Small-Angle X-Ray Investigation of the Porosity in Coals

Kalliat, M.; Kwak, Chul; Schmidt, P. W.

doi:10.1021/bk-1981-0169.ch001

Cited by 37 publications

(24 citation statements)

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“…47 In 1981, Kalliat et al used small angle x-ray scattering to show that there were three classes of pore systems in coal. 41 These results were somewhat consistent with adsorption data interpretation at that time. Small angle x-ray scattering was used later on by Setek et al in 1983 to determine the micropore structure of brown coal.…”

Section: Sans Saxs and Light Scatteringsupporting

confidence: 88%

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Molecular Accessibility in Oxidized and Dried Coals

Kispert¹

1999

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Changes in physical and chemical structure of the micropore system in eight solvent swelled Argonne Premium Coal Sample (APCS) coals upon weathering were studied using the EPR spin probe method. Spin probes, which are allowed to diffuse into the coal structure during swelling, are trapped when the swelling solvent is removed. Excess spin probes are removed from the coal surface and larger pores so that only the presence of spin probes trapped in pores which closely approximate the size of the spin probe are detected. Detailed explanations and illustrations of the experimental procedure used are given.Careful examination of the weathering process on coal as a function of rank was accomplished using the EPR spin probe method. The retention of spin probes in eight APCS coals provided valuable insight into both the loss of water and the oxidation which occur during the weathering process. The results could be explained in terms of the autoxidation process observed in other polymeric systems. It was shown that initial oxidation of coal can result in increased cross-linking in the coal structure. As the oxidation process continued, both the covalent and hydrogen bonded character of the coal were significantly altered. The retention character of some coals during oxidation was shown to change by as much as three orders of magnitude. Experiments were performed to study the effects of short term oxidation and dehydration on coal structure by exposing the coal samples to argon or oxygen for time periods up to five minutes. The results indicate that the structure of coal is extremely sensitive to environmental changes and exhibits significant changes in as little as 30 seconds. Exposure of Illinois #6 coal to argon or oxygen for 30 seconds caused a decrease in the retention of polar spin probes by as much as an order of magnitude.The studies presented here suggest that the structure of coal is dynamic in nature, and has an intimate relationship with the nature of its environment. This method has been shown to be very sensitive to structural changes brought about in coal by oxidation and dehydration, and can be used to follow changes in coal during the swelling process. Additional ideas for future studies using the EPR spin probe method are also discussed.iv

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Section: Sans Saxs and Light Scatteringsupporting

confidence: 88%

“…[41][42][43][44][45][46] It was determined from these studies that the micropores in low-rank coal had elongated cylindrical shapes which had diameters of about 5.2A. More recently, SAXS has been used to study the pore structure during fluid extraction.…”

Section: Sans Saxs and Light Scatteringmentioning

confidence: 99%

Molecular Accessibility in Oxidized and Dried Coals

Kispert¹

1999

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“…Though we have never used a Bonse-Hart system to measure the small-angle scattering for other coals at q<0.01 //~k -1, in our small-angle scattering studies of coal (Bale, Carlson, Kalliat, Kwak & Schmidt, 1984;Kalliat, Kwak & Schmidt, 1981) we have rarely if ever found powerlaw scattering with exponents of magnitude less than 4 (i.e. coals that had surface-fractal pore boundaries) in coals other than lignites.…”

Section: Porous Solidsmentioning

confidence: 85%

Small-angle scattering studies of disordered, porous and fractal systems

Schmidt¹

1991

J Appl Crystallogr

Self Cite

567

390

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Small-angle X-ray and neutron scattering are important techniques for studying the structure of fractals and other disordered systems on a scale of lengths from about 10 to 2000 A. This review begins with a brief outline of some properties of fractals. The small-angle scattering from fractal systems is then discussed and the effect of polydispersity is considered. The intensity of small-angle scattering from fractals and other disordered systems is often proportional to a negative power of the quantity q = 4~,t-Isin(0/2), where 0 is the scattering angle and ,~ is the X-ray or neutron wavelength. From the magnitude of the exponent that describes this type of scattering, which is often called power-law scattering, much important information can be obtained. Some situations in which power-law scattering can be expected are described. To illustrate the scattering from fractals and disordered systems, several experimental investigations of mass-fractal silicas and porous solids are reviewed and some calculations of the small-angle scattering from model fractal systems are outlined.

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“…(6.27) and (6.30), and taking into account that the radius of gyration of pores R g and the Debye correlation length a in Eq. (6.27) are related via R g ¼ a ffiffi ffi 6 p , we get [47,48]:…”

Section: Activated Carbonsmentioning

confidence: 99%

Structural Characterization of Porous Materials Using SAS

Melnichenko

2016

Small-Angle Scattering From Confined and Interfacial Fluids

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This chapter begins with an overview of various engineered and naturally occurring porous solids and their applications in modern technologies. Different modes of confinement, such as topological, chemical, biological, and interfacial, can affect structural and kinetic aspects of the fluid phase equilibria, mechanical and viscoelastic properties, diffusion, and flow in confined spaces. Such dramatic modification of the fluid properties under confinement can be efficiently exploited in a variety of technologies, provided there are ways of controlling the internal structures and surface chemistry of the target porous material at the macroscopic, mesoscopic, microscopic, and molecular levels. SAS represents a nonintrusive technique that can provide information on the structure of porous media that is inaccessible to other methods of structural characterization. The rest of the chapter is devoted to the description of SAS structural analysis of porous silicas, carbons, membranes, polymer monoliths, sedimentary rocks and other common materials.

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Small-Angle X-Ray Investigation of the Porosity in Coals

Cited by 37 publications

References 0 publications

Molecular Accessibility in Oxidized and Dried Coals

Molecular Accessibility in Oxidized and Dried Coals

Small-angle scattering studies of disordered, porous and fractal systems

Structural Characterization of Porous Materials Using SAS

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