Structural characteristics of pyrocarbon-fumed silica

Influence of morphology and composition of fumed oxides on changes in their structural and adsorptive characteristics on hydrothermal treatment in steam phase at different temperatures

“…(1) and a modified regularization procedure [35] under a nonnegativity condition (f (R p ) 0 at any R p ) for a fixed regularization parameter α = 0.01 using a model of cylindrical pores at R p > 0.7 nm and slit-like pores (gaps between adjacent primary particles) at 0.2 nm < R p < 0.7 nm. This hybrid model of pores gives the PSDs close to that calculated for a model of gaps between spherical particles [36][37][38][39]. However, application of this model to fumed oxides after HTT is questionable, since the type of primary particle linkage changes depending on HTT conditions.…”

“…Thus, changes in the primary particle size distributions and their random packing in the secondary structures may contribute this scatter. For instance, lower hydration of the nonstandard initial fumed silicas described previously [22][23][24][25][26][36][37][38][39] may correspond to lower coordination numbers (N c = 2-3) of primary particles in aggregates [1] (i.e., two to three particles adjacent to a given one) that reduces capillary condensation of water in "two-dimensional" aggregates in comparison with that for "three-dimensional" (i.e., denser) aggregates characterized by greater N c = 4-5. Notice that such aggregates characterized by different N c values were observed experimentally by TEM and SEM methods [19,20,[22][23][24][25][26]56,57].…”

“…As a whole fumed oxides before and after HTT can be assigned to "mesoporous" materials, since the main PSD peaks lie at R p > 10 nm, and the contribution of micropores at R p < 1 nm is very low. Mesopores at R p be- tween 1 and 5 nm can be assigned to relatively narrow gaps between adjacent primary particles in aggregates [22][23][24][25][26][36][37][38][39], and HTT leads to filling and plugging of these gaps (as well as micropores) due to reactions with grafted (mobile) Si(OH) 4 …”

“…5-8) caused by enhancement of particle aggregation (with the formation of three-dimensional secondary particles, which are denser at a smaller size of primary particles (see Figs. 12e and 12f)) [19,20,[36][37][38][39]56,57]. This displacement is greater for initial samples because of larger differences between their S BET values (30-409 m 2 /g), since the maximal S BET value af- ter HTT is less by a factor of 2.5-3.…”

Effect of preparation conditions of carbon–silica adsorbents based on mesoporous silica gel Si-100 and carbonised glucose on their pore structure

“…Glucose was deposited in the amounts of 0.01, 0.03, and 0.05 mol/10 g portions of Si-100. To this end, the mixture of the aqueous glucose solution and silica gel was shortly ultrasonicated, then the solvent was evaporated in a vacuum evaporator at 330-345 K. The prepared samples were carbonised under dynamic conditions using the flow rotary reactor [15] or in the high-pressure autoclave. The pyrolysis was carried out in the rotary reactor in the nitrogen atmosphere fed at the rate of 100 ml/min using following temperature program: heating from 293 to 773 K for 2 h, isothermal heating at 773 K for 5 h; and then cooling to room temperature for 1 h. The initial silica gel Si-100 was heated in the same conditions, giving adsorbent Si-100T.…”