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71.
Jakub Čížek Ivan Procházka Radomír Kužel Rinat K. Islamgaliev 《Monatshefte für Chemie / Chemical Monthly》2002,133(6):873-887
Summary. Ultra-fine grained (UFG) Cu (grain size 80 nm) containing 0.5 wt.% Al2O3 nanoparticles (size 20 nm) was prepared by high pressure torsion (HPT). Positron lifetime spectroscopy was employed to characterize
the microstructure of this material, especially with respect to types and concentration of lattice defects. The evolution
of microstructure with increasing temperature was studied by positron lifetime spectroscopy and X-ray diffraction measurements.
The thermal stability of the Cu + 0.5 wt.% Al2O3 nanocomposite was compared with that of pure UFG Cu prepared by the same technique. The processes taking place during thermal
recovery of the initial nanoscale structure in both studied materials are described.
Received October 5, 2001. Accepted (revised) December 20, 2001 相似文献
72.
The paper deals with the chemical and physical factors influencing the stoichiometry of thermal decomposition of solid coordination compounds. Nickel(II) coordination compounds were used as examples: the problem of the relationship between the structure of the initial compound (and of its intermediates) and the stoichiometry of thermal decomposition is discussed; experimental conditions are shown to affect this decomposition, and the conceptions of the apparent and real stoichiometries of thermal decomposition are discussed. The results obtained may have a more general meaning.
Reported at the 7th Seminar on Modern Methods in Inorganic Chemistry. Harmonia-Bratislava, 1977. 相似文献
Zusammenfassung Der Beitrag befa\t sich mit den chemischen und physikalischen Faktoren, welche die Stöchiometrie der thermischen Zersetzung fester Koordinationsverbindungen beeinflussen. Koordinationsverbindungen von Nickel(II) wurden als Beispiel eingesetzt; das Problem des Zusammenhanges zwischen Struktur der Ausgangsverbindung (und seiner IntermediÄrprodukte) und der Stöchiometrie der thermischen Zersetzung wird erörtert; die die Zersetzung beeinflussenden Versuchsbedingungen werden gezeigt und das Konzept der sogenannten scheinbaren und tatsÄchlichen Stöchiometrie der thermischen Zersetzung wird beschrieben. Die erhaltenen Ergebnisse dürften von allgemeinerer Bedeutung sein.
Résumé L'article considère les facteurs chimiques et physiques qui influencent la stchiométrie des réactions de décomposition thermique des composés de coordination solides. Les composés de coordination du nickel(II) ont été choisis pour illustrer le problème des relations entre la structure du composé initial (et de ses intermédiaires) et la stchiométrie de la réaction de décomposition thermique. On montre que les conditions expérimentales influencent la décomposition et on discute le principe des réactions stchiométriques de décomposition thermique dites «apparentes» et «réelles». Les résultats obtenus sont probablement de portée plus générale.
, . $ (II) $ ( ) $ . , $ , $ . .
Reported at the 7th Seminar on Modern Methods in Inorganic Chemistry. Harmonia-Bratislava, 1977. 相似文献
73.
Development of new reactions requires finding and understanding of novel reaction pathways. In challenging reactions such as C–H activations, these pathways often involve highly reactive intermediates which are the key to our understanding, but difficult to study. Mass spectrometry has a unique sensitivity for detecting low abundant charged species; therefore it is increasingly used for detection of such intermediates in metal catalysed- and organometallic reactions. This perspective shows recent developments in the field of mass spectrometric research of reaction mechanisms with a special focus on going beyond mass-detection. Chapters discuss the advantages of collision-induced dissociation, ion mobility and ion spectroscopy for characterization of structures of the detected intermediates. In addition, we discuss the relationship between the condensed phase chemistry and mass spectrometric detection of species from solution.Modern approaches of mass spectrometry can identify reaction intermediates and provide a unique insight into their structure, properties and kinetics. 相似文献
74.
The extraction of ion-pairs of monovalent organic acid anions and inorganic anions with 4-(4-diethylaminophenylazo)-N-alkylpyridinium cation (azo-dye cation) is described. The alkyl groups studied were methyl, ethyl, propyl, butyl and benzyl groups. The ion association, distribution and extraction constants for the ion-pairs were determined from partition equilibrium studies. These azo-dye cations can extract chelate anions containing sulfonic acid groups into chloroform. The cobalt complex of 2-nitroso-1-naphthol-4-sulfonic acid is extracted quantitatively into chloroform with the propyl derivative as a 1:3 Co: dye complex; measurement of the absorbance of the extracted ion-pair provides a very sensitive determination of cobalt, the apparent molar absorptivity in chloroform being 1.66 × 105 l mol-1 cm-1 at 566 nm. The methyl derivative is suitable for cation extraction of monovalent anions such as the complex nickel anion of 4-chloro-2-nitroso-1-naphthol, and anionic surfactants. The possibilities for application of these azo-dye cations in extraction-spectrophotometric determinations are very large. 相似文献
75.
V. Jedináková J. Cibulková J. Teplý M. Novák J. Žilková 《Journal of Radioanalytical and Nuclear Chemistry》1979,51(2):355-362
The radiation stability was investigated of organic phases containing tertiary benzyldialkylamines and quaternary benzyltrialkylammonium
salts which are sultable for the separation of lanthanides and americium from irradiated nuclear fuel. Attention was paid
to changes of the extraction properties in Eu(III) and Am(III) extraction. The influence of the individual components forming
the organic phase (extractant, solvent, solubilizer and nitric acid) on the decrease of the extraction capacity of the organic
phase after irradiation is discussed. The greatest changes in the distribution coefficients DEu and DAm after irradiation were shown for extraction in the presence of nitric acid. As regards the absorbed dose, these systems can
be considered as stable in comparison with organophosphorus extractans. 相似文献
76.
