title: Preparation and characterisation of double doped-CeO₂ systems

authors: Torrens, Rob

abstract: Potential Solid Oxide Fuel Cell (SOFC) electrolyte materials of the composition Ce₀.₈Gd₀.₂₋ₓMₓO₂₋δ (M = Pr or Sm, x = 0.005 - 0.05) were prepared by two wet-chemical methods: oxalic acid co-precipitation and a variant of the Pechini method. 

X-ray diffraction of the oxide powders indicates that they are single-phase cubic fluorite materials. High temperature x-ray diffraction studies show that there is no evolution of secondary phases up to the maximum temperature of testing, 1273 K. Thermal expansion coefficients, calculated from lattice parameters measured at different temperatures, reveal the praseodymia containing samples to have a higher coefficient of thermal expansion, 1.3 x 10⁻⁵ K⁻¹ as opposed to 1.0 x 10⁻⁵ K⁻¹ for Ce₀.₈Gd₀.₂O₂δ.

There was little variation in particle size (measured by laser diffraction) or surface area (measured by gas adsorption) between the powder prepared by the different preparation techniques and no systematic variation with double dopant concentration. Scanning electron microscopy (SEM) of the powders showed the preparation techniques produced particles with different morphologies; co-precipitated particles were elongated crystals composed of primary crystallites, while Pechini method particles appeared to be porous agglomerates of primary crystallites. Powders produced by the Pechini method proved to be more difficult to fabricate into pellets, with problems arising during pressing and sintering, resulting in a high rejection rate. 

X-ray microscopy of pressed and sintered pellets indicates that the use of a binder/lubricant reduces intra-pellet density variations. 

Sintering studies indicate that, while the Pechini method powders had rapid initial densification, the co-precipitated powders were more able to obtain closed porosity (96% of the theoretical density) at lower temperatures. Praseodymia containing samples exhibited enhanced sintering compared to the other samples, achieving 98-99% of theoretical density after sintering for 10 hours at 1400 ℃.

SEM investigation of sintered pellets indicates that both of the double dopant species acted to retard grain growth. 

Impedance spectroscopy results show the praseodymia double doped materials to have higher conductivities than the base Ce₀.₈Gd₀.₂O₂δ material. The praseodymia containing composition showing the highest conductivity was Ce₀.₈Gd₀.₁₈₅Pr ₀.₀₁₅O₂δ with a conductivity of 1.3 x 10⁻² S cm⁻¹ 1 (at 600 ℃, in air). Samaria double doping also increased conductivity, though not to the same extent as praseodymia double doping. The highest conductivity obtained for a samaria containing sample was 1.0 x 10⁻² S cm⁻¹ (at 600 ℃, in air) for the composition Ce₀.₈Gd₀.₁₉Sm₀.₀₁O₂δ. The samples exhibiting the highest conductivities also had the lowest activation energies for conduction. Impedance spectroscopy results at low oxygen partial pressures indicate no difference in ionic domain boundaries. 

The thesis concludes with a list of future work needed to carry on these studies.

text: Preparation and characterisation of double doped-CeO₂ systems Potential Solid Oxide Fuel Cell (SOFC) electrolyte materials of the composition Ce₀.₈Gd₀.₂₋ₓMₓO₂₋δ (M = Pr or Sm, x = 0.005 - 0.05) were prepared by two wet-chemical methods: oxalic acid co-precipitation and a variant of the Pechini method. 

X-ray diffraction of the oxide powders indicates that they are single-phase cubic fluorite materials. High temperature x-ray diffraction studies show that there is no evolution of secondary phases up to the maximum temperature of testing, 1273 K. Thermal expansion coefficients, calculated from lattice parameters measured at different temperatures, reveal the praseodymia containing samples to have a higher coefficient of thermal expansion, 1.3 x 10⁻⁵ K⁻¹ as opposed to 1.0 x 10⁻⁵ K⁻¹ for Ce₀.₈Gd₀.₂O₂δ.

There was little variation in particle size (measured by laser diffraction) or surface area (measured by gas adsorption) between the powder prepared by the different preparation techniques and no systematic variation with double dopant concentration. Scanning electron microscopy (SEM) of the powders showed the preparation techniques produced particles with different morphologies; co-precipitated particles were elongated crystals composed of primary crystallites, while Pechini method particles appeared to be porous agglomerates of primary crystallites. Powders produced by the Pechini method proved to be more difficult to fabricate into pellets, with problems arising during pressing and sintering, resulting in a high rejection rate. 

X-ray microscopy of pressed and sintered pellets indicates that the use of a binder/lubricant reduces intra-pellet density variations. 

