The Kinetics of Formation Of Nanocrystalline γ-Ni-Fe During Mechano-Chemical Synthesis

1999 ◽  
Vol 577 ◽  
Author(s):  
P. Knorr ◽  
B.S. Kim ◽  
J.S. Lee
Keyword(s):  
Solid Solution ◽  
Experimental Study ◽  
Chemical Synthesis ◽  
Reaction Rates ◽  
Kinetics Of Formation ◽  
Kinetics Of

ABSTRACTAn experimental study of the kinetics of the three partial processes involved in the mechano-chemical synthesis of nanocrystalline (nc) Ni-Fe is presented. These processes are the reduction of nc NiO, the reduction of nc Fe2O3, and the alloying of Ni and Fe to a γ-Ni-Fe solid solution. Fr the reaction rates of the reduction of nc NiO and nc Fe2O3 activation enthalpies of 82 kJ mol−1 and 47 kJ mol− were obtained. The progress of the overall synthesis was found to follow the sequence ‘NiO red. → Fe2O3 red. → γ-Ni-Fe form.’.

An Evaluation of the Plane Strain Compression Test. III. Experimental Study of the Friction Test: The Role of the Metallurgical Parameters of Die and Sheet

1982 ◽  
Vol 104 (4) ◽  
pp. 538-544 ◽  
Author(s):  
F. Delamare ◽  
J. Kubie´
Keyword(s):  
Experimental Study ◽  
Shear Stress ◽  
Chemical Nature ◽  
Marked Effect ◽  
Friction Test ◽  
Good Reliability ◽  
Plane Strain Compression Test ◽  
Kinetics Of Formation ◽  
Kinetics Of

This paper deals with the influence of the metallurgical parameters of dies and sheet on the friction shear-stress which could be measured by P.S.C.T. The metallurgical parameters of the dies have a marked effect on the kinetics of formation of transfer layers. The metallurgical parameters of the sheet have an effect both on the kinetics of formation, and the chemical nature of the transfer layers. Many parameters must be controlled to have good reliability in PSCT. Then the results can be correlated with boundary lubrication in cold rolling.

Formation kinetics of nanocrystalline Fe–4 wt.% Al solid solution during ball milling

1997 ◽  
Vol 12 (6) ◽  
pp. 1429-1432 ◽  
Author(s):  
H. G. Jiang ◽  
R. J. Perez ◽  
M. L. Lau ◽  
E. J. Lavernia
Keyword(s):  
Solid Solution ◽  
Ball Milling ◽  
Structural Evolution ◽  
Milling Process ◽  
Avrami Equation ◽  
Scanning Calorimetry ◽  
Diffusion Controlled ◽  
Interphase Boundaries ◽  
Kinetics Of Formation ◽  
Kinetics Of

Formation of nanocrystalline Fe–4 wt.% Al solid solution has been achieved through SPEX ball milling of blended elemental Fe and Al powders. Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) have been employed to follow the structural evolution during the ball-milling process. Exothermic peaks exhibited in DSC diagrams of the powders milled for 10 to 60 min yielded thermal enthalpies corresponding to the formation of Fe–4 wt.% Al solid solution, from which the kinetics of formation were found to follow the Johnson–Mehl–Avrami equation. Assessment of the kinetic parameter n reveals a diffusion controlled mechanism, in which grain and interphase boundaries may play a crucial role, during the solid solution formation of Fe–4 wt.% Al.

Etude cinétique du système Cu(II)–adénine

1973 ◽  
Vol 51 (20) ◽  
pp. 3322-3328
Author(s):  
G. Boivin ◽  
M. Zador
Keyword(s):  
Exchange Reaction ◽  
Reaction Rates ◽  
Stopped Flow ◽  
Parallel Reaction ◽  
Kinetics Of Formation ◽  
Protonated Species ◽  
Kinetics Of

The kinetics of formation and dissociation of Cu(II)–adenine complexes have been studied by stopped flow and relaxation methods.Between pH 3.5 and 5 the formation of Cu(II)•aH is too fast to be measured; formation of Cu(II)•(aH)2 has been studied and rate parameters have been determined. At pH < 3 protonated species make an important contribution to measured reaction rates. In basic media two different complexes have been investigated. The exchange reaction with EDTA proceeds by two parallel reaction paths.The mechanism of these reactions is discussed and compared with that proposed for the Cu(II)–adenosine system.La cinétique de la formation et de la dissociation de divers complexes Cu(II)–adénine a été étudiée par les méthodes de la relaxation thermique et du "flux stoppé".

