@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/81924,
    title ="Comparison of effective conductivities calculated by the effective medium approximation and the self consistent approximation for core-shell particulate composites",
    author = "Gavalas, George R.",
    journal = "AIP Advances",
    volume = "7",
    number = "9",
    pages = "Art. No. 095222",
    month = "September",
    year = "2017",
    doi = "10.1063/1.4999331",
    issn = "2158-3226",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20170929-120230481",
    note = "© 2017 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).\n\nReceived 7 August 2017; accepted 21 September 2017; published online 29 September 2017.",
    revision_no = "10",
    abstract = "The effective conductivity of composites containing simple or core-shell particles has been estimated in the literature using the Mean Field Approximation (MFA) and the Self-Consistent Approximation (SCA) among other techniques. It is shown here that for both simple and core-shell particles the two approximations agree to first order in the particle volume fraction but differ at the second order term. For simple particles the coefficient of the second order term calculated by SCA is at much better agreement with previous exact results than the coefficient calculated by MFA. For core-shell particles the results of the two approximations are almost identical up to particle volume fraction 0.20 but diverge with increasing volume fraction and particle-to-matrix conductivity ratio.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/47490,
    title ="Extension of Rayleigh–Ritz method for eigenvalue problems with discontinuous boundary conditions applied to vibration of rectangular plates",
    author = "Gavalas, George R. and El-Raheb, Michael",
    journal = "Journal of Sound and Vibration",
    volume = "333",
    number = "17",
    pages = "4007-4016",
    month = "August",
    year = "2014",
    doi = "10.1016/j.jsv.2014.03.030 ",
    issn = "0022-460X",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20140725-075706960",
    note = "© 2014 Elsevier Ltd.\n\nReceived 10 May 2013;\nReceived in revised form\n21 March 2014;\nAccepted 24 March 2014.\nHandling Editor: H. Ouyang.\nAvailable online 10 May 2014.",
    revision_no = "10",
    abstract = "The Rayleigh–Ritz (R–R) method is extended to eigenvalue problems of rectangular plates with discontinuous boundary conditions (DBC). Coordinate functions are defined as sums of products of orthogonal polynomials and consist of two parts, each satisfying the BC in its respective region. These parts are matched by minimizing the mean square error of functions and their x-derivatives at the interface between regions. Matching defines a positive definite 2N^2 × 2N^2 matrix Q whose eigenvectors form the orthogonal coordinate functions. The corresponding eigenvalues measure the matching error of the two parts at the interface. When applying the R–R method, the total error is the sum of the matching error and that arising from the finite number of coordinate functions. Although most of the coordinate functions correspond to the zero eigenvalue, these do not suffice and additional functions corresponding to small but finite eigenvalues must be included. In three examples with discontinuous BC of the clamped, simply supported and free kind, the calculated frequencies match closely those from a finely discretized finite element method.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60815,
    title ="Diffusion in Microporous Membranes: Measurements and Modeling",
    author = "Gavalas, George R.",
    journal = "Industrial & Engineering Chemistry Research",
    volume = "47",
    number = "16",
    pages = "5797-5811",
    month = "August",
    year = "2008",
    doi = "10.1021/ie800420z",
    issn = "0888-5885",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150209770",
    note = "© 2008 American Chemical Society. \n\nReceived for reView March 14, 2008 Revised manuscript receiVed May 5, 2008; Accepted May 16, 2008.",
    revision_no = "10",
    abstract = "Permeation of gases and vapors through microporous membranes, principally zeolite membranes, is reviewed, focusing on macroscopic diffusion models, measurement techniques, and applications of models to experimental data. Brief reference is made to the choice of adsorption isotherms for single components or mixtures. Concerning diffusion, the Maxwell−Stefan (M-S) model is reviewed in some detail, as it is the one universally adopted in recent literature. Emphasis is placed on the coverage dependence of the diffusion coefficients and on the proper handling of the cross terms. In the experimental technique section, the key distinctions are between steady state and transient measurements, and between the use or nonuse of a sweep gas. A few special techniques are also briefly reviewed. Interpretation of transient measurements using the time lag method is reviewed in some detail, especially for coverage-dependent diffusion coefficients. Several of the studies reviewed focus on the ability of the M-S model to match the measurements, and specifically on the suitability of various simplifying approximations. Two common approximations are (i) to treat the M-S diffusion coefficients as coverage-independent and (ii) to neglect the cross terms.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60816,
