Procesamiento y caracterización de materiales porosos de fases MAX

Mención Internacional en el título de doctorLas fases MAX son un grupo de compuestos ternarios cuya fórmula general es Mn+1AXn, (siendo M un elemento de transición, A un elemento generalmente de los grupos IIIA o IVA, X puede ser C o N, y n=1-3). Tienen una estructura cristalina nanolaminada que les confiere propiedades inusuales. Aúnan propiedades típicas de metales y cerámicos, como alta rigidez, buenas propiedades mecánicas a alta temperatura, alta resistencia a corrosión y oxidación, buena conductividad térmica y eléctrica. Además, presentan un mecanismo de amortiguación mecánica característico de los materiales laminados: deforman creando bandas de tipo “kink”, similares a pliegues, lo que les permite absorber gran cantidad de energía. Con el fin de potenciar estas propiedades, esta tesis doctoral trata de optimizar el procesamiento en forma porosa y con control de la porosidad (cantidad, tamaño, morfología y distribución). En esta tesis doctoral se plantea el procesamiento y la caracterización de estructuras porosas de Ti2AlC y Ti3SiC2, pertenecientes a la familia de las “fases MAX”. Las estructuras porosas se han elaborado a partir del material en polvo mediante dos técnicas pulvimetalúrgicas (i) por vía seca utilizando el método del espaciador y (ii) por vía húmeda mediante técnicas coloidales y el empleo de una plantilla de sacrificio. Se han optimizado los parámetros del procesamiento, se ha estudiado la porosidad (cantidad, tamaño, morfología y distribución) y se ha vinculado esta con los parámetros del procesamiento para poder diseñar propiedades a medida desde la etapa de procesamiento. Por el método del espaciador, vía seca, se han procesado el Ti2AlC y Ti3SiC2. El método incluye mezclado, compactación, disolución y sinterización. Se ha estudiado la compresibilidad de los materiales, se han optimizado las condiciones de eliminación del espaciador y se ha estudiado el efecto del sinterizado en la composición de las fases. Con el fin de controlar la cantidad de porosidad y tamaño de poro en la estructura porosa, se han introducido distintas cantidades de espaciador y tamaños de espaciador. Se ha estudiado la influencia de los parámetros del procesamiento sobre la microestructura de las estructuras porosas producidas. Por la vía húmeda, se han elaborado suspensiones acuosas mediante técnicas coloidales. Para obtener una suspensión estable que genere una estructura con propiedades óptimas, se ha caracterizado la suspensión mediante el estudio del potencial-ζ. Se ha optimizado el pH y la cantidad de dispersante. Mediante reología se ha estudiado la cantidad óptima de contenido en sólidos. El comportamiento reológico se ha optimizado con la adición de metilcelulosa como agente espesante. Mediante un infiltrado en plantilla polimérica se ha conseguido la estructura porosa. La microestructura de los materiales porosos se ha estudiado en profundidad mediante análisis de imagen de SEM y tomografía de RX y se ha vinculado con los parámetros del procesamiento. Se han caracterizado las fracciones sólida y porosa cuantificando: espesor de las paredes, distribución de la fracción de sólido a lo largo de la muestra, homogeneidad de la porosidad, morfología de la porosidad (tamaño medio de poro, relación de aspecto, circularidad, esfericidad y elongación) y fracción de porosidad. A continuación, se estudiaron las propiedades funcionales de los porosos de Ti2AlC y Ti3SiC2 y el efecto de los parámetros de la porosidad. El aumento de la porosidad ha mostrado una disminución lineal de la conductividad térmica (a temperatura ambiente y hasta 300ºC) y la conductividad eléctrica (a temperatura ambiente y hasta 500ºC). El aumento del tamaño de poro incrementa el espesor de las paredes y aumenta la conductividad térmica; la conductividad eléctrica disminuye con el aumento de tamaño de poro debido a que se incrementa la tortuosidad en la estructura porosa. La resistencia a oxidación ha mostrado la misma tendencia que los materiales completamente densos a 1000ºC (Ti2AlC) y a 900ºC (Ti3SiC2) durante 240 h en ciclos de 24 horas. No se ha producido espalación en los porosos mostrando así la buena resistencia y calidad de los materiales elaborados en esta tesis doctoral. La variación de las propiedades elásticas (E, G y ν) con la porosidad se ha ajustado con precisión a modelos matemáticos. Se ha comprobado que las propiedades elásticas dependen principalmente de si existe o no interconectividad en la porosidad y que esta característica influye más en las propiedades elásticas que el tamaño de poro. Las propiedades mecánicas se han caracterizado frente a la porosidad. Se ha determinado cómo el espesor de las paredes modula la resistencia a compresión: el espesor de pared aumenta al disminuir la porosidad y aumentar el tamaño de poro, y esto incrementa la resistencia a compresión. La adición de porosidad permite modular las propiedades finales del material para ajustarlas a aplicaciones específicas desde la etapa de procesamiento. El Ti2AlC y Ti3SiC2 en forma porosa obtenidos en esta tesis han resultado bien consolidados y robustos. El ajuste de las características de la porosidad permite modularlos para una gama de aplicaciones como intercambiadores de calor, filtros de gas caliente, materiales con alta tolerancia al impacto, soportes para dispositivos catalíticos en automóviles, biomateriales, colectores o captadores solares, etc.MAX