Influence of Graphene Sheets on Compaction and Sintering Properties of Nano-Zirconia Ceramics

Abstract

The use of a nanostructured graphene-zirconia composite will allow the development of new materials with improved performance properties and a high functionality. This work covers a stepwise study related to the creation of a nanostructured composite based on ZrO2 and graphene. A composite was prepared using two suspensions: nano-zirconia obtained by sol-gel synthesis and oxygen-free graphene obtained sonochemically. The morphology of oxygen-free graphene sheets, phase composition and the morphology of a zirconia powder, and the morphology of the synthesized composite were studied. The effect of the graphene sheets on the rheological and sintering properties of a nanostructured zirconia-based composite powder has been studied. It has been found that graphene sheets in a hybrid nanostructure make it difficult to press at the elastic deformation stage, and the composite passes into the plastic region at a lower pressure than a single nano-zirconia. A sintering mechanism was proposed for a composite with a graphene content of 0.635 wt%, in which graphene is an important factor affecting the process mechanism. It has been determined that the activation energy of the composite sintering is more than two times higher than for a single nano-zirconia. Apparently, due to the van der Waals interaction, the graphene sheets partially stabilize the zirconia and prevent the disordering of the surface monolayers of its nanocrystals and premelting prior to the sintering. This leads to an increase in the activation energy of the composite sintering, and its sintering occurs, according to a mixed mechanism, in which the grain boundary diffusion predominates, in contrast to the single nano-zirconia sintering, which occurs through a viscous flow.

Mixed Electronic-Ionic Conductivity and Stability of Spark Plasma Sintered Graphene-Augmented Alumina Nanofibres Doped Yttria Stabilized Zirconia GAlN/YSZ Composites

“…It can be assumed that GAlN significantly affects the mechanism of zirconia matrix sintering. According to [ 32 ], the addition of graphene to the zirconia matrix results in the mixed mechanism of sintering with a grain boundary diffusion predominance. Indeed, the increase of graphenated alumina nanofibres with a super-high aspect ratio (the length-to-diameter ratio is ∼100) to 3–5 wt.% induces the overall elongation of grains and formation of the grain boundaries network in zirconia-based composites (see Figure 5 , Figure 6 and Figure 7 ).…”

“…Graphene-augmented γ-Al 2 O 3 nanofibres (GAlN) were used as a modifier for ceramic composite manufacturing. For that, GAlN were successfully synthesized in the group of prof. Hussainova according to techniques listed in [ 28 , 30 , 32 ] and provided to authors for the present experiment. The γ-Al 2 O 3 nanofibres were synthesized by controlled aluminium liquid phase oxidation The nanofibres were subjected to the chemical vapour deposition (CVD) process at 1273 K using N 2 and CH 4 gas mixture, and were cooled to room temperature in a stream of pure N 2 [ 38 ].…”

“…Sintered specimens were then cooled to room temperature (with an approximate speed of 30 K/min). The conditions of sintering were chosen based on data from [ 28 , 30 , 32 ]. The temperature measurement took place in the vicinity of the powder compact centre, which gives a much more correct value than the measurement of the die temperature.…”

“…The structure of rGO is similar to pristine graphene, but contains residual functional groups and structural defects at the edge, which makes it more stable towards agglomeration in the metallic and ceramic matrices. Also, in the series of works [ 9 , 18 , 21 , 26 , 32 , 33 ] the effect of the sintering and shaping conditions on the structure and the properties of rGO/YSZ composites was studied. Based on the dilatometry data authors of [ 32 ] have shown that graphene-zirconia composites demonstrate the mixed mechanism of sintering with a grain boundary diffusion predominance.…”

“…Also, in the series of works [ 9 , 18 , 21 , 26 , 32 , 33 ] the effect of the sintering and shaping conditions on the structure and the properties of rGO/YSZ composites was studied. Based on the dilatometry data authors of [ 32 ] have shown that graphene-zirconia composites demonstrate the mixed mechanism of sintering with a grain boundary diffusion predominance. Such techniques as spark plasma sintering (SPS) [ 9 , 10 , 19 , 33 ], sintering using silicon carbide bed [ 21 ], sintering in the air [ 18 ], tape casting [ 26 ] and hot pressing [ 33 ] are used in the literature to produce zirconia/graphene composites.…”