Silver Powder

Allyl Iodide. Use 29 g. (34 ml.) of allyl alcohol and 340 g. (200 ml.) of 57 per cent, hydriodic acid 84 g. of crude iodide are obtained. Upon adding 29 g. (34 ml.) of allyl alcohol to the combined residue in the flask and the aqueous layer and distilling as before, a further 72 g. of crude allyl iodide may be isolated. B.p. 99-101° (mainly 100°). The compound is very sensitive to light the distillation should therefore be conducted in a darkened room and preferably in the presence of a little silver powder. 

If the iodide is deeply coloured, it may be decolourised with a little sodium bisulphite. A perfecUy colourless product can be obtained by distilling in the dark or in dilfusod light from a little silver powder. The iodide should be preserved in a bottle containing a short coil of copper wire made by wrapping coppor wire round a glass rod or tube. 

In a 1-litre three-necked flask, fitted with a mechanical stirrer, reflux condenser and a thermometer, place 200 g. of iodoform and half of a sodium arsenite solution, prepared from 54-5 g. of A.R. arsenious oxide, 107 g. of A.R. sodium hydroxide and 520 ml. of water. Start the stirrer and heat the flask until the thermometer reads 60-65° maintain the mixture at this temperature during the whole reaction (1). Run in the remainder of the sodium arsenite solution during the course of 15 minutes, and keep the reaction mixture at 60-65° for 1 hour in order to complete the reaction. AUow to cool to about 40-45° (2) and filter with suction from the small amount of solid impurities. Separate the lower layer from the filtrate, dry it with anhydrous calcium chloride, and distil the crude methylene iodide (131 g. this crude product is satisfactory for most purposes) under diminished pressure. Practically all passes over as a light straw-coloured (sometimes brown) liquid at 80°/25 mm. it melts at 6°. Some of the colour may be removed by shaking with silver powder. The small dark residue in the flask solidifies on cooling. 

Keep a coil of copper wire (prepared by winding copper wire round a glass tube) or a little silver powder in the bottle, which should be of brown or amber glass the methyl iodide will remain colourless indefinitely. Ethyl iodide may sometimes give more satis factory results. 

Metallic Powders. These are usually either aluminum or bronze flakes and vary ia shades from silver to gold, depending on the composition of the metal used. The silver powders can also be toned with organic pigments to produce golds or copper shades usiag transparent yellow or red pigments. 

The positive plates are siatered silver on a silver grid and the negative plates are fabricated from a mixture of cadmium oxide powder, silver powder, and a binder pressed onto a silver grid. The main separator is four or five layers of cellophane with one or two layers of woven nylon on the positive plate. The electrolyte is aqeous KOH, 50 wt %. In the aerospace appHcations, the plastic cases were encapsulated in epoxy resins. Most usehil cell sizes have ranged from 3 to 15 A-h, but small (0.1 A-h) and large (300 A-h) sizes have been evaluated. Energy densities of sealed batteries are 26-31 W-h/kg. 

Maler-koUk, -krankheit, /. painter s colic, plumbism. -leim, m. painter s size, -lein-wand, /. painter s canvas, -silber, n. painter s silver, silver powder, -stift, m. artist s pencil, -tuch, n. canvas. 

Above 140°C its exothermic decomposition to metal and carbon dioxide readily becomes explosive [1], A 1 kg batch which had been thoroughly dried at 50°C exploded violently when mechanical grinding in an end-runner mill was attempted [2], Explosions have been experienced when drying the oxalate as low as 80°C [6], It is a compound of zero oxygen balance. The explosion temperature of the pure oxalate is lowered appreciably (from 143 to 122°C) by application of an electric field [3], The salt prepared from silver nitrate with excess of sodium oxalate is much less stable than that from excess nitrate [4], Decomposition at 125°C in glycerol prevents explosion in the preparation of silver powder [5],... 

Fig. 6.8. Scheme of a composite heat exchanger realized with sintered silver powder [14-15]. 

Aluminium, copper, nickel and silver powders or flakes are used to obtain EMI (electromagnetic interference) grades. The other properties - colour, modulus, impact strength. .. are modified. 

Activation of Silver Powder for Ethylene Epoxidation at Vacuum and Atmospheric Pressures... 

Transient response techniques are used to investigate the activation of silver powder for ethylene epoxidation at vacuum and atmospheric pressures. Results indicate that the activation process is qualitatively the same in both pressure regimes. Numerical simulation of the process indicates that activation involves the concurrent incorporation of oxygen into surface and subsurface sites. The reaction selectivity parallels the incorporation of oxygen into the subsurface. 

Figure 3. TPSR spectra of the activation process over pretreated silver powder at 800 torr with a 3 1 oxygen/ethylene feed ratio.

The value obtained for ka can be used to calculate the sticking coefficient Sq for oxygen on clean silver powder at 240 °C using the relationship (34) ... 

The positive electrodes are usually fabricated by sintering of silver powders and... 

Passivation of silver and current oscillations were observed [389] during anodic dissolution of silver in H2SO4 solutions. During dissolution of the electrode, silver powder was accumulated at the surface, which affected diffusion to the electrode and led to oscillations. 

Fig. 9.23 SEM images of monodisperse silver powders obtained by reduction of AgNOj in ethylene glycol in the presence of PVP (a) quasi-spherical particles obtained by spontaneous nucleation (dm = 0.64 pun, cr = 0.13 p.m) (b) rodlike particles obtained by heterogeneous nucleation using H2PtCl6 as nucleating agent (particle dimensions 3 xm long and 0.3 xm thick). (From Ref. 13.)...

Table 9.23 Influence of Temperature and of the Relative Amount of the Protective Agent on the Size and Size Distribution of Silver Powders Obtained in Ethylene Glycol...

To 1 g of pure silver powder, placed in a flask, was added a mixture of 8.5g of nitric acid (d 1.42) 8t 1.2g water preheated to 90-95° and this was left at RT until complete dissoln of silver... 

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