Magnesium substitution

Clays are composed of extremely fine particles of clay minerals which are layer-type aluminum siUcates containing stmctural hydroxyl groups. In some clays, iron or magnesium substitutes for aluminum in the lattice, and alkahes and alkaline earths may be essential constituents in others. Clays may also contain varying amounts of nonclay minerals such as quart2 [14808-60-7] calcite [13397-26-7] feldspar [68476-25-5] and pyrite [1309-36-0]. Clay particles generally give well-defined x-ray diffraction patterns from which the mineral composition can readily be deterrnined. 

Sverjensky DA, Shock EL, Helgeson HC (1997) Prediction of flie thermodynamic properties of aqueous metal complexes to 1000°C and 5 kb. Geochim Cosmochim Acta 61 1359-1412 Tarutani T, Clayton RN, Mayeda TK (1969) The effect of polymorphism and magnesium substitution on oxygen isotope fractionation between calcium carbonate and water. Geochim Cosmochim Acta 33 987-996... 

Florisil Mg03Si Polar adsorbent Florisil is a magnesium-substituted silica with a highly polar surface typically has a relatively large particle size (approximately 200 pm), and therefore high flow rates are possible even with viscous samples used with many official methods, and in cases where the Lewis acidity of alumina would be problematic... 

Similar approaches were applied for studying the crystallisation of magnesium-substituted A1PO of type-36 (MgAPO-36).188From the obtained data, it was apparent that there exist two types of microstructural region in which five types of P(nAl) (n = 2-4) units could be identified. A three-stage mechanism of crystallisation was proposed. 

Feldstedt M, Boesgaard S, Bouchelouche P, Svenningsen A, Brooks L, Lech Y, Aldershvile J, Skagen K, Godtfredsen J. Magnesium substitution in acute ischaemic heart syndromes. Eur Heart J 1991 12(11) 1215-18. 

A range of magnesium-substituted calcites is also formed. 

In this reaction, 6.5 wt.% hydrogen can be reversibly stored with potential storage up to 10 wt.%. However, the current operating temperature is outside of the vehicular operating window. On the other hand, the temperature of this reaction can be lowered to 220°C with magnesium substitution. 

Studies of this type have shown that incorporation of magnesium into the CHA aluminophosphate structure can be random, within the Af site. In the aluminophosphate form of sodalite, (AlPO-20) magnesium substitutes in an ordered way for aluminium, and Barrie and Klinowski interpret the observed P NMR intensities in terms of an ordered distribution where there are never two magnesium cations in the same 4MR. ... 

Among the other mieroporous solid acids, SAPOs and MAPOs tend to possess acidities that are weaker than those found for aluminosilicates. Not all substituted aluminophosphates are weak acids, however. Magnesium-substituted AIPO4-36, for example, gives a strong performance in acid catalysed alkane cracking. " ... 

Carrodeguas RG, De Aza AH, TurriUas X, Pena P, De Aza S. New approach to the beta-alpha polymorphic transformation in magnesium-substituted tricalcium phosphate and its practical impUcations. J Am Ceram Soc. 2008 91(4) 1281-6. 

Electrostatic potential (EP), electric field (EF), and electric field gradient (EFG) values were calcirlated in periodic models of magnesium-substituted phillipsite forms using periodic DFT [08L1]. The EP was interpreted in terms of framework ionicity. In siliceous zeolites, the angular Si-O-Si dependence of the O EFG asymmetry was also discussed. 

Based on observed tissue response, synthetic bone-graft substitutes can be classified into inert (e.g., alumina, zirconia), bioactive (e.g., hydroxyapatite, bioactive glass), and resorbable substitutes (e.g., tricalcium phosphate, calcium sulfate). Of these, resorbable bone-graft substitutes are preferred for bone defect filling because they can be replaced by new natural bone after implantation, p-tricalcium phosphate (Ca3(PO )2, p-TCP) is one of the most widely used bone substitute material, due to its faster dissolution characteristics. Preparation of magnesium-substituted tricalcium phosphate ((Ca, Mg)3(PO )2, p-TCMP) has been reported by precipitation or hydrolysis method in solution. These results indicate that the presence of Mg stabilizes the p-TCP structure (LeGeros et al., 2004). The incorporation of Mg also increases the transition temperature from p-TCP to a-TCP and decreases the solubility of p-TCP (Elliott, 1994 Ando, 1958). 

Lilley, K. J., Gbureck, U., Knowles, J. C., Farrar, D. F., and Barralet, J. E. 2005. Cement from magnesium substituted hydroxyapatite. Journal of Materials Science Materials in Medicine 16 455-60. 

Suchanek, W., Byrappa, K., Shuk, P., Riman, R., (anas, V. and TenHuisen, K. (2004) Preparation of magnesium-substituted hydroxyapatite powders by the medianochemical-hydrothermal method. Biomaterials, 25, 4647-57. 

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