Dielectric Relaxation Based on Adsorbed Water in Wood Cell Wall under Non-Equilibrium State 2

Holzforschung ◽  
2001 ◽  
Vol 55 (1) ◽  
pp. 87-92 ◽  
Author(s):  
C. Jinzhen ◽  
Z. Guangjie
Keyword(s):  
Cell Wall ◽  
Equilibrium State ◽  
Dielectric Relaxation ◽  
Adsorption Process ◽  
Wood Cell Wall ◽  
Adsorbed Water ◽  
Thermodynamic Quantities ◽  
Frequency Spectra ◽  
Adsorption Sites ◽  
Non Equilibrium

Summary In order to explain, on molecular level, the unusualness of wood physical properties under moisture non-equilibrium state, the dielectric temperature and frequency spectra of Sikkim spruce (Picea spinulosa Griff.) specimens were measured during the adsorption process in 20°C, 60% R.H. environment. Furthermore, the dielectric relaxation based on adsorbed water was separated from that based on the methanol groups in the amorphous region of wood cell wall, so that the thermodynamic quantities of adsorbed water associated with the adsorption process could be evaluated. Consequently, the molecular reorientation model of adsorbed water molecules during the dielectric relaxation process was constructed. The results show that the activation enthalpy ∆H and activation entropy ∆S of adsorbed water both increase linearly with the adsorption time. During the initial adsorption period ∆S appears as a negative value. According to the values of thermodynamic quantities, especially the ∆H values, it can be inferred that the average number of hydrogen bonds formed between each adsorbed water molecule with its surrounding wood adsorption sites increases gradually with developing adsorption. The model based on the obtained data in this experiment shows that after 7 hours' adsorption the number is between two and three, after 24 hours it is three and later it approaches four.

Dielectric Relaxation Based on Adsorbed Water in Wood Cell Wall under Non-Equilibrium State. 1

Holzforschung ◽  
2000 ◽  
Vol 54 (3) ◽  
pp. 321-326 ◽  
Author(s):  
Cao Jinzhen ◽  
Zhao Guangjie
Keyword(s):  
Cell Wall ◽  
Dielectric Relaxation ◽  
Relaxation Process ◽  
Wood Cell Wall ◽  
Adsorbed Water ◽  
Amorphous Region ◽  
Oh Groups ◽  
Adsorption Processes ◽  
Initial Adsorption ◽  
State 1

Summary In order to make clear the molecular mechanism of the dielectric relaxation based on adsorbed water in wood cell wall during moisture changing process, the temperature and frequency spectrums of dielectric processes of Sikkim spruce (Picea spinulosa Griff.) were measured in three different adsorption processes. Three levels of relative humidity used were 40, 80 and 100 %, respectively, and the temperature was kept at 20°C. In oven-dry state, relaxation process I based on the reorientation of CH2OH groups in amorphous region of wood cell wall was observed. While in moist state, relaxation process II based on ionic conductivity and relaxation process III based on the additive reorientation of CH2OH groups and adsorbed water molecules occurred. Within higher humidity region, relaxation process IV concerned with adsorbed water in lignin was observed in the initial adsorption period, but it vanished with further adsorption.

Characterizing spatial distribution of the adsorbed water in wood cell wall of Ginkgo biloba L. by μ-FTIR and confocal Raman spectroscopy

Holzforschung ◽  
2017 ◽  
Vol 71 (5) ◽  
pp. 415-423 ◽  
Author(s):  
Xin Guo ◽  
Yiqiang Wu ◽  
Ning Yan
Keyword(s):  
Raman Spectroscopy ◽  
Cell Wall ◽  
Spatial Distribution ◽  
Water Distribution ◽  
Water Concentration ◽  
Physical And Mechanical Properties ◽  
Adsorbed Water ◽  
Confocal Raman Spectroscopy ◽  
Adsorption Sites ◽  
Confocal Raman

Abstract The adsorbed water influences significantly, the physical and mechanical properties of wood. In the present paper, the spatial distribution of adsorbed water in wood cell walls has been studied by μ-Fourier transform infrared (μ-FTIR) and confocal Raman spectroscopy. In situ μ-FTIR spectra were collected from three randomly selected areas in different cell wall regions, which were exposed to an environment with 0% to 96% relative humidity (RH). The water adsorption sites were easily detectable based on OH, C=O, and C-O group vibrations and it was shown that the adsorbed water concentration was not uniform in different regions. Confocal Raman spectroscopy images were collected from the cell corner (CC) and middle layer of the secondary wall (S2) and the non-uniformity of water distribution could also be confirmed by this approach. It was demonstrated that both μ-FTIR and confocal Raman spectroscopy provide valuable information about the spatial distribution of adsorbed water in morphologically distinct cell wall regions.