phases are a group of ternary compounds whose general fomula is Mn+1AXn (where M is a transition element, A an element generally from groups IIIA o IVA, X may be C or N, and n=1-3). They have a nanolaminated structure that gives them unusual properties. They combine typical metal and ceramic properties, such as high rigidity, good mechanical properties at high temperatures, high resistance to corrosion and oxidation and good thermal and electrical conductivity. Furthermore, they show the mechanical damping (shock-absortion) characteristic of laminated materials: they deform forming kink bands, which allows them to absorb large amounts of energy. With a view to boost these properties, this doctoral thesis attempted to optimize their processing in a porous form and with control of porosity (amount, size, morphology and distribution). This doctoral thesis approaches the processing and characterization of porous structures of Ti2AlC and Ti3SiC2, both belonging to the MAX phase family. The porous structures were produced from powder material using two powder metallurgy techniques (i) dry processing using a spacer and (ii) wet processing with colloidal techniques using a sacrifice template. Processing parameters were optimized, porosity (amount, size, morphology and distribution) was analyzed and linked with the processing parameters in order to design custom properties from the processing stage. Both Ti2AlC and Ti3SiC2 were dry-processed using a spacer method. The method employed includes mixing, compacting, dissolution and sintering. The compressibility of the materials was analyzed, spacer removal conditions were optimized and we studied the effect of sintering on the phases. To monitor porosity and pore size in the resulting porous structure, the spacer was introduced in varying quantities and sizes. The impact of processing parameters on the microstructure of the resulting porous structures was analyzed. Also, aqueous suspensions were generated through colloidal techniques in wet processing. To obtain a stable suspension capable of producing a structure showing optimal properties, the suspension was characterized by analyzing its ζ potential. We also optimized the pH and the amount of dispersing agent. The optimal quantity of solid content was analyzed using rheology. Rheological behavior was optimized by the adition of metilcelulose as a thickening agent. The porous structure was generated by infiltration in a polymeric template. The microstructure of the porous material was analyzed through SEM image analysis and RX tomography, and it was linked to processing parameters. Solid and porous fractions were characterized quantifying the following: wall thickness, solid fraction distribution in the sample, uniformity of porosity, and porosity morphology (average pore size, aspect ratio, circularity, esfericity and elongation) and fraction. Then, functional properties of porous Ti2AlC and Ti3SiC2 and the effect of the parameters on porosity were analyzed. Increases in porosity produced a linear decrease in thermal conductivity (from room temperature up to 300ºC) and in electrical conductivity (from room temperature up to 500ºC). Increasing pore size increases wall thickness and thermal conductivity along with it; electrical conductivity decreases as pore size increases due to the concomittant increase in tortuosity in the porous structure. Resistance to oxidation showed the same tendency observed in the respective dense materials at 1000ºC (Ti2AlC) and at 900ºC (Ti3SiC2) in 24 hour cycles for a total of 240 hours. No spallation was produced in the porous materials, thus showing the high resistance and quality of the materials produced in this doctoral thesis. Elastic property (E, G and ν) variation with porosity was precisely adjusted to mathematical models. We have verified that elastic properties depend mainly on the existence of interconectivity in the porosity, so that this characteristic has a higher impact on elastic properties than does pore size. Mechanical properties vs porosity were also characterized. We have seen how wall thickness modulates resistance to compression: wall thickness increases as porosity decreases and as pore size increases, which augments resistance to compression. Adding porosity allows modulation of the final properties of the material from the processing stage to fine-tune them to specific applications. The resulting porous Ti2AlC and Ti3SiC2 obtained in this thesis work showed good consolidation and robustness. Fine-tuning porosity characteristics allows their adaptation to a range of applications such as heat exchangers, hot gas filters, high impact tolerance materials, catalytic devices in automobiles, biomaterials, solar energy collectors, etc.Esta Tesis Doctoral ha sido realizada en la Universidad Carlos III de Madrid y ha sido financiada por los proyectos: MULTIMAT-CHALLENGE-CM. “Materiales Multifuncionales para los Retos de la Sociedad” (Ref. S2013/MIT-2862), MITICO “Diseño de la microestructura y la microarquitectura de materiales metal-cerámicos utilizando tecnologías coloidales y pulvimetalúrgicas” (Ref. MAT2012-38650-C02-01) y ESTRUMAT Materiales Estructurales Avanzados TP-UC3M (Ref. S2009/MAT-1585) y por una Beca PIF, Personal Investigador en Formación, UC3M 01-1314.Programa Oficial de Doctorado en Ciencia e Ingeniería de MaterialesPresidente: José Ygnacio Pastor Caño.- Secretario: Antonio Jiménez Morales.- Vocal: Emilio López Lópe

