CN110540212A - Low modulus sodium silicate solution and preparation method thereof - Google Patents

Abstract

The invention relates to a low modulus sodium silicate solution and a preparation method thereof. The preparation method of the low-modulus sodium silicate solution comprises: adding nanometer _SiO2 particles into the NaOH solution at normal temperature, stirring and dispersing to obtain the low-modulus sodium silicate solution with a set modulus. The invention also provides an alkali-activated gelling material prepared by using the low-modulus sodium silicate solution prepared by the method as an activator. The present invention is based on the principle that nano-SiO ₂ particles dissolve rapidly in a strong alkali solution at normal temperature to form monomer [SiO _n (OH) ^4-n ] ^n- principle, and the nano-SiO ₂ particles play a fast supplementary role to the soluble silicon in the solution, Quickly obtain sodium silicate solution with low modulus, low viscosity and strong stability. No matter the low-modulus sodium silicate solution prepared by the preparation method of the present invention is ready-to-use or stored for a long time, the nano- _SiO2 particles can exert its effect to improve the performance of the alkali-activated gelling material.

Description

Low modulus sodium silicate solution and preparation method thereof

technical field

The invention relates to the technical field of water glass, in particular to a low modulus sodium silicate solution and a preparation method thereof.

Background technique

The alkali activator is the most important component of the alkali-activated gelling material, which dissolves the silicon-aluminum raw material particles and releases silicon and aluminum monomers. The release process of silicon and aluminum monomers is the controlling process of the silicon-aluminum polymerization reaction, so the alkali activator has a crucial influence on the setting hardening performance, microstructure development and performance development of the gelled material. Different raw materials have different requirements for the characteristics of the alkali activator. For high-calcium, high-silicon, and low-aluminum raw materials such as slag, high modulus (n=SiO ₂ /Na ₂ O) water glass solution can not only provide a suitable alkaline environment, but also supply soluble silicon ((poly)silicate ions) It is sufficient to ensure the smooth progress of the silicon-aluminum polymerization reaction. For low-calcium, high-aluminum, and high-silicon raw materials such as fly ash, it is necessary to have a sufficiently strong alkaline environment material to release silicon and aluminum monomers, so a high-concentration NaOH solution is usually used. However, for the cementitious material system prepared with fly ash as raw material, only having enough alkaline environment is not enough to make it release silicon and aluminum monomers quickly at room temperature, that is, its coagulation and hardening are extremely slow at room temperature. In order to increase the reaction speed, the curing temperature is usually increased to promote the condensation hardening process, promote the formation of microstructure, and increase the strength. This method not only consumes a lot of energy, but is only suitable for prefabricated components, so it is urgent to develop normal temperature curing technology.

In order to achieve normal temperature curing, it is a feasible method to supplement silicon monomer in the form of soluble silicon in the cementitious material system. The source of soluble silicon can be sodium silicate solution (water glass). For the cementitious material prepared from fly ash, due to the need for a sufficiently strong alkaline environment, the suitable water glass solution (made by adding NaOH to the high modulus water glass solution, needs to be aged for more than 24 hours. reach equilibrium) must have a low modulus (n<1.0) feature. For low-modulus water glass, it has the characteristics of strong alkali and ionic soluble silicon, and is extremely unstable. Crystallization and delamination will occur after a few days of storage. It can be seen that using low-modulus water glass as an activator will bring many uncertain factors to material preparation and performance regulation, which is extremely unfavorable to industrial production. Therefore, alternatives to the supply of soluble silicon need to be sought.

Contents of the invention

The main purpose of the present invention is to provide a kind of preparation method of low-modulus sodium silicate solution (water glass), and the technical problem to be solved is that low-modulus sodium silicate solution is ready-to-use (without long-time aging) and its The stability is improved (storage for a long time), and it has the characteristics of strong alkali and fast supply of soluble silicon.

The purpose of the present invention and the solution to its technical problems are achieved by adopting the following technical solutions. According to the preparation method of a kind of low modulus sodium silicate solution proposed by the present invention, it comprises:

Under the condition of normal temperature, add nanometer SiO ₂ particles into the NaOH solution, stir and disperse to obtain a low modulus sodium silicate solution with a set modulus.

The purpose of the present invention and its technical problems can also be further realized by adopting the following technical measures.

