Structure Stability in Plasma Chemistry

1998 ◽  
Vol 544 ◽  
Author(s):  
Ji-Tao Wang ◽  
David Wei Zhang ◽  
Zhi-Jie Liu ◽  
Jian-Yun Zhang ◽  
Shi-Jin Ding ◽  
...  
Keyword(s):  
Metastable Phase ◽  
Equilibrium Phase ◽  
Plasma Chemistry ◽  
Cvd Diamond ◽  
Low Pressure ◽  
Diamond Growth ◽  
Stable Phase ◽  
Structure Stability ◽  
Pressure Equilibrium ◽  
Saturated Structure

AbstractDiamond is a metastable phase, while graphite is a stable phase in low pressure equilibrium phase diagrams of carbon. However, diamond with saturated structure of π bonds is more stable than graphite with unsaturated structure of n bonds during the existence of activated particles generated by plasma. That provides an excellent explanation for the plasma and other activated CVD diamond growth under low pressure taking place with simultaneous graphite etching.

Effect of Heat Treatment on the Resistivity and Mechanical Property of Low-Pressure Semi-Solid Die Cast Aluminum Alloy Wheel

2015 ◽  
Vol 1120-1121 ◽  
pp. 1064-1068
Author(s):  
Rui Wang ◽  
Ling Qi Meng ◽  
Heng Hua Zhang
Keyword(s):  
Heat Treatment ◽  
Solid Solution ◽  
Metastable Phase ◽  
Dynamic Balance ◽  
Low Pressure ◽  
Stable Phase ◽  
Cast Aluminum Alloy ◽  
Cast Aluminum ◽  
Die Cast ◽  
Semi Solid

Study the property and resistivity of Low-pressure semi-solid die casting ( LPSSDC) aluminum wheel hub after heat treatment. The Brinell hardness has reached more than 100HB in all position. Tensile properties at inner rim and outer rim are both reached 280MPa. The result of resistance analysis on LPSSDC aluminum wheel hub is below. The resistivity of the material is only influenced by the supersaturated solid solution (SSSS), GP zone, metastable phase β 'and stable phase β (Mg2Si). The resistivity has a decline during aging 0-0.5h and 0.75-8h, and an increasing during 0.5-0.75h. The resistivity remains stably when the decomposition of the solid solution achieved a dynamic balance after 8h aging time.

Synthesis of Metastable Diamond

1989 ◽  
Vol 162 ◽  
Author(s):  
Thomas R. Anthony
Keyword(s):  
Atomic Hydrogen ◽  
High Pressures ◽  
Metastable Phase ◽  
Equilibrium Phase ◽  
Diamond Surface ◽  
Diamond Growth ◽  
Hydrocarbon Gases ◽  
Carbon Solubility ◽  
Carbon Radicals ◽  
Liquid Metal Solution

ABSTRACTDiamond can be grown as an equilibrium phase from a liquid metal solution containing carbon at high pressures and high temperatures. Diamond can also be grown as a metastable phase at subatmospheric pressures and moderate temperatures from hydrocarbon gases in the presence of atomic hydrogen. Atomic hydrogen serves several critical roles in CVD diamond growth, namely: 1) stabilization of the diamond surface, 2) reduction of the size of the critical nucleus, 3) “dissolution” of carbon in the gas, 4) production of carbon solubility minimum, 5) generation of condensable carbon radicals in the gas, 6) abstraction of hydrogen from hydrocarbons attached to surface, 7) production of vacant surface sites, 8) etching of graphite, 9) suppression of polycycic aromatic hydrocarbons. A search for substitutes for atomic hydrogen have been unsuccessful to date but several new processes that do not use atomic hydrogen are currently under study.

Thermodynamic coupling effect and catalyst effect for the artificial diamond growth

1997 ◽  
Vol 12 (6) ◽  
pp. 1530-1535 ◽  
Author(s):  
Ji-Tao Wang ◽  
Zhong-Qiang Huang ◽  
Yong-Zhong Wan ◽  
David Wei Zhang ◽  
Hong-Yong Jia
Keyword(s):  
Coupling Effect ◽  
Chemical Vapor ◽  
Cvd Diamond ◽  
Low Pressure ◽  
Diamond Growth ◽  
Basic Question ◽  
Thermodynamic Coupling ◽  
Catalyst Effect ◽  
Artificial Diamond ◽  
Coupled Reaction

The activated chemical vapor deposition (CVD) diamond process became one of the worldwide interesting projects in the 1980s. The basic question is why diamond can grow under activated low pressure conditions. The driving force of the transformation from graphite to diamond under low pressure is coming from a coupled reaction of the association of superequilibrium atomic hydrogen. The thermodynamic coupling effect in the activated CVD process is different from the catalyst effect in the high pressure, catalyst-assisted process for the artificial diamond growth.

