Three-dimensional Diffusion Research Articles

Preliminary assessments of variations in the form-function-based maximum pin power in CANDU analyses

In the current CANDU full-core physics analysis, the maximum pin power within a bundle is determined by multiplying the bundle power obtained from solving the three-dimensional neutron diffusion equation with a ratio of the highest pin power to the average pin power, obtained from burnup-dependent infinite lattice calculations. Since the geometry of the fuel channel changes during the life of the reactor, the ratio of the highest to the average pin power changes as well. The objective of the current paper is to quantify such variations. Two sources of variation are considered: (i) pressure tube diametral creep (PTDC); and (ii) the placement of the fuel bundle inside the fuel channel in the lattice model. The results from the study indicate that the maximum pin power could vary up to 1.2%, depending on the amount of the PTDC, the fuel burnup, and the fact that a concentric or non-concentric lattice model is used. Therefore, it is recommended that the lattice model used for deriving the form function be as consistent as possible to the core condition being analysed, especially with respect to the PTDC value.

Determination of the three-dimensional diffusion optimal path

The diffusion of passing over the saddle point of a three-dimensional quadric potential energy surface was studied by analytically solving a set of coupled generalized Langevin equations. An accurate expression of the passing probability was obtained. The effect of the coupling between different degrees of freedom which is represented by the off-diagonal elements of the inertia, friction and potential-curvature tensors was analyzed in detail. It is found that some of the coupling have great influence on the diffusion process, while others not. The combination of them results in an optimal injecting direction of the diffusing particles, revealing an optimal three-dimensional diffusion path.

Global deblurring for continuous out-of-focus images using a depth-varying diffusion model.

The phenomenon of continuous out-of-focus imaging often occurs in high-magnification optical microscopy when observing large-scale targets. Lacking of accurate depth-varying point spread functions (DVPSFs) for blurred regions at different depths, it is difficult to locally reconstruct the clear images of these blurred regions using traditional deblurring methods, making it unreasonable to globally observe the optical features of large-scale targets in high-magnification optical microscopy. This paper proposes a global deblurring method for continuous out-of-focus images of large-scale sphere samples. In this study, first we analyze the energy diffusion characteristics of the optical imaging process, integrating the relationship between high-frequency energy parameters, optical range distance, and depth of field, and we propose a three-dimensional continuous energy diffusion model for optical imaging. Next, we propose an adaptive weight depth calculation method for a continuously changing surface based on the depth varying diffusion model by introducing the sample surface curvature variation and light direction. Finally, we propose a universal method for deblurring continuous out-of-focus images of large-scale sphere samples for the purpose of observing the global optical features in high-magnification optical microscopy. Moreover, we use dynamic microspheres of different sizes to verify the effectiveness of our proposed method. The results prove that our proposed method can accurately calculate the depth of the sample surface and the energy diffusion parameters at each depth, and it can achieve the image deblurring of a continuously changing surface and the global deblurring of multiple samples in a wide field of view.

Thermal decomposition kinetic study of Fe5C2 nanoparticles

In this study, the thermal stability and decomposition kinetics of Hägg iron carbide nanoparticles synthesized via a wet chemical method have been investigated. Results of Mössbauer spectroscopy were in consonance with x-ray diffraction to prove the formation of Fe5C2 nanoparticles. The activation energy of the transformation was evaluated by thermogravimetric analysis, performed at different heating rates from room tempearture to 573 K, employing the Flynn-Wall-Ozawa and Coats-Redfern models. Using the Criado model, degradation kinetics was determined to be a three-dimensional diffusion type. Thermal x-ray analysis, high resolution transmission electron microscopy, and vibrating sample magnometer measurements were performed both before and after thermal treatment of the nanoparticles to compare phase structure, morphology, and magnetic properties. Results show that the high magnetic, high density Hägg iron carbide with a core-shell structure converts to the lower density magnetite with moderate magnetization and core shell structure.

