Cure Kinetics Study of Unfilled and Carbon Black Filled Synthetic Isoprene Rubber

2009 ◽  
Vol 82 (2) ◽  
pp. 149-169 ◽  
Author(s):  
Ximei Sun ◽  
Avraam I. Isayev
Keyword(s):  
Carbon Black ◽  
Rate Constants ◽  
Induction Time ◽  
Cure Kinetics ◽  
Curing Temperature ◽  
Time Model ◽  
Isothermal Cure ◽  
Temperature Dependences ◽  
The Difference ◽  
Arrhenius Temperature

Abstract The reversion type cure kinetic and induction time models were successfully utilized to predict the isothermal and nonisothermal evolution of the state of cure in vulcanization of the unfilled and carbon black (CB)-filled IR compounds measured by APA 2000. The rate constants for the reversion reaction and the formation of the stable and unstable crosslinks and the parameters of the induction time function with the Arrhenius temperature dependences were determined from the isothermal cure measurements. The equation was proposed to adequately describe the measured dependence of the difference between the maximum and minimum torques as a function of isothermal curing temperature. The measured induction time as a function of heating rate and step temperature variation was successfully predicted based on parameters of the isothermal induction time model. Isothermal cure modeling at each curing temperature individually or at all the curing temperatures simultaneously showed the excellent agreement with the experimental data for both curing and reversion. More severe reversion in the CB-filled IR in comparison with the unfilled IR was explained by comparing their reversion rate constants.

Cure Kinetics of Neat and Nanophased Polyurethane Foams

2008 ◽  
Author(s):  
Sriram Mohan ◽  
Anandh Balakrishnan ◽  
Mrinal C. Saha
Keyword(s):  
Rate Constants ◽  
Preliminary Investigation ◽  
Cure Kinetics ◽  
Testing Procedure ◽  
Reaction Rates ◽  
Polyurethane Foams ◽  
Second Phase ◽  
Foam Sample ◽  
Isothermal Cure ◽  
Nanocomposite Foams

In this work, the isothermal cure behavior of a two part polyurethane foam system has been evaluated at temperatures between 25°C–80°C via a rheokinetic method. An ATD CSS 1000-Advanced Polymer Analyzer (APA) rheometer operating in torsion mode was used for this purpose. In the first phase of our work, neat polyurethane foams were investigated and the effects of cure temperature on the final cure modulus and density were documented. The testing procedure consisted of measuring G* as a function of time. The data obtained was fit to a generalized cure kinetics model to evaluate various parameters such as rate constants, reaction orders and activation energies. The rate constants as a function of temperature exhibited a straight line Arrhenius relationship. In the second phase of the work, 1% by weight of cloisite-15A nanoclay was used to manufacture nanocomposite foams. Isothermal cure tests were performed on the nanocomposite foam sample at 25°C. A preliminary investigation of the effect of nanoclay infusion on the final cure properties revealed no significant change. However the nanoclay foam sample exhibited higher reaction rates than its neat counterpart at the same temperature. The cell structures of these foams were studied using a JEOL 960 Scanning Electron Microscope. The micrographs supported the observations that neat foam samples showed an increased density and modulus at lower temperatures than at higher temperatures. The nanoclay sample also showed a higher density relative to its neat counterpart.

Effect of titanium alloys elasticity modulus on warping of stamped blanks during cooling

2021 ◽  
pp. 221-227
Author(s):  
M.O. Smirnov ◽  
A.M. Zolotov ◽  
A.M. Tyukhtyaev
Keyword(s):  
Mathematical Modeling ◽  
Titanium Alloys ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Elasticity Modulus ◽  
Preliminary Deformation ◽  
Wide Spread ◽  
Temperature Dependences ◽  
Cumulative Deformation ◽  
The Difference

Wide spread in the values of the elasticity modulus of the titanium VT6 alloy and its analogs Ti—6Al—4V, Ti—6Al—4V ELI at room temperature and at elevated temperatures is revealed аs result of the literature sources analysis. The data are ambiguous, the available temperature dependences of the elasticity modulus have very different values starting from the temperature T l 500 °C. Mathematical modeling of the warping process is carried out on the example of figurine-shaped stamped blank of turbine blade using various dependences of the elasticity modulus on temperature. Cases of warping during cooling of stamped blank after cooling-down in stamp with and without cumulative deformation are considered. The difference in the course of thermal deformations during the cooling of the workpiece is obtained using different temperature dependences of the elasticity modulus. The presence of preliminary deformation increases the warping of the workpieces.

scholarly journals Reconstruction of input functions from a dynamic PET image with sequential administration of 15O2 and H215O for noninvasive and ultra-rapid measurement of CBF, OEF, and CMRO2

