8 mol % Yttria Stabilised Zirconia Powder – 8YSZ from Innovnano

By AZoNano

Table of Contents

Introduction
Ionic Conductivity
Purity and Impurities
Particle Size and Grain Growth
About Innovnano

Introduction

Innovnano has developed a dense, yttria stabilised zirconia powder with characteristics exclusively designed for optimal end-use performance - 8YSZ. Zirconium oxide doped with relatively high proportions of yttria is used extensively as the solid oxide electrolyte component of high temperature energy conversion systems, such as Solid Oxide Fuel Cells (SOFC) and in sensors (NOx and O2). At levels of 8-10 mol%, yttria stabilises the zirconium oxide lattice structure in the cubic phase, even at increased temperatures, and offers high intrinsic oxygen ion conductivity and mechanical strength.

Ionic Conductivity

Using Innovnano's innovative physiochemical manufacturing process, the company is able to produce industrial–scale quantities of 8 and 10 mol % yttria stabilised zirconia nanopowders. Decades of experience in chemical production has enabled our engineers to control the process parametres that produce high quality nanopowders fine-tuned to the individual requirements of the applications of its clients. Designed specifically for SOFC applications, these high density yttria stabilised zirconia nanopowders, having a homogeneous dispersion of yttria throughout each zirconia particle, possess excellent chemical and physical properties, for demanding processing applications.

Table 1. Mechanical properties of A href="http://www.azonano.com/ads/abmc.aspx?b=5639" target=_blank>8YSZ

MECHANICAL PROPERTIES 8YSZ 10YSZ
Hardness (Hv 10) 1400 1400
Bending Strength (MPa) 400 250
Sintering Temperature (ºC) 1400 1400
Density (g/cm3) 5.9 5.8
Grain Size (nm) < 250 < 400
Ionic Conductivity (S/m) > 4.0 > 3.0

Extensive testing of these powders shows small average crystallite sizes and a high surface area, with good thermal expansion characteristics and high ionic conductivity values, making them an excellent choice for SOFC manufacture. The specific grain boundary ionic conductivity of nano-crystalline yttria stabilised zirconia has been reported as 2 orders of magnitude more than that of micro yttria stabilised zirconia.

Figure 1. SEM shows how lower sintering behaviour and controlled sintering conditions results in sub-micrometre grain sizes of a fired ceramic component for superior mechanical performance

Purity and Impurities

The latest production equipment and control systems at Innovnano's brand new manufacturing facility, in Coimbra, ensure that the purity of the materials produced is of superior quality. Impurities can modify the properties of ceramics in different ways: some improve; however, many negatively affect both the ceramic and significantly its end-use. 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 change the sintering mechanism, preferentially forming secondary liquidus phases at zirconia grain boundaries, resulting in high density material with poor mechanical properties. Impurities at grain boundaries cause grain blocking and, consequently, decrease ionic conductivity. However, small amounts of alumina can reduce the deleterious effect of silica through silica-scavenging, and, thereby, increase the ionic conductivity.

CHEMICAL ANALYSIS 8YSZ 10YSZ
ZrO2 + HfO2 + Y2O3 + Al2O3 (%) > 99.9 > 99.9
Y2O3 (%) 13.3 ± 0.2 15.5 ± 0.2
Al2O3 (%) < 0.02 < 0.02
SiO2 (%) 0.02 0.02
Fe2O3 (%) 0.02 0.02
Na2O (%) < 0.01 < 0.01

Particle Size and Grain Growth

As mechanical properties improve with the number of grain boundaries present in the nanostructure, it is very important to keep grain growth to a minimum and have a nanostructured powder feed stock with small crystallite and primary particle sizes. As grain growth increases with increase in temperature, achieving the highest product density requires sintering the powder at the lowest possible temperature. Innovnano’s 8YSZ powder's nanometric primary particle sizes and nanostructure (crystallites) facilitate substantially lower sintering temperatures, retaining small grain size and ensuring excellent mechanical properties.

PHYSICAL ANALYSIS 8YSZ 10YSZ
Crystallite Size (nm) 18 15
Primary Particle Size (nm) 50 50
Aggregate Size (nm) 200 200
Granule (μm) 60 60
Specific Surface Area (m2/g) 16 ± 3 16 ± 3

Figure 2. SEM shows soft aggregation of primary particles with narrow particle distribution

Conventional powders with particle sizes in the micrometre region, even those possessing some nanostructure, need higher temperatures to reach an acceptable density, which inevitably results in higher grain growth. Based on the particle size of the powder feed stock, some agglomeration can occur, however, ‘strong’ agglomerates, that reduce the densification rate and introduce undesirable porosity, are not usually formed unless designed into their manufacture. This granulation process has a number of benefits such as improvement in powder compaction, decrease in the incidence of defects in the compacted body, facilitation of easy powder handling and minimization of atmospheric dust. Granulation can be used to customize the powder size and rheological properties in applications that require granular powders with a specific particle size range and good flow ability.

Figure 3. SEM of atomised granule with morphology for good rheological spherical properties and flow-ability

Figure 4. Optimum particle size distribution of primary particles for ceramic parts with improved homogeneity and performance

Figure 5. Dilatometry shows a significant reduction in the sintering temperature required for full densification

About Innovnano

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.

Date Added: May 8, 2012 | Updated: Jul 15, 2013
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