RU2540754C1 - Method of producing high-silica porous glass with magnetic properties - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: composition of basic alkali-borosilicate glass includes Fe₂O₃ and FeO in amount of 20 wt % with respect to Fe₂O₃. The glass is heat-treated at 550°C for 130-150 hours. After heat treatment, the biphase alkali-borosilicate glass is held in a 3 M solution of inorganic acids at 50-100÷C and washed in distilled water, followed by combined drying in air at 20-120°C. The glass has pore volume of 0.2-0.6 cm³/cm³.

EFFECT: obtaining porous glass in the form of solid articles with thickness of 0,1-2 mm with crystallite size of 5-20 nm.

4 cl, 7 dwg, 1 tbl

Description

The invention relates to the technology of porous high-silica glasses and can be used in the manufacture of nanoporous matrices in the form of massive articles (plates, disks) with magnetic properties due to the presence of the magnetic phase Fe ₃ O ₄ (magnetite) in the glass, which can be used as blanks for creating new nanocomposite semiconductor and dielectric materials for microelectronics.

To assess the novelty and technical level of the claimed solution, we consider a number of technical means known to the applicant for a similar purpose, characterized by a combination of features similar to the claimed invention, known from the information that became public until the priority date of the invention.

A known method of manufacturing porous glass by composing a charge, introducing a reducing agent into the charge, melting glass and forming a glass tape, characterized in that the glass tape is formed on a molten metal, and a mixture of aluminum metal and graphite powders in an amount of 0.44- is introduced as a reducing agent 1.2 wt.% With a ratio of aluminum and graphite equal to 1: (0.1-1), see RF patent No. 2172303.

Known methods for producing high silica porous glasses with pore sizes of the nanometer range, described, for example, in AC SU No. 1304339, No. 1544737, 1779674, which consist in the fact that alkaline borosilicate glass with a two-frame structure formed as a result of metastable segregation during heat treatment of glass, treated in acid solutions, washed in water and dried. So, for example, in the method according to A.S. No. 1779674 high-silica porous glass is obtained by heat treatment of alkali-borosilicate glass and etching in 0.1-5 M hydrochloric acid solutions, while etching is continued with exposure to ultrasonic vibrations with an amplitude of 3-15 to increase the leaching rate after exposure to acid for 5-20 hours ApoR, where ApoR is the amplitude of oscillations corresponding to the threshold of cavitation. In order to optimize the regime, the oscillation amplitude of the emitter is determined by the maximum rise of the solution in a glass capillary placed vertically in a working container with a solution of hydrochloric acid. The method allows to speed up the leaching process by 2-5 times.

However, porous glasses obtained by these technologies, although they have parameters of the porous structure close to those required, do not possess magnetic properties, since they do not contain a magnetic phase.

A known method of manufacturing porous magnetic glasses and crystal according to US patent No. 4395271, which includes the preparation of a sample, which during heat treatment is separated into at least two vitreous phases and at least one crystalline phase, and then subjected to etching, leaving a structure that contains magnetic crystals especially suitable for use in biological analyzes.

Closest to the claimed technical solution is a method for producing porous glasses with magnetic properties according to US patent No. 4233169. According to this method, the initial glass (basic compositions, wt.%: 3-15 Na ₂ O and / or K ₂ O; 10-25 Fe ₂ O ₃ ; 10-40 B ₂ O ₃ and 34-70% SiO ₂ without / with the addition of 0-10 Al ₂ O ₃ , 0-10 CaO, 0-5 MnO, 0-5 CdO, 0-3 Li ₂ O, 0-5 PbO, 0-5 MgO, 0-3 P ₂ O ₅ , 0-10 ZnO, 0-5 NiO, 0-5 CoO, 0-3 Cr ₂ O ₃ , 0-3 V ₂ O ₃ , 0-3 MoO ₃ , 0-5 TiO ₂ and 0-5 ZrO ₂ ) are synthesized according to the method of cooking from a mixture in the air for 16 hours at 1400-1650 ° C, followed by annealing and one-stage heat treatment at 500 ° C for 69 hours, at 600 ° C for 60 hours or two-stage heat treatment at 700 ° C for 4 h and 600 ° C for 60 h for phase separation. The ground samples in the form of powders (the predominant fraction size is ≤2.4 microns) are treated in a 0.5-3.0 N HNO ₃ solution for 1 ÷ 3 h at 95-100 ° C, washed several times with water with stirring and with magnetic separation between washes. Then the glass powder is treated in a 0.5 ÷ 1.25 N NaOH solution for 0.5 ÷ 1.25 hours at 20 ÷ 50 ° C, washed in water to a pH below 8 with magnetic separation between washes. There was thus obtained vysokokremnezemnyh porous material which has a porosity of 0.14 ÷ 0.75 cm ³ / cm ^3, an average pore radius of 17.5 ÷ 210 nm, and may have a coercive force (Hc = 16 ÷ 304 Oe) due to the presence of iron crystallite size of ≤ (50 ÷ 100 ) nm. Such material is used in biochemical analysis to immobilize biological components.

