Thin layer melting

Coextrusion. An increasingly popular technique to produce tailored film or sheet products is to coextmde one or more polymer types in two or more layers of melt (6). In this fashion the benefits of specific polymer types or formulations may be combined. Thus high cost barrier resins may be combined with a low cost thicker layer of standard resin to achieve an optimum barrier film at lower cost. Thin sUp-control layers may be used on the surface of a bulk layer of opticaUy clear resin to obtain an aesthetic film with good handleabUity. Lower melting outer layers may be used to provide heat sealing for polymers that seal with difficulty by themselves. 

Powder Coating. Teflon PEA is also available in a finely divided powder form. It can be used to produce thin layers on various surfaces by heating these surfaces above the melting point of PEA and then bringing the powder in contact with them. This allows a thin layer of the powder to melt on the surface of the substrate. 

Some materials that are prepared in the molten state are converted advantageously to flake form by cooling a thin layer continuously on the surface of a rotating drum. Another way is to spray cool from the melt, using a spray diyer with cold air. Thus, massive cooling and subsequent pulverizing are avoided. See the Index for details of these other methods. 

Amino acids have high melting or decomposition points and are best examined for purity by paper or thin layer chromatography. The spots are developed with ninhydrin. Customary methods for the purification of small quantities of amino acids obtained from natural sources (i.e. l-5g) are ion-exchange chromatography (see Chapter 1). For general treatment of amino acids see Greenstein and Winitz [The Amino Acids, Vols 1-3, J.Wiley Sons, New York 1961] and individual amino acids in Chapters 4 and 6. 

A mixture of 4.98 g of acetoacetic acid N-benzyl-N-methylaminoethyl ester, 2.3 g of aminocrotonic acid methyl ester, and 3 g of m-nitrobenzaldehyde was stirred for 6 hours at 100°C in an oil bath. The reaction mixture was subjected to a silica gel column chromatography (diameter 4 cm and height 25 cm) and then eluted with a 20 1 mixture of chloroform and acetone. The effluent containing the subject product was concentrated and checked by thin layer chromatography. The powdery product thus obtained was dissolved in acetone and after adjusting the solution with an ethanol solution saturated with hydrogen chloride to pH 1 -2, the solution was concentrated to provide 2 g of 2,6-dimethyl-4-(3 -nitrophenyl)-1,4-dihydropyridlne-3,5-dicarboxylic acid 3-methylester-5- -(N-benzyl-N-methylamino)ethyl ester hydrochloride. The product thus obtained was then crystallized from an acetone mixture, melting point 136°Cto 140°C (decomposed). 

Reprecipitation from acetone/pentane is repeatedly effected until the condensation product suits in flaky form. Further purification is effected in that the crude product is chromatographed on silica gel. The fractions which are uniform in accordance with thin layer chromatography are combined and yield crystals from absolute alcohol. Pure 4 -demethylepipo-dophyllotoxin-/3-D-thenylidene glucoside has a melting point of 242°C to 246°C (last residue up to 255°C). 

The moist cells were suspended in 750 parts of volume of ethanol and extracted by warming at 60°C for 1 hour. A total of 3 extractions were carried out in a similar manner and the extracts were pooled, diluted with water and further extracted three times with 1,000 parts of volume portions of n-hexane. The n-hexane layer was concentrated to dryness under reduced pressure to recover 4.12 parts of a yellow oil. This oily residue was dissolved in 6 parts by volume of benzene and passed through a column (500 parts by volume capacity) packed with Floridil (100 to 200 meshes). Elution was carried out using benzene and the eluate was collected in 10 parts by volume fractions. Each fraction was analyzed by thin-layer chromatography and color reaction and the fractions rich in ubiquinone-10 were pooled and concentrated under reduced pressure. By this procedure was obtained 0.562 part of a yellow oil. This product was dissolved in 5 parts by volume of chloroform, coated onto a thin layer plate of silica gel GF254 (silica gel with calcium sulfate) and developed with benzene. The fractions corresponding to ubiquinone-10 were extracted, whereby 0.054 part of a yellow oil was obtained. This oil was dissolved in 10 parts by volume of ethanol and allowed to cool, whereupon 0.029 part of yellow crystals of ubiquinone-10 were obtained, its melting point 4B°to 50°C. 

