Al2O3-3YTZP-Graphene multilayers produced by tape casting and spark plasma sintering

This work aims to establish a colloidal route to obtain laminates of alumina zirconia combining layers with and without graphene. Green tapes of alumina, alumina with 5 vol.% of 3Y-TZP and alumina with 5 vol.% of 3Y-TZP and graphene-oxide (2 vol.%) were obtained by aqueous tape casting. It is possible to design materials for different structural applications with a controlled microstructure with a high number of different layers. The tapes were punched into 20-mm discs, joined to form laminates alternating up to 18-layers, and sintered in one-step by spark plasma sintering (SPS) at 1400 degrees C. It has demonstrated that there is a significant graphite diffusion provoked by the required graphite holders into the SPS-furnace. Dense laminates with layer thicknesses similar to 100 mu m and good cohesion between layers were obtained. Nanoindentation results showed that hardness and elastic modulus values were higher than 27 GPa and 300 GPa, respectively, and similar for all layers. Crown Copyright (C) 2014 Published by Elsevier Ltd. All rights reserved.This work has been supported by Spanish Ministry of Economy and Competitiviness (MAT2012-31090). A. S. A. Chinelatto thanks to CAPES - Programa Ciencias sem Fronteiras (Brazil) for the concession of a fellowship for post-doctoral sabbatical grant in ICV-CSIC, Spain. A. Borrell, acknowledges the Spanish Ministry of Science and Innovation for her Juan de la Cierva contract (JCI-2011-10498) and the Generalitat Valenciana by the financial support for the BEST/2012/302 grant. Authors thank to Nanoinnova Technologies (Spain) for supplying the graphene oxide and helpful discussions.Rincón, A.; Moreno, R.; Chinelatto, ASA.; Gutierrez-Gonzalez, CF.; Rayón Encinas, E.; Salvador Moya, MD.; Borrell Tomás, MA. (2014). Al2O3-3YTZP-Graphene multilayers produced by tape casting and spark plasma sintering. Journal of the European Ceramic Society. 34(10):2427-2434. https://doi.org/10.1016/j.jeurceramsoc.2014.02.011S24272434341

Colloidal processing of fully stabilized zirconia laminates comprising graphene oxide-enriched layers

Multilayer materials have demonstrated to provide an efficient mechanism for toughening by deflection of a propagating crack by weak interlayers. Therefore, the aim of this work is to study the colloidal processing of 8 mol% yttria stabilized zirconia (8YSZ) based laminates by intercalating thin layers of graphene enriched with 8YSZ, and to evaluate the advantages of such multilayered structure in the propagation of cracks induced by indentation. Green tapes of 8YSZ and graphene-oxide with YSZ were obtained by aqueous tape casting and sintered in one-step by spark plasma sintering at 1400 degrees C. Microindentation results showed that the indentation cracks propagate within the horizontal direction within the ceramic layer, but in the cross-sectional direction the presence of the GO-rich layers stops the cracks without deflection or bifurcation. The hardness and elastic modulus values were higher than 17.6 GPa and 230 GPa, respectively, and similar for all layers.This work has been supported by the Spanish Ministry of Economy and Competitiveness (project MAT2015-67586-C3-R) and the Generalitat Valenciana by the financial support for the GV/2014/009 project. M.D. Salvador thanks to CAPES-Programa Ciencias sem Fronteiras (Brazil) for the concession of a PVE project No. A086/2013. A. Borrell, acknowledges the Spanish Ministry of Economy and Competitiveness for her Juan de la Cierva-Incorporacion contract (IJCI-2014-19839).Rincón, A.; Moreno, R.; Gutierrez González, FC.; Sainz, R.; Salvador Moya, MD.; Borrell Tomás, MA. (2016). Colloidal processing of fully stabilized zirconia laminates comprising graphene oxide-enriched layers. Journal of the European Ceramic Society. 36(7):1797-1804. https://doi.org/10.1016/j.jeurceramsoc.2016.01.035S1797180436

