The gas phase ion chemistry and proton affinity of hexamethyldisiloxane studied by high pressure mass spectrometry

1987 ◽  
Vol 65 (10) ◽  
pp. 2454-2460 ◽  
Author(s):  
Xiaoping Li ◽  
John Alfred Stone
Keyword(s):  
Proton Transfer ◽  
Proton Affinity ◽  
Rate Constants ◽  
Negative Temperature ◽  
Positive Temperature Coefficient ◽  
Ion Source ◽  
Positive Temperature ◽  
Ion Chemistry ◽  
Gas Phase Ion Chemistry ◽  
Proton Transfer Reactions

The ion chemistry of hexamethyldisiloxane ((CH3)3SiOSi(CH3)3, HMDS) has been studied under chemical ionization conditions at ion source temperatures of 300–600 K and pressures of 2–4 Torr. Highly exothermic proton transfer to HMDS from CH5+ and C2H5+ leads mainly to loss of CH3 but with decreasing exothermicity the yield of HMDSH+ increases such that transfer from t-C4H9+ (ΔH0 = −7.5 kcal mol−1) yields almost exclusively HMDSH+. Although HMDSH+ transfers (CH3)3Si+ rather than a proton to most reference bases, the proton affinity of HMDS has been determined from van't Hoff plots using the equilibrium method with methylaromatics as reference bases. PA(HMDS) = 203.4 kcal mol−1 is in excellent accord with an earlier estimate of 203 kcal mol−1 obtained by the bracketing method. The rate constants for these proton transfer reactions show very large negative temperature coefficients in the exothermic directions which are consistent with the reactions of charge delocalized ions and/or reactions in which considerable loss of rotational freedom occurs along the reaction coordinate. The rate constants in the reverse directions have a positive temperature coefficient only when the endothermicity is significant (>2.5 kcal mol−1).

Ethyl cation transfer from diethylchloronium to alkyl aromatics studied by high pressure mass spectrometry

1988 ◽  
Vol 66 (5) ◽  
pp. 1239-1248
Author(s):  
Peggy Jane Mathews ◽  
John A. Stone
Keyword(s):  
High Pressure ◽  
Temperature Coefficient ◽  
Rate Constants ◽  
Negative Temperature ◽  
Ion Source ◽  
Positive Temperature ◽  
Reaction Rate Constants ◽  
Benzene Toluene ◽  
Double Well Potential ◽  
Ethyl Cation

Diethylchloronium (C2H5)2Cl+) has been formed in a high pressure (2–4 Torr) ion source using a C2H5Cl/CH4 mixture. (C2H5)2Cl+ reacts with C2H5Cl (Ea = 22 ± 2 kcal mol−1) at temperatures above 500 K to give [Formula: see text]. The reaction of (C2H5)2Cl+ with B (B = benzene, toluene, isopropylbenzene, mesitylene) yields mainly C2H5B+ at temperatures below 500 K but BH+ is also formed at higher temperatures. The further reactions of C2H5B+ include proton transfer to B yielding BH+ (mesitylene), hydride transfer from B (isopropylbenzene), and reaction with C2H5Cl+ (C2H5)2B+ (toluene and benzene) and (C2H5)3B+ (benzene). The rate constants for the reaction (C2H5)2Cl+ + B → C2H5B+ + C2H5B+ + C2H5Cl increase in the order of increasing reaction exothermicity (mesitylene > isopropylbenzene > toluene > benzene). Mesitylene has a negative temperature coefficient, isopropylbenzene has no temperature coefficient, and toluene and benzene show positive temperature coefficients of reaction rate constants consistent with the double well potential theory for gas phase SN2 reactions.

Gas-phase proton-transfer reactions of the hydronium ion at 298 K

1979 ◽  
Vol 57 (12) ◽  
pp. 1518-1523 ◽  
Author(s):  
Gervase I. Mackay ◽  
Scott D. Tanner ◽  
Alan C. Hopkinson ◽  
Diethard K. Bohme
Keyword(s):  
Proton Transfer ◽  
Gas Phase ◽  
Rate Constants ◽  
Transfer Reactions ◽  
Flowing Afterglow ◽  
Hydronium Ion ◽  
Proton Transfer Reactions

Rate constants measured with the flowing afterglow technique at 298 ± 2 K are reported for the proton-transfer reactions of H3O+ with CH2O, CH3CHO, (CH3)2CO, HCOOH, CH3COOH, HCOOCH3, CH3OH, C2H5OH, (CH3)2O, and CH2CO. Dissociative proton-transfer was observed only with CH3COOH. The rate constants are compared with the predictions of various theories for ion–molecule collisions. The protonation is discussed in terms of the energetics and mechanisms of various modes of dissociation.

