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
UCM identifierDialnet ID

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Now showing 1 - 10 of 15
  • Publication
    New data on the microporosity of bentonites
    (Elsevier, 2022-01) Súarez Barrios, Mercedes; Lorenzo, Adrián; García Vicente, Andrea; Morales, Juan; García Rivas, Javier; García Romero, Emilia
    This 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.
  • Publication
    Presence of oriented fibers in palygorskite powders and its influence on X-Ray diffractograms
    (Elsevier, 2020-09-15) García Rivas, Javier; Súarez Barrios, Mercedes; García Romero, Emilia; Sánchez del Río, Manuel
    Palygorskite 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.
  • Publication
    Creación de una Colección Multimedia de Minerales al Microscopio Petrográfico: Un Aspecto Central en la Formación en Geociencias
    (2023-07-28) Pérez Garrido, Carlos; García Rivas, Javier; Forjanes Pérez, Pablo Cayetano; Luque del Villar, Francisco Javier; Fernández Díaz, María Lourdes; Astilleros García Monge, José Manuel; Yesares Ortiz, María Dolores; Carmona Tijerín, Victor; Esteban Ruiz, Paula; Fernández Riveras, Camila Isabel; García Herrador, Miguel; Sánchez Acosta, Rubén; Garrido Sánchez, Azael
    Este Proyecto Innova Docente tiene como objetivo realizar una labor apenas desarrollada hasta ahora: la digitalización de muestras de minerales transparentes de la colección de las asignaturas “Mineralogía I” de GG y “Cristalografía y Mineralogía” de GIG del Departamento de Mineralogía y Petrología de la UCM. A través de la digitalización de las muestras (fotos y vídeos) se busca crear un repositorio (accesible a través de la página web del departamento y material para el Campus Virtual de las asignaturas implicadas) en el que los estudiantes puedan consultar fácilmente las propiedades ópticas de los minerales vistos en prácticas, incluyendo sus cambios en función de las diferentes orientaciones. Este repositorio multimedia pretende marcar una clara diferencia con otros repositorios de otras universidades, en los cuáles únicamente se dispone de fotografías, las cuales por si solas no permiten observar claramente muchas de las características distintivas en minerales anisótropos. Consideramos que la digitalización de estas colecciones serán de gran ayuda para el adecuado aprendizaje y estudio de las diferentes asignaturas que utilizan la microscopía de luz transmitida, ya que la accesibilidad a este tipo de microscopios por parte de los alumnos fuera de la universidad es nula o muy limitada. Además, estos materiales serán esenciales en caso de suspensión de la actividad presencial o como apoyo a las actividades realizadas por los alumnos en el aula. También se pretende involucrar a estudiantes de las asignaturas en cuestión en el desarrollo de este Proyecto, tanto los incluidos en la convocatoria como otros alumnos de la asignatura que, a posteriori, quieran sumarse a la tarea.
  • Publication
    Crystalochemical Complexity of Magnesic Clays from the Tajo Basin
    (Sociedad Española de Mineralogía, 2014-07) García Rivas, Javier; Súarez Barrios, Mercedes; García Romero, Emilia
  • Publication
    Caracterización de palygorskitas españolas
    (Sociedad Española de Mineralogía, 2014) García Romero, Emilia; García Rivas, Javier; Síarez Barrios, Mercedes
  • Publication
    Spanish palygorskites: geological setting, mineralogical, textural and crystal-chemical characterization
    (E Schweizerbart Science Publishers, 2018) Suárez, Mercedes; García Rivas, Javier; Sánchez Migallón, Juan Morales; García Romero, Emilia
    A 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.
  • Publication
    Cuantificación del contenido en esmectitas mediante espectroscopía VNIR-SWIR en mezclas binarias
    (Sociedad Española de Mineralogía, 2022-06) Santamaría López, Ángel; García Rivas, Javier; Lorenzo Hernández, Adrián; García Romero, Emilia; Súarez Barrios, Mercedes
  • Publication
    On the structural formula of smectites: a review and new data on the influence of exchangeable cations
    (International Union of Crystallography, 2021-02) García Romero, Emilia; Lorenzo, Adrián; García Vicente, Andrea; Morales, Juan; García Rivas, Javier; Súarez Barrios, Mercedes
    The 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.
  • Publication
    Review and new data on the surface properties of palygorskite: A comparative study
    (Elsevier, 2021-10-17) Súarez Barrios, Mercedes; García Rivas, Javier; Morales, Juan; Lorenzo, Adrián; García Vicente, Andrea; García Romero, Emilia
    Palygorskite 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.
  • Publication
    VNIR-SWIR spectroscopic study of samples from the sepiolite-palygorskite polysomatic series
    (Sociedad Española de Mineralogía, 2022-06) García Rivas, Javier; García Romero, Emilia; Santamaría López, Ángel; Súarez Barrios, Mercedes