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
6 results
Search Results
Now showing 1 - 6 of 6
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 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 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 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 Spanish palygorskites: geological setting, mineralogical, textural and crystal-chemical characterization(European Journal of Mineralogy, 2018) Suárez, Mercedes; García Rivas, Javier; Sánchez Migallón, Juan Morales; García Romero, EmiliaA representative group of palygorskites from the six most important Spanish deposits and six other occurrences were studied comparing their mineralogy, textural features, crystal-chemistry, and surface properties. These palygorskites have different geological origin: (1) sedimentary in large Tertiary continental basins, (2) hydrothermally altered volcanic rocks in the southern Spanish Peninsula, also Tertiary in age; and (3) fault-hosted pure palygorskites. The most common impurities are quartz and carbonates, both calcite and dolomite, but also feldspar, illite, smectite, and sepiolite have been identified. The structural formulae obtained show great variability between samples, as well as with respect to the theoretical formula for palygorskite, as they range from magnesian to aluminous palygorskites. The most common fibre length ranges between 1 and 10 µm but the palygorskites of hydrothermal origin are much longer, with lengths over 10 µm. The shorter fibres give rise to tightened textures, while longer fibres usually generate more open textures. These properties, along with the degree of compaction, condition the porosity of the sample, which in turn influences its surface properties. The specific surface areas obtained range between 30 m2 g−1 and 263 m2 g−1, depending on the impurities content and on the texture and crystal-chemistry; the highest values correspond to Mg-rich palygorskite.Item 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, Mercedes