Kinetics study of heavy metal removal from the lead smelting slag by carbothermic reduction: Effect of phase transformation

As an environmentally hazardous waste, the lead smelting slag was considered as a potential secondary resource of valuable metals (Zn, Pb, and Sn) if recycled. In this study the removal mechanism and kinetics of Zn, Pb, and Sn from the lead slag by carbothermic reduction at 1423–1473 K were investigated. Microstructure evolution of the pellets and phase transformation of heavy metals was analyzed by XRD and SEM/EDS. The kinetics behaviors of heavy metal volatilization were associated to the phase transformation. The results showed that Zn, Pb and Sn removal were controlled by the three-dimensional internal diffusion. Interestingly, the volatilization of Zn presented a consistent kinetics behavior, because the volatile phases of Zn were always metallic Zn in the whole reaction process. However, the volatilization of Sn and Pb conformed to a two-staged kinetics model. It was because that the nonvolatile polymetallic sulfides (Fe-Sn-Pb-S) and Fe-Pb-Sn alloy generated with metallic iron at a higher metallization degree, which hindered the internal diffusion of Sn and Pb. On the basic of this, a staged kinetics model of heavy metal removal was established, and the apparent rate constants and activation energies were determined.

Effect of Carbonized 2-Methylnaphthalene on the Hydrogen Storage Performance of MgH2

Mg-based hydride materials (MgH2) are in the spotlight of hydrogen storage due to their high gravimetric density. Yet, its large-scale utilization is limited by the poor thermodynamic stability and slow kinetics. Herein, we report a novel and straightforward way to prepare MgH2 with amorphous carbon by cosintering 2-methylnaphthalene (CMN) organics with pure Mg and a hydriding combustion synthesis method, where the amorphous carbon formed from the CMN not only improves the dehydrogenation/hydrogenation capacity but also enhances the kinetics of the Mg/MgH2 system. The dehydrogenation capacity of the CMN-MgH2 composite reaches 4.88 wt % of H2 at 623 K, nearly 2 times of pure MgH2, and its onset dehydrogenation temperature decreases to 560 K, 90 K lower than that of pure MgH2; in addition, at a lower temperature of 473 K, the composite remarkably absorbs 4.54 wt % of H2 within 42 s while the absorption is only 0.71 wt % H2 for the pure MgH2. Moreover, the activation energy greatly decreases from 165.35 to 101.52 kJ/mol. Further research reveals that the evolution of hydrogenation changes from a three-dimensional diffusion process to a one-dimensional diffusion process, attributed to the formation of the amorphous carbon. This work is expected to provide inspiration to design and prepare effective additives for the improvement of hydrogen storage performance of Mg-based hydrides.

Properties, combustion behavior, and kinetic triplets of coke produced by low-temperature oxidation and pyrolysis: Implications for heavy oil in-situ combustion

This work aimed at investigating the crucial factor in building and maintaining the combustion front during in-situ combustion (ISC), oxidized coke and pyrolyzed coke. The surface morphologies, elemental contents, and non-isothermal mass losses of the oxidized and pyrolyzed cokes were thoroughly examined. The results indicated that the oxidized coke could be combusted at a lower temperature compared to the pyrolyzed coke due primarily to their differences in the molecular polarity and microstructure. Kinetic triplets of coke combustion were determined using iso-conversional models and one advanced integral master plots method. The activation energy values of the oxidized and pyrolyzed cokes varied in the range of 130–153 kJ/mol and 95–120 kJ/mol, respectively. The most appropriate reaction model of combustion of the oxidized and pyrolyzed cokes followed three-dimensional diffusion model (D3) and random nucleation and subsequent growth model (F1), respectively. These observations assisted in building the numerical model of these two types of cokes to simulate the ISC process.

Evaluation of the Thermal Behavior, Synergistic Catalysis, and Pollutant Emissions during the Co-Combustion of Sewage Sludge and Coal Gasification Fine Slag Residual Carbon

The conversion of solid waste into energy through combustion is sustainable and economical. This study aims to comprehensively evaluate and quantify the co-combustion characteristics, synergistic catalysis, and gaseous pollutant emission patterns of sewage sludge (SS) and coal gasification fine slag residual carbon (RC) as well as their blends through thermogravimetry coupled with mass spectrometry (TG-MS). The results showed that the co-combustion of SS and RC can not only improve the ignition and burnout property but also maintain the combustion stability and comprehensive combustion performance at a better level. The kinetic analysis results showed that a first-order chemical reaction and three-dimensional diffusion are the reaction mechanisms during the co-combustion of SS and RC. The synergistic catalysis between SS and RC can well explain the changes in activation energy and reaction mechanism. Furthermore, the blending ratio of SS is recommended to be maintained at 40% because of the lowest activation energy (Ea = 81.6 kJ/mol) and the strongest synergistic effect (Xi = 0.36). The emission of gaseous pollutants is corresponding to the primary combustion stages of SS, RC, and their blends. In co-combustion, the NH3, HCN, NOx, and SO2 emissions gradually rise with the increase of SS proportion in the blends due to the high content of organic compounds in SS.