Preferably, the preparation method of aforementioned low modulus sodium silicate solution, wherein said nano-SiO _The addition of particle satisfies formula (1):

m=30×c×V×n (1)

In formula (1),

m is the addition amount of nanometer SiO particles in _NaOH solution, unit g;

c is the concentration of NaOH solution, unit mol/L;

V is the volume of NaOH solution, unit L;

n is the setting modulus, where 0<n<1.

Preferably, in the aforementioned method for preparing the low-modulus sodium silicate solution, the specific surface area of the nano-SiO ₂ particles is 120-400 m ² /g, and the particle size D0.5 is 7-200 nm.

Preferably, the aforementioned method for preparing the low modulus sodium silicate solution, wherein the nano-SiO ₂ particles are hydrophilic nano-SiO ₂ particles.

Preferably, the aforementioned low modulus sodium silicate solution preparation method, wherein the stirring is mechanical stirring, the stirring speed is 500-900r/min, and the time is 10-30min; the dispersion is ultrasonic dispersion, which Followed by mechanical stirring, the dispersion time is 5-10 minutes.

Preferably, the preparation method of the aforementioned low-modulus sodium silicate solution, wherein when the modulus n≥0.6 is set, the nano- _SiO2 particles are divided into two parts with similar masses, and are added in two times to avoid one-time addition and Make it impossible to stir.

The purpose of the present invention and the solution to its technical problems are also achieved by the following technical solutions. According to the present invention, a low modulus sodium silicate solution is prepared by the preparation method described in any one of the foregoing.

Preferably, the aforementioned low modulus sodium silicate solution, wherein the viscosity of the low modulus sodium silicate solution is 10-20 mPa·s.

The purpose of the present invention and the solution to its technical problems are also achieved by the following technical solutions. According to an alkali-activated gelling material proposed by the present invention, the aforementioned low-modulus sodium silicate solution is used as an alkali-activator.

The purpose of the present invention and its technical problems can also be further realized by adopting the following technical measures.

Preferably, the aforementioned alkali-activated gelling material, wherein the low-modulus sodium silicate solution is a clear solution, can be used immediately to prepare the alkali-activated gelling material without aging after mechanical stirring and ultrasonic dispersion.

By means of the above-mentioned technical scheme, a kind of low modulus sodium silicate solution and preparation method thereof proposed by the present invention have at least the following advantages:

1. The preparation method of the present invention is to add a certain amount of nano-SiO particles to the _NaOH solution at normal temperature, mechanically stir and ultrasonically disperse to obtain a low-modulus sodium silicate solution, which can be ready-to-use, without It needs to be aged, simple and fast.

2. For the ready-to-use low-modulus sodium silicate solution in the preparation method of the present invention, the nano- _SiO2 particles only have part of the particles dissolved, and at this time it can play the chemical role of "providing soluble silicon", and the undissolved particles can also be recovered. It can play the role of physical filling and crystal nucleus of ultrafine particles, which has a significant effect on improving the early strength of alkali-activated gelling materials; for the low-modulus sodium silicate solution that has been aged for a long time, the nano-SiO ₂ particles have been completely dissolved, At this time it only plays a chemical role of "providing soluble silicon". Although there is a lack of physical filling and crystal nucleation, the supply of soluble silicon is larger, that is, the chemical action is more fully exerted, and the strength of the alkali-activated gelled material will also be significantly improved. Therefore, whether the low-modulus sodium silicate solution prepared by this method is ready-to-use or stored for a long time, the nano-SiO ₂ particles can exert its effect and improve the performance of the alkali-activated gelling material.

3. The nano- _SiO2 particles added in the method of the present invention have high activity characteristics, and can quickly supplement the highly active silicon monomer ([SiO _n (OH) _4-n ] ^n- ) of the system, thereby realizing high silicon, high Aluminum raw materials (such as fly ash) are used to prepare alkali-activated cementitious materials at room temperature, avoiding heating and curing, which not only has significant energy-saving significance, but also expands the application range of the material (it can be used for prefabricated components, but also for cast-in-place structure).

4. The low-modulus sodium silicate solution prepared by the preparation method of the present invention not only has low viscosity characteristics, its viscosity is 10-20mPa·s, and it can be stored for a long time due to the change of the supply state of soluble silicon, which is obviously beneficial to Industrial production and application of alkali-activated gelling materials.

5. The method of the present invention has no influence on the pH value of the solution. The added nano-SiO ₂ particles dissolve quickly and provide monomeric [SiO _n (OH) ^4-n ] ^n- , without aggregation and without changing the solution characteristics.