This analogue is inherent in the set of features closest to the set of essential features of the invention, and therefore this known technical solution is selected as a prototype of the claimed invention.

A significant disadvantage of the prototype, which does not allow us to solve the problem posed by us, is that porous glass is obtained in the form of powder, which limits the possibility of its practical use, for example, in microelectronics. This disadvantage, firstly, is due to the specific problem solved by the prototype, which consists in creating a powdery material for immobilization of biological material suspended in a liquid. Secondly, the duration of heat treatment of the base glass used in the prototype at temperatures of 550 ÷ 600 ° C is insufficient to induce a two-frame structure necessary to obtain surviving porous glasses in the form of massive products, as well as to form the required magnetic phase.

The aim of the invention is to provide porous glasses in the form of bulk products (plates, disks) with a thickness of 0.1 ÷ 2 mm containing the magnetic phase Fe ₃ O ₄ with optimal crystallite sizes (5 ÷ 20) nm, while maintaining a pore volume of 0.2 ÷ 0.6 cm ³ / cm ³ and an average pore diameter of 5 ÷ 60 nm.

The essence of the claimed invention as a technical solution is expressed in the following set of essential features, sufficient to achieve the above technical result provided by the invention

A method of obtaining porous high-silica glass with magnetic properties, having a pore volume of 0.2 ÷ 0.6 cm ³ / cm ³ and an average pore diameter of 5 ÷ 60 nm, by heat treatment of alkali borosilicate glass, exposure of two-phase glass in a 3M solution of mineral acids at a temperature of 50 ÷ 100 ° C, multi-stage washing in distilled water and combined drying in air at temperatures of 20 ÷ 120 ° C, characterized in that Fe ₂ O ₃ and FeO are introduced into the base alkaline borosilicate glass in an amount of 20 wt.% in terms of Fe ₂ O ₃ and other they heat it at 550 ° C for 130-150 hours.

This is the totality of essential features that provides a technical result in all cases to which the requested amount of legal protection applies.

In addition, the claimed technical solution is characterized by the presence of a number of additional optional features, namely:

- HCl is used as a mineral acid;

- HNO _{3 is} used as a mineral acid;

- after exposure of two-phase glass in a 3 M solution of mineral acids, intermediate additional exposure is carried out in a 0.5 M KOH solution at 20 ° C for 0.5-6 hours, depending on the thickness of the sample.

The technical result achieved by using the claimed method is to provide the possibility of obtaining surviving samples with given pore sizes and the formation of optimal magnetic clusters in them, for which two factors are included in the claimed method: introduction of glass (Fe ₂ O ₃ + FeO) and an increase in the duration of heat treatment of glass at 550 ° C for the time required to achieve phase equilibrium (≥130 h).

The invention is illustrated by illustrative materials, where figure 1 shows dilatometric curves of samples of two-phase glass, heat-treated at 550 ° C for 70 (1) and 144 (2) hours, figure 2 - electron microscopic photographs of samples of two-phase glass, after heat treatment at 550 ° C for 70 (a) and 144 (b) hours, in Fig.3 - x-ray patterns of samples of two-phase glass, after heat treatment at 550 ° C for 70 (a) and 144 (b) hours, in Fig. .4 - radiographs of samples of biphasic alkali borosilicate glasses that have passed heat treatment at 550 ° C for 144 hours, with different iron contents in terms of Fe ₂ O ₃ , wt.%: 15 - 1; 20 - 2; 25 - 3. The numbering of the glasses corresponds to the numbering in Table 1, in Fig. 5 electron microscopic photographs of samples of porous glasses: MIP (a) and MAP (b) obtained from biphasic glass preforms that underwent heat treatment at 550 ° C for 144 hours , Fig.6 - the distribution of pore sizes in samples of porous glasses (L = 0.5 mm): MIP (a) and MAP (b) obtained from biphasic glass preforms that underwent heat treatment at 550 ° C for 144 hours, Fig. .7 - X-ray diffraction patterns of porous MIP (1) and MAP (2) glasses in comparison with the initial two-phase glass that passed t Heat treatment at 550 ° C for 144 hours (3). L = 0.5 mm.

The method is as follows.

The initial iron-containing alkali-borosilicate glass composition (by synthesis, mol.%): 5 Na ₂ O, 15 V ₂ O ₃ , 60 SiO ₂ , 20 Fe ₂ O _{3 are} synthesized by cooking from a charge in an electric silica furnace in air at temperatures of 1540-1560 ° C in a platinum crucible with periodic mechanical mixing of the melt with a platinum stirrer at a speed of 50-60 rpm The total cooking time is 10 hours; the total melt mixing time is 5 hours.

