scholarly journals Corundum α-Al2O3Formation from the Dehydration of Boehmite γ-AlOOH under Hydrothermal Conditions. I. Factors Determining the Grain Size of Corundum and a Proposal for the Formation Mechanism

1963 ◽  
Vol 36 (9) ◽  
pp. 1155-1158 ◽  
Author(s):  
Goro Yamaguchi ◽  
Hiroaki Yanagida
Keyword(s):  
Grain Size ◽  
Formation Mechanism ◽  
Hydrothermal Conditions

Paleoenvironmental context of the evolution of the Baodun Culture at Chengdu Plain, Sichuan Province, China

The Holocene ◽  
2019 ◽  
Vol 29 (11) ◽  
pp. 1731-1742 ◽  
Author(s):  
Ming Huang ◽  
Cheng Zhu ◽  
Chunmei Ma ◽  
Kunyu He ◽  
Jiajia Xu
Keyword(s):  
Grain Size ◽  
Climatic Conditions ◽  
Alluvial Fan ◽  
Human Migration ◽  
Cultural Groups ◽  
Hydrothermal Conditions ◽  
Chengdu Plain ◽  
Minjiang River ◽  
Archeological Evidence ◽  
Better Than

The Baodun Culture (4600–3700 a BP) is currently the earliest archeological culture found at the Chengdu Plain in southwestern China. Archeological evidence has shown that the Baodun Culture likely originated from the upper reaches of the Minjiang River, with two possible routes for human migration into the lower Chengdu Plain proposed: (1) At about 5000 a BP, favorable climatic conditions in the upper reaches of the Minjiang stimulated the growth of populations and the development of agriculture in the region. Due to this shift, some groups expanded from the upper Minjiang River to sites in the northern area of the Chengdu Plain, such as the Guiyuanqiao site; (2) during 4800–4300 a BP, a drying event occurred in the upper regions of the river valley causing a reduction in agricultural harvests and the migration of populations into sites – including the Baodun site – from this area of the Minjiang to the southwest piedmont of the Chengdu Plain. A multi-facetted study of the T3321 profile at Baodun site, including pollens, grain size, and geochemistry, demonstrates that after 6000 a BP, the climate of the Chengdu Plain shifted from cool, toward warmer and dryer conditions. However, as the Chengdu Plain is located in an alluvial fan, hydrothermal conditions here are still generally better than those in the upper reaches of Minjiang River. A change in the proportion of Concentricystes seen in the profile T3321 also indicates that after 4700 a BP, the lake and marsh areas associated with the Baodun site further decreased. However, as a result of this reduction, more terrestrial surfaces were exposed, providing favored space for Baodun Cultural groups in the area of the site. Due to such conditions, by about 4600 cal. a BP, people in the upper reaches of the Minjiang River had primarily moved to the southwest piedmont regions of the Chengdu Plain.

Synthesis of TiO2-Based Nanotube on Ti Substrate by Hydrothermal Treatment

2007 ◽  
Vol 7 (2) ◽  
pp. 668-672 ◽  
Author(s):  
Bo Chi ◽  
Erick S. Victorio ◽  
Tetsuro Jin
Keyword(s):  
Aspect Ratio ◽  
Pore Size ◽  
Hydrothermal Treatment ◽  
Formation Mechanism ◽  
High Aspect Ratio ◽  
Hydrothermal Conditions ◽  
Titanate Nanotube ◽  
Naoh Solution ◽  
Nanofiber Film

TiO2-based titanate nanotube film was directly synthesized by hydrothermal treatment of Ti substrate in NaOH solution. The prepared high aspect ratio nanotubes have diameter of 10nm and pore size of 5 nm with length of several microns. The nanotubes show the same structure and component characteristics as the nanotubes prepared through hydrothermal treatment of TiO2. Other nanostructured titanate as oriented nanofiber film and translucent film were also prepared by adjusting the hydrothermal conditions. The formation mechanism of nanostructured titanate was discussed.

Formation mechanism of barium titanate nanocrystals under hydrothermal conditions

1997 ◽  
Vol 40 (5) ◽  
pp. 479-488 ◽  
Author(s):  
Weizhuo Zhong ◽  
Changtai Xia ◽  
Erwei Shi ◽  
Buguo Wang ◽  
Wenjun Li ◽  
...  
Keyword(s):  
Barium Titanate ◽  
Formation Mechanism ◽  
Hydrothermal Conditions

scholarly journals Geomimetics for green polymer synthesis: highly ordered polyimides via hydrothermal techniques

2014 ◽  
Vol 5 (12) ◽  
pp. 3771-3776 ◽  
Author(s):  
Bettina Baumgartner ◽  
Michael J. Bojdys ◽  
Miriam M. Unterlass
Keyword(s):  
Formation Mechanism ◽  
High Performance ◽  
Polymer Synthesis ◽  
Hydrothermal Crystallization ◽  
Hydrothermal Conditions ◽  
Ore Formation ◽  
High Performance Polymers ◽  
Green Polymer

We mimic a geological ore formation mechanism, so-called hydrothermal crystallization, to obtain highly crystalline high-performance polymers. After only 1 h under hydrothermal conditions, a fully condensed polyimide depicting microflower morphologies is obtained.

