Theory on the Crystallization and Melting of Unvulcanized Rubber I. Crystallization

1951 ◽  
Vol 24 (1) ◽  
pp. 54-64
Author(s):  
Ryoichi Kikuchi
Keyword(s):  
Constant Temperature ◽  
Crystallization Temperature ◽  
Average Rate ◽  
Amorphous State ◽  
Experimental Results ◽  
Half Time ◽  
Melting Range ◽  
Melting Region ◽  
Different Temperatures ◽  
Volume Decrease

Abstract Recently Wood and Bekkedahl have reported new experimental results on the crystallization and melting of unvulcanized rubber in the unstretched state at different temperatures. Their results are summarized as follows: (1). When a specimen of vulcanized amorphous rubber is kept at a constant temperature between about +15° and −50° C, it begins to crystallize and its volume gradually decreases, as seen in Figure 1. We shall denote the ordinate, “Decrease in volume (in per cent)” of Figure 1 by w (t), which is a function of time t for a constant temperature. (2). The arrows in Figure 1 indicate the estimated values for half the total decrease of volume at each temperature. Wood and Bekkedahl considered the reciprocal of this time to be a measure of the average rate of crystallization during the first half of the volume decrease, and it is plotted against temperature in Figure 2. We should like to call this time briefly the half-time, and denote it by th. (3). As the temperature of crystallized rubber is gradually raised, its volume increases suddenly in some region of temperature, and eventually reaches the value corresponding to amorphous state as shown in Figure 3. This phenomenon seems to be the melting of the crystal, but peculiarly the location and the width of this melting-region varies according to the previous crystallization temperature. (4). The range of melting does not depend on the extent of crystallization and is definitely determined by the temperature at which crystallization occurs. Figure 4 is derived from Figure 3 and shows the relation between the melting range and the temperature of crystallization. In the present paper the author tries to explain these results theoretically and consistently, with certain reasonable assumptions.

Synthesis and Characterization of Nanocrystalline ZnO Powders by a Direct Thermal Decomposition Route Using Zinc Nitrate Hexahydrate

2013 ◽  
Vol 770 ◽  
pp. 68-71 ◽  
Author(s):  
Supphadate Sujinnapram ◽  
Uraiphorn Termsuk ◽  
Atcharawan Charoentam ◽  
Sutthipoj Sutthana
Keyword(s):  
Thermal Decomposition ◽  
Crystallization Temperature ◽  
Zinc Nitrate ◽  
Zinc Nitrate Hexahydrate ◽  
Absorption Peak ◽  
Synthesis And Characterization ◽  
Nitrate Hexahydrate ◽  
Different Temperatures ◽  
Zno Powders

The nanocrystalline ZnO powders were synthesized by a direct thermal decomposition using zinc nitrate hexahydrate as starting materials. The precursor was characterized by TG-DTA to determine the thermal decomposition and crystallization temperature which was found to be at 325 oC. The precursors were calcined at different temperatures of 400, 500, and 600°C for 4 h. The structure of the prepared samples was studied by XRD, confirming the formation of wurtzite structure. The synthesized powders exhibited the UV absorption below 400 nm (3.10 eV) with a well defined absorption peak at around 285 nm (4.35 eV). The estimated direct bandgaps were obtained to be 3.19, 3.16, and 3.14 eV for the ZnO samples thermally decomposed at 400, 500, and 600°C, respectively.

scholarly journals An Experimental Study of the Decomposition and Carbonation of Magnesium Carbonate for Medium Temperature Thermochemical Energy Storage

Energies ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1316
Author(s):  
Daniel Mahon ◽  
Gianfranco Claudio ◽  
Philip Eames
Keyword(s):  
Thermal Analysis ◽  
Thermal Decomposition ◽  
Energy Storage ◽  
Magnesium Carbonate ◽  
Experimental Results ◽  
Future Research ◽  
Medium Temperature ◽  
Different Temperatures ◽  
Decomposition Enthalpy ◽  
Co2 Atmosphere

