Grain growth of precursor-derived nanocrystalline gallium nitride powder

2002 ◽  
Vol 17 (2) ◽  
pp. 353-357 ◽  
Author(s):  
M. Puchinger ◽  
D. J. Kisailus ◽  
F. F. Lange ◽  
T. Wagner
Keyword(s):  
Gallium Nitride ◽  
Grain Growth ◽  
Activation Energies ◽  
Nitride Powder ◽  
Polymeric Precursor ◽  
Growth Mechanisms ◽  
Material Transport ◽  
Temperature Range ◽  
Transport Path ◽  
Ammonia Atmosphere

Nanocrystalline gallium nitride powder was synthesized from a gallium dimethylamide-derived polymeric precursor by pyrolysis in ammonia atmosphere to study the grain growth mechanisms in the temperature range 800–1150 °C. In particular, growth exponents and activation energies were determined. Up to 900 °C, grain growth was inhibited, whereas, above 1000 °C, evaporation–condensation was identified as the dominant material transport path.

Activation energies of grain growth mechanisms in aluminum coatings

2005 ◽  
Vol 491 (1-2) ◽  
pp. 61-65 ◽  
Author(s):  
Alan Jankowski ◽  
James Ferreira ◽  
Jeffrey Hayes
Keyword(s):  
Grain Growth ◽  
Activation Energies ◽  
Growth Mechanisms ◽  
Aluminum Coatings

Non-isothermal crystallization behavior of spinel crystals in FeO-SiO2-TiO2-V2O3-Cr2O3 slag

2018 ◽  
Vol 116 (1) ◽  
pp. 110
Author(s):  
Lixiong Shao ◽  
Jiang Diao ◽  
Wang Zhou ◽  
Tao Zhang ◽  
Bing Xie
Keyword(s):  
Cooling Rate ◽  
Crystallization Behavior ◽  
Crystal Size ◽  
Growth Mechanisms ◽  
Vanadium Slag ◽  
Growth Behaviour ◽  
Temperature Range ◽  
Chromium Spinel ◽  
Mean Diameter ◽  
The Mean

The growth behaviour of spinel crystals in vanadium slag with high Cr2O3 content was investigated and clarified by statistical analyses based on the Crystal Size Distribution (CSD) theory. The results indicate that low cooling rate and Cr2O3 content benefit the growth of spinel crystals. The chromium spinel crystals firstly precipitated and then acted as the heterogeneous nuclei of vanadium and titanium spinel crystals. The growth mechanisms of the spinel crystals at the cooling rate of 5 K/min consist two regimes: firstly, nucleation control in the temperature range of 1873 to 1773 K, in which the shapes of CSD curves are asymptotic; secondly, surface and supply control within the temperature range of 1773 to 1473 K, in which the shapes of CSD curves are lognormal. The mean diameter of spinel crystals increases from 3.97 to 52.21 µm with the decrease of temperature from 1873 to 1473 K.

scholarly journals High-Temperature Deformation of Naturally Aged 7010 Aluminum Alloy

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 581
Author(s):  
Abdulhakim A. Almajid
Keyword(s):  
Activation Energy ◽  
Aluminum Alloy ◽  
High Temperature ◽  
Threshold Stress ◽  
Activation Energies ◽  
Temperature Deformation ◽  
High Temperature Range ◽  
Temperature Range ◽  
True Activation Energy ◽  
Two Temperatures

