Gold and nickel mining are a common land use in the semiarid Eastern Goldfields region of Western Australia,, A frequent outcome of mining activity is highly saline landforms that result from the widespread use of hypersaline (> 50 g L(subscript)-1 NaCl) groundwater for mineral processing and hydraulic tailings reclamation, and from saline horizons in soils, subsoils and mullock. Under State government legislation, all mined land must be rehabilitated to a stable and sustainable landform at the completion of mining activities.There was little land rehabilitation carried out in the mining industry until the mid1980s. At that time, legislation was introduced and, in due course, guidelines were issued on recommended approaches to rehabilitation. Today, rehabilitation of disturbed areas is usually integrated into the mining program and has become the rule rather than the exception. There has, however, been limited innovation in recent years and the established methods are not suitable for every land rehabilitation scenario, especially those where very high salinity is an important factor. The aims of this thesis were to make a contribution towards a better understanding of the ecology of halophytes suitable for use in revegetation and the likely physical requirements for their sustainable establishment on post-mining landforms.In terms of germination, many of the halophytes currently used for rehabilitation of saline substrates are well suited in that they are able to germinate in solutions of up to 20 g L(subscript)-1 NaCl. Furthermore, when higher salinities are encountered, seed dormancy is induced until salinity is reduced to a level at which germination can occur. There were differences observed between germination of annual and perennial chenopods that reflected their successional roles where annual chenopods tend to have a higher salt tolerance and germinate more ++ / rapidly. I developed a tolerance index to enable different germination responses to be readily compared. Values for the tolerance index ranged from 5.7 to 25.3 for the halophytic species compared with a value of 0.2 for the glycophytic Secale cereale. Values for saltbushes (Atriplex) and bluebushes (Maireana) ranged from 6.5 to 9.8 while values for samphires (Halosarcia) were higher (10.7-17.4).Germination and early growth of taxa in the succulent genus, Halosarcia, were also studied. Though a member of the Chenopodiaceae, with a number of species occurring commonly throughout the region, Halosarcia spp. are not widely used in rehabilitation. This is in part attributable to the poor level of knowledge of germination and growth characteristics compared with saltbushes and bluebushes, many of which are widely used. Two species studied, H. halocnemoides subsp. halocnemoides and H. pruinosa, are more salt-tolerant for germination than some other chenopods more widely used. Furthermore, in terms of their early growth, each taxon continued to grow in salinities up to 40 g L(subscript)-1 NaCl, although root .Production and mass were reduced at that concentration. Another taxon, H. pergranulata subsp. pergranulata, was found to have a partial physical dormancy attributable to the testa, a phenomenon rare among halophytes. Dormancy was alleviated by scarification but was most effective where this occurred near the micropyle.Field trials were conducted to assess methods of rehabilitating severely salt-affected surfaces (EC(subscript)e > 50 dS m(subscript)-1). In the initial trial, a number of surface treatments, including ripping, rock mulching and mounding, were shown to reduce soil EC, in loam soils over a long period of time (seven years) compared with the control. In a subsequent trial, the use of good quality waste water, in conjunction with ponding banks, strongly ++ / promoted the establishment of vegetation by supplementing soil moisture and enhancing soil P although a reduction in soil EC(subscript)e was not observed. The depth and duration of ponding influenced the species that established and the cover achieved. Methods by which a soil cover could be established over hypersaline tailings surfaces were also investigated. The absence of a capillary break layer resulted in severe salinisation (EC(subscript)e > 100 dS m(subscript)-1) of a non-saline clay loam soil cover and likely severe difficulties in establishing and maintaining vegetation on the cover. Two types of capillary break layer, a synthetic membrane and a layer of coarse iron fayalite granules (nickel slag), were both effective at preventing the capillary rise of salts into the soil cover.The physical and biological characteristics of the shores of Lake Lefroy, a large salt lake in the Eastern Goldfields region, were analysed using multivariate techniques.Physical characteristics were strongly influenced by the orientation of the shore relation to the predominant winds, and by depth to the saline groundwater table. Plant species were distributed in zones across the lake shores with small changes in elevation resulting in substantial changes in species distributions. Those plant species occurring at the lowest elevations (Zone I), including Halosarcia spp., exhibited a very high tolerance of saline soil and groundwater through an ability to accumulate Na+ and Cl- and make the necessary osmotic adjustments, and a capacity to tolerance high groundwater levels. Under certain conditions, the lake shore environment could be a useful model for a rehabilitated landform.

