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12 pages, 22174 KiB

Open AccessArticle

Fabrication of Porous Alumina Structures by SPS and Carbon Sacrificial Template for Bone Regeneration

by Manuela González-Sánchez, Pedro Rivero-Antúnez, Rafael Cano-Crespo and Víctor Morales-Flórez

Materials 2022, 15(5), 1754; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15051754 - 25 Feb 2022

Cited by 5 | Viewed by 1302

In this work, a procedure for fabricating porous alumina with the use of a carbon sacrificial template has been tested in order to optimize the fabrication of porous structures mimicking the porosity and mechanical properties of the human cortical bone. Two different sources [...] Read more.

In this work, a procedure for fabricating porous alumina with the use of a carbon sacrificial template has been tested in order to optimize the fabrication of porous structures mimicking the porosity and mechanical properties of the human cortical bone. Two different sources of sacrificial carbon were used and compared, and different sintering and calcination routes were considered. The porosity of the alumina structures studied by Hg porosimetry revealed that the amount of porosity and the size and shape of the pores are still below the required values, although some acicular pores were clearly observed by SEM. Moreover, measured mechanical properties (Young’s modulus) remained below that of the bone, suggesting the need for further consolidation treatments. In summary, these encouraging results drive the optimization of future fabrication routes. Full article

(This article belongs to the Special Issue Mechanical Properties and Electrical Conductivity of Ceramics)

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10 pages, 1777 KiB

Open AccessEditor’s ChoiceArticle

Superplastic Deformation of Alumina Composites Reinforced with Carbon Nanofibers and with Graphene Oxide Sintered by SPS—Experimental Testing and Theoretical Interpretation

by Rafael Cano-Crespo, César Retamal, Miguel Lagos and Francisco Luis Cumbrera

Materials 2022, 15(4), 1396; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15041396 - 14 Feb 2022

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Abstract

The superplastic behavior of alumina-based nanostructured ceramics (Al₂O₃) is an important issue in the world of materials. The main body of this paper is an analysis of the creep behavior of polycrystals, with grain boundary sliding as the main [...] Read more.

The superplastic behavior of alumina-based nanostructured ceramics (Al₂O₃) is an important issue in the world of materials. The main body of this paper is an analysis of the creep behavior of polycrystals, with grain boundary sliding as the main deformation mechanism at high temperatures. Concomitant accommodation of grain shapes to preserve spatial continuity has a comparatively small effect on the strain rate. The constitutive equations for small deformations, relating strain and strain rate, derived from two models for grain sliding, are compared with the experimental data with their respective uncertainties. The data follow from experiments on the plastic deformation of alumina composites reinforced, on the one hand by graphene oxide, and on the other hand by carbon nanofibers sintered by SPS. The results show good agreement between experiment and theory for these advanced ceramics, particularly for one of the assumed models. The values obtained of ξ² for model A were in the interval 0.0002–0.1189, and for model B were in the interval 0.000001–0.0561. The values obtained of R² for model A were in the interval 0.9122–0.9994, and for model B were in the interval 0.9586–0.9999. The threshold stress was between (3.05 · 10⁻¹⁵–25.68) MPa. Full article

(This article belongs to the Special Issue Mechanical Properties and Electrical Conductivity of Ceramics)

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17 pages, 7056 KiB

Open AccessArticle

The Possible Detriment of Oxygen in Creep of Alumina and Zirconia Ceramic Composites Reinforced with Graphene

by Rafael Cano-Crespo, Pedro Rivero-Antúnez, Diego Gómez-García, Rodrigo Moreno and Arturo Domínguez-Rodríguez

Materials 2021, 14(4), 984; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14040984 - 19 Feb 2021

Cited by 4 | Viewed by 1594

Abstract

This paper is aims to give an answer to the following question: is the oxidation of graphene a critical issue for high-temperature plasticity in graphene-reinforced ceramics? To give a convincing reply, we will focus on two very different graphene-based ceramic composites: reduced graphene [...] Read more.

This paper is aims to give an answer to the following question: is the oxidation of graphene a critical issue for high-temperature plasticity in graphene-reinforced ceramics? To give a convincing reply, we will focus on two very different graphene-based ceramic composites: reduced graphene oxide (rGO)-reinforced alumina (α-Al₂O₃) and reduced graphene oxide (rGO)-reinforced yttria tetragonal zirconia (t-ZrO₂). The processing of the powders has been made using a colloidal route, and after that, a spark plasma sintering process was performed in order to densify the samples. Creep tests were performed at temperatures between 1200–1250 °C in an argon atmosphere. The microstructure obtained by an SEM of the sintered and tested specimens was characterized quantitatively to elucidate the deformation mechanism. Raman spectroscopy was carried out to check the integrity of the graphene. The average grain size was in the order of 1 µm and the shape factor was 0.7 for all the studied materials. The integrity of the graphene was checked before and after the creep experiments. The careful analysis of the creep tests shows that graphene oxide or its reduced version are not efficient phases for creep resistance improvement in general, contrary to what is reported elsewhere. However, the results permit the suggestion of a creep improvement in nanocomposites at a very high temperature regime due to an enhanced reactivity of oxygen between carbon and alumina interfaces. In the case of zirconia, the results give us the conclusion that the oxidation of graphene is a highly detrimental issue regarding the improvement of high-temperature plasticity. Full article

(This article belongs to the Special Issue Mechanical Properties and Electrical Conductivity of Ceramics)

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