Excess Thermodynamic Properties of Nanophase Titanium Dioxide Prepared by Chemical and Physical Methods

1992 ◽  
Vol 286 ◽  
Author(s):  
Chrysanthe D. Terwilliger ◽  
Yet-Ming Chiang
Keyword(s):  
Grain Boundary ◽  
Lattice Strain ◽  
Excess Enthalpy ◽  
Oxygen Deficiency ◽  
Excess Heat Capacity ◽  
Inert Gas ◽  
Scanning Calorimetry ◽  
Planar Defects ◽  
Physical Methods ◽  
Gas Condensation

ABSTRACTThe excess enthalpy and excess heat capacity of nanophase TiO2 prepared by a chemically-derived process and by inert gas condensation have been measured using differential scanning calorimetry. In comparison to the chemically-derived samples, the excess enthalpy of the inert gas condensed samples is significantly larger, perhaps due to the presence of intragranular planar defects that accomm oate oxygen deficiency. Significant extraneous contributions from planar defects, lattice strain, phase transformation, oxidation, or sintering have been ruled out for the chemically-derived samples. A grain boundary enthalpy of 13-1.6 J/m2 in the temperature range 600-1000°C is obtained from scanning measurements. However, the data also indicate a grain size and/or temperature dependence of the grain boundary enthalpy.

Synthesis And Characterization Of Ball-Milled Nanocrystalline Fcc Metals

1991 ◽  
Vol 238 ◽  
Author(s):  
J. Eckert ◽  
J. C. Holzer ◽  
C. E. Krill ◽  
W. L. Johnson
Keyword(s):  
Grain Size ◽  
Melting Point ◽  
Grain Boundary ◽  
Bulk Modulus ◽  
Ball Milling ◽  
Lattice Strain ◽  
Boundary Migration ◽  
General Relation ◽  
Heat Of Fusion ◽  
Scanning Calorimetry

ABSTRACTNanocrystalline fee metals (Al, Cu, Ni, Pd, Rh, Ir) have been prepared by ball milling. The development of the microstructure is investigated by x-ray diffraction, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The final grain sizes range from 6 to 22 nm and scale with the melting point and the bulk modulus of the elements: metals with higher melting point and bulk modulus have a smaller final grain size. From this a general relation between the deformation mechanism during ball milling and the ultimate grain size achievable by this technique is inferred. With decreasing grain size the lattice strain is enhanced and deformation enthalpies of up to 40 % of the heat of fusion are stored in the material. The contributions of the lattice strain and of die excess enthalpy of the grain boundaries to the stored enthalpies are critically assessed. The kinetics of grain growth are investigated by mermal analysis. The activation energy for grain boundary migration is derived from a modified Kissinger analysis and estimates of the grain boundary enthalpy are given.

MgH2 by Gas Phase Condensation: Nanostructure Morphology and Hydrogen Sorption Behaviour

2007 ◽  
Vol 1042 ◽  
Author(s):  
Ennio Bonetti ◽  
Elsa Callini ◽  
Amelia Montone ◽  
Luca Pasquini ◽  
Emanuela Piscopiello ◽  
...  
Keyword(s):  
Gas Phase ◽  
Inert Gas ◽  
Desorption Kinetics ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Sorption Behaviour ◽  
X Ray ◽  
Gas Condensation ◽  
Inert Gas Condensation ◽  
Pressure Differential Scanning Calorimetry

AbstractInert gas condensation was employed to prepare nanoparticles of Mg and MgH2 which morphology, clustering degree and structural stability have been investigated by X-ray diffraction and electron microscopy. Thermodynamic functional properties of the Mg and MgH2 nanostructured samples were investigated by high pressure differential scanning calorimetry. Some specific features of the morphology of the samples prepared by inert gas condensation are compared with powders obtained by ball milling through desorption kinetics behavior.

Hydrogen Desorption from MgH2 Based Nano-Micro Composites

2006 ◽  
Vol 971 ◽  
Author(s):  
Ennio Bonetti ◽  
Anna Lisa Fiorini ◽  
Luca Pasquini ◽  
Nadica Abazovic ◽  
Amelia Montone ◽  
...  
Keyword(s):  
Hydrogen Desorption ◽  
Sorption Kinetics ◽  
Inert Gas ◽  
Mechanical Processing ◽  
Mechanical Spectroscopy ◽  
Scanning Calorimetry ◽  
Sorption Behaviour ◽  
Similar Composition ◽  
Gas Condensation ◽  
Inert Gas Condensation

ABSTRACTThe microstructure and hydrogen sorption behaviour of MgH2 based nano-hydrides with different additives prepared by ball milling and inert gas condensation has been investigated by XRD, Differential Scanning Calorimetry and Mechanical Spectroscopy. Preliminary results on materials with similar composition and different nanostructures show that suitable mechanical processing and additive additions induce in the nanostructured composites tailored channels for improved ab/de-sorption kinetics at reduced temperatures.