Effect of graphene and CNFs addition on the mechanical and electrical properties of dense alumina-toughened zirconia composites

Fully dense carbon/alumina-toughened zirconia composites were prepared by using a combination of aqueous colloidal powder processing and spark plasma sintering technique (SPS). Various carbon elements were introduced in alumina-toughened zirconia matrix (ZA) as filler; carbon nanofibers (CNFs) and graphene oxide (GO). The influence of the addition of different carbon forms on the microstructure and on the mechanical and electrical properties was investigated. In the case of the ZAGO composites, the SPS technique allowed, in one-step, the in situ reduction of the graphene oxide during the sintering process. The fracture toughness increases for ZAGO composites in comparison to the ZA material while the hardness decreases slightly with carbon elements addition. The electrical conductivity of the ZA composite drastically increased with the addition of graphene oxide, and it reached 10 Omega cm at 2 vol%. CrownA. Borrell acknowledges the Spanish Ministry of Economy and Competitiveness for her Juan de la Cierva contract (JCI-2011-10498) and the Generalitat Valenciana by the financial support for the GV/2014/009 project. M.D. Salvador thanks to CAPES - Programa Ciencias sem Fronteiras (Brazil) for the concession of a PVE project No. A086/2013. A.S.A. Chinelatto thanks to CAPES for the concession of a post-doctoral fellowship in ICV-CSIC.Rincón, A.; Moreno, R.; Chinelatto, ASA.; Gutierrez, CF.; Salvador Moya, MD.; Borrell Tomás, MA. (2016). Effect of graphene and CNFs addition on the mechanical and electrical properties of dense alumina-toughened zirconia composites. Ceramics International. 42(1):1105-1113. https://doi.org/10.1016/j.ceramint.2015.09.037S1105111342

Development of low cost waste-derived sintered glass-ceramics for energy saving and recovery

