Person: García Rivas, Javier
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First Name
Javier
Last Name
García Rivas
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Geológicas
Department
Mineralogía y Petrología
Area
Cristalografía y Mineralogía
Identifiers
9 results
Search Results
Now showing 1 - 9 of 9
Item Review and new data on the surface properties of palygorskite: A comparative study(Applied clay science, 2021) Súarez Barrios, Mercedes; García Rivas, Javier; Morales, Juan; Lorenzo, Adrián; García Vicente, Andrea; García Romero, EmiliaPalygorskite is a mineral used in a wide number of industrial sectors. Currently, there are hundreds of studies in which palygorskite is a part of different nanocomposites and bionanocomposites. The surface properties are essential for these applications, and in this work, an in-depth revision of these properties is done, showing that the high variability found cannot be explained only by the number of impurities or by differences in the analysis conditions. To further deepen the knowledge of the surface properties of palygorskite and palygorskitic clays, a comparative study of a wide group of high purity samples is also performed, and new data on these surface properties are provided with the determination of the specific surface area (SSA), micropore surface area (SSAμp), micropore volume (Vμp), external surface area (SSAEx), and mean equivalent pore diameter. Both the bibliographic data and new data show that SSA varies from a few tens of m2g−1 to almost 300 m2g−1, and the microporosity and external surface proportions also vary greatly. The experimental data obtained show that 1) ordinary soft vacuum conditions produce structural folding, which limits the accessibility to the inner part of the structural tunnels; 2) microporosity is related to the intra- and inter-fibre microporosity, depending first on the fibre size, because the shorter the fibre, the higher the partial accessibility to the entrance of the channels; 3) the crystal chemistry of the samples also influences the SSA because the Mg-rich terms, which have higher content of sepiolite polysome proportions in their structure as well as wider and more accessible intracrystalline channels than palygorskite polysomes.Item Crystalochemical Complexity of Magnesic Clays from the Tajo Basin(Macla: revista de la Sociedad Española de Mineralogía, 2014) García Rivas, Javier; Súarez Barrios, Mercedes; García Romero, EmiliaItem New data on the microporosity of bentonites(Engineering geology, 2022) Súarez Barrios, Mercedes; Lorenzo, Adrián; García Vicente, Andrea; Morales, Juan; García Rivas, Javier; García Romero, EmiliaThis comparative study on a very wide group of samples shows that the crystal size and crystalline defects of smectites influence microporosity of bentonite considerably more than previously considered. The smectite crystals and surface properties, including microporosity and micropore volume, were studied using high resolution transmission electron microscopy and N2 adsorption, respectively. The specific surface area obtained varied between 25 and 278 m2g−1. The micropore area ranged between 6 and 76 m2g−1, and the external area ranged from 18 to 208 m2g−1. The external surface area was related to the size of the crystals in [001] direction because of the smaller particles with few stacked 2:1 layers have more basal surfaces accessible to the N2 molecules. However, the microporosity can be related to 1) the size of the crystals, owing to the partial ability of N2 to penetrate into the interlayer space, 2) the abundance of crystalline defects affecting the stacking of the 2:1 layers, and 3) the arrangement of the crystals forming particles, in which sub-parallel aggregates generate micro and mesopores. The study shows that these bentonites have pores in the full range, from smaller micropores (related to the crystalline structure in the interior of the interlayer) to micrometric macropores. The amounts of micro, meso, and macropores varied between samples but were similar and characteristic for samples from the same geological area.Item Crystal–chemical and diffraction analyses of Maya blue suggesting a different provenance of the palygorskite found in Aztec pigments(Archaeometry, 2021) Sánchez del Río, Manuel; García Rivas, Javier; Súarez Barrios, Mercedes; García Romero, EmiliaMaya blue is a pigment found in different archaeological sites of different cultures from Mesoamerica, and also in colonial buildings in Mexico and Cuba. The pigment is made from a thermally treated mixture of indigo and palygorskite. Pigment samples from Aztec and non‐Aztec archaeological sites as well as reference Yucatecan palygorskites were studied in this paper to assess their differences. The characterization of the samples was carried out by a combination of a crystal–chemical‐point analyses using electron microscopy to obtain the structural formulae of the palygorskite crystals, and studied using high‐resolution X‐ray diffraction. The data show evidence that the palygorskite used by non‐Aztec cultures, such as the Maya, is compatible with palygorskite from known sources in the Yucatan Peninsula, while the palygorskite used by the Aztec culture is different in its structure and has an origin that is still unknown.Item Mineralogical characterisation and surface properties of sepiolite from Polatli (Turkey)(Applied clay science, 2016) Súarez Barrios, Mercedes; García Rivas, Javier; García Romero, Emilia; Jara, N.Sepiolite is one of the most important industrial minerals, due primarily to its surface properties related to its structure. Sepiolite contains alternating 2:1 polysomes