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Description of consolidation forces on nanometric powders
Turki, D.;Fatah, N.;
Brazilian Journal of Chemical Engineering , 2010, DOI: 10.1590/S0104-66322010000400007
Abstract: the experiments and analyses performed included measurements of the physical properties of tio2 powder such as the particle size, density, and consolidation. experiments with nanometric tio2powder of 204 nm average diameter show that, during consolidation, the adhesion of particles under normal stress is principally due to the van der waals force for particle radii less than 300nm and the application of external force has no effect on the cohesion of the primary particles within this range; for particle radii around 300nm to 1.0μm the cohesion of the powder system is due to plastic deformation and the application of external force change the cohesion force to a plastic deformation between the agglomerates formed under these forces. this can be observed in the arrangement of the primary particles into dispersed agglomerates with sizes greater than the individual particles. the results obtained with the nanometric tio2 powders show a more complex behavior than the micronic powders. this behavior is related to the structure of the nanometric particles in the packed bed; the evolution of this structure is made up of individualized and spherical agglomerate shapes. it has been experimentally observed that the powder structure is not perturbed by stresses of low intensities. a development of the different forces involved in interparticle contacts is outlined. the description of these forces involved in particle cohesion will help to understand the powder cohesion under consolidation.
Cerium oxide based nanometric powders: synthesis and characterization  [PDF]
Nini? M.,Bo?kovi? S.,Nenadovi? M.,Zec S.
Science of Sintering , 2007, DOI: 10.2298/sos0703301n
Abstract: Nanometric powders of solid solutions of cerium oxide were obtained by a modified glycine nitrate procedure. Solid solutions of the host compound CeO2 with one or more dopants in the lattice were synthesized. Rare earth cations (Re=Yb, Gd and Sm) were added to ceria in total concentration of x= 0.2 that was kept constant. The criterion in doping was to keep the value of lattice parameter of ceria unchanged. The lattice parameters were calculated by using the model that takes into account the existence of oxygen vacancies in the structure.


物理学报 , 1991,
Abstract: Fe20Al80 amorphous powders were prepared by ball milling through 180 hours. X-ray diffraction and transmission electron microscope experiments indicate the powder sample is amorphous and also show the average particle size and crystallization products. The paramagne-tism and crystallinity of amorphous material are determined by M?ssbauer effect measurements.
PZT Powders Synthesized by Hydrothermal Method
ZHU Kong-Jun, ZHU Ren-Qiang, DONG Na-Na, GU Hong-Hui, QIU Jin-Hao, JI Hong-Li
无机材料学报 , 2012, DOI: 10.3724/sp.j.1077.2012.00507
Abstract: Lead zirconate titanate (PZT) powders with single―phase, cubic morphology and average size of 1 μm were synthesized using hydrothermal methods. Effects of KOH concentration, hydrothermal treatment time and Pb excess were investigated. The results show that KOH concentration has an important influence on the solid solubility of Pb ion in A―site of PZT perovskite structure. The concentration of Pb2+ vacancies increased with the increase of OH― concentration. However, this kind of deficiency could be compensated by adding more Pb ions in the raw materials, and more Pb ions were needed to add with higher alkaline concentration in the starting solution. But excessive compensation of Pb ions would result in the appearance of the second phase.
Temperature Effects on the Crystallization and Coarsening of Nano-CeO2 Powders  [PDF]
H. F. Lopez,H. Mendoza
ISRN Nanomaterials , 2013, DOI: 10.1155/2013/208614
Abstract: The effect of temperature on nano-CeO2 particle coarsening is investigated. The nanoceria powders were synthesized using the microemulsion method and then exposed to temperatures in the range of 373–1273?K. It was found that the nanoparticles exhibited a strong tendency to form agglomerates and through the application of ultrasound these agglomerates could be broken into smaller sizes. In addition average nanoparticle sizes were determined by powder X-ray diffraction (XRD). The outcome of this work indicates that the initial nano-CeO2 powders are amorphous in nature. Annealing promotes CeO2 crystallization and a slight shift in the (111) XRD intensity peaks corresponding to CeO2. Moreover, at temperatures below 773?K, grain growth in nano-CeO2 particles is rather slow. Apparently, mass transport through diffusional processes is not likely to occur as indicated by an estimated activation energy of 20?kJ/mol. At temperatures above 873?K, the measured activation energy shifted to 105?kJ/mol suggesting a possible transition to Ostwald-Ripening type mass transport mechanisms. 1. Introduction Nanocrystalline ceria possesses unique properties which enable it to be widely used in various industrial applications. Among the different uses of nanoceria are acting as coatings for high temperature oxidation protection in alloys [1–4], acting as catalysts and gas sensors [5, 6], being used for absorption and redistribution of UV radiation, [7]. Typical applications involve high temperature exposure above 873?K. Under these conditions mass transport mechanisms become active, particularly oxygen anions due to their inherently high mobility in the nanoceria crystal lattice [8]. In contrast, the diffusivity of cerium ions does not seem to be significant at these temperatures, but there is no data available on actual diffusivity values. Despite the lack of diffusivity data, it is expected that the nanosized CeO2 particles will exhibit appreciable coarsening upon exposure to elevated temperatures. Coarsening in nanoparticle dispersions at high temperatures is typically driven by chemical potential differences associated with curvature effects on the particle interfacial energies. This phenomenon, known as Ostwald-Ripening (O-R), has been widely investigated in conventional materials exposed to high temperatures [9, 10]. From the published literature [11], it is apparent that O-R also occurs in nanometallic and nanoceramic compounds. Eastman [12] reported grain growth exponents, of approximately 3 in nano-TiO2 or in yttria-stabilized nano-ZrO2 systems indicating that O-R
Nanocrystalline zirconia based powders synthesized by hydrothermal method
Viktoria Tsukrenko,Elena Dudnik,Alexey Shevchenko
Processing and Application of Ceramics , 2012,
Abstract: Nanocrystalline powders in the ZrO2-Y2O3-CeO2-CoO-Al2O3 system with 1 and 10 mol% Al2O3 were prepared via hydrothermal treatment in alkaline medium. The characteristics of nanocrystalline powders after heat treatment in the temperature range from 500 to 1200 °C were investigated by XRD phase analysis, scanning electron microscopy, petrography and BET measurements. It was found that hydrothermally treated powders contained metastable low-temperature cubic solid solution based on ZrO2 and addition of Al2O3 increased temperature of phase transformation of the metastable cubic- ZrO2 to tetragonal-ZrO2. It was evidenced that both powders remained nanocrystalline after all processing steps with the average particle sizes from 8 to 20 nm. The addition of 0.3 mol% CoO allows one to obtain composites with good sinterability at 1200 °C.
Preparation of Mg55Ni35Si10 Amorphous Powders by Mechanical Alloying and Consolidation by Vacuum Hot Pressing
YANG Deng-Ke,WEN Cui-E,HAN Fu-Sheng,WANG Qing-Zhou,LI Hai-Jin,