A new technique for the production of cellular glass and glass-ceramics foams is the main goal of the hereby presented research activities. It is based on a combination of alkali-activation of silica-rich materials, with subsequent inorganic gel casting foaming by means of a surfactant and final heat treatment trough sinter-crystallisation process. This new process is less expensive and more environmentally sustainable than the current procedures based on mixtures of glass powders and foaming agents, which decompose and release gases at a temperature significantly above the softening glass point, and is conceived as an alternative route to valorise silica-rich waste materials The alkali activation of glass waste allows to obtain well-dispersed concentrated suspensions, undergoing gelation by treatment at low temperature (40-80 °C), due to the formation of silicate hydrates. An extensive direct foaming was achieved by mechanical stirring of partially gelified suspensions, also comprising a surfactant. The final microstructure (total amount of porosity, cell size) can be directly correlated with the degree of gelation. A sintering treatment, at only 700 °C, was finally applied to stabilise the structures and limit the leaching of alkaline ions. The approach proved to be extended to different glasses and industrial waste mixtures leading to different gels after alkali activation. Alkali activation of soda-lime waste glass was exploited through mixing with iron-rich inorganic waste from a copper slag and fly ash from coal combustion. The approach was also extended to different glass-based material coming from waste, such as an alumino-boro-silicate glass from the recycling of pharmaceutical vials, and vitrified bottom ashes from municipal solid waste incinerators. A considerable number of processing parameters combinations (such as surfactants, activating solution, curing times, conditions for heating treatments etc.) were explored and understood. Apart from waste-derived materials and applications in the building industry, the technique was also applied to create highly porous bioactive glass-ceramics scaffolds; the successful production of highly homogeneous foams proves the versatility in the approach. The progressive hardening associated with inorganic polymerisation configuring an ‘inorganic gel casting’ has also been used to produce advanced ceramics, such as mullite and cordierite foams and scaffolds. These materials were obtained through the thermal treatment of engineered alkali activated suspensions consisting of a Na-geopolymer enriched with reactive γ-Al2O3 powders in the case of mullite, and reactive γ-Al2O3 and talc in the synthesis of cordierite. The gelation was studied in order to have a proper viscosity for trapping air during vigorous mechanical stirring or maintaining the shape of the scaffold struts obtained by direct ink writing. After the hardened samples were obtained, sodium ions were extracted through ion exchange in ammonium nitrate solution. Finally, the ion-exchanged foams were successfully converted into pure mullite or cordierite foams and scaffolds with the application of a firing treatment. Alkali activation was the basis for the manufacturing of lightweight granules according to a ‘spheroidisation technique’ consisting in the casting of fine glass powders on a rotary drum, before firing. The hardened suspensions of soda-lime glass obtained from alkaline activation, were reduced into fragments and cast on a rotary drum with dry glass. The firing of green granules was accompanied by a significant foaming, owing to the decomposition of hydrated compounds.L’obiettivo delle attività di ricerca presentate è l’individuazione di una nuova tecnica per la produzione di schiume di vetro e vetroceramiche, basata sulla combinazione di un processo di attivazione alcalina di materiali ricchi di silice e successiva schiumatura del gel inorganico mediante un tensioattivo e un trattamento termico finale mediante sinterizzazione e cristallizzazione (“sinter-crystallisation”). Si tratta di un processo più economico ed ecologicamente sostenibile rispetto alle attuali procedure, basate su miscele di polveri di vetro e agenti schiumogeni, che sono soggette a decomposizione e rilasciano gas a una temperatura significativamente superiore al punto di rammollimento (“softening point”) del vetro. Questa nuova tecnica offre una strategia alternativa per la valorizzazione di materiali di scarto ad alto contenuto di silice. L'attivazione alcalina degli scarti di vetro consente di ottenere sospensioni concentrate ben disperse, le quali subiscono una gelificazione mediante trattamento a bassa temperatura (40-80°C), ascrivibile alla formazione di idrati di silicato. Si è ottenuta una schiumatura diretta ed estesa mediante agitazione meccanica di sospensioni parzialmente gelificate, con l’ausilio di un tensioattivo. La microstruttura finale (livello totale di porosità, dimensione delle celle) può essere direttamente correlata al grado di gelificazione. È stato infine applicato un trattamento di sinterizzazione a soli 700°C, per stabilizzare le strutture e limitare la lisciviazione (“leaching”) di ioni alcalini. È stata dimostrata l’applicabilità di tale approccio a diverse tipologie di vetro e miscele di rifiuti industriali, ottenendo diversi gel in seguito all'attivazione alcalina. L'attivazione alcalina del vetro sodico-calcico di scarto è stata sfruttata attraverso la miscelazione con rifiuti inorganici ricchi di ferro da scorie di rame e ceneri volatili prodotte dalla combustione del carbone. L'approccio è stato esteso anche a diversi materiali a base di vetro provenienti da rifiuti, come il vetro borosilicato proveniente dal riciclaggio di fiale farmaceutiche e ceneri pesanti vetrificate provenienti dagli inceneritori di rifiuti solidi urbani. Sono state esplorate e comprese diverse combinazioni di parametri di processo (tensioattivi, soluzioni di attivazione, tempi di polimerizzazione, condizioni per il trattamento termico ecc.). Oltre che per la creazione di materiali derivati dai rifiuti e l’individuazione di possibili applicazioni nel settore dell'edilizia, la tecnica è stata utilizzata anche per creare scaffold vetroceramici bioattivi altamente porosi, a dimostrazione della versatilità dall'approccio. L'indurimento progressivo associato alla polimerizzazione inorganica che configura un "gel inorganico" è stato inoltre sfruttato per produrre ceramiche avanzate, come schiume e scaffold di mullite e cordierite. Questi materiali sono stati ottenuti mediante il trattamento termico di sospensioni ingegnerizzate attivate alcalinamente, costituite da un geopolimero a base di sodio arricchito con polveri reattive γ-Al2O3, nel caso della mullite, e γ-Al2O3 reattivo e talco, nella sintesi della cordierite. La gelificazione è stata studiata allo scopo di ottenere una viscosità appropriata per intrappolare l'aria in condizioni di vigorosa agitazione meccanica o per mantenere la forma dei filamenti negli scaffold ottenuti mediante stampa diretta. In seguito all’ottenimento dei campioni induriti, sono stati estratti gli ioni di sodio mediante scambio ionico in soluzione di nitrato di ammonio. Infine, le schiume sottoposte a scambio ionico sono state convertite in schiume e scaffold di mullite o cordierite pura con l'applicazione di un trattamento di cottura. L'attivazione alcalina è stata la base di partenza per la produzione di granuli leggeri tramite una "tecnica di sferoidizzazione" che consiste nella aggregazione di polveri di vetro sottili su un tamburo rotante, prima del tratamento termico. Una volta indurite, le sospensioni di vetro sodico-calcico ottenute dall’attivazione alcalina sono state ridotte in frammenti e collocate su un tamburo rotante con polvere di vetro secco. Il tratamento termico dei granuli verdi ha determinato una significativa formazione di schiuma, dovuta alla decomposizione dei composti idrati

