Critical Behaviour in Confined Systems

2005 ◽  
Author(s):  
Eldred H. Chimowitz
Keyword(s):  
Physical Adsorption ◽  
Chemical Separation ◽  
Main Question ◽  
Inorganic Membranes ◽  
Complex Materials ◽  
Fluid Mixture ◽  
Materials Engineering ◽  
Surface Areas ◽  
Confined Fluid ◽  
Two Phases

The prediction of properties in complex materials is a problem of importance in many applications in chemical and materials engineering; by the term “complex material” we mean a heterogeneous substance, like a porous material containing a confined fluid. Such materials appear in many technological applications, including: (1) processes using supercritical fluids to dry porous aeorogels and thin films [1], (2) physical adsorption of trace components from gaseous effluents, (3) gas storage using microporous materials [2], and (4) chemical separation using inorganic membranes [3]. Inorganic membranes are often highly porous and randomly structured materials with large surface areas available for adsorption, a property that makes them useful in chemical separation and as catalyst supports. In addition to their heterogeneity, complex materials have another distinguishing characteristic that relates to the structure of the heterogeneity itself. Is it periodic, or is it dispersed throughout in some random fashion? These two situations are quite distinct and may, in each instance, show critical behavior for a confined fluid belonging to entirely different universality classes, an issue that to the present time is still unsettled in the literature. In this chapter, we investigate the critical properties of fluids confined in randomly structured host materials like that found in porous silicon. The main question we address is: how does confinement in a porous structure affect the critical point or phase behavior of a fluid mixture? Before investigating some of the more advanced ideas in this area, we look at the basic thermodynamics of interfaces, and the phenomenon of capillarity in a single idealized pore structure. This simple example provides the impetus for a more detailed study of confinement effects. Consider two phases in equilibrium separated by an interface. The total energy of the composite system is the sum of the energy of each phase plus the energy associated with the interface. In formulating the fundamental thermodynamic equation for energy in this system, we presume that the formation of an interface requires energy; therefore, the energy equation must reflect this fact.

Studies on the surface area of zeolites, as determined by physical adsorption and X-ray crystallography

1968 ◽  
Vol 46 (10) ◽  
pp. 1695-1701 ◽  
Author(s):  
D. J. C. Yates
Keyword(s):  
Surface Area ◽  
Physical Adsorption ◽  
Independent Method ◽  
Linear Portion ◽  
Adsorbed Molecules ◽  
X Ray ◽  
X Ray Crystallography ◽  
Surface Areas

The determination of the surface areas of zeolites is discussed. It is shown that it is incorrect to use the multilayer isotherm method of Brunauer, Emmett, and Teller for solids where only little more than one monolayer can be adsorbed, in cavities little larger than the adsorbed molecules. The areas of such materials can, however, be determined from the beginning of the linear portion of their isotherms (point B). In addition, X-ray spectra can provide an independent method of measuring changes in the surface areas of zeolites.

Synthesis and Photocatalytic Properties of ZnO-Volcanics Composites

2013 ◽  
Vol 331 ◽  
pp. 497-502
Author(s):  
Ai Hua Wang ◽  
Ping Che ◽  
Jie Min Liu ◽  
Gui Hua Wang
Keyword(s):  
Calcination Temperature ◽  
Physical Adsorption ◽  
Sol Gel ◽  
Degradation Efficiency ◽  
X Ray Diffraction ◽  
Photocatalytic Reactor ◽  
Decolorization Rate ◽  
Surface Areas ◽  
Transmission Electron ◽  
Average Grain Size

in this paper, nano-ZnO were synthesized via a sol-gel method, and ZnO-volcanics composites (ZVCs) were prepared via physical adsorption process. The morphology and structure of ZnO/ ZnO-volcanics composites (ZVCs) samples were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM).BET surface areas of the catalysts were determined by N2 adsorption (BET). According the data of XRD, the average grain size of ZnO is 15.1 nm consistent with the result observed by TEM (16.3 nm). Photocatalytic performance of ZnO and ZVCs were carried out in sprinkling photocatalytic reactor, with methylene blue (MB) as pollutants model. Decolorization rate is select as the evaluation parameters for the degradation effect. The effect of catalyst dosage, MB initial concentration, calcination temperature and pH on the degradation efficiency have been investigated. The MB degradation efficiency was 99.2% when the concentration of MB, the ZVCs, the pH and the calcination temperature were 10 mg/L, 20 g/L, and 10.03, 500 oC respectively. In the catalysts recycle experiments, the decolorization rate of MB using ZVCs is 90.2% after utilization for six times, overwhelmingly higher than that of ZnO (22.6%), indicating immobilization is efficient.

