The precursory reaction was identified as the decompn. In flowing dry N2, the thermal decompn. CO2 and water vapor influence differently the overall kinetics of the thermal decompn. Added gas phase of CO2 slightly inhibits the overall rate because of the increasing contribution of the surface reaction.
Under higher water vapor pressure, the physico-geometrical mechanism of the surface reaction changes drastically, indicating the preliminary reformation of reactant surface and the formation of needle crystals of solid product on the surface. The mechanistic change and extended contribution of the surface reaction result in the deceleration of the surface reaction and acceleration of the established reaction.
- 1 INTRODUCTION.
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The kinetics and mechanism of the thermal dehydration of magnesium acetate tetrahydrate were investigated as a typical example of the glass formation process via the thermal decompn. Formation of an intermediate fluid phase was identified as the characteristic phenomenon responsible for the formation of anhyd. Because of variations in the mechanism of release of the water vapor with changes in the reaction temp.
The formation of hollow anhyd. The mechanism of formation is discussed in terms of complementary interpretations of the morphol. On further heating, the as-produced anhyd. The crystn. Thermal decompn. Based on comparative investigation of thermal decompn. The reaction stages involve the formation of a surface product layer and an internal reaction in the as-produced core-shell structure of the reacting particles.
Immediately after the formation of the surface product layer, the structural phase transitions of Ag2CO3 to two different high-temp. Under these conditions, the thermal decompn. The growth of Ag2O particles in the surface product layer produces possible channels for the diffusion of CO2.
The relative rates of the formation of the diffusion channels in the surface product layer and the increase in the internal partial pressure det. The sample and reaction conditions influence the kinetic behavior of different component processes, resulting in the complex thermal decompn.
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The reaction mechanism and overall kinetics of the thermal decompn. The reaction proceeds via a surface reaction and subsequent advancement of the as-produced reaction interface toward the center of the crystals, where the seemingly smooth mass-loss behavior can be described by the apparent activation energy Ea of ca. However, considering the rate behavior, as the reaction advances, it is expected that the secondary reaction step characterized by an autocatalytic rate behavior takes part in the overall reaction. The hindrance of the diffusional removal of the evolved gases by the surface product layer, Na2CO3, is the most probable reason for the change in the reaction mechanism.
In the deceleration part of the first reaction step, the second reaction step is accelerated due to an increase in the water vapor pressure at the reaction interface inside the reacting particles. We also expect the self-generated reaction condition of the high water vapor pressure and the existence of liq. A relevant reaction model for the thermal decompn.coutnhalnewswatch.tk
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A discussion is presented on the observation of the surface and interior of crystals of oxalic acid dihydrate, sodium citrate dihydrate, and copper II sulfate pentahydrate during thermal dehydration for instruction in the thermal decompn. Microscopy is used to study a representative group of solid-state reactions, i. The kinetics of the thermal dehydration of single crystals of Cu II acetate monohydrate were measured by isothermal TG and compared with corresponding theor.
Polarizing micrographs were capable of showing the dehydration mechanism. This thermal dehydration would be suitable for school demonstrations.
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Thermal Analysis Techniques - Part I. Thermobalances J. Thermal analysis techniques. The use of a simple DTA app. An undergraduate thermal analysis experiment. A lab.
Transformation, Crystallization, Kinetics and Thermodynamics
The expt. The following 2 thermal anal. The thermometric titrimetry expts. Using mol. An expt. The expts. Two different kinds of chalk, consisting of calcium carbonate or calcium sulfate, may be found. A set of expts. Students become acquainted with a no. Thermal Analysis of Plastics J.
Journal of Chemical Education, Dept. This lab expt. TGA in the measurement of polymer properties: percent crystallinity, glass transition temp. This dry lab, consisting of a series of exercises, has been performed by second-semester students in a new two-semester general chem. The measurement of mass in different surroundings allows one to measure the d.
Although most curricula cover the use of anal. We describe some of the current instrumentation and applications in this area, including a novel and inexpensive method for measuring magnetic susceptibility. It is a straightforward expt. The students identify an unknown salt by detg. Wiley-Liss, Inc. A review. Most solid-state kinetic principles were derived from those for homogeneous phases in the past century. Rate laws describing solid-state degrdn. Solid-state kinetic reactions can be mechanistically classified as nucleation, geometrical contraction, diffusion, and reaction order models.
Many math. These methods generally fall into one of 2 categories: model-fitting and model-free. Controversies have arisen with regard to interpreting solid-state kinetic results, which include variable activation energy, calcn. Solid-state kinetic studies have appeared in the pharmaceutical literature over many years; some of the more recent ones are discussed in this review.
A physical chemistry experiment. The temp. The inner decompn. The higher b. The exptl.
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A solid-state chemistry experiment. Non-isothermal Kinetics J. Kinetic anal. An inorganic solid state experiment. The different theories and equations to be applied and the mechanism derived from the kinetic results are discussed.
Elsevier B. Influences of the product gases on the kinetics of the thermal decompn. CO2 and H2O, resp. The kinetic rate behavior under controlled atm. The effects of atm. CO2 and H2O on the apparent kinetic parameters were appeared as the decreases in both the values of Ea and A and the increase in the value of A, resp. Quantitative analyses of evolved gases. For the quant.