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31.
Agustín Urretabizkaia Gurutze Arzamendi María J. Unzu Jos M. Asua 《Journal of polymer science. Part A, Polymer chemistry》1994,32(9):1779-1788
A method for the calculation of the optimal monomer addition policies for polymer composition control in emulsion terpolymerization is developed. The method is applied to reactors with and without limited heat removal capacity. A mathematical model that incorporates the main features of the vinyl acetate/methyl methacrylate/butyl acrylate high solids content emulsion terpolymerization system allows the calculation of the composition of the initial charge of the reactor and the time-dependent monomer addition rates required. © 1994 John Wiley & Sons, Inc. 相似文献
32.
For many applications poly(styrene) must
be treated to reduce its flammability. This is usually done by incorporating
a flame retardant additive, usually an organohalogen compound, into the formulation
as the polymer is being processed. A potentially very efficient way of introducing
flame retardance would be to incorporate a suitable structural unit directly
into the polymer. This can be done by using 2,4,4,5,5-pentaphenyl-1,3,2-dioxaphospholane
as an initiator for styrene polymerization. The strained carbon–carbon
bond of the phospholane undergoes homolysis at moderate temperatures to generate
a diradical which initiates polymerization. The resulting polymer contains
an O–P–O unit in the mainchain. Thermogravimetry indicates that
the thermal stability of the polymer is quite comparable to that of poly(styrene)
generated by conventional methods. 相似文献
33.
Anna Kowalska Zygmunt Kowalski Andrzej Kotarba Andrzej Barański 《Mikrochimica acta》1990,100(5-6):349-353
The analytical procedure of determination of Fe(II) in the presence of Fe(III) in milligram samples is proposed. A solid sample is dissolved in hydrochloric acid in argon atmosphere. Subsequently, the pH-value of the solution is fixed and Fe(III) complexed by phosphoric buffer. At the next step Fe(II) is oxidized by -molybdosilicic acid. Finally, the intensity of colouring caused by the reduced form of the acid is measured at the wavelength 770 nm. The proper treatment of the sample during oxidation, and immediately before, is decisive for the accuracy of the analysis. The method was verified by means of the analysis of synthetic magnetite. The theoretical content of Fe(II) was 24.12%, the determined one was 24.02 ± 0.10%. The method was applied to the determination of the homogeneity of an iron catalyst for ammonia synthesis. 相似文献
34.
In the present study was combined the use of high resolution TGA with the isoconversion method, giving us a suitable methodology for determining the stages that occur during a reaction, and providing further insights about the kinetics of the processes involved. As a model reaction was used the thermal dehydration of KNbWO6·H2O. The results shown that the dehydration process is controlled by internal water diffusion (intra-crystallite); with activation energy values between 43 and 36 kJ/mol. This value is consistent with a diffusion mechanism dominated by van der Waals attractions. The estimated kinetic parameters are supported with a structural analysis, that suggest lower dimensionality character for water diffusion due to the specific orientations of 〈1 1 0〉 open channels in the pyrochlore framework. This would explain why the two-dimensional (D2) mechanism appears to be the most probable. 相似文献
35.
K. K. Turgunov A. G. Tojiboev B. Tashkhodjaev KH. M. shakhidoyatov 《Journal of inclusion phenomena and macrocyclic chemistry》2005,53(1-2):23-26
The crystal structures of hydrate (1) and anhydrate (2) forms of 2,3-pentamethylene-3,4-dihydroquinazolin-4-one hydrochloride have been determined by X-ray structure analysis. Crystal data of 1 are 2(C13H14N2O)*3(HCl)*4.5 (H2O), triclinic P?1, Z=2, a=8.004(5), b=13.129(7), c=15.725(7) Å, α=106.45(4), β=92.61(4), γ=97.98(5), R=0.0652 and 2 are C13H14N2O*HCl, monoclinic C2/c, Z=8, a=21.360(4), b=5.954(1), c=21.263(4), β=117.89(3), R=0.0556. The crystal of the hydrate form 1is unstable. This form collapses easily with evaporation of H2O and part of HCl molecules from crystals. By recrystallizing destroyed form has been obtained stable crystal form 2. 相似文献
36.