2017 ◽  
Vol 38 (5) ◽  
pp. 780-792 ◽  
Author(s):  
Nobuyuki Kudomi ◽  
Yukito Maeda ◽  
Hiroyuki Yamamoto ◽  
Yuka Yamamoto ◽  
Tetsuhiro Hatakeyama ◽  
...  
Keyword(s):  
Rate Constants ◽  
Human Subjects ◽  
Invasive Procedure ◽  
Invasive Technique ◽  
Invasive Approach ◽  
Non Invasive ◽  
Sequential Administration ◽  
Invasive Method ◽  
The Difference ◽  
Arterial Input Functions

CBF, OEF, and CMRO2 images can be quantitatively assessed using PET. Their image calculation requires arterial input functions, which require invasive procedure. The aim of the present study was to develop a non-invasive approach with image-derived input functions (IDIFs) using an image from an ultra-rapid O2 and C15O2 protocol. Our technique consists of using a formula to express the input using tissue curve with rate constants. For multiple tissue curves, the rate constants were estimated so as to minimize the differences of the inputs using the multiple tissue curves. The estimated rates were used to express the inputs and the mean of the estimated inputs was used as an IDIF. The method was tested in human subjects ( n = 24). The estimated IDIFs were well-reproduced against the measured ones. The difference in the calculated CBF, OEF, and CMRO2 values by the two methods was small (<10%) against the invasive method, and the values showed tight correlations ( r = 0.97). The simulation showed errors associated with the assumed parameters were less than ∼10%. Our results demonstrate that IDIFs can be reconstructed from tissue curves, suggesting the possibility of using a non-invasive technique to assess CBF, OEF, and CMRO2.

scholarly journals KINETICS OF OZONE REACTIONS WITH ADENINE AND CYTOSINE IN AQUEOUS SOLUTIONS

2020 ◽  
Vol 63 (10) ◽  
pp. 17-22
Author(s):  
Aigul A. Maksyutova ◽  
Elvina R. Khaynasova ◽  
Yuriy S. Zimin
Keyword(s):  
Aqueous Solutions ◽  
Rate Constants ◽  
Correlation Coefficients ◽  
Activation Parameters ◽  
Second Order ◽  
Order Kinetic ◽  
Temperature Dependences ◽  
Ozone Reactivity ◽  
Kinetics Of ◽  
Ozone Reactions

The ultraviolet spectroscopy method has been applied to study the kinetics of the ozone reactions with nitrogenous bases (NB), namely adenine and cytosine in aqueous solutions. At the first research stage, the range of NB working concentrations has been determined. It was found that linear dependences between optical densities and concentrations of nitrogenous bases aqueous solutions are quite reliable, with correlation coefficients r ≥ 0.998, are satisfied up to [NB] = 2.3 ∙ 10–4 mol/l. According to the Bouguer-Lambert-Beer law, adenine and cytosine extinction coefficients in aqueous solutions were determined and subsequently used to calculate their residual concentrations. At the next stage, the kinetics of nitrogenous bases ozonized oxidation was studied with equal initial concentrations of the starting substances ([NB]0 = [О3]0). The results revealed that the kinetic consumption curves of the starting reagents are fairly well linearized (r ≥ 0.996) in the second-order reaction equation coordinates. As found with the bubbling installation, 1 mol of the absorbed ozone falls on 1 mol of the used NB. Thus, the reactions of ozone with adenine and cytosine explicitly proceed according to the second-order kinetic laws (the first – according to О3 and the first – according to NB). The rate constants were calculated by the integral reaction equations, the values of which indicate a higher ozone reactivity in relation to nitrogen bases. The temperature dependences of the second-order rate constants was studied ranging 285-309 K, and the activation parameters (pre-exponential factors and activation energies) of the ozone reactions with adenine and cytosine in aqueous solutions were determined.

Regularities of changes in microhardness in the volume of EDT-69N binder cured at different temperatures

2020 ◽  
Vol 4 ◽  
pp. 65-71
Author(s):  
E.A. Veshkin ◽  
◽  
V.I. Postnov ◽  
V.V. Semenychev ◽  
E.V. Krasheninnikova ◽  
...  
Keyword(s):  
Cross Section ◽  
High Sensitivity ◽  
Sample Volume ◽  
Curing Temperature ◽  
Molding Temperature ◽  
Parabolic Law ◽  
Dimensionless Coefficient ◽  
Straight Line ◽  
Different Temperatures ◽  
The Difference