Ti2AlC and Ti3SiC2 MAX phase foams: processing, porosity characterization and connection between processing parameters and porosity

Proceeding of: World PM2016 Congress Proceedings. New materials and applications, biomedical applicationsMAX phases Ti2AlC and Ti3SiC2 foams with controlled porosity and pore size were produced using the space holder method. The foams were processed using water-leachable crystalline carbohydrate as space holder that involves: mixing, cold isostatic pressing, dissolution and sintering. Three combinations of volume percentage (20%-60%) and size distribution (250-1000 mum) of space holder were introduced during mixing. The foams were characterized and compared with the material without space holder. The characterization included: morphology (overall, open and closed porosity by Archimedes method) and gas permeability. Foams with porosity up to about 60 vol% and pore size distribution ranging from about 250 to 1000 mum were produced. Experimental porosity was compared to the theoretical expected porosity. The results show a bimodal porosity that can be customized by the sintering and the space holder. This study connects the processing parameters to the porosity created and allows control of porosity and pore size to produce tailor-made properties.The authors would like to thank the funding provided for this research by the Regional Government of Madrid- Dir. Gral. Universidades e Investigación, through the project S2013/MIT-2862 (MULTIMAT-CHALLENGE-CM), and by Spanish Government through Ramón y Cajal contract RYC-2014-15014 and the project MAT2012/38650-C02-0

Differences in psychosocial risks and Burnout between Spanish textile industry's workers

El objetivo de esta investigación fue estudiar las diferencias en la percepción de riesgo psicosocial y en burnout en una muestra de 35 trabajadores pertenecientes a una fábrica textil de la provincia de Toledo, formada por 19 maquinistas, 12 planchadores y 4 jefes de unidad. Se les aplicaron dos instrumentos: Cuestionario DECORE para evaluar el riesgo psicosocial y MBI-General Survey para evaluar burnout. Los resultados muestran diferencias en la percepción de los factores de riesgo psicosocial evaluados al comparar los tres grupos profesionales, compartiendo todos ellos la percepción de falta de control en su trabajo en un nivel de emergencia. A pesar de no mostrar altos niveles de burnout, son los jefes de unidad los que presentan mayor desgaste emocional respecto al resto de subgrupos. Estos resultados muestran la posibilidad de comparar distintos grupos profesionales dentro del sector textil en lo referente a la evaluación del riesgo psicosocial y burnout

Higher COVID-19 pneumonia risk associated with anti-IFN-α than with anti-IFN-ω auto-Abs in children

We found that 19 (10.4%) of 183 unvaccinated children hospitalized for COVID-19 pneumonia had autoantibodies (auto-Abs) neutralizing type I IFNs (IFN-alpha 2 in 10 patients: IFN-alpha 2 only in three, IFN-alpha 2 plus IFN-omega in five, and IFN-alpha 2, IFN-omega plus IFN-beta in two; IFN-omega only in nine patients). Seven children (3.8%) had Abs neutralizing at least 10 ng/ml of one IFN, whereas the other 12 (6.6%) had Abs neutralizing only 100 pg/ml. The auto-Abs neutralized both unglycosylated and glycosylated IFNs. We also detected auto-Abs neutralizing 100 pg/ml IFN-alpha 2 in 4 of 2,267 uninfected children (0.2%) and auto-Abs neutralizing IFN-omega in 45 children (2%). The odds ratios (ORs) for life-threatening COVID-19 pneumonia were, therefore, higher for auto-Abs neutralizing IFN-alpha 2 only (OR [95% CI] = 67.6 [5.7-9,196.6]) than for auto-Abs neutralizing IFN-. only (OR [95% CI] = 2.6 [1.2-5.3]). ORs were also higher for auto-Abs neutralizing high concentrations (OR [95% CI] = 12.9 [4.6-35.9]) than for those neutralizing low concentrations (OR [95% CI] = 5.5 [3.1-9.6]) of IFN-omega and/or IFN-alpha 2

