Preparation from Melts

Synthetic ruby 2 %Ct20 in a-Al203) for lasers is made industrially by the Verneuil method as are single crystals of corund itself, sapphire, rutile, spinels, and strontium titanate. In this method the oxide particles are dropped through a flame, 

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The simplest case of fibre structure is the step-index one, characterized by a constant circular refractive index profile in the core and polymer cladding of lower refractive index (Figure 3). The refractive indexes of the core and cladding depend on the materials used. The cores of these structures can be prepared from melts as well as from preforms without radial and azimutal variations of the refractive index. To obtain suitable mechanical... 

Infrared spectroscopy is a relatively simple technique, nondestructive, and versatile enough to analyze solids, liquids, and gases with a minimum of sample preparation. Polymers can be mixed with potassium bromide and then pressed into pellets. Films can be prepared from melt or cast from solution and can be studied easily. In bulk samples or powders, or if a concentration profile is needed, the reflectance technique is probably more suitable than transmission. 

The rhombohedral form is prepared from melt solutions15. W-S mixtures, in 1 2 ratio compressed at 45 kbars and heated at 1800 °C for 2 to 3 minutes, gave a silver-gray product which was completely rhombohedral23. No evidence was found for the existence of lower tungsten sulfides, such as W2S31S. ... 

The compound K20 A1203 Si02 described by Weyberg [26] was prepared from melts with the aid of a flux (kaolin with K2Cr04). Bowen [22] in 1917 obtained this same compound while preparing the orthorhombic form of KAlSi04 with the aid of fluxes. The compound was present in the sample in small amounts as octahedra. 

Many of the fluoride complexes are anhydrous, being prepared from melts, and even hydrates are not numerous among those prepared from aqueous solution. In the case of hydrates, the refractivity of water must be allowed for. An example of a hydrate, (NH4)3CeF7 H2O obtained in the NH4F-CeF4-H20 system (81, 86), is shown in Fig. 12. When the refractivity of H2O is subtracted, the point for the yet unknown anhydrous (NH4)sCeF7 compound falls on the line established by the known anhydrous ammonium fluoride-cerium tetrafluoride complexes. 

The variation obtained when one person measures the same quantity several times using the same instmment. A thermoplastic material, prepared from melt-processed scrap or reject parts, or from nonstandard or nonuniform virgin material. The term scrap does not necessarily connote feedstock that is less desirable or usable than the virgin material from which it may have been generated. Reprocessed plastic may or may not be reformulated by the addition of fillers, plasticizers, stabilizers, or pigments. 

Though crystallinity of PHAs has been well documented in the literature along with their X-ray diffraction analysis, here we shall only briefly discuss certain salient features worth mentioning of the crystalline forms of PHB and some other PHAs. PHB can result in lamellar crystalline structures when crystallized from dilute solutions or into spherulites when prepared from melt processing. Typically, the crystals of P(3HB) are lath-shaped of 5-10 pm length with a thickness of 4-10 nm. °... 

In this chapter, we review the enzymatic degradation mechanisms of PLA prepared from melt-crystallized, solvent-cast, and blend films, mainly by using proteinase K enzyme molecules. The degradation mechanisms of thin films with thickness of about lOOnm and solution-grown lamellar crystals are also discussed. 

This reaction is not complete in experiments performed by the author, but since K2O is definitely a chain breaker or a ring opener, it can be seen why potassium trimetaphosphate can be formed thermally, at lower temperatures, where it would not normally be expected to form. Formation of K2CO3 removes K2O from the reaction zone. This reaction is similar to a well-known reaction of NH4CI with basic phosphates to make MCI and a more condensed phosphate. This lower-temperature chemistry is worthy of more study and should yield many surprising ways to make compounds that are not phase diagram entities, as they are prepared from melts. 

Solid-state Aims of suitable thickness can be prepared from melts or solution. Such Aims are most suitable for amorphous materials, especially polymers. Crystalline films may scatter light and show nonreproducible orientation effects from special orientations of the crystal on the IR window surface. A sample can be heated between two salt plates until molten and allowed to solidify. Solutions... 

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