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Search Results: 1 - 10 of 197 matches for " clays "
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Argilas organofílicas: características, metodologias de prepara??o, compostos de intercala??o e técnicas de caracteriza??o
Paiva, L. B. de;Morales, A. R.;Díaz, F. R. V.;
Ceramica , 2008, DOI: 10.1590/S0366-69132008000200012
Abstract: clays are materials used since historical periods and nowadays have several applications due to their interesting properties. the surface modification of clays is one area that has received enough attention from researchers because through modification it is possible to prepare new materials and find applications. the purpose of this paper is to present a review on the use of clays for obtaining organophilic clays, especially those used in polymeric nanocomposites. several studies have been done based on different techniques and process conditions of these materials. the review includes clays of different regions, different modification agents and applications.
Simulation of 5-Fluorouracil Intercalated into Montmorillonite Using Spartan ’14: Molecular Mechanics, PM3, and Hartree-Fock  [PDF]
John H. Summerfield
Open Journal of Physical Chemistry (OJPC) , 2015, DOI: 10.4236/ojpc.2015.53006
Abstract:

Molecular mechanics calculations, based on equations such as the one below, are used to investigate a colorectal cancer drug, 5-fluorouracil, intercalated into a clay, montmorillonite. This combination is currently being considered as a drug delivery system. The swelling of clays has been studied since the 1930s and is still not fully understood. Spartan ’14 is used for the calculations. Semi-empirical and ab initio basis set scaling is also examined since there are roughly 300 atoms involved in the full model.

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Argilas especiais: o que s?o, caracteriza??o e propriedades
Coelho, Antonio C. Vieira;Santos, Pérsio de Souza;Santos, Helena de Souza;
Química Nova , 2007, DOI: 10.1590/S0100-40422007000100026
Abstract: special clays are a group of clays different from the large volume of clay mineral products named "industrial clays": kaolins, ball clays, refractory clays, bentonites, fuller's earths, common clays. two groups of special clays exist: rare, as in the case of hectorite and sepiolite and restricted areas, as in the case of white bentonite, halloysite and palygorskite (attapulgite). a review is given of the most important producers of the special clays and their properties in the western world, as well as a discussion of the occurrence of these types of clays in brazil.
α-Endosulfan Removal from Water by Adsorption over Natural Clays from Burkina Faso: An Isothermal Study  [PDF]
Arsène H. Yonli, Hermann A. Kabore, Jean Koulidiati
Journal of Materials Science and Chemical Engineering (MSCE) , 2014, DOI: 10.4236/msce.2014.211007
Abstract: The present study carried out the α-endosulfan removal from water by adsorption over natural clays from the western region of Burkina Faso. The adsorption experiments were performed over raw clay samples at room temperature in batch reactor and the obtained adsorption isotherms were well fitted by Fowler-Guggenheim model. It was pointed out for all samples that α-endosulfan was physisorbed in the interlayer space of the clay samples. The maximal adsorption capacities were respectively about 9.12, 6.98 and 4.13 mg/g for KO2, KO1 and KW1 samples. The differences in terms of adsorption capacity for the three samples were due to the presence of illite in the samples KO2 and KO1 when the KW1 sample contained essentially kaolinite in its structure. When the interlayer space was large enough as for samples with illite a greater amount of α-endosulfan molecules were adsorbed. It was also shown that the samples with the higher surface area were the most efficient for the removal of α-endosulfan molecules from water. Moreover, this study exhibited that the α-endosulfan adsorption depended on the crystallites size; the samples presenting largest crystallites had the greatest adsorption capacities.
Using Trace Metals, Peroxide, Acid and Iodine Values to Characterize Oils Bleached Using Clays from Central and Eastern Uganda  [PDF]
Is’harq-Zubair Mukasa-Tebandeke, Pancras John Mukasa Ssebuwufu, Steven A. Nyanzi, Andreas Schumann, George W. Nyakairu, Festo Lugolobi
American Journal of Analytical Chemistry (AJAC) , 2014, DOI: 10.4236/ajac.2014.517136
Abstract: Bleaching of edible oils is known to alter the composition of oils as it removes impurities and certain food nutrients. The characteristics of bleached oil are strongly related to type bleaching medium, temperature at which bleaching is done and other factors. In this study, we compare peroxide, free fatty acid, acid and iodine values, copper and iron content of bleached and crude oils to establish the characteristics of edible oils bleached using smectite and kaolinite-rich clays. Oil industries spend large sums of money purchasing bleaching earths yet no country lacks natural clays which can be developed to bleach oils. In Uganda alone more than US$ 700,000 is spent every month yet many clay deposits are unexploited. In this study, we have documented trace metal composition, peroxide values, acid values, iodine values and free fatty acid content of bleached and unbleached cotton-seed and sunflower seed oils. The bleached oils were found to be fit for human use. Clays are either kaolinites or smectites, but the clays used to bleach edible oils are montmorillonites or bentonites. The decrease in content of iron in the bleached oils was highest for all oils bleached. The content of copper showed the smallest change. The content of copper in cotton oils decreased from 0.5 ppm to 0.15 ppm using Kajansi clay leached in 20% acid yet when Chelel clay leached under similar conditions was used decrease was from 0.5 to 0.1 ppm. The content of iron in sunflower oils bleached using Kajansi clay leached in 20% acid decreased from 1.6 to 0.2 ppm yet that bleached with Chelel clay under similar conditions decreased to 0.1 ppm. The acid values showed that the acidity in sunflower oils is largely due to oleic acid as the average value for acids is in the range close to oleic acid, cotton-seed oil corresponded to linoleic acid. The levels of free fatty acid were found to lie in range from 3.8 - 3.2 for all clays used showing no significant rise. The peroxide values of bleached oils lay between 1.2 and 0.8.
