Non-aqueous cements

The low permittivity of these liquids compared with water inhibits dissociation of the acids so that cement formation demands much more reactive basic oxides. Oxides and hydroxides that are capable of cement formation are ZnO, CuO, MgO, CaO, Ca(OH)2, BaO, CdO, HgO, PbO and BiaOj (Brauer, White Moshonas, 1958 Nielsen, 1963). In practice these are confined to two calcium hydroxide and special reactive forms of zinc oxide. 

Examples of liquid organic acids suitable for cement formation are  

These examples are drawn from the work of Brauer, White Moshonas (1958), Nielsen (1963), Brauer, Argentar Durany (1964), Stansbury, Argentar Brauer (1981), and Brauer, Argentar Stansbury (1982). 

Related to these cements are the long chain aliphatic acids and aryl-substituted butyric acid (Skinner, Molnar Suarez, 1964). These materials are on the market as non-eugenol cementing agents but they are unduly 

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Generally, cement-forming liquids are aqueous solutions of inorganic or organic adds. These adds include phosphoric add, multifunctional carboxylic adds, phenolic bodies and certain metal halides and sulphates (Table 2.1). There are also non-aqueous cement-forming liqtiids which are multidentate acids with the ability to form complexes. 

This concept covers most situations in the theory of AB cements. Cements based on aqueous solutions of phosphoric acid and poly(acrylic acid), and non-aqueous cements based on eugenol, alike fall within this definition. However, the theory does not, unfortunately, recognize salt formation as a criterion of an acid-base reaction, and the matrices of AB cements are conveniently described as salts. It is also uncertain whether it covers the metal oxide/metal halide or sulphate cements. Bare cations are not recognized as acids in the Bronsted-Lowry theory, but hydrated... 

The Arrhenius definition is not suitable for AB cements for several reasons. It cannot be applied to zinc oxide eugenol cements, for these are non-aqueous, nor to the metal oxychloride and oxysulphate cements, where the acid component is not a protonic acid. Indeed, the theory is, strictly speaking, not applicable at all to AB cements where the base is not a water-soluble hydroxide but either an insoluble oxide or a silicate. 

The use of ISEs in non-aqueous media(for a survey see [125,128]) is limited to electrodes with solid or glassy membranes. Even here there are further limitations connected with membrane material dissolution as a result of complexation by the solvent and damage to the membrane matrix or to the cement between the membrane and the electrode body. Silver halide electrodes have been used in methanol, ethanol, n-propanol, /so-propanol and other aliphatic alcohols, dimethylformamide, acetic acid and mixtures with water [40, 81, 121, 128]. The slope of the ISE potential dependence on the logarithm of the activity decreases with decreasing dielectric constant of the medium. With the fluoride ISE, the theoretical slope was found in ethanol-water mixtures [95] and in dimethylsulphoxide [23], and with PbS ISE in alcohols, their mixtures with water, dioxan and dimethylsulphoxide [134]. The standard Gibbs energies for the transfer of ions from water into these media were also determined [27, 30] using ISEs in non-aqueous media. 

In 1996, OxyVac was used at a cement products manufacturing site in Salt Lake City, Utah, to treat 6400 to 14,000 yd of soil and sediment contaminated with VOCs. Groundwater and light non-aqueous-phase liquids (LNAPLs) were also treated to a depth of 7 to 15 ft in an area of 25,000 sft. Total costs at this site were 230,000 (D10341T, p. 16 D215751, pp. 13, 14). 

Costa cl al. (C58) showed that superplasticizers increase the fluidity of C,S pastes much as they do that of cement pastes. Studies on individual anhydrous and hydrated compounds in aqueous and non-aqueous media indicate that calcium lignosulphonate and superplasticizers are adsorbed by C -S-H, AFm phases or CH but not by C,S, C,A or C,AH (R54, R55,R56,C58,M 105), though they appear to be taken up by unhydrated P-CiS (C59). The admixtures also enter interlayer sites of C4AF1. and perhaps also of C -S--H (R55). Intercalation of organic molecules in C4AH, is a well-established effect (Section 6.1.1),... 

Pre-mixed products are the easiest to use because they do not require any mixing and any transfer into an appropriate delivery system. Moreover, there is no time constraint to use the product once it is open. However, pre-mixing is not a versatile approach to deliver a product, since the mixture composition is already pre-defmed. Moreover, it is not adapted to CPC formulations. Presently, only two methods have been proposed to package ready-to-use cement formulations. First, the reactive cement components are combined with a non-aqueous liquid to form a non-reactive pasty mixture. Reaction then occurs in vivo, when the non-aqueous hquid is slowly replaced with physiological fluids. Unfortunately, the setting reaction is difficult to control and the mechanical properties are poor." The second approach is to freeze down the cement components." However, it is not clear how injectable such mixtures would be and how the... 

Both sodium silicate and silico fluoride solutions are applied to clean, dry, sound concrete floors as dilute aqueous solutions (10-15 per cent solids) in two to three applications, taking care to ensure that all material penetrates and is absorbed into the concrete surface. The silicate or silico fluoride reacts with the small amount of free lime in the cement to form glassy inert materials in the surface, and the successful application of both materials depends upon filling the micropores in the surface of good-quality concrete, leaving its surface appearance and non-skid characteristics virtually unchanged. 

Oxysalt bonded cements are formed by acid-base reactions between a metal oxide in powdered solid form and aqueous solutions of metal chloride or sulphate. These reactions typically give rise to non-homo-geneous materials containing a number of phases, some of which are crystalline and have been well-characterized by the technique of X-ray diffraction. The structures of the components of these cements and the phase relationships which exist between them are complex. However, as will be described in the succeeding parts of this chapter, in many cases there is enough knowledge about these cements to enable their properties and limitations to be generally understood. 

PE has a non-polar, nonporous, and inert surface. For this reason, adhesives cannot link chemically or mechanically to untreated PE surfaces. Although PE is relatively inert to most solvents, solvent cementing cannot be used. For bonding to itself or to other materials, an adhesive with a suitable surface preparation method must be used. There are a number of surface treatment techniques in use, including chemical, electronic, flame, and primer methods. Oxidation treatments are the most successful. These include immersion in a chromic-acid solution, exposure to corona discharge, flame oxidation, immersion in an aqueous solution of chlorine, or exposure to chlorine gas in the presence of ultraviolet light. The chromic acid oxidation method is probably the most convenient for use with molded plastic parts of diverse contour. 

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