Showing papers on "BET theory published in 1978"

Kinetics of silica deposition from simulated geothermal brines

Abstract: Supersaturated brines were passed through columns packed with several forms of silica (crystalline ..cap alpha.. quartz, polycrystalline ..cap alpha.. quartz, and porous Vycor). Also, silica deposition on ThO/sub 2/ microspheres and titanium powder was studied under controlled conditions of supersaturation, pH, temperature, and salinity. The residence time was varied by adjustments of flow rate and column length. The silica contents of the input and effluent solutions were determined colorimetrically by a molybdate method which does not include polymers without special pretreatment. Essentially identical deposition behavior was observed once the substrate was thoroughly coated with amorphous silica and the BET surface area of the coated particles was taken into account. The reaction rate is not diffusion limited in the columns. The silica deposition is a function of the monomeric Si(OH)/sub 4/ concentration in the brine. The deposition on all surfaces examined was spontaneously nucleated. The dependence on the supersaturation concentration, hydroxide ion concentration, surface area, temperature and salinity were examined. Fluoride was shown to have no effect at pH 5.94 and low salinity. The empirical rate law which describes the data in 1 m NaCl in the pH range 5-7 and temperatures from 60 to 120/sup 0/C is given.

Fabrication of poly(p‐phenylene) by powder‐forming techniques

Abstract: Application of powder-metallurgical forming techniques to poly(p-phenylene), PB, resulted in solid objects with tensile strengths as high as 35 MPa (5000 psi). Powders were characterized by BET surface area, x-ray crystallinity, scanning electron microscopy (SEM), and impurity levels in an effort to relate intrinsic powder properties with strengths attainable on fabrication. High surface area (>35m2/g) and low Cl impurity levels were generally associated with highest strengths. Forming variables were studied in some detail. Tough objects were obtained in a narrow sintering range of about 580°–615°C. Perchloropoly(p-phenylene) was also successfully fabricated.

Surface properties of heat-treated chromia of narrow particle size distribution

Abstract: Spherical particles of chromium(III) hydrous oxide having a very narrow size distribution have been prepared on a multigram scale by the sulfate process of Matijevic and characterized with regard to texture, chemical composition, and particle size distribution. Also, the surface properties have been determined as a function of activation temperature (room temperature through 1000°C) under vacuum. The unheated chromia is amorphous and hydrophilic and likely has a chain-like molecular structure. Its water sorption characteristics correlate with its bulk dehydration properties. The initial product contains considerable amounts of sulfate, i.e., the chromium to sulfate ratio in unwashed samples approaches three; this sulfate can be removed readily by washing with acid or base. Neutral water, however, is much less effective. Particle size and shape are not significantly altered by washing. The surface properties of the heat-treated chromia are reproducible and depend on the sulfate content of the original sol. The BET surface area increases progressively up to an activation temperature of ca. 450°C, mainly because of the formation of micropores. Further increase in activation temperature results in the transformation of the micropores into mesopores on account of crystallization. The analysis of argon adsorption of the micro- and mesporous samples was carried out by using the αs-method of Sing and Brunauer's corrected modelless method, respectively. The estimated external area of the microporous samples agrees with the particle size estimated by electron microscopy. The volume to surface ratio of the micropores (a measure of their size) remains unchanged during their progressive growth with activation temperature (200–450°C). The mesopores formed have a very narrow size distribution. The uniformity of the micropores and the mesopores is attributed to the relatively narrow particle size distribution of the original hydrous oxide.

Process for producing a catalyst comprising a graphite containing carbon, a transitional metal and a modifying metal ion

Abstract: Catalyst for the synthesis of ammonia from hydrogen comprises (1) as support on graphite containing carbon having (a) a basal plane surface area of at least 100 m 2/G (b) a ratio of BET surface area to basal plane surface area of not more than 5:1 and (c) a ratio of basal plane surface area to edge surface area of at least 5:1 and (ii) as active component (a) 0.1 to 50% by weight of a transition metal and (b) 0.1 to 4 times by weight of (a) of a modifying metal or ion selected from the alkali or alkaline earth metals or ions. The modifying metal or ion is actively associated with the transition metal rather than the support.

Manufacture of semiconductive mixture

Abstract: PURPOSE: To obtain a mixture of a small hygroscopic property and good extrusibility by compounding specific characteristics of two forms of conductive carbon blacks with a thermal plastic resin in a specific proportion. CONSTITUTION: A thermal plastic resin is compounded with a conductive carbon black of a DBP oil absorption of more than 250 ml/100g and a BET surface area of 500 to 1500 m 2 /g and a conductive carbon black of a BET surface area of less than 100 m 2 /g in a proportion of 1:2 to 10 to prepare a semiconductive mixture of a volume intrinsic resistivity of less than 10 5 ohm-cm. For example, 100 parts of an ethylen-vinyl acetate copolymer, 0.3 parts of an antioxidant, 5 parts of a conductive carbon black of a DBP oil absorption of 340 ml/100g and a surface area 1000 m 2 /g, and 25 parts of an acetylene black of a DBP oil absorption of 115 ml/100g and a surface area of 60 m 2 /g are mixed together by a Banbury mixer to obtain a semiconductive mixture of a volume intrinsic resistivity of 120 ohm-cm. COPYRIGHT: (C)1979,JPO&Japio

An examination of possible errors in the determination of nitrogen isotherms on hydrated cements

Abstract: A review of the literature on the determination and interpretation of nitrogen isotherms for hydrated portland cement is presented, showing the importance of sample preparation. The technique of nitrogen sorption is described and applied to a colloidal silica standard (tk 800), to a number of hardened cement pastes and to a suspension-hydrated cement. If hydrated cement specimens are soaked in methanol before out-gassing, a large increase in the nitrogen bet surface area is obtained together with an increase in the fine mesopore volume. /Author/TRRL/

Determination of the number of v5+=o species on the surface of vanadium oxide catalyst

Abstract: The number of V5+=O species on the surface of V2O5 was determined by detecting the concentration profile of N2 produced by the NO–NH3 reaction on V2O5 using the rectangular pulse technique The quantity of V5+=O species on the surface obtained agreed with the BET surface area of the catalyst