Papers by Keyword: Amorphisation

Abstract: The reaction ball milling can produce the solid state amorphization of covalent ceramic, SiC, including the mechanical alloying (MA) of the elemental crystalline powder mixture of Si and C and the mechanical grinding (MG) of the commercial β-SiC particle and MG of the nanocrystalline β-SiC powder as synthesized via ’high-energy’ MA. An increase in amorphous volume (X) by decreasing crystallite size (d) during MG is expressed by a relation of X= 1-{d/(d+∆)}3 with the intercrystal thickness (∆) of 1 nm. The rotating-arm reaction ball milling is used to synthesize nanocrystalline (nc) hydroxyapatite by MA of the powder mixture at 303 K, according to a reaction of 6CaHPO4･2H2O+4Ca(OH)2→nc-Ca10(PO4)6(OH)2+8H2O with JMA exponent of 1. By employing the pulse electric discharge consolidation, the amorphous SiC powder compact shows a rapid densification during Newtonian viscous flow as expressed by an Arrhenius relation with the activation energy of 495 kJ･mol-1, and then obtain the full densification at 2033 K under 100 MPa. The nanocrystalline hydroxyapatite powder with the crystallite size of 8 nm can be consolidated at full-density at 1023 K under 150 MPa, following a rapid shrinkage during superplastic flow from 900 K. The fracture toughness (KIC), as deduced from the indentation microfracture method, is the high level of 13 MPa･m0.5 for nanocrystalline SiC with 12 nm.

Abstract: Strontium ferrites powders were obtained by high energy milling process after calcinations of iron oxide and barium carbonate. Phase formations and crystallite size was determined using X-ray diffraction. Morphology, particle size and agglomeration stages were analyzed using scanning and transmission electron microscopy. Results show particles in the range of 14 to 40 nanometers, large agglomerates and crystalline phases formation.

Abstract: In this conference we try to give a survey of the main characteristics of aging of oxides under irradiation in the perspective of the recent developments of the ab-initio modeling capabilities. After a brief recall of the relevant radiation – matter interactions, we present the main aspects of materials aging under irradiation, I) defect creation either elastically or inelastically, ii) microstructure evolution due to defect elimination, iii) radiation enhanced diffusion, iv) phase changes under irradiation.

Abstract: in the present study, amorphous ti50cu35-xni15snx (x=0~7) alloy powders were synthesized by mechanical alloying technique. the amorphization behavior of ti50cu28ni15sn7 alloy powders was examined in details by scanning electron microscopy, differential scanning calorimeter, x-ray diffraction, and synchrotron x-ray absorption spectroscopy. the results show that fully amorphous powders formed after 7 hours of milling. The thermal stability of the Ti50Cu35-xNi15Snx amorphous powders was investigated by differential scanning calorimeter. The amorphous Ti50Cu35Ni15 powders (i.e., x=0) exhibit no glass transition behavior. However, the amorphous Ti50Cu35-xNi15Snx (x=3~7) powders were found to exhibit a supercooled liquid region before crystallization. Amorphous Ti50Cu28Ni15Sn7 alloy powders exhibits a wide supercooled liquid region of 61 K.

Abstract: The changes in the microhardness and Young’s modulus of the 2 MeV C+ ion–irradiated IG-110 isotropic nuclear graphite were evaluated by a dynamic ultra-microhardness test. Indentation depth and load dependency of the hardness and elastic modulus were observed possibly due to the formation of a range. Both the hardness and Young’s modulus (E) – dpa curves have shown an incubation dose for about ı 0.3 mdpa. After the incubation dose, both the hardness and E showed a rapid increase with the dose. The doses that corresponds to these rapid increases in the hardness and E coincides with the dose that corresponds to the beginning of the irradiationinduced surface distortion, and the loss of the graphite crystallinity (amorphization).

Abstract: Atomic-level simulations are used to determine defect production, cascade-overlap effects, and defect migration energies in SiC. Energetic C and Si collision cascades primarily produce single interstitials, mono-vacancies, antisite defects, and small defect clusters, while amorphous clusters are produced within 25% of Au cascades. Cascade overlap results in defect stimulated cluster growth that drives the amorphization process. The good agreement of disordering behavior and changes in volume and elastic modulus obtained computationally and experimentally provides atomic-level interpretation of experimentally observed features. Simulations indicate that close-pair recombination activation energies range from 0.24 to 0.38 eV, and long-range migration energies for interstitials and vacancies are determined.