Hydrothermal synthesis and sintering of ultrafine CeO2 powders

1993 ◽  
Vol 8 (7) ◽  
pp. 1680-1686 ◽  
Author(s):  
Y.C. Zhou ◽  
M.N. Rahaman
Keyword(s):  
Grain Size ◽  
Hydrothermal Synthesis ◽  
Oxygen Vacancies ◽  
Maximum Density ◽  
Full Density ◽  
Particle Sizes ◽  
Heating Rates ◽  
Hydrothermal Conditions ◽  
Average Grain Size ◽  
Constant Heating

Undoped CeO2 and Y2O3-doped CeO2 powders, with particle sizes of ≍10–15 nm, were prepared under hydrothermal conditions of 10 MPa at 300 °C for 4 h. The compacted powders were sintered freely in air or in O2 at constant heating rates of 1–10 °C/min up to 1350 °C. The undoped CeO2 started to sinter at ≍800–900 °C and reached a maximum density of 0.95 of the theoretical at 1200 °C, after which the density decreased slightly. Isothermal sintering at 1150 °C produced a sample with a relative density of ≍0.98 and an average grain size of ≍100 nm. The samples sintered above 1200 °C exhibited microcracking. The decrease in density and the microcracking above 1200 °C are attributed to a redox reaction leading to the formation of oxygen vacancies and the evolution of O2 gas. Doping with Y2O3 produced an increase in the temperature at which measurable sintering commenced and an increase in the sintering rate, compared with the undoped CeO2. Sintered samples of the doped CeO2 showed no microcracks. The CeO2 doped with up to 3 mol% Y2O3 was sintered to almost full density and with a grain size of ≍200 nm at 1400 °C.

Synthesis and some aspects of the formation mechanism of carbon structures under hydrothermal conditions

2013 ◽  
Vol 58 (12) ◽  
pp. 1542-1546 ◽  
Author(s):  
E. M. Kozhbakhteev ◽  
V. M. Skorikov ◽  
T. I. Milenov ◽  
P. M. Rafailov ◽  
G. V. Avdeev
Keyword(s):  
Formation Mechanism ◽  
Hydrothermal Conditions ◽  
Carbon Structures

Grain-Size Characteristics of Mullite Nanocomposites Prepared by Open-System Hydrothermal Crystallization Method

2010 ◽  
Vol 105-106 ◽  
pp. 729-732
Author(s):  
Nan Chun Chen ◽  
Han Mei Ao ◽  
Quan Hong Li ◽  
Quan Tang
Keyword(s):  
Grain Size ◽  
Reaction Temperature ◽  
Hydrothermal Reaction ◽  
Normal Pressure ◽  
Holding Time ◽  
Precursor Concentration ◽  
Hydrothermal Conditions ◽  
Oxidation Reduction ◽  
Uniform Dispersion ◽  
Multi Phase

In this research, raw kaolin is processed by oxidation-reduction fining method and then baked to produce mullite precursor, which can prepared multi-phase mullite nanocrystals at low temperature hydrothermal conditions under normal pressure. According to the analysis of the controlling factors of NaOH mole ratio in the hydrothermal system, reaction temperature, holding time and the precursor concentration, etc., we studied the effect of above-mentioned factors on the grain size of product. The results show that when NaOH concentration 3mol/L, hydrothermal reaction temperature 80°C, holding time 3 h, precursor concentration 0.15g/ml, the morphology of the prepared nanocomposite with grains size of 60 ~ 90nm appears spherical-like, also the uniform dispersion can be acquired.

The formation mechanism of TiO2 polymorphs under hydrothermal conditions based on the structural evolution of [Ti(OH)h(H2O)6−h]4−h monomers

2019 ◽  
Vol 7 (19) ◽  
pp. 5764-5771 ◽  
Author(s):  
Jun Zhang ◽  
Peng Sun ◽  
Peng Jiang ◽  
Zhaoying Guo ◽  
Wenxiu Liu ◽  
...  
Keyword(s):  
Hydrothermal Synthesis ◽  
Formation Mechanism ◽  
Condensation Reaction ◽  
Structural Evolution ◽  
Hydrothermal Conditions

In the hydrothermal synthesis of TiO2, [Ti(OH)h(H2O)6−h]4−h (h is the hydrolysis ratio) monomers are generated by the dissolution of the precursor containing titanium ions and then, the monomers form TiO2 polymorphs via a condensation reaction.

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