Dielectric Relaxation Based on Adsorbed Water in Wood Cell Wall under Non-Equilibrium State. Part 3. Desorption

Holzforschung ◽  
2002 ◽  
Vol 56 (6) ◽  
pp. 655-662 ◽  
Author(s):  
C. Jinzhen ◽  
Z. Guangjie
Keyword(s):  
Dielectric Constant ◽  
Dielectric Relaxation ◽  
Adsorbed Water ◽  
Second Step ◽  
Relaxation Processes ◽  
Relaxation Time Distribution ◽  
Dielectric Parameters ◽  
Frequency Spectra ◽  
Desorption Process ◽  
Content Change

Summary The temperature and frequency spectra of dielectric constant ε′ and dielectric loss factor ε″ of Sikkim spruce (Picea spinulosa Griff.) were measured to investigate the change in dielectric relaxation of water in wood during desorption. In order to control the rate of moisture content change, the measurements were carried out in three steps: from fiber saturation point to 80% RH, from 80% RH to 60% RH and from 60% RH to 20% RH, at 25°C. Two dielectric relaxation processes were observed in different temperature and frequency regions which changed their position and strength with the desorption process. Using the ε′ and ε″ spectra, two groups of Cole-Cole plots were obtained, on which basis two groups of dielectric parameters including the static dielectric constant εS, optic dielectric constant ε∞, relaxation strength (εS–ε∞), and the relaxation time distribution coefficient α were calculated. Both groups of parameters showed similar trends, that is, ε∞ remained nearly constant during the whole desorption process. εS and (εS–ε∞)changed little during the first step of desorption, decreased obviously during the second step and declined slightly during the third step. The α value obtained from the lower frequency data changed significantly during the second and third desorption steps, while there was little change in the other group of α values. These differences can be explained by different mechanisms of the relaxation processes in the lower and higher frequency regions.

Review of Applications of Rate-Controlled Constrained-Equilibrium in Combustion Modeling

2020 ◽  
Vol 45 (1) ◽  
pp. 59-79 ◽  
Author(s):  
Guangying Yu ◽  
Fatemeh Hadi ◽  
Ziyu Wang ◽  
Hameed Metghalchi
Keyword(s):  
Equilibrium State ◽  
Order Reduction ◽  
Second Law Of Thermodynamics ◽  
Equilibrium States ◽  
Computational Time ◽  
Thermodynamic Quantities ◽  
Constrained Equilibrium ◽  
Rate Controlled ◽  
Order Reduction Method ◽  
Non Equilibrium

AbstractDeveloping an effective model for non-equilibrium states is of great importance for a variety of problems related to chemical synthesis and combustion. Rate-Controlled Constrained-Equilibrium (RCCE), a model order reduction method that originated from the second law of thermodynamics, assumes that the non-equilibrium states of a system can be described by a sequence of constrained-equilibrium states kinetically controlled by a relatively small number of constraints within acceptable accuracy. The full chemical composition at each constrained-equilibrium state is obtained by maximizing (or minimizing) the appropriate thermodynamic quantities, e. g., entropy (or Gibbs functions), subject to the instantaneous values of RCCE constraints. Regardless of the nature of the kinetic constraints, RCCE always guarantees a correct final equilibrium state. This paper reviews the fundamentals of the RCCE method, its constraints, constraint potential formulations, and major constraint selection techniques, as well as the application of the RCCE method to combustion of different fuels using a variety of combustion models. The RCCE method has been proven to be accurate and to reduce computational time in these simulations.