To improve the energy efficiency of an industrial process thermochemical energy storage (TCES) can be used to store excess or typically wasted thermal energy for utilisation later. Magnesium carbonate (MgCO3) has a turning temperature of 396 °C, a theoretical potential to store 1387 J/g and is low cost (~GBP 400/1000 kg). Research studies that assess MgCO3 for use as a medium temperature TCES material are lacking, and, given its theoretical potential, research to address this is required. Decomposition (charging) tests and carbonation (discharging) tests at a range of different temperatures and pressures, with selected different gases used during the decomposition tests, were conducted to gain a better understanding of the real potential of MgCO3 for medium temperature TCES. The thermal decomposition (charging) of MgCO3 has been investigated using thermal analysis techniques including simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), TGA with attached residual gas analyser (RGA) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) (up to 650 °C). TGA, DSC and RGA data have been used to quantify the thermal decomposition enthalpy from each MgCO3.xH2O thermal decomposition step and separate the enthalpy from CO2 decomposition and H2O decomposition. Thermal analysis experiments were conducted at different temperatures and pressures (up to 40 bar) in a CO2 atmosphere to investigate the carbonation (discharging) and reversibility of the decarbonation–carbonation reactions for MgCO3. Experimental results have shown that MgCO3.xH2O has a three-step thermal decomposition, with a total decomposition enthalpy of ~1050 J/g under a nitrogen atmosphere. After normalisation the decomposition enthalpy due to CO2 loss equates to 1030–1054 J/g. A CO2 atmosphere is shown to change the thermal decomposition (charging) of MgCO3.xH2O, requiring a higher final temperature of ~630 °C to complete the decarbonation. The charging input power of MgCO3.xH2O was shown to vary from 4 to 8136 W/kg with different isothermal temperatures. The carbonation (discharging) of MgO was found to be problematic at pressures up to 40 bar in a pure CO2 atmosphere. The experimental results presented show MgCO3 has some characteristics that make it a candidate for thermochemical energy storage (high energy storage potential) and other characteristics that are problematic for its use (slow discharge) under the experimental test conditions. This study provides a comprehensive foundation for future research assessing the feasibility of using MgCO3 as a medium temperature TCES material. Future research to determine conditions that improve the carbonation (discharging) process of MgO is required.

scholarly journals The Investigation of Effects of Temperature and Nanoparticles Volume Fraction on the Viscosity of Copper Oxide-ethylene Glycol Nanofluids

2017 ◽  
Author(s):  
Mohammad Hemmat Esfe
Keyword(s):  
Ethylene Glycol ◽  
Copper Oxide ◽  
Volume Fraction ◽  
Relative Viscosity ◽  
Experimental Results ◽  
Different Temperatures ◽  
Nanoparticles Volume Fraction ◽  
Effects Of Temperature ◽  
Nanofluid Viscosity ◽  
Experimental Values

In the present article, the effects of temperature and nanoparticles volume fraction on the viscosity of copper oxide-ethylene glycol nanofluid have been investigated experimentally. The experiments have been conducted in volume fractions of 0 to 1.5 % and temperatures from 27.5 to 50 °C. The shear stress computed by experimental values of viscosity and shear rate for volume fraction of 1% and in different temperatures show that this nanofluid has Newtonian behaviour. The experimental results reveal that in a given volume fraction when temperature increases, viscosity decreases, but relative viscosity varies. Also, in a specific temperature, nanofluid viscosity and relative viscosity increase when volume fraction increases. The maximum amount of increase in relative viscosity is 82.46% that occurs in volume fraction of 1.5% and temperature of 50 °C. Some models of computing nanofluid viscosity have been suggested. The greatest difference between the results obtained from these models and experimental results was down of 4 percent that shows that there is a very good agreement between experimental results and the results obtained from these models.

scholarly journals Predicting the Tensile Behavior of Ti-6.6Al-3.3Mo-1.8Zr-0.29Si Alloy via the Temperature-Dependent Crystal Plasticity Method

