Papers by Keyword: Reaction Kinetics

Abstract: Investigation of the reaction kinetics between Ni film and 4H-SiC substrate at temperatures which are usually used for ohmic contacts formation provides valuable insights into the studies on fundamental properties of ohmic contacts to 4H-SiC, which are limiting the switching speed, energy efficiency and high-temperature thermal stability of SiC MOSFETs. High Resolution Scanning Electron Microscope (HRSEM) and Raman spectroscopy were used to elaborately characterize the interfacial reaction products under various annealing conditions and to assess the thicknesses of reaction diffusion layers. The square of reaction layer thicknesses versus time followed parabolic law and the apparent active energy of interfacial reaction was derived as 1.5 eV (145 kJ/mol). For Raman spectra, the intensity ratio of two Raman peaks for each nickel silicide detected varied monotonically with temperature in the same trend, indicating that crystal quality of nickel silicide film was improved with annealing temperature rising at micron scale. The red-shift of Ni₂Si peak locations at about 140 cm^-1 with temperature was suggestive of the polycrystalline Ni₂Si film with weaker stress/strain status. Moreover, the in-plane size of graphite cluster aggregating at top surface increased with annealing temperature rising until about 1000°C, which is detrimental to the ohmic contacts from the perspective of device applications.

Abstract: Microfluidic chip injection photocuring is a new method for microfluidic chip fabrication. The accuracy of microfluidic chip photocuring has an important impact on the reliability of microfluidic chip. The reaction rate of photocuring system directly affects the final quality and efficiency of microfluidic chip. The rapid reaction rate of photocuring system will lead to poor feeding effect of the reaction system. The forming accuracy is affected, and the reaction rate is too slow, which will increase the forming time and affect the forming efficiency. In this paper, the conversion rate and reaction rate of different active monomers and oligomers used in the formulation system of microfluidic chips were measured on-line. The photocuring reaction kinetics of microfluidic chips was studied, and the influence of the formulation system on the photocuring reaction was explored, which laid a foundation for optimizing the formulation of microfluidic chips.

Abstract: Reactive multilayer thin films are well-defined heterogeneous nanostructured energetic materials which can release chemical energy through a self-sustainable reaction. They have attracted intense interests due to potential applications in diverse fields such as joining, igniters, and high energy density power sources. In this paper, Ti/Ni, Ti/Al and Ni/Al multilayer films were prepared by magnetron sputtering. The reaction kinetics, microstructure and phase variation of these free-standing films are comparatively investigated. During slow heat reaction, the reaction products of reactive multilayer Ti/Ni nanofoils change from B2-TiNi austenite phase into TiNi₃, illustrating an evolution of the phase transformation during reaction. These intermediate phases are also identified by slow heating and quenching. The fast speed imaging exhibits that the front speed is 0.47m/s, 0.8m/s and 3m/s respectively for as-deposited Ti/Ni, Ti/Al, and Ni/Al films. Differential thermal analysis yields that the corresponding releasing heat is 551.44 J/g, 434.18 J/g, and 562.5 J/g for these three composites. The theoretical minimum multilayer thickness for melting a tin solder layer has been calculated on the base of these characterizations, which proved the application potential of joining using the as-deposited film.

Abstract: In semiconductor manufacturing of 3-D nano-structures, modified kinetics have been encountered for the aqueous chemical etching of thin films in nano-confined spaces. A popular explanation relies on changes in reactant concentration from the overlap of electrostatic double layers (EDL) on opposite walls of the nano-structures. In this study, the cycloaddition of dibenzylcyclooctyne-PEG3-alcohol (DBCO) to a linear azide-terminated SAM was performed in nanochannels of width varying from 62 to 32 nm. ATR-FTIR was used to monitor the reaction kinetics, characterize water structuring and determine the pH in nanochannels. Reaction kinetics were slower in nanochannels as compared to a planar surface, while pH shifts were observed in absence of EDL overlap, with a significant influence of channel width. Actually only the overall decrease in reaction rate could be explained by EDL overlap. The discussion shows that the water structuring measured in nanochannels may play a significant role in the observed phenomena.