The initial reagents for the preparation of the mixture are:

Anhydrous silicic acid (or quartz sand) - chemical grade;

Boric acid - chemical grade;

Sodium carbonate - chemical grade;

Iron oxide III - chemically pure

At the end of cooking, the melt is cast onto a metal plate heated to 60-80 ° C. After casting, the glass is annealed: after a short isothermal exposure (10-15 minutes) in an electric muffle in air at 600 ° C, the glass is cooled to room temperature at a rate of 3 deg./min.

Then, special heat treatment of the annealed glass is carried out - isothermal exposure at a temperature of 550 ° C for 130-150 hours in order to obtain two-phase glass with interpenetrating phases, one of which is chemically unstable. The phase structure parameters in heat-treated glass are monitored using transmission electron microscopy using an EM-125 instrument.

In the claimed method, the time of heat treatment of glass (130-150 hours) exceeds the time of heat treatment (~ 70 hours) used at this temperature in the closest to the claimed technical solution method for producing porous glasses with magnetic properties according to US patent No. 4233169. The increase in the time of heat treatment of glass to 130-150 hours ensures the achievement of phase equilibrium (Figure 1), as well as the formation of the crystalline phase of magnetite in a significantly larger amount than during processing for 70 hours, and the formation of an optimal size nanostructure of magnetite inclusions (~ 8 nm), which is confirmed by the data obtained using methods of transmission electron microscopy (TEM) (Figure 2) and x-ray phase analysis (XRD) (Figure 3). This heat treatment mode makes it possible subsequently to obtain surviving samples of porous glasses in the form of plates during chemical etching of two-phase glass, in contrast to the powders obtained in US Pat. No. 4,233,169.

Figure 1 shows that 70-hour heat treatment is not enough to achieve equilibrium phase separation. Dilatometric data show that heat treatment for 70 hours leads to a partial phase separation, but with an increase in the exposure time, a further segregation process proceeds. This is evidenced by the fact that the glass transition temperature of the low-melting phase T _g increases from T _g = 465 ° C during a 70-hour heat treatment to T _g = 495 ° C with an increase in the heat treatment time to 144 hours.

In the latter case, on the dilatometric curve at 590 ° C, the second glass transition temperature of the refractory phase is observed, which is evidence of the formation of two interpenetrating structures in the glass, which is confirmed by TEM data (Figure 2).

Figure 2 shows that an increase in the duration of heat treatment of glass contributes to the formation of a pronounced two-frame structure in heat-treated glass formed by interpenetrating silica and chemically unstable alkaline borate phases with a uniform distribution of uniformly sized inclusions of the iron-containing phase, the total volume of which is greater than with less prolonged heat treatment glass.

This is confirmed by the XRD data (Figure 3), according to which smaller samples of magnetite are formed in samples of glass subjected to heat treatment for a longer time (D = 8 nm). In this case, the value of S, equal to the product of the half-width of the main peak and its height, proportional to the magnetite content, increases with an increase in the duration of heat treatment of glass by about 1.5 times.

The iron content (20 wt.% In terms of Fe ₂ O ₃ ) in the base glass containing 50-60 wt.% SiO ₂ is optimal from the point of view of the formation of the magnetite phase in it during heat treatment at 550 ° C for 130- 150 hours. This conclusion is illustrated by Figure 4, which presents a comparison of x-ray diffraction patterns of several biphasic iron-containing glasses, the compositions of which are shown in Table 1. The results of particle size estimation of Fe ₃ O ₄ according to XRD are also shown in Table 1.

Table 1 Compositions of iron-containing alkali-borosilicate glasses and particle sizes of magnetite, the phase of which is formed as a result of heat treatment of glasses at 550 ° C for 130-150 hours The composition of the glass for the synthesis, wt.% The particle size of magnetite (the main peak), nm Fe ₂ O ₃ SiO ₂ B ₂ O ₃ Na ₂ O one 25 fifty twenty 5 thirty 2 twenty 60 fifteen 5 8 3 fifteen 60 twenty 5 fifteen

From Figure 4 and Table 1 it can be seen that in a glass of the claimed composition with 20 wt.% Fe ₂ O ₃ (Glass 2) an optimum magnetite phase is formed in terms of particle size and volume compared to glasses with a smaller (15 wt.%) And large ( 25 wt.%) Content of Fe ₂ O ₃ . In a glass with 15 wt.% Fe ₂ O ₃ (Glass 1), the magnetite phase content is lower than in Glass 2, as evidenced by the smaller width of the main peak (at an angle of 2θ = 35 degrees) with a similar scattering intensity, and the dimensions particles are much larger. In a glass with 25 wt.% Fe ₂ O ₃ (Glass 3), the content of the magnetite phase is greater, as evidenced by the high intensity of the main peak at an angle of 2θ = 35 degrees. (4), and the particle size of Fe ₃ O ₄ is substantially greater. This is accompanied by bulk crystallization of biphasic glass and leads to its destruction during further chemical etching, which does not allow to obtain porous glass in the form of a massive sample (plate).

