Thick crystallinity

A concept gaining support is a hybrid approach to making thick crystalline silicon efficient in thin layers. Although conventional crystalline silicon cells have gone from 400—600-p.m thick to 200—300-p.m, thin-film crystalline silicon cells have reached 10% efficiency while being only 10-p.m thick. 

A solid somewhat sticky residue of 231.2 g was obtained. After removal of last traces of chloroform by repeated swishing with petroleum ether, the cake was finally refluxed with about 500 ml petroleum ether (BP 30° to 60°C) until a thick crystalline slurry was obtained. After refrigeration for a day, the white crystalline mass was filtered by suction, washed with petroleum ether (2 x 125 ml), then n-heptane (2 x 125 ml) and again with petroieum ether (2 x 125 ml). After air drying at room temperature to constant weight, 180.6 g of the dl-2-(N-formylamino)isocamphane melting at 160° to 165°C was obtained. 

The thus-washed crude product is dissolved in a mixture of 12 parts of ethanol and 20 parts of benzene, with mild warming if necessary. 1 Part of sodium chloride and 1.5 parts of saturated aqueous sodium chloride solution are added to the obtained solution in ethanol-benzene, and whole thoroughly admixed. When the brine layer has settled. It is separated and the afore-described washing repeated. The clear solution is concentrated under reduced pressure until incipient formation of crystals and is then poured into 30 parts of benzene, whereupon a thick crystalline pulp is forthwith formed which, after being cooled to room temperature, is centrifuged off. The so-obtained 5-allyl-5-( 3-hydroxypropyl)-barbituric acid is dried at 70°C under reduced pressure and can be used for therapeutic purposes without further purification. Melting point 164 °C to 165°C. Yield 5 parts. 

To decompose the acetone semicarbazone, warm 58 g. with 50 ml. of concentrated hydrochloric acid until it jiist dissolves. Cool in ice the semicarbazide hydrochloride separates as a thick crystalline mass. Filter at the pump through a sintered glass funnel, and wash with a small quantity of alcohol and then with ether dry in the air. The yield of pure semicarbazide hydrochloride, m.p. 173° (decomp.), is 35 g. A further quantity of product may be obtained either by saturating the mother liquor with hydrogen chloride or by treating it with twice its volume of alcohol and then with ether. 

To decompose the semicarbazone it is gently warmed with concentrated hydrochloric acid (8 c.c. for each 10 g. of material) until dissolution is just complete. On cooling the solution semicarbazide hydrochloride sets to a thick crystalline mass which is filtered dry at the pump and washed, first with a little cold hydrochloric acid (1 1), then twice with 3 to 5 c.c. portions of ice-cold alcohol. The salt is dried in a desiccator. Yield 22-25 g. 

Straight chain saturated hydrocarbon molecules from propane (C3H8) to octane (CgHis) were deposited from the vapor phase on platinum and silver(l 11) crystal surfaces in the temperature range 100—200 K. The ordered monolayer was produced first and then, with decreasing temperature a thick crystalline film was condensed and the surface structures of these organic crystals were also studied by LEED ... 

Nitromannitol can be obtained by nitrating mannitol with a mixture of nitric acid and sulphuric acid. The method is inconvenient, however, since the reaction produces a thick crystalline mass and the nitration proceeds unevenly [8]. Generally therefore, mannitol is dissolved in a five-fold amount of nitric acid (d — 1.51) at a temperature below 0°C, which is maintained while a ten-fold quantity of sulphuric acid (d = 1.84) is added to the solution. Fine crystals of the product are precipitated which were separated on a vacuum filter. The product is slightly impure due to the presence of mannitol pentanitrate. The acid product is drowned quickly in cold water, filtered again, washed with cold water, neutralized by means of dilute sodium bicarbonate solution and once again washed with water. Nitromannitol is crystallized from alcohol, to which a stabilizer (diphenylamine) is added. 

Owing to the highly explosive nature of the diazobenzene nitrate, its preparation should never be undertaken except the compound is wanted for research or some special purpose. 20 gms. of aniline are placed in a beaker, well cooled, and boiled-out nitric acid, previously diluted with half its volume of water, oarefully added till the mixture sets to a thick crystalline paste—aniline nitrate. The crystalline mass is filtered off at the pump, and washed with a little cold water. 5 gms. of the moist salt are finely powdered and placed in a small flask with enough water just to cover the substance. The flask is now well cooled in ice-water, and nitrous fumes (for preparation, see p. 513) are led in with frequent agitation until all the aniline nitrate has disappeared. At no time must the temperature of the flask rise above 10°. Should there not be sufficient water to keep all the diazobenzene nitrate formed in solution, its crystalline form will easily enable it to be distinguished from the aniline salt. When the reaction is finished the contents of the flask are poured into 3 times their volume of absolute alcohol, and ether is added to this mixture as long as crystals separate. If too much water has been added to the aniline nitrate from the beginning, a thick aqueous solution of diazobenzene nitrate separates out in place of the crystals. If this occurs, the ether-alcohol is decanted off, and the residue redissolved in absolute alcohol, and reprecipitated with ether. On no account must... 

The temperature is then allowed to rise to 18° C., and after standing for thirty minutes the mixture is poured upon ice, the product separating as a thick, crystalline mass. It crystallises from water in long yellow needles, from which the water of crystallisation may be removed by drjdng at 75° C. 

Properties (1) Yellowish-white needles (2) yellowish-white, thick, crystalline tablets mp (1) 217C (2) 172C) (1) sparingly soluble in pyridine (2) soluble in pyridine bp (1) sublimes (2) decomposes. 

Figure 2. Transmission spectrum of a 1.0 mm thick crystalline colloidal array formed from 131-nm diameter poly(heptafluorobutyl methacrylate) particles. The particle volume fraction was 6.13%.

The properties of PLA, as indeed those of other polymers, depend on its molecular characteristics, as well as on the presence of ordered structures, such as crystalline thickness, crystallinity, spherulite size, morphology and degree of chain orientation. The physical properties of polylactide are related to the enantiomeric purity of the lactic acid stereo-copolymers. Homo-PLA is a linear macromolecule with a molecular architecture that is determined by its stereochemical composition. PLA can be produced in a totally amorphous or with up to 40 per cent crystalline. PLA resins containing more than 93 per cent of L-lactic acid are semi-crystalline, but, when it contains 50-93 per cent of it, it is entirely amorphous. Both meso- and D-lactides induce twists in the very regular PLLA architecture. Macromolecular imperfections are responsible for the decrease in both the rate and the extent of PLLA crystallization. In practise, most PLAs are made up of L-and D,L-lactide copolymers, since the reaction media often contain some meso-lactide iir turities. 

Examples of ordered organic monolayers are normal paraffins on platinum and silver (111) surfaces. If straight-chain saturated hydrocarbon molecules from propane (CsHg) to octane (CgHig) are deposited from the vapor phase onto Pt or Ag (111) between 100 and 200 K ordered monolayers are produced. As the temperature is decreased a thick crystalline film can condense. The paraffins adsorb with their chain axis parallel to the platinum substrate, and their surface unit cell increases smoothly with increasing chain length as shown in Fig. 15. 

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