A. K. Galwey 《Journal of Thermal Analysis and Calorimetry》2006,86(1):267-286
This critical
survey argues that the theory, conventionally used to interpret kinetic data
measured for thermal reactions of initially solid reactants, is not always
suitable for elucidating reaction chemistry and mechanisms or for identifying
reactivity controls. Studies of solid-state decompositions published before
the 1960s usually portrayed the reaction rate as determined by Arrhenius type
models closely related to those formulated for homogeneous rate processes,
though scientific justifications for these parallels remained incompletely
established. Since the 1960s, when thermal analysis techniques were developed,
studies of solid-state decompositions contributed to establishment of the
new experimental techniques, but research interest became redirected towards
increasing the capabilities of automated equipment to collect, to store and
later to analyze rate changes for selected reactions. Subsequently, much less
attention has been directed towards chemical features of the rate processes
studied, which have included a range of reactants that is much more diverse
than the simple solid-state reactions with which early thermokinetic studies
were principally concerned. Moreover, the theory applied to these various
reactants does not recognize the possible complexities of behaviour that may
include mechanisms involving melting and/or concurrent/consecutive reactions,
etc. The situation that has arisen following, and attributable to, the eclipse
of solid-state decomposition studies by thermal analysis, is presented here
and the consequences critically discussed in a historical context. It is concluded
that methods currently used for kinetic and mechanistic investigations of
all types of thermal reactions indiscriminately considered by the same, but
inadequate theory, are unsatisfactory. Urgent and fundamental reappraisal
of the theoretical foundations of thermokinetic chemical studies is now necessary
and overdue.
While there are important, but hitherto unrecognized,
delusions in thermokinetic methods and theories, an alternative theoretical
explanation that accounts for many physical and chemical features of crystolysis
reactions has been proposed. However, this novel but general model for the
thermal behaviour and properties of solids has similarly remained ignored
by the thermoanalytical community. The objective of this article is to emphasize
the now pressing necessity for an open debate between these unreconciled opinions
of different groups of researchers. The ethos of science is that disagreement
between rival theories can be resolved by experiment and/or discussion, which
may also strengthen the foundations of the subject in the process. As pointed
out below, during recent years there has been no movement towards attempting
to resolve some fundamental differences of opinion in a field that lacks an
adequate theory. This should be unacceptable to all concerned. Here some criticisms
are made of specific features of the alternative reaction models available
with the stated intention of provoking a debate that might lead to identification
of the significant differences between the currently irreconciled views. This
could, of course, attract the displeasure of both sides, who will probably
criticise me severely. Because I intend to retire completely from this field
soon, it does not matter to me if I am considered to be ‘wrong’,
if it contributes to us all eventually agreeing to get the science ‘right’. 相似文献
37.
A new percolation problem is posed where the sites on a lattice are randomly occupied but where only those occupied sites with at least a given numberm of occupied neighbors are included in the clusters. This problem, which has applications in magnetic and other systems, is solved exactly on a Bethe lattice. The classical percolation critical exponents=gg=1 are found. The percolation thresholds vary between the ordinary percolation thresholdp
c
(m=1)=l/(z – 1) andp
c(m=z) =[l/(z – 1)]1/(z–1). The cluster size distribution asymptotically decays exponentially withn, for largen, p p
c
.Supported in part by National Science Foundation grant DMR78-10813. 相似文献
38.
A model of disordered medium is proposed to describe the monolayer adsorption isotherm on heterogeneous surfaces. The model
is based on the premise that adsorption medium consists of separate regions in each of which there is a permanent local equilibrium
constant, the character of the changes of which is determined by the disorder parameter of the medium.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 3, pp. 189–193, May–June, 2006. 相似文献
39.
S.?Krishnan A.?KleinEmail author M.?S.?El-Aasser E.?D.?Sudol 《Colloid and polymer science》2005,283(8):836-844
Emulsion copolymerizations involving water-soluble functional monomers such as N-methylolacrylamide often result in the formation of water-soluble polymer that remains in the aqueous phase of the latex. A simple procedure is developed to determine the amount of water-soluble polymer in the aqueous phase of a high-solids latex using ultracentrifugation. Dilution of the latex with water is usually found necessary for good separation during ultracentrifugation. If the latex contains a surface-active species (surfactant) in amounts comparable to the amount of water-soluble polymer, calculation of the amount of water-soluble polymer in the serum of the original latex will require information about dilution dependent partitioning of the surfactant between the surface of the particles and the aqueous phase. This paper outlines a procedure that enables determination of the amount of water-soluble polymer in the aqueous phase of the original latex, by ultracentrifugation of the latex diluted to different concentrations. The procedure also gives the Henrys constant for the adsorption of the surfactant on the surface of the polymer particles in the latex. 相似文献
40.
C. Aslangul M. Barthélémy N. Pottier D. Saint-James 《Journal of statistical physics》1991,65(3-4):695-713
The random walk of a particle on a directed Bethe lattice of constant coordinanceZ is examined in the case of random hopping rates. As a result, the higher the coordinance, the narrower the regions of anomalous drift and diffusion. The annealed and quenched mean square dispersions are calculated in all dynamical phases. In opposition to the one-dimensional (Z=2) case, the annealed and quenched mean quadratic dispersions are shown to be identical in all phases.We shall employ indifferently the expressions Bethe lattice or infinite Cayley tree to denote an infinite ramified lattice of constant coordinanceZ.(4, 5) 相似文献