Hydrothermal Preparation and Sintering of Fine Ceramic Powders

1983 ◽  
Vol 24 ◽  
Author(s):  
Shigeyuki Sōmiya
Keyword(s):  
Hydrothermal Reaction ◽  
Metal Powders ◽  
Hydrothermal Crystallization ◽  
Ceramic Powders ◽  
Hydrothermal Conditions ◽  
Hydrothermal Preparation ◽  
Fine Ceramic ◽  
Fine Powders ◽  
Hydrothermal Oxidation ◽  
Hydrothermal Precipitation

ABSTRACTHydrothermal preparation is one of the methods to make fine ceramic powders. There are: (1) hydrothermal oxidation, (2) hydrothermal precipitation, (3) hydrothermal synthesis, (4) hydrothermal decomposition, (5) hydrothermal crystallization, etc. Starting materials for hydrothermal oxidation is mainly metal. Reaction between metal and high temperature-high pressure solution occurs to form oxide. Therefore, starting materials for very fine powders are: (1) metal powders or chips, (2) gel, solutions, etc., (3) oxides and solutions, (4) solids, and (5) hydrous material. This paper describes hydrothermal crystallization and oxidation. Fine powders of ZrO2, Al2O3, HfO2, and Al2O3-ZrO2 are described.Sintered bodies are also able to get under hydrothermal conditions with reactions. Hydrothermal reaction sintered bodies of iron oxides, Cr2O3, ZrO2 and HfO2 were obtained under 100 MPa above 1000°C with 1–5 μm grains.

VPS Deposition of Spherical Ti-Based Powders Produced by Plasma Atomization

1998 ◽  
Author(s):  
S. Grenier ◽  
T. Brzezinski ◽  
P. Tsantrizos ◽  
F. Allaire
Keyword(s):  
Value Added ◽  
Vacuum Plasma Spray ◽  
Metal Powders ◽  
Coating Quality ◽  
Atomization Process ◽  
Fine Powders ◽  
Vacuum Plasma ◽  
Titanium Coatings ◽  
Reactive Metals ◽  
Value Added Products

Abstract A new plasma atomization process was developed for the production of spherical metal powders. This process, unique in its ability to produce large quantities of fine powders (< 75 µm), is especially interesting for value added products such as refractory or reactive metals/alloys powders. The excellent feeding characteristics of spherical powders make them ideal for applications such as injection molding and vacuum plasma spray (VPS) deposition. Powders are known to have a significant influence on the final characteristics of VPS deposited coatings. A variety of factors will control the coating quality, including: powder chemistry, morphology, microstructure, and feeding behaviour. This article includes a review of titanium coatings, and new results obtained using plasma atomized spherical powders.

Low Temperature Hydrothermal Synthesis of Nanophase BaTiO3 and BaFe12O19 Powders

1996 ◽  
Vol 457 ◽  
Author(s):  
Fatih Dogan ◽  
Shawn O'rourke ◽  
Mao-Xu Qian ◽  
Mehmet Sarikaya
Keyword(s):  
Particle Size ◽  
Hydrothermal Reaction ◽  
Average Particle Size ◽  
Reaction Times ◽  
Nanocrystalline Powders ◽  
Molar Ratio ◽  
Average Particle ◽  
Hydrothermal Conditions ◽  
Processing Variables ◽  
Xrd And Tem

ABSTRACTNanocrystalline powders with an average particle size of 50 nm has been synthesized in two materials systems under hydrothermal conditions below 100°C. Processing variables, such as temperature, concentration and molar ratio of reactants and reaction time were optimized to obtain particles of reduced size and stoichiometric compositions. Hydrothermal reaction takes place between Ba(OH)2 solution and titanium/iron precursors in sealed polyethylene bottles in the BaTiO3 and BaFe12O19 systems, respectively. While crystalline BaTiO3 forms relatively fast within a few hours, formation of fully crystalline and stoichiometric BaFei20i9 require considerably longer reaction times up to several weeks and strongly dependent on the Ba:Fe ratio of the precursors. The structural and compositional evaluation of the nanophase powders were studied by XRD and TEM techniques.

