Ammonium silicate

Under salts, el cetera, are included malic acid and gum, nitrogenous "subatanoes, fatty matters, aromatic substances, coloring matters, essential oil, chlorophyle, malamide, oxalate and phosphate of lime, phosphata of magnesia, chloride of, ammonium, silicate, nitrate, sulphate, and oxalate of potassa oxalate of soda, chlorides of sodium and potassium, peetates and pectinates of... 

SILICATES (Soluble). The most common and commercially used soluble silicates are those of sodium and potassium. Soluble silicates are systems containing varying proportions of an alkali metal or quaternary ammonium ion and silica. The soluble silicates can be produced over a wide range of stoichiometric and nonstoicluometric composition and are distinguished by the ratio of silica to alkali. This ratio is generally expressed as the weight percent ratio of silica to alkali-metal oxide (SiOj/MjO). Particularly with lithium and quaternary ammonium silicates, the molar ratio is used. 

It is possible to obtain such silicates as solids by evaporation to dryness of the organic quaternary ammonium silicate aqueous solutions. In this case, however, the process is very slow and accordingly a problem of impurity incorporation arises. It was reported that silicate solids consisting of the double four-membered ring structure were abruptly separated out after an exothermal reaction on stirring the mixture of (2-hydroxyethyl)trimethylammonium hydroxide aqueous solution and tetraethoxysilane (26). 

In the first section of this paper, formation of silicate species with cage-like structures in organic quaternary ammonium silicate solutions are reviewed. In the last section, the process of the rapid selective formation of the silicate solids having the... 

Effect of Temperature. The temperature of a silicate solution also affects the polymerization of silicate anions in the solution. The distribution of silicate anions in an organic quaternary ammonium silicate solution at a fixed N/Si ratio and SiC concentration varies with the temperature of the solution (7,8,13,14,16). Ray and Plaisted (8) reported the temperature dependence of the distribution of silicate anions in the tetramethylammonium silicate aqueous solution at a N/Si ratio of 2/3 and a SiC>2 concentration of 1.0 mol dm. The amount of the cubic octamer in the solution decreases with increasing temperature, and the cubic octamer practically disappears above 50 °C, indicating that the cubic octamer is unstable at higher temperatures. However, Groenen et al. (14) found that the cubic octamer remained in a significant concentration even at 85 °C, which was close to the temperature of actual zeolite formation, in the tetramethylammonium silicate aqueous solution at a N/Si ratio of 1.0 and a Si02 concentration of 1.3 mol dm-. ... 

Rapid Solidification of Organic Quaternary Ammonium Silicates... 

In this section, the results of our study on the rapid solidification of organic quaternary ammonium silicates are presented. 

Inorganic zinc-rich primers consist of zinc and a reactive binder such as an alkali metal silicate (sodium, potassium, lithium or quaternary ammonium silicate) or hydrolyzed ethyl silicate as binder. On mixing hard and cohesive films of silicate are formed. The structure of the inorganic zinc-rich silicate may appear as shown in Figure 1.66. 

Ammonium silicate.—No ammonium salt of silicic acid has been isolated.16 Experiments on the electrical conductivity of solutions of silicic acid in aqueous ammonia indicate the probability of the formation of a true ammonium silicate in solution.17... 

Korneev, Agafonov, and co-workers (Technological Institute and Pigment Science Industrial Association, both in Leningrad) (116, 117) synthesized aqueous solutions of systems that have high modulus and low alkalinity and are based on silicates of quaternary ammonia (SQA). The decomposition of SQA took place at —190 °C. The calcined product of SQA has amorphous and crystalline phases. Aqueous solutions of quaternary ammonium silicates can be used as binders they are not flammable, explosive, or toxic. 

Foreign cations were added to the powder according to the incipient wetness method from nitrate salts for Mg2+, Y3+, and A13+, and from tetraethyl ammonium silicate for Si. A subsequent washing with water was achieved in order to eliminate nitrates from the powder surface. The residual concentration in nitrates was lower than 0.015 at %. The samples were then calcined at 723 K in the ambiant air for four hours. Final concentrations of the foreign cations added were fixed equal to 0.5, 1.0, 2.0 and 10.0 at %. 

This type of silica is made first as a crystalline quaternary ammonium silicate, for example, tetrapropylammonium silicate (TPA) O-485102 H 0. It is then heated to red heat to remove the organic matter and water, leaving uniform cylindrical channels throughout the three-dimensional crystalline framework of silica. 

Since silica dissolves above about pH 10.7-11.0, silicates can be prepared with organic bases having dissociation constants greater than about 10 , although some silica will dissolve in aqueous solutions of weaker bases with constants as low as lO" or 10" (123-125). Merrill and Spencer (124) reported the preparation of a number of water-soluble quaternary ammonium silicates by grinding silica gel with a solution of the free base. However, the compounds all appear to have a ratio of 2 1 when expressed as SiOj (NR )jO by analogy with the alkali metal system. 

Some of the available quaternary ammonium silicates have been listed by Weldes and Lange (19), although the nature of the ion was not disclosed. Molar ratios of Si0j (NR4)20 range from 1,2 1 to 30 1 and silica contents of the solutions from 10 to 45%. Hydrated amorphous powders are also listed with ratios of 15.6 1 and 19.7 1. These dissolve rapidly in water and are remarkably soluble in mixtures of water and water-miscible organic solvents such as acetone and the lower alcohols. 

Reference also should be made here to the unique, highly siliceous crystalline zeolite-like insoluble quaternary ammonium silicates from which the organic ions can be removed, leaving anhydrous, hydrophobic, microcrystallinc SiOj of an entirely new type discovered and described by Flanigen and Grose (see Chapter 1, refs. 71c, 7Id). 

It is possible that with a quaternary ammonium base and in the absence of metal cations, aluminosilicate anions may remain in solution, for example, (HO)aSiOAl(OH)20Si(OH)3 . Flanigen (69b) reported that quaternary ammonium silicate and aluminale remained in solution until a sodium salt was added. 

Improved bond strength in ceramic bodies is attained with mixtures of monoaluminum phosphate and colloidal silica when used with finely divided refractory powders of zircon, zirconia, or alumina (480). The reaction of P,0, with silica at relatively low temperature develops high bond strength in refractory compositions thus silica sol may be mixed with ammonium phosphate or other P,Os precursors at relatively low pH and used in minimal quantities as a binder in refractories (481,482). According to Lee, the binding properties of colloidal silica are improved by adding a soluble quaternary ammonium silicate such as tetramethylammonium silicate which is sufficiently alkaline to interact with the colloidal silica and cdhlesce it in a cement structure (483). 

Inorganic paint for asbestos board can be made with silica as a binder. Hard, weather-resistant paint is made with a combination of colloidal silica, lithium hydroxide and potassium silicate or alkali metal phosphate, clay, and pigment, and baked on in the presence of steam (629). Collidal silica stabilized with tetraethanol ammonium silicate was used as a binder for iron oxide and clay pigments (630). A heatproof coating for asbestos or metals consisted of colloidal silica and magnesium hydrogen phosphate (631) and was hardened at 200 C. 

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