Adsorption Behavior of Acid-Leached Clays in Bleaching of Oil  [PDF]
I. Z. Mukasa-Tebandeke, P. J. M. Ssebuwufu, S. A. Nyanzi, G. W. Nyakairu, M. Ntale, F. Lugolobi, Schumann Andreas
American Journal of Analytical Chemistry (AJAC) , 2015, DOI: 10.4236/ajac.2015.66049
Abstract: The available data have shown that acid-leached clays had sites for adsorption of impurities in oils. Data obtained on residual impurities in cotton and sunflower-seed oils bleached with the same clay materials produced linear Langmuir and Freundlich isotherms. The increase in constant, k with increase in both temperature of thermal activation and concentration of acid used to leach the clay, suggests that bleaching efficiency increased. The value of n decreased with increase in temperature of activation and concentration of acid used to leach the clay suggesting that bleaching capacity increased. The mineral compositions of the clays influenced their surface, structural and bleaching properties.
The Influence of Metakaolin from Saaba (Burkina Faso) over Physico-Mechanical and Durability Properties of Mortars  [PDF]
Fabrice Ntimugura, Seick Omar Sore, Latifou Bello, Adamah Messan
Open Journal of Civil Engineering (OJCE) , 2017, DOI: 10.4236/ojce.2017.73027
Abstract: The paper evaluates the feasibility of reducing clinker in the Portland Cement production using local metakaolin in Burkina Faso. Standardized testing methods have been used for this purpose, and experiments were performed on mortar prisms containing different amounts of metakaolin. Important results about the physical, mechanical and durability characterization of blended mortars were carried out in this study. The obtained results are discussed based on available literature data. These results have shown increased physical and durability properties for blended mortars. Although the mechanical strengths remained relatively low for higher MK incorporations, the latter grow to surpass these of PC mortars (the reference) at 28, 56 and 90 days of curing. The results in the paper, have confirmed the possibility of using metakaolin to partially substitute cement, a possibility to reduce the CO2 production by the cement industry in Burkina Faso.
Alkylation of benzene with 1-dodecene catalyzed by modified clays
Oberto,Tania; Sánchez,Jorge; González,Eduardo; Solano,Roger; Carruyo,Gabriela; Morán,César; Moronta,Alexander;
Revista Técnica de la Facultad de Ingeniería Universidad del Zulia , 2007,
Abstract: a natural smectite clay (stx-1, usa), was ion-exchanged with al, cr and fe or pillared with the same cations. samples combining these two treatments were also obtained. the prepared solids were characterized by x-ray fluorescence diffraction (xrf), x-ray diffraction (xrd), thermogravimetric analysis (tga) and n2 adsorption. the catalytic activity was evaluated by using the alkylation of benzene with 1-dodecene. xrf results showed an increase in the metal content, giving evidence that the metal was effectively exchanged or deposited over the starting material. al- and fe-pillared clays showed a significant increase of the surface area, but this was not observed for the cr-pillared one. ion exchanged clays showed similar surface areas to that of the starting clay. from xrd results, only the al-pillared clay gave an increase of the d-spacing. all catalysts showed low conversions towards the product of interest, and this is perhaps attributed to lack of molecular accessibility in the clay gallery or that there are no strong acid sites able to catalyze the alkylation, but strong enough to induce 1-dodecene isomerization. moderate conversions were observed (27% for the most active catalyst, cr/st-p-al)
Prediction of Swelling Kinetics of Expansive Soils of Rufisque (Senegal, West Africa)  [PDF]
Papa Sanou Faye, Issa Ndoye, Mapathé Ndiaye, Abib Tall, Ibrahima Khalil Cissé, Jean Pierre Magnan
Open Journal of Civil Engineering (OJCE) , 2017, DOI: 10.4236/ojce.2017.72017
Abstract: The disorders caused by the swelling of the soil on the structures have been observed for several years in the city of Rufisque. This article presents the results of the study of swelling kinetics of expansive soils in Rufisque and their prediction based on the hyperbolic rule. The odometer is used as an instrument for measuring swelling and the tests are carried out on some intact samples at their sampling water content. The present study shows that in Rufisque the most swelling layer is marl. The results show two phases of development. The first phase is very fast and represents 77% of the final deformation and the second one is slower. The prediction of the issue by the hyperbolic rule shows that it underestimates the first phase but gives a good prediction of the second phase of the swelling rate. There is a good correlation between the final swelling rates. However, the model gives a bad approximation of the half-swelling time.
The Utility of Nanocomposites in Fire Retardancy
Linjiang Wang,Xuejun He,Charles A. Wilkie
Materials , 2010, DOI: 10.3390/ma3094580
Abstract: Nanocomposites have been shown to significantly reduce the peak heat release rate, as measured by cone calorimetry, for many polymers but they typically have no effect on the oxygen index or the UL-94 classification. In this review, we will cover what is known about the processes by which nanocomposite formation may bring this about. Montmorillonite will be the focus in this paper but attention will also be devoted to other materials, including carbon nanotubes and layered double hydroxides. A second section will be devoted to combinations of nanocomposite formation with conventional (and unconventional) fire retardants. The paper will conclude with a section attempting to forecast the future.
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