An experimental study on oxygen isotope exchange reaction between CAI melt and low-pressure water vapor under simulated Solar nebular conditions

Calcium-aluminum-rich inclusions (CAIs) are known as the oldest high-temperature mineral assemblages of the Solar System. The CAIs record thermal events that occurred during the earliest epochs of the Solar System formation in the form of heterogeneous oxygen isotopic distributions between and within their constituent minerals. Here, we explored the kinetics of oxygen isotope exchange during partial melting events of CAIs by conducting oxygen isotope exchange experiments between type B CAI-like silicate melt and 18O-enriched water vapor (PH2O = 5 × 10−2 Pa) at 1420 °C. We found that the oxygen isotope exchange between CAI melt and water vapor proceeds at competing rates with surface isotope exchange and self-diffusion of oxygen in the melt under the experimental conditions. The 18O concentration profiles were well fitted with the three-dimensional spherical diffusion model with a time-dependent surface concentration. We determined the self-diffusion coefficient of oxygen to be ∼1.62 × 10−11 m2 s−1, and the oxygen isotope exchange efficiency on the melt surface was found to be ∼0.28 in colliding water molecules. These kinetic parameters suggest that oxygen isotope exchange rate between cm-sized CAI melt droplets and water vapor is dominantly controlled by the supply of water molecules to the melt surface at PH2O < ∼10−2 Pa and by self-diffusion of oxygen in the melt at PH2O > ∼1 Pa at temperatures above the melilite liquidus (1420–1540 °C). To form type B CAIs containing 16O-poor melilite by oxygen isotope exchange between CAI melt and disk water vapor, the CAIs should have been heated for at least a few days at PH2O > 10−2 Pa above temperatures of the melilite liquidus in the protosolar disk. The larger timescale of oxygen isotopic equilibrium between CAI melt and H2O compared to that between H2O and CO in the gas phase suggests that the bulk oxygen isotopic compositions of ambient gas at ∼1400 °C in the type B CAI-forming region is preserved in the oxygen isotopic compositions of type B CAI melilite. Based on the observed oxygen isotopic composition, we suggest that a typical type B1 CAI (TS34) from Allende was cooled at a rate of ∼0.1–0.5 K h−1 during fassaite crystallization.

In-situ measurement of mineral phase transition and kinetics in roasting process of Bayan Obo mixed rare earth concentrate by sodium carbonate

In this study, the Bayan Obo rare earth concentrates mixed with Na2CO3 were used for roasting research. The phase change process of each firing stage was analyzed. The kinetic mechanism model of the continuous heating process was calculated. This study aims to recover valuable elements and optimize the production process to provide a certain theoretical basis. Using X-ray diffraction (XRD), Fourier infrared spectroscopy, scanning electron microscopy with energy dispersive spectrometry, the reaction process and the existence of mineral phases were analyzed. The variable temperature XRD and thermogravimetric method were used to calculate the roasting kinetics. The phase transition results show that carbonate-like substances first decompose into fine mineral particles, and CaO, MgO, and SiO2 react to form silicates, causing hardening. Further, REPO4 and NaF can directly generate CeF3 and CeF4 at high temperatures, and a part of CeF4 and NaF forms a solid solution substance Na3CeF7. Rare earth oxides calcined at a high temperature of 750 °C were separated to produce Ce0.6Nd0.4O1.8, Ce4O7, and LaPrO3+x. Then, BaSO4, Na2CO3, and Fe2O3 react to form barium ferrite BaFe12O19; the kinetic calculation results show that during the continuous heating process, the apparent activation energy E reaches the minimum in the entire reaction stage in the temperature range of 440–524 °C, and the reaction order n reaches the maximum, which indicates that the decomposition product REFO significantly impacts the reaction system and reduces the activation energy. The mechanism function is F(α) = [−ln (1−α)]1/3. The reaction order n reaches the minimum in the temperature range of 680–757 °C, and the apparent activation energy E is large. The difficulty of the reaction increases during the final stage. The reaction mechanism function is F(α) = [1−(1−α)1/3]2. Observing the entire reaction stage, the step of controlling the reaction rate changes from random nucleation to three-dimensional diffusion (spherical symmetry).

