Sealed ampoule technique

Sealed Ampoule Technique Development. In order to overcome the difficulty with vaporization interfering with measurements of decomposition, a method was developed using samples sealed in melting point capillaries for DSC analysis. First it was necessary to compare results of conventional DSC runs in crimped aluminum pans with those of the new technique. An example of results of this technique compared with a run in an aluminum pan is shown in Figure 1. Also included is a... 

The classical procedures used by the chemist or engineer to obtain polymerization rate data have usually involved dilatometry, sealed ampoules, or samples withdrawn from model reactors—batch, tubular, and CSTR s alone or in various combinations. These rate data, together with data on molecular weight can be used to obtain the chain initiation constant and certain ratios such as kp2/kt and ktr/kp. Some basic relationships are shown in Figure 5. To determine individual rate constants such as kp and kt, other techniques are needed. For example, by periodic photochemical initiation it is possible to obtain kp/kt. If the ratio kp2/kt (discussed above) is also known, kp and kt can each be calculated. Typical techniques are described by Flory (20). 

The difficulty of removing acetaldehyde completely by distillation is indicated by the fact that a sample, presumably purified by Nozaki and Bartlett s [22] best techniques still contained about 3 X 10 A/acetaldehyde as estimated by UV spectroscopy at 290 nm (the absorption maximum for acetaldehyde) [13]. Using as a criterion the conversion after 4 hr when the purified monomer is warmed at 45°C with benzoyl peroxide (cone 8.27 X 10 moles/ liter), after two degassing cycles at oil pump pressure of 30 min each, in sealed ampoules, the most satisfactory procedure used by them consisted of fractional distillation through a distillation column of at least 50 theoretical plates (cf. Table III). 

CAUTION The simplest emulsion polymerizations have been carried out in closed bottles or sealed ampoules [130, 138, 139]. We generally do not consider these procedures safe. They are also of questionable value if the nature of the latex particles is to be studied. Two examples are given here only to illustrate the techniques used. 

The diffusion constant of Cd in single-crystal material was measured using a photoluminescence/etch technique. Diffusion was performed in sealed ampoules using cadmium metal and cadmium selenide powder as dopant sources. For cadmium metal sources,... 

Fast, solid state, microwave-assisted, synthesis. A short history of reactions carried out in the solid state under the influence of microwaves was reported by Kniep (1993) who presented this technique as characteristic of a fast solid-state chemistry and described the preparation of CuInS2 by using a method first developed by Whittaker and Mingos (1992) and extended by Landry and Barron(1993). Copper, indium and sulphur (all powders between 100 and 300 mesh) in a molar ratio 1 1 2 were thoroughly mixed and loaded into a silica ampoule. This, sealed under vacuum, was placed in a domestic microwave oven and irradiated at 400 W and 2450 MHz. 

An alternative, and more expensive, technique involves the application of commercial glass inserts, which are offered by Wilmad for all commercial MAS NMR rotor types. Approximately 60 or 200 mg of catalyst powder can be filled into a 4-mm or 7-mm glass insert, respectively. After calcination of the catalyst and adsorption of reactant molecules introduced from a vacuum line, the glass insert is sealed at the waist (Fig. 7). To prevent heating of the sample, the glass ampoule is clamped in one of the chucks and cooled by liquid nitrogen. 

A newer technique which shows promise but has not yet been fully tested is based upon the preparation and separation of aldonitrile acetates of reducing sugars (Equation 9.12). The dried sugar is dissolved in pyridine and treated with hydroxylamine hydrochloride in a sealed glass ampoule at 90°C for 0.5 hr. The mixture is cooled, acetic anhydride added, and another 30-min reaction is carried out in the resealed ampoule. Actual formation of the nitrile may occur in the injector of the gas chromatograph. Nonreducing sugars apparently do not form the nitrile but are present as the... 

Gd Cg2 was generated by arc discharge using a Gd-graphite rod and isolated by a multistage HPLC technique SWCNT bundles were prepared by pulsed-laser evaporation. The doping of Gd C82 into the inner hollow space of SWCNTs was carried out in a sealed glass ampoule at 500 °C for 24 h. Prior to the introduction of SWCNTs to the ampoule, the SWCNTs were heated in dry air at 420 °C for 20 min [267]. 

Typical thermal and photolytic techniques may be used but a common method is to fill an ampoule, fitted with a break-seal, with the reactant or reactants, dose, quench in liquid nitrogen, and reattach to the vacuum. This is followed by conventional analysis. Facilities for heating the sample at the radiation source can be employed. RV s are constructed from Pyrex or metal " and may in some cases be coated with graphite. However, with different surfaces, different products can result . Thin-walled RV s have to be used for a-particle-induced reactions . In the radon-sensitised reaction of Hj and O2, Lind has shown that the rate coefficient is inversely proportional to the square of the diameter of a spherical RV. 

A glass ampoule sample holder, as described in Chiu (125), is shown in Figure 6,17. Such a sealed sample container has been found to withstand an internal pressure of up to 1800 psi and is suitable to be used as a microreactor to study most chemical reactions. An ampoule holder, constructed from silver or aluminum metal, is used to support the ampoule in the DSC sample chamber. Liquid or solid samples are introduced into the ampoules by a syringe. The ampoule sealing technique has been described elsewhere (126). 

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