Table of ContentsIntroductionParticle Size and Grain GrowthMechanical PropertiesPurity and ImpuritiesAbout Innovnano
A dense, yttria-stabilized zirconia powder with properties designed for optimal processability, 3YSZ, has been developed by Innovnano. Due to sintering temperatures under 1300 °C, lower than those used for ‘conventional’ powders, fired ceramic parts retain their small grain size and benefit from improved ageing resistance and mechanical performance as well as bending strength and fracture toughness.
Particle Size and Grain Growth
Since the mechanical properties of a powder are dependent on the number of grain boundaries present in the nanostructure, it is essential to keep grain growth to a minimum and have a nanostructured powder feed stock with tiny crystallite and primary particle sizes. As high temperatures promote grain growth, the highest densities are achieved by sintering at the lowest possible temperature. The nanometric primary particle size of 3YSZ and 12 nm nanostructure (crystallites) enable comparatively low sintering temperature, retaining small grain size and ensuring superior mechanical properties. Traditional powders, which have particle sizes in the micrometer region, including those that have some nanostructure, need a higher temperature to reach the desired density, resulting in higher grain growth.
Figure 1. TEM of crystallites showing dense, nanostructure for improved sinter-activity
Based on the particle size of the powder feed stock, agglomeration is possible, however, ‘strong’ agglomerates, which bring down the densification rate and cause undesirable porosity, are not normally formed unless intentionally designed into their manufacture. There are a number of benefits of the granulation process, which include improvement of powder compaction, decrease in the incidence of defects in the compacted body and facilitation of easier powder handling as well as minimization of atmospheric dust. In applications that need granular powders with a specific particle size range and good flow ability, granulation can be utilized for customization of powder size and rheological properties.
Table 1. Physical properties of 3YSZ:
|Crystallite Size (nm)
|Primary Particle Size (nm)
|Aggregate Size (nm)
|Specific Surface Area (m2/g)
||16 ± 3|
Figure 2. SEM shows soft aggregation of primary particles with narrow particle size distribution
Figure 3. Narrow particle size distribution of primary particles for ceramic parts with improved homogeneity and performance
Figure 4. Particle size distribution of granules
Figure 5. SEM of atomised granule with spherical morphology for good rheological properties and flow-ability
The bending strength of a ceramic material is a structure-sensitive property that depends on various factors, including:
density, and therefore porosity
bonding strength of grain boundaries
presence of impurities or dopants.
The hardness of 3YSZ increases linearly with product density and with decreasing grain size. Zirconia becomes harder with increasing concentration of yttria, assuming a homogenous distribution of the yttria throughout the zirconia lattice structure. Cubic zirconia displays a higher Vickers hardness level than the tetragonal phase.
Whilst it is possible to achieve high toughness in nanocrystalline ceramics, it requires a very precise dopant-grain size combination that places the ceramic very near the phase transformation boundary.
Table 2. Mechanical properties of 3YSZ:
|Hardness (Hv 10)
|Bending Strength (MPa) @ 25ºC
|Fracture Toughness (MPa.m0.5)
|Sintering Temperature (ºC)
|Grain Size (nm)
Purity and Impurities
Sophisticated production equipment and control systems at the new Innovnano manufacturing facility, in Coimbra, ensure that the purity of the materials produced is of excellent quality. The properties of ceramics can be modified by impurities in several ways, both positively and negatively. In the case of zirconia, oxides of Si, Fe, Cu, Ca and the alkali metals have a detrimental effect on the densification of its green state and, therefore, its final microstructure (grain size, density). Specifically, SiO2 and Fe2O3 impurities will modify the sintering mechanism, preferentially forming secondary liquid phases at the zirconia grain boundaries, causing high density material with poor mechanical properties. Conversely, low levels of Al2O3 and MgO can promote densification without excessive grain growth and improve mechanical properties.
Table 3. Chemical composition of 3YSZ:
|ZrO2 + HfO2 + Y2O3 + Al2O3
||5.2 ± 0.2|
Figure 6. SEM shows how lower sintering behavior and controlled sintering conditions results in sub-micrometer grain sizes of a fired ceramic component for superior mechanical performance.
Figure 7. Dilatometry shows a significant reduction in the sintering temperature required for full densification
Headquartered in Lisbon, we are part of CUF, the largest chemical company in Portugal and an organisation with decades of invaluable expertise in the development and commercialisation of novel, efficient industrial processes. Based on this technology platform and an extensive R&D collaboration programme with leading industry and university partners, our innovative industrial-scale process produces customisable, high quality nano-structured powders and products with excellent physical, chemical and mechanical properties.
Innovnano’s production capacity increased significantly with the opening of our new manufacturing and technology facility (Coimbra, Portugal) in early 2012. A European based production centre, it is built on a modular design, facilitating future expansion to meet the rapidly growing demands of the industries taking advantage of high performance nano-structured materials. Their patented process utilises feedstock precursors from sustainable sources, ensuring both a reliable and economical continuity of supply.
This information has been sourced, reviewed and adapted from materials provided by Innovnano.
For more information on this source, please visit Innovnano.