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

Abstract

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 ºC.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 17.6GPa and 230 GPa, respectively, and similar for all layers. Introduction8 mol% yttria stabilized zirconia (8YSZ) has been extensively used as an electrolyte because of its low electronic and high oxide ion conductivity over wide ranges of temperature and oxygen partial pressure, as well as excellent chemical stability under reduced and oxidized atmospheres at a high temperature. These properties make 8YSZ a powerful material for applications as oxygen sensors and solid oxide fuel cells [1][2][3][4][5]. The basic structure of a solid oxide fuel cell (SOFC) comprises at least three layers of ceramics or cermet:i.e., electrolyte, anode and cathode layers [6,7]. The electrolyte is a dense ceramic, typically yttria stabilized zirconia (YSZ) or gadolinium doped ceria (CGO), whereas the electrodes must be porous and can be either a ceramic or a cermet. Typical anode materials are Ni-YSZ and Ni-CGO while LSM (La, Sr, produced by different techniques, such as tape casting and screen printing, which are the most suitable to produce large surfaces and fast, low cost mass production. Because of the multi-layer nature of the cells, any mismatch in the free sintering kinetics of the individual layers leads to stress and distortion during the sintering process [13][14][15]. Hence, the electrolyte layer must have high fracture strength and toughness, good thermal conductivity and a thermal expansion coefficient similar to that of the other components. Fully stabilized zirconia has not the excellent mechanical properties that partially stabilized zirconia has so that the development of strengthening mechanisms is strongly desired to meet the requirements of SOFCs.The main reinforcing mechanisms for zirconia ceramics are those based on the phase transformation of zirconia from tetragonal to monoclinic induced by mechanical stresses, and the use of composites with second phase particles, whiskers, platelets or fibers and, more recently, the development of ceramic matrix nanocomposites is receiving great attention [16][17][18][19]. The use of such nanocomposites has shown to significantly enhance the mechanical properties even at high tempe...

From bulk to cellular structures: A review on ceramic/graphene filler composites

“…Therefore, we are now in a position to take a challenged step forward for tailoring new materials based on the layered concept, this time including graphene into the ceramic structure. At the present, very few works on ceramic/graphene layered materials have been reported [90][91][92][93][94], which could be classified in two different categories according to their processing approaches. In the first approach, each layer, or some of them, is formed by a bulk ceramic/GO composite [90,93,94] and, hence, will be labelled as "layered composites".…”

“…At the present, very few works on ceramic/graphene layered materials have been reported [90][91][92][93][94], which could be classified in two different categories according to their processing approaches. In the first approach, each layer, or some of them, is formed by a bulk ceramic/GO composite [90,93,94] and, hence, will be labelled as "layered composites". The second approach consisted in 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 36 alternating a ceramic layer and a graphene film [91,92], thus being labelled as "layered ceramic/graphene materials".…”

“…Within the "layered composites" group, Rincon et al [90,93] diameter discs and then laminated in an A/AZ/AZGO sequence applying a small pressure and using few drops of water as gluing agent between the discs. A symmetric stack with 9 layers were first processed and 2 stacks were piled up and SPSed at 1400 ºC.…”

“…The authors confirmed that the electrical resistance of the AZGO layers was much lower than that of the A and AZ ones. In a later work [93], the authors tape casted 8YSZ layers and some of them were coated with 8YSZ/GO composition by dipping a rectangular 8YSZ substrate into an 8YSZ/GO (volume ratio of 30:70) suspension. By alternating uncoated and coated layers, two different layered configurations were developed: one containing 5 stacks of 3 layers 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64…”

Colloidal processing: enabling complex shaped ceramics with unique multiscale structures

“…Significant progress has been made in incorporating carbon nanomaterials into ceramic matrices using colloidal processing techniques. [94][95][96][97][98][99] The objective of this review was to highlight the types of unique multiscale structures that can be created in complex shaped components using wet colloidal techniques that cannot be produced via traditional dry processes. These include porous or cellular ceramics produced by a variety of techniques including replica, particle-stabilized foams, and ice templating.…”