It was quite recently reported that La can be electrodeposited from chloroaluminate ionic liquids [25]. Whereas only AlLa alloys can be obtained from the pure liquid, the addition of excess LiCl and small quantities of thionyl chloride (SOCI2) to a LaCl3-sat-urated melt allows the deposition of elemental La, but the electrodissolution seems to be somewhat Idnetically hindered. This result could perhaps be interesting for coating purposes, as elemental La can normally only be deposited in high-temperature molten salts, which require much more difficult experimental or technical conditions. Furthermore, La and Ce electrodeposition would be important, as their oxides have interesting catalytic activity as, for instance, oxidation catalysts. A controlled deposition of thin metal layers followed by selective oxidation could perhaps produce cat-alytically active thin layers interesting for fuel cells or waste gas treatment. 

Many confections are coated in a thin layer of chocolate. The latter is a mixture of chocolate, cocoa butter and other fats, blended to form a suitable coating material. This layer melts at a temperature generally in the range 27-34°C. The manufacturer wishes to coat the confection in a thin, continuous layer, and then harden this layer so that the product can be wrapped and packed with the least delay on the production line. 

Fig. 70. IR transmission spectroscopy. A thin layer of melt is held and heated by the net.

Two modifications of the technique are used emission from thin layers [339 - 341] and emission from thick layers of the melt [342],... 

Measurements were performed on a potassium nitrite melt (KNO3) at 450°C. Fig. 73, curve 1 presents the spectrum obtained for a melt layer 0.05-0.1 mm thick, which was placed on a reflective surface (polished platinum). Fig. 73, curve 2 presents the inverted spectrum (relative to curve 1) of a relatively thin layer placed on an absorptive bottom surface (carbon-glass). 

In the first case, a typical emission spectrum of a thin layer melt is observed, because the emission from the bottom surface is negligible compared to that from the melt itself. In the second case, the relationship between the emission from the bottom surface and the emission from the melt is reversed, so that the spectrum reverts to being similar to a regular absorption spectrum. 

Opposite behavior was displayed by molten fluoride systems. For instance, no bands were observed in the thin layer emission spectrum of a KF - K2SiF6 melt, whereas increasing the melt layer to 10-20 mm led to the appearance of two intensive bands at 730 and 476 cm 1. These bands correspond to v3 and v4 vibrations of the complex ion SiF62 Solid K2SiF6 is characterized by IR absorption bands at 741 and 483 cm 1 [343]. 

Electrolytic Tinplate. Much of the tin mill product is made into electrolytic tinplate (ETP). A schematic of an ETP cross section is given in Figure 1. The steel strip is cleaned electrolytically in an alkaline bath to remove rolling lubricants and dirt, pickled in dilute mineral acid, usually with electric current applied to remove oxides, and plated with tin. It is then passed through a melting tower to melt and reflow the tin coating to form the shiny tin surface and the tin-iron alloy layer, chemically treated to stabilize the surface to prevent growth of tin oxide, and lubricated with a thin layer of synthetic oil. 

The nozzle of original design was fabricated from a niobium alloy coated with niobium silicide and could not operate above 1320°C. This was replaced by a thin shell of rhenium protected on the inside by a thin layer of iridium. The iridium was deposited first on a disposable mandrel, from iridium acetylacetonate (pentadionate) (see Ch. 6). The rhenium was then deposited over the iridium by hydrogen reduction of the chloride. The mandrel was then chemically removed. Iridium has a high melting point (2410°C) and provides good corrosion protection for the rhenium. The nozzle was tested at 2000°C and survived 400 cycles in a high oxidizer to fuel ratio with no measurable corrosion.O l... 

Boron implant with laser anneal. Boron atoms are accelerated into the backside of the CCD, replacing about 1 of 10,000 silicon atoms with a boron atom. The boron atoms create a net negative charge that push photoelectrons to the front surface. However, the boron implant creates defects in the lattice structure, so a laser is used to melt a thin layer (100 nm) of the silicon. As the silicon resolidihes, the crystal structure returns with some boron atoms in place of silicon atoms. This works well, except for blue/UV photons whose penetration depth is shorter than the depth of the boron implant. Variations in implant depth cause spatial QE variations, which can be seen in narrow bandpass, blue/UV, flat fields. This process is used by E2V, MIT/LL and Samoff. 

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