Clonal chromosomal mosaicism and loss of chromosome Y in elderly men increase vulnerability for SARS-CoV-2

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, COVID-19) had an estimated overall case fatality ratio of 1.38% (pre-vaccination), being 53% higher in males and increasing exponentially with age. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, we found 133 cases (1.42%) with detectable clonal mosaicism for chromosome alterations (mCA) and 226 males (5.08%) with acquired loss of chromosome Y (LOY). Individuals with clonal mosaic events (mCA and/or LOY) showed a 54% increase in the risk of COVID-19 lethality. LOY is associated with transcriptomic biomarkers of immune dysfunction, pro-coagulation activity and cardiovascular risk. Interferon-induced genes involved in the initial immune response to SARS-CoV-2 are also down-regulated in LOY. Thus, mCA and LOY underlie at least part of the sex-biased severity and mortality of COVID-19 in aging patients. Given its potential therapeutic and prognostic relevance, evaluation of clonal mosaicism should be implemented as biomarker of COVID-19 severity in elderly people. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, individuals with clonal mosaic events (clonal mosaicism for chromosome alterations and/or loss of chromosome Y) showed an increased risk of COVID-19 lethality

Effect of remote ischaemic conditioning on clinical outcomes in patients with acute myocardial infarction (CONDI-2/ERIC-PPCI): a single-blind randomised controlled trial.

BACKGROUND: Remote ischaemic conditioning with transient ischaemia and reperfusion applied to the arm has been shown to reduce myocardial infarct size in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI). We investigated whether remote ischaemic conditioning could reduce the incidence of cardiac death and hospitalisation for heart failure at 12 months. METHODS: We did an international investigator-initiated, prospective, single-blind, randomised controlled trial (CONDI-2/ERIC-PPCI) at 33 centres across the UK, Denmark, Spain, and Serbia. Patients (age >18 years) with suspected STEMI and who were eligible for PPCI were randomly allocated (1:1, stratified by centre with a permuted block method) to receive standard treatment (including a sham simulated remote ischaemic conditioning intervention at UK sites only) or remote ischaemic conditioning treatment (intermittent ischaemia and reperfusion applied to the arm through four cycles of 5-min inflation and 5-min deflation of an automated cuff device) before PPCI. Investigators responsible for data collection and outcome assessment were masked to treatment allocation. The primary combined endpoint was cardiac death or hospitalisation for heart failure at 12 months in the intention-to-treat population. This trial is registered with ClinicalTrials.gov (NCT02342522) and is completed. FINDINGS: Between Nov 6, 2013, and March 31, 2018, 5401 patients were randomly allocated to either the control group (n=2701) or the remote ischaemic conditioning group (n=2700). After exclusion of patients upon hospital arrival or loss to follow-up, 2569 patients in the control group and 2546 in the intervention group were included in the intention-to-treat analysis. At 12 months post-PPCI, the Kaplan-Meier-estimated frequencies of cardiac death or hospitalisation for heart failure (the primary endpoint) were 220 (8·6%) patients in the control group and 239 (9·4%) in the remote ischaemic conditioning group (hazard ratio 1·10 [95% CI 0·91-1·32], p=0·32 for intervention versus control). No important unexpected adverse events or side effects of remote ischaemic conditioning were observed. INTERPRETATION: Remote ischaemic conditioning does not improve clinical outcomes (cardiac death or hospitalisation for heart failure) at 12 months in patients with STEMI undergoing PPCI. FUNDING: British Heart Foundation, University College London Hospitals/University College London Biomedical Research Centre, Danish Innovation Foundation, Novo Nordisk Foundation, TrygFonden

MAX phase Ti2AlC foams using a leachable space-holder material

MAX phase foams from commercial Ti2AlC powder were prepared by a novel powder processing method using raw sugar as space-holder. Manufacturing MAX phase foams using this method involves mixing Ti2AlC powder with raw sugar, pressing the mixture to form a green body followed by space-holder removal and sintering. Green bodies were formed using cold uniaxial pressing and porosity was controlled varying the size and amount of the raw sugar space-holder. Three different space-holder particles sizes in the range of 250-1000 μm and four different volume amounts (20%, 40%, 60% and 80%) of space-holder were studied. The foams produced were characterized, and the size distribution and amount of resulting porosity was compared with the theoretically expected values. Optimal conditions using this novel processing technique for this material were established aiming towards controlling the final microstructures and properties, of porous Ti2AlC MAX phase.The authors wish to thank the Ministry of Education and Science for funding through R & D project MAT2012-38650-C02-01, and the Community of Madrid for its funding through ESTRUMAT program (S-2009/MAT-1585).Publicad

