The Influence of Tribophysical Activation on Solid-State Reaction during Thermal Treatment of ZnO-Cr2O3 (original) (raw)
Related papers
Microstructural characterization of mechanically activated ZnO–Cr 2O 3 system
Journal of The European Ceramic Society, 2005
An equimolar mixtures of starting ZnO and Cr 2 O 3 powders were mechanically activated by grinding using a planetary ball mill for various periods of time (40-320 min). Formation of nanocrystalline ZnCr 2 O 4 as normal spinel structure at room temperature is detected in all samples-after ball-milling.
Materials Science Forum, 2004
Mixtures of starting ZnO and Cr 2 O 3 powders in equimolar quantities were mechanically activated by grinding using a high energy vibro-mill for 0, 40 and 80 minutes. Qualitative X-ray diffraction analysis made after sintering at 900 o C for 240 min showed the presence of a wellcrystallized spinel-type phase, ZnCr 2 O 4 , in all examined samples. A detailed structural analysis of lattice parameters, average primary crystallite sizes, and crystal lattice microstrains was made by the pattern decomposition technique, performed in accordance with the procedure based on the KOALARIET-XFIT program. Due to importance of cation distributions for the chemical and physical properties of spinels, a study of site occupation factors of ZnCr 2 O 4 spinels, i.e. changes in the stoichiometry, was conducted. Calculations based on atomistic methods for the simulation and description of perfect and defect spinel ZnCr 2 O 4 crystal lattices were made, and the presence of individual structural defects was determined.
Evolution of the microstructure of disperse Zinc-oxide during tribophysical activation
Journal of materials …, 1999
The process of macro-and microstructural transformations of zinc-oxide powders, which were tribophysically activated by grinding in a vibro-mill was investigated using methods of transmission electron microscopy, infrared spectroscopy and X-ray. It is shown that tribophysical activation contributes to a gradual modification of the fine defect structure of zinc-oxide powders. In the starting stage agglomerates and bigger, longer particles are destroyed first of all. As a result of the formation of both volume and surface defects and changes of the character of interparticles interactions the plate-like polycrystal particles are created. They actually present sets of coherent scattering region.
Solid-State Reactivity of the ZnO-xMn2O3 System During Heat Treatment
Journal of the American Ceramic Society, 2006
Using X-ray, infrared, and electron paramagnetic resonance methods, the reactivity of ZnO1xMn 2 O 3 systems during heat treatment was studied. Results showed that the solubility of manganese (Mn) in zinc oxide (ZnO) is lower than 3% and that reaction diffusion occurs. Reaction processes that take place in this system promote disintegration of Mn 2 O 3 particles into microfragments and causes them to move along the surface of the ZnO particles (solid-state reactive wetting process).
Synthesis and Characterization of Powder Zinc Oxide (ZnO) Calcined at Different Temperatures
This paper aims to synthesize Zinc Oxide (ZnO) powder by Sol-Gel technique modified by Reaction for Ion Coordination (RIC), calcining the samples at different temperatures (800°C and 950°C) with the intention to characterize them through X-Ray Diffraction (XRD) and analyze its morphological properties using Scanning Electron Microscopy (SEM). The results showed that in both calcination temperature of the powder, ZnO was formed, however, the morphology of each of the samples showed different characteristics.
Microstructural characterization of mechanically activated ZnO powders
In this paper, changes of microstructural characteristics of disperse systems during mechanical activation of zinc oxide (ZnO) have been investigated. ZnO powder was activated by grinding in a planetary ball mill in a continuous regime in air during 300 min at the basic disc rotation speed of 320 rpm and rotation speed of bowls of 400 rpm but with various balls-to-powder mass ratios. During ball milling in a planetary ball mill, initial ZnO powder suffered high-energy impacts. These impacts are very strong, and large amounts of microstructural and structural defects were introduced in the milled powders. The morphology and dispersivity of particles and agglomerates of all powders were investigated by scanning electron microscopy and scanning transmission electron microscopy. The specific surface area of initial ZnO powder was determined as 3.60 m 2 g −1 and it increased to 4.42 m 2 g −1 in mechanically activated powders. An increase of the ball-to-powder mass ratio led to a decrease of particle dimensions as well as increased the tendency for joining into quite compact agglomerates, that is aggregates, compared with the very loose, soft initial agglomerates. The obtained results pointed out that activation of ZnO powders produces a highly disperse, nano-scaled mixture of small particles, that is crystallites with sizes in the range of 10-40 nm. Most of these particles are in the form of aggregates with dimensions of 0.3-0.1 μm. The crystallite and aggregate size strongly depend on milling conditions, that is ball-to-powder mass ratio, as shown in this investigation.
