Stuffed silicas

Silica polymorph Stuffed silica structure Reference... 

The substitution of aluminum for silicon in a silica covalent network leads to a charge unbalance, which must be compensated by extra-framework cations, mostly alkaline. This occurs in the cases of the so-called stuffed silicas these materials have structures strictly related to the crystalline forms of silica, but with cations in the interstices to counterbalance the presence of A1 ions substituting for Si. This is the case, for example, of Eucriptite (LaAlSi04, a stuffed /3-quartz) or nepheline (NaAlSiOa, a stuffed tridymite). A similar mechanism also occurs in the amorphous networks of glasses [175]. 

Bmno E, Pentinghaus H (1974) Substitution of cations in natural and synthetic feldspars. In MacKenzie WS, Zussmarm, J (eds) The Feldspars. Manchester Uitiv Press, Manchester, p 574-609 Buerger MJ (1951) Crystallographic aspects of phase transformations. In Smoluchowski R (ed) Phase Transformations in Solids. Wiley, New York, p 183-211 Buerger MJ (1954) The stuffed derivatives of the silica stiuctures. Am Mineral 39 600-614 Bulenda M, Schwabl F, Tauber UC (1996) Defect-induced condensation and the central peak at elastic phase transitions. Phys Rev B 54 6210-6221... 

Palmer DC (1994) Stuffed derivatives of the silica polymorphs. Rev Mineral 29 83-122 Palmer DC, Bismayer U, Salje EKH (1990) Phase transitions in leucite order parameter behavior and the Landau potential deduced from Raman spectroscopy and birefringence studies. Phys Chem Minerals 17 259-265... 

Stuffing box Pfaudler high-duty type with bronze sleeve Chlorine diffuser 1-in. silica tube with twenty-five M in. tangential jets Gaskets Corning Type R-3... 

In addition to LLE, the two other major types of analyte isolation and recovery are sohd-phase extraction (SPE) and supercritical fluid extraction (SEE) extraction. SPE refers to those techniques that isolate the analyte from a sample matrix and partition the analytes of interest onto a chemically bonded silica surface. SEE refers to those techniques that isolate the analyte from a sample matrix and partition it into a liquid that has been heated and pressurized beyond its critical temperature and pressure. It is indeed overly simpHstic to think that a striped bass can be stuffed into a GC as a means to conduct TEQA ... 

Mg " increases the thermal expansion behavior (Strnad 1986). For example, the thermal expansion of stuffed P-quartz at the cordierite stoichiometry (Mg2Al4Si50jg) from 25°-870°C averages 47.2 X 10-7 K K The three cations Mg7, and Zn " can therefore be used to tailor a thermal expansion coefficient very close to zero or, indeed, any value between —50 X 10 7 and +50 X 10 7 over a wide range of silica contents. 

Because of this isotypical relationship of the berlinite modification of AlPQi to quartz, the question now arises Have stuffed derivatives been observed in AlPQj-based crystals as they have been in silica quartz At this... 

Palmer D.C., "Stuffed Derivatives of the Polymorphs" pp. 83-122 in Silica, Physical Behavior, Geochemistry and Materials Applications. Edited by P.J. Heaney, C.T. Prewitt, and G.V. Gibbs. Mineral Society Of America, Washington D.C., 1994. 

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