scholarly journals Adsorption process and mechanism of heavy metal ions by different components of cells, using yeast (Pichia pastoris) and Cu2+ as biosorption models

RSC Advances ◽  
2021 ◽  
Vol 11 (28) ◽  
pp. 17080-17091
Author(s):  
Xinggang Chen ◽  
Zhuang Tian ◽  
Haina Cheng ◽  
Gang Xu ◽  
Hongbo Zhou
Keyword(s):  
Heavy Metal ◽  
Pichia Pastoris ◽  
Metal Ions ◽  
Cell Walls ◽  
Heavy Metal Ions ◽  
Adsorption Process ◽  
Yeast Pichia Pastoris ◽  
Adsorption Sites

The Cu2+ first bound to the outer mannan and finally entered the cytoplasm. During the whole adsorption process, the number of adsorption sites in the outer and middle cell walls was the largest, and then gradually decreased.

Acetyl Group Distribution in Acetylated Wood Investigated by Microautoradiography

Holzforschung ◽  
2001 ◽  
Vol 55 (3) ◽  
pp. 270-275 ◽  
Author(s):  
Marie Rosenqvist
Keyword(s):  
Cell Wall ◽  
Weight Gain ◽  
Acetic Anhydride ◽  
Wood Cell Wall ◽  
Environmental Scanning Electron Microscopy ◽  
Environmental Scanning ◽  
Accurate Information ◽  
Concentration Gradients ◽  
Good Opportunity ◽  
Acetyl Group

Summary Sapwood of Scots pine (Pinus silvestris L.) was acetylated with 14C- and 3H-labelled acetic anhydride. The distribution of acetyl groups was investigated with microautoradiography and microautoradiographs were evaluated with ESEM, Environmental Scanning Electron Microscopy. The investigation showed that the impregnation of wood with radioisotope-labelled substances provides a good opportunity to investigate the location of substances covalently bonded to the wood material. Introduced 14C-labelled acetyl groups show an even distribution in the wood cell wall, with no discernible concentration gradients at acetylation levels of about 5, 15 and 20% weight gain. 3H-labelled acetyl groups show an even distribution in the wood cell wall at 15 and 20% weight gain, with no discernible concentration gradients. At the 5% weight gain level, however, an uneven distribution of 3H-labelled acetyl groups over the cell wall is observed. Nevertheless, the unevenness is random and no concentration gradient is discernible at this level. 3H with a relatively high resolution, 0.5–1 μm, compared to 14C with a resolution of 2–5 μm, gives more accurate information about where exactly the acetyl groups are situated in the wood cell wall. Acetic anhydride was evenly distributed when a full impregnation procedure was used. The chemical and physical properties of acetic anhydride allow a uniform penetration into the pine cell wall and a complete acetylation takes place when the specimens are heated.

scholarly journals Water and Carbon Dioxide Adsorption on CaO(001) Studied via Single Crystal Adsorption Calorimetry

2021 ◽  
Author(s):  
J. Seifert ◽  
S. J. Carey ◽  
S. Schauermann ◽  
S. Shaikhutdinov ◽  
H.-J. Freund
Keyword(s):  
Adsorption Energy ◽  
Adsorbed Water ◽  
Spectroscopic Studies ◽  
Detector Response ◽  
Adsorption Calorimetry ◽  
Instrument Response Function ◽  
Line Shapes ◽  
Adsorption Sites ◽  
Saturation Coverage ◽  
Initial Adsorption

AbstractA new method to analyze microcalorimetry data was employed to study the adsorption energies and sticking probabilities of D2O and CO2 on CaO(001) at several temperatures. This method deconvolutes the line shapes of the heat detector response into an instrument response function and exponential decay functions, which correspond to the desorption of distinct surface species. This allows for a thorough analysis of the adsorption, dissociation, and desorption processes that occur during our microcalorimetry experiments. Our microcalorimetry results, show that D2O adsorbs initially with an adsorption energy of 85–90 kJ/mol at temperatures ranging from 120 to 300 K, consistent with prior spectroscopic studies that indicate dissociation. This adsorption energy decreases with increasing coverage until either D2O multilayers are formed at low temperatures (120 K) or the surface is saturated (> 150 K). Artificially producing defects on the surface by sputtering prior to dosing D2O sharply increases this adsorption energy, but these defects may be healed after annealing the surface to 1300 K. CO2 adsorbs on CaO(001) with an initial adsorption energy of ~ 125 kJ/mol, and decreases until the saturation coverage is reached, which is a function of surface temperature. The results showed that pre-adsorbed water blocks adsorption sites, lowers the saturation coverage, and lowers the measured adsorption energy of CO2. The calorimetry data further adds to our understanding of D2O and CO2 adsorption on oxide surfaces.