Materials ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3138
Author(s):  
Jun Zhang ◽  
Yang Wang ◽  
Peng Wang ◽  
Junhong Chen ◽  
Songlin Zheng
Keyword(s):  
Crystal Plasticity ◽  
Experimental Results ◽  
Uniaxial Tensile ◽  
Published Data ◽  
Initial Yield Stress ◽  
Polycrystal Plasticity ◽  
Different Temperatures ◽  
Polycrystalline Model ◽  
Critical Resolved Shear Stress ◽  
Relationship Of

Uniaxial tensile flow properties of a duplex Ti-6.6Al-3.3Mo-1.8Zr-0.29Si alloy in a temperature range from 213 K to 573 K are investigated through crystal plasticity modelling. Experimental results indicate that the initial yield stress of the alloy decreases as the temperature increases, while its work-hardening behavior displays temperature insensitivity. Considering such properties of the alloy, the dependence of the initial critical resolved shear stress (CRSS) on temperature is taken into account in the polycrystal plasticity modelling. Good coincidence is obtained between modelling and the experimental results. The determined values of CRSS for slip systems are comparable to the published data. The proposed polycrystalline model provides an alternative method for better understanding the microstructure–property relationship of α + β titanium alloys at different temperatures in the future.

Analysis on Diffusion Parameters of Rolling Mill Bearing Alloy-Interface

2010 ◽  
Vol 145 ◽  
pp. 177-180 ◽  
Author(s):  
Hai Bin Li ◽  
Qing Xue Huang ◽  
Jian Mei Wang ◽  
Qin Ma
Keyword(s):  
Activation Energy ◽  
Theoretical Analysis ◽  
Rolling Mill ◽  
Experimental Results ◽  
Reaction Process ◽  
Diffusion Parameters ◽  
Different Temperatures ◽  
Bearing Alloy

In this paper, the diffusion quantity of different temperatures and unit time have been investigated basing on experimental results and theoretical analysis. The diffusing parameters of molten tin in the reaction process is investigated according to diffusing formula. The results within the range of 260～350°C indicates that the diffusing activation energy is increased with the time until the reaction ceases and it is decreased with the increasing of the temperature and substrate vacancy, but the average diffusing constant of tin increased with the temperature.

Annealing induced interdiffusion and crystallization in sputtered amorphous Si/Ge multilayers

1997 ◽  
Vol 12 (9) ◽  
pp. 2255-2261 ◽  
Author(s):  
Zs. Czigány ◽  
G. Radnóczi ◽  
K. Järrendahl ◽  
J-E. Sundgren
Keyword(s):  
Crystallization Temperature ◽  
Diffusion Constant ◽  
Amorphous State ◽  
Diffraction Measurement ◽  
Individual Layer ◽  
Cross Sectional ◽  
Short Period ◽  
Amorphous Si ◽  
Si Content ◽  
20 Nm

The intermixing and crystallization of amorphous Si/Ge multilayers (with individual layer thickness between 1.5 and 20 nm) and SiGe alloys produced by dc magnetron sputtering have been studied by cross-sectional transmission electron microscopy and x-ray diffraction. Measurement of the crystallization temperature as a function of the Si content showed that multilayers and alloys with equal composition crystallized at the same temperature. This implies that intermixing precedes crystallization in the multilayers. Close to the crystallization temperature, formation of Kirkendall voids was observed in the short-period Si/Ge multilayers. These voids were found at positions corresponding to the original Si layers, indicating that Si diffuses faster in amorphous Ge than Ge in amorphous Si. The Ge layers in short-period Si/Ge multilayers retained their amorphous state to much higher temperatures than thick amorphous Ge layers. This is shown to be due to inhibition of nucleation by the presence of the layer interfaces. A lower estimate for the Si diffusion constant in crystalline Ge is also determined.

