Arrhenius Theory Research Articles

Apparent sintering activation energy for densification of nanosized TiO2 ceramic powders

TiO2 powder samples with an average particle size of 50 nm were sintered in air at 1200°C at different heating rates of 1, 3, 5 K min–1. The apparent sintering activation energy was determined from dilatometer shrinkage data using the Arrhenius theory. The results give an activation energy of 115 ± 10 kJ mol–1 for the present material, which is in good agreement with values reported in the literature. It is concluded that the constant rate of heating method can be used to measure activation energy.

Effects of storage temperature and water activity on the survival of bifidobacteria in powder form

Effects of water activity and storage temperature on survival of bifidobacteria in powder form were investigated and kinetic analyses were performed to reveal characteristics of the stability. A significant positive correlation was observed between water activity and natural logarithm of the inactivation rate constant of bifidobacteria powder, indicating that higher water activity induced lower stability of bifidobacteria in powder form. Also, higher temperature condition induced lower survival rate, which was supported by that the stability was followed the Arrhenius theory. These findings constructed a prediction model for bifidobacteria survival in powder form.

Durability of GFRP Reinforcing Bars Embedded in Moist Concrete

This paper presents mechanical, microstructural, and physical characterization of glass fiber-reinforced polymer (GFRP) bars exposed to concrete environment. GFRP bars were embedded in concrete and exposed to tap water at 23, 40, and 50°C to accelerate the effect of the concrete environment. The measured tensile strengths of the bars before and after exposure were considered as a measure of the durability performance of the specimens and were used for long-term properties prediction based on the Arrhenius theory. In addition, Fourier transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy were used to characterize the aging effect on the GFRP reinforcing bars. The results showed that the durability of mortar-wrapped GFRP bars and exposed to tap water was less affected by accelerated aging than the bars exposed to simulated pore-water solution. These results confirmed that the concerns about the durability of GFRP bars in concrete, based on simulated laboratory studies in alkaline solutions, do not properly correspond to the actual service life in concrete environments.

Stability of bifidobacteria in powdered formula

SummaryTwo stability tests of bifidobacteria in powdered formula were conducted. In a strain comparison test, three kinds of bifidobacterial powders; Bifidobacterium longum BB536, Bifidobacterium breve M‐16V and Bifidobacterium infantis M‐63 powders, admixed in follow‐up formula were used. In a commercial product evaluation, powdered formulas for toddlers containing bifidobacteria sold in the Indonesian market were analysed. When the inactivation rate constant of each sample, which was used as an index of the loss rate, was determined from the stability tests, B. longum was the most stable strain. The mean inactivation rate constant of commercial products was significantly lower than those obtained in strain comparison, although the same strains (B. longum BB536 and B. breve M‐16V) were used. A possible reason was the lower water activity of commercial products compared to the follow‐up formula. Also, higher storage temperature yielded lower stability in all strains or samples, which obeys the Arrhenius theory.

Temperature Dependency of Chloride Induced Corrosion in Concrete

Maintenance of reinforced concrete is a major concern around the world. In particular, special attention is now given to chloride induced corrosion, which is considered as one of the most serious causes of concrete deterioration. Since corrosion is an electrochemical process, the influence of temperature on the deterioration of reinforced concrete should be considered. From these backgrounds, the objective of this study is to investigate the influence of temperature on the deterioration process of chloride induced corrosion in reinforced concrete. The results show that the rates of diffusion of substances and corrosion of steel bars rise with increases in temperature and these phenomena are explained by the Arrhenius theory using the concept of activation energy.