Synthesis and Formation Process of a Typical Doped Solid-Solution Ye’elimite (Ca3.8Na0.2Al5.6Fe0.2Si0.2SO16): Experiments and Kinetic Analysis

Ye’elimite is a dominant phase in calcium sulfoaluminate cement, which is a promising alternative type of cementitious binder. Ca3.8Na0.2Al5.6Fe0.2Si0.2SO16 (abbreviated as ss-C4A3$) is a kind of typical doped solid-solution ye’elimite. In this study, the formation process of ss-C4A3$ was investigated. Clinkers of ss-C4A3$ were sintered at various temperatures for different holding times. X-ray diffraction tests and Rietveld quantitative phase analysis were conducted to determine the phase compositions of the clinkers. Meanwhile, the formation process of ss-C4A3$ was analyzed by kinetic theory. The results show that solid reactions between intermediate phases (calcium aluminate phases) and anhydrite mainly resulted in the formation of ss-C4A3$. In the conditions of 1150–1250 °C, ss-C4A3$ tended to be formed and stable until 4 h. However, when the sintering temperature was 1300 °C, the ss-C4A3$ decreased to generate calcium aluminate phases after 2 h. Compared to other kinetic models, the three-dimensional diffusion model mostly conformed with the formation process of ss-C4A3$, and the fitting results obtained by the Jander model exhibited the highest correlation coefficients. The activation energy of ss-C4A3$ formation equaled 285.6 kJ/mol, which was smaller than that of stoichiometric ye’elimite.

Defect accumulation and evolution in refractory multi-principal element alloys

Refractory multiple principal elemental alloys (MPEAs) hold great promise for structural materials in future nuclear energy systems. Compared to the extensively studied face-centered cubic (FCC) MPEAs, the irradiation resistance of body-centered cubic (BCC) refractory MPEAs is relatively less known. In this work, we study defect accumulation and evolution in two BCC VTaTi and VTaW MPEAs comparatively through atomistic simulations. For this purpose, we have parameterized the Embedded Atom Method (EAM) potential parameters for V metals. Combined with available potential parameters for other elements, we construct average atom models for the considered alloys to elucidate the effects of chemical complexities in BCC MPEAs. Our results based on Frenkel pair accumulation simulations suggest that the major influence of chemical fluctuations in BCC MPEAs is on the clustering behavior of defects, which leads to discrete point defects or small defect clusters, in contrast to the large defect clusters observed in the average atom model. We further show that the diffusion of interstitial clusters exhibits different modes due to chemical complexity. While interstitials show either three-dimensional or one-dimensional diffusion in the average atom model, the mean free path of interstitials in the random alloy is strongly suppressed. These results provide fundamental insights into the irradiation response of BCC MPEAs and pinpoint the critical role of chemical complexity on defect evolution, which lay the basis for the future development of irradiation-resistant structural materials based on BCC MPEAs.

Three-dimensional Li-ion transportation in Li2MnO3-integrated LiNi0.8Co0.1Mn0.1O2

Ni-rich layered cathodes (LiNixCoyMnzO2) have recently drawn much attention due to their high specific capacities. However, the poor rate capability of LiNixCoyMnzO2, which is mainly originated from the two-dimensional diffusion of Li ions in the Li slab and Li+/Ni2+ cation mixing that hinder the Li+ diffusion, has limited their practical application where high power density is needed. Here we integrated Li2MnO3 nanodomains into the layered structure of a typical Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) material, which minimized the Li+/Ni2+ cationic disordering, and more importantly, established grain boundaries within the NCM811 matrix, thus providing a three-dimensional diffusion channel for Li ions. Accordingly, an average Li-ion diffusion coefficient (DLi+) of the Li2MnO3-integrated LiNi0.8Co0.1Mn0.1O2 (NCM811-I) during charge/discharge was calculated to be approximately 6*10−10 cm2 S−1, two times of that in the bare NCM811 (3*10−10 cm2 S−1). The capacity delivered by the NCM811-I (154.5 mAh g−1) was higher than that of NCM811 (141.3 mAh g−1) at 2 C, and the capacity retention of NCM811-I increased by 13.6% after 100 cycles at 0.1 C and 13.4% after 500 cycles at 1 C compared to NCM811. This work provides a valuable routine to improve the rate capability of Ni-rich cathode materials, which may be applied to other oxide cathodes with sluggish Li-ion transportation.

Radiomics-based MRI for predicting Erythropoietin-producing hepatocellular receptor A2 expression and tumor grade in brain diffuse gliomas.

