Browsing by Author "Nickolov R."

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    Dependence of the C constant in the brunauer-emmett-teller equation on water pre-adsorbed on activated carbon
    (1992-01-01) Mehandjiev D.; Nickolov R.
    The dependence of the C constant in the BET equation on the amount of pre-adsorbed water has been investigated by low temperature nitrogen adsorption on activated carbon containing different amounts of water pre-adsorbed at the same relative water vapour pressure. It is suggested that the rapid decrease in the surface area as determined by the BET method in comparison with the C value in cases of low degrees of sorption volume filling is associated with blocking of part of carbon texture and the parallel formation of extremely narrow micropores.
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    Effect of activated carbons on the dielectric and microwave properties of natural rubber based composites
    (2017-10-01) Al-Sehemi A.; Al-Ghamdi A.; Dishovsky N.; Nickolov R.; Atanasov N.; Manoilova L.
    The effect of six different types of activated carbons has been studied in view of their applicability as functional fillers upon the dielectric and microwave properties of natural rubber based composites. It is found that the textural characteristics of the studied active carbons exert influence both on the real part of dielectric permittivity and dielectric loss angle tangent, as well as on the microwave properties of the studied composites. The composite containing activated carbon on the basis of wooden material possesses the highest value of the total shielding effectiveness in comparison with the composites, containing another activated carbons. It has the lowest values of specific surface area, area and volume of micropores and the highest values of external surface area, volume of mesopores and average pore diameter. With gradually increasing the values of the indices in the first group and gradually decreasing the values of the indices in the second group, the value of total shielding effectiveness decreases. It is obvious that these indices have influence on the rubber matrix-filler particle interactions, such as multicontact chain adsorption to the surface of the filler. The spatial inhomogeneities formed give rise to polarization phenomena and to a frequency dependence of the dielectric properties.
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    On the possibility of surface modification of an alumina support with amphiphilic carbonaceous material
    (1998-01-01) Nickolov R.; Mehandjiev D.
    A carbon-coated support has been prepared by the impregnation of commercial alumina with an ammoniacal solution of amphiphilic carbonaceous material. It was established that the method used for the deposition of the carbon coating on the support allowed control of both the layer thickness and the degree of filling of the surface in the low carbon content region. Equations proposed for the approximate determination of the thickness of the deposited carbon layer and of the surface occupied by this layer enabled a tentative prediction to be made of the most desirable parameters for such a system.
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    Porous texture of CuO prepared from copper oxalate precursor
    (2006-07-01) Nickolov R.; Donkova B.; Milenova K.; Mehandjiev D.
    The porous texture of CuO obtained from CuC2O4 • 0.5H2O as a precursor, as well as the interconnection between the texture of the initial oxalate and that of the copper oxide obtained, has been studied by physisorption, XRD, XPS and SEM methods. The dimensions of the particle aggregates and the crystalline particles were altered as a consequence of the thermal decomposition of CuC2O4·0.5H2O to CuO, and this led to an increase of ca. 1.5-times in the specific surface of the CuO obtained relative to that of the initial substance. The comparatively non-uniform sizes of the intra-aggregate mesopores in CuC2O4·0.5H2O were transformed into considerably smaller intra-aggregate mesopores in CuO. A finite increase in the volume of the intra-crystallite pores in CuO was also observed, although this did not change the average size of the intra-crystallite pores in the oxide obtained nor the character of the pore-size distribution with respect to the starting material. In addition, as a result of the thermal decomposition of CuC2O4·0.5H2O, the mesoporosity of the prepared oxide also developed. However, the CuO component retained the textural type characteristic of the initial CuC2O4·0.5H2O.
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    Study of K2SO3 supplements impact on the protection properties of a new type of gas mask carbons in respect to Cl3CNO2 and HCN (CN)2 vapors
    (2020-01-01) Manoilova L.; Nickolov R.
    The dynamic adsorption capacities of new types of activated materials are studied (gas mask carbons) in respect to poisonous substances. They represent the main types of action mechanisms of gas mask carbons-physical adsorption (Cl3CNO2) and catalytic sorption (HCN). The study is run to determine the impact of the modifier K2SO3 (2 mass. %-8 mass. %) on the protection properties of the newly acquired carbon catalysts.
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    Study on the impact of the modifier K2CO3 on the texture parameters of Newly synthesized gas mask carbons
    (2019-01-01) Manoilova L.; Nickolov R.
    A new type of active materials (gas mask carbons) is obtained with an active phase differing from that of ASC Whetlerite carbons (Cu-Ag-Cr). It is intended for air purification from vapors of potential terroristic poisonous substances. The new type of the carbon catalysts are based on Cu and Zn in presence and absence of Mo and a minimal amount of Cr6+. The impact of the modifier K2CO3 (2 mass % - 8 mass %) on the synthesized specimens texture parameters is studied.