The Australian National Disability Insurance Scheme and People With Disabilities From CALD Backgrounds

2020 ◽  
Vol 9 (3) ◽  
pp. 1-23
Author(s):  
Hossein Adibi
Keyword(s):  
Implementation Process ◽  
People With Disabilities ◽  
Disability Insurance ◽  
Main Question ◽  
Positive Outcomes ◽  
Insurance Scheme ◽  
Vulnerable People ◽  
People With Disability ◽  
Two Phases ◽  
Trial Implementation

The National Disability Insurance Scheme (NDIS) is considered to be the second greatest reform in healthcare in Australia after the introduction of Medicare in Australia in 1983. This reform was introduced in 2012 in two phases. The first phase as a trial took place for three years. The expectation was that the reform will be rolled out by 2019 or 2020. This article argues that the trial implementation process has achieved very positive outcomes in the lives of a great number of people with disability in Australia. At the same time, NDIS is facing many serious challenges in some areas. One of the obvious challenges is that this reform is a market approached reform. The second challenge relates to meeting the needs of minorities. People with disabilities from Culturally and Linguistically Divers (CALD) backgrounds are one of the five most venerable, underutilised users of NDIS services in Australia. They have no strong voice and negotiable abilities. The main question here is how NDIS is to meet its commitment to satisfy the needs of these vulnerable people in Australia.

scholarly journals Immobilization of lipase onto mesoporous silica KIT-6 and montmorillonite K10 for enzymatic hydrolysis of tributyrin

2016 ◽  
Vol 12 (1) ◽  
Author(s):  
Noorulsyahidaini Golbaha ◽  
Zainab Ramli ◽  
Salasiah Endud
Keyword(s):  
Mesoporous Silica ◽  
Incubation Temperature ◽  
Physical Adsorption ◽  
Immobilized Lipase ◽  
High Surface ◽  
Candida Rugosa ◽  
High Surface Area ◽  
Nitrogen Adsorption ◽  
Surface Areas ◽  
Hydrolysis Of

Mesoporous silica KIT-6 and montmorillonite (MMT) K-10 clay were prepared and used for immobilization of the enzyme, Candida rugosa lipases (CRL), aiming at their use as biocatalysts for the hydrolysis of tributyrin. Immobilization of the enzymes onto the supports was performed by physical adsorption using 0.1 M phosphate buffer solutions (pH 7) as the dispersion medium. The activity of the immobilized CRL for tributyrin hydrolysis was investigated at incubation temperature of 40 °C during 120 min and different concentration of the lipase solution for both the supports. Characterization by XRD showed that the long-ranged ordering in the KIT-6 and crystallinity of the MMT K-10 material were affected slightly by the lipase immobilization. This result gives an indication to the present of lipase-support interaction in the immobilized lipase system. Additionally, the results of FTIR spectroscopy verified the presence of silanols on the surfaces of MMT K-10 and KIT-6 materials, while the nitrogen adsorption data showed the resulting immobilized enzyme catalysts were rendered porous, with the KIT-6 giving higher specific surface areas and higher pore diameters in a narrow distribution of sizes ranging from 4 to 12 nm. The immobilization of CRL on KIT-6 and MMT K-10 through hydrogen bonding with the silanol groups, led to an increase in the hydrolysis activity compared to that of free lipase. However, the activity of KIT-6 immobilized CRL was higher than was observed on MMT K-10 immobilized CRL. Furthermore, lipase immobilized on mesoporous silica KIT-6 was shown to be recyclable up to 5 times in aqueous medium. The high surface area and the unique pore system of the mesoporous silica KIT-6, having may be the crucial factors that play an important role in retaining the enzyme in the support, and consequently, improving the lipase activity and stability. 

