153 research outputs found
Gel casting of silicon nitride foams using biopolymers as gelling agents
Abstract Si3N4-based foams were prepared by the gel casting route using egg-albumen, agar-agar, or methylcellulose as biopolymer gelling agents. Microstructural, permeability, and mechanical properties of the foams were determined. The use of a variety of environmentally friendly gelling agents produced Si3N4 foams with a wide range of porosity (79â89%), mean cell size (199â852 ÎŒm), and mean window size (51â152 ÎŒm). The pressureless sintering method was successfully applied and resulted in Si3N4 foams with compressive strengths ranging from 1.6 to 9.4 MPa when treated at 1600 °C and up to 33.5 MPa when sintered at 1700 °C, due to the formation of the ÎČâSi3N4 phase. Darcian (k1) and non-Darcian (k2) permeability coefficients were 4.41 Ă 10â12 to 1.61 Ă 10â10 m2 and 5.07 Ă 10â7 to 1.02 Ă 10â6 m, respectively, allowing the produced Si3N4 foams to be used in a wide variety of fluid flow and filtering applications
LZS/Al2O3 nanostructured composites obtained by colloidal processing and spark plasma sintering
[EN] Li2O-SiO2-ZrO2 (LZS) glass-ceramics have high mechanical strength, hardness, resistance to abrasion and chemical attack, but also a high coefficient of thermal expansion (CTE), which can be reduced adding alumina nanoparticles. The conventional glass-ceramic production is relatively complex and energy consuming, since it requires the melting of the raw materials to form a glass frit and a two-step milling process to obtain particle sizes adequate for compaction. This study describes the preparation of LZS glass-ceramics through a colloidal processing approach from mixtures of SiO2 and ZrO2 nanopowders and a Li precursor (lithium acetate obtained by reaction of the carbonate with acetic acid). Concentrated suspensions were freeze-dried to obtain homogeneous mixtures of powders that were pressed (100 MPa) and sintered conventionally and by spark plasma sintering. The effect of the alumina nanoparticles additions on suspensions rheology, sintering behavior and properties such as thermal expansion, thermal conductivity, hardness and Young's modulus were evaluated. (C) 2017 Elsevier Ltd. All rights reserved.This work has been supported by Ministerio de Economia y Competitividad (MINECO) and FEDER Funds under grant No MAT2016-67586-C3-R. Authors greatly acknowledge the financial Support of CAPES in the frame of the International Cooperation Program Science without Borders for Special Visiting Researcher PVE (MEC/MCTI/CAPES/CNPQ/FAPs/No 71/2013), Project no. A011/2013. A. Borrell acknowledges the MINECO for her Juan de la Cierva-Incorporacion contract (IJCI-2014-19839).Arcaro, S.; Novaes De Oliveira, A.; Gutierrez-Gonzalez, C.; Salvador Moya, MD.; Borrell TomĂĄs, MA.; Moreno, R. (2017). LZS/Al2O3 nanostructured composites obtained by colloidal processing and spark plasma sintering. Journal of the European Ceramic Society. 37(16):5139-5148. https://doi.org/10.1016/j.jeurceramsoc.2017.03.023S51395148371
Properties of LZS/nanoAl2O3 glass-ceramic composites
[EN] The LZS glass-ceramic (19.58 Li2O center dot 11.10ZrO(2)center dot 69.32SiO(2)) have a high coefficient thermal expansion (CTE) which can be a limitation in some applications. The addition of alumina in a LZS glass-ceramic matrix is able to reduce the CTE significantly. This happens because of the alumina affinity with respect to lithium silicates to form beta-spodumene (LiAlSi2O6), a crystalline phase having a CTE nearly zero (0.9 x 10(-6) degrees C-1).In this work, (1-5 vol%) Al2O3 nanoparticles (13 nm) were added to a LZS (3.5 mu m) glass-ceramic matrix to prepare composites with the main goal of evaluation the influence of Al2O3 on their mechanical, thermal and electrical properties. Each composition was wet homogenized and then dried at 110 degrees C for 48 h for disaggregation. The composites, sintered at 900 degrees C for 30 min, with relative densities between 92% and 98%, showed zircon and beta-spodumene as main crystalline phases. The incorporation of increasing additions of nanosized alumina progressively decreases the final density. This makes the properties to slightly decrease, also. The Young's modulus significantly decreases from 111 to 78 GPa of hardness due to the exponential variation with porosity, but the changes of toughness and hardness are much lower. The electrical conductivity was maintained within +/- 10-7 S. cm(-1), and the dielectric constant ranged from 5 to 6 for all compositions. Thermal conductivity ranged around 4.2 to 3.5 W/mK. (C) 2017 Elsevier B.V. All rights reserved.This work has been supported by CAPES