Kinetics of cyclization of S-ethoxycarbonylmethylisothiouronium chloride to 2-imino-4-thiazolidone

1979 ◽  
Vol 44 (3) ◽  
pp. 912-917 ◽  
Author(s):  
Vladimír Macháček ◽  
Said A. El-bahai ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrochloric Acid ◽  
Dilute Hydrochloric Acid ◽  
Base Catalysis ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Kinetics Of Formation ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of formation of 2-imino-4-thiazolidone from S-ethoxycarbonylmethylisothiouronium chloride has been studied in aqueous buffers and dilute hydrochloric acid. The reaction is subject to general base catalysis, the β value being 0.65. Its rate limiting step consists in acid-catalyzed splitting off of ethoxide ion from dipolar tetrahedral intermediate. At pH < 2 formation of this intermediate becomes rate-limiting; rate constant of its formation is 2 . 104 s-1.

Cyclization and acid-catalyzed hydrolysis of O-benzoylbenzamidoximes

1986 ◽  
Vol 51 (12) ◽  
pp. 2786-2797
Author(s):  
František Grambal ◽  
Jan Lasovský
Keyword(s):  
Reaction Rate ◽  
Kinetic Isotope ◽  
Acid Base Equilibrium ◽  
Mineral Acids ◽  
Kinetics Of Formation ◽  
Acid Catalyzed ◽  
Ph Scale ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Derivatives Of

Kinetics of formation of 1,2,4-oxadiazoles from 24 substitution derivatives of O-benzoylbenzamidoxime have been studied in sulphuric acid and aqueous ethanol media. It has been found that this medium requires introduction of the Hammett H0 function instead of the pH scale beginning as low as from 0.1% solutions of mineral acids. Effects of the acid concentration, ionic strength, and temperature on the reaction rate and on the kinetic isotope effect have been followed. From these dependences and from polar effects of substituents it was concluded that along with the cyclization to 1,2,4-oxadiazoles there proceeds hydrolysis to benzamidoxime and benzoic acid. The reaction is thermodynamically controlled by the acid-base equilibrium of the O-benzylated benzamidoximes.

Kinetics of esterification of monoisopropylphenols with phosphoryl trichloride

1989 ◽  
Vol 54 (5) ◽  
pp. 1311-1317
Author(s):  
Miroslav Magura ◽  
Ján Vojtko ◽  
Ján Ilavský
Keyword(s):  
Liquid Phase ◽  
Rate Constants ◽  
Reaction Rates ◽  
Activation Energies ◽  
The Individual ◽  
Kinetics Of

The kinetics of liquid-phase isothermal esterification of POCl3 with 2-isopropylphenol and 4-isopropylphenol have been studied within the temperature intervals of 110 to 130 and 90 to 110 °C, respectively. The rate constants and activation energies of the individual steps of this three-step reaction have been calculated from the values measured. The reaction rates of the two isomers markedly differ: at 110 °C 4-isopropylphenol reacts faster by the factors of about 7 and 20 for k1 and k3, respectively. This finding can be utilized in preparation of mixed triaryl phosphates, since the alkylation mixture after reaction of phenol with propene contains an excess of 2-isopropylphenol over 4-isopropylphenol.

scholarly journals Oxidation behavior of non-stoichiometric (Zr,Hf,Ti)Cx carbide solid solution powders in air

2021 ◽  
Author(s):  
Huilin Lun ◽  
Yi Zeng ◽  
Xiang Xiong ◽  
Ziming Ye ◽  
Zhongwei Zhang ◽  
...  
Keyword(s):  
Solid Solution ◽  
Oxidation Resistance ◽  
Oxidation Behavior ◽  
Group Iv ◽  
Hypersonic Vehicles ◽  
Metal Carbides ◽  
Initial Oxidation ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Kinetics Of

AbstractMulti-component solid solutions with non-stoichiometric compositions are characteristics of ultra-high temperature carbides as promising materials for hypersonic vehicles. However, for group IV transition-metal carbides, the oxidation behavior of multi-component non-stoichiometric (Zr,Hf,Ti)Cx carbide solid solution has not been clarified yet. The present work fabricated four kinds of (Zr,Hf,Ti)Cx carbide solid solution powders by free-pressureless spark plasma sintering to investigate the oxidation behavior of (Zr,Hf,Ti)Cx in air. The effects of metallic atom composition on oxidation resistance were examined. The results indicate that the oxidation kinetics of (Zr,Hf,Ti)Cx are composition dependent. A high Hf content in (Zr,Hf,Ti)Cx was beneficial to form an amorphous Zr-Hf-Ti-C-O oxycarbide layer as an oxygen barrier to enhance the initial oxidation resistance. Meanwhile, an equiatomic ratio of metallic atoms reduced the growth rate of (Zr,Hf,Ti)O2 oxide, increasing its phase stability at high temperatures, which improved the oxidation activation energy of (Zr, Hf, Ti)Cx.

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