    title ="Measurement of concentration-dependent gas diffusion coefficients in membranes from a psuedo-steady state permeation run",
    author = "Villet, Michael C. and Gavalas, George R.",
    journal = "Journal of Membrane Science",
    volume = "297",
    number = "1-2",
    pages = "199-205",
    month = "July",
    year = "2007",
    doi = "10.1016/j.memsci.2007.03.045",
    issn = "0376-7388",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150210067",
    note = "© 2007 Elsevier. \n\nReceived 10 January 2007; received in revised form 20 March 2007; accepted 24 March 2007; Available online 1 April 2007. \n\nSupport by NSF grant CTS-0084155 is gratefully acknowledged.",
    revision_no = "10",
    abstract = "Transient permeation measurements were conducted for carbon dioxide through a PDMS membrane and for carbon dioxide and methane through a ZSM-5 zeolite membrane. After pressurization the feed tank was shut off from the supply and pressure and flux measurements were conducted while the feed-side pressure gradually declined over the course of each run. A series of steady state runs were also conducted for the same range of feed-side pressures. In all runs the transient fluxes were close to the steady state fluxes at corresponding feed-side pressures indicating that the transient evolved at a pseudo-steady state. A dimensionless parameter depending on the feed tank volume, membrane geometry, and adsorption properties was defined to characterize the deviation from steady state. \n\nConcentration-dependent diffusion coefficients were estimated from (i) steady state fluxes from a sequence of runs, (ii) transient fluxes from a single run, and (iii) transient pressure measurements from a single run. The fluxes and the diffusion coefficients obtained from a single transient run, and from a sequence of steady state runs are compared and the observed differences are discussed.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60817,
    title ="Preparation of Oxygen Ion Conducting Ceramic Hollow-Fiber Membranes",
    author = "Liu, Shaomin and Gavalas, George R.",
    journal = "Industrial & Engineering Chemistry Research",
    volume = "44",
    number = "20",
    pages = "7633-7637",
    month = "September",
    year = "2005",
    doi = "10.1021/ie040279i",
    issn = "0888-5885",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150210337",
    note = "© 2005 American Chemical Society. \n\nReceived for review November 15, 2004; Accepted March 22, 2005. \n\nWe gratefully acknowledge the support provided by the Petroleum Research Fund of the American Chemical Society (Grant 38162-AC5).",
    revision_no = "10",
    abstract = "Hollow-fiber membranes of mixed conducting perovskite Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ) were prepared using a sequence of extrusion, gelation, and sintering steps. For this purpose, a finely divided mixture of the component oxides was prepared by the modified Pechini technique and suspended in a polymer solution. The suspension was extruded through a spinneret and gelled in water. The resulting fiber was first heated at 800 °C to remove the polymer and then at 1100 °C to form the perovskite and simultaneously sinter the particles to a gastight membrane. The fibers were characterized by scanning electron microscopy and tested for air separation at ambient pressure and temperature between 700 and 950 °C. The maximum oxygen flux measured was 3.9 mL/min/cm^2 at 950 °C and 0.022 atm of average permeate oxygen partial pressure.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60818,
    title ="Oxygen selective ceramic hollow fiber membranes",
    author = "Liu, Shaomin and Gavalas, George R.",
    journal = "Journal of Membrane Science",
    volume = "246",
    number = "1",
    pages = "103-108",
    month = "January",
    year = "2005",
    doi = "10.1016/j.memsci.2004.09.028",
    issn = "0376-7388",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150210599",
    note = "© 2004 Elsevier. \n\nReceived 22 June 2004; received in revised form 9 September 2004; accepted 15 September 2004; Available online 19 November 2004. \n\nThe authors gratefully acknowledge the support provided by the Petroleum Research Fund of the American Chemical Society, Grant No. 38162-AC5.",
    revision_no = "10",
    abstract = "Oxygen ion conducting Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3−δ) hollow fiber membranes with o.d. 1.15 mm and i.d. 0.71 mm were fabricated using a sequence of extrusion, gelation, coating and sintering steps. The starting ceramic powder was synthesized by combined EDTA–citrate complexing followed by thermal treatment at 900 °C. The powder was then dispersed in a polymer solution, and extruded through a spinerette. After gelation, an additional thin coating of the ceramic powder was applied on the fiber, and sintering was carried out at 1190 °C to obtain the final ceramic membrane. The fibers were characterized by SEM, and tested for air separation at ambient pressure and at temperatures between 700 and 950 °C. The maximum oxygen flux measured was 5.1 mL/min/cm^2 at 950 °C.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60819,