A indústria aeronáutica está constantemente à procura de materiais que ofereçam benefícios em termos de redução de peso, desempenho e custo. Corrosão e fadiga em ligas de alumínio são questões importantes na avaliação da vida útil em estruturas de aeronaves e na gestão de frotas. O objetivo deste trabalho foi avaliar os processos de corrosão e corrosão-fadiga nas ligas 2198-T851 e 7081-T73511, que são promissoras substitutas das ligas 2524-T3 e 7050-T7451 normalmente utilizada pela indústria aeronáutica. As técnicas de potencial de circuito aberto (PCA), polarização potenciodinâmica, polarização potenciodinâmica em eletrodo cilíndrico rotatório, espectroscopia de impedância eletroquímica (EIE), eletrodo vibratório de alta resolução (SVET) e mapeamento de potencial (SKP) foram utilizadas para esclarecer e quantificar os mecanismos de corrosão destas ligas de alumínio. Os ensaios de fadiga e corrosão-fadiga foram realizados com uma razão de carga (R) de 0,1 e frequência de 15 Hz em ar e 0,1 Hz em meio de névoa salina. As amostras, antes e após os testes de corrosão e corrosão-fadiga foram analisadas usando microscopia eletrônica de varredura (MEV). As características localizadas das quatro ligas estão essencialmente relacionadas com a existência de compostos intermetálicos que, devido à sua natureza diferente, podem ser catódicos ou anódicos em relação à matriz de alumínio. Os resultados de corrosão-fadiga mostraram uma ligeira redução no limite de fadiga para as ligas da série 2XXX e 7XXX. Essa redução pode ser atribuída à formação de cavidades de corrosão (pites). Considerando o estágio de propagação de trinca, o ambiente salino aumentou a taxa de crescimento de trinca para um mesmo intervalo de fator de intensidade de tensão. / The aircraft industry is constantly looking for improved materials which offer benefits in terms of performance, weight and cost savings. Corrosion and fatigue of aluminium alloys are major issues in the service life assessment of aircraft structures and in the management of aging air fleets. The aim of this study was to evaluate the corrosion and corrosion fatigue processes of 2198-T851 and 7081-T73511 aluminium alloys, which are promising substitutes for the base line 2524-T3 and 7050-T7451 aluminium alloys normally used in aircraft fabrication. Open circuit potential monitoring (OCP), potentiodynamic polarization, potentiodynamic polarization in rotating cylindrical electrode, eletrochemical impedance spectroscopy (EIS), Scanning vibrating electrode technique (SVET) and Scanning Kelvin Probe (SKP) techniques have been used to clarify and quantify the corrosion mechanisms of these Al alloys. Fatigue and corrosion fatigue tests were carried out an applied stress ratio (R) of 0.1, 15 Hz frequency for air and 0.1 Hz frequency for salt spray using a sinusoidal wave form in all cases. The specimens, before and after corrosion and corrosion-fatigue testing were analyzed using scanning electron microscope (SEM). The localised features of all the four alloys are essentially related to the existence of intermetallics that, due to their different nature, may be cathodic or anodic sites in relation to the Al matrix. SEM and EDS analysis allowed to identify the intermetallics that are more active in determining the corrosion behavior of the specimens. The fatigue corrosion results show a slightly reduction in the fatigue life limit by chloride environment for the 2XXX and 7XXX aluminium alloys in each aged condition might be partially attributed to the formation of corrosion pits. Considering the crack propagation stage, the saline environment increased the fatigue crack growth rate for the same range of stress intensity factor.

A indústria aeronáutica está constantemente à procura de materiais que ofereçam benefícios em termos de redução de peso, desempenho e custo. Corrosão e fadiga em ligas de alumínio são questões importantes na avaliação da vida útil em estruturas de aeronaves e na gestão de frotas. O objetivo deste trabalho foi avaliar os processos de corrosão e corrosão-fadiga nas ligas 2198-T851 e 7081-T73511, que são promissoras substitutas das ligas 2524-T3 e 7050-T7451 normalmente utilizada pela indústria aeronáutica. As técnicas de potencial de circuito aberto (PCA), polarização potenciodinâmica, polarização potenciodinâmica em eletrodo cilíndrico rotatório, espectroscopia de impedância eletroquímica (EIE), eletrodo vibratório de alta resolução (SVET) e mapeamento de potencial (SKP) foram utilizadas para esclarecer e quantificar os mecanismos de corrosão destas ligas de alumínio. Os ensaios de fadiga e corrosão-fadiga foram realizados com uma razão de carga (R) de 0,1 e frequência de 15 Hz em ar e 0,1 Hz em meio de névoa salina. As amostras, antes e após os testes de corrosão e corrosão-fadiga foram analisadas usando microscopia eletrônica de varredura (MEV). As características localizadas das quatro ligas estão essencialmente relacionadas com a existência de compostos intermetálicos que, devido à sua natureza diferente, podem ser catódicos ou anódicos em relação à matriz de alumínio. Os resultados de corrosão-fadiga mostraram uma ligeira redução no limite de fadiga para as ligas da série 2XXX e 7XXX. Essa redução pode ser atribuída à formação de cavidades de corrosão (pites). Considerando o estágio de propagação de trinca, o ambiente salino aumentou a taxa de crescimento de trinca para um mesmo intervalo de fator de intensidade de tensão. / The aircraft industry is constantly looking for improved materials which offer benefits in terms of performance, weight and cost savings. Corrosion and fatigue of aluminium alloys are major issues in the service life assessment of aircraft structures and in the management of aging air fleets. The aim of this study was to evaluate the corrosion and corrosion fatigue processes of 2198-T851 and 7081-T73511 aluminium alloys, which are promising substitutes for the base line 2524-T3 and 7050-T7451 aluminium alloys normally used in aircraft fabrication. Open circuit potential monitoring (OCP), potentiodynamic polarization, potentiodynamic polarization in rotating cylindrical electrode, eletrochemical impedance spectroscopy (EIS), Scanning vibrating electrode technique (SVET) and Scanning Kelvin Probe (SKP) techniques have been used to clarify and quantify the corrosion mechanisms of these Al alloys. Fatigue and corrosion fatigue tests were carried out an applied stress ratio (R) of 0.1, 15 Hz frequency for air and 0.1 Hz frequency for salt spray using a sinusoidal wave form in all cases. The specimens, before and after corrosion and corrosion-fatigue testing were analyzed using scanning electron microscope (SEM). The localised features of all the four alloys are essentially related to the existence of intermetallics that, due to their different nature, may be cathodic or anodic sites in relation to the Al matrix. SEM and EDS analysis allowed to identify the intermetallics that are more active in determining the corrosion behavior of the specimens. The fatigue corrosion results show a slightly reduction in the fatigue life limit by chloride environment for the 2XXX and 7XXX aluminium alloys in each aged condition might be partially attributed to the formation of corrosion pits. Considering the crack propagation stage, the saline environment increased the fatigue crack growth rate for the same range of stress intensity factor.