On Microfaceting Instability of Pt(110) Under Catalytic Oxidation of Adsorbed Co

1992 ◽  
Vol 263 ◽  
Author(s):  
M. Papoular
Keyword(s):  
Catalytic Oxidation ◽  
Oxidation Reaction ◽  
Nucleation And Growth ◽  
Point Of View ◽  
Momentum Balance ◽  
Layer By Layer ◽  
Adsorption Of Co ◽  
Specific Temperature ◽  
Energy And Momentum ◽  
Sawtooth Profile

ABSTRACTAs demonstrated by recent STM [1] and LEED [2] experiments the platinum (110) surface undergoes, at carbon monoxide submonolayer coverages, a phase transition from the 1 x 2 “missing-row” (reconstructed) state to the 1 x 1(bulk-like) state under specific temperature and partial-pressure conditions. The catalytic oxidation reaction CO + 1/2 → CO2 drives a microfaceting instability [3] [4] of the Pt(110) surface which ends up in a regular sawtooth profile with a period ≈ 200 Å, along the [110] direction.We introduce the idea that the rather extensive Pt mass transport, as involved in the process, could be energetically assisted by the reaction itself. Energy and momentum-balance considerations lead us to expect an energy ≲ 0.5 eV to be transferrable to thesubstrate. This should efficiently contribute to initiating the “scraping”process that leads to the microfaceted pattern.A simple model for nucleation and growth of facets is presented (see ref. 5), yielding characteristic times of order minutes (at T = 500 K), in fair agreement with experiment.Independently of the structural/catalytic problem, adsorption of CO at submonolayer coverages on, e.g., Pt(110) might be of interest from a surfactantphysics point of view (see ref. 6 for a very recent study on layer-by-layer homoepitaxial metal growth).

Rapid Thermal Processing-Based Heteroepitaxy: Material and Device Challenges

1995 ◽  
Vol 387 ◽  
Author(s):  
J. L. Hoyt ◽  
P. Kuo ◽  
K. Rim ◽  
J. J. Welser ◽  
R. M. Emerson ◽  
...  
Keyword(s):  
Thermal Processing ◽  
Rapid Thermal Processing ◽  
Atomic Layer ◽  
Layer Growth ◽  
Point Of View ◽  
Atomic Layer Epitaxy ◽  
Future Research ◽  
Layer By Layer ◽  
Limited Growth ◽  
Measurement And Control

AbstractMaterial and device challenges for Rapid Thermal Processing (RTP) of heterostructures are discussed, focusing on RTP-based epitaxy in the Si/Si1−xGex system. While RTP-based heteroepitaxy offers enhanced processing flexibility, it also poses significant challenges for temperature measurement and control. Several examples of Si/Si1−xGex device structures are discussed from the point of view of the sensitivity of device parameters to variations in layer thickness and composition. The measured growth kinetics for Si and Si1−xGex are then used to estimate growth temperature tolerances for these structures. Demanding applications are expected to require temperature control and uniformity to within 0.5°C.Future research challenges include the fabrication of structures with monolayer thickness control using self-limited growth techniques. Atomic layer epitaxy (ALE) is a well-known example of such a growth technique. In ALE, the wafer is cyclically exposed to different reactants, to achieve layer-by-layer growth. An RTP-based atomic layer epitaxy process, and its application to the growth of CdTe films, is briefly discussed. The extension to Column IV alloys follows readily. The RTP-based process enables self-limited growth for precursor combinations for which isothermal ALE is not feasible.

Kinetic Model of the 1,2-Propanediol Oxidation Reaction in the Presence of 3wt%Pd/α-Al2O3 Catalyst

2021 ◽  
Vol 903 ◽  
pp. 143-148
Author(s):  
Svetlana Cornaja ◽  
Svetlana Zhizhkuna ◽  
Jevgenija Vladiko
Keyword(s):  
Activation Energy ◽  
Lactic Acid ◽  
Kinetic Model ◽  
Catalytic Oxidation ◽  
Molecular Oxygen ◽  
Oxidation Reaction ◽  
Main Product ◽  
Oxidation Process ◽  
Water Solution ◽  
Reaction Conditions

Supported 3wt%Pd/α-Al₂O₃ catalyst was tested in selective oxidation of 1,2-propanediol by molecular oxygen. It was found that the catalyst is active in an alkaline water solution. Lactic acid was obtained as the main product of the reaction. Influence of different reaction conditions on 1,2-PDO conversion and oxidation process selectivity was studied. Partial kinetic orders of the reaction with respect to 1,2-propanediol, c0(NaOH), p(O2), n(1,2-PDO)/n(Pd)) were determined and an experimental kinetic model of the catalytic oxidation reaction was obtained. Activation energy of the process was calculated and was found to be about 53 ± 5 kJ/mol.