Environmental effects on glass fiber reinforced polypropylene thermoplastic composite laminate for structural applications

AbstractThis article presents the mechanical and microstructural characterization of glass fiber reinforced polypropylene thermoplastic composite laminates (PP/Glass) exposed to tap water, salt solution, and freeze/thaw cycles. PP/Glass specimens were immersed at 23, 50, and 70°C in tap water to simulate the relative humidity of the direct environment and in a salt solution of 3% NaCl to simulate the effect of de‐icing salt. The measured flexural strengths of the specimens before and after exposure were considered as a measure of the durability performance of the specimens and were used for long‐term properties prediction based on the Arrhenius theory. In addition, the durability of PP/Glass to freeze/thaw cycles was studied for as received specimens and specimens saturated with tap water. Scanning electron microscopy was also used to characterize the effect of aging on the PP/Glass specimens. The results showed that the durability of PP/Glass composite is related to the quality of their consolidation. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

An effort to generalize the thermal isomerization of 6,6-dimethylbicyclo[3.1.1]heptanes and 6,6-dimethylbicyclo[3.1.1]heptenes: Comparative pyrolysis of pinane, α-pinene, and β-pinene

This article, based on a presentation at the 18th International Symposium on Analytical and Applied Pyrolysis in Costa Teguise, May 18–23, 2008, will give a brieve approach for systematization of thermal rearrangements occurring within the series of pinane- and pinene-type compounds. To reach this goal, gas-phase pyrolysis experiments with the most abundant pinane- and pinene-type monoterpenes ( cis-pinane, trans-pinane, α-pinene, and β-pinene) were performed in a flow-type apparatus using nitrogen as carrier gas. Performance of kinetic experiments under similar reaction conditions allows for the comparison of the activation parameters calculated from Arrhenius and Eyring theory. Thus it was possible to gain a deeper insight into the reaction mechanisms and the reaction intermediates the reactions pass through. Results are compressed in five general rules allowing for description of the pyrolysis processes of compounds in the bicyclo[3.1.1]heptane- and bicyclo[3.1.1]heptene-series.

Nd:YAG surgical laser effects in canine prostate tissue: temperature and damage distribution

An in vitro model was used to predict short-term, laser-induced, thermal damage in canine prostate tissue. Canine prostate tissue samples were equipped with thermocouple probes to measure tissue temperature at 3, 6, 9 and 12 mm depths. The tissue surface was irradiated with a Nd:YAG laser in contact or non-contact mode for up to 20 s, using powers from 5 to 20 W. Prediction of thermal damage using Arrhenius theory was discussed and compared to the in vitro damage threshold, determined by histological evaluation. The threshold temperature for acute thermal tissue damage was 69 ± 6 °C (means ± SD), irrespective of exposure time. Contact mode laser application caused vaporization of tissue, leaving a crater underneath the fiber tip. The mean extent of tissue damage underneath the vaporization crater floor was 0.9 ± 0.6 mm after 5, 10 or 20 s of contact mode laser irradiation at 10 W, whereas 20 W non-contact exposure up to 20 s causes up to 4.7 ± 0.2 mm coagulation necrosis. It was concluded that short-term acute thermal tissue damage can be comprehensively described by a single threshold temperature.

Apparent activation energy for densification of α-Al2O3 powder at constant heating-rate sintering

The apparent activation energy for densification is a characteristic quantity that elucidates the fundamental diffusion mechanisms during the sintering process. Based on the Arrhenius theory, the activation energy for densification of α-Al2O3 at constant heating-rates sintering has been estimated. Sintering of α-Al2O3 powder has been executed by the way of a push rod type dilatometer. It is shown that the apparent activation energy does not have a single value but depends directly on the relative density. The apparent activation energy corresponding to lower relative density was higher than that corresponding to higher relative density. In addition, the value of the evaluated activation energy is different at the same density level when the Arrhenius plot involves different heating rates.

Thermal degradation of allicin in garlic extracts and its implication on the inhibition of the in-vitro growth of Helicobacter pylori.

