Carbon crystallizing modifications

Calcium carbonate crystal distortion or crystal modification,... 

Fluoran compounds have an optically active spiro-carbon atom. Consequently, some fluoran compounds, especially those having an alkylamino group of four or more carbon atoms at 3 -position, have been found to exhibit crystal modifications as determined by X-ray diffraction. Each crystal modification reveals different physical properties such as melting point, solubility, and affinity with acidic compounds, resulting in different characteristics regarding use for carbonless copying papers, thermosensitive recording papers, and the like. 

Scratch resistance depends on the hardness of the added particles. The problem of a lack of this property can be addressed by adding chemically identical particles of different crystal modification and Mohs hardness. The preferred additives are silica, alumina, layered silicates such as kaolin, titania, barium sulfate and calcium carbonate. The latter is only suitable for the DMT process owing to side reaction caused by acidity during the terephthalic acid (TPA) route. 

Calcium carbonate has a number of crystal modifications,but the calcite form is the one that is principally used for filler appHcations. Pure calcite is a relatively soft material (Moh hardness 3.0) with a specific gravity of 2.7. 

The production process is able to produce all three crystal modifications of calcium carbonate and a wide variety of particle sizes and shapes, including plates and acicular forms [107]. However, only the calcite form with a rhombic shape and a low aspect ratio seems to have found much commercial application in polymers. For filler applications the particles have an ultimate particle size of 50-100 nanometers, a specific surface area of 15-25 m g and a low aspect ratio. 

In subsequent steps, DAS is treated in acidic aqueous solution at 0-5 °C with cyanuric chloride dissolved in ethyl methyl ketone. The remaining chlorine atoms are then replaced by aliphatic, cycloaliphatic, or aromatic amines at 15-35 °C and then at ca. 60 °C. The addition of electrolytes (e.g., sodium carbonate, sodium hydroxide) or water-soluble aprotic solvents at 90 to 100 °C or above leads to the desired 3 crystal modification, which is nearly colorless. 

In a similar experiment, 2.5 g of zinc oxide prepared by precipitation from zinc nitrate solution by sodium carbonate, calcination, and attempted reduction under similar conditions as previously employed, gave a catalyst of surface area of 40 m2/g, which yielded less than 10 9 kg of methanol per square meter of the catalyst per hour under the standard conditions used for the testing of the copper catalyst. The zinc oxide was in its wurtzitic crystal modification as in most laboratory as well as industrial catalysts, was free of surface impurities, and had a morphology shown in Fig. 4. Details of the pore structure of this catalyst are given in reference (38). 

Two crystal modifications yellow, low temperature fern, face-centered cubic symmetry red, high-temperature fotra, tetragonal symmetry. Darkens in color on healing, chocolate brown at sublimation temp of 885. Dec into the dements at 5(X> under vacuum slowly reduced to the metal in hydrogen at 200. Heat of formation 30 kcal/mole. Sol in aq solns of ammonium carbonate, phosphoric acid. 

Elemental silicon does not occur free in nature rather it is found as silicon dioxide (sometimes called silica Si02) and in an enormous variety of silicate minerals. In contrast to the oxides of carbon, which are volatile molecular species held together by London forces in the solid state, Si02 forms very stable, nonvolatile, three-dimensional network crystals. One of the three crystal modifications of SiOj has a lattice that may be considered to be derived from the diamond lattice, with silicon atoms replacing carbon atoms and an oxygen atom midway between each pair of them. 

Similar to other polyesters, PLA displays crystal polymorphism and four different crystal modifications have been identified so far, named a-, P-, y-, and e-forms. The a-form of PLA grows upon melt- or cold-crystallization, as well as from solution [18-25]. Hot-drawn, melt-spun, or solution-spun PLA fibers of a high-draw ratio show the P-form [21-23]. The y-form is obtained via epitaxial crystallization on hexamethylbenzene substrate [24] and the s-modification is a crystalline complex formed below room temperature in the presence of specific organic solvents such as tetrahydrofuran and Af,Af-dimethylformamide [25]. Besides these four main crystal polymorphs, two disordered modifications of the a-form, named a and a , were recently proposed for PLA. The a -crystals grow via melt- or cold-crystallization below 110 °C [21, 26-29], whereas the a"-form develops upon crystallization under special processing conditions, below the glass transition temperature and in the presence of carbon dioxide [30]. 

Calcium carbonate exists in three crystal modifications, aragonite, calcite and vaterite, but only the calcite form is of real importance. Because of calcite s perfect rhombohedral cleavage, it is a soft mineral with a Mohs hardness of 3.0. It has a specific gravity of 2.7 and is birefringent having refractive indices of 1.65 and 1.48. 

Figure 1.3 Carbon crystallizing in two different modifications - as graphite and as diamond -having different lattice arrangements.

Because of the high ceramic volume fraction, the mechanical properties of the shells are mainly determined by those of the ceramic. The ceramic component is aragonite, a rhombic crystal modification of calcium carbonate CaCOa, forming prismatic crystals. Young s modulus of aragonite is approximately 100 GPa, its fracture toughness is rather low, with a value of about 0.5 MPai/in. 

The structure and properties of biofibers, mainly of cellulose, were described in this chapter. First, the hierarchy microstructure of natural plant fiber and then a variety of crystal modifications of cellulose were mentioned. The ultimate mechanical properties (modulus of 138 GPa and strength of 17.8 GPa) and thermal properties (thermal expansion coefficient of 10 order) were emphasized as quite excellent for cellulosic fiber, enough for use as reinforcement in the composites. With the manifestation of these intrinsic properties in macroscopic material, the oH-cellulose composite was shown to possess excellent mechanical properties, thermal resistance, and optical transparency, besides being composed of fully sustainable resources and hence, biodegradable. Nowadays, the interest in cellulosic nanocomposites has increased considerably [60, 61] and they are expected to be used in many fields such as electronic devices, vehicles, and windmills to replace glass and/or carbon fibers. 

Antimony Trioxide. Antimony(III) oxide (antimony sesquioxide) [1309-64-4] Sb203, is dimorphic, existing in an orthorhombic modification valentinite [1317-98-2] is colorless (sp gr 5.67) and exists in a cubic form and senarmontite [12412-52-17, Sb O, is also colorless (sp gr 5.2). The cubic modification is stable at temperatures below 570°C and consists of discrete Sb O molecules. The molecule is similar to that of P40 and As O and consists of a bowed tetrahedron having antimony atoms at each corner united by oxygen atoms lying in front of the edges. This solid crystallizes in a diamond lattice with an Sb O molecule at each carbon position. 

Methylfurfural may be prepared by a modification of this method, which is more rapid but gives lower yiddsd A solution of 800 g. of sucrose in i 1. of hot water is allowed to flow slowly into a boiling solution of 500 g. of stannous chloride crystals, 2 kg. of sodium chloride, and 4 1. of 12 per cent sulfuric acid in a 12-I. flask. The aldehyde distils ofl as rapidly as it is formed and is steam-distilled from the original distillate after rendering it alkaline witlr sodium carbonate. The product is isolated by benzene extraction of the second distillate and distillation under reduced pressure. The yield is 27-35 g- (10-13 per cent of the theoretical amount). 

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