Calcium aluminate glasses

Navrotsky A., Peraudeau G, McMillan R, and Coutures J. P. (1982). A thermochemical study of glasses and crystals along the joins silica-calcium aluminate and silica-sodium alumi-nate. Geochim. Cosmochim. Acta, 46 2039-2047. 

Figure 39 Illustration of a possible lanthanum phosphate-calcium aluminate glass structure for lower LaP04 content in calcium aluminate, derived from Raman and NMR data. For clarity, only a segment of the network is portrayed, with some oxygen atoms removed from the diagram. Taken from Ref. [168].

Several other anhydrous calcium aluminosilicates are known, including grossular or garnet (C3AS3), which is a high-pressure phase, various dehydration products of zeolites, and various products formed metastably by crystallization from melts or glasses. Most are too acid in composition to be of clear relevance to cement chemistry, but some of the devitrification products, especially those with compositions near to CA and structures similar to those of nepheline (Na3KAl4Si40i6) or kalsilite (KAlSiOj (Y4), are of possible interest in relation to the formation of calcium aluminate cements. 

Mylius (M60) described the preparation of many calcium aluminate hydrates and related compounds. As with C-S-H, it is normally essential to exclude atmospheric CO2 and to avoid prolonged contact with glass apparatus. Dosch and Keller (D20) described methods for obtaining many AFm phases by anion exchange or other special procedures. 

Other types of admixtures used with calcium aluminate cements include water reducers and superplasticizers (Section 11.4), which also act as retarders, and thickening agents, such as carboxymethylcellulose. Complex formulations may be used for special purposes for example, a ready-mix mortar for high-performance road repair might contain 55% Ciment Fondu and 45% sand, with glass fibre, aluminium powder, Li2C03, sodium gluconate and methyl ethyl cellulose (M93). 

P.F. McMillan, B. Piriou, and A. Navrotsky, A Raman spectroscopic study of glasses along the join silica-calcium aluminate, silica-sodium aluminate, and silica-potassium aluminate. Geochim. Cosmochim. Acta 46, pp. 2021-2037 (1982). 

Carlson, K. and Hall, M.. Streaming potential measurements performed on silicate and calcium aluminate glass microspheres, Colloids Surf. A, 325, 101. 2008. 

Glasses and ceramics based on the Al203-based systems have important applications as ceramic materials, optical materials, and biomedical materials. Aluminate materials include alkaline earth aluminates, such as those in the CaO-A Cf system, which are refractory cousins of hydrous Portland cement [1-3]. Calcium aluminates have a role as both traditional ceramic and cement materials and are used for example as refractory cements however, calcium aluminates are also important for more novel applications... 

Neutron and combined neutron and X-ray diffraction data for 64 36 and 50 50 calcium aluminate glasses [40, 48] have been used to determine Al-0 and Ca-0 coordination... 

Calcium aluminate glasses can be made quite easily by air quenching liquids of 61 39 composition, which is the composition most extensively used for glass fiber production [20, 44], The glass-forming ability is considerably enhanced by adding components such as BaO, SrO, and NaO [21] without affecting the optical performance. 

W.A. King, and J.E. Shelby, Strontium calcium aluminate glasses. Phys. Cltem. Glasses 37(1), 1-3 (1996). 

C.J. Benmore, et al., A neutron and x-ray diffraction study of calcium aluminate glasses. J. Phys. Conden Matter 15(31), S2413-S2423 (2003). 

M.S.F. Da Rocha, et al., Radiation-induced defects in calcium aluminate glasses. Radiat. Eff. Defects Solids 158(1-6), 363-368 (2003). 

RJ. Magabhai, and F. Glasses (eds.), Calcium Aluminate Cements, Proc. Int. Symposium on Calcium Aluminate Cements, Edinburgh, Scotland, Maney Publications, UK, luly 2001. 

Ceramics used in fabricating implants can be classified as nonabsorbable (relatively inert), bioactive or surface reactive (semi-inert) [Hench, 1991,1993] and biodegradable or resorbable (non-inert) [Hentrich et al., 1971 Graves et al., 1972]. Alumina, zirconia, silicone nitrides, and carbons are inert bioceramics. Certain glass ceramics and dense hydroxyapatites are semi-inert (bioreactive) and calcium phosphates and calcium aluminates are resorbable ceramics [Park and Lakes, 1992]. 

The overall glass composition is by far the most important factor in controlling the batch-free time. Simple oxide mixtures, such as those used to produce calcium aluminate glasses, often form eutectic mixtures which melt directly with very short batch-free times. Many non-silicate melts are very fluid at any temperature above the melting point of their components and rapidly dissolve all batch particles. Borate, phosphate, and germanate melts can be formed at much lower temperatures than are typically required for silicate melts. As a result, it is usually easier to decrease their viscosity by increases in temperature, e.g., an increase in temperature from 1000 to 1200 C is more easily attained than an increase from 1400 to 1600 C. 

Navrotsky, A., Persudeau, G., McMillan, P. and Courtures, J. P. (1982) A Thermodynamic Study of Glasses and Crystals Along the Joins Silica-Calcium Aluminate... 

However, Kondo [3 ] is of the opinion that the hydrolysis of the glass in water occurs and the calcium ions are released initially to the liquid phase. Simultaneously on the surface of slag grains an acid, colloidal shell of silica-alumina gel is formed. This shell has low permeability and hence the further slag reaction with water is hindered. In the presence of Ca(OH)2, added as alkaline activator, the siUcon and aluminum from the shell are released to the solution (Fig. 8.2). The solubiUty of aluminum compounds becomes considerably increased in the solution of pH higher than 12.5 because in this condition the Al(OH) ions are formed [4]. The concentration of aluminum in the liquid phase is increasing because the calcium aluminates crystallize a httle later, primarily the C-S-H (1) is formed. Simultaneously the solubility of hydrates formed in this condition is reduced. 

Due to the absence of Ca(OH)2 in the calcium aluminate cement paste a higher durabiUty of glass fibers was expected in fiber reinforced composites. Majumdar [26] proved that the calcium aluminate cement composites had much better mechanical properties, but only the case of alkali resistant glass. 

Glass fiber reinforced systems made with calcium aluminate cements... 

This calcium aluminate fiber was evaluated in structural applications but it was not suitable for the evaluation of infrared optical properties because it contained bound water as evidenced by a strong hydroxyl band at 29 jjm in the IR transmission spectra. Hydroxyl-free compositions were made in carbon crucibles [17] by the Davy process [39], i.e., by a procedure [40] by which disposable optical calcium aluminate bulk glasses are prepared for commercial applications in optical windows. 

Quaternary calcium aluminate glass fibers were also downdrawn from preforms on a laboratory [9] and a development unit [41], Downdrawing is a valid, but costly, method for fiberizing fragile melts. In addition, only one of >500 compositions could be fiberized on a conventional melt fiberizing unit [17], This process is not suitable for fragile melts. 

Quaternary calcium aluminate glass fibers made by updrawing from a supercooled fragile melt offer superior mechanical properties and sapphire-like infrared transmission spectra. 

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