InAlGaP Heterostructures and LEDs optimization

2016 ◽  
Vol 845 ◽  
pp. 30-33
Author(s):  
Sergey Didenko ◽  
Oleg Rabinovich ◽  
Sergey Legotin ◽  
Irina Fedorchenko ◽  
Andrey Krasnov ◽  
...  
Keyword(s):  
Active Region ◽  
Performance Characteristics ◽  
Experimental Results ◽  
Junction Area ◽  
Different Temperatures ◽  
Main Thing

Changing LED performance characteristics, depending on Indium atoms concentration and at different temperatures were simulated. It was suggested that a heterostructure having p-n junction area S0 can be considered as a sum of “SmallLEDs (SLEDs)” electrically connected in parallel. Good correlation in simulation and experimental results has been obtained. It was determined that the best AlGaInP heterostructure contains 5 wide QW (width 10 nm each) in active region. The main thing is that in central ones there is maximum radiation and at the both ends of active region are “barriers” which help to concentrate electrons/holes in active region and additionally “protect” QW from different defects.

Messungen und Berechnungen zum elektronenmikroskopischen Streukontrast für 17 bis 1200 keV-Elektronen

1968 ◽  
Vol 23 (10) ◽  
pp. 1569-1582 ◽  
Author(s):  
L. Reimer ◽  
K.H. Sommer
Keyword(s):  
Electron Energy ◽  
Scattering Amplitude ◽  
Amorphous State ◽  
Small Mass ◽  
Experimental Results ◽  
Large Contribution ◽  
Exponential Law ◽  
Atomic Scattering ◽  
The Difference ◽  
Pt Films

Electron transmission experiments under electron microscope conditions were done with C-, Ge- and Pt-films to get information about the influence of electron energy and objective aperture. One gets an exponential law of transmission for small mass thicknesses x of the objects and can calculate the “contrast thickness” xk (in T = exp(— x/xk)). Using the Lenz theory, two constants Xa and ϑ0 are determined, for each element and electron energy, from the measurements of xk at four different objective apertures. xa is related to the total elastic scattering cross section and ϑ0 is the half width of the atomic scattering amplitude ƒ(ϑ). The variation of xa and ϑ0 with electron energy is not in agreement with the theory using the first Born approximation and a simple screened atomic potential. But using these two experimentally determined constants in a plural scattering theory of LENZ, good agreement between calculated and experimental deviations from the exponential law of transmission up to mass thicknesses of 300 µg · cm-2 is obtained.To get better theoretical values of xk, the complex atomic scattering amplitudes were calculated quantum theoretically with the WKB-method and Hartree potentials. The values agree with the experimental results for Ge- and Pt-films. For carbon there is a large contribution by inelastic scattering making a direct comparison with experimental results difficult.The energy dependence of xa shows saturation for high voltages, as expected by theory. At high voltages the difference in the xk-values for films with different atomic numbers is larger, resulting in lower xk-values for platinum. But at very low voltages the xk-values of carbon are lower than those of platinum. Some measurements of xk at 60 keV on targets of noble gases confirm the absence of a large difference in contrast between atoms in the gaseous and condensed amorphous state.

Effect of Post-Deposition Annealing on some Optical Properties of Thermally-Evaporated V2O5 Thin Film

2012 ◽  
Vol 329 ◽  
pp. 139-145
Author(s):  
S.A. Aly
Keyword(s):  
Optical Properties ◽  
Amorphous State ◽  
X Ray Diffraction ◽  
Post Deposition Annealing ◽  
X Ray ◽  
Spectral Behaviour ◽  
Before And After ◽  
Different Temperatures ◽  
Reflectance Measurements ◽  
Post Deposition

A Vanadium Pentoxide Sample with a Film Thickness of 75 Nm Has Been Thermally Evaporated on Unheated Glass Substrate Using V2O5High Purity Powder. the Sample Was Subjected to a Subsequent Post-Deposition Annealing in Air at Different Temperatures for a Period of One Hour. the Optical Properties Were Studied by Transmittance and Reflectance Measurements. the Integrated Visible ,TVis, and Solar, TSol, Transmittance Were Calculated. the Spectral Behaviour of the Refractive Index as Well as the Absorption Coefficient before and after Post-Deposition Heat-Treatment Was Also Reported. X-Ray Diffraction Confirmed that the Film in the as-Deposited as Well as after Annealing up to 400 °C Is in the Amorphous State.

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