Hydrofluoric acid, 99 crystal structure

The optimal calcination method for zeolite beta was established by thermogravimetric analysis using a PL-Thermal Sciences STA 1500 apparatus. Chemical compositions of the zeolites were determined by atomic absorption spectroscopy on a Varian AAIO spectrometer after dissolution of the samples in hydrofluoric acid. The structure was confirmed by x-ray diffraction on a Siemens D-5000 diffractometer and with infrared spectroscopy on a Mattson Instruments Galaxy 2000 spectrometer. Total surface area, micropore area and micropore volume of the samples were determined by argon adsorption on a Micromeritics ASAP 200M volumetric analyzer using standard techniques. Crystal diameters were determined by scanning electron microscopy. 

White, loose powder. M.p. 2530"C d 29. Very sparingly soluble in water (about 0.20 g. per liter). Its solubility in acids depends i ion the calcination temperature dissolves most readily in hydrofluoric acid. Crystallizes in structure type B4. 

These two metals are not attacked by mineral acids (with the exception of hydrofluoric) they are readily soluble in a mixture of concentrated hydrofluoric and nitric acids. Crystal structure A 2 (W) type. 

Figure 17.4 The phase diagrams of the systems (a) HF/H2O and (b) HCI/H2O. Note that for hydrofluoric acid all the solvates contain >1HF per H2O, whereas for hydrochloric acid they contain <1HC1 per H2O. This is because the H bonds F-H F and F-H O are stronger than O-H O, whereas C1-H---C1 and C1-H---0 are weaker than 0-H---0. Accordingly the solvates in the former system have the crystal structures [HsOJ+F , [H30]+[HF2] and [H30] [H3F4], whereas the latter are [H30]+C1 , [H502]" C1 and [H502]" CP. H2O. The structures of HCI.6H2O and the metastable HCI.4H2O are not known.

In 1976, an X-ray powder diffraction analysis of a substance obtained from Te02, dissolved in concentrated hydrofluoric acid, was performed (96). The orthorhombic crystals had the composition H2Te203F4. The structure was shown to be characterized by... 

Exists in two adotropic modifications. Crystalline sihcon is made up of grayish-black lustrous needle-hke crystals or octahedral platelets cubic structure Amorphous sdicon is a brown powder. Other physical properties are density 2.33g/cm3 at 25°C melts at 1,414°C high purity liquid silicon has density 2.533 g/cm at its melting point vaporizes at 3,265°C vapor pressure 0.76 torr at 2,067°C Mohs hardness 6.5. Brinell hardness 250 poor conductor of electricity dielectiric constant 13 critical temperature 4°C calculated critical pressure 530 atm magnetic susceptibility (containing 0.085%Fe) 0.13x10 insoluble in water dissolves in hydrofluoric acid or a mixture of hydrofluoric and nitric acids soluble in molten alkalies. 

White, heavy, amorphous powder or monoclinic crystals refractive index 2.13 density 5.68 g/cm Mohs hardness 6.5 transforms to tetragonal structure above 1,100°C and cubic form above 1,900°C melts at 2,710°C and vaporizes at about 4,300°C insoluble in water soluble in hydrofluoric acid and hot sulfuric, nitric and hydrochloric acids. 

Atomic weight 50.95. Light-gray metal, ductile when pure. M.p. 1900°C d 6.11. Insoluble in hydrochloric and sulfuric acids, soluble in nitric and hydrofluoric acids. High affinity for O, N, C and H. Surface reactionwith atmospheric Og starts already at 20°C this can lead, particularly in the case of a fine powder, to considerable contamination. Crystal structure type Ag. 

The results of microstructure studies on microsections etched for 0.5 to 1.0 min with hydrofluoric acid or a mixture of hydrofluoric and nitric acids (Fig. 1), clearly indicate that alloys containing 47.13 0.13 wt.% Si (by analysis) have a typically single-phase structure. However, in slow directional crystallization in a weak tenqierature gradient, followed by drastic... 

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