Expert System to Model and Forecast Time Series of Epidemiological Counts with Applications to COVID-19

We developed two models for real-time monitoring and forecasting of the evolution of the COVID-19 pandemic: a non-linear regression model and an error correction model. Our strategy allows us to detect pandemic peaks and make short- and long-term forecasts of the number of infected, deaths and people requiring hospitalization and intensive care. The non-linear regression model is implemented in an expert system that automatically allows the user to fit and forecast through a graphical interface. This system is equipped with a control procedure to detect trend changes and define the end of one wave and the beginning of another. Moreover, it depends on only four parameters per series that are easy to interpret and monitor along time for each variable. This feature enables us to study the effect of interventions over time in order to advise how to proceed in future outbreaks. The error correction model developed works with cointegration between series and has a great forecast capacity. Our system is prepared to work in parallel in all the Autonomous Communities of Spain. Moreover, our models are compared with a SIR model extension (SCIR) and several models of artificial intelligence

Diferencias en riesgos psicosociales y burnout entre trabajadores del sector textil español

The aim of this research was to study the differences in the perception of psychosocial risk and burnout in a sample of 35 workers from a textile factory in the province of Toledo. Specifically, 19 swing machine operators, 12 persons who do the ironing and 4 team leaders. Two instruments have been applied to the sample (DECORE Questionnaire and MBI-General Survey). The results show differences in the perception of psychosocial risk factors assessed by comparing the three professional groups, all sharing the perception of lack of control over their work in an emergency level. Also, despite not appearing high levels of burnout, team leaders are those with greater emotional exhaustion compared to other sub-groups. These results thus show the possibility to compare different professional groups within the textile sector in relation to psychosocial risk assessment and burnout.El objetivo de esta investigación fue estudiar las diferencias en la percepción de riesgo psicosocial y en burnout en una muestra de 35 trabajadores pertenecientes a una fábrica textil de la provincia de Toledo, formada por 19 maquinistas, 12 planchadores y 4 jefes de unidad. Se les aplicaron dos instrumentos: Cuestionario DECORE para evaluar el riesgo psicosocial y MBI-General Survey para evaluar burnout. Los resultados muestran diferencias en la percepción de los factores de riesgo psicosocial evaluados al comparar los tres grupos profesionales, compartiendo todos ellos la percepción de falta de control en su trabajo en un nivel de emergencia. A pesar de no mostrar altos niveles de burnout, son los jefes de unidad los que presentan mayor desgaste emocional respecto al resto de subgrupos. Estos resultados muestran la posibilidad de comparar distintos grupos profesionales dentro del sector textil en lo referente a la evaluación del riesgo psicosocial y burnout

Thermophysical properties of porous Ti2AlC and Ti3SiC2 produced by powder metallurgy

The physicochemical properties of porous Ti2AlC and Ti3SiC2 MAX phase compounds with controlled porosity and grain size obtained by powder metallurgy techniques was studied in depth in order to access their suitability of applications such as catalytic devices on vehicles, heat exchangers or impact resistant structures. The study was performed on isostatic consolidated samples with different amount (20-60 vol%) and size of space holder (250-1000 µm) and in samples without space holder. Oxidation tests were performed at different temperatures for each material depending on their maximum service temperature. In order to understand the oxidation mechanism, oxidation kinetics were analysed to determine the influence of size and amount of porosity in each case. In addition, the microstructure and composition of the oxide layers formed after the tests were analysed by scanning electron microscopy (SEM). Electrical and thermal conductivity where studied at room temperature and at temperature up to 1000 degrees C. The effect of pore size and cell wall thickness is discussed. Permeability of foams was also measured. The effect of micro porosity and macro porosity on permeability is discussed. The coefficient of thermal expiation was also measured for all foams produced. It is established that these porous MAX phases have suitable properties for their use as catalytic substrates, heat exchanges, high temperature filters or volumetric solar receivers.This research was funded by the Regional Government of Madrid (program ADITIMAT-CM. ref. S2018/NMT-4411) and by the Ministry of Economy and Competitiveness of Spain (program MINECO Ramón y Cajal contract RYC-2014-1504). Dr. Beatriz Valasco is grateful for the funding provided by the Insitituto Alvaro Alonso Barba (Universidad Carlos III de Madrid) for the research stay at the IFAM. Dresden