    title ="Glass−Carbon Composite Hollow Fibers",
    author = "Liu, Shaomin and Gavalas, George R.",
    journal = "Industrial & Engineering Chemistry Research",
    volume = "43",
    number = "12",
    pages = "3137-3140",
    month = "June",
    year = "2004",
    doi = "10.1021/ie0308644",
    issn = "0888-5885",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150210837",
    note = "© 2004 American Chemical Society. \n\nReceived for review December 9, 2003; Revised manuscript received April 7, 2004; Accepted April 16, 2004. \n\nThe authors gratefully acknowledge the research funding provided by the U.S. Department of Energy (Grant DE-FG26-00NT40817).",
    revision_no = "10",
    abstract = "Glass−carbon composite hollow fibers were prepared by extruding a suspension of glass particles in an N-methylpyrrolidone solution of poly(ether sulfone). The fibers were gelled in water and pyrolyzed for 0.5−30 min in a furnace preheated to 1100−1200 °C. The resulting composite carbon−glass fibers had about 2.1 mm o.d. and 1.3 mm i.d. Scanning electron microscopy was used to examine fiber morphology, while the nitrogen permeance was about 7 × 10^(-5) mol/m^2·Pa·s, indicating pores of micron size. Compared to pure glass fibers, which are easily deformed at 900 °C, the composite fibers could withstand temperatures up to 1200 °C without suffering deformation.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60820,
    title ="Intrapore Synthesis of Silicalite Membranes at Temperatures below 100 °C",
    author = "Kang, Beom Seok and Gavalas, George R.",
    journal = "Industrial & Engineering Chemistry Research",
    volume = "41",
    number = "13",
    pages = "3145-3150",
    month = "June",
    year = "2002",
    doi = "10.1021/ie010918e",
    issn = "0888-5885",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150211096",
    note = "© 2002 American Chemical Society. \n\nReceived for review November 13, 2001. Revised manuscript received March 28, 2002. Accepted April 2, 2002. \n\nThis work was funded by the Department of Energy, National Energy Technology Laboratory, Grant DE-FG26-00NT40817.",
    revision_no = "10",
    abstract = "Growth of silicalite membranes inside the pores of α-Al_2O_3 support tubes was carried out at 95 °C. The support tubes had a 1-μm mean pore diameter and were seeded by impregnation in a suspension of 0.1-μm silicalite particles prior to membrane growth. The membranes were weighed to determine the total reaction product and examined by SEM and EDS to estimate the spatial distribution. Reaction product was found at a depth of 100 μm or more inside the pores of the support. The membranes were tested in single gas permeations of hydrogen, nitrogen, n-butane, and isobutane and in the separation of n-butane/isobutane mixtures. After three growth periods, mixture measurements gave n-butane permeances of 10−17 MPU [1 MPU = 10^(-8) mol/(m^2 s Pa)] and n-butane/isobutane selectivities of 30−40 at room temperature. The selectivity results are discussed in terms of gaps between the intrapore crystals.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60821,
    title ="A multiple microreactor system for parallel catalyst preparation and testing",
    author = "Pantu, Piboon and Gavalas, George R.",
    journal = "AIChE Journal",
    volume = "48",
    number = "4",
    pages = "815-819",
    month = "April",
    year = "2002",
    doi = "10.1002/aic.690480415",
    issn = "0001-1541",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150211344",
    note = "© 2002 American Institute of Chemical Engineers (AIChE). \n\nManuscript received May 21, 2001, and revision received Oct. 15, 2001.",
    revision_no = "10",
    abstract = "A system containing nine catalytic microreactors for parallel preparation and testing of heterogeneous catalysts is described. The catalyst samples are prepared in the form of thin films coated on thin quartz rods by dip-coating in solutions of different composition. Catalyst-coated rods are placed within thin tubes housed inside a wider tube heated in an electrical furnace. A multiport valve serves to sequentially conduct the reaction products from each microreactor to a mass spectrometer for analysis. The system was tested with the reaction of methane reforming with carbon dioxide over Pt/Ce_(1−x)Gd_xO_(2−0.5x) and Pt/Ce_(1−x)Sm_xO_(2−0.5x) at 650 and 700°C. Individual catalysts were characterized by X-ray analysis, and induction-coupled plasma mass spectrometry for catalyst mass and elemental composition. The measurements showed that Pt/CeO_2 had the highest activity among the series of catalysts tested and generally the activity increased with the cerium oxide content. After exposure to the feedstream for 2–3 h at 700°C, most catalysts suffered significant deactivation except the mixed oxides with 25–85% samarium oxide that maintained relatively stable activity.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60822,