EphA2 is a key factor underlying invasive propensity of gliomas, and is associated with poor prognosis of tumors. We aimed to develop a radiomics-based imaging index for predicting EphA2 expression in diffuse gliomas, and further estimating its value for grading of tumors. A total of 182 patients with diffuse gliomas were included. All subjects underwent pre-operative MRI and post-operative pathological diagnosis. EphA2 expression of tumors was scored on pathological sections with immunohistochemical staining using monoclonal EphA2 antibody. MRI radiomics features were extracted from three-dimensional contrast-enhanced T1-weighted imaging and diffusion kurtosis imaging. Predictive models were constructed using machine learning-based radiomics features selection and three classifiers for predicting EphA2 expression and tumor grade. Features of best EphA2 expression model were subsequently used to construct another model of tumor grading. For each model, 146 cases (80%) were randomly picked as training and the rest 36 (20%) were testing cohorts. EphA2 expression was further correlated to the radiomics features in both grade models using Spearman's correlation. Logistic regression model presented highest performance for predicting EphA2 expression (AUC: 0.836/0.724 in training/validation set). Tumor gradings model guided by features from EphA2 expression model demonstrated comparable performance (AUC: 0.930/0.983) to that constructed directly using imaging radiomics features (AUC: 0.960/0.977). Two radiomics features which included in both LR-grade models showed strong correlation (P < 0.05) with EphA2 expression. The expression of EphA2 in gliomas could be predicted by radiomics features extracted from diffusion kurtosis MRI, which could also be used to assist tumor grading.

Lithium diffusion in La2/3–xLi3xTiO3 (x = 0.115) with 3D-ordered configurations

The present molecular dynamics study investigated lithium-ion diffusion in La2/3–xLi3xTiO3 (x = 0.115) with various structural configurations. The diffusion path and conductivity vary significantly depending on the configuration despite the constant lithium content. A highly-ordered configuration in the in-plane or out-of-plane directions tends to require higher activation energy for diffusion. In each configuration, the largest bottleneck area is found in the principal migration path with the short of Ti–Ti distance along the path. A comparison between various models revealed that the activation energy depends not on the size of the bottleneck area but on the dimensionality of lithium motion: a higher dimensionality such as three-dimensional diffusion lowers the activation energy.

Effects of surface wettability on pool boiling process: Dynamic and thermal behaviors of dry spots and relevant critical heat flux triggering mechanism

In this paper, we investigate experimentally and numerically the influences of surface wettability on the boiling process from nucleate boiling to critical heat flux (CHF). The boiling surfaces with four different wettabilities (apparent contact angles) are examined. Using a simple optic setup, sequential phase distribution images on the boiling surfaces were acquired, and we analyzed the dynamics of microlayer, bulk liquid region, and dry spots with the processed images. The variation of surface wettability significantly affected the liquid and vapor phase behaviors on the boiling surface, such as the growth and shrinkage of the microlayer and dry spot, wetting velocity and area portion of the dry spot. As a result, the CHF increased with the surface wettability, and we found the CHF is triggered from a local dry spot where the liquid wets the spot no longer and is violently scattered by strong evaporation at the triple contact line. Our numerical simulation results, in which the three-dimensional transient heat diffusion equation was solved for the boiling substrate using the phase distribution images as boundary conditions, indicated that certain dry spots (critical dry spot) can be highly overheated under high heat flux condition, and they lead significant heat transfer degradation and, eventually, the CHF. With the numerical results and observation of the phase distribution images at the CHF conditions, we postulated the allowable wetting temperature and formulated it as a function of surface wettability through considering the balance between vapor recoil and surface tension forces. The wetting temperature increased with surface wettability, and it was confirmed by the numerical results. Finally, we proposed a qualitative relation to elucidate the influence of surface wettability on the CHF based on the heat conduction via the vapor on a critical dry spot and heat flux partitioning concept.

Study on the Physical, Chemical and Combustion Characteristics of Pyrolysis Semi-coke