On Temperature Dependence of Excess Gibbs Energy

1999 ◽  
Vol 64 (7) ◽  
pp. 1093-1099 ◽  
Author(s):  
Ivona Malijevská ◽  
Anatol Malijevský
Keyword(s):  
Heat Capacity ◽  
Gibbs Energy ◽  
Temperature Dependence ◽  
Excess Gibbs Energy ◽  
Excess Enthalpy ◽  
Excess Heat Capacity ◽  
Wilson Equation ◽  
Excess Heat ◽  
Energy Excess ◽  
Wilson And Nrtl Equations

Temperature dependence of GE is discussed for three widely used equations linear and nonlinear in parameters. It is shown that the Wilson equation predicts always positive excess heat capacity regardless of values of its parameters. Several temperature modifications of the Redlich-Kister, Wilson and NRTL equations are discussed with respect to the sign of the excess Gibbs energy, excess enthalpy and excess heat capacity.

Highly Size-Controlled Synthesis of Metal Nanoclusters by Inert-Gas Condensation for Nano-Devices

2010 ◽  
Vol 10 (5) ◽  
pp. 3667-3670 ◽  
Author(s):  
Il-Suk Kang ◽  
Hyun-Sang Seo ◽  
Deuk-Han Kim ◽  
Taek-Yeong Lee ◽  
Jun-Mo Yang ◽  
...  
Keyword(s):  
Inert Gas ◽  
Controlled Synthesis ◽  
Metal Nanoclusters ◽  
Gas Condensation ◽  
Inert Gas Condensation ◽  
Size Controlled

Reduction in the Thermal Conductivity of Thermoelectric Titanium Oxide by Introduction of Planar Defects

2009 ◽  
Vol 1218 ◽  
Author(s):  
Shunta Harada ◽  
Katsushi Tanaka ◽  
Haruyuki Inui
Keyword(s):  
Thermal Conductivity ◽  
Titanium Oxide ◽  
Hot Pressing ◽  
Oxygen Deficiency ◽  
Nominal Composition ◽  
Titanium Oxides ◽  
X Ray Diffraction ◽  
Planar Defects ◽  
Magnéli Phase ◽  
Magneli Phase

AbstractThermoelectric properties of a homologous series of Magnéli phase titanium oxides TinO2n-1 (n = 2, 3..) have been investigated. Dense polycrystalline specimens with nominal composition of TiO2-x (x = 0.10, 0.20) have been prepared by conventional hot-pressing. X-ray diffraction analysis has revealed that prepared specimens are slightly reduced during hot-pressing. Electrical conduction is of n-type for all prepared titanium oxides and electrical resistivity and absolute values of Seebeck coefficient decrease with increasing oxygen deficiency. The carrier concentration of Magnéli phase titanium oxide increases with increasing oxygen deficiency. Lattice thermal conductivity decreases with increasing oxygen deficiency by more than 60% at room temperature and 40% at 773K compared to TiO2, which can be due to the presence of dense planar defects. The largest thermoelectric figure of merit Z, 1.6×10-4 K-1 at 773K, was obtained in TiO1.90 hot pressed specimen.

Modern Models of Grain Boundary Diffusion

2011 ◽  
Vol 312-315 ◽  
pp. 1116-1125
Author(s):  
Vladimir V. Popov
Keyword(s):  
Plastic Deformation ◽  
Grain Boundary ◽  
Severe Plastic Deformation ◽  
Nanocrystalline Materials ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Coarse Grained ◽  
Gas Condensation ◽  
Non Equilibrium

Recent models of grain-boundary diffusion are briefly reviewed. Models of diffusion along equilibrium boundaries of recrystallization origin in coarse-grained materials and along non-equilibrium boundaries in nanocrystalline materials obtained by gas condensation and compacting or by severe plastic deformation are considered separately.

Inert gas condensation of Sb, Bi and Pb clusters

1981 ◽  
Vol 106 (1-3) ◽  
pp. A170
Author(s):  
J. Mühlbach ◽  
E. Recknagel ◽  
K. Sattler
Keyword(s):  
Inert Gas ◽  
Gas Condensation ◽  
Inert Gas Condensation
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