    title ="Methane partial oxidation on Pt/CeO_2 and Pt/Al_2O_3 catalysts",
    author = "Pantu, Piboon and Gavalas, George R.",
    journal = "Applied Catalysis A: General",
    volume = "223",
    number = "1-2",
    pages = "253-260",
    month = "January",
    year = "2002",
    doi = "10.1016/S0926-860X(01)00761-X",
    issn = "0926-860X",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150211577",
    note = "© 2002 Elsevier. \n\nReceived 28 March 2001; received in revised form 24 July 2001; accepted 25 July 2001.",
    revision_no = "11",
    abstract = "Partial oxidation of methane to synthesis gas over 0.5 wt.% Pt/Al_2O_3 and 0.5 wt.% Pt/CeO_2 catalysts was studied in a packed-bed reactor and supplementary runs of methane reforming with carbon dioxide were carried out. Fresh and used catalysts were characterized by nitrogen adsorption (BET method) for total surface area, and by H_2 and CO chemisorption or by the rate of propene hydrogenation for metal surface area. At temperatures up to 650°C, the Pt/CeO_2 catalyst gave considerably higher methane conversion and higher selectivity to CO and H_2 but above 700°C, the activities and selectivities of both catalysts were comparable. The Pt/CeO_2 catalyst maintained high selectivity to CO and H_2 when the CH_4:O_2 feed ratio varied from 1.7 to 2.3 while the Pt/Al_2O_3 catalyst had lower activity and selectivity under methane-rich conditions. The Pt/CeO_2 catalyst was also more active for methane reforming by carbon dioxide.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60823,
    title ="Parallel Synthesis of ZSM-5 Zeolite Films from Clear Organic-Free Solutions",
    author = "Lai, Re and Kang, Beom Seok",
    journal = "Angewandte Chemie International Edition",
    volume = "40",
    number = "2",
    pages = "408-411",
    month = "January",
    year = "2001",
    doi = "10.1002/1521-3773(20010119)40:2<408::AID-ANIE408>3.0.CO;2-V",
    issn = "1433-7851",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150211841",
    note = "© 2001 WILEY-VCH. \n\nReceived: August 30, 2000. Revised: November 2, 2000. \n\nThis study was funded by the Chevron Research and Technology Co.",
    revision_no = "10",
    abstract = "Twenty-one zeolite films were grown on a 2.5 cm alumina disk using a multiwell reactor (see picture). This parallel synthesis from clear organic-free solutions offers an interesting approach to the preparation of catalytic libraries. The morphologies of the films produced were found to be similar to those synthesized under conventional conditions but their X-ray diffraction patterns indicated a lower degree of orientation of crystallites.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/61922,
    title ="Intrapore Synthesis of Silicalite Membranes",
    author = "Kang, Beom Seok and Gavalas, George R.",
    journal = "PMSE Preprints",
    volume = "85",
    
    pages = "290-291",
    month = "January",
    year = "2001",
    
    
    issn = "1550-6703",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151106-072040903",
    note = "© 2001 American Chemical Society.",
    revision_no = "10",
    abstract = "The zeolitic layer of most supported zeolite membranes lies\npartially outside of the pores and partially inside the pores of the support. Coronas t al prepared ZSM-5 membranes by two techniques, one resulting in an external layer with little pore infiltration, the other resulting in a patchy external layer and a deep internal layer, the fatter structure having better separation properties. Generally, it has proven difficult to determine which of the two layers is responsible for the separation properties. Intrapore separation layers have the advantage that they can be grown on supports of lesser quality and are not\nsusceptible to crack formation during calcination.\nIn this study intrapore membrane growth was achieved by means of seeding inside the pores of the support. Subsequent growth of the seeds led to pore filling by the zeolite up to a certain depth from the external surface. In a departure from previous ZSM-5 membrane studies, growth of the zeolite layer was carried out at temperatures below 100°C that dispenses with pressure vessels and allows facile\nstirring and midsynthesis change of solution.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60824,
    title ="Spontaneous Formation of Periodically Patterned Deposits by Chemical Vapor Deposition",
    author = "Tsapatsis, Michael and Vlachos, Dionisios G.",
    journal = "Journal of the American Chemical Society",
    volume = "122",
    number = "51",
    pages = "12864-12865",
    month = "December",
    year = "2000",
    doi = "10.1021/ja002228s",
    issn = "0002-7863",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150212176",
    note = "© 2000 American Chemical Society. \n\nReceived June 22, 2000. \n\nM.T. acknowledges support from a NSF CAREER Award, a David and Lucile Packard Foundation Fellowship in Science and Engineering, and a Henry and Camille Dreyfus Teacher-Scholar Award. M.T. and D.G.V. thank Prof. H. K. Henisch for stimulating their interest in LR phenomena.",
    revision_no = "10",