6. The present invention is based on the principle that nano-SiO ₂ particles are quickly dissolved in a strong alkali solution at room temperature to form monomer [SiO _n (OH) ^4-n ] ^n- , and nano-SiO ₂ particles can quickly supplement the soluble silicon in the solution It can quickly obtain sodium silicate solution with low modulus, low viscosity and strong stability.

The above description is only an overview of the technical solutions of the present invention. In order to understand the technical means of the present invention more clearly and implement them according to the contents of the description, the preferred embodiments of the present invention and accompanying drawings are described in detail below.

Description of drawings

Fig. 1 is the exothermic rate curve of solution after adding nanometer _SiO2 particle in NaOH solution in the embodiment of the present invention;

Fig. 2 is that embodiment of the present invention adds nano-SiO in _NaOH solution The shading degree change curve of solution after particle;

Fig. 3 is that embodiment of the present invention adds nano-SiO in _NaOH solution The viscosity change curve of solution after particle;

Fig. 4 is the FTIR vibration characteristic change curve of solution after adding nanometer _SiO2 particle in NaOH solution in the embodiment of the present invention;

Fig. 5 is the hydration heat release rate curve of a sample excited by a low modulus sodium silicate solution in an embodiment of the present invention.

Detailed ways

For further elaborating the technical means and effect that the present invention takes to reach the intended invention purpose, below in conjunction with accompanying drawing and preferred embodiment, to the low modulus sodium silicate solution that proposes according to the present invention and its preparation method its specific implementation , structure, feature and effect thereof, detailed description is as follows. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. Furthermore, the particular features, structures or characteristics of one or more embodiments may be combined in any suitable manner.

The embodiment of the present invention proposes a kind of preparation method of low modulus sodium silicate solution, it comprises:

Under the condition of normal temperature, add nanometer SiO ₂ particles into the NaOH solution, stir and disperse to obtain a low modulus sodium silicate solution with a set modulus.

In the embodiment of the present invention, the addition amount of nano-SiO ₂ particles is determined according to the set modulus and the concentration of the NaOH solution. Before adding nano- _SiO2 particles, it is necessary to prepare NaOH solution that meets the set water-cement ratio and concentration in advance. This is to facilitate the dispersion of nano- _SiO2 particles and make them dissolve quickly and maintain low viscosity, so as to avoid insufficient water in the solution. Additional water needs to be added when the alkali-activated gelling material is formed, in order to avoid the phenomenon that the solution may be too viscous or even jelly-like due to insufficient water in the solution.

As preferably, described nano-SiO _The addition amount of particle satisfies formula (1):

m=30×c×V×n (1)

In formula (1),

m is the addition amount of nanometer SiO particles in _NaOH solution, unit g;

c is the concentration of NaOH solution, unit mol/L;

V is the volume of NaOH solution, unit L;

n is the setting modulus, where 0<n<1.

It should be emphasized that the low modulus of the present invention is relative to the current common commercial products. The modulus of the commercial product (water glass solution, i.e. the aqueous solution of sodium silicate dissolved therein) is usually 2.0～2.4 and 3.0～3.4, so the modulus range (0.0～1.0) announced by the present invention is lower than the modulus of the commercial product.

In the embodiment of the present invention, before adding the nano-SiO ₂ particles, a NaOH solution that satisfies the set water-cement ratio and the required concentration of the alkali-activated gelling material is firstly prepared. Generally, 450g of powder raw material is required for the mortar experiment of alkali-activated cementitious materials. Assuming that the water-cement ratio is γ, the dosage of low-modulus sodium silicate solution is β(%, based _on the Na2O content in the alkali-activated cementitious material The mass percent of the powder raw material), then the NaOH solution water demand m' (unit g) of the preparation required concentration satisfies formula (2):

m'=450×γ (2)

In formula (2),

m' is the water demand of the NaOH solution of required concentration, unit g;

γ is the set water-cement ratio (the mass of water divided by the mass of powder raw materials) of the alkali-activated gelling material.

The required concentration c of NaOH solution satisfies formula (3):

c=10×β/(31×γ) (3)

In formula (3),

c is the required concentration of NaOH solution, unit mol/L;

β is the dosage of low modulus sodium silicate solution, expressed in %, based _on the mass percentage of its Na2O content in the powder raw material in the alkali-activated gelling material;

γ is the set water-cement ratio (the mass of water divided by the mass of powder raw materials) of the alkali-activated gelling material.

