Crystalline Handling

The technique of the filtration of hot solutions has already been described in Section 11,28. The filtration of cold solutions will now be considered this operation is usually carried out when it is desired to separate a crystalline solid from the mother liquor in which it is suspended. When substantial quantities of a solid are to be handled, a Buchner funnel of convenient size is employed. The ordinary Buchner fimnel (Fig. 11,1, 7, a) consists of a cylindrical porcelain funnel carrying a fixed, flat, perforated porcelain plate. It is fitted by means of a rubber stopper or a good cork into the neck of a thick-walled filtering flask (also termed filter flask, Buchner flask or suction flask) (Fig. 11,1, 7, c), which is connected by means of thick-walled rubber tubing (rubber pressure tubing) to a similar flask or safety bottle, and the latter is attached by rubber pressure tubing to a filter pump the safety bottle or trap is essential since a sudden fall in water pressure may result in the water sucking back. The use of suction renders rapid filtration possihle... 

Polymers are difficult to model due to the large size of microcrystalline domains and the difficulties of simulating nonequilibrium systems. One approach to handling such systems is the use of mesoscale techniques as described in Chapter 35. This has been a successful approach to predicting the formation and structure of microscopic crystalline and amorphous regions. 

Both RDX and HMX are stable, crystalline soHds, somewhat less sensitive to impact than PETN. Both may be handled with no physiological effect if appropriate precautions are taken to assure cleanliness of operations. Both RDX and HMX detonate to form mostiy gaseous, low molecular weight products and some intermediate formation of soHd carbons. The calculated molar detonation products of RDX are 3.00 H2O, 3.00 N2, 1.49 CO2, and 0.02 CO. RDX has been stored for as long as 10 months at 85°C without perceptible deterioration. 

The ease of sample handling makes Raman spectroscopy increasingly preferred. Like infrared spectroscopy, Raman scattering can be used to identify functional groups commonly found in polymers, including aromaticity, double bonds, and C bond H stretches. More commonly, the Raman spectmm is used to characterize the degree of crystallinity or the orientation of the polymer chains in such stmctures as tubes, fibers (qv), sheets, powders, and films... 

Liquid crystalline compounds are not very dangerous and only basic precautions should be used in handling them. They are not poisonous or carcinogenic, and do not cause problems when in contact with skin (see also Biphenyls and terphenyls Cinnamic acid Stilbene dyes). 

Crystalline Structures. Crystal shape of amino acids varies widely, for example, monoclinic prisms in glycine and orthorhombic needles in L-alanine. X-ray crystallographic analyses of 23 amino acids have been described (31). L-Glutamic acid crystallizes in two polymorphic forms (a and P) (32), and the a-form is mote facdely handled in industrial processes. The crystal stmeture has been determined (33) and is shown in Figure 1. 

Urea is soluble in water, and the crystalline solid is somewhat hygroscopic, tending to cake when exposed to a humid atmosphere. For this reason, urea is frequendy pelletized or prilled (formed into litde beads) to avoid caking and making it easy to handle. 

Sihca and aluminosihcate fibers that have been exposed to temperatures above 1100°C undergo partial conversion to mullite and cristobaUte (1). Cristobahte is a form of crystalline siUca that can cause siUcosis, a form of pneumoconiosis. lARC has deterrnined that cristobaUte should be classified as 2A, a probable carcinogen. The amount of cristobahte formed, the size of the crystals, and the nature of the vitreous matrix in which they are embedded are time- and temperature-dependent. Under normal use conditions, refractory ceramic fibers are exposed to a temperature gradient, thus only the hottest surfaces of the material may contain appreciable cristobahte. Manufacturers Material Safety Data Sheets (MSDS) should be consulted prior to handling RCF materials. 

Milling not only provides intimate mixing, but also eliminates variation in ribbon thickness and cmshes lumpy materials, eg, overdried soap, which might impact finished bar texture. Milling is also used for the formation of the proper bar soap crystalline phase, which plays a critical role in both the performance properties of the soap bar and the handling characteristics of the in-process soap. For example, too hot a milling temperature can create sticky soap that is difficult to process further. 

Shipment ndStora.ge. The crystalline material is shipped as a nonha2ardous material, in polyethylene-lined fiber dmms. The solution can be shipped in dmms or bulk. Suitable materials of constmction for handling ammonium thiocyanate are aluminum, 316 stainless steel, mbber, poly(vinyl chloride), and glass-reinforced epoxy. Steel, 304 stainless steel, and copper alloys should be avoided (375,376). 

Stannic Chloride Pentahydrate. Stannic chloride pentahydrate [10026-06-9] is a white, crystalline, deHquescent soHd that is soluble in water or methanol and stable at 19—56°C. It is used in place of the anhydrous chloride where anhydrous conditions are not mandatory. It is easier to handle than the fuming anhydrous Hquid form. The pentahydrate is prepared by dissolving stannic chloride in hot water, thereby forming the pentahydrate at a temperature above the melting point and crystallizing by cooling. The cake is broken into small lumps for packaging. 

Halo- and dihalobismuthines are crystalline soHds, most of which have melting poiats above 100°C. They are, ia general, very reactive compounds and are decomposed by moisture, alcohols, and ammonia (118). Dialkylhalobismuthines are especially sensitive substances. They are spontaneously indammable ia air and may decompose even when water and oxygen are excluded. The diaryl compounds are more stable, but they should also be handled with caution. Some of them are powerhil stemutators (119). 

The batch handling of wet or semidry crystalline materials is substantially more difficult than the storing and handling of dry crystalline materials. A batch operation has economic application only on a relatively small scale or when temperature or product characteristics require unusual precautions. 

Arnold Press 1966]. It can exists in five crystalline forms and is steam volatile. It is a strong IRRITANT to skin and mucous membranes and can become a chronic irritant— handle with CARE. 

Phenol is supplied commercially either in the solid (crystalline) state or as a solution in water (water content 8-20%). Where supplied as a solid it is usually handled by heating the phenol, and the molten material is pumped into the resin kettles or into a preblending tank. If the solution is used care must be taken to avoid the phenol crystallising out. 

Phosphorus exists as white and red phosphorus. The former allotrope may be preserved in the dark at low temperatures but otherwise reverts to the more stable red form. The white form is a waxy, translucent, crystalline, highly-toxic solid subliming at room temperature and inflaming in air at 35°C, so it is handled under water. The red form is a reddish violet crystalline solid which vaporizes if heated at atmospheric pressure and condenses to give white phosphorus. The red form ignites in air at 260°C. Both are insoluble in water, and white phosphorus can be stored beneath it. Phosphorus forms a host of compounds such as phosphine, tri- and penta-halides, tri-, tetra- and penta-oxides, oxyacids including hypophosphorous, orthophosphorous and orthophosphoric acids. 

C), and is much less reactive it is therefore safer and easier to handle, and is essentially non-toxic. The amorphous material can be transformed into various crystalline red modifications by suitable heat treatment, as summarized on the right hand side of Fig. 12.3. It seems likely that all are highly polymeric and contain three-dimensional networks formed by breaking one P-P bond in each P4 tetrahedron and then linking the remaining P4 units into chains or rings of P atoms each of which is pyramidal and 3 coordinate as shown schematically below ... 

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