    abstract = "Patterns of colloidal origin that are formed in ionic precipitation-diffusion systems and are known as Liesegang Rings (LR) have fascinated researchers since the beginning of the century and have been the subject of numerous theoretical, numerical, and experimental studies. The terms recurrent, rhythmic, or periodic precipitation are often used to describe the temporal pattern evolution in such systems. Pattern formation in the vapor phase reaction of NH_3 and HCl has also been reported since 1930. It has been suggested that any reaction giving an insoluble product is capable of LR pattern formation. However, the potential of such self-organized deposition for the fabrication of materials (other than NH_4Cl) from vapor precursors has not been demonstrated. Moreover, reproducible LR patterns are usually characterized by uneven spacing (Matalon-Packter law) and band thickness, although nearly periodic patterns have been reported as well. Here we propose, for the first time, a connection of LR phenomena, with the spontaneous (i.e., involving no external concentration, temperature, or other parameter forcing) formation of micrometer size periodic stripes of nanocrystalline titania deposited in mesoporous glass by counter diffusion chemical vapor deposition (CVD) using titanium chloride and water.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60825,
    title ="Preparation of supported carbon membranes from furfuryl alcohol by vapor deposition polymerization",
    author = "Wang, Huanting and Zhang, Lixiong",
    journal = "Journal of Membrane Science",
    volume = "177",
    number = "1-2",
    pages = "25-31",
    month = "August",
    year = "2000",
    doi = "10.1016/S0376-7388(00)00444-0",
    issn = "0376-7388",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150212434",
    note = "© 2000 Elsevier. \n\nReceived 28 March 2000; received in revised form 27 April 2000; accepted 28 April 2000. \n\nFunding by a grant from Mobil Technology Company is gratefully acknowledged.",
    revision_no = "10",
    abstract = "Supported carbon membranes were prepared from furfuryl alcohol (FA) precursor by vapor deposition polymerization (VDP). For this purpose γ-Al_2O_3/α-Al_2O_3 or glass/α-Al_2O_3 support tubes were pretreated with an acid catalyst and exposed to FA vapors at 90°C. The tubes were then heated at 200°C to crosslink the poly(furfuryl alcohol) (PFFA) polymer and carbonized slowly to 600°C. The polymerization and carbonization cycle was repeated once to improve the permeation properties. The membranes were examined by scanning electron microscopy (SEM) and tested in a permeation cell with single gases (H_2, N_2, O_2, CO_2, CH_4) and with the mixture CO_2–CH_4. After the first polymerization/carbonization cycle the membranes had little selectivity for gas separations. After the second polymerization/carbonization cycle the membranes had ideal selectivities 10–13 for O_2:N_2, 80–90 for CO_2:CH_4, and 90–350 for H_2:N_2 at room temperature. The permeance was 0.6–2.5 for H_2, 0.27–0.58 for CO_2 and 0.08 for O_2, all in MPU (1 MPU=10^(−8) mol/m^2 Pa s). The permeances were sharply higher at 150°C but the selectivities were lower, e.g. one of the membranes had H2 permeance 10.6 MPU and H_2:N_2 ideal selectivity 30.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60827,
    title ="Mesoporous glass films supported on α-Al_2O_3",
    author = "Wang, Huanting and Gavalas, George R.",
    journal = "Journal of Membrane Science",
    volume = "176",
    number = "1",
    pages = "75-85",
    month = "August",
    year = "2000",
    doi = "10.1016/S0376-7388(00)00432-4",
    issn = "0376-7388",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150212970",
    note = "© 2000 Elsevier. \n\nReceived 21 January 2000; received in revised form 17 April 2000; accepted 20 April 2000. \n\nDr. Chi Ma in Division of Geological and Planetary Sciences at Caltech helped with EPMA sample preparation and measurements. Funding by a grant from Mobil Technology Company is gratefully acknowledged.",
    revision_no = "10",
    abstract = "Glass–alumina composites were developed for possible use as membrane supports. Preparation involved dip-coating of α-Al_2O_3 tubes with a suspension of borosilicate glass particles (9.1% Na_2O–29.7% B_2O_3–61.2% SiO_2), sintering to convert the particle layer into a nonporous layer of phase separated glass, and leaching the glass with a strong acid to remove the soluble phase and obtain the final porous layer of about 10 μm thickness. In some preparations a 10% α-Al_2O_3 powder was added to the initial suspension. The composite supports were characterized by SEM, EDAX and EPMA for elemental composition, XRD for crystalline phase content, nitrogen adsorption for surface area and pore size distribution, and by permeation measurements with single gases and mixtures. After leaching the glass layers had pore size 1–4 nm, and contained varying amounts of boron, sodium, and aluminum oxides, in addition to silica. The nitrogen permeance of the composite supports was 10–100 times higher than that of standard porous Vycor tubing.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60828,
    title ="ZSM-5 membrane synthesis with organic-free mixtures",
