Search results for "Induction Period"
showing 10 items of 16 documents
New Features in the dynamics of a ferroin-catalyzed Belousov-Zhabotinsky reaction induced by a zwitterionic surfactant
2008
Abstract Interactions between reaction–diffusion systems and aggregated host environments are a subject of widespread interest. In this work, the behavior of the Belousov–Zhabotinsky reaction was investigated in a micellar environment formed by the zwitterionic surfactant N-tetradecyl-N,N-dimethylamine oxide (C14DMAO). The appearance of an induction period with a threshold-like dependence upon the surfactant concentration, was detected at [C14DMAO] = 5.0 × 10−3 mol dm−3. These new features were explained in terms of the segregation ability typical of the amphiphilic self-assembling systems. Numerical simulations were also performed to confirm the proposed mechanism.
Importance of the liquid to solid weight ratio in the powdered solid-liquid reactions Example drawn from cement constituent hydration
1997
Abstract It seems justified to wonder if the chemical processes which have been evidenced from diluted stirred suspensions are or are not in accordance with those involved in a stagnant paste. The present paper is aimed at clarifying this question which is in connection with the problem of the so called ‘dormant period’ or ‘induction period’ at the beginning of the hydration of Portland cement.
Deuterium isotope effect on the induction period of the cerium catalyzed Belousov-Zhabotinsky reaction
2009
Abstract In this work we present results about the deuterium isotopic effect on the global kinetics of a cerium catalyzed Belousov–Zhabotinsky reaction. A nonlinear dependence of the induction period upon the percentage of deuterated reactants was found in batch conditions. In order to understand this result, we investigated two reaction pathways responsible for the length of the induction period, namely: (a) the reaction between the enolic form of the malonic acid with molecular bromine and (b) the oxidation of malonic acid by the Ce(IV) ion. In both cases we obtained a linear dependence of the kinetic constants on the percentage of deuterated reactants. Nevertheless, by inserting the expe…
Isotopic Effect on the Kinetics of the Belousov-Zhabotinsky Reaction
2007
In this work we present results about the deuterium isotope effect on the global kinetics of a Belousov-Zhabotinsky reaction in batch conditions. A nonlinear dependence of the Induction Period upon the percentage of deuterated reactants was found. The isotopic effect on the bromination reaction of malonic acid was evaluated.
Effects of non-ionic micelles on transient chaos in an unstirred Belousov-Zhabotinsky reaction.
2001
The behaviour of the Ce(IV)-catalyzed Belousov-Zhabotinsky (BZ) system has been monitored at 20.0 degrees C in unstirred batch conditions in the absence and presence of different amounts of the non-ionic micelle-forming surfactants hexaethylene glycol monodecyl ether (C10E6) and hexaethylene glycol monotetradecyl ether (C14E6). The influence of the non-ionic surfactants on both the kinetics of the oxidation of malonic acid (MA) by Ce(IV) species and the behaviour of the BZ reaction in stirred batch conditions has also been studied over a wide surfactant concentration range. The experimental results have shown that, in unstirred batch conditions, at surfactant concentrations below the critic…
Porous structure and mechanical strength of cement-lime pastes during setting
2015
Abstract The acceleration of a cement paste setting as a result of lime addition may be shown from isothermal calorimetry measurements. We investigated the underlying mechanisms through two techniques that provide information on porous structure (using Nuclear Magnetic Resonance) and mechanical properties (elastic modulus measured by rheometry). The correlation of the two sets of results on a cement paste clearly reveals the successive steps of setting, and particularly highlights the so-called induction period. We show that this induction period disappears in the presence of lime, leading to an acceleration of the setting. We also show that beyond some critical concentration of added lime …
Selective, homogeneous hydrogenation of cycloheptatriene to cycloheptene catalyzed by (η4-cycloocta-1,5-diene)(η6-cyclohepta-1,3,5-triene)ruthenium(0)
1980
Abstract In the presence of small amounts of [Ru(η 4 -COD)](η 6 -C 8 H 10 )] (1), cycloheptatriene is hydrogenated to cycloheptene, under one atmosphere of hydrogen at room temperature in homogeneous phase. The formation of a small amount of cyclooctene and the existence of an induction period, which do not occur when [Ru(η 4 -COD)(η 6 -C 7 H 8 )] (2) is used as the catalyst, suggest that 2 is the real catalyst. The selectivity of this hydrogenation is 100% in n-hexane as solvent, 99.5% in THF, and low in ethanol. Conversion is quantitative in THF and ethanol, but not more than 65% in n-hexane. In the presence of 1 or 2, cycloheptene is rapidly hydrogenated to cycloheptane in THF and ethano…
A novel colorimetric experimental technique for the characterisation of metal hydroxides reactive crystallization phenomena
2021
The reactive crystallization of metal hydroxides constitutes a field of raising interest driven by the importance of metals recovery and the wide industrial applications of their hydroxides. A popular example is related to the case of magnesium hydroxide (Mg(OH)2), which is widely employed in the fields of water treatment, desulphurization of fuel gases, pharmaceutical industry, refractory field and flame retardants
Melt stabilisation of high-density film-grade polyethylene
2001
The thermoxidative degradation of a high-density polyethylene stabilised either with standard and novel kinds of antioxidants was examined at many different temperatures. The aim of this work was to investigate the degradation response (crosslinking or chain-breakage) on the polyolefin molecular structure in terms of low shear rate melt viscosity increment and oxidation induction time both studied through steady and dynamic shear flow tests performed in a rotational rheometer. Lactone type antioxidants, especially the one containing P-EPQ phosphite component, exhibit the lowest thermoxidative degradation at high temperatures. Vitamine E, used in blend with a phosphite, appears to be a good …
Anomalien bei der kationischen copolymerisation von trioxan. 32. Mitt. über polyoxymethylene
1967
Die kationische Copolymerisation von Trioxan mit Styrol, 1,3-Dioxolan und anderen Comonomeren last sich wegen folgender Nebenreaktionen nicht durch die ubliche MAYO-sche Copolymerisationskinetik erfassen: 1. Depolymerisation der Trioxymethylenbausteine zu Formaldehyd wahrend der Induktionszeit und daher Bildung sehr styrolreicher bzw. dioxolanreicher Prapolymerer. 2. Bildung und Polymerisation von Formaldehyd, welcher wahrend der gesamten Polymerisation in seiner ceiling-Gleichgewichtskonzentration zugegen ist. 3. Abspaltung oxacyclischer Verbindungen von den aktiven Kettenenden; Bildung von Tetroxan und 4-Phenyl-1,3-dioxan bei der Copolymerisation von Trioxan mit Styrol. 4. Ubertragung am …