Amber imitation? Two unusual cases of Pinus resin-coated beads in Iberian Late Prehistory (3rd and 2nd millennia BC)

A group of beads from the artificial cave of La Molina (Lora de Estepa, Sevilla) and Cova del Gegant (Sitges, Barcelona) were made from a biogenic raw material and intentionally covered by a layer of resin. This is the first time this type of treatment has been documented on elements of adornment in the Late Prehistory of the Iberian Peninsula. The composition and nature of the coatings are analysed and the symbolic role of such alterations and imitations of prehistoric adornments is discussed.Ministerio de Economía y Competitividad HAR2012- 34620, HAR2017-83474-

Tailoring the Band Gap in the ZnS/ZnSe System: Solid Solutions by a Mechanically Induced Self-Sustaining Reaction

The complete ZnSxSe1−x solid solution was successfully obtained by the mechanochemical process denoted as a mechanically induced self-sustaining reaction. Excellent control of the chemical stoichiometry of the solid solution was possible by adjusting the atomic ratio of the starting Zn/S/Se elemental mixture subjected to milling. A mixture of both wurtzite-2H (hexagonal) and zinc blende (cubic) structures was always obtained, although for a similar milling time the proportion of the zinc blende structure increased with the Se content in the solid solution. However, wurtzite was the major phase for S-rich compositions when milling was stopped just after ignition. It was demonstrated that milling induces the wurtzite-to-zinc blende phase transition. The 8H hexagonal polytype was also observed in samples subjected to long milling times. Variation of the lattice parameters for both structures with the x value in the solid solution presented an excellent linearity, confirming the validity of Vegard’s law. However, variation of the band-gap energy (Eg) with x was not perfectly linear, and a small bowing parameter of 0.34 was obtained. It was possible to tune the Eg value between those of the end members of the solid solution in a continuous manner by adjusting the stoichiometry of the solid solution. The morphology and crystalline domain size can also be controlled by adjusting, in this case, the postignition milling time of the mechanochemical process.Fondo Europeo de Desarrollo Regional (FEDER) y Ministerio de Ciencia e Innovación español (Programa Ramón y Cajal)-RYC-2013-1243

Aplicación de las vermiculitas de Andalucía a la síntesis de cerámicas avanzadas

Después de una introducción sobre la estructura de la vermiculita, en este trabajo se exponen en primer lugar las clásicas aplicaciones generales de las vermiculitas como material principalmente aislante y semirrefractario. A continuación se muestran otras aplicaciones a las cuales pueden destinarse este tipo de silicatos: preparación de películas delgadas como aislantes térmicos para recubrimiento de fibra de vidrio y como espumas rígidas inorgánicas. Después se describen brevemente los yacimientos de vermiculita existentes en Andalucía y sus características quúnicas y mineralógicas generales. Seguidamente, se exponen y discuten las nuevas aplicaciones en las cuales se investiga actualmente utilizando las materias primas anteriores: (1) materiales piro-expandidos; (2) vidrios y materiales vitrocerámicos; (3) síntesis de nitruros y sialones. Se muestran algunos resultados de gran interés que ilustran sobre la importancia y las posibilidades de utilización de vermiculitas existentes en Andalucía como materia prima de síntesis de materiales avanzados, en las cuales nuestro grupo de investigación centra actualmente su interés.After a brief introduction on the structure of vermiculite, their general applications as insulating and semirefractory materials are shown. Next, other applications of vermiculite are described: preparation of thermal insulating films used as coating of glass fibers and inorganic rigid foams. After the above exposition, the vermiculite deposits of Andalusia and their general chemical and mineralogical characteristics are briefly described and summarized. The new applications of vermiculite from Andalusia that are now under research are discussed: (1) pyro-expanded materials, (2) glass and glass-ceramic materials, and (3) synthesis of nitrides and sialon. Some results of great interest are shown to illustrate the importance and the possibilities of application of vermiculite from Andalusia as raw material in the synthesis of advanced materials, in which our research group is currently involved.Peer reviewe

Síntesis de materiales cerámicos avanzados mediante la reducción carbotérmica de vermiculita

