Triclinic

Dielectric properties Thermal expansion coefficient Pyroelectric properties 

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Figure C2.3.3. Molecular packing of SDS monohydrate viewed as projected on the ac plane. This polymoriDh crystallizes in a triclinic cell with unit cell constants a, b and c of 10.423 A, 5.662 A and 28.913 A, respectively, and with a = 86.70°, (3 = 93.44°, y = 89.55°. There are four molecules per unit cell. Adapted from figure 2 of [18].

Triclinic Rhombohedral Three unequal axes intersecting obliquely Two equal axes making equal angle with each other No planes or axes of symmetry a b c y 90°... 

The racemic acid is not a primary product of plant processes but is formed readily from the dextrorotatory acid by heating alone or with strong alkaU or strong acid. The methods by which such racemic compounds can be separated into the optically active modifications were devised by Pasteur and were apphed first to the racemic acid. Racemic acid crystallizes as the dihydrate triclinic prisms. It becomes anhydrous on drying at 110°C... 

Iodine is a bluish black, crystalline soHd having a metallic luster. It is obtained in shiny flakes or prills that can be easily cmshed to powder. Iodine crystallines in rhomboidal plates belonging to the triclinic system. 

Sodium metaniob ate (1 1) [67211-31-8] Na20 Nb20 7H20 or Na2Nb20g-7H20, separates as colorless triclinic crystals as a result of concentrating the mother Hquor from the preparation of the 7 6 sodium niobate by spontaneous evaporation. It also can be obtained by fusion of the anhydrous pentoxide in sodium hydroxide or carbonate. 

Elemental composition, ionic charge, and oxidation state are the dominant considerations in inorganic nomenclature. Coimectivity, ie, which atoms are linked by bonds to which other atoms, has not generally been considered to be important, and indeed, in some types of compounds, such as cluster compounds, it caimot be appHed unambiguously. However, when it is necessary to indicate coimectivity, itaUcized symbols for the connected atoms are used, as in trioxodinitrate(A/,A/), O2N—NO . The nomenclature that has been presented appHes to isolated molecules (or ions). Eor substances in the soHd state, which may have more than one crystal stmcture, with individual connectivities, two devices are used. The name of a mineral that exemplifies a particular crystal stmcture, eg, mtile or perovskite, may be appended. Alternatively, the crystal stmcture symmetry, eg, rhombic or triclinic, may be cited, or the stmcture may be stated in a phrase, eg, face-centered cubic. 

Besides the amorphous red P which is a commercial product, there are perhaps five other crystalline or poorly crystalline red modifications that are not produced commercially. These include a triclinic, an orthorhombic, a high temperature form, and two poorly crystalline forms. Red phosphoms varieties are rather stable in air and are of lower reactivity than white phosphoms. 

Properties of PET Molding Resins. The fliU crystal stmcture of poly(ethylene terephthalate) has been estabhshed by x-ray diffraction (134—137). It forms triclinic crystals with one polymer chain per unit cell. The original cell parameters were estabhshed in 1954 (134) and numerous groups have re-examined it over the years. Cell parameters are a = 0.444 nm, b = 0.591 nm, and c = 1.067 nm a = 100°, (3 = 117°, and 7 = 112° and density = 1.52 g/cm. One difficulty is determining when crystallinity is fliUy developed. PET has been aimealed at up to 290°C for 2 years (137). 

Physical Properties of PBT. Unlike PET, the polymer PBT exists in two polymorphs called the a- and p-forms, which have distinctly different crystal stmctures. The two forms are interconvertible under mechanical stress (158,159). Both crystal forms are triclinic and the crystal parameters are shown in Table 7. 

The acid occurs both as colorless triclinic prisms (a-form) and as monoclinic prisms ( 3-form) (8). The P-form is triboluminescent and is stable up to 137°C the a-form is stable above this temperature. Both forms dissolve in water, alcohol, diethyl ether, glacial acetic acid, anhydrous glycerol, acetone, and various aqueous mixtures of the last two solvents. Succinic acid sublimes with partial dehydration to the anhydride when heated near its melting point. 

The most common form of calcium thiosulfate is the hexahydrate [10035-02-6] CaS202 6H20, which has triclinic crystals and a density of 1.872 g/cm at 16°C (84). Heating, however, does not give the anhydrous salt because of decomposition at 80°C. At lower temperatures, dehydration stops at the monohydrate [15091-91-5]. The solubiUty of calcium thiosulfates in water is as follows ... 

As mentioned above, uranium trioxide exists in six weU-defined modifications with colors ranging from yeUow to brick-red. Of these phases, the y-phase has been found to be the most stable, however, other phases, especially a and 3, are also frequently used and studied. The stmcture of the a-modification is based on sheets of hexagons, whereas the 3-, y-, and 8-modifications contain an infinite framework. AH of these topologies have been fliUy described (105,106). They are a-brown, hexagonal 3-orange, monoclinic y-yeUow, rhombic 5-red, cubic S-brick red, triclinic and Tj-rhombic. 

Sohd uranium—phosphate complexes have been reported for the IV and VI oxidation states, as well as for compounds containing mixed oxidation states of U(IV) and U(VI). Only a few sohd state stmctures of U(IV) phosphates have been reported, including the metaphosphate U(P03)4, the pyrophosphate U(P202), and the orthophosphate, CaU(PO4)2. The crystal stmcture of orthorhombic CaU(POis similar to anhydrite (194). Compounds of the general formula MU2(PO4)3 have been reported for M = Li, Na, and K, but could not be obtained with the larger Rb and Cs ions (195). In the sohd state, uranium(IV) forms the triclinic metaphosphate, U(P03)4. Each uranium atom is eight-coordinate with square antiprismatic UOg units bridged by... 

Forms of Boric Acid. Orthoboric acid, B(OH)3, formula wt, 61.83, crystaUi2es from aqueous solutions as white, waxy plates that are triclinic ia nature sp gi 4, 1.5172. Its normal melting poiat is 170.9°C, however, when heated slowly it loses water to form metaboric acid, HBO2, formula wt, 43.82, which may exist ia one of three crystal modifications. Orthorhombic HBO2-III or a-form d = 1.784 g/mL, mp = 176° C) forms first around 130°C and gradually changes to monoclinic HBO2-II or P-form (d = 2.045 g/mL, mp = 200.9° C). Water-vapor pressures associated with these decompositions foUow. To convert kPa to mm Hg, multiply by 7.5. 

Sodium Metaborate Tetrahydrate. Sodium metaborate tetrahydrate, NaB02 4H2O or Na20 B2O3 -8H20 formula wt, 137.86 triclinic sp gr, 1.743 is easily formed by cooling a solution containing borax and an amount of sodium hydroxide just in excess of the theoretical value. It is the stable... 

Sodium perborate tnhydrate, NaBO 3H2O or Na2B2(02)2(0H)4 4H2O, triclinic, contains 11.8 wt % active oxygen (96). It has been claimed to have better thermal stabiUty than the tetrahydrate but has not been used commercially. The tnhydrate can be made by dehydration of the tetrahydrate or by crystallization from a sodium metaborate and hydrogen peroxide solution in the present of tnhydrate seeds. Between 18 and 50°C the tnhydrate is more stable but slower to crystallize than the tetrahydrate. Below 15°C the tnhydrate is spontaneously converted into the tetrahydrate. 

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