The structural characteristics of amorphous silicas

Zulumyan, N. H.; Isaakyan, A. R.; Pirumyan, P. A.; Beglaryan, H. A.

doi:10.1134/s003602441004031x

Cited by 16 publications

(3 citation statements)

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“…On the other hand, strengthening of unsatur ated Si-O bonds in siloxane bridges formed under low temperature conditions occurs within the same temperature range of (950-1050°C) [15,16]. For this reason, in our view, when the rock is heated within this temperature range, simultaneous dehydration and talc crystal lattice destruction are accompanied by strengthening of unsaturated Si-O bonds and the for mation of enstatite.…”

Section: Resultsmentioning

confidence: 68%

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The influence of mechanical treatment on the silicate network of talc

Zulumyan

Papakhchyan

Isahakyan

et al. 2012

Russ. J. Phys. Chem.

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INTRODUCTIONIt is known that, the most usual paragenetic talc forms finally produced in the process most often called steatitization are hydrothermally changed ultrabasic minerals and silica dolomites that underwent low stage thermal metamorphism [1]. It was found for many occurrences that steatitization, which follows serpentization, is a result of silicization and carboniza tion of serpentines or the transfer of СО 2 into them [1, p. 151; 2, p. 8]. It is therefore quite natural that, when these processes occur, silicate networks of serpentines, largely unchanged, become the anionic component of talc crystalline structure. Therefore, the peculiarities revealed in serpentines [3] should to a certain degree be inherent in talc.Serpentine peculiarities are first of all Si-O bonds with unusual strengths present in "hexagonal" rings of SiO 4 tetrahedra in silicate networks [3]. If siloxane bridges are formed at comparatively low temperatures (below 500°C), the bonds which form in them are inferior in strength to Si-O bonds of metasilicate chains passed into the silicate layer from primary ultrabasic minerals. Just the presence of such Si-O bonds which differ in electronic saturation in silicate networks of minerals causes their destruction under mechanical treatments (mechanoactivation) and also upon heating, when, starting from 400°C, the dehy dration of serpentines is accompanied by the destruc tion of their crystal lattices [3][4][5][6][7][8]. The degree and character of the destruction of silicate networks which result in different ratios between isolated ortho , oligo , and polysilicate components formed depends on both the ratio between primary ortho and metasil icate anions, which participated in the formation of serpentine silicate networks, and their distribution in silicate layers [9]. Note also the direct role played by hydroxyls, because the breakage of weak Si-O bonds is closely related to the detachment and formation of hydroxyl water [3].The talc silicate network is mainly borrowed from serpentine (Mg 6 [Si 4 O 10 ](OH) 8 ). It is therefore quite natural that the above reasoning concerning the spe cial features of serpentine silicate networks with cer tain restrictions imposed by the structure of talc (Mg 3 [Si 4 O 10 ](OH) 2 ) relates to talc silicate networks. It follows that it is quite reasonable to study the influence of mechanical treatment on talc silicate networks using the physicochemical approach applied to ser pentinites [3]. The results can be compared with the data on serpentinites.In view of this, the purpose of this work was to per form a physicochemical study of thermally treated and mechanically activated talc and quantitatively deter mine magnesium, silicon, etc. compounds extracted from thermally treated and mechanically activated samples using a new approach to acid treatment of ser pentinized minerals [10,11]. EXPERIMENTALWe performed chemical analysis of two different talc samples, Russian (I) and Taiwan (II). Their chem ical composition is given in Table 1.For mechanical activat...

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Section: Resultsmentioning

confidence: 68%

“…compounds extracted from thermally treated and mechanically activated samples using a new approach to acid treatment of ser pentinized minerals [10,11].…”

Section: Introductionmentioning

confidence: 99%

The influence of mechanical treatment on the silicate network of talc

Zulumyan

Papakhchyan

Isahakyan

et al. 2012

Russ. J. Phys. Chem.

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“…However, a new approach to the acid treatment of thermally treated serpentines (Mg(Fe)) 6 [Si 4 O 10 ](OH) 8 made it possible to obtain amorphous silica that strongly differs in its specifi c structural features from the known conventional forms of SiO 2 and can signifi cantly simplify the process of obtaining β-wollastonite [18,19].…”

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confidence: 99%

Synthesis of β-wollastonite on the basis of silica formed from silicate layers of serpentine

et al. 2015

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Two-stage method for synthesis of β-wollastonite via reaction of calcium hydroxide and silica formed from silicate layers of serpentine and calcination of the resulting compounds was examined. It was found that the specifi c structural features of the silica used for this purpose make it possible to avoid a many hours' autoclave treatment and obtain such amorphous calcium hydro-and hydroxo-silicates that are converted under annealing, beginning at 800-810°C, to β-wollastonite by mixing a suspension of Ca(OH) 2 , SiO 2 , and H 2 O heated to its boiling point under atmospheric pressure. The optimal synthesis parameters, molar ratio of the starting substances and agitation duration, are determined.

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