Desde su creación en el año 1986, en el Instituto de Ciencia de Materiales de Sevilla se viene desarrollando una línea de investigación denominada “síntesis y preparación de nuevos materiales a partir de silicatos naturales”. Dentro de este campo específico se enmarca la presente Tesis Doctoral, en la que se realiza un estudio sobre la síntesis de materiales cerámicos avanzados mediante la reducción carbotérmica de vermiculita.Se consideranmateriales cerámicos avanzados aquellos compuestos inorgánicos policristalinos, no metálicos, consolidados mediante tratamiento térmico a alta temperatura y que poseen excelentes propiedades mecánicas, eléctricas, magnéticas, ópticas, o bien, excepcional resistencia a altas temperaturas y ambientes corrosivos.Lareduccióncarbotérmica es uno de los métodos de preparación de materiales cerámicos avanzados más utilizados en la industria y consiste en el tratamiento de un compuesto oxidado a alta temperatura, generalmente entre 1300 ºC y 1700 ºC, en una atmósfera controlada y en presencia de un reductor. Existen numerosos ejemplos en la bibliografía en los que se utiliza este métodos, utilizando como materiales primas sílice, alúmina o silicatos.La presente Tesis Doctoral tiene como objetivo el estudio del proceso de la reducción carbotérmica devermiculita, la cual no se había usado con anterioridad en este tipo de reacciones.Teniendo en cuenta la composición de la vermiculita, como se ha mencionado formada por silicio, aluminio, magnesio, hierro, oxígeno e hidrógeno, los productos que cabe esperar se obtengan al final del proceso son:nitruros de silicio, nitruros de aluminio, oxinitruros de silicio y aluminio (sialones) y carburos de silicio. De estos compuestos, así como de la vermiculita y del poliacrilonitrilo, se ha realizado una minuciosa revisión bibliográfica, con anterioridad al desarrollo del trabajo experimental, con el propósito de tener una base a partir de la cual avanzar en las investigaciones objeto de la Tesis.De acuerdo con lo expuesto anteriormente, cabe destacar que las innovaciones que se investigan dentro del objetivo general de la presente Tesis Doctoral son:- Estudio de la evolución térmica de la vermiculita hasta una temperatura de 1400 ºC, para conocer sus transformaciones y servir de referencia para tratamientos posteriores.- Estudio del tratamiento mecánico realizado sobre la vermiculita en molino de anillos, para investigar el efecto de la molienda en el silicato y su influencia en la reactividad.- Preparación del complejo de intercalación de vermiculita con poliacrilonitrilo, para conseguir el máximo grado de interacción ente la red del silicato y la cadena carbonada.- Utilización de la vermiculita en una reacción de reducción carbotérmica en atmósfera controlada, para estudiar la síntesis de los materiales avanzados que puedan obtenerse

Self-propagating combustion synthesis via an MSR process: An efficient and simple method to prepare (Ti, Zr, Hf)B2-Al2O3 powder nanocomposites

The synthesis of (Ti1-xZrx)B2-Al2O3, (Ti1-xHfx)B2-Al2O3 and (Zr1-xHfx)B2-Al2O3 (x=0, 0.5 and 1) powder nanocomposites via a mechanochemical method using TiO2, ZrO2, HfO2, HBO2 and Al as the raw materials was investigated. The formation of the nanocomposites proceeds via a mechanically-induced self-sustaining reaction (MSR) process that involves several simultaneous reactions. The aluminothermic reductions of the TMO2 and HBO2 produce Al2O3 and transition metal and boron elements, which in turn react to yield the diboride phase. The ignition of the complex combustion reaction occurred after a short milling time (15-30min), instantly transforming most of the reactants into products. The sample composition was marked by the stoichiometry of the combustion reaction, and the resulting nanocomposites were analysed using XRD, ED, SEM, TEM and EDX techniques. The X-ray results confirmed the biphasic character of the prepared composite powder (TMB2 and Al2O3 structures); minor amounts of the Zr and Hf oxides were also observed. The achieved microstructure was characterised by the agglomeration of Al2O3 nanocrystallites and diboride crystals with a diffraction domain size ranging between 100 and 300nm. © 2014 Elsevier B.V.Peer Reviewe

Formation of the complete range of Ti5Si3−xGex solid solutions via mechanically induced self-sustained reactions

The complete range of Ti5Si3–Ti5Ge3 solid solutions was synthesised from elemental mixtures of Ti, Si, and Ge under an inert atmosphere via mechanically induced self-sustaining reactions (MSR). The stoichiometry of Ti5Si3−xGex solid solutions was controlled by adjusting the Si/Ge ratio of the initial mixture. The chemical composition and lattice parameters of the materials confirmed that Ti5Si3–Ti5Ge3 solid solutions with good chemical homogeneity could be produced via MSR.This work was supported by Spanish government under grant No. MAT2010-17046, which is financed in part by European Regional Development Fund of 2007–2013. E. Chicardi and J. M. Córdoba were supported by CSIC through JAE-Pre and JAE-Doc grants, respectively, which are financed in part by European Social Fund (ESF).Peer Reviewe

Sintering by SPS of ultrafine TiCxN1-x powders obtained using mechanically induced self sustaining reaction

