The reaction pathway and mechanistic features of the synthesis of SnO 2 via the oxidative decomposition of tin(II) oxyhydroxide in air were investigated using thermoanalytical techniques and morphological observations. Furthermore, the detailed kinetics of each component process were analyzed by applying an empirical kinetic deconvolution method. The thermal behavior of tin(II) oxyhydroxide in air is characterized by two overall processes: (1) the mass-change process, which involves thermal decomposition (mass loss) and in situ oxidation (mass gain), followed by (2) crystal growth of the product SnO 2 . The mass-change process comprises largely overlapping consecutive processes such as primary endothermic thermal decomposition and subsequent exothermic oxidation. It was deduced from the kinetic results that the overall mass-change process is regulated by the overlapping structures of the surface product layers of the primary and subsequent reactions and the counter diffusion of the H 2 O generated in the primary reaction and the reactant O 2 required for the subsequent reaction in the outer layer. The crystal growth of the asproduced SnO 2 occurs via two concurrent kinetic processes that result in the development of a two-dimensional stacking structure. These kinetic features are the key to controlling the overall reaction process and the morphology of the SnO 2 product.

This study focuses on the physico-geometrical mechanism and the overall kinetics of the microstructural tin(IV) oxide formation process by the thermally induced oxidative decomposition of tin(II) oxalate in flowing air. Two tin(II) oxalate samples with different morphologies were subjected to a kinetic study involving thermogravimetrical and morphological observations. The reactions exhibited different behaviors at different steps (multistep behaviors); therefore, the overall reactions were resolved into each reaction step using kinetic analyses based on the cumulative kinetic equation. Oxidative decomposition is characterized by a phase boundary controlled reaction initiated by the surface reaction. The formation of the surface product layer at an early stage of the reaction inhibits diffusion of the product and reactant gases. Gaseous diffusion channels are produced via reformulation of the surface product layer by the reaction itself, and the residual reaction advances in the manner of autocatalytic reaction. The kinetic behavior is regulated by the self-generated reaction conditions under specific, transiently formed structural characteristics of the reacting particles, which vary depending on the applied reaction conditions. Therefore, the process control of the oxidative decomposition is an important factor for controlling the microstructure and physicochemical properties of the resulting tin(IV) oxide.

A laboratory exercise for the education of students about thermal runaway reactions based on the reaction between aluminum and hydrochloric acid as a model reaction is proposed. In the introductory part of the exercise, the induction period and subsequent thermal runaway behavior are evaluated via a simple observation of hydrogen gas evolution and measurement of the temperature, which also provide basic information on the mechanistic features of the thermal runaway reaction. The exercise also includes PC aided thermometric measurements of the reaction and kinetic analysis of the induction period. The initiation time of the thermal runaway behavior under certain reaction conditions is calculated using the kinetic parameters determined experimentally by the students. The laboratory exercise provides a fundamental understanding of the mechanistic features of a thermal runaway reaction, recognition of the need for adopting safety measures when performing chemical reactions, and experience of using kinetic analysis for safety assessment.

An elastic convolver based on a nonlinear effect in surface acoustic wave (SAW) on a Y-Z⋅LiNbO3 is widely used as a functional device in the area of communication system. Therefore, the efficiency, which is an important parameter for the SAW convolver, is quite low. There have been many reports on electrode structures and convolver materials for improving the efficiency. In this work, theoretical and experimental results are reported for the optimum width of a (Δ=v/v) waveguide which has high convolver efficiency. The theoretical calculation was obtained by using the scalar potential approximation. The efficiency has a peak at a waveguide width of around 1λ. In order to increase the power density multistrip beam width compressors have been used. Performance of a device having a 4-μs waveguide length, a central frequency of 43 MHz and using 10:1 beam width compressors is described. The validity of the theory is proven experimentally, and, therefore, the optimum waveguide width for the convolver efficiency in a conventional elastic convolver is around one wavelength of the input SAW.