Seven species of seals were hunted in the Falkland Islands and Dependencies in the 18th to 20th centuries. Sealing probably began in the Falkland Islands in 1766 after French settlers arrived in 1764. The potential of an industry was not realized until American whalers arrived by 1774. Continued sealing was prevented by the War of Independence, except for an unsuccessful American attempt to establish a wartime fleet at the islands, shipping oil to London. Postwar economic depression prevented Americans returning, sealing instead being done by British southern whale fishery vessels from 1786. Oil was taken from hair seals, and skins from fur seals. Both were shipped to London. Americans returned by 1792 for fur seal skins for the expanding Canton fur trade. This they subsequently monopolized, British merchants being constrained by the East India Company's trading monopoly. Unregulated killing to supply Canton and London markets virtually exterminated fur seals on the Falkland Islands and South Georgia by the late 18th-early 19th centuries. Increased oil demand in America caused elephant seals to be depleted by the mid 19th century. Discovery of the South Shetland, South Orkney Islands and South Sandwich Islands resulted in stocks on these islands also quickly depleted, particularly to supply an American market. Lack of permanent government and settlement in the Falkland Islands in the 18th and early 19th centuries prevented control being exerted over sealers, although attempts were made by colonists from 1828 and by a British administration from 1833. Lack of patrol vessels prevented enforcement. Sealing legislation was introduced by 1881, but stocks and markets had declined to the point where a domestic sealing industry was difficult to establish. This was exacerbated by Canadian and Chilean pelagic sealing and poaching from 1902 to 1911. Stocks gained some respite during World War 1. Fur sealing was prohibited from 1915 in South Georgia and 1921 in the Falkland Islands, where a sea lion oil industry was developed in 1929. This operated sporadically until 1951. Production costs, fluctuating oil prices, and distance from markets are seen as contributory reasons preventing establishment of an industry. The last sealing licence for the Colony was issued in 1967. Elephant seals increased in the late 19th and early 20th centuries at South Georgia to the point where they could again be utilized. The Compaftia Argentina da Pesca began sealing in 1909, beginning an industry which continued successfully until the licencee left the island after the 1964 season due to the poor economics of whaling. 250,000 seals were taken in a well regulated industry, providing an important contribution to the company's revenue from the island. The numbers of elephant seals and fur seals on South Georgia have increased since whaling and sealing ended. Present anti-sealing concerns, lack of markets, exploitation costs and potential tourist attraction make future sealing in the Falkland Islands and Dependencies unlikely.

The double-cone ring gasket used as a static seal for high pressure operates on the principle of unsupported area by which the pressure applied to the gasket produces a large pressure at the seating surfaces thus maintaining a tight joint. An analysis based on elastic behaviour and simplifying assumptions is developed for predicting the sealing forces and the strains in the gasket. An apparatus was built for testing the effectiveness of the gasket for sealing pressures to 10,000 psi. Gaskets of several different proportions were tested and all were found to seal satisfactorily. Strain measurements made during the tests showed satisfactory agreement with predicted values for the assembly condition, but there were discrepancies between the predicted and observed values for the gaskets under pressure. These discrepancies indicate that the simple assumptions used in the analysis are not sufficiently accurate. The general conclusions are that the double-cone ring gasket is satisfactory for high pressure static seals and that the proportions of the ring cross section are not critical to the effectiveness of the seal. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

"New high performance optical systems require highly durable, broadband window materials in larger sizes than are currently available. To meet this need, a low cost edge-bonding process was developed for producing large area sapphire windows from smaller, melt-grown blanks. The method uses a polycrystalline alumina interlayer to promote diffusion and single crystal conversion at the interface between two sapphire substrates and produce high strength bonds. The goal of the current research effort is to determine the optimal alumina composition for maximum bond strength. Polycrystalline alumina fillets containing various chemical additives were prepared by tape casting for use in bonding trials. Oriented sapphire blanks were edge bonded in a furnace with special fixtures to accurately align and apply a load to the components during heat treatment. This approach is consistent with and builds upon the methods used in the previous edge-bonding studies. Flexure strength of the bonded samples, as compared to monolithic sapphire, was used as the performance metric. Additional bonding runs were carried out using the highest performing fillet composition in order to provide a sufficient number of specimens to conduct a Weibull analysis of the failure probability of the bonded material as a function of applied stress. A high purity alumina composition containing 3 wt.% SiO2, 0.05 wt.% MgO, and 0.05 wt.% Ti, produced the highest strength bonds. This composition yielded an average fracture strength of 255 MPa (37 kpsi), a Weibull modulus of 8.2, and a characteristic strength of 269 MPa (39 kpsi). These results compare favorably to monolithic sapphire specimens which yielded an average fracture strength of 284 MPa (41 kpsi)."