After special heat treatment of glass, two-phase glass blocks are cut on an electric saw with a diamond wheel into blanks (in the form of plane-parallel plates) of a given size, their grinding and polishing.

Then, polished billets of two-phase glasses are chemically processed to obtain porous glasses with different pore structure parameters (the so-called microporous (MIP) and macroporous (MAP) glasses) in accordance with the procedure, which consists in sequential through etching of the glass first in aqueous 0.5-4 M a solution of mineral acid (HCl, HNO ₃ ) at boiling (MIP glass) and then in an aqueous 0.1-0.5 KOH solution at room temperature (MAP glass).

Chemical etching is used for chemical etching of two-phase alkaline borosilicate glasses:

Hydrochloric acid - analytical grade;

Nitric acid - analytical grade;

Distilled water (bidistilled);

Potassium hydroxide - analytical grade

The ratio of the surface area S _{0 of the} samples to the volume of the etching solution V should be not less than S ₀ / V = 0.02 cm ^-1 . The duration of the chemical treatment of glass in these etching solutions is based on the kinetics of the chemical etching of glass in acid-salt and alkaline solutions, which is controlled using an MIN-8 optical microscope and is determined by the thickness of the plate (L).

For example, at L = 0.5-2 mm, the processing time of biphasic glass in an aqueous 3 M solution of mineral acid during boiling to obtain MIP glass is 2-8 hours, the time of additional processing of MIP glass in 0.5 M KOH solution at 20 ° C to obtain MAP glass is 1-6 hours.

During chemical etching of two-phase glass, the components of a chemically unstable phase are removed from the segregation channels either partially (one-stage etching) or almost completely (two-stage etching). The result is a plate of porous glasses.

For example, when the sample thickness L = 0.5 mm, the synthesized porous glasses (Fig. 5) have the composition (according to analysis, wt.%): 0.2-1.0 Na ₂ O, 0-0.5 K ₂ O, 2.0-6.0 B ₂ O ₃ , 85.0-97.0 SiO ₂ , 3.0-15.0 Fe ₂ O ₃ and have a porous structure with the following parameters (Figure 6): for MIP glass, the average diameter is D = 5 nm and the porosity is W ~ 30%; MAP glass has a bimodal pore structure (average pore diameter D ₁ ~ 5 nm and D ₂ ~ 50-60 nm) and porosity W ~ 60%.

The nanoscale crystalline phase of magnetite, which is present in the initial two-phase glass, is preserved after its through chemical etching in samples of porous glasses (Fig. 7).

After chemical treatment, the obtained porous glasses are washed in distilled water with a ratio of glass to water volume of 1: 200 at room temperature for 3-5 days with a daily change of water. After washing, the samples of porous glasses are dried on a filter in air at room temperature for 1 day and then in an oven at a temperature of 120 ° C for 1 hour. The dried samples are stored in bottles in desiccators with a desiccant (for example, CaCl ₂ ).

Thus, the claimed method allows to obtain porous high-silica glasses with pore sizes (5 ÷ 60) nm in the form of massive articles (plates, disks) containing magnetite crystallites of size (5 ÷ 20) nm and therefore possessing magnetic properties: values of magnetic coercive induction the fields of the samples are ~ 80–100 mT, and an anomaly of the magnetic response is observed at a temperature of ~ 120 K, corresponding to the Verwey transition in bulk Fe ₃ O ₄ .

Claims (4)

1. The method of obtaining high silica porous glass with magnetic properties, having a pore volume of 0.2 ÷ 0.6 cm ³ / cm ³ and an average pore diameter of 5 ÷ 60 nm, by heat treatment of alkali borosilicate glass, exposure of two-phase glass in a 3 M solution of mineral acids at a temperature of 50 ÷ 100 ° C, multi-stage washing in distilled water and combined drying in air at temperatures of 20 ÷ 120 ° C, characterized in that Fe ₂ O ₃ and FeO are introduced into the base alkaline borosilicate glass in an amount of 20 wt.% In terms of Fe ₂ O ₃ and provo they are heat treated at 550 ° C for 130-150 hours. 2. The method according to claim 1, characterized in that Hcl is used as a mineral acid. 3. The method according to claim 1, characterized in that HNO _{3 is} used as a mineral acid. 4. The method according to claim 1, characterized in that after the exposure of biphasic glass in a 3 M solution of mineral acids, an additional intermediate exposure is carried out in a 0.5 M KOH solution at 20 ° C for 0.5-6 hours.

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