed on samples before use. While some other factors such as the surface doping can be used to improve or control behaviors of samples at the time of use, these factors seem to be intimately related to the hard-to-control ones. After a brief review of studies of the oxygen states on zinc oxide surface, a discussion is developed concerning the photoconductive properties and the electrophotographic charge acceptance of zinc oxide bearing various degrees of zinc excess. The potential barrier at the surface of microcrystals, the height of which is estimated from dark conductivities, gives a good measure for the charge acceptance. Further, based upon the conventional theory of barrier development by oxygen chemisorption, the photo-to-dark conductivity ratio is argued in terms of the donor density, the barrier height, and other factors.