L. N. Pivovarova

Formation of Mg3Si2O5(OH)4 Nanotubes under Hydrothermal Conditions

The formation of nanotubes of magnesium hydrosilicate Mg3Si2O5(OH)4 with a chrysotile structure is investigated. It is found that the nanotubes of magnesium hydrosilicate Mg3Si2O5(OH)4 are formed through different mechanisms depending on the initial state of reactants, the composition of the hydrothermal solution, and temperature. It is shown that the rate of formation of nanotubes is determined by the stability of intermediate compounds, the chemical composition of the reaction mixture, and the synthesis temperature.

Hydrothermal synthesis of nanotubes based on (Mg,Fe,Co,Ni)3Si2O5(OH)4 hydrosilicates

Hydrosilicate nanotubes of the variable composition (Mg,Fe,Co,Ni)3Si2O5(OH)4 with a chrysotile structure have been synthesized under hydrothermal conditions at temperatures of 250–450°C and pressures of 30–100 MPa in media of different compositions. The conditions and ranges of formation of nanotubular hydrosilicates of the compositions under investigation have been determined. It has been demonstrated that the type of cation of the octahedral layer in the chrysotile structure has a decisive effect on the physicochemical conditions, mechanism, and rate of formation of nanotubes, as well as on their structure, morphology, and sizes.

Hydrothermal synthesis of nanotubular Mg-Fe hydrosilicate

Magnesium iron hydrosilicate nanotubes with a chrysotile ((Mg,Fe)3Si2O5(OH)4) structure have been synthesized hydrothermally at t = 250–450°C and p = 30–100 MPa. In the hydrothermal synthesis of (Mg,Fe)3Si2O5(OH)4 chrysotile, part of the Fe2+ ions oxidize to Fe3+ and are incorporated into the octahedron and tetrahedron layers of the chrysotile structure. The limiting iron content of chrysotile has been determined up to which cylindrically rolled layers can form to yield nanotubes. The hydrothermal treatment of precursors richer in FeO yields platelike hydrosilicates. The iron ions present in the starting components affect the synthesis parameters, morphology, size, optical properties, and thermal stability of the nanotubes.

Influence of the physicochemical parameters of synthesis on the growth of nanotubes of the Mg3Si2O5(OH)4 composition under hydrothermal conditions

The growth of nanotubes of the Mg3Si2O5(OH)4 composition with a chrysotile structure has been investigated under hydrothermal conditions. It has been established that the nanotubes in the axial and radial directions grow through the step mechanism due to the recrystallization and mass transfer of the components. The introduction of seeds considerably promotes the growth process, especially at the nanotube ends. The evolution of chrysotile nanotubes with a variation in different physicochemical parameters of synthesis, such as the temperature, time, NaOH concentration in the reaction medium, and introduction of seeds, has been traced. It has been demonstrated that the controllable variation in these parameters makes it possible to perform a controlled hydrothermal synthesis of chrysotile nanotubes with specified lengths and aspect ratios.

Hydrothermal synthesis of nanotubular Co-Mg hydrosilicates with the chrysotile structure

Nanotubes of the chrysotile structure were obtained under hydrothermal conditions in the series of hydrosilicates of the Mg3Si2O5(OH)4-Co3Si2O5(OH)4 system. Substitution of cobalt ions for magnesium ions affects the conditions of formation, morphology, and size of the nanotubes. The formation of nanotubes on hydrothermal treatment of the starting mixtures of cobalt metasilicate and magnesium, cobalt, and, silicon oxides and hydroxides occurs in stages, and the stage of nanotube formation is always preceded by the formation of a lammellar structure.

Synthesis and growth of nanotubes Mg3Si2O5(OH,F)4 composition under hydrothermal conditions

Nanotubes of magnesium hydrosilicate Mg3Si2O5 (OH, F)4 having the structure of chrysotile and increased thermostability in comparison with hydroxyl-chrysotile were synthesized under hydrothermal conditions at temperatures of 300–450°C and pressure of 30–100 MPa from mixtures of oxides of magnesium and silicon with the use NaF and NaOH as mineralizers. The conditions of the synthesis of the chrysotile nanotubes with varying content of fluorine (0.4–4.0 wt %) in the composition of chrysotile were determinated. The effect of the physical-chemical parameters of the synthesis on the growth of the OH-F-chrysotile tubes was tracked. The core role of concentration of F-containing mineralizer was shown.

Aromatic polyamidoimides modified with hydrosilicate nanoparticles of different structure and morphology for membrane technologies

New organic–inorganic composites based on aromatic polyamidoimide with ribbon-like particles of fibrous triple chain Na2Mg4Si6O16(OH)2 hydrosilicate have been obtained with the subsequent characterization of their structure, morphology, and transport properties. A comparative analysis of polyimide composites with ribbon-like Na2Mg4Si6O16(OH)2 hydrosilicates and tubular Mg3Si2O5(OH)4 hydrosilicate nanoparticles has been implemented.

Effect of temperature on the synthesis of nanoparticles with different morphology in the system MgO–SiO2–TiO2–H2O under hydrothermal conditions

Nanoparticles with different morphology have been obtained by hydrothermal method in the system MgO–SiO2–TiO2–H2O. It has been found that in the investigated temperature–time interval the formation of nanotubes of hydrosilicate with the structure of chrysotile with a small amount of impurity phases predominantly takes place.

Thermochemical modification of Mg3Si2O5(OH)4 hydrosilicate nanotubes by silver nitrate solutions

The interaction of an aqueous solution of silver nitrate with Mg3Si2O5(OH)4 hydrosilicate nanotubes under atmospheric conditions at 50 and 80°C and under dynamic conditions with subsequent annealing at 300°C has been investigated. The intercalation of AgNO3 solutions into the internal channel and interlayer spaces of the nanotube structure and the crystallization of the silver particles of the spherical shapes on the nanotube surface have been established.