Ammonothermal growth of GaN utilizing negative temperature dependence of solubility in basic ammonia

2004 ◽  
Vol 831 ◽  
Author(s):  
Tadao Hashimoto ◽  
Kenji Fujito ◽  
Feng Wu ◽  
Benjamin A. Haskell ◽  
Paul T. Fini ◽  
...  
Keyword(s):  
Weight Loss ◽  
Temperature Dependence ◽  
Fluid Transport ◽  
Defect Density ◽  
Negative Temperature ◽  
Solubility Limit ◽  
Temperature Zone ◽  
Free Standing ◽  
Lower Temperature ◽  
Ammonothermal Growth

ABSTRACTAmmonothermal growth of GaN was studied to determine its eventual utility for mass production of GaN bulk crystals. Dissolution of GaN in supercritical ammonia with 1 M NaNH2 was investigated through a weight loss method. The time dependence of the weight loss was examined at 500°C and 525°C. Since the weight loss did not reach saturation as a function of time, the solubility limit was not realized. However, experiments demonstrate that GaN has a negative temperature dependence of solubility in supercritical ammonobasic solutions. Based on this result, GaN was grown via fluid transport from metallic Ga to a free-standing GaN single crystal seed by placing the seed crystal in a higher temperature zone and the nutrient in a lower temperature zone. GaN films with thickness of 5 μm (Ga face) and 4 μm (N face) were simultaneously grown on the seed in three days. The surface morphology, optical property, and defect density were found to be different for films on Ga face and N face.

scholarly journals Computational study on the mechanism and kinetics for the reaction between HO2 and n-propyl peroxy radical

RSC Advances ◽  
2019 ◽  
Vol 9 (69) ◽  
pp. 40437-40444
Author(s):  
Zhenli Yang ◽  
Xiaoxiao Lin ◽  
Jiacheng Zhou ◽  
Mingfeng Hu ◽  
Yanbo Gai ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Temperature Regime ◽  
Computational Study ◽  
Peroxy Radical ◽  
Negative Temperature ◽  
Mechanism And Kinetics ◽  
Lower Temperature

The negative temperature dependence for the HO2 + n-C3H7O2 reaction in lower temperature regime.

Optimization of Organic Fibres%[Kevlar/Arobocel/Acrylic] in NAO Brake Pad Application and its Effect on Thermal Stability & Friction Characteristics

2012 ◽  
Vol 531-532 ◽  
pp. 8-12
Author(s):  
M.A. Sai Balaji ◽  
K. Kalaichelvan
Keyword(s):  
Thermal Stability ◽  
Weight Loss ◽  
Minimum Weight ◽  
Friction Material ◽  
Brake Pad ◽  
Temperature Zone ◽  
Good Thermal Stability ◽  
Friction Testing ◽  
Brake Application ◽  
The Stability

Organic fibres (Kevlar/ Arbocel / Acrylic) have good thermal stability, higher surface area and bulk density. The optimization of organic fibres percentage for thermal behaviour is considered using TGA. The temperature raise during brake application will be between 150-4000 C and this temperature zone is very critical to determine the fade characteristics during friction testing. Hence, three different friction composites are developed with the same formulation varying only the Kevlar, Arbocel and Acrylic fibres which are compensated by the inert filler namely the barites and are designated as NA01, NA02 and NA03 respectively. After the fabrication, the TGA test reveals that the composite NA03 has minimum weight loss. The friction coefficient test rig is then used to test the friction material as per SAE J661a standards. The results prove that the brake pad with minimum weight loss during TGA has higher friction stability. Thus, we can correlate the thermal stability with the stability of friction.

Negative Temperature-Dependence of Stress-Induced R→B19′ Transformation in Nanocrystalline NiTi Alloy

2021 ◽  
Author(s):  
Taotao Wang ◽  
Xiangxiang Rao ◽  
Daqiang Jiang ◽  
Yang Ren ◽  
Lishan Cui ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Niti Alloy ◽  
Negative Temperature

Mineral partitioning in milk and milk permeates at high temperature

2011 ◽  
Vol 79 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Divina D Kaombe ◽  
Yanhong Du ◽  
Michael J Lewis
Keyword(s):  
High Temperature ◽  
Calcium Phosphate ◽  
Temperature Dependence ◽  
Casein Micelle ◽  
Soluble Phase ◽  
Ionic Calcium ◽  
Separation Temperature ◽  
Two Temperatures ◽  
Lower Temperature ◽  
Mineral Partitioning

The soluble phase of milk was separated at 20 and 80°C using ultrafiltration. The resulting permeates were then subjected to further ultrafiltration and dialysis at close to these two temperatures. It was found that pH, Ca2+ and soluble Ca decreased as the separation temperature increased both in original UF permeates and in dialysates obtained from these permeates, but P decreased only slightly. The major reason for these changes was due to the precipitation of calcium phosphate/citrate complexes onto the casein micelle with concomitant release of H+. The pH of both permeates and dialysates from milk at 20°C were slightly higher than for milk. When UF permeates collected at 20 and 80°C, were each dialysed at both these temperatures, the dialysate collected at 80°C showed much less temperature dependence for pH and ionic calcium compared with that collected at 20°C. This is in contrast to milk, which shows considerable temperature dependence for pH and ionic calcium. Further experiments revealed that the pH and Ca2+ concentration of permeates showed high temperature dependence above the temperature at which they were separated, but a much lower temperature dependence below that temperature. These findings suggest that dialysis and UF of milk at high temperature provide the best means yet for estimating the pH and ionic calcium of milk at that temperature.