    author = "Lai, Re and Gavalas, George R.",
    journal = "Microporous and Mesoporous Materials",
    volume = "38",
    number = "2-3",
    pages = "239-245",
    month = "August",
    year = "2000",
    doi = "10.1016/S1387-1811(00)00143-8",
    issn = "1387-1811",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150213210",
    note = "© 2000 Elsevier. \n\nReceived 7 October 1999; accepted 22 December 1999. \n\nThis study was funded by a grant from NSF and by Chevron Research and Technology Co.",
    revision_no = "11",
    abstract = "Preparation of supported ZSM-5 membranes using a TPA-free synthesis gel was investigated. After exploring the effect of reaction mixture the composition SiO_2:0.0125Al_2O_3:0.2675Na_2O:46H_2O was selected for membrane synthesis. Membranes were prepared by hydrothermal reaction on asymmetric α-Al_2O_3 tubular supports. The membranes were characterized by scanning electron microscopy, EDS, X-ray diffraction and Ar and N_2 adsorption. Permeation measurements with single gas and mixtures yielded selectivities for H_2 over n-butane above 104 and those for O2 over N_2 were 9–10. Permeation was strongly activated with the activation energies increasing sharply with molecular sizes.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60829,
    title ="Growth of ZSM-5 films on alumina and other surfaces",
    author = "Lai, Re and Yan, Yushan",
    journal = "Microporous and Mesoporous Materials",
    volume = "37",
    number = "1-2",
    pages = "9-19",
    month = "May",
    year = "2000",
    doi = "10.1016/S1387-1811(99)00188-2",
    issn = "1387-1811",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150213451",
    note = "© 2000 Elsevier. \n\nReceived 18 July 1999; accepted for publication 26 September 1999. \n\nThis study was funded by NSF Grant CTS 9504901 and by Chevron Research and Technology Co.",
    revision_no = "10",
    abstract = "Growth of ZSM-5 films on porous α-Al2O3 and other substrates was studied with the main focus on the effect of the substrate on surface gel formation and zeolitization. The films formed on the substrate and the powders that settled at the bottom of the autoclave were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Adsorption of Ar and iso-butane was used to estimate the crystalline fraction of the product formed on and in the pores of the substrate. The presence of alumina substrates accelerated bulk zeolitization for certain solution compositions. Aluminum added to the solution had dual effects, to induce gel layer formation on the substrate surface and to retard zeolitization of that layer as well as retard zeolitization in the bulk of the solution.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60830,
    title ="Methane Pyrolysis in a Hot Filament Reactor",
    author = "Sun, Qi and Tang, Yongchun",
    journal = "Energy and Fuels",
    volume = "14",
    number = "2",
    pages = "490-494",
    month = "March",
    year = "2000",
    doi = "10.1021/ef9901995",
    issn = "1520-5029",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150213697",
    note = "© 2000 American Chemical Society. \n\nReceived September 13, 1999. Revised Manuscript Received January 19, 2000. \n\nFunding of this work was provided by Chevron Research and Technology Company.",
    revision_no = "10",
    abstract = "An electrically heated platinum filament mounted inside a quartz tube was used as a high temperature flow reactor for methane pyrolysis. The reaction products included carbon and a mixture of hydrocarbons, mainly C1−C5 alkanes, alkenes, and benzene. The hydrocarbons were measured by gas chromatography and the carbon gravimetrically. At 1275 °C filament temperature and 100ms residence time in the hot region of the reactor, methane conversion was 19.7% and selectivity of hydrocarbon products 68%. Lowering the flow rate increased the conversion but lowered sharply the selectivity of hydrocarbon products. Coking of the filament surface gradually lowered the filament temperature and the conversion of methane. This deactivation process could be slowed by adding a few percent of oxygen to the methane feed.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60837,
    title ="Methane partial oxidation on Pt/CeO_2–ZrO_2 in the absence of gaseous oxygen",
    author = "Pantu, Piboon and Kim, Kiseok",
    journal = "Applied Catalysis A: General",
    volume = "193",
    number = "1-2",
    pages = "203-214",
    month = "February",
    year = "2000",
    doi = "10.1016/S0926-860X(99)00429-9",
    issn = "0926-860X",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151007-090423328",
    note = " © 2000 Elsevier. \n\nReceived 23 June 1999; received in revised form 13 September 1999; accepted 13 September 1999.",
    revision_no = "11",