Estimating Zonal Flow Contributions in Deep Water Assets From Pressure and Temperature Data

2017 ◽  
Author(s):  
A. Rashid Hasan ◽  
Rayhana N. Sohel ◽  
Xiaowei Wang
Keyword(s):  
Turbulent Flows ◽  
Deep Water ◽  
Fluid Pressure ◽  
Zonal Flow ◽  
Temperature Data ◽  
Sensitivity Analyses ◽  
Momentum Balance ◽  
Flow Profile ◽  
Flowing Fluid ◽  
Energy And Momentum

Producing hydrocarbon from deep water assets is extremely challenging and expensive. A good estimate of rates from multiple pay zones is essential for well monitoring, surveillance, and workover decisions. Such information can be gleaned from flowing fluid pressure and temperature; deep-water wells are often well instrumented that offers such data on a continuous basis. In this study a model is presented that estimates zonal flow contributions based on energy and momentum balances. Kinetic and heat energy coming from the reservoir fluid to the production tubing is accounted for in the model. The momentum balance for wellbore takes into account differing flow profile in laminar and turbulent flows. In addition, when sandface temperature data are not available, a recently developed analytical model to estimate the effect of Joule-Thompson expansion on sandface temperature was used to estimate sandface temperature from reservoir temperature. The model developed can be applied to any reservoir with multiple pay zones and is especially useful for deep-water assets where production logging is practically impossible. Available field data for multiphase flow was used to validate the model. Sensitivity analyses were performed that showed accurate temperature data is essential for the model to estimate zonal contribution accurately.

scholarly journals Nature itself in a mirror space–time

2015 ◽  
Vol 93 (10) ◽  
pp. 1005-1008 ◽  
Author(s):  
Rasulkhozha S. Sharafiddinov
Keyword(s):  
Dirac Equation ◽  
Minkowski Space ◽  
Space Time ◽  
Point Of View ◽  
Classical Solutions ◽  
Left Handed ◽  
Minkowski Space Time ◽  
Energy And Momentum ◽  
The Right ◽  
Structure Of Matter

The unity of the structure of matter fields with flavor symmetry laws involves that the left-handed neutrino in the field of emission can be converted into a right-handed one and vice versa. These transitions together with classical solutions of the Dirac equation testify in favor of the unidenticality of masses, energies, and momenta of neutrinos of the different components. If we recognize such a difference in masses, energies, and momenta, accepting its ideas about that the left-handed neutrino and the right-handed antineutrino refer to long-lived leptons, and the right-handed neutrino and the left-handed antineutrino are short-lived fermions, we would follow the mathematical logic of the Dirac equation in the presence of the flavor symmetrical mass, energy, and momentum matrices. From their point of view, nature itself separates Minkowski space into left and right spaces concerning a certain middle dynamical line. Thereby, it characterizes any Dirac particle both by left and by right space–time coordinates. It is not excluded therefore that whatever the main purposes each of earlier experiments about sterile neutrinos, namely, about right-handed short-lived neutrinos may serve as the source of facts confirming the existence of a mirror Minkowski space–time.

scholarly journals Nucleation and growth controlled reduced graphene oxide–supported palladium electrocatalysts for methanol oxidation reaction

2019 ◽  
Vol 9 ◽  
pp. 184798041982717 ◽  
Author(s):  
Jen Chao Ng ◽  
Chou Yong Tan ◽  
Boon Hoong Ong ◽  
Atsunori Matsuda ◽  
Wan Jefrey Basirun ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Reduced Graphene Oxide ◽  
Methanol Oxidation ◽  
Oxidation Reaction ◽  
Direct Methanol Fuel Cells ◽  
Precursor Solution ◽  
Nucleation And Growth ◽  
Methanol Oxidation Reaction ◽  
Reduced Graphene ◽  
Supported Palladium

In spite of advantages of direct methanol fuel cells, low methanol oxidation reaction and fuel crossover from anode to cathode, there remains a challenge that inhibits it from being commercialized. Active electrocatalysts are in high demand to promote the methanol oxidation reaction. The methanol reached at the anode can be immediately reacted, and thus, less methanol to cross to the cathode. The performance of electrocatalysts can be significantly influenced by varying the concentration of precursor solution. Theoretically, concentrated precursor solution facilitates rapid nucleation and growth; diluted precursor solution causes slow nucleation and growth. Rapid nucleation and slow growth have positive effect on the size of electrocatalysts which plays a significant role in the catalytic performance. Upon the addition of appropriate concentration of graphene oxide, the graphene oxide was reported to have stabilizing effect towards the catalyst nanoparticles. This work synthesized reduced graphene oxide–supported palladium electrocatalysts at different concentrations (0.5, 1.0, 2.0, 3.0 and 4.0 mg mL−1) with fixed volume and mass ratio of reduced graphene oxide to palladium by microwave-assisted reduction method. Results showed that reduced graphene oxide–supported palladium synthesized at a concentration of 1.0 mg mL−1 gave the best methanol oxidation reactivity (405.37 mA mg−1) and largest electrochemical active surface area (83.57 m2 g−1).

