BET Parameters Research Articles

Phase diagram prediction and experimental verification of a binary hydrated salt mixture as phase change thermal storage materials

As an important inorganic phase change materials (PCMs), hydrated salts have many advantages such as high latent heat, moderate thermal conductivity, low cost and excellent fire safety compared with organic PCMs. The phase change process of hydrated salts has a significant effect on thermal storage performance. It is meaningful to predict the phase change process by the thermodynamic models. The modified BET model is an effective method to predict the phase diagram of water–salt system. In this work, an applicability of modified BET model used for Na2SO4·10H2O and KAl(SO4)2·12H2O binary hydrated salt mixture was confirmed. According to the BET parameters and solubility constants, the solubility phase diagram of this binary hydrated salt mixture was predicted with modified BET model, and Na2SO4·7H2O was found when Na2SO4·10H2O was lower than 44 wt%. Besides, the phase diagram and the existence of Na2SO4·7H2O were validated in the DSC and XRD measurements. The function of Na2SO4·7H2O to eliminate phase separation was interpreted as that it acts as a thickener to prevent water molecules from escaping from the liquid and avoids the formation of anhydrous Na2SO4. This work could guide the design of binary hydrated salt mixtures as thermal storage materials, and provide new insights for phase separation elimination of hydrated salt mixtures.

Deactivation and Regeneration of Palladium Catalysts for Hydrogenation Debenzylation of 2,4,6,8,10,12-Hexabenzyl-2,4,6,8,10,12-Hexaazaisowurtzitane (HBIW)

2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW, also known as CL-20) is an important energetic compound. As one of the representatives of the third generation of energetic materials, it has an excellent performance, providing broad application prospects for the development of new weapons and equipment. The synthesis of CL-20 is usually obtained from 2,4,6,8,10,12-hexabenzyl-2,4,6,8,10,12-hexaazaisowurtzitane (HBIW) through two catalytic hydrogenolysis and debenzylation reactions, followed by nitration. The most critical step is the hydrogenolysis debenzyl-acetylation process of HBIW because this process requires a large amount of expensive palladium-based catalyst, and the catalyst is completely deactivated after one use. In response to this problem, there is no suitable solution at present, resulting in the high cost of the entire synthesis process. Therefore, reducing the production cost of CL-20 by increasing the catalyst stability is one of the current research priorities. By using AAS, XRD, XPS, TEM, BET, TG and other characterization techniques, the reasons for catalyst deactivation were explored. Studies have shown that the main reason for catalyst deactivation is that a large number of blockages accumulate in the pores of the catalyst after the reaction, which greatly weakens the transfer of the reactant HBIW, intermediate substances, and product 2,6,8,12-tetraacetyl-4,10-dibenzyl-2,4,6,8,10,12-hexaazaisowurtzitane (TADBIW) in the catalyst pores, and the blockage may block the active site of the catalyst. A regeneration treatment method for catalyst deactivation was developed. This method uses chloroform and glacial acetic acid as reagents, which, when combined with stirring and ultrasonic operation, finally restores the activity of the Pd(OH)2/C catalyst. The BET and TG parameters of the regenerated catalyst indicate that catalyst textural and structural properties have greatly recovered, indicating that this treatment method can remove the blockages in the catalyst pores.

Effects of Hydrophobic Modification of Linear- and Branch-Structured Fluorinated and Nonfluorinated Silanes on Mesoporous Silica Particles.

This work reports a comparison of hydrophobic surface modification on mesoporous silica particles (MSPs) obtained by large-scale production using a batch reactor with linear and branched fluorinated and nonfluorinated silanes. Fluorinated silanes were used with TDF-TMOS and TFP-TMOS as a linear and branched structure, respectively. Nonfluorinated silanes were used with OD-TEOS and HMDS as a linear and branched structure, respectively. These four silanes were grafted on the surface of the MSPs as the function of the concentrations, and then, the water contact angles (WCAs) were measured. The WCA of the four silane-grafted MSPs was higher in the branch-structured silanes, namely, TFP-TMOS@MSPs and HMDS@MSPs than in linear-structured silanes, namely, TDF-TMOS and OD-TEOS due to the higher hydrophobicity by a lot of −F and −CH3 groups. Furthermore, the relationship between the WCA and BET parameters was demonstrated using the surface areas, pore volumes, and grafted amounts of the four silane-grafted MSPs. The structural characterization was demonstrated by solid-state 29Si MAS NMR to determine the bonding environment of Si atoms between the grafted silane and the surfaces of MSPs using the T3/T2 and Q3/Q4 ratios of the fluorinated and nonfluorinated silane-grafted MSPs. Among the four silanes, nonfluorinated HMDS@MSPs had a high contact angle of 135° as fluorinated TFP-TMOS@MSPs. When 5 wt % of HMDS@MSPs mixed with gravure ink was coated on a biodegradable polylactic acid (PLA) film, the contact angle was improved to 131.8 from 83.3° of the natural PLA film.