An experimental study of the reactivity and relative basicity of the methoxide anion in the gas phase at room temperature, and their perturbation by methanol solvation

1982 ◽  
Vol 60 (20) ◽  
pp. 2594-2605 ◽  
Author(s):  
Gervase I. Mackay ◽  
Asit B. Rakshit ◽  
Diethard K. Bohme
Keyword(s):  
Proton Transfer ◽  
Gas Phase ◽  
Rate Constants ◽  
Solvent Free ◽  
Transfer Reactions ◽  
Free Proton ◽  
Proton Transfer Reactions ◽  
Intrinsic Reactivity ◽  
Relative Acidity ◽  
Methoxide Anion

Flowing afterglow measurements at 296 ± 2 K are reported which explore three aspects of the gas-phase acid–base chemistry of the methoxide anion. Firstly, the intrinsic reactivity of this ion has been determined from measurements of rate constants for solvent-free proton-transfer reactions with molecules more acidic than methanol including CH2=C=CH2, C6H5CH3, C2H5OH, C2H2, CH3CN, CH3COCH3, CH3CHO, CH3NO2, and HCN. Secondly, equilibrium constant measurements have been performed for solvent-free proton-transfer reactions which provide a gas-phase scale of acidities for these molecules relative to the acidity of methanol. Finally, rate constants were measured for the reactions of these acids with methoxide ions solvated with up to three molecules of methanol. The results establish trends in reactivity as a function of step–wise solvation when relative acidity is preserved and when a reversal occurs in the relative acidity upon solvation.

Temperature Dependence of Impact Ionization Coefficients in 4H-SiC

2014 ◽  
Vol 778-780 ◽  
pp. 461-466 ◽  
Author(s):  
Hiroki Niwa ◽  
Jun Suda ◽  
Tsunenobu Kimoto
Keyword(s):  
Temperature Dependence ◽  
Temperature Coefficient ◽  
Breakdown Voltage ◽  
Elevated Temperatures ◽  
Phonon Scattering ◽  
Impact Ionization ◽  
Negative Temperature ◽  
Positive Temperature Coefficient ◽  
Positive Temperature ◽  
Ionization Coefficients

Impact ionization coefficients of 4H-SiC were measured at room temperature and at elevated temperatures up to 200°C. Photomultiplication measurement was done in two complementary photodiodes to measure the multiplication factors of holes (Mp) and electrons (Mn), and ionization coefficients were extracted. Calculated breakdown voltage using the obtained ionization coefficients showed good agreement with the measured values in this study, and also in other reported PiN diodes and MOSFETs. In high-temperature measurement, breakdown voltage exhibited a positive temperature coefficient and multiplication factors showed a negative temperature coefficient. Therefore, extracted ionization coefficient has decreased which can be explained by the increase of phonon scattering. The calculated temperature dependence of breakdown voltage agreed well with the measured values not only for the diodes in this study, but also in PiN diode in other literature.

Influence of CF on PTC Properties of LDPE/Carbon Fiber Composites

2014 ◽  
Vol 1056 ◽  
pp. 20-24 ◽  
Author(s):  
Wen Long Zhang ◽  
Yu Ping Wan ◽  
Ya Jie Dai ◽  
Yan Gao ◽  
Chen Wang ◽  
...  
Keyword(s):  
Carbon Fiber ◽  
Temperature Coefficient ◽  
Low Cost ◽  
Negative Temperature ◽  
Treatment Method ◽  
Positive Temperature Coefficient ◽  
Carbon Fiber Composites ◽  
Positive Temperature ◽  
Short Lifespan ◽  
Cost Characteristics