A. Žilinskas 《Journal of Global Optimization》1992,2(2):145-153
A review of statistical models for global optimization is presented. Rationality of the search for a global minimum is formulated axiomatically and the features of the corresponding algorithm are derived from the axioms. Furthermore the results of some applications of the proposed algorithm are presented and the perspectives of the approach are discussed. 相似文献
77.
J. Žofka 《Czechoslovak Journal of Physics》1982,32(3):321-325
Hypernuclear structure models are briefly reviewed. Phenomena related to hypernuclear polarization are displayed. A discussion is given of nuclear and hypernuclear neutron orbitals extraction. Preliminary results on
– angular distributions for the reaction6Li(K
–, –)
6
Li are presented.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.The collaboration of Dr. M. Sotona and Dr. L. Majling in the speedy preparation of the AD results and discussions with them and with Prof. B. Povh are greatly acknowledged. 相似文献
78.
Tomislav P. Živković 《Journal of mathematical chemistry》2002,32(1):39-71
Interaction of quantum system S
a
described by the generalised × eigenvalue equation A|
s
=E
s
S
a
|
s
(s=1,...,) with quantum system S
b
described by the generalised n×n eigenvalue equation B|
i
=
i
S
b
|
i
(i=1,...,n) is considered. With the system S
a
is associated -dimensional space X
a
and with the system S
b
is associated an n-dimensional space X
n
b
that is orthogonal to X
a
. Combined system S is described by the generalised (+n)×(+n) eigenvalue equation [A+B+V]|
k
=
k
[S
a
+S
b
+P]|
k
(k=1,...,n+) where operators V and P represent interaction between those two systems. All operators are Hermitian, while operators S
a
,S
b
and S=S
a
+S
b
+P are, in addition, positive definite. It is shown that each eigenvalue
k
i
of the combined system is the eigenvalue of the × eigenvalue equation
. Operator
in this equation is expressed in terms of the eigenvalues
i
of the system S
b
and in terms of matrix elements
s
|V|
i
and
s
|P|
i
where vectors |
s
form a base in X
a
. Eigenstate |
k
a
of this equation is the projection of the eigenstate |
k
of the combined system on the space X
a
. Projection |
k
b
of |
k
on the space X
n
b
is given by |
k
b
=(
k
S
b
–B)–1(V–
k
P})|
k
a
where (
k
S
b
–B)–1 is inverse of (
k
S
b
–B) in X
n
b
. Hence, if the solution to the system S
b
is known, one can obtain all eigenvalues
k
i
} and all the corresponding eigenstates |
k
of the combined system as a solution of the above × eigenvalue equation that refers to the system S
a
alone. Slightly more complicated expressions are obtained for the eigenvalues
k
i
} and the corresponding eigenstates, provided such eigenvalues and eigenstates exist. 相似文献
79.
A packed-bed enzyme reactor with immobilized carboxypeptidase Y was used in tandem with a displacement chromatograph for the preparation of N-benzoyl-L-arginyl-L-methioninamide, from N-benzoyl-L-arginine and L-methioninamide. The pumps and valves of the coupled enzyme reactor and displacement chromatograph were controlled by a microprocessor. The enzyme was immobilized on microparticulate amino-silica by glutaraldehyde and packed into a 60 X 4.6 mm I.D. column. The packed-bed reactor was used in the recirculating mode and components of the reaction mixture were subsequently separated by displacement chromatography on a 250 X 4.6 mm octadecyl-silica column using butoxyethoxyethanol as the displacer. Unreacted L-methioninamide was returned to the reaction mixture. Both the progress of the reaction and the extent of separation by displacement chromatography were monitored by high-performance liquid chromatographic analysis. The system was designed so that enzymatic peptide synthesis, separation by displacement chromatography, and column regeneration were carried out simultaneously by using two identical columns in parallel. An amount of 460 mg of N-benzoyl-L-arginyl-L-methioninamide having purity greater than 99% could be obtained in 24 h with this system. The tandem operation of the enzyme reactor and liquid chromatograph operated in the displacement mode offers a means for the synthesis and purification of peptides. 相似文献
80.
Jana Porubsk Bob Alince Theo G. M. van de Ven 《Colloids and surfaces. A, Physicochemical and engineering aspects》2002,210(2-3):223-230
The effects of cationic polyethylenimine (PEI) on the colloidal stability of anionic fines (microcrystalline cellulose or thermomechanical fines), fillers (clay) and their mixtures in deionized and tap water were investigated, using a photometric dispersion analyzer. Measurements confirmed that PEI flocculates all used materials by charge neutralization. As expected, higher additions of PEI lead to electrostatic stabilization of microcellulose and clay suspensions, but it was not possible to stabilize the suspension of fines using high additions of PEI. This is ascribed to the mechanical entanglements of fibrillar fines. In tap water, much more PEI is needed to reach optimum flocculation conditions than in deionized water. Heteroflocculation between PEI-coated clay and fines takes place with a rate which, for high fines concentration and a constant clay concentration, is independent of fines concentration. A theoretical model for the heteroflocculation of fines with PEI-coated clay has been developed, which explains the observed trends. In essence, clay particles can act as bridging agents for fines flocculation. 相似文献