Flash Spark Plasma Sintering (FSPS) of Pure ZrB2

Export Date: 19 August 2014 CODEN: JACTA Correspondence Address: Reece, M.J.; School of Engineering and Material Science, Queen Mary University of London, London E1 4NS, United Kingdom; email: [email protected] Funding Details: EP/K008749/1, EPSRC, European Commission Funding Details: FP7 2007-2013, EC, European Commission References: Cologna, M., Rashkova, B., Raj, R., Flash Sintering of Nanograin Zirconia in <5 s at 850°C (2010) J. Am. Ceram. Soc., 93 (11), pp. 3556-3559; Downs, J.A., Sglavo, V.M., Electric Field Assisted Sintering of Cubic Zirconia at 390°C (2013) J. Am. Ceram. Soc., 96 (5), pp. 1342-1344; Muccillo, R., Muccillo, E.N.S., An Experimental Setup for Shrinkage Evaluation during Electric Field-Assisted Flash Sintering: Application to Yttria-Stabilized Zirconia (2013) J. Eur. Ceram. Soc., 33 (3), pp. 515-520; Muccillo, R., Muccillo, E.N.S., Electric Field-Assisted Flash Sintering of Tin Dioxide (2014) J. Eur. Ceram. Soc., 34 (4), pp. 915-923; Jha, S.K., Raj, R., The Effect of Electric Field on Sintering and Electrical Conductivity of Titania (2014) J. Am. Ceram. Soc., 97 (2), pp. 527-534; Zapata-Solvas, E., Bonilla, S., Wilshaw, P.R., Todd, R.I., Preliminary Investigation of Flash Sintering of SiC (2013) J. Eur. Ceram. Soc., 33 (1314), pp. 2811-2816; Grasso, S., Sakka, Y., Rendtorff, N., Hu, C., Maizza, G., Borodianska, H., Vasylkiv, O., Modeling of the Temperature Distribution of flash sintered Zirconia (2011) Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi/J. Ceram. Soc. Jpn., 119 (1386), pp. 144-146; Park, J., Chen, I.W., In Situ Thermometry Measuring Temperature Flashes Exceeding 1,700°C in 8 mol% Y2O3-Stablized Zirconia under Constant-Voltage Heating (2013) J. Am. Ceram. Soc., 96 (3), pp. 697-700; Zapata-Solvas, E., Jayaseelan, D.D., Lin, H.T., Brown, P., Lee, W.E., Mechanical Properties of ZrB2- and HfB2-Based Ultra-High Temperature Ceramics Fabricated by Spark Plasma Sintering (2013) J. Eur. Ceram. Soc., 33 (7), pp. 1373-1386; Grasso, S., Sakka, Y., Maizza, G., Electric Current Activated/Assisted Sintering (ECAS): A Review of Patents 1906-2008 (2009) Sci. Technol. Adv. Mater., 10 (5), p. 053001; Mallik, M., Kailath, A.J., Ray, K.K., Mitra, R., Electrical and Thermophysical Properties of ZrB2 and HfB 2 Based Composites (2012) J. Eur. Ceram. Soc., 32 (10), pp. 2545-2555; Steil, M.C., Marinha, D., Aman, Y., Gomes, J.R.C., Kleitz, M., From Conventional Ac Flash-Sintering of YSZ to Hyper-Flash and Double Flash (2013) J. Eur. Ceram. Soc., 33 (11), pp. 2093-2101; Ortiz, A.L., Zamora, V., Rodríguez-Rojas, F., A Study of the Oxidation of ZrB2 Powders during High-Energy Ball-Milling in Air (2012) Ceram. Int., 38 (4), pp. 2857-2863; Porwal, H., Tatarko, P., Grasso, S., Hu, C., Boccaccini, A.R., Dlouhý, I., Reece, M., Toughened and Machinable Glass Matrix Composites Reinforced with Graphene and Graphene-Oxide Nano Platelets (2013) Sci. Technol. Adv. Mater., 14, p. 055007 Pure ZrB2 powder was Flash sintered in an SPS furnace (FSPS). The samples were densified up to 95.0% in 35 s under an applied pressure of 16 MPa. Compared to Conventional SPS (CSPS), the newly developed FSPS technique resulted in an unprecedented energy and time savings of about 95% and 98% respectively. ZrB2 monoliths obtained by CSPS and FSPS were compared with respect to microstructures, densification behavior, and grain growth. The developed methodology might find application to a wide range of highly conductive ceramics as such refractory borides and carbides. © 2014 The American Ceramic Society.Export Date: 19 August 2014 CODEN: JACTA Correspondence Address: