Tapered joint ends

A solution of product A (0.31 g, 0.5 mmol) and L12C03 (0.15 g, 2.0 mmol) in a mixture of 10 mL ethanol, 26 pL (0.5 mmol) acetonitrile, and 2,4-dimethylpenta-1,3-diene (Aldrich) (0.38 g, 4.0 mmol) is heated at reflux for 4 h in a 100-mL round-bottomed flask with a standard tapered joint. The solvent is evaporated under reduced pressure, and the flask is connected to a short, straight, water-cooled reflux condenser (Fig. 1). The top of the reflux condenser is attached to a high-vacuum pump, and the brown cmde product is purified by sublimation at 80°C and 10 bar. The yellow solid product is collected from the lower end of the reflux condenser. On a larger scale, it is more convenient to extract the dry brown cmde product with diethyl ether, filter the solution through a pad of alumina, evaporate the solvent, and then sublime the product. Yield 95%. 

G. Variations in Schlenk Ware. A large number of modifications of the basic Schlenk ware are in use. The double-ended filter is a commonly used variant of the standard Schlenk filter. The particular unit illustrated in Fig. 1.29 is equipped with O-ring joints rather than standard taper joints. (See Chapter 8 for a discussion of joints and O-ring materials.) Either conventional or modified O-ring joints, such as the Fischer and Porter Co. Solv-Seals, have several advantages over standard taper joints for Schlenk apparatus these O-joints are more resistant to solvents than the conventional standard taper ware, the O-joints are more readily clamped together, and, unlike standard taper joints, the two halves... 

This preparation is divided into three steps (1) the reaction of phosphorus (V) chloride with ammonium chloride in an inert solvent, (2) the rapid distillation from the solvent and from the nondistillable, rubber-forming higher polymers, and (3) the fractionation of the trimeric and tetra-meric compounds. The reaction apparatus consists of a 5-1. three-necked flask with standard-taper joints fitted with a thermometer and a motor-driven, heavy-duty stirrer, and heated by an electric mantle. For the preliminary removal of water from the solvent a Dean and Stark trap is used at a side joint in conjunction with a long water-jacketed condenser, the latter having a calcium chloride drying tube at its upper end. 

Alternatively, you may attach the helium leak detector to any of the demountable connections that you already have on your system, such as standard taper joints (see Fig. 7.63). Always use a hose clamp on both ends of the tube connecting the helium leak detector and the vacuum system being tested to ensure a leak-tight fit. 

A mercury-filled 6-mm o.d. glass tube with a platinum wire sealed through the lower end was used. The tube was bent to fit the contour of the flask. It was connected to the flask through a 24/40 standard-taper-joint Teflon thermometer adapter (Ace Glass, Vineland, NJ). Contact to the mercury was made with a platinum wire as shown (Figure 1). 

The checker reports that standard filtration techniques can be substituted for the centrifugation steps. The reaction of hydrous niobium (V) oxide is done in a 100-ml. round-bottomed flask fitted with an outer standard-taper joint. The solution of niobium(V) chloride in thionyl chloride is filtered by attaching a filter tube (having a standard-taper inner joint at each end) with a medium-porosity sin-tered-glass filter to the neck of the reaction flask, attaching another 100-ml. round-bottomed flask to the opposite end of the filter tube, and inverting the assembly. The residue can be washed with small aliquots of thionyl chloride. With this kind of apparatus the synthesis can be scaled up by a factor of 10 or more. 

A mixture of ca. 85 g. of lead(II) fluoride with glass powder is packed into a reaction tube (15 mm. o.d. x 200 mm. long) fitted with standard-taper joints and with the ends plugged with glass wool. 

A convenient apparatus for the reaction is shown in Fig. 1. A molybdenum boat is folded from thin sheet or foil to contain the metal. The fused silica cylinder ( 30-mm o.d.) which holds this is not necessary but does make product removal easier. The outer fused silica tube ( 40-mm o.d.) is terminated on the outlet end through a standard taper joint to a (Pyrex) cap with stopcock and connection to an exit bubbler (H2S04, not H20) which prevents back diffusion of air. The inlet end (which is slightly elevated) is connected through a stopcock and joint to a (Pyrex) mixing manifold, the three inlets of which connect through bubblers filled with H2S04 for flow measurement to sources of HC1, H2, and Ar or He (not N2). 

The most common method for reducing stress concentration in lap joints is by tapering the adherends, in a tapered lap joint (Figure 7.22a). Stress at the joint ends is reduced, allowing for a more uniform stress distribution. Modeling studies indicate that both adhesive peel and shear stresses... 

Figure 7.22 Joints used to reduce stress in adhesive bonding, (a) A tapered lap joint reduces stress at the joint ends, (b) A step lap joint avoids a large change in stress concentration from the middle to the ends of the joint when long overlap lengths are necessary. ...

Similarly, despite Thamm s advice, some designers choose to try and reduce the stresses at the joint ends by reducing the stiffness. This is best achieved by tapering, although single or multiple grooves or milled ends may be used as shown in Fig. 72. 

Other examples of joint-end modifications for joint transverse stress reduction but using external tapers are those of Sancaktar and Nirantar (2003) and Kaye and Heller (2005). Kaye and Heller (2005) used numerical optimization techniques in order to optimize the shape of the adherends. This is especially relevant in the context of repairs using composite patches bonded to aluminum structures (see Sect. 27.5) due to the highly stressed edges. 

The Lala (5-2S g) and somewhat more than the stoichiometric amount of Lat (13.46% of Lala by weight) are weighed in the dry box and transferred into the crucible. If an open crucible is used, this is placed in the closed end of a fused-silica tube long enough so that the upper end, which is equipped with a standard taper joint, will extend 10-15 cm from the (vertical) furnace. This end is capped with a Pyrex top equipped with a standard taper joint and stopcocks to allow evacuation and introduction of a noble gas. The joint... 

In North America the individual blocks of carbon used in the hearth bottom have exceeded 6 m in length. In Europe and Asia these blocks are much shorter because of manufacturing capabiHties. The longer bottom blocks permit the spanning of the hearth diameter with only two pieces, which prevents flotation of the carbon by the denser molten iron. This is because the bearing provided by the dead load of the hearth walls, which rest on the ends of the carbon block "beams," anchors the bottom blocks and prevents flotation. If smaller blocks are utilized with two or more joints across the bottom, special reverse taper mating surfaces or interlocking techniques are required to prevent block flotation. 

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