Peroxy Silicates

The only mention by Vail (1) of peroxide structures in relation to silicates is the stabilizing effect of sodium silicate in combination with magnesium silicate in stabilizing peroxide bleaching baths, probably by adsorbing and inactivating traces of catalytically active metals such as copper. 

Hydrogen peroxide is useful as a blowing agent, along with MgO and paraformaldehyde, in making low density foams from a solution of sodium silicate (216). 

Soluble Silicates (ACS Monograph Series), Vols. 1 and 2, Reinhold, New York, (1952). 

Anders (Selas Corp., Dresher, Pa.), Proc. Fall Meeting, Material Equipment White Wares Diva., Amer. Ceram. Soc, 1970, p. 94. 

Truhlarova and O. Veprek, Sb. Vys. Sk. Chem. Technol. Praze, Anorg. Chem. Technol., 13, 89 (1969) [Chem. Abstr., 73, 123152r] Clastech. Ber., 40 (7), 257 (1967) [Chem. Abstr., 67, 102416r]. 

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Solid Peroxygen Compounds. Hydrogen peroxide reacts with many compounds, such as borates, carbonates, pyrophosphates, sulfates, silicates, and a variety of oiganic carboxylic acids, esters, and anhydrides to give peroxy compounds or peroxyhydrates. A number of these compounds are stable solids that hydrolyze readily to give hydrogen peroxide in solution. 

O dimers may appropriately be called peroxy anions, 022 . In a silicate matrix they appear to occur as peroxy links or, more generally, peroxy entities, X/00 Y where X,Y = Si4+,A13+, Fe3+... Chemically a peroxy entity represents an extra oxygen it may be called an interstitial oxygen atom though this does not correctly convey the covalent binding in the 0-0 bond. 

The point to retain is that, according to eqs. (2a/b), peroxy may derive from traces of dissolved "water" (JLl). Since traces of "water" are ubiquitous in oxide and silicate... 

Peroxy entities may indeed represent an ubiquitous type of defects in oxides and silicates, both natural and synthetic. The reason is that traces of dissolved "water" are everywhere. In optical waveguide fibers made of low-OH fused silica a dramatic increase of Si-OH and attendant loss of transmittance have been reported upon exposure to H2 probably by way of the reaction Si/°° Si + H2 2 Si-OH (15,35). ... 

Other catalysts investigated include Cu, Cr and Ce silicates, with t-BuOOH as the oxidant. The conversion achieved, however, is generally lower than 5% under the conditions investigated [27c-fj. A high activity was instead obtained with Cr-MCM-41 [27g], with HP in an acetic acid solvent in this case, peroxy acetic acid also had a role in reaction acceleration. 

H2 is generated in a solid-state reaction within silicate minerals that have incorporated trace water impurities, typically as -OH, into their lattice during formation. As the rock cools, formation of peroxy linkages from -OH impurities... 

The peroxy spedes occurs both in silica and aluminium silicates as a lattice defect, the particular structure of which is determined by the conditions of synthesis and post-synthetic history of the materials. One of the typical treatments imdergone by these materials, both in industrial applications and often in the laboratory, is calcination in an oxidising atmosphere. An interaction with extra oxygen, as postulated in the literature [59], should result in the following reactions ... 

In our recent work employing a PW91/DNP periodic model based on the siliceous sodalite as a host material, we have studied these reactions by calculating the energy minimum defect configurations and proposed a number of alternative routes leading to the formation and transformation of the peroxy species [76] cf. other theoretical work [77-79]). 

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