Scavanging nitrophenol from aquatic effluents with triethyl amine catalyzed ambient pressure dried carbon aerogel

Removal of 4-Nitophenol from aquatic effluents through adsorption effected by ambient pressure dried carbon aerogel, was explored in the present investigation. Carbon aerogel was derived from thermal carbonization of Resorcinol-formaldehyde (RF) aerogel at 1050 °C under inert atmosphere. RF aerogel was obtained through sol-gel poly-condensation reaction between resorcinol and formaldehyde catalyzed by a non-conventional organic tertiary amine catalyst (triethyl amine). Gel drying was accomplished through cost effective ambient pressure drying process. Ambient pressure drying technique yielded RF aerogels with almost zero volume shrinkage. Carbon aerogel so obtained, had a very large population of sub-micro, micro and meso pores which were found to be highly conducive to adsorption engineered removal of 4-nitrophenol from aquatic effluent system. The organic amine catalyst was employed at various resorcinol-catalyst mole ratios (R/C), viz.: 100, 250, 500, 1000, 2000 and 3000. The carbon aerogels used in this study showed substantially high affinity for 4-nitrophenol (∼350 mgg−1). Carbon aerogel based adsorption was studied through various models, such as Langmuir, Freundlich, Dubinin-Radushkevich, Temkin and John-Sivanandan Achari (JSA). Specific surface areas of carbon aerogel were calculated from the adsorption data which are very close to those obtained with the BET parameters. Carbon aerogel corresponding to R/C ratio of 2000, is found to be more effective towards adsorption of 4-nitrophenol among the various aerogels considered for the present study. It is further observed that adsorption takes place in multiple stages.

Physico-chemical properties prediction of hydrochar in macroalgae Sargassum horneri hydrothermal carbonisation

ABSTRACT This study evaluates and compares several machine learning methods on the effects of different parameters in the hydrothermal carbonisation (HTC) process of macroalgae Sargassum horneri. Reaction temperature, residence time, biomass particle size, the amount of catalyst and loaded biomass were considered as inputs and three variables of BET, higher heating value (HHV) and energy recovery were regarded as outputs. For analysing the input parameters, the Taguchi method was used for experimental designs and the obtained results were utilised here as training sets. Various data mining approaches like support vector machine (SVM), group method of data handling, decision tree, random forest, radial basis function, adaptive neuro-fuzzy inference system (ANFIS) and multilayer perceptron (MLP) neural network were implemented to model the problem and two different optimisation techniques named BAT and Grasshopper Optimisation Algorithm (GOA) were employed with MLP and ANFIS model for optimising. By comparing different statistical parameters such as Average Absolute Relative Deviation (AARD), coefficient of determination (R2), Root Mean Square Error (RMSE) and Standard Deviation (SD), It is found out that SVM method has a considerably better performance relative to other methods for estimating both the BET, HHV and energy recovery parameters. Furthermore, coupling of MLP and ANFIS with GOA increases the accuracy of these models for BET, HHV and energy recovery estimations.

Application of the modified BET model to concentrated salt solutions with relatively high water activities: Predicting solubility phase diagrams of NaCl + H2O, NaCl + LiCl + H2O, and NaCl + CaCl2 + H2O

Solubility phase diagrams of mixtures of salts and water are of interest in various application fields and can be calculated using the modified BET model. In comparison with other thermodynamic models, the modified BET model requires only two salt-specific model parameters and has shown to possess a predictive capability. In this work, the modified BET equations are extended in order to calculate solubility phase diagrams of concentrated salt solutions with relatively high water activities within the range of undersaturation. As an example, BET parameters of NaCl are determined and applied to calculate solubility phase diagrams of NaCl + H2O, NaCl + LiCl + H2O, and NaCl + CaCl2 + H2O within the temperature range of around 250–500 K. In the ternary systems, the best agreement with solubility data from literature is obtained using constant BET parameters of NaCl and an additional temperature-dependent regular solution parameter to account for salt-salt interaction.