Conception and numerical simulation of heat and mass transfer in a solid state hydrogen storage reactor

2019 ◽  
Vol 87 (2) ◽  
pp. 20902 ◽  
Author(s):  
Amine Alaoui-Belghiti ◽  
Mourad Rkhis ◽  
Said Laasri ◽  
Abdelowahed Hajjaji ◽  
Mohamed Eljouad ◽  
...  
Keyword(s):  
Energy Storage ◽  
Solid State ◽  
Hydrogen Storage ◽  
Physical Phenomenon ◽  
Point Of View ◽  
Momentum Balance ◽  
Bed Temperature ◽  
Hydrogen Supply ◽  
Hydrogen Storage Performance ◽  
The Impact

Nowadays energy storage seems to be a vital point in any new energy paradigm. It has become an important and strategic issue, to ensure the energetic sufficiency of humanity. Indeed, hydrogen storage in solids has been proved and revealed as clean and efficient energy storage. Moreover, it can be thought as a seriously considered solution to enable renewable energy to be a part of our quotidian life. To achieve storing hydrogen in solid form, the present study aimed to concepts and simulates a solid-state hydrogen storage reactor (tank). An investigation of the parameters influencing the hydrogen storage performance is carried out. Meanwhile, to understand the physical phenomenon taking place during the storage of hydrogen, a 2D numerical modelling for a metal hydrides-based in hydrogen reactor is presented. A strong coupling between energy balance, kinetic law, as well as a mass momentum balance at sorbent bed temperature under a non-uniform pressure was resolved based on finite element method. The temporal evolutions of pressure, the raising temperature in the bed during the hydriding process as well as the impact of the hydrogen supply pressure within the tank are analysed and validated by comparison with the experimental work in literature, a good agreement is obtained. From an industrial point of view, this study can be used to design and manufacture an optimal solid-state hydrogen storage reactor.

The Stimulated Crystallization of Amorphous SiO2 Films on Si Substrates Induced By Laser and Thermal Treatments

1988 ◽  
Vol 116 ◽  
Author(s):  
Felix Edelman
Keyword(s):  
Incubation Time ◽  
Crystallization Process ◽  
Laser Flash ◽  
Nucleation And Growth ◽  
Point Of View ◽  
Growth Theory ◽  
Thermal Treatments ◽  
Kinetic Characteristics ◽  
Amorphous Sio2 ◽  
Si Substrates

AbstractThe transformation of amorphous to crystal (a-c) structure of Si02 layers, thermally grown on both (100) and (111) Si substrates, was carried out by CO2 laser, flash-lamp, and furnace heat: treatments. All the treatments resulted in S102 crystallization according to two different mechanisms: normal and self-sustained growth processes. The kinetic characteristics of the S102 crystallization process such as incubation time, rates of nucleation and growth, and the microstructure of the Si-Si02 interface were investigated and are discussed from the point of view of growth theory. The a-c transformation in Si3N4 and SixOyNz films on Si substrates is also discussed.

scholarly journals Research into the reaction process and the effect of reaction conditions on the simultaneous removal of H2S, COS and CS2 at low temperature

RSC Advances ◽  
2018 ◽  
Vol 8 (13) ◽  
pp. 6996-7004 ◽  
Author(s):  
Xin Sun ◽  
Haotian Ruan ◽  
Xin Song ◽  
Lina Sun ◽  
Kai Li ◽  
...  
Keyword(s):  
Low Temperature ◽  
Catalytic Oxidation ◽  
Oxidation Reaction ◽  
Reaction Process ◽  
Hydrolysis Reaction ◽  
Simultaneous Removal ◽  
Catalytic Hydrolysis ◽  
Reaction Conditions ◽  
Removal Processes

The removal processes of COS, CS2 and H2S could be divided into two parts: a catalytic hydrolysis reaction and a catalytic oxidation reaction.

scholarly journals CONTRIBUTIONS TO THE MARINE PROPELLERS HYDRODYNAMIC DESIGN

2014 ◽  
Vol 13 (2) ◽  
pp. 41
Author(s):  
B. I. Favacho ◽  
J. R. P. Vaz ◽  
A. L. A. Mesquita
Keyword(s):  
Control Volume ◽  
Computational Cost ◽  
Momentum Balance ◽  
Marine Propellers ◽  
Energy And Momentum ◽  
Thrust And Torque ◽  
The Mathematical Model ◽  
Low Computational Cost ◽  
Bem Theory ◽  
Good Agreement

The navigation in Amazon region is very important due to the length of navigable rivers and the lack of alternative road network, as well as being a form of transportation costless for the flow of agricultural and manufacturing production. This kind of transportation present social, economic and technological importance for this region. Thus, this work objective to develop a mathematical approach for the marine propellers design, using a formulation for chord and pitch angle optimization, taken into account the equations of mass, energy and momentum balance for the theoretical calculation of thrust and torque relationships on an annular control volume, ie, the mathematical model is based in the Blade Element Momentum (BEM) theory. The proposed hydrodynamic model present low computational cost and it is easy to implement. The results are compared with classical Glauert's theory and the experimental data of the Wageningen B3-50 propeller, presenting good agreement.

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