    abstract = "Partial oxidation of methane to synthesis gas over platinum or ruthenium supported on Ce_(1−x)Zr_xO_2 (x = 0, 0.2 and 0.5) was studied at 550–700°C in the absence of gaseous oxygen. The reaction was carried out in a packed-bed reactor under continuous or pulsed flows of methane. Oxidation utilized oxide oxygen and was initially very fast but slowed down as the oxide support became progressively reduced. Addition of ZrO_2 into CeO_2 considerably increased the rate of methane oxidation and enhanced the reducibility of CeO_2 but decreased the selectivity to carbon monoxide and hydrogen. Specifically it was found that significant production of carbon dioxide and water occurred on the freshly oxidized solid until a certain degree of reduction was reached beyond which the selectivity to carbon monoxide and hydrogen rose to over 90%. This critical degree of reduction was 10%, 40% and 65% for the solid compositions x = 0, 0.2 and 0.5, respectively. Additional experiments carried out using carbon monoxide pulses showed that carbon monoxide oxidation declines sharply and becomes negligible beyond this degree of reduction while oxidation of methane continues much further. Comparison of the two metals showed that platinum is more active but the reaction rate did not change much in the range of platinum loadings of 0.25–1 wt.%.",
}
@book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60826,
    title ="Chemical vapor deposition membranes",
    author = "Tsapatsis, M. and Gavalas, G. R.",
    
    
    number = "6",
    pages = "397-416",
    month = "January",
    year = "2000",
    doi = "10.1016/S0927-5193(00)80017-0",
    
    isbn = "978-0-444-50272-8",
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151006-150212735",
    note = "© 2000 Elsevier.",
    revision_no = "12",
    abstract = "This chapter is divided into four sections the first of which treats issues of general relevance to Chemical Vapor Deposition (CVD) of membranes, the second reviews work on dense silica membranes, the third is devoted to Y_2O_3-stabilized ZrO_2 (YSZ) membranes, and the fourth treats CVD of Pd membranes.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60838,
    title ="Molecular Dynamics Simulations of Diffusion in Mesoporous Glass",
    author = "Fernandes, Neil E. and Gavalas, George R.",
    journal = "Industrial & Engineering Chemistry Research",
    volume = "38",
    number = "3",
    pages = "723-730",
    month = "March",
    year = "1999",
    doi = "10.1021/ie9801150",
    issn = "0888-5885",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151007-090423856",
    note = "© 1999 American Chemical Society. \n\nReceived for review February 18, 1998. Revised manuscript received September 4, 1998. Accepted October 19, 1998. \n\nThis research was supported by DOE University Coal Research Program (Grant DE-FG22-92PC92525).",
    revision_no = "10",
    abstract = "The effect of gas−solid intrapore potential and surface roughness on diffusion in a single capillary was investigated by molecular dynamics simulations. Calculations were carried out for nitrogen and isobutane under free molecular flow conditions in pores of diameter 4−14 Å at temperatures of 200−800 K. The gases were treated as Lennard-Jones atoms and the pore surface was taken as cylindrical, exerting a 9−3 potential. No energy transfer was considered between the gas and solid, but interaction with the roughened pore wall provided the scattering required for diffusive transport. Two effects of the gas−solid potential were examined in some detail. One is the enhanced intrapore gas concentration which increases the flux, and the other is the bending of the molecular trajectories which decreases the flux. In pores of radius 20 Å, both effects were significant for temperatures as high as 500 K and were enhanced as the temperature decreased. For nitrogen, the two effects partially canceled each other over the temperature range examined, resulting in a temperature dependence similar to that of Knudsen diffusion. For isobutane, the partitioning effect dominated the path curvature effect at temperatures as high as 500 K.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/61883,
    title ="Synthesis of Porous Inorganic Membranes",
    author = "Tsapatsis, Michael and Gavalas, George R.",
    journal = "MRS Bulletin",
    volume = "24",
    number = "3",
    pages = "30-35",
    month = "March",
    year = "1999",
    doi = "10.1557/S0883769400051885",
    issn = "0883-7694",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151105-083817088",
    note = "© 1999 Materials Research Society.",
    revision_no = "11",
    abstract = "Here we will attempt a brief overview of recent synthetic efforts for micropore and lower-end mesopore membranes. We will not address the very important classes of nonporous membranes, such as dense metals and solid electrolytes with applications in H_2 and O_2 separations, or meso- and macroporous membranes, which find applications in food processing and water treatment. Microporous materials provide high permselectivities for molecules encountered in the chemical-processing industry but suffer from low intrinsic permeabilities. Therefore, in order to bring microporous membrane materials to commercial applications, functional composites with small effective thicknesses (in the micron or submicron range) must be developed. For example, to achieve economical membrane-reactor sizes, fluxes as high as 0.1 mol/(m^2 s) are desirable. Approaches to microporous membranes include modification of mesoporous membranes by sol-gel and chemical-vapor-deposition (CVD) techniques, carbonization of polymers to form molecular-sieve carbon, and polycrystalline-film growth of zeolites and other molecular sieves.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/4755,