Salts Forming Low-Melting Eutectics with Water: BET Parameters

The BET parameters r for the number of sites and e for the excess molar enthalpy for adsorption of water on the salts, were obtained from their osmotic coefficients in concentrated aqueous salt solutions, as functions of their molalities, from the literature. The salts dealt with are those that form low melting eutectics with water that have not been studied in this respect previously. Most of the data pertain to 298.15 K, but a few data at other temperatures could also be dealt with.

Electrochemistry of TiO2/CdS composite electrodes for supercapacitor applications

This paper outlines a sol–gel method for the synthesis of TiO2/CdS composites with different CdS concentrations for use in supercapacitor applications. Composite electrodes of TiO2/CdS containing zinc (0.25, 0.5, 0.75, and 0.1 M) and sulphide (0.5, 0.1, 1.5, and 2 M) in a 1:2 molar ratio were prepared and are labelled TC1, TC2, TC3, and TC4, respectively. The X-ray diffraction patterns displayed peaks for TiO2 and CdS. A gradual change in morphology from rod like to spherical as the CdS content increased was observed using FE-SEM and confirmed by TEM analysis. Furthermore, the electrochemical properties of all prepared electrodes were analysed using techniques such as cyclic voltammetry (CV), galvanostatic charge–discharge (GV), electrochemical impedance spectroscopy (EIS), and cycle life testing. Among the studied electrodes, CV analysis of TC1 indicated a capacitance of 1296 Fg−1 at a low scan rate of 10 mVs−1, whereas GV analysis showed the value to be 1320 Fg−1 at a scan rate of 10 Ag−1. Also, the significant increase in the energy density and power density of the TC1 electrode may open a new path to supercapacitor applications. The improved electrochemical performance of TC1 can be largely attributed to its increased BET parameters, rod-like morphology, and low charge transfer resistance. Furthermore, an asymmetric capacitor (ASC) was fabricated using the TC1 electrode as the cathode material and activated carbon as the anode. The fabricated ASC had a capacitance of 685 Fg−1 at a scan rate of 10 Ag−1 with a high energy density of 219 kWh kg−1. The repeatability test results imply that even after 500 cycles of operation, the as-fabricated ASC exhibits 95% capacitance retention. Additionally, on charging, the as-fabricated ASC has the ability to glow green in a light-emitting diode. Therefore, the TC1 electrode is a suitable cathode material for next-generation supercapacitors in high-energy density storage systems.

The influence of surface hydrophobicity in fluidization of ultrafine Al2O3 particles

A new approach is hereby presented to study the influence of surface properties on ultrafine alumina (Al2O3) particles towards a fluidized performance by changing the ultrafine particles (Al2O3) surface hydrophobic degree. A number of variables that affects fluidization performance of ultrafine particles (Al2O3), including hydrophobicity has been studied. The minimum full fluidization velocities (Umff), average bed pressure drop (ΔPa), standard deviation in pressure drop (σp) and so on, has been found to depend on the hydrophobic degree, which is a function of the ultrafine particles (Al2O3) surface properties. After treatment of the ultrafine particles (Al2O3) with a surfactant, the liquid-solid contact angle on the ultrafine particles (Al2O3) raises, thus changing the interaction between the ultrafine particles (Al2O3) and also between the ultrafine particles (Al2O3) with the micro-fluidized bed wall surface. Furthermore, some changes in important parameters such as particle size (simple agglomerate size), bulk density, flow function plots, maximum wall friction angle, BET parameters and so on were also evaluated. The fluidization of ultrafine particles is attractive, if the interaction forces between the ultrafine particles (Al2O3) and also between the ultrafine particles (Al2O3) with the micro-fluidized bed wall surface can be artificially controlled. Moreover, it is possible to achieve a better fluidization performance on the ultrafine particles (Al2O3). However, more investigation is required to improve the fluidization performance of the ultrafine particles.

Preparation and characterization of activated carbon from cotton stalk by microwave assisted chemical activation—Application in methylene blue adsorption from aqueous solution

The activated carbon prepared from cotton stalk with ZnCl 2 as activation was investigated under microwave radiation. Effects on the yield and adsorption capacities of activated carbon were evaluated then, such as, microwave power, microwave radiation time and the impregnation ratio of ZnCl 2. It indicated that the optimum conditions were as follows: microwave power of 560 W, microwave radiation time of 9 min and the impregnation ratio of ZnCl 2 was 1.6 g/g. Iodine number, amount of methylene blue adsorption and the yield of activated carbon prepared under optimum conditions were 972.92 mg/g, 193.50 mg/g and 37.92%, respectively. Laboratory prepared activated carbons were characterized by pH ZPC, SEM, FT-IR, S BET and pore structural parameters. Then they were used as adsorbent for the removal of methylene blue from aqueous solutions under varying conditions of initial concentration, carbon dosage and pH. It indicated that Langmuir isotherm was fitter than Freundlich isotherm and Temkin isotherm.