Hydrothermal Oxidation of Industrial Alkali Lignin for Producing Small Molecular Organic Acids

2012 ◽  
Vol 608-609 ◽  
pp. 1399-1406 ◽  
Author(s):  
Guang Yi Zhang ◽  
Ju Wei Zhang ◽  
Jian Yu ◽  
Yin Wang
Keyword(s):  
Acetic Acid ◽  
Organic Acids ◽  
Paper Industry ◽  
Black Liquor ◽  
Total Yield ◽  
Reaction Times ◽  
Hydrothermal Conditions ◽  
Alkali Lignin ◽  
Hydrothermal Oxidation ◽  
Acetic Acids

To control the serious pollution caused by alkaline pulping in paper industry and utilize alkali lignin – the main organic ingredient residing in black liquor, an experimental research on hydrothermal oxidation of industrial alkali lignin for producing small molecule organic acids (mostly formic and acetic acids) was conducted using batch reactors. The results showed that the yields of acetic acid almost entirely increased and then decreased with oxygen supplies, reaction times and reaction temperatures, while the yields of formic acid fell in a narrow range of ~ 4% irrespective of all the hydrothermal conditions. A highest total yield of formic and acetic acids of 23.0% was achieved at the conditions of 300 °C, a 100% oxygen supply and a 60 s reaction time, and at the same time a highest yield of acetic acid of 20.3% was obtained. Based on the products recognized, the main pathways for producing small molecular organic acids, particularly formic and acetic acids were discussed.

Preparation and Thermodynamic Study of Self-Dispersal Nano-AIOOH

2012 ◽  
Vol 512-515 ◽  
pp. 100-105
Author(s):  
Hai Da Liao ◽  
Wei Ping Zhang ◽  
Xiao Ming Sun ◽  
Jia Qing Meng ◽  
Yan Wei ◽  
...  
Keyword(s):  
Driving Force ◽  
Raw Materials ◽  
Dispersion Property ◽  
Hydrothermal Time ◽  
Hydrothermal Crystallization ◽  
Dispersion Method ◽  
Hydrothermal Conditions ◽  
Hydrothermal Temperature ◽  
Thermodynamic Driving Force ◽  
And Control

Abstracts: Self-dispersal nano-AlOOH crystal powder was prepared via sol-hydrothermal crystallization and charging method, using aluminum salt and ammonium as raw materials. TEM, XRD and UV-vis absorption spectroscopy were used to study effects of the hydrothermal temperature and hydrothermal time on precursor’s crystallization and charging, the product’s dispersion property and mean particle size. Thermodynamic and dynamic analysis on the preparation process was carried out. Results and analysis suggested that the influence of hydrothermal temperature on product’s dispersion property was larger than that of hydrothermal time. Modification and control of the hydrothermal conditions could make AlOOH crystal grow along the C-axis and form needle-like particle with lowered surface energy and improved dispersion property. Thermodynamic analysis suggested that the phase transition from Al2O3nH2O into crystalline AlOOH could spontaneously occur at a temperature within the range of 100oC - 150oC. In the preparation of AlOOH crystal powder via the hydrothermal crystallization and charging composite dispersion method, the reaction condition was mild with a strong thermodynamic driving force and small activation energy of 24.11kJ/mol.

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 and dry-heat fixation of K by soil clays and the effects on C.E.C., surface area and mineralogy

Clay Minerals ◽  
1971 ◽  
Vol 9 (2) ◽  
pp. 219-230 ◽  
Author(s):  
C. E. Davis ◽  
N. Ahmad ◽  
R. L. Jones
Keyword(s):  
Ion Exchange ◽  
Hydrothermal Reaction ◽  
Degree Of Crystallinity ◽  
New Mineral ◽  
Hydrothermal Conditions ◽  
Dry Heat ◽  
Surface Areas ◽  
Soil Clays ◽  
Dry Heating ◽  
Georgia Kaolinite

AbstractFixation of K by soil clays and selected reference clay minerals was induced by dry heat and hydrothermal procedures, at 100°C, 200°C and 380°C. Appreciable amounts were fixed at all temperatures. In the cases of the samples treated hydrothermally the amounts fixed increased with pressure.Fixation by dry heating at 380°C was significantly greater than at 100°C and 200°C respectively. Fixation under hydrothermal conditions increased in order 380°C > 200°C > 100°C.Reductions in cation exchange capacities (and surface areas) were associated with fixation, indicating that some fixation was due to ion exchange. Changes in mineralogy in some of the samples also support the conclusion that ion exchange was partly responsible for fixation. Some of the fixation under hydrothermal conditions was due to the formation of insoluble K-compounds - as for example the synthesis of a new mineral when one sample was treated.The lattice-iron content of the clays may have influenced their hydrothermal behaviour. Thus the Princes Town Clay ( > 7-5 % lattice-iron) and three nontronites (≫ 7-5 % lattice-iron) showed appreciable lattice collapse after hydrothermal treatment, while Wyoming bentonite and hectorite (<3-5%) lattice-iron) showed no collapse at all.The degree of crystallinity of the mineral may also have influenced its hydrothermal reaction. For example, the highly disordered soil kaolinite (St John's) was much more reactive than the more ordered Georgia kaolinite. Also, the more-ordered reference clays fixed relatively less K at 380°C than the less-ordered soil clays.

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