Synthesis of ZnO and ZrO2 Powders by Mechanochemical Processing
Materials Science Forum, 2007
The ZnO and ZrO2 powders were prepared by mechanochemical processing and subsequent heat treatment of the starting powder of precursors mixture of ZnCl2 and Ca(OH)2, and ZrOCl2·8H2O and NaOH, respectively. Inert salt matrix, ether CaCl2 or NaCl, which prevents particle agglomeration was formed during mechanochemical solid state reaction. After mechanochemical treatment, samples were calcined at various temperatures. Selective removal of the matrix phase by washing the resulting powder with appropriate solvent yields almost pure ZnO and ZrO2 powders. Characterization of the powders was performed by X-ray diffraction (XRD), differential thermal and thermo gravimetric analysis (DTA−TG) and scanning electron microscopy (SEM).
Physical changes of sintered ceramics obtained from freeze-dried ZnO+(CH3COO)2Cu·H2O powders
Materials Letters, 2003
Freeze-drying was used to produce highly homogeneous mixtures of powders containing ZnO and (CH 3 COO) 2 CuÁH 2 O (copper(II) acetate monohydrate, denoted by CuAcH 2 O). Mixtures of ZnO + CuAcH 2 O, in specific concentrations of Cu 2 + , i.e., ZnO + x mol% Cu (0.01 V x V 5.0) were obtained by freeze-drying. Due to the polymeric characteristic of CuAcH 2 O, pellets of those mixtures were compacted without any pressing additives. After sintering at temperature range 750 -1150 jC in air for 1 h, physical changes such as mass loss, shrinkage and density were evaluated. The results showed that all physical changes increased as the concentration of CuAcH 2 O increased. The mass loss was nearly independent of the sintering temperature, especially from 750 to 1050 jC, and directly proportional to the concentration of CuAcH 2 O. The mass loss was mainly related to dehydration and thermal decomposition of CuAcH 2 O, although the presence of water excess or sublimation of copper(II) acetate (CuAc) could not be neglected. In addition, contributions to mass loss were supposed to be related to sublimation of ZnO or reduction of CuO to Cu 2 O, for sintering temperature above 1050 jC. Shrinkage and density were nearly independent of the sintering temperature above 850 jC, which indicates that sintering (grain growth) may occur in that temperature range. Shrinkage and densification increased as the concentration of CuAcH 2 O increased, especially for ZnO + x mol% Cu (x>1.0). The presence of CuO particles on the ZnO surface, originated from thermal decomposition of CuAcH 2 O during heating, is believed to promote shrinkage and densification. D
Journal of Magnetism and Magnetic Materials, 2011
Experimental results of electron paramagnetic resonance spectra, X-ray diffraction, scanning electron microscopy and infrared spectroscopy demonstrate that the kinetic of the physical and chemical processes that takes place during prolonged intensive mechanical processing (MP, 0 o t MP 4 3120 min) of powder mixtures of 50%wt ZnO þ 50%wt MnO 2 can be described as a three stage process. (1) 0 o t MP 4 30 min, particles destruction, formation of superficial defects, fast increment of sample average temperature (from 290 to $ 600 K) and annealing of defects with the lowest energy of activation E ac. (2) 30 o t MP 4 390 min, further particle destruction, slow increment of sample average temperature (from $ 600 to $ 700 K), formation and growth of a very disordered layer of b-MnO 2 around ZnO particles, dehydration of MnO 2 , formation of solid solution of Mn 2 þ ions in ZnO, formation of nano-quasiamorphous states in the ZnO-MnO 2 mixture and onset of the formation of the ZnMnO 3 phase. (3) 390 o t MP 4 3120 min, the sample average temperature remains constant ($ 700 K), the reaction is completed and the spinel ZnMnO 3 phase with a unit cell a ¼ 8.431(1)Å and space group Fd3m is the only phase present in the sample. No ferromagnetism at room temperature was detected in this study.
Materials Letters, 2006
A columbite-like phase of zinc niobate, ZnNb 2 O 6 , has been synthesized by a solid-state reaction via a rapid vibro-milling technique. The formation of the ZnNb 2 O 6 phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that single-phase ZnNb 2 O 6 powders were successfully obtained for calcination condition of 600°C for 2 h or 550°C for 6h with heating/cooling rates of 30°C/min. Clearly, this study has demonstrated the potentiality of a vibro-milling technique as a significant time-saving method to obtain single-phase ZnNb 2 O 6 nanopowders (∼50-300nm) at low calcination temperature.