scholarly journals The kinetics of the reaction between hydrogen and nitrous oxide III—Effect of oxygen

1934 ◽  
Vol 146 (859) ◽  
pp. 760-775 ◽  
Keyword(s):  
Nitrous Oxide ◽  
Chain Length ◽  
Thermal Reactions ◽  
Explosion Limits ◽  
Feature Characteristic ◽  
One Step ◽  
Effect Of Oxygen ◽  
Kinetics Of

One of the most striking dissimilarities between the hydrogen-oxygen and hydrogen-nitrous oxide reactions is the absence in the latter of sharp explosion limits, a feature characteristic of the former. Another important difference is that propagation of chains in the H 2 -N 2 O mixtures is rather less easy than in H 2 -O 2 , for the photochemical chain length is smaller for H 2 -N 2 O than for H 2 -O 2 at the same temperatures and pressures (see below). It has, however been postulated that the carriers in the two reactions are identical and that at least one step, viz., OH+H 2 →H 2 O+H, is common to both reactions. The differences in the propagation factors would therefore be due to these reactions H+N 2 O=OH+N 2 and H+H 2 +O 2 = OH+H 2 O, or H+O 2 = HO 2 HO 2 +H 2 = OH + H 2 O. It may be anticipated that termination processes will be somewhat similar, and consequently the observed differences in the thermal reactions will also be partly due to initiation reactions.

Circular dichroism and infrared study of β-turn formation in repeat peptides of elastin

1987 ◽  
Vol 52 (5) ◽  
pp. 1356-1361
Author(s):  
S. Abdel Rahman ◽  
M. Elsafty ◽  
A. Hattaba
Keyword(s):  
Circular Dichroism ◽  
Solid State ◽  
Ir Spectra ◽  
Chain Length ◽  
Room Temperature ◽  
Infrared Study ◽  
Feature Characteristic ◽  
C 50 ◽  
The Stability ◽  
Circular Dichroïsm

The conformation of elastin-like peptides Boc-Ala-Pro-Gly-Val-APEGM, Boc-Ala-Pro-Gly-Val-Gly-Val-APEGM, Boc-Ala-Pro-Gly-Val-Ala-Pro-Gly-Val-Gly-Val-APEGM, Boc-Ala-Pro-Gly-Val-Gly-Val-Ala-Pro-Gly-Val-Gly-Val-APEGM were examined in solution using circular dichroism at 30 °C, 50 °C, and 70 °C and in solid state by IR at room temperature. The studies show that the β-turn is a significant conformational feature for peptides under investigation in solution at 30 °C and 50 °C, but at 70 °C the tetra, hexa, and decapeptides show the CD feature characteristic of the β-structure while the dodecapeptide spectra show the presence of β-turn which indicates the stability of the β-turn at this chain length. The IR spectra show that in the solid state at room temperature all investigated peptides assume essentially a β-turn except the tetrapeptide which present evidence of antiparallel β-structure. The β-turn contribution in the IR spectra increases with the increase of the chain length of the peptide.

THE KINETICS OF THE THERMAL REACTIONS OF ETHYLENE OXIDE

1963 ◽  
Vol 41 (12) ◽  
pp. 2956-2961 ◽  
Author(s):  
M. Lynne Neufeld ◽  
Arthur T. Blades
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Ethylene Oxide ◽  
Thermal Reactions ◽  
Kinetics Of

The thermal reactions of ethylene oxide in the presence of an excess of propylene have been studied as a function of pressure and it has been found that there are two sets of products, acetaldehyde and free radicals, presumably methyl and formyl. These products are believed to arise from an excited acetaldehyde intermediate. Some evidence has been obtained for the occurrence of a surface-catalyzed rearrangement to acetaldehyde but the free radical products are uninfluenced by surface.

scholarly journals Determination of Dental Adhesive Composition throughout Solvent Drying and Polymerization Using ATR–FTIR Spectroscopy

Polymers ◽  
2021 ◽  
Vol 13 (22) ◽  
pp. 3886
Author(s):  
Arwa Almusa ◽  
António H.S. Delgado ◽  
Paul Ashley ◽  
Anne M. Young
Keyword(s):  
Light Exposure ◽  
Light Emitting Diode ◽  
Attenuated Total Reflectance ◽  
Drying Time ◽  
Light Emitting ◽  
Spectral Changes ◽  
One Step ◽  
Urethane Dimethacrylate ◽  
Kinetics Of

The of this study aim was to develop a rapid method to determine the chemical composition, solvent evaporation rates, and polymerization kinetics of dental adhesives. Single-component, acetone-containing adhesives One-Step (OS; Bisco, USA), Optibond Universal (OU; Kerr, USA), and G-Bond (GB; GC, Japan) were studied. Filler levels were determined gravimetrically. Monomers and solvents were quantified by comparing their pure Attenuated Total Reflectance-Fourier Transform Infra-Red (ATR–FTIR) spectra, summed in different ratios, with those of the adhesives. Spectral changes at 37 °C, throughout passive evaporation for 5 min, then polymerisation initiated by 20 s, and blue light emitting diode (LED) (600 mW/cm2) exposure (n = 3) were determined. Evaporation and polymerisation extent versus time and final changes were calculated using acetone (1360 cm−1) and methacrylate (1320 cm−1) peaks. OS, OU, and GB filler contents were 0, 9.6, and 5.3%. FTIR suggested OS and OU were Bis-GMA based, GB was urethane dimethacrylate (UDMA) based, and that each had a different diluent and acidic monomers and possible UDMA/acetone interactions. Furthermore, initial acetone percentages were all 40−50%. After 5 min drying, they were 0% for OS and OU but 10% for GB. Whilst OS had no water, that in OU declined from 18 to 10% and in GB from 25 to 20% upon drying. Evaporation extents were 50% of final levels at 23, 25, and 113 s for OS, OU, and GB, respectively. Polymerisation extents were all 50 and 80% of final levels before 10 and at 20 s of light exposure, respectively. Final monomer polymerisation levels were 68, 69, and 88% for OS, OU, and GB, respectively. An appreciation of initial and final adhesive chemistry is important for understanding the properties. The rates of evaporation and polymerisation provide indications of relative required drying and light cure times. UDMA/acetone interactions might explain the considerably greater drying time of GB.

