scholarly journals Thermally prepared Ti/RhOx electrodes: II H2 evolution in acid solution

2002 ◽  
Vol 56 (6) ◽  
pp. 231-237 ◽  
Author(s):  
Mario Campari ◽  
Ana Tavares ◽  
Sergio Trasatti
Keyword(s):  
Thermal Decomposition ◽  
Cyclic Voltammetry ◽  
Steady State ◽  
Reaction Mechanism ◽  
Acid Solution ◽  
Reaction Order ◽  
H2so4 Solution ◽  
H2 Evolution ◽  
Final Settlement ◽  
Fractional Reaction

Ti/RhOx electrodes were prepared at 400-600?C by thermal decomposition of Rh chloride. Oxide layers were studied by SEM, cyclic voltammetry and steady-state E-j curves In 0.5 mol dm-3 H2SO4 solution. Voltammetric charge exhibits a maximum at 430?C with fresh electrodes which shifts to 470?C after use for H2 evolution. H2 discharge first produces a decrease in voltammetric charge, then an activation with final settlement to a constant behaviour for "aged" electrodes. H2 evolution on stable RhOx surfaces takes place with 40 mV Tafel slope and a reaction order of 2.5. The fractional reaction order indicates that the surface response to pH is that typical of oxides even for "aged" electrodes. A reaction mechanism is proposed.

Microwave Synthesis and Characterization of Nanoscale Lanthanum Cobaltite

2012 ◽  
Vol 476-478 ◽  
pp. 1322-1326
Author(s):  
Xiao Yu Jiang ◽  
Jin Chen ◽  
Wen Zhe Chen
Keyword(s):  
Cyclic Voltammetry ◽  
Steady State ◽  
Microwave Irradiation ◽  
Reaction Order ◽  
Synthesis And Characterization ◽  
Cyclic Voltammogram ◽  
Lanthanum Cobaltite ◽  
Bet Analysis ◽  
Perovskite Type

Nanoscale lanthanum cobaltite with perovskite-type was successfully synthesized by microwave irradiation directly and was characterized by XRD, SEM, XPS and BET analysis. The results show that the size of particle was 18 nm averagely, the surface area to be 31.0 m2 g−1. The electrochemical properties were studied by cyclic voltammetry and steady state polarization. The cyclic voltammogram between 0 and 0.55 V exhibited two pairs of redox peaks prior to the onset of O2 evolution in 1 mol dm−3 KOH. The Tafel slope and the reaction order with respect to concentration of OH− were found to be 60 mV decade−1 and ca. 1, respectively.

Reaction mechanism of rat-liver ADH with ethanol and NAD in the steady state

1977 ◽  
Vol 2 (3) ◽  
pp. 171-177 ◽  
Author(s):  
M. Feraudi ◽  
M. Kohlmeier ◽  
G. Schmolz
Keyword(s):  
Steady State ◽  
Reaction Mechanism ◽  
Rat Liver

scholarly journals Study of thermal behavior of phytic acid

2013 ◽  
Vol 49 (2) ◽  
pp. 275-283 ◽  
Author(s):  
André Luis Máximo Daneluti ◽  
Jivaldo do Rosário Matos
Keyword(s):  
Thermal Decomposition ◽  
Thermal Behavior ◽  
Mass Loss ◽  
Kinetic Study ◽  
Phytic Acid ◽  
Absorption Spectroscopy ◽  
Elemental Analysis ◽  
Reaction Order ◽  
Dehydration Process ◽  
Thermogravimetric Method