This study is focused on the deformation mechanism and behavior of naturally aged 7010 aluminum alloy at elevated temperatures. The specimens were naturally aged for 60 days to reach a saturated hardness state. High-temperature tensile tests for the naturally aged sample were conducted at different temperatures of 573, 623, 673, and 723 K at various strain rates ranging from 5 × 10−5 to 10−2 s−1. The dependency of stress on the strain rate showed a stress exponent, n, of ~6.5 for the low two temperatures and ~4.5 for the high two temperatures. The apparent activation energies of 290 and 165 kJ/mol are observed at the low, and high-temperature range, respectively. These values of activation energies are greater than those of solute/solvent self-diffusion. The stress exponents, n, and activation energy observed are rather high and this indicates the presence of threshold stress. This behavior occurred as a result of the dislocation interaction with the second phase particles that are existed in the alloy at the testing temperatures. The threshold stress decreases in an exponential manner as temperature increases. The true activation energy was computed by incorporating the threshold stress in the power-law relation between the stress and the strain. The magnitude of the true activation energy, Qt dropped to 234 and 102 kJ/mol at the low and high-temperature range, respectively. These values are close to that of diffusion of Zinc in Aluminum and diffusion of Magnesium in Aluminum, respectively. The Zener–Hollomon parameter for the alloy was developed as a function of effective stress. The data in each region (low and high-temperature region) coalescence in a segment line in each region.

Control of Morphology and Growth Direction of Gallium Nitride Nanostructures

2003 ◽  
Vol 789 ◽  
Author(s):  
Seung Yong Bae ◽  
Hee Won Seo ◽  
Jeunghee Park
Keyword(s):  
Electron Microscopy ◽  
Gallium Nitride ◽  
Large Scale ◽  
Chemical Vapor ◽  
Growth Direction ◽  
Chemical Vapor Deposition Method ◽  
X Ray Diffraction ◽  
Oxide Mixture ◽  
Temperature Range ◽  
Transmission Electron

ABSTRACTVarious shaped single-crystalline gallium nitride (GaN) nanostructures were produced by chemical vapor deposition method in the temperature range of 900–1200 °C. Scanning electron microscopy, transmission electron microscopy, electron diffraction, x-ray diffraction, electron energy loss spectroscopy, Raman spectroscopy, and photoluminescence were used to investigate the structural and optical properties of the GaN nanostructures. We controlled the GaN nanostructures by the catalyst and temperature. The cylindrical and triangular shaped nanowires were synthesized using iron and gold nanoparticles as catalysts, respectively, in the temperature range of 900 – 1000 °C. We synthesized the nanobelts, nanosaws, and porous nanowires using gallium source/ boron oxide mixture. When the temperature of source was 1100 °C, the nanobelts having a triangle tip were grown. At the temperature higher up to 1200 °C the nanosaws and porous nanowires were formed with a large scale. The cylindrical nanowires have random growth direction, while the triangular nanowires have uniform growth direction [010]. The growth direction of the nanobelts is perpendicular to the [010]. Interestingly, the nanosaws and porous nanowires exhibit the same growth direction [011]. The shift of Raman, XRD, and PL bands from those of bulk was correlated with the strains of the GaN nanostructures.

Graphitization of diamond at zero pressure and at a high pressure

1972 ◽  
Vol 328 (1574) ◽  
pp. 413-427 ◽  
Keyword(s):  
High Pressure ◽  
Activation Volume ◽  
Activation Energies ◽  
Single Atom ◽  
Diamond Surface ◽  
Temperature Range ◽  
Natural Diamonds ◽  
Rate Controlling Step

Natural diamonds have been heated in the temperature range of 1850 to 2000 °C at zero pressure and the rates at which diamond transforms to graphite measured. For {111} and {110} surfaces activation energies of 253+18 and 174+12 kcal mol -1 (1159 + 75 and 728 + 50 kJ/mol) respectively have been obtained. Diamonds have also been heated in the temperature range of 1950 to 2200 °C under a pressure of 48 + 3 kbar (4.8 + 0.3 GPa) and an activation volume of about 10 cm 3 mol -1 obtained for both {111} and {110} surfaces. It is proposed that the rate controlling process in the graphitization of diamond is the detachment of a single atom from the diamond surface. This is contrary to previous proposals in which the detachment of groups of atoms have been considered to be the rate-controlling process. In the present work, it is suggested that the rate-controlling step for graphitization is the detachment of a triply bonded atom from a {111} surface and of a doubly bonded atom from a {110} surface.