Reaction Synthesis and Oxidation Behaviours of Ludwigite

2010 ◽  
Vol 146-147 ◽  
pp. 475-480 ◽  
Author(s):  
Ran Liu ◽  
Xing Juan Wang ◽  
Yong Liang Gao ◽  
Qing Lu ◽  
Xiang Xin Xue
Keyword(s):  
Weight Loss ◽  
Mass Loss Rate ◽  
Mass Gain ◽  
Raw Material ◽  
X Ray Diffraction ◽  
Blast Furnace Smelting ◽  
Isothermal Tg ◽  
Lower Temperature ◽  
Xrd Techniques ◽  
Furnace Smelting

Using ludwigite as raw material, the phase transformation and mass loss rate of ludwigite in the process of oxidizing roasting are investigated by DTA, isothermal TG, scanning electron microscopy (SEM), X-ray diffraction (XRD) techniques. The results showed that magnetite is transformed into hematite, serpentine is decomposed into forsterite at lower temperature (T＜700°C). The weight of ludwigite has a small loss below 600°C. The decomposed of szaibelyite dehydrated and formed into suanite about 700°Cis the main reason of causing ludwigite mass losses. By comparing the curves of ludwigite at different temperature from 700 to 900°C, the process of oxidizing roasting can be divided into three phases: characterized by a period of fast weight loss, and then followed by a mass gain. Finally, weight of sample is no longer change with prolongation of time. The final weight loss is 6.062%, 6.658% and 7.442% respectively for test temperature. Suanite can not be decomposed to form B2O3 and volatilized when the temperature of oxidizing roasting is below 1142 °C. It is found by XRD that paigeite and magnoferrite are the most stable composition without deterioration on oxidizing roasting. The experiment results can provide theoretical references for agglomeration and blast furnace smelting of ludwigite.

MECHANISM AND KINETICS OF THE CH3CH2C(O)OCH2CH3 + OH REACTION: A THEORETICAL STUDY

2011 ◽  
Vol 10 (05) ◽  
pp. 691-709 ◽  
Author(s):  
CONG HOU ◽  
CHENG-GANG CI ◽  
TONG-YIN JIN ◽  
YONG-XIA WANG ◽  
JING-YAO LIUM
Keyword(s):  
Rate Constants ◽  
Hydrogen Abstraction ◽  
Negative Temperature ◽  
State Theory ◽  
Measured Temperature ◽  
Temperature Range ◽  
Global Rate ◽  
Abstraction Reaction ◽  
Lower Temperature ◽  
Kinetic Calculations

The hydrogen abstraction reaction of CH 3 CH 2 C(O)OCH 2 CH 3 + OH has been studied theoretically by dual-level direct dynamics method. Six H-abstraction channels were found for this reaction. The required potential energy surface information for the kinetic calculations was obtained at the MCG3-MPWB//M06-2X/aug-cc-pVDZ level. The rate constants were calculated by the improved canonical variational transition-state theory with small-curvature tunneling correction (ICVT/SCT) approach in the temperature range of 200–2000 K. It is shown that the "methylene H-abstraction" from the alkoxy end of the ester CH 3 CH 2 C(O)OCH 2 CH 3 is the dominant channel at lower temperature (< 400 K), while the other channels from the acetyl end should be taken into account as the temperature increases and become the competitive ones at higher temperature. The calculated global rate constants are in good agreement with the experimental ones in the measured temperature range and exhibit a negative temperature dependence below 500 K. A four-parameter rate constant expression was fitted from the calculated kinetic data between 200–2000 K.

On Applicability of Time-Resolved Optical Techniques for Characterization of Differently Grown 3C-SiC Crystals and Heterostructures

2012 ◽  
Vol 711 ◽  
pp. 159-163 ◽  
Author(s):  
Patrik Ščajev ◽  
Pavels Onufrijevs ◽  
Georgios Manolis ◽  
Mindaugas Karaliūnas ◽  
Saulius Nargelas ◽  
...  
Keyword(s):  
Room Temperature ◽  
Defect Density ◽  
Growth Conditions ◽  
Free Carrier ◽  
Band Edge Emission ◽  
Free Carrier Absorption ◽  
Free Standing ◽  
Optical Techniques ◽  
Time Resolved ◽  
Photoelectrical Properties

We applied a number of time-resolved optical techniques for investigation of optical and photoelectrical properties of cubic SiC grown by different technologies on different substrates. The excess carriers were injected by a short laser pulse and their dynamics was monitored by free-carrier absorption, light-induced transient grating, and photoluminescence techniques in a wide excitation range. Combining an optical and electrical probe beam delay, we found that free carrier lifetimes in differently grown layers vary from few ns up to 20 μs. Temperature dependences of carrier diffusivity and lifetime revealed a pronounced carrier trapping in thin sublimation grown layers. In free-standing layers and thick sublimation layers, the ambipolar mobility was found the highest (120 cm2/Vs at room temperature). A linear correlation between the room-temperature band edge emission and carrier lifetime in differently grown layers was attributed to defect density, strongly dependent on the used growth conditions.

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