Up-Cycling of Iron-Rich Inorganic Waste in Functional Glass-Ceramics

The intensive mechanical stirring of suspensions of recycled glass and inorganic waste powders in ‘weakly alkaline’ aqueous solutions (e.g., 2.5–3 NaOH), followed by viscous flow sintering at 800–1000 °C, easily yields highly porous glass-ceramic foams. The firing determines just the consolidation of powders with concurrent incorporation of pollutants from iron-rich waste, such as fly ash from coal combustion (FA). Engineered mixtures allow for the obtainment of chemically stable foams from treatments in air. Treatments in nitrogen are even more significant since they extend the conditions for stabilization and promote novel functionalities. In addition, the change in the atmosphere favors the formation of magnetite (Fe3O4), in turn enabling ultra-high dielectric permittivity and semiconductivity. Such a condition was further evidenced by preliminary tests on recycled glass combined with residues from the Bayer processing of aluminum ores or red mud (RM)

A new hybrid suspension and solution precursor thermal spray for wear-resistant silicon carbide composite coatings

Silicon Carbide (SiC) coatings offer exceptional wear resistance and excellent tribological characteristics; however, it is a challenging material to be thermally sprayed due to a lack of melting point. In this study, a hybrid, single-step suspension and solution precursor feedstock design is proposed, consisting of a SiC suspension modified with Yttrium Aluminium Garnet (YAG) precursors, for thermal spraying of SiC/YAG coatings. The decomposition of SiC was restricted in all spray campaigns. The solid loading of SiC (from 10 wt% to 20 wt%) and YAG phase (from 20 wt% and up to 50 wt%) were varied in an attempt to improve wear performance, enhance coating cohesion, and minimise porosity of the studied coatings. Among all studied coatings, 60 wt% SiC/40 wt% YAG and 50 wt% SiC/50 wt% YAG coatings at a 10 wt% solid loading were the best-performing coatings, demonstrating a promising wear resistance up to a sliding distance up of 1000 m, a dense coating structure with porosity at 0.4 ± 0.2%. The feedstock design opens up a new method to process materials which are difficult, if not impossible, to process using a conventional thermal route

Colloidal processing of fully stabilized zirconia laminates comprising graphene oxide-enriched layers

