Hard glasses

The sodium fusion and extraction, if performed strictly in accordance with the above directions, should be safe operations. In crowded laboratories, however, additional safety may be obtained by employing the follow ing modification. Suspend the hard-glass test-tube by the rim through a hole in a piece of stout copper sheet (Fig. 69). Place 1 -2 pellets of sodium in the tube, and heat gently until the sodium melts. Then drop the organic compound, in small quantities at a time, down — =. the tube, allowing the reaction to subside after each addition before the next is made. (If the compound is liquid, allow two or three small drops to fall at intervals from a fine dropping-tube directly on to the molten sodium.) Then heat the complete mixture as before until no further reaction occurs. 

Reduction. Mix together intimately in a dry hard-glass test-tube o-i g. of... 

Action of heat. Heat about 0 2 g. of uric acid in a hard-glass test-tube. Note the charring and also the formation of a white sublimate on the cooler parts of the tube. 

Hardness. Glass hardness tests usually measure the resistance to abrasion by grinding or grit-blasting, resistance to scratching, or penetration by an indenter. The method to be used depends on expected service conditions. Knoop hardness (Table 4) is commonly used, because other methods usually fracture the glass. 

A Combustion Tube of Hard Glass.—It should be about 13 mm. inside diameter, and the walls not more than i 5 mm. thick. Its length should be such that it projects at least 5 cm. (2 in.) beyond the furnace at either end. After cutting the required length, the ends of the tube are carefully heated in the flame until the sharp edges are just rounded. The tube is filled as follows. Push in a loose asbestos plug about 5 cm. (2 in.) from... 

Heat a little of the substance in a small, hard-glass tube and observe whether the substance melts, chars, explodes, sublimes, or volatilises whether an inflammable gas, water, etc., is evoKed also notice the smell. 

Contains Nitrogen.—First test the original solid ni liquid by heating in a hard-glass tube with soda-lime (p. 2), and notice if the smell is that of ammonia (ammonia salt, amide or cyanide), an amine (amine or amino-acid) or a pyridine base (alkaloid). 

This is made by the General Electric Co., and is used for medical ampoules. It loses very little alkali to aqueous solutions. The linear expansion coefficient is 7-3 x 10 from 20 to 350°C. This is intermediate between the soft and hard glasses, and M.6. is sometimes used in graded seals. 

Simple pumps for circulating gas or liquid can be made using two valves with a chamber between them. One ingenious pump uses a heat engine (A. R. Pearson and J. S. G. Thomas, 1925). The hard glass or silica bulb A (Figure 80, T) contains air initially at atmospheric pressure. This is heated with tap T closed and when the... 

Transmission electron microscopy (TEM) is a powerful and mature microstructural characterization technique. The principles and applications of TEM have been described in many books [16 20]. The image formation in TEM is similar to that in optical microscopy, but the resolution of TEM is far superior to that of an optical microscope due to the enormous differences in the wavelengths of the sources used in these two microscopes. Today, most TEMs can be routinely operated at a resolution better than 0.2 nm, which provides the desired microstructural information about ultrathin layers and their interfaces in OLEDs. Electron beams can be focused to nanometer size, so nanochemical analysis of materials can be performed [21]. These unique abilities to provide structural and chemical information down to atomic-nanometer dimensions make it an indispensable technique in OLED development. However, TEM specimens need to be very thin to make them transparent to electrons. This is one of the most formidable obstacles in using TEM in this field. Current versions of OLEDs are composed of hard glass substrates, soft organic materials, and metal layers. Conventional TEM sample preparation techniques are no longer suitable for these samples [22-24], Recently, these difficulties have been overcome by using the advanced dual beam (DB) microscopy technique, which will be discussed later. 

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