A thermally grown oxide (TGO) such as the alumina scale formed on a bondcoat enhances the oxidation and corrosion resistance of thermal barrier coating (TBC)- bondcoat-superalloy substrate systems. As the external alumina scale lies between the thermal barrier coating and bondcoat, its first spallation and subsequent TBC delamination become critical. Once the external alumina scale spalls, it will spall together with the TBC, leaving the system with no temperature barrier protection. Operational factors such as thermal cycling conditions, water vapour in the oxidation atmosphere, and alloying elements comprising the bondcoat system affect alumina scale adherence. Another problem that arises for the majority of bondcoat systems, β (Ni,Pt)Al and MCrAlY (M=Metal), are rich in aluminium. This causes aluminium to diffuse into the substrate, enriching it with aluminium during service, transforming phases in the substrate alloying system. The purpose of this study was to develop bondcoat materials that promote formation of a strongly adherent TGO, but have an aluminium content near the substrate composition. Cyclic oxidation experiments were performed with Ni-Al, Ni-Pt-Al, and Ni-Pt-Al-Ir alloys in dry air and air-12%H2O. Thermal cycles of 1 hr at 1200OC and 10 minutes at 80OC were carried out in flowing gases at a total pressure of 1 atm. Experiments in N2- 12%H2O were performed only on Ni-Al binary alloys. Binary Ni-Al cast alloys were tested for fundamental study purposes, while Ni-Pt-Al and Ni-Pt-Al-Ir cast alloys were intended to be models for aluminide coatings, with attention focused on γ+γ' -Ni-(20 to 23)Al. Comparisons were made with β-Ni-50Al, as it forms an external alumina scale and was found to have the smallest weight loss rate during testing of binary alloys. Assessments of Pt and Pt-Ir additions, with and without hafnium, to the γ+γ' binary alloy were made. Compared to binary alloys, platinum was found to reduce the total weight loss caused by scale spallation. Experiments in air-12%H2O led to more rapid weight loss than in dry air. This was due to enhanced spallation. However, the degradation rate was slower than in platinum-free alloys exposed to the same atmosphere. Partial replacement of platinum with iridium was found to improve alloy scale adherence during exposure in both dry and wet air. Addition of 1wt% hafnium was found to reduce oxide thickness and increase the oxide adherence simultaneously. The hafnium addition was essential in order to reduce spallation rate in wet air. Water vapour in the presence of oxygen generally increased the spallation rate. It weakened the oxide metal interface, causing subsequent spallation to be increased, but only if the gas had access to the alloy-scale interface. Water vapour did not affect the spallation rate of the strongly adherent oxide grown on Ni-22Al-30Pt+1wt%Hf and Ni- 20Al-15Pt-10Ir+1wt%Hf.

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A thermally grown oxide (TGO) such as the alumina scale formed on a bondcoat enhances the oxidation and corrosion resistance of thermal barrier coating (TBC)- bondcoat-superalloy substrate systems. As the external alumina scale lies between the thermal barrier coating and bondcoat, its first spallation and subsequent TBC delamination become critical. Once the external alumina scale spalls, it will spall together with the TBC, leaving the system with no temperature barrier protection. Operational factors such as thermal cycling conditions, water vapour in the oxidation atmosphere, and alloying elements comprising the bondcoat system affect alumina scale adherence. Another problem that arises for the majority of bondcoat systems, β (Ni,Pt)Al and MCrAlY (M=Metal), are rich in aluminium. This causes aluminium to diffuse into the substrate, enriching it with aluminium during service, transforming phases in the substrate alloying system. The purpose of this study was to develop bondcoat materials that promote formation of a strongly adherent TGO, but have an aluminium content near the substrate composition. Cyclic oxidation experiments were performed with Ni-Al, Ni-Pt-Al, and Ni-Pt-Al-Ir alloys in dry air and air-12%H2O. Thermal cycles of 1 hr at 1200OC and 10 minutes at 80OC were carried out in flowing gases at a total pressure of 1 atm. Experiments in N2- 12%H2O were performed only on Ni-Al binary alloys. Binary Ni-Al cast alloys were tested for fundamental study purposes, while Ni-Pt-Al and Ni-Pt-Al-Ir cast alloys were intended to be models for aluminide coatings, with attention focused on γ+γ' -Ni-(20 to 23)Al. Comparisons were made with β-Ni-50Al, as it forms an external alumina scale and was found to have the smallest weight loss rate during testing of binary alloys. Assessments of Pt and Pt-Ir additions, with and without hafnium, to the γ+γ' binary alloy were made. Compared to binary alloys, platinum was found to reduce the total weight loss caused by scale spallation. Experiments in air-12%H2O led to more rapid weight loss than in dry air. This was due to enhanced spallation. However, the degradation rate was slower than in platinum-free alloys exposed to the same atmosphere. Partial replacement of platinum with iridium was found to improve alloy scale adherence during exposure in both dry and wet air. Addition of 1wt% hafnium was found to reduce oxide thickness and increase the oxide adherence simultaneously. The hafnium addition was essential in order to reduce spallation rate in wet air. Water vapour in the presence of oxygen generally increased the spallation rate. It weakened the oxide metal interface, causing subsequent spallation to be increased, but only if the gas had access to the alloy-scale interface. Water vapour did not affect the spallation rate of the strongly adherent oxide grown on Ni-22Al-30Pt+1wt%Hf and Ni- 20Al-15Pt-10Ir+1wt%Hf.