    title ="Vapor-phase transport synthesis of ZnAPO-34 molecular sieve",
    author = "Zhang, Lixiong and Gavalas, George R.",
    journal = "Chemical Communications",
    volume = "1999",
    number = "1",
    pages = "97-98",
    month = "January",
    year = "1999",
    
    issn = "1359-7345",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:ZHAcc99",
    note = "© Royal Society of Chemistry 1999 \n\nReceived (in Bloomington, IN, USA) 3rd September, 1998, Revised manuscript received 19th November 1998, Accepted 20th November 1998 \n\nFunding of this work by Elf Atochem, North America, Inc. is greatly appreciated. We thank Ms Lin Luo for analyzing the XRD patterns.",
    revision_no = "7",
    abstract = "ZnAPO-34 molecular sieve can be synthesized by the vapor-phase transport technique using triethylamine as a structure-directing agent.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60839,
    title ="Surface Seeding in ZSM-5 Membrane Preparation",
    author = "Lai, Re and Gavalas, George R.",
    journal = "Industrial & Engineering Chemistry Research",
    volume = "37",
    number = "11",
    pages = "4275-4283",
    month = "November",
    year = "1998",
    doi = "10.1021/ie980265a",
    issn = "0888-5885",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151007-090424153",
    note = "© 1998 American Chemical Society. \n\nReceived for review April 27, 1998. Revised manuscript received August 18, 1998. Accepted August 21, 1998. \n\nThis study was funded by NSF grant CTS 9504901 and by Chevron Research and Technology Co. Micromeritics Corp. provided a grant for the ASAP 2000 instrument.",
    revision_no = "10",
    abstract = "ZSM-5 zeolite membranes were prepared by in situ hydrothermal synthesis on macroporous α-alumina tubes coated with silicalite seeds. Seed particles were prepared by hydrothermal synthesis at 95 °C to mean size 0.4 or 2 μm, purified of unconverted reactants, and suspended in a buffered aqueous solution. The support tubes were seeded by immersion in the particle suspension under ultrasonication. Membrane growth on seeded supports was carried out at temperatures 110−150 °C and different reaction times. An external polycrystalline layer gradually grows on top of the support, with siliceous deposits accumulating as deep as 100 μm inside the pores of the support. Thermogravimetric analysis and nitrogen and argon adsorption measurements indicate graduate conversion of deposits from amorphous to crystalline. Pure gas permeation results are presented for membranes prepared using 0.4 and 2 μm seeds under different compositions and temperatures.",
}
@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/60840,
    title ="Gas transport in porous Vycor glass subjected to gradual pore narrowing",
    author = "Fernandes, Neil E. and Gavalas, George R.",
    journal = "Chemical Engineering Science",
    volume = "53",
    number = "5",
    pages = "1049-1058",
    month = "February",
    year = "1998",
    doi = "10.1016/S0009-2509(97)00399-0",
    issn = "0009-2509",
    
    url = "https://resolver.caltech.edu/CaltechAUTHORS:20151007-090424422",
    note = "© 1998 Elsevier. \n\n(Received 23 April 1997; in revised form 30 October 1997; accepted 2 November 1997) \n\nThe authors would like to acknowledge the DOE funding of this research through the University Coal Research Program, Grant DE-FG22-92PC92525.",
    revision_no = "11",
    abstract = "Porous Vycor® glass was modified by deposition of silica on the internal pore surface using consecutive cycles of liquid-phase silylation with silicon tetrachloride, and hydrolysis. Macroscopically uniform deposition was achieved by exploiting the self-limiting nature of the reaction and the extent of deposition was monitored by the weight change of the samples. Weight increases as high as 24% were recorded and the average pore diameter was estimated to decrease from ∼44 Å to ∼20 Å. Permeation measurements were conducted in the Henry’s law region at various levels of deposition for hydrogen, methane, isobutane and nitrogen, at temperatures between 60°C and 180°C. The measurements were compared to values calculated with a model using the effective medium approximation to treat network effects and Clausing’s correction to account for conductances in pores of finite aspect ratio. The calculated values proved to be inaccurate for hydrogen, overestimating the permeance by a factor of 2 at high levels of deposition possibly because of non-ideal pore shapes accentuated by the deposition. For nitrogen and methane the agreement between calculations and measurements was better due to a fortuitous cancellation of deviations caused by the enhanced potential energy well within the pores and the non ideal pore shape. The intrapore potential energy effect was especially strong for isobutane and as a result the calculated flux was always less than the experimental.",
}