Autoclave technique

The first two groups are distinguished by the fact that autoclave syntheses are used mainly by the Soviet (or Russian) cluster school [1,2,11,16-22], while the American and other schools do not use autoclave techniques [1,23-35]. This distinction is historical and applies not only to technetium compounds, but also to other cluster compounds of d-transition elements [36-41]. Cotton et al. [28] did use an autoclave method once, but it was not further developed [1]. 

With autoclave syntheses a high yield of clusters is achieved, and it is possible for researchers to follow the reaction path in solution by gradually changing (from experiment to experiment) the working parameters of the synthesis (temperature, pressure, exposure at working temperatures, etc). All these advantages of the autoclave technique have resulted in an abundance of new forms of technetium clusters (particularly, polynuclear ones) because it has been possible to develop and improve the method of obtaining these compounds. 

Goswami and Sarkar3 claimed to have prepared methyl and ethyl fluoroformates by the action of thallium fluoride on the corresponding chloroformates. These fluoroformates were described as powerful lacrimators. We found that no appreciable reaction took place between potassium fluoride and ethyl chloroformate in boiling carbon tetrachloride or nitrobenzene. Ethyl fluoroformate could, however, be readily produced by the action of potassium fluoride on ethyl chloroformate by using the autoclave technique. It was found not to have the lacrimatory properties claimed for it, and was non-toxic in comparison with M.F.A. This non-toxicity was to be expected, as the fluoroformate contains the COF and not the CH2F- group. 

Chemical reactions of the hydroxyl groups were reported by Stober eJ, al. (225). y-AlaOj of high surface area (80 m /gm) was esterified with alcohols using the autoclave technique. About 7.7 OCH3 groups per 100 A were formed with methanol. The surface alcoholates are very sensitive to hydrolysis, however. Therefore, the reaction products were... 

Hunt, N. C. A., Attanoos, R., and Jasani, B. 1996. High temperature antigen retrieval and loss of nuclear morphology A comparison of microwave and autoclave techniques. J. Clin. Pathol. 49-101-110. 

The exclusion of asphaltenes in Kuwait resid is observed by an autoclave technique at 212°F with several catalysts having... 

The effect of antimicrobial agents on serum folate level was studied using the standard autoclaving technique of Lactobacillus casei microbial assay. The blood for serum folate assay was obtained from adult human subjects before and 2 hours after a 24 hours test dose of the antibiotic (72). The results show that lincomycin produced a falsely low serum folate level. 

Phaneuf et al. have developed a novel biomaterial surface that provides both localised infection resistance and haemostatic properties. Functional groups were created with woven Dacron material through exposure to ethylenediamine (C-EDA) and the antibiotic ciprofloxacin was then applied to the C-EDA using the pad/autoclave technique followed by surface immobilisation of the coagulation cascade enzyme thrombin. It was found that the antimicrobial activity of the treated fabric surface persisted for 5 days compared with the untreated fabric. Thrombin surfaces had 2.6-and 105-fold greater surface thrombin activity compared with non-specifically bound thrombin and ciprofloxacin-dyed surfaces, respectively. This study demonstrated that ciprofloxacin and thrombin can be simultaneously incorporated onto a biomaterial surface while maintaining their respective biological activities (Phaneuf et al., 2005). 

Figure 5.2 shows voids in a unidirectional carbon/epoxy composite made by the autoclave technique [3]. The two sections, cut parallel and perpendicular to the fibre... 

One of the ways considered to reduce the cost of manufacturing by the autoclave technique is to eliminate external pressure and use vacuum pressure only. One study looked at the effect of moisture formation resulting from dissolved moisture in the prepregs [4]. Significant voids resulted in this case when the pressure was not applied. Figure 5.3 shows an example of the voids formed. On the other hand, eliminating vacuum in the autoclave technique also produces voids. An example of this is shown in Figure 5.4 [5]. 

Figure 5.4 An example of voids formed between piepiegs when vacuum is eliminated Horn the standard autoclave technique for manufacturing composite laminates.

Molding can be achieved using a matched metal, a press-clave or an autoclave technique. Since the press-clave is a laboratory simulated version of a production autoclave, a brief description will be given (Figure 17.34). 

Although being a relatively old technology to process composites, the autoclave technique is still a matter of research. Besides the previously mentioned microwave development, research is being conducted to simulate the autoclave process and to derive models for time-based cost calculations [5,6]. In addition, efforts are being undertaken in the field of tooling and the effect of the tool on the part quality [7,8]. 

A controlled flow 177 C cure epoxy with 149 C dry and 93 C wet, service temperatures. An excellent resin for producing non-porous, void-free honeycomb sandwich structures as well as laminates for aircraft components, using autoclave techniques. Is typically impregnated via the solution technique. 

The chlorine/fluorine exchange reaction is an equilibrium reaction and can be influenced by altering the pressure, time, temperature and the ratio of the reactants. Usually high-temperature igh-pressure autoclave technique was used for shifted the equilibrium to fluorinated product. Anhydrous potassium fluoride in tetraglyme with a catalytic amount of dicyclohexano-18-crown-6 at 15-16 °C converted 2,4-dichloropyrimidine into 2,4-difluoropyrimidine. This process solved the problem of having to use an autoclave or dimethylformamide as solvent, because in tetraglyme (bp 275-276 °C) the more volatile fluoro products could be distilled directly from the reaction mixture uncontaminated by solvent. Under similar conditions 2-chloro-5-methoxypyrimidine was converted into the 2-fluoro analogue [65]. 

Processing is normally carried out in a preheated press at 370 °C with pressure maintained at 0.03 MPa for 30 s. The pressure is then increased to 0.6—1.4 MPa, and the glue line temperature is maintained at 370 °C for 3 h. The temperature is then reduced to 260 °C or less, and the assembly is removed from the press. Autoclave techniques can also be employed. For improved mechanical properties, postcuring in an inert atmosphere (nitrogen, helium, or vacuum oven) is recommended. The desirable conditions are 24 h each at 316 °C, 345 °C, 370 C, and 400 °C followed by 8 h at 427 °C in air to achieve maximum properties. Obviously, these literature recommendations should be checked against manufacturers recommendations, but they provide a starting point for PBI processing. 

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