Phytic acid is a natural compound widely used as depigmenting agent in galenic cosmetic emulsions. However, we have observed experimentally that phytic acid, when heated to 150 ºC for around one hour, shows evidence of thermal decomposition. Few studies investigating this substance alone with regard to its stability are available in the literature. This fact prompted the present study to characterize this species and its thermal behavior using thermal analysis (TG/DTG and DSC) and to associate the results of these techniques with those obtained by elemental analysis (EA) and absorption spectroscopy in the infrared region. The TG/DTG and DSC curves allowed evaluation of the thermal behavior of the sample of phytic acid and enabled use of the non-isothermal thermogravimetric method to study the kinetics of the three main mass-loss events: dehydration I, dehydration II and thermal decomposition. The combination of infrared absorption spectroscopy and elemental analysis techniques allowed evaluation of the intermediate products of the thermal decomposition of phytic acid. The infrared spectra of samples taken during the heating process revealed a reduction in the intensity of the absorption band related to O-H stretching as a result of the dehydration process. Furthermore, elemental analysis results showed an increase in the carbon content and a decrease in the hydrogen content at temperatures of 95, 150, 263 and 380 °C. Visually, darkening of the material was observed at 150 °C, indicating that the thermal decomposition of the material started at this temperature. At a temperature of 380 °C, thermal decomposition progressed, leading to a decrease in carbon and hydrogen. The results of thermogravimetry coupled with those of elemental analysis allow us to conclude that there was agreement between the percentages of phytic acid found in aqueous solution. The kinetic study by the non-isothermal thermogravimetric method showed that the dehydration process occurred in two stages. Dehydration step I promoted a process of vaporization of water (reaction order of zero), whereas dehydration step II showed an order of reaction equal to five. This change in reaction order was attributed to loss of chemically bonded water molecules of phytic acid or to the presence of volatile substances. Finally, the thermal decomposition step revealed an order of reaction equal to one. It was not possible to perform the kinetic study for other stages of mass loss.

scholarly journals PENGEMBANGAN BAHAN AJAR KIMIA RINTISAN SMA BERTARAF INTERNASIONAL KELAS XI MATERI LAJU REAKSI

2012 ◽  
Vol 13 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Inova Putri Carera ◽  
I Wayan Dasna
Keyword(s):  
High School ◽  
High School Students ◽  
Reaction Mechanism ◽  
Reaction Rate ◽  
Reaction Order ◽  
Average Score ◽  
School Students ◽  
Factors Affecting ◽  
Rate Law

This study was aimed to develop teaching materials about chemical reaction rate which covered materials adapted to A-Level High School students of grade XI in Pioneer International Standard High School (RSMA-BI). The developmental research was adopting the instructional development model 4D which include four stages of development, namely define, design, develop, and disseminate. Instructional materials were written in English consist of seven topics titled: Reaction Rate Concept, The Exchange's Expressions, Rate Law and Reaction Order, Experimental Determination of a Rate Law, Reaction Mechanism, Theories of Reaction Rate, Factors Affecting Reaction Rate. Results of content validation from content experts obtained the average score of 3. 56 of 14 range of scores which means valid / good / decent. Test limited to high school students of RSBI obtained an average score of 3.35 (valid / good / decent). The results of the use of teaching materials obtained a score of 77.8 which is above the minimal passing grade (75). Therefore it can be concluded that the materials were feasible to be used in the classroom.Penelitian ini bertujuan untuk mengembangkan bahan ajar laju reaksi dengan cakupan materi yang disesuaikan dengan A-Level untuk siswa kelas XI Rintisan Sekolah Menengah Atas Bertaraf Internasional (RSMA-BI. Rancangan penelitian pengembangan mengadaptasi model pengembangan bahan ajar Model 4D yang meliputi empat tahap pengembangan, yaitu define, design, develop dan disseminate. Produk pengembangan adalah bahan ajar kimia RSMA-BI kelas XI materi laju reaksi yang ditulis dalam bahasa Inggris menggunakan pendekatan kontekstual. Bahan ajar terdiri atas empat bagian utama yaitu pendahuluan, materi, evaluasi dan penutup. Materi tersusun atas tujuh sub materi yaitu Reaction Rate Concept, The Rates Expressions, Rate Law and Reaction Order, Experimental Determination of a Rate Law, Reaction Mechanism, Theories of Reaction Rate, Factors Affecting Reaction Rate. Hasil validasi isi dari ahli materi diperoleh nilai rata-rata 3,56 dari rentang skor 1-4 dengan kriteria valid/baik/layak. Hasil uji terbatas pada siswa SMA RSBI diperoleh nilai rata-rata 3,35 dari rentang skor 1-4 dengan kriteria valid/baik/layak. Hasil uji penggunaan bahan ajar diperoleh skor sebesar 77,8. Skor ini diatas SKM (Skor Kelulusan Minimal) yaitu 75 sehingga dapat disimpulkan bahwa bahan ajar telah layak dan dapat digunakan dalam pembelajaran di kelas.

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