Reece, M.J.; School of Engineering and Material Science, Queen Mary University of London, London E1 4NS, United Kingdom; email: [email protected] Funding Details: EP/K008749/1, EPSRC, European Commission Funding Details: FP7 2007-2013, EC, European Commission References: Cologna, M., Rashkova, B., Raj, R., Flash Sintering of Nanograin Zirconia in <5 s at 850°C (2010) J. Am. Ceram. Soc., 93 (11), pp. 3556-3559; Downs, J.A., Sglavo, V.M., Electric Field Assisted Sintering of Cubic Zirconia at 390°C (2013) J. Am. Ceram. Soc., 96 (5), pp. 1342-1344; Muccillo, R., Muccillo, E.N.S., An Experimental Setup for Shrinkage Evaluation during Electric Field-Assisted Flash Sintering: Application to Yttria-Stabilized Zirconia (2013) J. Eur. Ceram. Soc., 33 (3), pp. 515-520; Muccillo, R., Muccillo, E.N.S., Electric Field-Assisted Flash Sintering of Tin Dioxide (2014) J. Eur. Ceram. Soc., 34 (4), pp. 915-923; Jha, S.K., Raj, R., The Effect of Electric Field on Sintering and Electrical Conductivity of Titania (2014) J. Am. Ceram. Soc., 97 (2), pp. 527-534; Zapata-Solvas, E., Bonilla, S., Wilshaw, P.R., Todd, R.I., Preliminary Investigation of Flash Sintering of SiC (2013) J. Eur. Ceram. Soc., 33 (1314), pp. 2811-2816; Grasso, S., Sakka, Y., Rendtorff, N., Hu, C., Maizza, G., Borodianska, H., Vasylkiv, O., Modeling of the Temperature Distribution of flash sintered Zirconia (2011) Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi/J. Ceram. Soc. Jpn., 119 (1386), pp. 144-146; Park, J., Chen, I.W., In Situ Thermometry Measuring Temperature Flashes Exceeding 1,700°C in 8 mol% Y2O3-Stablized Zirconia under Constant-Voltage Heating (2013) J. Am. Ceram. Soc., 96 (3), pp. 697-700; Zapata-Solvas, E., Jayaseelan, D.D., Lin, H.T., Brown, P., Lee, W.E., Mechanical Properties of ZrB2- and HfB2-Based Ultra-High Temperature Ceramics Fabricated by Spark Plasma Sintering (2013) J. Eur. Ceram. Soc., 33 (7), pp. 1373-1386; Grasso, S., Sakka, Y., Maizza, G., Electric Current Activated/Assisted Sintering (ECAS): A Review of Patents 1906-2008 (2009) Sci. Technol. Adv. Mater., 10 (5), p. 053001; Mallik, M., Kailath, A.J., Ray, K.K., Mitra, R., Electrical and Thermophysical Properties of ZrB2 and HfB 2 Based Composites (2012) J. Eur. Ceram. Soc., 32 (10), pp. 2545-2555; Steil, M.C., Marinha, D., Aman, Y., Gomes, J.R.C., Kleitz, M., From Conventional Ac Flash-Sintering of YSZ to Hyper-Flash and Double Flash (2013) J. Eur. Ceram. Soc., 33 (11), pp. 2093-2101; Ortiz, A.L., Zamora, V., Rodríguez-Rojas, F., A Study of the Oxidation of ZrB2 Powders during High-Energy Ball-Milling in Air (2012) Ceram. Int., 38 (4), pp. 2857-2863; Porwal, H., Tatarko, P., Grasso, S., Hu, C., Boccaccini, A.R., Dlouhý, I., Reece, M., Toughened and Machinable Glass Matrix Composites Reinforced with Graphene and Graphene-Oxide Nano Platelets (2013) Sci. Technol. Adv. Mater., 14, p. 055007 Pure ZrB2 powder was Flash sintered in an SPS furnace (FSPS). The samples were densified up to 95.0% in 35 s under an applied pressure of 16 MPa. Compared to Conventional SPS (CSPS), the newly developed FSPS technique resulted in an unprecedented energy and time savings of about 95% and 98% respectively. ZrB2 monoliths obtained by CSPS and FSPS were compared with respect to microstructures, densification behavior, and grain growth. The developed methodology might find application to a wide range of highly conductive ceramics as such refractory borides and carbides. © 2014 The American Ceramic Society.S.G. was supported by EPSRC (EP/K008749/1, XMat). T.S. was supported by EC FP7 2007-2013 (ADMACOM). O.C. was supported by CONACYT (Consejo Nacional de Ciencia y Tecnología, México)

