Lithium-aluminium casting alloys and their associated metal-mould reactions

Aluminium - lithium alloys are specialist alloys used exclusively by the aerospace industry. They have properties that are favourable to the production of modern military aircraft. The addition of approximately 2.5 percent lithium to aluminium increases the strength characteristics of the new alloys by 10 percent. The same addition has the added advantage of decreasing the density of the resulting alloy by a similar percentage. The disadvantages associated with this alloy are primarily price and castability. The addition of 2.5 weight percent lithium to aluminium results in a price increase of 100% explaining the aerospace exclusivity. The processability of the alloys is restricted to ingot casting and wrought treatment but for complex components precision casting is required. Casting the alloys into sand and investment moulds creates a metal - mould reaction, the consequences of which are intolerable in the production of military hardware. The primary object of this project was to investigate and characterise the reactions occurring between the newly poured metal and surface of the mould and to propose a method of counteracting the metal - mould reaction. The constituents of standard sand and investment moulds were pyrolised with lithium metal in order to simplify the complex in-mould reaction and the products were studied by the solid state techniques of powder X-Ray diffraction and magic angle spinning nuclear magnetic resonance spectroscopy. The results of this study showed that the order of reaction was: Organic reagents> > Silicate reagents> Non silicate reagents Alphaset and Betaset were the two organic binders used to prepare the sand moulds throughout this project. Studies were carried out to characterise these resins in order to determine the factors involved in their reaction with lithium. Analysis revealed that during the curing process the phenolic hydroxide groups are not reacted out and that a redox reaction takes place between these hydroxides and the lithium in the molten alloys. Casting experiments carried out to assess the protection afforded by various hydroxide protecting agents showed that modern effective, protecting chemicals such as bis-trimethyl silyl acetamide and hexamethyldisilazane did not inhibit the metal - mould reaction to a sufficiently high standard and that tri-methylchlorosilane was consistently the best performer. Tri-methyl chlorosilane has a simple functionalizing mechanism compared to other hydroxide protecting reagents and this factor is responsible for its superior inhibiting qualities. Comparative studies of 6Li and 7Li N.M.R. spectra (M.A.S. and `off angle') establish that, for solid state (and even solution) analytical purposes 6Li is the preferred nucleus. 6Li M.A.S.N.M.R. spectra were obtained for thermally treated laponite clay. At temperatures below 800oC both dehydrated and rehydrated samples were considered. The data are consistent with mobility of lithium ions from the trioctahedral clay sites at 600oC. The superior resolution achievable in 6Li M.A.S.N.M.R. is demonstrated in the analysis of a microwave prepared lithium exchanged clay where 6Li spectroscopy revelaed two lithium sites in comparison to 7Li M.A.S.N.M.R. which gave only a single lithium resonance.

Precipitation casting of drug-loaded microporous PCL matrices:incorporation of progesterone by co-dissolution

Microporous, poly(ε-caprolactone) (PCL) matrices were loaded with progesterone by precipitation casting using co-solutions of PCL and progesterone in acetone. Progesterone loadings up to 32% w/w were readily achieved by increasing the drug content of the starting PCL solution. The kinetics of steroid release in PBS at 37°C over 10 days could be described effectively by a diffusional release model although the Korsmeyer-Peppas model indicated the involvement of multiple release phenomena. The diffusion rate constant (D) increased from 8 to 24 μg/mg matrix/day0.5 as the drug loading increased from 3.6 to 12.4% w/w. A total cumulative release of 75%-95% indicates the high efficiency of steroid delivery. Increasing the matrix density from 0.22 to 0.39 g/cm3, by increasing the starting PCL solution concentration, was less effective in changing drug release kinetics. Retention of anti-proliferative activity of released steroid was confirmed using cultures of breast cancer epithelial (MCF-7) cells. Progesterone released from PCL matrices into PBS at 37°C over 14 days retarded the growth of MCF-7 cells by a factor of at least 3.5 compared with progesterone-free controls. These findings recommend further investigation of precipitation-cast PCL matrices for delivery of bioactive molecules such as anti-proliferative agents from implanted, inserted or topical devices.

A 'sexy space' for women? Heterosexual women's experiences of a male strip show venue

The rise of male strip shows marketed towards heterosexual women has called into question the idea that only men can 'gaze' or be 'sexual scrutinizers' in public leisure spaces. This paper details the findings of an ethnographic study of a male strip event 'Cheeky's',1 located in the Midlands, England. Utilising observation, informal interviews and photography, the paper describes the physical environment and the atmosphere of the event, and analyses interview data with female customers. The paper questions what spaces such as Cheeky's mean for female sexualities, sexual roles and desires. The findings are twofold. On the one hand the club was a relatively novel sexual space, as some women spectators experienced it as an 'empowering' space in which they could be 'sexually aggressive'; on the other hand, the character of the club was actively and adeptly manufactured by the Master of Ceremonies (MC), and male dancers, so as to encourage - and even to coercively elicit - extrovert behaviour from women customers. Despite shifting normative gendered expectations of women's sexual behaviour to some extent, ultimately the club structured women's sexual experiences around traditional heterosexist lines. The club did not encourage women's autonomous sexual expression, and many women claimed they had not found it a very 'sexy space'. © 2011 Taylor & Francis.