The change in the microhardness over the thickness of samples made of EDT-69N binder cured in vacuum and at atmospheric pressure at temperatures from 130 to 170°C was investigated. It was found that the change in microhardness along the thickness of the samples occurs according to the parabolic law, with the maximum values being achieved in the middle of the sample cross-section along the thickness. With an increase in the molding temperature, the microhardness in the middle section of the sample increases from 222 MPa at a molding temperature of 130°C to 410 MPa during molding at 170°C. At the critical molding temperature (170°C), the microhardness in all zones of the specimen cross section (subsurface, semi-average, and core) levels off, while the parabolic dependence degenerates into a straight line. It is shown that the method of scratching (sclerometry) demonstrated a sufficiently high sensitivity to the state of samples cured at different temperatures. With an increase in the molding temperature, the width of the sclerometric grooves decreases. At a critical molding temperature of 170°C, the groove width is stabilized and becomes constant throughout the sample thickness. To characterize the difference in the values of the microhardness of the cured binder in the sample volume, it is proposed to use a dimensionless “coefficient of volume anisotropy,” which can take a positive, negative or zero value. With an increase in the curing temperature of the binder and, accordingly, with an increase in the microhardness of the sample, the coefficient of volume anisotropy decreases, and when the samples are molded at the critical temperature, it turns to zero, which indicates the absence of anisotropy.

On the Chemical Reactivity of the Phytochrome Chromophore in the Pr and Pfr Form

1985 ◽  
Vol 40 (3-4) ◽  
pp. 215-218 ◽  
Author(s):  
Fritz Thümmler ◽  
Peter Eilfeld ◽  
Wolfhart Rüdiger ◽  
Doo-Khil Moon ◽  
Pill-Soon Song
Keyword(s):  
Reaction Kinetics ◽  
Rate Constants ◽  
Chemical Reactivity ◽  
Order Reaction ◽  
First Order Reaction ◽  
Limiting Factor ◽  
Pseudo First Order Reaction ◽  
First Order ◽  
Pseudo First Order ◽  
The Difference

The reactivity of the phytochrome chromophore and related tetrapyrroles towards ozone and tetranitromethane was investigated. Both oxidizing reagents cause bleaching of the main absorp­tion band of the pigment. The rate constants for this bleaching were determined under conditions of pseudo first order reaction kinetics. The rate constants for the reaction with ozone are similar for native phytochrome and for freely accessible tetrapyrroles (biliverdin, small chromopeptides from phytochrome) indicating that accessibility is not the limiting factor for the reaction with ozone. Under a variety of conditions, the Pfr chromophore reacts by about 10% faster than the Pr chromophore. This may reflect the true difference in reactivity. The rate constants for the reaction with tetranitromethane are much larger for biliverdin, bilirubin and small chromopeptides from phytochrome than for native phytochrome. The limiting factor for this reaction in native phytochrome therefore is the accessibility of the chromophore by the reagent. Previous conclusions on the difference in exposure of the tetrapyrrole chromophore in Pr and Pfr are confirmed.

Effects of Curing Systems on the Strength and Microstructure of Reactive Powder Concrete with Iron Tailing Sands

2014 ◽  
Vol 548-549 ◽  
pp. 247-253
Author(s):  
Zhi Gang Zhu ◽  
Bei Xing Li ◽  
Jin Cheng Liu ◽  
Xing Dong Lv
Keyword(s):  
Point Of View ◽  
Hot Water ◽  
Curing Temperature ◽  
Reactive Powder Concrete ◽  
Curing Time ◽  
Submicroscopic Structure ◽  
Curing Conditions ◽  
The Difference ◽  
Reactive Powder ◽  
Curing Systems

To produce 130MPa reactive powder concrete with iron tailing sands as aggregation in an economic hot curing system, the effects of curing temperature, curing time and curing conditions on the reactive powder concrete was studied, the reasons of the strength of reactive powder concrete in different curing systems has the difference from the submicroscopic structure point of view was analyzed. The results show that use 90°C hot water to cure reactive powder concrete for 48h can lead it’s 28 day compressive strength reaches 140MPa, the flexural strength reaches 28MPa.

scholarly journals Non-isothermal cure kinetics of aerogel/epoxy composites using differential scanning calorimetry

2019 ◽  
Vol 58 (16) ◽  
pp. 1757-1765 ◽  
Author(s):  
Suryanarayanan Krishnaswamy ◽  
Veronica Marchante ◽  
Hrushikesh Abhyankar ◽  
Zhaorong Huang ◽  
James Brighton
Keyword(s):  
Differential Scanning Calorimetry ◽  
Cure Kinetics ◽  
Epoxy Composites ◽  
Scanning Calorimetry ◽  
Isothermal Cure ◽  
Kinetics Of
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