scholarly journals Enhancement of the physical and mechanical properties of wood using a novel organo-montmorillonite/hyperbranched polyacrylate emulsion

Holzforschung ◽  
2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Jianfeng Xu ◽  
Xiaoyan Li ◽  
Ling Long ◽  
Ru Liu
Keyword(s):  
Mechanical Properties ◽  
Cell Wall ◽  
Pinus Radiata ◽  
Wood Sample ◽  
Wood Cell Wall ◽  
Physical And Mechanical Properties ◽  
Radiata Pine ◽  
Compact Structure ◽  
Populus Cathayana ◽  
Modified Wood

AbstractIn this work, a novel waterborne hyperbranched polyacrylate (HBPA) dispersed organo-montmorillonite (OMMT) emulsion was synthesized and used for the treatment of wood in a vacuum environment in order to enhance the physical and mechanical properties of the wood. The sapwood of Cathay poplar (Populus cathayana Rehd.) and Radiata pine (Pinus radiata D.Don) were used as the samples for experimentation. The results showed that the physical and mechanical properties of the wood improved significantly due to the successful penetration of the OMMT and HBPA into the wood cell wall. From it was also observed that OMET completely exfoliated from the HBPA matrix and formed a hydrophobic film covering on the inside walls of the cell lumen. Further, it was observed that the poplar sample displayed better mechanical properties than the pine sample because the pine has a more compact structure when compared to poplar and contains rosin. Furthermore, it was also observed that the mechanical properties of the modified wood sample gradually improved with an increase in the concentration of the emulsion. However, excessive concentration (>4 wt%) did not lead to further improvement.

Ostwald´s Rule and the Principle of the Shortest Way

2010 ◽  
Vol 224 (06) ◽  
pp. 929-934 ◽  
Author(s):  
Herbert W. Zimmermann
Keyword(s):  
Melting Point ◽  
Equilibrium State ◽  
Entropy Production ◽  
Thermodynamic Stability ◽  
Lagrange Equation ◽  
Classical Mechanics ◽  
Geodesic Line ◽  
Final Equilibrium State ◽  
Relevant Variables ◽  
Non Equilibrium

AbstractWe consider a substance X with two monotropic modifications 1 and 2 of different thermodynamic stability ΔH1 < ΔH2. Ostwald´s rule states that first of all the instable modification 1 crystallizes on cooling down liquid X, which subsequently turns into the stable modification 2. Numerous examples verify this rule, however what is its reason? Ostwald´s rule can be traced back to the principle of the shortest way. We start with Hamilton´s principle and the Euler-Lagrange equation of classical mechanics and adapt it to thermodynamics. Now the relevant variables are the entropy S, the entropy production P = dS/dt, and the time t. Application of the Lagrangian F(S, P, t) leads us to the geodesic line S(t). The system moves along the geodesic line on the shortest way I from its initial non-equilibrium state i of entropy Si to the final equilibrium state f of entropy Sf. The two modifications 1 and 2 take different ways I1 and I2. According to the principle of the shortest way, I1 < I2 is realized in the first step of crystallization only. Now we consider a supercooled sample of liquid X at a temperature T just below the melting point of 1 and 2. Then the change of entropy ΔS1 = Sf 1 - Si 1 on crystallizing 1 can be related to the corresponding chang of enthalpy by ΔS1 = ΔH1/T. Now it can be shown that the shortest way of crystallization I1 corresponds under special, well-defined conditions to the smallest change of entropy ΔS1 < ΔS2 and thus enthalpy ΔH1 < ΔH2. In other words, the shortest way of crystallization I1 really leads us to the instable modification 1. This is Ostwald´s rule.

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