that produce tunnels at the inner part of the fibre and channels at the edge of the fibre. Sepiolite is a mineral with notably wide variations in the crystal-chemistry, crystallinity and texture, depending on the formation conditions, which results in highly different characteristics and properties. In this work, six sepiolite samples from the Polatli area (Turkey) are studied, comparing their mineralogical and textural features. The mineralogical composition of the samples is similar: carbonates constitute the main impurities, dolomite appears in all samples studied in different proportions, and small amounts of calcite, quartz and palygorskite have been identified. There is a variation in almost all the reflections of sepiolite, the 110 d-spacing ranges between 12.31 Å and 12.05 Å, this variation is related to the crystal-chemistry of the mineral. The impurities are clearly identified in the IR spectra, in which in addition to the carbonates the presence of the palygorskite polysomes is also detected by the band located at ~ 3620 cm− 1. The differences in the surface properties found in this study (specific surface area between 122 m2 g− 1 and 376 m2 g− 1 and microporous area between 55 m2 g− 1 and 168 m2 g− 1) cannot be related only with the content in impurities, but with the texture and the possible presence of intergrowths.Item Presence of oriented fibers in palygorskite powders and its influence on X-Ray diffractograms(Applied clay science, 2020) García Rivas, Javier; Súarez Barrios, Mercedes; García Romero, Emilia; Sánchez del Río, ManuelPalygorskite is a clay mineral whose structure has not been successfully deciphered, even considering the simultaneous presence of the orthorhombic and monoclinic phases within the same sample. An interesting question, which has barely been considered until the moment to explain the difficulty of the resolution of its structure, is whether the fibrous morphology of palygorskite might enhance the presence of possibly oriented fibers which could influence some reflections in random powder diffraction experiments. To observe this influence of orientation, computer simulations considering a slight variation of the structural models proposed by Chisholm (1992) were performed. These simulations were added in different proportions to study the role that certain proportions of oriented fibers play in the resulting diffractograms. The most interesting changes are in the region of interest comprised between 4.5 and 4.0 Å. Different contents in the two palygorskite phases with oriented components were also considered, affecting the resulting simulated diffractograms. The simulations were compared with experimental results, concluding that orientation can play a very important role in the diffractograms, therefore complicating even more the resolution of the structure of this mineral.Item VNIR-SWIR spectroscopic study of samples from the sepiolite-palygorskite polysomatic series(Macla, 2022) García Rivas, Javier; García Romero, Emilia; Santamaría López, Ángel; Súarez Barrios, MercedesItem Cuantificación del contenido en esmectitas mediante espectroscopía VNIR-SWIR en mezclas binarias(Macla, 2022) Santamaría López, Ángel; García Rivas, Javier; Lorenzo Hernández, Adrián; García Romero, Emilia; Súarez Barrios, MercedesItem On the structural formula of smectites: a review and new data on the influence of exchangeable cations(Journal of Applied Crystallography, 2021) García Romero, Emilia; Lorenzo, Adrián; García Vicente, Andrea; Morales, Juan; García Rivas, Javier; Súarez Barrios, MercedesThe understanding of the structural formula of smectite minerals is basic to predicting their physicochemical properties, which depend on the location of the cation substitutions within their 2:1 layer. This implies knowing the correct distribution and structural positions of the cations, which allows assigning the source of the layer charge of the tetrahedral or octahedral sheet, determining the total number of octahedral cations and, consequently, knowing the type of smectite. However, sometimes the structural formula obtained is not accurate. A key reason for the complexity of obtaining the correct structural formula is the presence of different exchangeable cations, especially Mg. Most smectites, to some extent, contain Mg2+ that can be on both octahedral and interlayer positions. This indeterminacy can lead to errors when constructing the structural formula. To estimate the correct position of the Mg2+ ions, that is their distribution over the octahedral and interlayer positions, it is necessary to substitute the interlayer Mg2+ and work with samples saturated with a known cation (homoionic samples). Seven smectites of the dioctahedral and trioctahedral types were homoionized with Ca2+, substituting the natural exchangeable cations. Several differences were found between the formulae obtained for the natural and Ca2+ homoionic samples. Both layer and interlayer charges increased, and the calculated numbers of octahedral cations in the homoionic samples were closer to four and six in the dioctahedral and trioctahedral smectites, respectively, with respect to the values calculated in the non-homoionic samples. This change was not limited to the octahedral sheet and interlayer, because the tetrahedral content also changed. For both dioctahedral and trioctahedral samples, the structural formulae improved considerably after homoionization of the samples, although higher accuracy was obtained the more magnesic and trioctahedral the smectites were. Additionally, the changes in the structural formulae sometimes resulted in changing the classification of the smectite.