Multilayer materials have demonstrated to provide an efficient mechanism for toughening by deflection of a propagating crack by weak interlayers. Therefore, the aim of this work is to study the colloidal processing of 8 mol% yttria stabilized zirconia (8YSZ) based laminates by intercalating thin layers of graphene enriched with 8YSZ, and to evaluate the advantages of such multilayered structure in the propagation of cracks induced by indentation. Green tapes of 8YSZ and graphene-oxide with YSZ were obtained by aqueous tape casting and sintered in one-step by spark plasma sintering at 1400 °C. Microindentation results showed that the indentation cracks propagate within the horizontal direction within the ceramic layer, but in the cross-sectional direction the presence of the GO-rich layers stops the cracks without deflection or bifurcation. The hardness and elastic modulus values were higher than 17.6 GPa and 230 GPa, respectively, and similar for all layers.This work has been supported by the Spanish Ministry of Economy and Competitiveness (project MAT2015-67586-C3-R) and the Generalitat Valenciana by the financial support for the GV/2014/009 project. M.D. Salvador thanks to CAPES—Programa Ciências sem Fronteiras (Brazil) for the concession of a PVE project No. A086/2013. A. Borrell, acknowledges the Spanish Ministry of Economy and Competitiveness for her Juan de la Cierva-Incorporación contract (IJCI-2014-19839).Peer Reviewe

Al2O3 // 3Y-TZP // Graphene multilayers produced by tape casting and spark plasma sintering. A rheological, sintering and characterization study

Trabajo presentado al 13th International Ceramics Congress celebrado en Montecatini Terme (Italia) del 9 al 17 de junio de 2014.The aim of this work is to propose a procedure to obtain dense and free defects multilayered alumina-zirconia coatings with graphene. Green tapes of alumina alumina+5vol.%3Y-TZP and alumina+5vol.%3Y-TZP mixed with graphene-oxide (2 vol.%) were obtained by aqueous tape casting. of the three compositions. The rheological behaviour of concentrated suspensions was optimized considering the sonication mode and time and the content of deflocculant. Green tapes were punched and laminated in order to form ceramic laminates alternating up to 18 layers The obtained multilayer discs with 20 mm in diameter were sintered by spark plasma sintering (SPS) technique at 1400 ºC under vacuum and with pressure. By means of optical and electronic microscope images of the ceramic cross-sections, it was revealed that the sintered laminates had a high green density and layer thicknesses of 100 µm without any apparent defect showing a good cohesion between them. Raman spectroscopy analysis confirmed the presence of tetragonal zirconia in alumina coatings and revealed carbon content inside all the samples. Nanoindentation results revealed that hardness and elastic modulus values were similar for all coatings, being higher than 27 GPa and 300 GPa, respectively.Peer Reviewe

Al2O3-3YTZP-graphene multilayers produced by tape casting and spark plasma sintering

This work aims to establish a colloidal route to obtain laminates of alumina-zirconia combining layers with and without graphene. Green tapes of alumina, alumina with 5. vol.% of 3Y-TZP and alumina with 5. vol.% of 3Y-TZP and graphene-oxide (2 vol.%) were obtained by aqueous tape casting. It is possible to design materials for different structural applications with a controlled microstructure with a high number of different layers. The tapes were punched into 20-mm discs, joined to form laminates alternating up to 18-layers, and sintered in one-step by spark plasma sintering (SPS) at 1400 °C. It has demonstrated that there is a significant graphite diffusion provoked by the required graphite holders into the SPS-furnace. Dense laminates with layer thicknesses ~100 μm and good cohesion between layers were obtained. Nanoindentation results showed that hardness and elastic modulus values were higher than 27. GPa and 300. GPa, respectively, and similar for all layers. © 2014.This work has been supported by Spanish Ministry of Economy and Competitiviness (MAT2012-31090). A. S. A. Chinelatto thanks to CAPES – Programa Ciências sem Fronteiras (Brazil) for the concession of a fellowship for post-doctoral sabbatical grant in ICV-CSIC, Spain. A. Borrell, acknowledges the Spanish Ministry of Science and Innovation for her Juan de la Cierva contract (JCI-2011-10498) and the Generalitat Valenciana by the financial support for the BEST/2012/302 grant.Peer Reviewe