Allicin, the main active principle related to Allium sativum chemistry, is considered to be responsible for the bacteriostatic properties of garlic. The work described here has demonstrated the direct implication of the allicin present in solvent-free garlic extracts obtained with ethanol (ethanolic garlic extract, EGE) and acetone (acetonic garlic extract, AGE) in the inhibition of the in-vitro growth of Helicobacter pylori (Hp), the bacterium responsible for serious gastric diseases such as ulcers and even gastric cancer. The evolution of allicin concentration as a function of time and temperature has been the subject of a kinetic study. The reaction order, activation energy, and preexponential factor (in accordance with Arrhenius theory) have been determined for the decomposition process of allicin in these organic media. First-order decomposition, an activation energy of 97.4 kJ/mol, and an Arrhenius preexponential factor of 8.9 x 10(10) s(-1) have been determined for allicin in EGE. For allicin in AGE the kinetic order determined was 1.5, the activation energy 184.5 kJ/mol, and the preexponential factor 3.1 x 10(24) s(-1) (mg/L)(-0.5). The presence or absence of allicin in these garlic products was found to be crucial for the inhibition of the in-vitro growth of Hp, as demonstrated by microbiological analysis for AGE. A relationship has been identified between the effectiveness and durability of the anti-Hp properties shown by AGE and the allicin content of these products. The bacteriostatic properties were active for up to 10 months if the samples were maintained at 6 degrees C.

Kinetic investigation of oxygen reduction reaction in sub-freezing acid media

A three-electrode system with 2 M H 2SO 4 as the electrolyte was developed to investigate the oxygen reduction kinetics on Pt/C catalyst at sub-freezing temperatures. This system successfully avoided the ice formation above −10 °C. Furthermore, the influence of different membrane electrode assembly (MEA) status, i.e. the membrane hydration and the electrode structure, on the kinetic results in a sub-freezing fuel cell was diminished in this method. By cyclic voltammetry (CV) test, the electrochemical active surface area (ECA) of Pt/C catalyst at sub-freezing temperatures was obtained. Results showed that the ECA at sub-freezing temperatures was almost the same as that at room temperature, either the H-desorption or the H-adsorption process at subzero temperatures still took place in the same way. According to the analysis of the linear scan voltammetry (LSV), the kinetics of oxygen reduction on Pt/C catalyst at sub-freezing temperatures was explored. The limiting current density decreased as temperature dropped and the exchange current density at subzero temperatures still obeyed the Arrhenius theory.

Exploring a first-principles-based model for zooplankton respiration

AbstractPackard, T. T., and Gómez, M. 2008. Exploring a first-principles-based model for zooplankton respiration. – ICES Journal of Marine Science, 65: 371–378. Oxygen consumption (R) is caused by the respiratory electron transfer system (ETS), not biomass. ETS is ubiquitous in zooplankton, determines the level of potential respiration (Φ), and is the enzyme system that ultimately oxidizes the products of food digestion, makes ATP, and consumes O2. Current respiration hypotheses are based on allometric relationships between R and biomass. The most accepted version at constant temperature (T) is R = i0M0.75, where i0 is a constant. We argue that, for zooplankton, a Φ-based, O2-consuming algorithm is more consistent with the cause of respiration. Our point: although biomass is related to respiration, the first-principles cause of respiration is ETS, because it controls O2 consumption. Biomass itself is indirectly related to respiration, because it packages the ETS. Consequently, we propose bypassing the packaging and modelling respiration from ETS and hence Φ. This Φ is regulated by T, according to Arrhenius theory, and by specific reactants (S) that sustain the redox reactions of O2 consumption, according to Michaelis–Menten kinetics. Our model not only describes respiration over a large range of body sizes but also explains and accurately predicts respiration on short time-scales. At constant temperature, our model takes the form: where Ea is the Arrhenius activation energy, Rg, the gas constant, and Km, the Michaelis–Menten constant.

