Powdery precipitates

Colourless aqueous solutions of lead(II) nitrate and potassium iodide, KI, are mixed together. A yellow powdery precipitate of lead(II) iodide, Pbl2, is immediately produced. 

The salt solution, sodium iodide, Nal, was used in place of aqueous potassium iodide, KI, in Item 12. A yellow powdery precipitate was again produced. 

A solution of 1.5g of the hexammine chloride in 30ml of water is added to a solution of 3g of anhydrous potassium hexathiocyanatochromate (III) (No. 63) in 10ml of water. The product settles out as pink plates in almost quantitative yield. If the two solutions used for metathesis are more concentrated, a non-crystalline powdery precipitate results. 

A nickel hydroxide dispersed in water was reduced with a sodium hypophosphite solution and then heated up to 90-100°. After a certain induction period, a black precipitate was suddenly formed, evolving hydrogen simultaneously. This powdery precipitate was washed with water at first, then with alcohol, and finally with ether, and can be dried in the air without oxidation at room temperature. 

If you perform the next step without waiting for the solution to cool fully, your purple product will form an inseparable precipitate with calcium oxalate. Waiting too long to add the calcium chloride solution, however, will result in the formation of a red powdery precipitate. This has Xmax of 375 and 525 nm and is highly insoluble in H2O. Attempts to revive the solution by addition of more calcium chloride and by the application of heat result in decomposition to a similar red precipitate. 

The growth mechanism of in situ deposited films proposed by Stejskal and coworkers210 has similarities to that described earlier for electrodeposited PAn. It is important to note that the in situ method produces both a surface coating as well as the normal powdery precipitate from the bulk of the solution. It is proposed by... 

Preparation of polymers from dithiooxamide 22 In a three-necked 100 mL flask, equipped with a reflux condenser and a glass inlet tube, a mixture of cobalt chloride hexahydrate (2.38 g, 0.01 mol) in 20 mL ethanol and dithiooxamide 22 (1.2 g, 0.01 mol) in 20 mL ethanol and 5 mL DMSO were added and stirred at 70-80 °C, under a thin stream of nitrogen gas, for 24 h. At the end of the reaction, the mixture was poured into 300 mL of distilled water. The dark powdery precipitated polymer complex was filtered by suction in a Buchner funnel, washed thoroughly five times with hot distilled water, twiee with diethyl ether and then dried under vacuum at 40 °C for 24 h. The light-brown polymerie eobalt complexes were obtained in a yield of 87%. IR (KBr) -1300-1390 (C-N), -1080-1170 (C=S) cm". ... 

Polypyrrole was one of the earliest conducting polymers produced. In 1968 DalT-Olio et al. [2] oxidized pyrrole in aqueous sulfuric acid to obtain a powdery precipitate on a platinum electrode. Pyrrole black, as this material became known, had a conductivity of 8 S cm". Chemical analysis determined the presence of 75% poly pyrrole and 25% sulfate anions. An intense electron paramagnetic resonance signal indicated that the polymer possessed a large number of free spins and gave a g value of 2.0026 (comparable to that of a free electron, g = 2.0023). 

Van et al. [197] studied the electrochemical behavior of pyridazine using cyclic voltammetry in acetonitrile with different supporting electrolytes. Dark, greenish-blue polypyridazine formed on the anode when either lithium perchlorate or ammonium tetrafluoroborate was used as the supporting electrolyte. Also investigated were variations in the acidity of the solution during the course of electrolysis and the effects of the synthetic conditions on the electrochemical and other properties of the films. The pyridazine rings are believed to be para linked and the perchlorate or tetrafluoroborate counteranions are present in a 2 1 molar ratio. Two isomers of pyridazine—pyrazine and pyrimidine—could also be oxidized, but these isomers yielded only yellowish, powdery precipitates and no films. 

A small amount of a brown powdery precipitate formed. The precipitate was filtered, and dried in vaouo. Extraction of the reaction mixture with chloroform and evaporation of solvent gave 2g of brown solid. 

The reaction solution became viscous immediately after the addition of methylene bis-(p-phenylisocyanate). The viscous polymeric solution was precipitated in water. The creamy powdery precipitate was filtered, washed and dried in vaouo. 

The Gunn and Venables method is based on different principles the dextrin present is precipitated with ethanol and carries the oil down with it, leaving a clear supernatant aqueous-alcoholic layer. Kaolin is added to obtain a powdery precipitate which, after filtration, can be washed free from oil with ether. 

The synthesis of oxide powders simunarized by Ganguli in the method based on thermal crystallization of gels refers to obtaining both bulk gels and nanosized powders called either powdery precipitates or gel powders. ... 

The DSC plots (refer Fig. 4.1) of the samples for the three heating rates exhibit similar thermal characteristics with sharp exothermic decomposition/oxidation peak of the powdery precipitates above 175 °C. The peak temperamres for the heating rates 6, 8 and 10 °C/min are observed at 256.0, 260.9 and 264.7 °C respectively. The fractional conversion (a) values were evaluated from the DSC plots by measuring the relative area under the curve with respect to the temperature and are shown in Fig. 4.2. 

The growth mechanism of in s/fw-deposited films proposed by Stejskal et al. has similarities to that described above for electrodeposited PAn. It is important to note that the in situ method produces both a surface coating and the normal powdery precipitate from the bulk of the solution. It is proposed by Stejskal that aniline radical cations adsorb on the substrate surface during an "induction period" before bulk polymerization is observed. The adsorbed species initially promote the formation of a dense film on the substrate surface. Once this film has formed, further growth occurs on the PAn surface in a manner similar to the growth of localized globules that occurs in the electropolymerization. The surface roughness of in situ PAn films may be further increased by the incorporation of PAn precipitates from the bulk solution into the surface film. 

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