in the frame of the International Cooperation Program Science without Borders for Special Visiting Researcher PVE (MEC/MCTI/CAPES/CNPq/FAPs/ No 71/2013), Project No A011/2013 (Brazil) and CNPq (National Council for Scientific and Technological Development, Brazil). This work has been also supported by Ministerio de Economia y Cornpetitividad and FEDER Funds under grant No MAT2016-67586-C3-R and grant ENE2013-49111-C2-1-R. A. Borrell acknowledges the MINECO for her Juan de la Cierva-Incorporacion contract (IJCI-2014-19839).Arcaro, S.; Moreno, B.; Chinarro, E.; Salvador Moya, MD.; Borrell TomĂĄs, MA.; Nieto, M.; Moreno, R.... (2017). Properties of LZS/nanoAl2O3 glass-ceramic composites. Journal of Alloys and Compounds. 710:567-574. https://doi.org/10.1016/j.jallcom.2017.03.299S56757471
Distribuição espacial da granulometria, cor e carbono orgùnico do solo ao longo de um transecto em microbacias na AmazÎnia meridional
Measurement of the p-pbar -> Wgamma + X cross section at sqrt(s) = 1.96 TeV and WWgamma anomalous coupling limits
The WWgamma triple gauge boson coupling parameters are studied using p-pbar
-> l nu gamma + X (l = e,mu) events at sqrt(s) = 1.96 TeV. The data were
collected with the DO detector from an integrated luminosity of 162 pb^{-1}
delivered by the Fermilab Tevatron Collider. The cross section times branching
fraction for p-pbar -> W(gamma) + X -> l nu gamma + X with E_T^{gamma} > 8 GeV
and Delta R_{l gamma} > 0.7 is 14.8 +/- 1.6 (stat) +/- 1.0 (syst) +/- 1.0 (lum)
pb. The one-dimensional 95% confidence level limits on anomalous couplings are
-0.88 < Delta kappa_{gamma} < 0.96 and -0.20 < lambda_{gamma} < 0.20.Comment: Submitted to Phys. Rev. D Rapid Communication
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt{s} = 1.96 TeV using Kinematic Characteristics of Lepton + Jets Events
We present a measurement of the top quark pair ttbar production cross section
in ppbar collisions at a center-of-mass energy of 1.96 TeV using 230 pb**{-1}
of data collected by the DO detector at the Fermilab Tevatron Collider. We
select events with one charged lepton (electron or muon), large missing
transverse energy, and at least four jets, and extract the ttbar content of the
sample based on the kinematic characteristics of the events. For a top quark
mass of 175 GeV, we measure sigma(ttbar) = 6.7 {+1.4-1.3} (stat) {+1.6- 1.1}
(syst) +/-0.4 (lumi) pb, in good agreement with the standard model prediction.Comment: submitted to Phys.Rev.Let
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s)=1.96 TeV using Lepton + Jets Events with Lifetime b-tagging
We present a measurement of the top quark pair () production cross
section () in collisions at TeV
using 230 pb of data collected by the D0 experiment at the Fermilab
Tevatron Collider. We select events with one charged lepton (electron or muon),
missing transverse energy, and jets in the final state. We employ
lifetime-based b-jet identification techniques to further enhance the
purity of the selected sample. For a top quark mass of 175 GeV, we
measure pb, in
agreement with the standard model expectation.Comment: 7 pages, 2 figures, 3 tables Submitted to Phys.Rev.Let
Measurement of the ratios of the Z/G* + >= n jet production cross sections to the total inclusive Z/G* cross section in ppbar collisions at sqrt(s) = 1.96 TeV
We present a study of events with Z bosons and jets produced at the Fermilab
Tevatron Collider in ppbar collisions at a center of mass energy of 1.96 TeV.
The data sample consists of nearly 14,000 Z/G* -> e+e- candidates corresponding
to the integrated luminosity of 0.4 fb-1 collected using the D0 detector.
Ratios of the Z/G* + >= n jet cross sections to the total inclusive Z/G* cross
section have been measured for n = 1 to 4 jet events. Our measurements are
found to be in good agreement with a next-to-leading order QCD calculation and
with a tree-level QCD prediction with parton shower simulation and
hadronization.Comment: 7 pages, 2 figures, slightly modified, submitted to Phys. Lett.
Measurement of the Isolated Photon Cross Section in p-pbar Collisions at sqrt{s}=1.96 TeV
The cross section for the inclusive production of isolated photons has been
measured in p anti-p collisions at sqrt{s}=1.96 TeV with the D0 detector at the
Fermilab Tevatron Collider. The photons span transverse momenta 23 to 300 GeV
and have pseudorapidity |eta|<0.9. The cross section is compared with the
results from two next-to-leading order perturbative QCD calculations. The
theoretical predictions agree with the measurement within uncertainties.Comment: 7 pages, 5 figures, submitted to Phys.Lett.
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