The Activation Energy of Superplastic Flow above the Critical Temperature for Steel CrWMn

By means of superplastic tensile test above the Ac1 temperature (γ→α transformation temperature), superplastic deformation activation energy of ultrafine-grained commercial die steel CrWMn is investigated on the basis of the Arrhenius theory equation, exp( / ) 1 ε& = Aσ m −Q RT , which indicates the resistance of the superplastic deformation. According to the Arrhenius equation, the activation energy is estimated from the log σt vs 1/T relationship at a constant of sensitivity index of strain rate. The results show that the strain rate sensitivity index is a constant and rather high at the conditions of superplastic deformation for the CrWMn steel, the activation energy for superplastic deformation of steel CrWMn above the critical temperature is 187KJ/mol, and the superplastic deformation activation energy is approached to the grain boundary diffusion activation energy of γ-Fe. This indicates that the grain boundary sliding (GBS) in superplastic deformation of CrWMn steel is controlled by grain boundary diffusion. The characters of superplastic deformation of the steel above the critical temperature, on the other hand, are also analyzed in this paper.

On isohydric solutions and buffer pH

A general derivation is given for the isohydric theory of Arrhenius, and its consequences for some aspects of buffer pH are considered.

Effects of mechanical and thermal stresses on electric degradation of polyolefins and related materials

AbstractDegradation under the simultaneous effects of mechanical stress and temperature in polyolefins (PE, PP), composites on their basis (PE+PP fibre, PP+PP fibre, PP+glass fibre) and radiation low‐density polyethylene (X‐LDPE) used in high‐voltage cables obeys the thermofluctuation theory of Zhourkov (in certain σ and τ0 intervals) based on the theory of Arrhenius is presented in the following form:τσ = τ0 exp[(U0 − γσ)/ RT] (1)where τ is durability. τ0 is a constant (10−12‐10−13s) equal to period of vibrations of atoms around equilibrium position, U0 is the activation energy of the mechanical destruction process (at σ = 0), γ is a structure‐sensitive parameter, T is absolute temperature and R is universal gas constant. Electric degradation under the effects of electric field and temperature in the materials mentioned above obeys the equation:τE = τ0 exp[(W0 − χE)/ RT] (2)Here, τE, W0 and χ are analogous to τσ, U0 and γ, respectively.It is assumed that the following equation is valid under the simultaneous effects of E, σ and T:τσ,E = τ0 exp[(U0 − (γσ + χE))/ RT]. (3)electric degradation

Reaction pathway and potential barrier for the CaH product in the reaction of Ca(4s4p1P1) + H2 --> CaH(X2Sigma+) + H.

The nascent CaH product in the reaction Ca(4s4p1P1) + H2 --> CaH(X2Sigma+) + H is obtained using a pump-probe technique. The CaH(v = 0,1) distributions, with a population ratio of CaH(v = 0)/CaH(v = 1) = 2.7+/-0.2, may be characterized by low Boltzmann rotational temperature. According to Arrhenius theory, the temperature dependence measurement yields a potential barrier of 3820+/-480 cm(-1) for the current reaction. As a result of the potential energy surfaces (PES) calculations, the reaction pathway favors a Ca insertion into the H2 bond along a (near) C2v geometric approach. As the H2 bond is elongated, the configurational mixing between the orbital components of the 4p and nearby low-lying 3d state with the same symmetry makes significant the nonadiabatic transition between the 5A' and 2A' surface in the repulsive limbs. Therefore, the collision species are anticipated to track along the 5A' surface, then undergo nonadiabatic transition to the inner limb of the 2A' surface, and finally cross to the reactive 1A' surface. The observed energy barrier probably accounts for the energy requirement to surmount the repulsive hill in the entrance. The findings of the nascent CaH product distributions may be reasonably interpreted from the nature of the intermediate structure and lifetime after the 2A'-1A' surface transition. The distinct product distributions between the Ca(4 1P1) and Mg(3 1P1) reactions with H2 may also be realized with the aid of the PES calculations.