Reactions of trifluoromethyl radicals. V. Hydrogen abstraction from methyl acetate and methyl (2H3)Acetate

1980 ◽  
Vol 33 (7) ◽  
pp. 1437
Author(s):  
NL Arthur ◽  
PJ Newitt
Keyword(s):  
Isotope Effect ◽  
Rate Constants ◽  
Methoxy Group ◽  
Methyl Acetate ◽  
Kinetic Isotope Effect ◽  
Hydrogen Abstraction ◽  
Activation Energies ◽  
Temperature Range ◽  
Kinetic Isotope ◽  
Acetyl Group

Hydrogen abstraction by CF3 radicals from CH3COOCH3 and CD3COOCH3 has been studied in the temperature range 78-242°, and data have been obtained for the reactions: CF3 + CH3COOCH3 → CF3H+[C3H5O2] �������������(3) CF3 + CH3COOCH3 → CF3H+CH2COOCH3������������ (4) CF3 + CD3COOCH3 → CF3D+CD2COOCH3������������ (6) CF3 + CD3COOCH3 → CF3H+CD3COOCH2������������ (7) The corresponding rate constants, based on the value of 1013.36 cm3 mol-1 S-1 for the recombination of CF3 radicals, are given by (k in cm3 mol-1 s-1 and E in J mol-1): logk3 = (11.52�0.05)-(35430�380)/19.145T ���� (3)logk4 = (11.19�0.07)-(34680�550)/19.145T ���� (4)logk6 = (11.34�0.06)-(46490�490)/19.145T ���� (6)logk7 = (11.26�0.05)-(36440�400)/19.145T ���� (7)At 400 K, 59% of abstraction occurs from the acetyl group, and 41 % from the methoxy group. The kinetic isotope effect at 400 K for attack on the acetyl group is 25, due mainly to a difference in activation energies.

Radiolysis of ferric hexafluoroacetylacetonate–toluene solutions

1976 ◽  
Vol 54 (13) ◽  
pp. 2116-2123 ◽  
Author(s):  
K. W. Chambers ◽  
E.A. Cherniak ◽  
G. Taylor ◽  
J. Yu
Keyword(s):  
Quantum Yield ◽  
Flash Photolysis ◽  
Total Yield ◽  
Activation Energies ◽  
Temperature Range

In the 120 krad/h, 60Co-γ radiolysis of air-free, anhydrous solutions of ferric hexafluoroacetylacetonate (Fe(HFA)3) in toluene at 27 °C, G(—Fe(HFA)3) = G(Fe(HFA)2) = 1.05 ± 0.03 molecules/100 eV and G(HHFA) = 0 where Fe(HFA)2 is radiolytically inert ferrous hexafluoroacetylacetonate and HHFA is hexafluoroacetylacetone. G(H2) = 0.13 ± 0.03 is not affected by Fe(HFA)3 while G(CH4)is reduced from 0.0088 &([a-z]+); 0.0020 to 0.0052 ± 0.0020 and [Formula: see text] is increased from 0.102 ± 0.019 to 0.307 ± 0.026 by Fe(HFA)3. Activation energies for the radiolytic formation of Fe(HFA)2, H2, CH4, and [Formula: see text] in the temperature range −95 to 27 °C, are 670 ± 130, 0, 1200 ± 900, and 1280 ± 25 cal mol−1, respectively.G(—Fe(HFA)3) = 1.05 represents the total yield of radicals scavenged since at the concentrations of solute used in the radiolyses the quantum yield for the disappearance of Fe(HFA)3 by reaction with solvent S1 and/or T1 states, generated by flash photolysis, is negligible [Formula: see text] Radicals trapped by Fe(HFA)3 are••CH3 (G ≈ 0.004) and unknown radicals (G ≈ 0.4) which are capable of combining with [Formula: see text] does not scavenge [Formula: see text] radicals (G ≈ 0.6). The formation of H2 in scavenger inaccessible spurs and CH4 and [Formula: see text] outside spurs has been confirmed.

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