Solid–liquid equilibrium diagrams of common ion binary salt hydrate mixtures involving nitrates and chlorides of magnesium, cobalt, nickel, manganese, and iron(III)

The solid–liquid equilibrium diagrams of binary mixtures involving magnesium nitrate hexahydrate with cobalt nitrate hexahydrate, nickel nitrate hexahydrate (partly), manganese nitrate tetrahydrate, and iron(III) nitrate nonahydrate and of magnesium chloride hexahydrate with cobalt and nickel chlorides hexahydrates and manganese chloride tetrahydrate, and the of two manganese salts were determined. Those diagrams that showed a simple eutectic were fitted by the Ott equation and where the required BET parameters were available, the magnesium salt rich parts of the liquidus were modeled by means of this method.

BET Modeling of Solid–Liquid Phase Diagrams of Common Ion Binary Salt Hydrate Mixtures. I. The BET Parameters

Solid–liquid phase diagrams of binary salt hydrate mixtures can be modeled by means of the BET method, next paper, which considers the water as if it were “adsorbed” on “sites” of the salt. The parameter r describes the average number of sites and e describes the molar enthalpy of adsorption in excess of the enthalpy of condensation of water vapor. The BET parameters r and e required for the modeling were obtained for a large number of salts from water activities or related quantities of concentrated aqueous solutions of them. This paper consists of a comprehensive compilation of these two BET parameters for a large number of salts.

BET Modeling of Solid–Liquid Phase Diagrams of Common-Ion Binary Salt Hydrate Mixtures. II. Calculation of Liquidus Temperatures

The BET method, according to which a molten salt hydrate is considered as if the water is “adsorbed” on “sites” of the salt, was used to model the liquidus temperatures of binary mixtures of common-ion salt hydrates. The method requires as input the BET parameters r, the number of sites and e, the energy of adsorption in excess of that of the condensation of water vapor, as derived in the preceding paper. Further needed input information is the melting temperature of the salt that crystallizes out and its latent heat of melting. It is possible to model the liquidus temperature of the branch of the phase diagram between the pure salt that crystallizes out and the (first) eutectic encountered in the system with this input. The method was applied successfully to binary salt hydrate systems involving magnesium nitrate with magnesium acetate and with aluminum or nickel nitrates, magnesium and nickel chlorides, and calcium chloride with its bromide and nitrate, and with magnesium nitrate.

Characterisation of QMB sensors by means of the BET adsorption isotherm

A calibration protocol was established for a quartz microbalance-based electronic nose (QMBE-nose) that was used for apple aroma measurements. A gas-mixing panel was built to generate a broad concentration range of single apple volatile compounds and of mixtures of two compounds. The response of each QMB sensor was modelled with BET adsorption isotherms. Results show that the affinity of the different sensors to relative humidity can be described well with the BET parameters. The sensors could also be characterised with this model for affinity towards single apple volatiles and mixtures of two apple volatile compounds. By means of multivariate analysis on all sensor responses, the different compounds could be discriminated well and also quantified accurately. The results showed the potential of the QMBE-nose to quantify and discriminate different apple volatile compounds. Also, the established calibration protocol offers an easy and fast tool to characterise new sensors or investigate new application possibilities.

Adsorption Equilibria of CFC-115 on Activated Charcoal

Equilibrium studies on the adsorption of chloropentafluoroethane (CFC-115, CF3CF2Cl) on an activated charcoal were carried out between 298 K and 358 K. Results were fitted with mathematical models such as Langmuir, Freundlich, and BET equations. The temperature dependence of BET parameters and the isosteric enthalpy of adsorption in the CFC-115−charcoal system are estimated. Among the two parameter models, the BET isotherm for CFC-115 fits the experimental results within 7% over the entired relative pressure range. Especially, the BET isotherm showed the best results with less than 2% in the higher relative pressure range. The enthalpies of adsorption of CFC-115 are of the same order of magnitude as the enthalpy of condensation, 14.62 kJ·mol-1.