Statistical evaluation for stability studies under stress storage conditions

During the pharmaceutical development of a new drug, it is necessary to select as soon as possible the formulation with the best stability characteristics. The current International Commission for Harmonisation (ICH) regulations regarding stability testing requirements for a Registration Application provide the stress testing conditions with the aim of assessing the effect of severe conditions on the drug product. In practice, the well-known Arrhenius theory is still used to make a rapid stability prediction, to estimate a drug product shelf life during early stages of its pharmaceutical development. In this work, both the planning of a stress stability study to obtain a correct stability prediction from a temperature extrapolation and the suitable data treatment to discern the reliability of the stability results are discussed. The study was focused on the early formulation step of a very stable drug, Mitonafide (antineoplastic agent), formulated in a parenteral solution and in tablets. It was observed, for the solid system, that the extrapolated results using Arrhenius theory might be statistically good, but far from the real situation if the stability study is not designed in a correct way. The statistical data treatment and the stress–stability test proposed in this work are suitable to make a reliable stability prediction of different formulations with the same drug, within its pharmaceutical development.

Long Exposure Growth of In-Vivo Interstitial Laser Photocoagulation Lesions

. An investigation of the temperature response and growth of thermal lesions resulting from in vivo, interstitial laser photocoagulation at long exposures was conducted to assess extended lesion growth characteristics and test the applicability of first order unimolecular rate kinetics (Arrhenius theory) to thermal lesion growth. Irradiations were performed in vivo in rabbit muscle using a continuous 805 nm diode laser source operating at 1.0 W coupled to an optical fibre with a precharred tip (i.e. point heat source). Temperature responses were measured using a linear array of five microthermocouples. Each temperature–time profile was fitted to a solution of the Weinbaum–Jiji bioheat transfer equation (W–J BHTE). Lesions were resected 48 h post-irradiation and the necrosis boundaries were determined histologically. Numerical integration of the Arrhenius damage integral using temperature–time data at the lesion boundary produced corresponding pairs of activation energy and pre-exponential factor (Ea, α) consistent with reported values for various other end-points and tissue types. Lesion radii were 6.0±0.6, 8.7±0.4 and 9.7±0.5 mm for 10, 20 and 30 min irradiations respectively. Thermal lesion growth predicted from Arrhenius theory was consistent with experimental results and is non-asymptotic by 30 min. Thermal parameters generally assumed to be constant when solving the W–J BHTE were found to vary with radial distance from the source, presumably due to a temperature dependence.

Species and specificity: an interpretation of the history of immunology

Part I. Specificity and Unitarianism in XIX Century Botany and Bacteriology: 1. The Unitarians 2. The Linnaeans 3. The dominance of specificity 4. The history of XIX century bacteriology from this point of view Part II. The Inherited Controversy: Specificity and Unitarianism in Immunology: 5. Dichotomy and classification in the thought of Paul Erlich 6. Max von Gruber and Paul Erlich 7. Max von Gruber and Karl Landsteiner 8. Unity, simplicity, continuity: the philosophy of Ernst Mach Part III. Chemical Affinity and Immune Specificity: The Argument in Chemical Terms: 9. Structural and physical chemistry in the late XIX century 10. Erlich's chemistry and its opponents: the dissociation theory of Arrhenius and Madsen 11. Erlich's chemistry and its opponents: the colloid theory of Landsteiner and Pauli 12. Erlich's chemistry and its opponents: the new structural chemistry of Landsteiner and Pick 13. The decline and persistence of Erlich's chemical theory Part IV. Absolute Specificity in Blood Group Genetics: 14. Immunology and genetics in the early XX century 15. The specificity of cells and the specificity of proteins 16. The last confrontation Conclusion.

Connecting parametric aging to catastrophic failure through thermodynamics

There have been numerous studies with Arrhenius theory in reliability. However, very few actually apply to parametric reliability analysis. This paper provides fundamental details in this area of reliability physics. The authors derive a thermally activated time-dependent model for both parametric and catastrophic Arrhenius aging. It is shown how aging dynamics depend upon thermodynamics specific to device reliability physics and how catastrophic phenomena can be correlated to device life dynamics.