Materiales multifuncionales de nitruro de silicio con nanoestructuras reforzanters basadas en grafeno
Entity
UAM. Departamento de Física AplicadaDate
2014-06-16Subjects
Nanoestructuras - Tesis doctorales; Nanotecnología - Tesis doctorales; FísicaNote
Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Aplicada. Fecha de lectura: 16-06-2014Esta obra está bajo una licencia de Creative Commons Reconocimiento-NoComercial-SinObraDerivada 4.0 Internacional.
Abstract
This work examines the fabrication and properties of silicon nitride / graphene based
nanostructures composites densified by the spark plasma sintering technique with the
aim of proving the mechanical reinforcement effect expected by the excellent properties
of the graphene fillers. Dense and homogeneous Si3N4 composites containing different
type of carbon nanofillers were processed by dispersion of pristine graphene
nanoplatelets, graphene oxide and unzipped multiwall carbon nanotubes into the
ceramic slurry containing the ceramic matrix powders and sintering additives. Spark
plasma sintering was selected as consolidation technique due to the lower temperatures
and shorter times required for densification, compared to conventional sintering
methods, preventing the damage of the carbon nanostructures.
Scanning and transmission microscopy combined with construction of Raman intensity
maps revealed differences in the exfoliation degree of the nanofillers, which also
influenced ceramic grain growth, and evidenced the orientation effect in the nanofillers
due to uniaxial pressure applied during sintering stage. The strong orientation clearly
differentiates the electrical and thermal behavior of the materials in the directions
parallel and perpendicular to the graphene plane having also a significant role in these
properties the crystalline quality of carbon lattice.
The low shear resistance between graphene layers in the nanostructures affects elastic
modulus and hardness of the materials compared to monolithic Si3N4 producing a
certain softening, however, the toughening effect of the three types of nanostructures
was demonstrated for crack propagating perpendicular to the nanofiller aligment
direction, being the bridging mechanism the main responsible of the toughness increase.
Reduced graphene oxide nanosheets were the most effective reinforcements achieving
135% higher fracture toughness than Si3N4 under the same sintering and testing
conditions.
On the top of that, the nanofillers induce an electrical response of the composites once
they form a connected network for small concentrations indeed, therefore, being quite
dependent of the exfoliation and again on the nanofiller orientation. Very similar
behavior is observed for the thermal conductivity of the composites, and with a heat
flow rate for the orientations matching the graphene plane.
These results have shown that graphene nanoplatelets and nanoribbons can be used as
effective fillers for ceramic composites with tailored properties intended not only for
applications that require good mechanical performance but wear resistance, good heat
conduction and electrical conductivity.
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Texto de la Tesis Doctoral
Google Scholar:Ramírez Maglione, María Cristina
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