APPLICATION OF THE BRUNAUER- EMMETT-TELLER ISOTHERM TO THE WATER-NITRIC ACID SYSTEM FOR THE DETERMINATION OF MEAN IONIC ACTIVITY COEFFICIENTS

The application of the BET model to determine ionic activity coefficients of the aqueous nitric acid system is investigated. BET parameters are determined from published data and the model is applied to predict activity coefficients up to very high concentrations. It is shown that the BET model can be used on systems where the reference state is not a regular solid crystal and which exhibit strong hydrogen bonding. Additionally, it is demonstrated that the BET model shows a good potential for application at concentrations an order of magnitude higher than previously investigated. It is revealed that the most important parameter in the BET model at very high concentrations is the choice of a reference state. The focus of this ongoing study is outlined.

Anaerobic threshold determination and its importance in chronic heart failure patients

The goal of this study was to compare various methods of anaerobic threshold (AT) determination and to estimate its importance for both the prescription of appropriate physical activity and long‐term follow‐up evaluation in patients with chronic heart failure (CHF). Twenty‐eight persons (New York Heart Association Classification II, III) passed a symptom‐limited spiroergometrical test; some of them were serially measured. The incremental work rate was graded by 0.25 W‐kg‐1 every 4 minutes. AT was determined from ventilatory parameters (VT), on the one hand, and from base excess changes (—BET), on the other. VT was determined in 79% and —BET in 50% of patients. The correlation between other functional parameters and both VT and ‐BET parameters was close (r = 0.94 for heart rate, for example). The possibility of making an AT determination decreased in Weber's class C patients. AT determination was also possible in persons showing a change in acid‐base balance at rest. Basic functional parameters (heart rate...

Precision Determination of Adsorption Layers on Stainless Steel Mass Standards by Mass Comparison and Ellipsometry: Part I: Adsorption Isotherms in Air

Adsorption layers on stainless steel mass standards (OIML classes E1 and E2) have been determined directly and precisely by the optical method of ellipsometry as a function of relative humidity in the range 0,03 ⩽ h ⩽ 0,77, the relevant influencing factors being surface cleanliness, roughness, steel composition and ambient temperature. Under the same environmental conditions, two pairs of 1 kg artefacts, having geometrical surfaces differing in area by about δ A = 390 cm2, but the same material properties and surface finish as the mass standards, have been compared on a 1 kg mass comparator. The two independent measuring techniques yield strongly correlated results, the standard uncertainties of the measured surface coverings being <or=0,005 μg cm-2. The sorption behaviour of carefully polished surfaces (average peak-to-valley height Rz ⩽ 0,12 μm) is well described by the BET equation for multilayer adsorption, the adsorption isotherm being of type II according to the BET classification. For clean, well-polished surfaces the BET parameters μm = 0,008 4 μg cm-2 and cB = 8,9 were found; the corresponding coefficient in the limited humidity range 0,30 ⩽ h ⩽ 0,60 is 31 × δh ng cm-2. The sorption behaviour of precision stainless steel mass standards is mainly influenced by the degree of surface cleanliness: uncleaned standards with an absolute surface covering of μ' ⩾ 0,7 μg cm-2 show sorption-induced mass variations which are greater by about a factor of 2,5 relative to the clean surfaces.

Adsorption characteristics of alkylketene dimer sized papers determined by inverse gas chromatography at finite concentration

Inverse gas chromatography was used to study the adsorption characteristics of AKD (alkylketene dimer) sized papers in the finite concentration region. The adsorption isotherms for three adsorbates, n-decane, mesitylene, and 1,4-dioxane, on various AKD sized papers were obtained from GC elution peaks at three different temperatures and analyzed. From the adsorption isotherms, the BET parameters and the specific surface areas were obtained. The differential thermodynamic parameters of adsorption were determined as a function of surface coverage. The spreading pressure at the saturated vapor pressure was calculated from the adsorption isotherms, and the surface energies of the papers were determined.

The Influence of the Calibration Procedure of a Volumetric Adsorption Apparatus on the Form of the Isotherm and its BET Parameters

An up-to-date piston-operated automatic adsorption apparatus has been tested. Statistical analysis of the results has shown that the adsorbate must be considered as a real gas if a precision of 1% in the adsorption isotherm is to be aimed for at points around 1 bar for gases having a second virial coefficient higher than about 30 cm3/mol. A quadratic calibration is recommended and the influence of operational variables demonstrated on a few examples. Results can be applied, mutatis mutandis, to any volumetric adsorption apparatus. It has then been shown that the generally applied linear calibration procedure gives deformed isotherms, their evaluation resulting in BET surface areas 2–12% lower than those obtained by subtracting the non-adsorbed part of the adsorbate with the quadratic, real gas, calibration curve. Finally, it has been shown that isotherms determined by the gravimetric method are the same as those determined with the real gas calibration and give the same BET surface areas.