Sintering studies indicate that, while the Pechini method powders had rapid initial densification, the co-precipitated powders were more able to obtain closed porosity (96% of the theoretical density) at lower temperatures. Praseodymia containing samples exhibited enhanced sintering compared to the other samples, achieving 98-99% of theoretical density after sintering for 10 hours at 1400 ℃.

SEM investigation of sintered pellets indicates that both of the double dopant species acted to retard grain growth. 

Impedance spectroscopy results show the praseodymia double doped materials to have higher conductivities than the base Ce₀.₈Gd₀.₂O₂δ material. The praseodymia containing composition showing the highest conductivity was Ce₀.₈Gd₀.₁₈₅Pr ₀.₀₁₅O₂δ with a conductivity of 1.3 x 10⁻² S cm⁻¹ 1 (at 600 ℃, in air). Samaria double doping also increased conductivity, though not to the same extent as praseodymia double doping. The highest conductivity obtained for a samaria containing sample was 1.0 x 10⁻² S cm⁻¹ (at 600 ℃, in air) for the composition Ce₀.₈Gd₀.₁₉Sm₀.₀₁O₂δ. The samples exhibiting the highest conductivities also had the lowest activation energies for conduction. Impedance spectroscopy results at low oxygen partial pressures indicate no difference in ionic domain boundaries. 

The thesis concludes with a list of future work needed to carry on these studies.

year: 2002

title: Publishing cooperative and work-integrated education literature: The Asia-Pacific Journal of Cooperative Education

authors: Zegwaard, Karsten E.

subjects: Citations

abstract: The Asia-Pacific Journal of Cooperative Education (APJCE) was founded in 1999, with the first volume published in 2000. The journal strongly adhered to the philosophy of having freely and readily accessible information, and opted to be a free, fully online, open access journal. Over the last 12 years, the journal has grown and has become well-established in the cooperative (co-op) and work-integrated learning (WIL) community. The number of publications per year has steadily increased and the number of submissions has shown strong growth, especially in the last three years. APJCE articles are increasingly cited in other journals and significant book publications, and both its author and user bases have become more international. This article will discuss the advantages from the APJCE perspective of being an open access journal and provide an analysis of the growth of APJCE. The article will also discuss the performance of the journal in the context of co-op/WIL literature internationally and discuss some recent developments for the journal.

text: Publishing cooperative and work-integrated education literature: The Asia-Pacific Journal of Cooperative Education The Asia-Pacific Journal of Cooperative Education (APJCE) was founded in 1999, with the first volume published in 2000. The journal strongly adhered to the philosophy of having freely and readily accessible information, and opted to be a free, fully online, open access journal. Over the last 12 years, the journal has grown and has become well-established in the cooperative (co-op) and work-integrated learning (WIL) community. The number of publications per year has steadily increased and the number of submissions has shown strong growth, especially in the last three years. APJCE articles are increasingly cited in other journals and significant book publications, and both its author and user bases have become more international. This article will discuss the advantages from the APJCE perspective of being an open access journal and provide an analysis of the growth of APJCE. The article will also discuss the performance of the journal in the context of co-op/WIL literature internationally and discuss some recent developments for the journal.

year: 2012

title: Waiwhakareke Restoration Plantings: Establishment of Monitoring Plots 2005-06

authors: Grove, E.

subjects: New Zealand

abstract: Waiwhakareke Natural Heritage Park is being developed to reconstruct native lowland and wetland ecosystems as were once widespread in the Waikato Region. The 60ha Natural Heritage Park is located on the north-west outskirts of Hamilton City and includes a peat lake (Horseshoe Lake) which is surrounded by introduced willow trees. There is some native marginal vegetation around the lake, including rushes and sedges, and an extensive area of gently sloping pasture completes the catchment. The restoration and recreation of the native plant and animal communities is being lead by the Hamilton City Council in partnership with The University of Waikato, Wintec, Nga Mana Toopu o Kirikiriroa Limited Resource Management and Cultural Consultants and Tui 2000 (McQueen 2005; McQueen & Clarkson 2003).

text: Waiwhakareke Restoration Plantings: Establishment of Monitoring Plots 2005-06 Waiwhakareke Natural Heritage Park is being developed to reconstruct native lowland and wetland ecosystems as were once widespread in the Waikato Region. The 60ha Natural Heritage Park is located on the north-west outskirts of Hamilton City and includes a peat lake (Horseshoe Lake) which is surrounded by introduced willow trees. There is some native marginal vegetation around the lake, including rushes and sedges, and an extensive area of gently sloping pasture completes the catchment. The restoration and recreation of the native plant and animal communities is being lead by the Hamilton City Council in partnership with The University of Waikato, Wintec, Nga Mana Toopu o Kirikiriroa Limited Resource Management and Cultural Consultants and Tui 2000 (McQueen 2005; McQueen & Clarkson 2003).

year: 2006