Abstract: Application of various pozzolanic materials is the current approach to obtain suitable environmental, economic and durability parameters of composites, in which they are used. Considerable interest is focused on the possibilities of finely ground ceramic powder (CP) exhibiting pozzolanic activity. Present paper is aimed at the experimental study on the monitoring of reaction kinetics in lime-ceramic powder system (1:1). Ceramic powders with controlled grading were used. Reaction capacity was assessed in time by means of thermogravimetry. The dominant effect of the finest fractions (up to 0.030 mm) on the pozzolanic reaction was proved; coarser fractions of used CP exhibited approximately the half reaction efficiency after 28 days of curing.

Abstract: In this study, esterification of lactic acid and ethanol to produce ethyl lactate using different cation-exchange resin catalysts was performed at 100 °C. The catalysts used for the esterification process were amberlyst 16 and dowex 50W8x cation-exchange resins. Two simplified mechanisms based on Langmuir-Hinshelwood model were employed to describe the components that adsorbed most on the surface of the catalysts. Fourier Transform Infrared (Nicolet iS10 FTIR) was employed to verify the rationality of the mechanisms. FTIR of the esterification product reflected C=O, H=O and C=C bonds on the spectra confirming water and ethanol as the most adsorbed components. The kinetic study of the retention time and the peak areas of the esterification produced with the different catalysts were compared using an autosampler gas chromatography/mass spectrometry (autosampler GC-MS). The chromatogram of the esterification product catalysed by amberlyst 16 showed a faster elution at 1.503 mins with the peak area of 1229816403 m² in contrast to the dowex 50W8x. The BET surface area and BJH pore size distribution of the resin catalysts were determined using liquid nitrogen adsorption (Quantachrome, 2013) at 77 K. The BET surface area results of amberlyst 16 resin catalysts was found to be 1.659m²/g compared to 0.1m²/g for the dowex 50W8x. The BJH results of the catalysts exhibited a type IV isotherm with hysteresis confirming that the materials were mesoporous with pore size in the region of 2 – 50 nm.

Abstract: Nowadays hydrogen as an important source of energy is still produced from fossil fuel processing largely, hence the separation of hydrogen from the gas mixture with high recovery ratio and purity arises as an important issue. In this paper we proposed a hydrogen recovery/production process from half-coke oven gas, and the material LaNi_4.3Al_0.7 was considered for use due to its low plateau pressure and good resistance to impurities. We use a Sieverts type volumetric apparatus to investigate the material properties,including P-C-T properties and hydriding/ dehydriding kinetics under different conditions. Based on the results obtained, the feasibility of using the material for gas separation purpose was discussed.Keywords: Gas separation; metal hydride; reaction kinetics; P-C-T properties; Sieverts method

Abstract: With Raney nickel catalyst and aniline solvent, the reaction kinetics of catalytic hydrogenation of isophthalonitrile (IPN) for meta-xylenediamine (MXDA) preparation is studied in this paper. The experiment is conducted in a 1L büchiglas high-pressure hydrogenation reactor under the condition of the reaction temperature (100°C) and the reaction pressure (35 bar). The results shows that the kinetics equation proposed in this paper can be used to predict the response speed of IPN accurately.

Abstract: The combustion characteristic and kinetic analysis of Malaysian poultry processing dewatered sludge (PPDS) from two different origins, namely as PPDS 1 and PPDS 2 using Thermogravimetric analysis (TGA) were examined. The non-isothermal step was practiced under oxidative atmosphere during the investigation. The temperature was ramped from 30oC to 1000oC at four different heating rates to allow the calculation of kinetic analysis parameter i.e. activation energy. Derivative thermogravimetric (DTG) curves for both samples resulted from TGA shows 3 different peaks. Calculation of apparent activation energy was adopted using iso-conventional model free method. The different of activation energy value embedded in each samples was due to the non-similarity of its fuel characteristic and combustion behavior.

Abstract: In this work, the ion exchange resin catalyst named D072 were used in the hydrolysis of a methyl acrylate to acrylic acid and methanol firstlyand chemical equilibrium would be achieved during the process of the reversible reaction system. The influences of parameters such as dosage of catalyst, initial reactants molar ratio and reaction temperature were investigated. Meanwhile, the reusability of cation-exchange resin was studied, and no phenomenon of deactivation was found with using of reused catalyst. Moreover, the experimental data were analyzed by the pseudo-homogeneous (PH) model and the hydrolysis dynamics equation of methyl acrylate was obtained and found that the activation energy of the reaction was 118.37 KJ/mol in the presence of D072. Based on the result, high energy would be needed to the hydrolysis of methyl acrylate in using D072 resin as catalyst.