scholarly journals Stable and Metastable Phase Equilibria Involving the Cu6Sn5 Intermetallic

2021 ◽  
Author(s):  
A. Leineweber ◽  
M. Löffler ◽  
S. Martin
Keyword(s):  
Phase Equilibria ◽  
Electron Backscatter Diffraction ◽  
Metastable Phase ◽  
Stable Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Heat Treated ◽  
Ordered Phases ◽  
Backscatter Diffraction ◽  
Kinetics Of

Abstract Cu6Sn5 intermetallic occurs in the form of differently ordered phases η, η′ and η′′. In solder joints, this intermetallic can undergo changes in composition and the state of order without or while interacting with excess Cu and excess Sn in the system, potentially giving rise to detrimental changes in the mechanical properties of the solder. In order to study such processes in fundamental detail and to get more detailed information about the metastable and stable phase equilibria, model alloys consisting of Cu3Sn + Cu6Sn5 as well as Cu6Sn5 + Sn-rich melt were heat treated. Powder x-ray diffraction and scanning electron microscopy supplemented by electron backscatter diffraction were used to investigate the structural and microstructural changes. It was shown that Sn-poor η can increase its Sn content by Cu3Sn precipitation at grain boundaries or by uptake of Sn from the Sn-rich melt. From the kinetics of the former process at 513 K and the grain size of the η phase, we obtained an interdiffusion coefficient in η of (3 ± 1) × 10−16 m2 s−1. Comparison of this value with literature data implies that this value reflects pure volume (inter)diffusion, while Cu6Sn5 growth at low temperature is typically strongly influenced by grain-boundary diffusion. These investigations also confirm that η′′ forming below a composition-dependent transus temperature gradually enriches in Sn content, confirming that Sn-poor η′′ is metastable against decomposition into Cu3Sn and more Sn-rich η or (at lower temperatures) η′. Graphic Abstract

The Metastable Phase Responsible for Hardenig in an Al-Mg Alloy Aged at 473K

2013 ◽  
Vol 748 ◽  
pp. 123-127 ◽  
Author(s):  
Koichiro Fukui ◽  
Ayaka Mori ◽  
Masanori Mitome ◽  
Mahoto Takeda
Keyword(s):  
Precipitation Hardening ◽  
Vickers Microhardness ◽  
Layer Structure ◽  
Metastable Phase ◽  
Mg Alloy ◽  
Stable Phase ◽  
Precipitation Behavior ◽  
Dsc Measurements ◽  
Β Phase ◽  
Phase Precipitate

The present work investigated precipitation behavior in an Al-17at%Mg alloy isothermally aged at 473K, by means of Vickers microhardness tests, DSC measurements and TEM observations. A quantitative analysis of DSC measurements revealed that the metastable β-phase precipitates mainly contribute to precipitation hardening of this alloy aged at 473K. The present STEM-EDX observations confirmed that the metastable β-phase precipitate has a layer structure with a composition similar to the stable phase (Al3Mg2).

Diamond growth on thin Ti wafers via chemical vapor deposition

1995 ◽  
Vol 10 (11) ◽  
pp. 2685-2688 ◽  
Author(s):  
Qijin Chen ◽  
Zhangda Lin
Keyword(s):  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Titanium Substrate ◽  
Chemical Vapor ◽  
Low Pressure ◽  
Diamond Growth ◽  
X Ray ◽  
Hot Filament ◽  
Insight Into

Diamond film was synthesized on thin Ti wafers (as thin as 40 μm) via hot filament chemical vapor deposition (HFCVD). The hydrogen embrittlement of the titanium substrate and the formation of a thick TiC interlayer were suppressed. A very low pressure (133 Pa) was employed to achieve high-density rapid nucleation and thus to suppress the formation of TiC. Oxygen was added to source gases to lower the growth temperature and therefore to slow down the hydrogenation of the thin Ti substrate. The role of the very low pressure during nucleation is discussed, providing insight into the nucleation mechanism of diamond on a titanium substrate. The as-grown diamond films were characterized by scanning electron microscopy (SEM), Raman spectroscopy, and x-ray analysis.

Investigation of silicon-vacancy centers formation during the CVD diamond growth of thin and delta doped layers

2021 ◽  
Author(s):  
Mikhail Lobaev ◽  
Alexey Gorbachev ◽  
Dmitry Radishev ◽  
Anatoly Vikharev ◽  
Sergey Bogdanov ◽  
...  
Keyword(s):  
Cvd Diamond ◽  
Diamond Growth ◽  
Color Centers ◽  
Silicon Vacancy ◽  
Silicon Doped ◽  
The Relationship

The results of a study of the deposition of silicon-doped epitaxial diamond layers in a microwave CVD reactor to create silicon-vacancy color centers are presented. The relationship between the optical...

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