PO/CB (Polyolefin/Carbon Black) PTC (Positive Temperature Coefficient) composite with easy processing, low cost characteristics has been applied widely. But it suffered from a relatively short lifespan because of its NTC (Negative Temperature Coefficient) effect and low PTC intensity. In order to overcome this shortcoming, the CF was calcination-treated to prepare LDPE/CF (Low Density Polyethylene/Carbon Fiber) PTC composite. Influence of length, content and treatment method of CF on PTC properties of composites was investigated. Results showed that 0.5mm length CF in composites had higher PTC intensity than that of 2mm length CF. PTC intensity of the composites was enhanced more effectively by calcination treated CF compared to the untreated CF. The maximum PTC intensity was 8.1 when CF’s content was at 8wt%.

scholarly journals Development of Auto Thermal Control Device For Space Air - Conditioning

2021 ◽  
pp. 193-204
Author(s):  
Akinde Olusola Kunle ◽  
Maduako Kingsley Obinna ◽  
Akande, Kunle Akinyinka ◽  
Adeaga Oyetunde Adeoye
Keyword(s):  
Temperature Coefficient ◽  
Room Temperature ◽  
Negative Temperature Coefficient ◽  
Negative Temperature ◽  
Thermal Control ◽  
Positive Temperature Coefficient ◽  
Control Device ◽  
Thermal Source ◽  
Positive Temperature ◽  
Ntc Thermistor

Auto Thermal Control device is an electronic based device which employs the application of temperature sensors to controlling household appliances without human interference directly. In this work, thermal source is used to regulate electrical fan and room heater depending on ambient temperature. The room heater, which is adjusted to a set temperature, switches ‘ON’ when the temperature of a room is low (cold). While the same is switches ‘OFF’ with increase in the room temperature. This triggers ‘ON’ an electric fan at different speeds, and thus cools the room. A temperature sensor, tthermistor, monitors change in room temperature. Two types of thermistor exists: Positive Temperature Coefficient, PTC. An increasee in the resistance of PTC results in increasee in temperature). In the Negative Temperature Coefficient, NTC; a decreasee in resistance yields to temperature increase. This article explored a NTC thermistor. The design could be a ready product in the market of the developing nation where environmental automation is yet fully deployed.

scholarly journals Temperature Self-Compensated Strain Sensors based on MWCNT-Graphene Hybrid Nanocomposite

2019 ◽  
Vol 3 (4) ◽  
pp. 96 ◽  
Author(s):  
Rajarajan Ramalingame ◽  
Jose Roberto Bautista-Quijano ◽  
Danrlei de Farias Alves ◽  
Olfa Kanoun
Keyword(s):  
Temperature Coefficient ◽  
Carbon Nanomaterials ◽  
Negative Temperature ◽  
Positive Temperature Coefficient ◽  
Gauge Factor ◽  
Positive Temperature ◽  
Hybrid Nanocomposite ◽  
Resistance Change ◽  
Influence Of Temperature ◽  
Dispersion Quality

Sensors based on carbon nanomaterials are gaining importance due to their tunable properties and their potentially outstanding sensing performance. Despite their advantages, carbon-based nanomaterial sensors are prone to cross-sensitivities with environmental factors like temperature. Thus, to reduce the temperature influence on the sensing material, compensation and correction procedures are usually considered. These methods may require the use of additional sensors which can themselves be subject to residual errors. Hence, a more promising approach consists of synthesizing a material that is capable of self-compensating for the influence of temperature. In this study, a hybrid nanocomposite based on multi-walled carbon nanotubes (MWCNT) and graphene is proposed, which can compensate, by itself, for the influence of temperature on the material conductivity. The hybrid nanocomposite material uses the different temperature behavior of MWCNTs, which have a negative temperature coefficient, and graphene, which has a positive temperature coefficient. The influence of the material ratio and dispersion quality are investigated in this work. Material composition and dispersion quality are analyzed using Raman spectroscopy and scanning electron microscopy (SEM). A composition of 70% graphene and 30% MWCNT exhibits a nearly temperature-independent hybrid nanocomposite with a sensitivity of 0.022 Ω/°C, corresponding to a resistance change of ~1.2 Ω for a temperature range of 25 to 80 °C. Additionally, a simple investigation of the strain sensing behavior of the hybrid material is also presented. The hybrid nanocomposite-based, thin-film strain sensor exhibits good stability over 100 cycles and a significantly high gauge factor, i.e., 16.21.

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