Characterization of the CaCO3 calcination process by the Porod invariant behaviour

2021 ◽  
Vol 54 (4) ◽  
Author(s):  
Salvino Ciccariello
Keyword(s):  
Amorphous Phase ◽  
Volume Fraction ◽  
Variable Density ◽  
Constant Density ◽  
Surface Areas ◽  
Third Phase ◽  
Powder Samples ◽  
Best Fitting ◽  
Two Phases

The concave behaviour of the Porod invariant observed during the calcination of CaCO3 powder samples suggests the following picture of the evolving internal structure of the samples. The outset sample is formed by a crystalline CaCO3 phase and a void phase. During the calcination, the first phase shrinks in volume at fixed density since the temperature increase breaks down the crystalline structure at the interface, leading to the formation of an amorphous phase comprising an equal number of CO2 and CaO atomic groups. The last groups gradually condense, forming a third phase of solid CaO of constant density and increasing volume fraction, while the companion CO2 groups flow out of the sample. The amorphous phase occupies, with a variable density, all the volume left free by the other two phases. At the end of the calcination, both the volume fraction of the first phase and the density of the amorphous phase vanish so that the sample will again be made up of two phases: the voids and the solid CaO. Best-fitting the resulting theoretical expressions of the Porod invariant and of the Porod law coefficient to the observed values, one can determine the matter densities, volume fractions and specific surface areas of the phases.

Physical adsorption of gases on porous solids. I. Comparison of loose powders and porous plugs

1951 ◽  
Vol 209 (1096) ◽  
pp. 59-69 ◽  
Keyword(s):  
Pore Volume ◽  
Capillary Condensation ◽  
Physical Adsorption ◽  
Particle Surface ◽  
Total Pore Volume ◽  
Internal Surface ◽  
Porous Solids ◽  
Porous Plug ◽  
Surface Areas ◽  
Total Particle

For the first time, comparison has been made of adsorption on a given surface both as a free surface and as the internal surface of a porous plug. In this way it has been possible to provide direct evidence both for capillary condensation and for blockage of capillaries with adsorbed layers in porous solids. Blockage produced well-marked effects only where the surface was of the order of 1000 m. 2 /g. and the porosity was less than 0·6. Where it was observed, it was to be noted that (i) molecules tended to be attracted into blocked capillaries, producing swelling, (ii) monolayer capacities and hence surface areas determined by the B. E. T. method were values which corresponded only to the unblocked surface area when the monolayer is nearly complete. At the low-pressure end of adsorption isotherms, plug and powder gave identical results within the limits of experimental error, i. e. better than 1%, so that, until blockage or capillary condensation was manifested, the total particle surface was accessible to adsorption. In agreement with this, the total pore volume was also accessible, since the volume adsorbed at saturation was not less than the pore volume.

Preparation and Properties of Carbon Nanotube-Reinforced Hydroxyapatite

2007 ◽  
Vol 361-363 ◽  
pp. 419-422 ◽  
Author(s):  
Ashley A. White ◽  
Alan H. Windle ◽  
Ian Kinloch ◽  
Serena Best
Keyword(s):  
Heat Treatment ◽  
Carbon Nanotubes ◽  
Carbon Nanotube ◽  
Medical Devices ◽  
Bet Surface Area ◽  
Multiwalled Carbon ◽  
Preparation Methods ◽  
Surface Areas ◽  
Treatment Conditions ◽  
Two Phases

Composites of hydroxyapatite (HA) and multiwalled carbon nanotubes (CNTs) have been prepared and characterised for potential application in major load-bearing medical devices. We have studied the effect of nanotube surface chemistry, composite preparation methods, and heat treatment conditions on the microstructure of the composites, dispersion of CNTs, and interaction between the HA and CNTs. The samples were characterised using SEM, XRD, FTIR, and BET surface area. It was found that, compared with pure HA, the composites had lower densities and higher surface areas. Additionally, functionalisation improved the dispersion of CNTs in the HA matrix and the interaction between the two phases.

