Chemical durability of the iron-containing sodium borosilicate glasses

Novel Inorganic Membranes Based on Magnetite-Containing Silica Porous Glasses for Ultrafiltration: Structure and Sorption Properties

“…The error in determining the D * values did not exceed ±0.7 × 10 −7 cm 2 /s. As noted previously [ 42 ], due to the absence of a metastable immiscibility diagram for the Na 2 O-B 2 O 3 -SiO 2 -Fe 2 O 3 system, and consequently, the lack of knowledge of the position of immiscibility isotherms and tie-lines, it is currently impossible to determine the compositions and volumes of coexisting phases, the density, C 1 , and the surface area of the chemically unstable boron-rich phase occupied on the sample surface. Therefore, the C 1 , composition, and density values for the whole glass were used in calculations.…”

“…However, the experimental values are somewhat lower (about 80–90%) compared to the theoretically possible ones since boron ions can be partially located in the silica phase or due to their precipitation in pores. Similarly to iron-containing glasses containing 70 mol% SiO 2 [ 42 , 73 ], the dependences of the component extraction rate ( Q = f (√ t )) for Na 2 O, B 2 O 3 , and Fe 2 O 3 for the investigated glasses with lower concentrations of SiO 2 were linear up until the values of Q exp /S 0 reached a plateau close to Q calc /S 0 ( Figure 3 ). SiO 2 practically does not get extracted from the glass into the acid-leaching solution due to the resistance of siloxane bonds in the silica-rich phase to acidic solutions and because of the polymerization and gelation processes of so-called secondary silica inside the leached glass layer [ 74 ].…”

“…The chemical durability and leaching kinetics were studied by leaching polished plates of phase-separated glasses with the size of 10 × 10 × 1 mm 3 in an aqueous 3M HCl solution at boiling according to the procedure described in great detail in [ 42 ]. To evaluate the extraction leaching rate and the kinetics of the components (Na 2 O, B 2 O 3 , SiO 2 , Fe 2 O 3 ) from the chemically unstable boron-rich phase of the glass during acid treatment (for 5 h), aliquots (15 mL) were taken 15, 30 min, 1, 2, 3, 4, and 5 h after placing the glass samples in boiling acid, to measure the concentrations of the components in the leaching solution.…”

“…The effective diffusion coefficients of Na, B, and Fe were calculated according to Equation (1), as described in detail in [ 42 ]: D * = π Q 2 /(4 C 1 2 t ), where D * is the effective diffusion coefficient (cm 2 /s); Q = Q exp / S 0 (gram atom/cm 2 ); C 1 —volumetric concentration of the component in glass (gram-atom/cm 3 ) calculated from the composition (wt%) and the glass density (g/cm 3 ); t is the time of leaching (s). The error in determining the D * values did not exceed ±0.7 × 10 −7 cm 2 /s.…”

“…However, impregnating PGs with iron oxides [ 25 ] is not the only way to obtain an inorganic membrane with magnetic properties. The introduction of Fe 2 O 3 into the NBS glass batch containing 70 mol% SiO 2 before melting was established to cause magnetite crystallization, which has ferrimagnetic properties [ 41 , 42 , 43 , 44 , 45 ]. Magnetite-containing PGs were used as a host matrix for multiferroic composite materials obtained by impregnating the pore space with ferroelectric phases [ 46 , 47 , 48 ].…”