中国物理快报 , 2006,
Abstract: Amorphous Mg55Ni35Si10 powders are fabricated by using a mechanical alloying technique. The amorphous powders are found to exhibit a relatively high crystallization temperature of 380°C. The as-milled amorphous Mg55Ni35Si10 powders are consolidated successfully into bulk body by vacuum hot pressing technique. Limited nanocrystallization is noticed. The Vickers microhardness range of the Mg55Ni35Si10 bulk sample is 7834 to 8048MPa. Its bending strength and compressive strength are 529MPa and 1466MPa, respectively.
The effect of nanometric zirconia particle additives on microstructure and mechanical properties of dense alumina
Lukasz Zych,Radoslaw Lach,Krzysztof Haberko,Pawel Rutkowski
Processing and Application of Ceramics , 2009,
Abstract: Zirconia additives have favourable influence on mechanical properties of dense alumina polycrystals. It results from the martensitic transformation of tetragonal zirconia particles into monoclinic symmetry at the crack tip propagating through a material. Usually applied zirconia particles were of sub-micrometer or micrometer sizes. In the present work nanometric zirconia particles prepared by hydrothermal crystallization technique were introduced into the alumina matrix. Both, zirconia and alumina powders were homogenized in an aqueous suspension of pH selected on the basis of the zeta (ξ) potential measurements. It was found that this factor influences greatly strength of the resulting powder agglomerates and hence mechanical properties of the sintered material.

ZHAO Tiemin,HAO Yunyan,XU Xiaorong,YANG Yuansheng,

材料研究学报 , 1998,
Abstract: Effect of magnetic field treatment on crystallization and magnetic properties of melt-spun Nd5.5Fe66B18.5Cr5Co5.Nd4.5Fe77B18.5 and Nd10.5Fe70B7.0Zr2.5Co10 powders were inves- tigated. Results show that an externally applied magnetic field during heat treatment of a melt-spun nanocomposite magnet can promote crystallization from amorphous State and increase the maximumeneny product. The stronger the applied magnetic field, the lower the crystallization temperature. The way to produce anisotropic NdFeB nanocomposite permanent magnet was also proposed.
Preparation of Al72Ni8Ti8Zr6Nb3Y3 amorphous powders and bulk materials  [PDF]
Yu Wu,Xin-fu Wang,Fu-sheng Han
- , 2016, DOI: https://doi.org/10.1007/s12613-016-1338-5
Abstract: Amorphous Al72Ni8Ti8Zr6Nb3Y3 powders were successfully fabricated by mechanical alloying. The microstructure, glass-forming ability, and crystallization behavior of amorphous Al72Ni8Ti8Zr6Nb3Y3 powders were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The isothermal crystallization kinetics was analyzed by the Johnson–Mehl–Avrami equation. In the results, the supercooled liquid region of the amorphous alloy is as high as 81 K, as determined by non-isothermal DSC curves. The activation energy for crystallization is as high as 312.6 kJ·mol?1 obtained by Kissinger and Ozawa analyses. The values of Avrami exponent (n) imply that the crystallization is dominated by interface-controlled three-dimensional growth in the early stage and the end stage and by diffusion-controlled two- or three-dimensional growth in the middle stage. In addition, the amorphous Al72Ni8Ti8Zr6Nb3Y3 powders were sintered under 2 GPa at temperatures of 673 K and 723 K. The results show that the Vickers hardness of the compacted powders is as high as Hv 1215.
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