The Kinetics of Free-Radical Polymerization: Fundamental Aspects

2002 ◽  
Vol 55 (7) ◽  
pp. 399 ◽  
Author(s):  
G. T. Russell
Keyword(s):  
Molecular Weight ◽  
Steady State ◽  
Free Radical ◽  
Radical Polymerization ◽  
Chain Length ◽  
Free Radical Polymerization ◽  
Length Dependence ◽  
Model Independent ◽  
Living Free Radical Polymerization ◽  
Kinetics Of

Some fundamental aspects of the kinetics of free-radical polymerization are reviewed. So-called classical results for rate and molecular-weight distribution are first of all presented. It is shown how this approach can be built upon when chain-length-dependent termination is allowed, which it always should be. Various termination models are considered, and it is illustrated that although the models are different, rather remarkably they give common, model-independent behaviour. Some leading experimental results regarding the chain-length dependence of termination are summarized, before the chain-length dependence of other reactivities, the variation of reactivities with conversion, and non-steady state experiments are briefly discussed. Finally, living free-radical polymerization as effected by a reversible termination agent is considered. An outline of the kinetics of these systems is given, with the oft-neglected importance of conventional termination being stressed.

One‐step synthesis of amino‐functionalised magnetic mesoporous silica and synergistic adsorption kinetics of tetracycline and copper

2018 ◽  
Vol 13 (8) ◽  
pp. 1219-1223 ◽  
Author(s):  
Mancheng Zhang ◽  
Wei Wang ◽  
Zengyin Zhu ◽  
Changsheng Qu ◽  
Qing Zhou ◽  
...  
Keyword(s):  
Mesoporous Silica ◽  
Adsorption Kinetics ◽  
One Step ◽  
Kinetics Of ◽  
Magnetic Mesoporous Silica

scholarly journals A novel nano zero-valent iron@chitosan for effective removal of Microcystin-LR: Kinetics and adsorption mechanism

2018 ◽  
Vol 53 ◽  
pp. 04004 ◽  
Author(s):  
Xiaofan Yang ◽  
Xueyu Wei ◽  
Xiaoping Xu ◽  
Zhigang Liu
Keyword(s):  
Low Cost ◽  
Spherical Shape ◽  
Step Method ◽  
Variable Parameters ◽  
Transmission Electron ◽  
Effective Removal ◽  
Initial Ph ◽  
Nano Zero Valent Iron ◽  
One Step ◽  
Kinetics Of

Microcystin-LR (MC-LR) is one of the most notorious toxins liberated from cyanobacteria in drinking water sources. In this study, a skillful method access to new nanozero-valent iron @chitosan (nZVIMC) was synthesized by a facile one step method. The as-prepared nZVIMC was employed as an adsorbent for the effective removal MC-LR from aqueous solution. Transmission electron microscopy (TEM) demonstrates that nZVIMC is in quasi-spherical shape with size of around 50 nm, effect of variable parameters such as pH, contact time, initial concentration of MC-LR and adsorption properties of nZVIMC on MC-LR was further investigated. Scanning electron microscope (SEM) reveals that the particles are nearly spherical in shape with agglomeration. The results indicated that good adsorption performance was achieved at an initial pH of 5. The adsorption kinetics of nZVIMC was better fitted by pseudo-secondorder kinetics. The adsorption isotherm data was fitted well to Langmuir isotherm and then to Freundlich model, with an adsorption capacity of 68.9 mg/g at 300K. Thus, we believe that nZVIMC can be used as a low cost material for efficient removal of MC-LR from water.

Kinetics of the pyrolysis of propylene. Part I

1970 ◽  
Vol 48 (2) ◽  
pp. 317-325 ◽  
Author(s):  
M. Simon ◽  
M. H. Back
Keyword(s):  
Molecular Weight ◽  
Chain Length ◽  
Sharp Increase ◽  
Pressure Range ◽  
Pressure Change ◽  
Short Chain ◽  
Short Chain Length ◽  
Radical Process ◽  
Initiation Step ◽  
Kinetics Of

The kinetics of the pyrolysis of propylene have been studied over the temperature range 743–873 °K and the pressure range 200–600 Torr. At the lower temperatures initial rates of formation of methane, propane, and C6 products were measured and shown to be formed by a radical process of very short chain length. The orders and activation energies of the rates were consistent with the occurrence of the bimolecular initiation step[Formula: see text]Measurement of the pressure change showed that products of molecular weight higher than C7 and not measured by the analysis were formed in the initial stages of the reaction at the lower temperatures. As these higher molecular weight compounds, which are more unstable than propylene, accumulated in the system their dissociation increased the concentration of radicals and caused a sharp increase in the rates of formation of the lower molecular weight stable products.

scholarly journals DECOMPOSITION KINETICS OF NITROUS OXIDE ON MANGANESE DIOXIDE

1974 ◽  
Vol 6 (5) ◽  
pp. 438-442 ◽  
Author(s):  
MASAYOSHI KOBAYASHI ◽  
HARUO KOBAYASHI
Keyword(s):  
Nitrous Oxide ◽  
Manganese Dioxide ◽  
Decomposition Kinetics ◽  
Kinetics Of
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