scholarly journals Nanothermodynamic Description and Molecular Simulation of a Single-Phase Fluid in a Slit Pore

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 165
Author(s):  
Olav Galteland ◽  
Dick Bedeaux ◽  
Signe Kjelstrup
Keyword(s):  
Single Phase ◽  
Chemical Potential ◽  
Confined Fluids ◽  
Surface Areas ◽  
Confined Fluid ◽  
Consistent Manner ◽  
Slit Pore ◽  
Slit Pores ◽  
Differential Properties ◽  
First Time

We have described for the first time the thermodynamic state of a highly confined single-phase and single-component fluid in a slit pore using Hill’s thermodynamics of small systems. Hill’s theory has been named nanothermodynamics. We started by constructing an ensemble of slit pores for controlled temperature, volume, surface area, and chemical potential. We have presented the integral and differential properties according to Hill, and used them to define the disjoining pressure on the new basis. We identified all thermodynamic pressures by their mechanical counterparts in a consistent manner, and have given evidence that the identification holds true using molecular simulations. We computed the entropy and energy densities, and found in agreement with the literature, that the structures at the wall are of an energetic, not entropic nature. We have shown that the subdivision potential is unequal to zero for small wall surface areas. We have showed how Hill’s method can be used to find new Maxwell relations of a confined fluid, in addition to a scaling relation, which applies when the walls are far enough apart. By this expansion of nanothermodynamics, we have set the stage for further developments of the thermodynamics of confined fluids, a field that is central in nanotechnology.

scholarly journals On the Microstructure and Properties of the Nb-23Ti-5Si-5Al-5Hf-5V-2Cr-2Sn (at.%) Silicide-Based Alloy—RM(Nb)IC

Metals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1868
Author(s):  
Nikos Vellios ◽  
Paul Keating ◽  
Panos Tsakiropoulos
Keyword(s):  
Oxidation Kinetics ◽  
Cast Alloy ◽  
Lamellar Microstructure ◽  
Isothermal Oxidation ◽  
Surface Areas ◽  
Young’S Moduli ◽  
Heat Treated ◽  
Two Temperatures ◽  
Intermetallic Composite ◽  
Two Phases

The microstructure, isothermal oxidation, and hardness of the Nb-23Ti-5Si-5Al-5Hf-5V-2Cr-2Sn alloy and the hardness and Young’s moduli of elasticity of its Nbss and Nb5Si3 were studied. The alloy was selected using the niobium intermetallic composite elaboration (NICE) alloy design methodology. There was macrosegregation of Ti and Si in the cast alloy. The Nbss, aNb5Si3, gNb5Si3, and HfO2 phases were present in the as-cast or heat-treated alloy plus TiN in the near-the-surface areas of the latter. The vol.% of Nbss was about 80%. There were Ti- and Ti-and-Hf-rich areas in the solid solution and the 5-3 silicide, respectively, and there was a lamellar microstructure of these two phases. The V partitioned to the Nbss, where the solubilities of Al, Cr, Hf, and V increased with increasing Ti concentration. At 700, 800, and 900 °C, the alloy did not suffer from catastrophic pest oxidation; it followed parabolic oxidation kinetics in the former two temperatures and linear oxidation kinetics in the latter, where its mass change was the lowest compared with other Sn-containing alloys. An Sn-rich layer formed in the interface between the scale and the substrate, which consisted of the Nb3Sn and Nb6Sn5 compounds at 900 °C. The latter compound was not contaminated with oxygen. Both the Nbss and Nb5Si3 were contaminated with oxygen, with the former contaminated more severely than the latter. The bulk of the alloy was also contaminated with oxygen. The alloying of the Nbss with Sn increased its elastic modulus compared with Sn-free solid solutions. The hardness of the alloy, its Nbss, and its specific room temperature strength compared favourably with many refractory metal-complex-concentrated alloys (RCCAs). The agreement of the predictions of NICE with the experimental results was satisfactory.

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