4 páginas, 6 figuras, 1 tabla.[EN]: In this work high purity and nanometer character titanium carbonitride TiCxN1-x powders were obtained by mechanically induced self sustaining reaction (MSR) in a high-energy planetary ball mill, from a mixture of titanium with graphite or carbon nanofiber (CNFs) in a nitrogen atmosphere. A promising method for developing these materials is the coupling of the MSR with SPS sintering technique. The product is sintered at 1400 ºC and 1700 ºC, obtaining a completely dense monolithic ceramic (>99% t.d). In this work, the influence of SPS treatment and carbon precursor on material microstructures was studied and the main mechanical properties of the end material were evaluated.[ES]: En el presente trabajo se han obtenido carbonitruros de titanio TiCxN1-x de alta pureza y con carácter nanométrico, por molienda reactiva (MSR) de alta energía en un molino planetario, a partir de la mezcla de titanio con grafito o nanofibras de carbono (CNFs) en una atmósfera de nitrógeno. Una metodología prometedora para el desarrollo de estos materiales consiste en el acoplamiento de la técnica MSR con el sinterizado por SPS. El producto obtenido se ha sinterizado a 1400 ºC y 1700 ºC, obteniéndose una cerámica monolítica totalmente densa (>99% d.t). En este trabajo se analizan las distintas microestructuras obtenidas en función del precursor de carbono y el tratamiento de SPS, evaluando las principales propiedades mecánicas de los materiales resultantes.Este trabajo ha sido llevado acabo con financiación procedente de los proyectos del plan nacional MAT2006-01783 y MAT2006-04911.Peer reviewe

Isosymmetric structural phase transition of the orthorhombic lanthanum gallate structure as a function of temperature determined by Rietveld analysis

High energy planetary ball milling has been used to synthesize pseudo-cubic highly-pure LaGaO in one hour from its oxide components in an air atmosphere. Calcination at different temperatures led to the crystallization of lanthanum gallate in an orthorhombic structure with its local lanthanum coordination number environment changing from 12 to 7 when the temperature was increased. This change was attributed to the thermal expansion of the Ga-O bonds that varied non-monotonically inducing GaO tilting. Rietveld analysis, Raman spectroscopy, and transmission electron microscopy were used to elucidate the LaGaO structures at different temperatures.This work was supported by the Spanish Government financed in part by the European Regional Development Fund through the Ramón y Cajal Program RYC-2013-12437

Thermal study of the effect of several solvents on polymerization of acrylonitrile and their subsequent pyrolysis

The polymerization of acrylonitrile to polyacrylonitrile (PAN) has been studied using several solvents: N,N-dimethylformamide (DMF), hexane, toluene, water, and in bulk form (no solvent). The addition of DMF is the only case where both monomer and polymer are soluble in the solvent. Thermal analyses of the resultant products after polymerization have been performed by differential scanning calorimetry and pyrolysis–gas chromatography: mass spectrometry. The effect of the solvents employed as media for polymerization is interpreted from the results of the thermal and structural (X-ray diffraction) methods. The polymer samples obtained when using water or toluene as solvents have the greater content of amorphous components compared to the others. The amide molecules are difficult to completely eliminate in the product obtained after the polymerization reaction and even after prolonged heating at 110°C and remain occluded. DMF can be considered to exert a plasticized effect on PAN and is even capable of forming complexes by dipolar bonding. As a result of this interaction, the thermogram is quite different from the other samples studied in the present work, showing a single sharp exothermic peak. This is associated with nitrile group polymerization (cyclization) of PAN. It is deduced that the amount of heat evolved as well as the temperature interval over which it is released are influenced by the chemical processing of PAN, in particular when using DMF as solvent for both monomer and polymer. Pyrolysis of the different PAN samples revealed the release of occluded solvent molecules, mainly when using DMF, and compounds produced from the thermal degradation processes. Different types of cyclized compounds, such as pyridine derivatives and aromatic nitriles were identified. All these compounds could be derived from cyclized PAN structures which are not completely degraded by the thermal treatment of pyrolysis. Alkyldinitriles have also been tentatively identified associated with the final molecular breakdown of cyclized structures with six-member rings by pyrolysis. Valuable complementary information on the structure of the PAN samples (homopolymer) obtained using the different processing approaches involving several solvent media has been provided by pyrolysis. The present results will improve our understanding of the evolution of the structure and properties of carbon and activated carbon fibres which will enable us to establish processing strategies in order to obtain these materials under adequate and reproducible conditions.Peer reviewe

Spark plasma sintering of ultrafine TiCxN1−x powders synthesized by a mechanically induced self-sustaining reaction

5 páginas, 8 figuras, 2 tablas.High-purity, nanometer-sized titanium carbonitride powders, TiyNb1−yCxN1−x, were obtained with a mechanically induced self-sustaining reaction (MSR) in a high-energy planetary ball mill from a mixture of titanium and different carbon precursors under a nitrogen atmosphere. A promising method for developing dense TiCxN1−x materials is the coupling of MSR with the spark plasma sintering (SPS) technique. The powders were sintered at different temperatures to provide a completely dense monolithic ceramic (>99% theoretical density). In this work, the influence of the carbon precursor and SPS treatment on the material microstructures were studied, and the main mechanical properties of the end material were evaluated.This work was financially supported by the National Plan projects MAT2006-01783 and MAT2006-04911.Peer reviewe