Functional determinants for general Sturm-Liouville problems

Simple and analytically tractable expressions for functional determinants are known to exist for many cases of interest. We extend the range of situations for which these hold to cover systems of self-adjoint operators of the Sturm-Liouville type with arbitrary linear boundary conditions. The results hold whether or not the operators have negative eigenvalues. The physically important case of functional determinants of operators with a zero mode, but where that mode has been extracted, is studied in detail for the same range of situations as when no zero mode exists. The method of proof uses the properties of generalised zeta-functions. The general form of the final results are the same for the entire range of problems considered.Comment: 28 pages, LaTe

Confined two-dimensional fermions at finite density

We introduce the chemical potential in a system of two-dimensional massless fermions, confined to a finite region, by imposing twisted boundary conditions in the Euclidean time direction. We explore in this simple model the application of functional techniques which could be used in more complicated situations.Comment: 15 pages, LaTe

On the behaviour of spin-orbit connection of exoplanets

Star-planet interactions play, among other things, a crucial role in planetary orbital configurations by circularizing orbits, aligning the star and planet spin and synchronizing stellar rotation with orbital motions. This is especially true for innermost giant planets, which can be schematized as binary systems with a very large mass ratio. Despite a few examples where spin-orbit synchronization has been obtained, there is no demographic study on synchronous regimes in those systems yet. Here we use a sample of 1,055 stars with innermost planet companions to show the existence of three observational loci of star-planet synchronization regimes. Two of them have dominant fractions of subsynchronous and supersynchronous star-planet systems, and a third less populated regime of potentially synchronized systems. No synchronous star-planet system with a period higher than 40 days has been detected yet. This landscape is different from eclipsing binary systems, most of which are synchronized. We suggest that planets in a stable asynchronous spin state belonging to star-planet systems in a supersynchronized regime offer the most favourable conditions for habitability.Comment: 15 pages, 1 figure in main paper, 6 supplementary figures. Published in Nature Astronomy, May 202

Gastrointestinal endoscopy during the coronavirus pandemic in the New York area: results from a multi-institutional survey.

Background and study aims  The coronavirus disease 2019 (COVID-19), and measures taken to mitigate its impact, have profoundly affected the clinical care of gastroenterology patients and the work of endoscopy units. We aimed to describe the clinical care delivered by gastroenterologists and the type of procedures performed during the early to peak period of the pandemic. Methods  Endoscopy leaders in the New York region were invited to participate in an electronic survey describing operations and clinical service. Surveys were distributed on April 7, 2020 and responses were collected over the following week. A follow-up survey was distributed on April 20, 2020. Participants were asked to report procedure volumes and patient characteristics, as well protocols for staffing and testing for COVID-19. Results  Eleven large academic endoscopy units in the New York City region responded to the survey, representing every major hospital system. COVID patients occupied an average of 54.5 % (18 - 84 %) of hospital beds at the time of survey completion, with 14.5 % (2 %-23 %) of COVID patients requiring intensive care. Endoscopy procedure volume and the number of physicians performing procedures declined by 90 % (66 %-98 %) and 84.5 % (50 %-97 %) respectively following introduction of restricted practice. During this period the most common procedures were EGDs (7.9/unit/week; 88 % for bleeding; the remainder for foreign body and feeding tube placement); ERCPs (5/unit/week; for cholangitis in 67 % and obstructive jaundice in 20 %); Colonoscopies (4/unit/week for bleeding in 77 % or colitis in 23 %) and least common were EUS (3/unit/week for tumor biopsies). Of the sites, 44 % performed pre-procedure COVID testing and the proportion of COVID-positive patients undergoing procedures was 4.6 % in the first 2 weeks and up to 19.6 % in the subsequent 2 weeks. The majority of COVID-positive patients undergoing procedures underwent EGD (30.6 % COVID +) and ERCP (10.2 % COVID +). Conclusions  COVID-19 has profoundly impacted the operation of endoscopy units in the New York region. Our data show the impact of a restricted emergency practice on endoscopy volumes and the proportion of expected COVID positive cases during the peak time of the pandemic

Investigating the highest melting temperature materials : a laser melting study of the TaC-HfC system

TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (\u3e4000 K) among other properties.  The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta1−xHfxC, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current  research, they were reassessed, for the first time in the last fifty years, using a laser heating technique.  They were found to melt in the range of 4041–4232 K, with HfC having the highest and TaC the lowest.  Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC0.98, (4232 ± 84) K, is the highest recorded for any compound studied until now