ABSTRACT Combustion is an effective method for large-scale utilization of pyrolytic semi-coke (SC), a high order carbon-based solid fuel with low volatile content. The combustion characteristics of SC can be deeply understood through the study of physical and chemical properties. Taking SC as the research object and anthracite (YQ) with similar chemical composition as the control, the activation energy (E) of SC and YQ was calculated respectively by using model-free method and model method (16 typical mechanism functions). The pre-exponential factor (A), the change of enthalpy (ΔH), the change of entropy (ΔS), and the change of Gibbs free energy (ΔG) during the reaction were calculated. As a result, the pore inside of the particle is the main part of the pore structure of SC. The total specific surface area, pore-volume, and fractal dimension of SC are all larger than that of YQ. There is a lot of amorphous carbon in both SC and YQ, and the lattice spacing and graphitization degree of SC is smaller than that of YQ, but the average aromatic carbon lateral size and crystallite volume are much larger than that of YQ. The carbon in SC and YQ mainly exists in the form of aromatic carbon and aliphatic carbon, and the relative content of aromatic carbon in SC and YQ is basically the same. For the model method, the E of SC and YQ calculated by the three-dimensional diffusion (Spherical symmetric) mechanism function is the closest to the E obtained by the model-free method. Different from YQ, the main combustion stage of SC is composed of fixed carbon combustion and CaCO3 decomposition, and basically, no NH3 and HCN are generated. The volatile content of SC, the total specific surface area, and the pore volume in the pore are larger than that of YQ, which results in that the ignition temperature of SC is lower than that of YQ. The E and burn-out temperature of SC are higher than that of YQ due to the lower oxygen-containing functional group content, higher aromatic carbon content, fractal dimension and larger crystallite volume. Comprehensive physical, chemical, and combustion characteristics results show that using SC by combustion is more difficult than YQ.

Efficient second-order ADI difference schemes for three-dimensional Riesz space-fractional diffusion equations

In this paper, a three-dimensional time-dependent Riesz space-fractional diffusion equation is considered, and an alternating direction implicit (ADI) difference scheme is proposed, in which a weighted and shifted Grünwald difference scheme (see Tian et al. (2015) [33]) is utilized for the discretizations of space-fractional derivatives, and a fractional-Douglas-Gunn type ADI method is utilized for the discretization of time derivative. The method is proved to be unconditionally stable and convergent with second-order accuracy both in time and space with respect to a weighted discrete energy norm. Efficient implementation of the method is carefully discussed, and then based on fast matrix-vector multiplications, a fast conjugate gradient (FCG) solver for the resulting symmetric positive definite linear algebraic system is developed. Numerical experiments support the theoretical analysis and show strong effectiveness and efficiency of the method for large-scale modeling and simulations. Finally, a linearized ADI scheme based on second-order extrapolation method is developed and tested for the nonlinear Riesz space-fractional diffusion equation.

Kinetic analysis of thermal degradation of Cedrela odorata, Marmaroxylon racemosum and Tectona grandis from timber industry

Thermal analysis is a powerful tool to predict the composition and thermal stability of different materials. In this work, thermogravimetric analysis of Cedrela odorata, Marmaroxylon racemosum and Tectona grandis was carried out at four different heating rates (5 °C·min-1, 10 °C·min-1, 20 °C·min-1 and 40 °C·min-1) in a non-isothermal condition. The degradation kinetics was evaluated based on Flynn-Wall-Ozawa and Criado methods. The half-life time of wood degradation reaction was also studied. The wood thermal degradation process in an oxidizing atmosphere can be divided in dehydration, devolatilization, and combustion. The kinetic results revels apparent activation energy values of 130-240 kJ·mol-1 for Tectona grandis, 150-191 kJ·mol-1 for Marmaroxylon racemosum and 188-205 kJ·mol-1 for Cedrela odorata, when conversion values ranged from 0,1-0,5. The most probable degradation mechanism for wood species studied is a diffusion model based on a three-dimensional diffusion. Cedrela odorata presented the lowest reaction half-life time while Marmaroxylon racemosum showed the highest. On the basis of these results, it can be concluded that Flynn-Wall-Ozawa and Criado methods associated with half-life time of reaction may contribute to better understand the wood degradation before use it in polymer composites

Dimensional stability and mechanical performance evolution of continuous carbon fiber reinforced polyamide 6 composites under hygrothermal environment

Abstract This study aimed to investigate moisture absorption behaviors, dimensional stability, and mechanical performance evolution of continuous carbon fibers reinforced with polyamide 6 composites (CF/PA6) under a hygrothermal environment. 3D Fickian model determined the principal three-dimensional (3D) diffusion coefficients by using an optimization algorithm. Three-dimensional changes of samples were measured to quantify the relationship between swelling coefficient and water content. After hygrothermal aging, the tensile properties of PA6 resin and CF/PA6 composites in the transverse direction decreased significantly, but the longitudinal tensile properties of CF/PA6 composites were insensitive to hygrothermal aging. DMA (Dynamic Mechanical Analysis), SEM (Scanning Electron Microscopy) and FTIR (Fourier Transform Infrared) tests were also applied to analyze the mechanism of mechanical properties degradation.