Under the above water demand and concentration conditions, it is necessary to prepare (9×γ/20)L NaOH solution to meet the set water-cement ratio of the alkali-activated gelling material; it is necessary to add (15×9×β×n /31)g nano-SiO ₂ particles can meet the set modulus.

The method of the invention adds nano- _SiO2 particles into the NaOH solution, so that the sodium silicate solution with low modulus can be obtained quickly, and the solution has the characteristics of low viscosity and long-term aging.

In the method of the present invention, for the ready-to-use low-modulus sodium silicate solution, the nano- _SiO2 particles only partially dissolve, and at this time it can play the chemical role of "providing soluble silicon", and the undissolved particles can also play super The physical filling effect and crystal nucleation effect of fine particles have a significant effect on improving the early strength of the alkali-activated gelled material; for the low-modulus sodium silicate solution that has been aged for a long time, the nano-SiO ₂ particles have been completely dissolved, and at this time its Executes only the chemistry of "providing soluble silicon". Although there is a lack of physical filling and crystal nucleation, the supply of soluble silicon is larger, that is, the chemical action is more fully exerted, and the strength of the alkali-activated gelled material will also be significantly improved. Therefore, whether the low-modulus sodium silicate solution is ready-to-use or stored for a long time, the nano-SiO ₂ particles can exert its effect and improve the performance of the alkali-activated gelling material.

The nano- _SiO2 particles added in the method of the present invention have high activity characteristics, and can quickly supplement the high-activity silicon monomer ([SiO _n (OH) _4-n ] ^n- ) of the system, thereby realizing high-silicon and high-alumina raw materials (such as fly ash) to prepare alkali-activated gelling materials under normal temperature conditions, avoiding heating and curing. The method of the present invention has no influence on the pH value of the solution. The added nano-SiO ₂ particles dissolve quickly and provide monomeric [SiO _n (OH) ^4-n ] ^n- , without aggregation and without changing the solution characteristics.

Compared with the existing commercial products, the embodiment of the present invention refers to the sodium silicate solution (0<n≤0.5) with a modulus less than or equal to 0.5 as an ultra-low modulus sodium silicate solution. The present invention has more prominent advantages in the preparation of ultra-low modulus sodium silicate solutions with n≤0.5: based on the rapid dissolution of nano-SiO ₂ particles in strong alkali solutions at room temperature to form monomers [SiO _n (OH) ^4-n ] Based on the principle of ^n- , nano-SiO ₂ particles can quickly supplement the soluble silicon in the solution, and quickly obtain a sodium silicate solution with ultra-low modulus, ultra-low viscosity, and strong stability.

Preferably, the specific surface area of the nano-SiO ₂ particles is 120-400 m ² /g, and the particle size D0.5 is 7-200 nm.

Preferably, the nano-SiO ₂ particles are hydrophilic nano-SiO ₂ particles.

Preferably, the stirring is mechanical stirring, the stirring speed is 500-900r/min, and the time is 10-30min; the dispersion is ultrasonic dispersion, which is carried out after mechanical stirring, and the dispersion time is 5~10min.

As a preference, when the modulus n≥0.6 is set, the nano-SiO ₂ particles are divided into two parts with similar mass, and added in two parts, so as to avoid failure to stir due to one-time addition.

The embodiment of the present invention also provides a low modulus sodium silicate solution, which is prepared by the aforementioned preparation method at normal temperature.

In the embodiment of the present invention, the preparation method of the low-modulus sodium silicate solution is simple and fast, and it is carried out at room temperature, ready to use after mixing, and does not need to be aged for a long time to achieve equilibrium.

The present invention adopts the function of "providing compensation for soluble silicon" of highly active nano- _SiO2 , so that the obtained low-modulus sodium silicate solution has the characteristics of high activity, low viscosity and good stability.

The low-modulus sodium silicate solution of the present invention not only has the characteristics of ultra-low viscosity, but also can be stored for a long time due to changes in the supply state of soluble silicon, which is obviously beneficial to the industrial production and application of alkali-activated gelling materials.

Preferably, the viscosity of the low modulus sodium silicate solution is 10-20 mPa·s.

The embodiment of the present invention also provides an alkali-activated gelling material, which uses the aforementioned low-modulus sodium silicate solution as an alkali activator, and the low-modulus sodium silicate solution is a clear solution, mechanically stirred and ultrasonically dispersed It can be used immediately to prepare alkali-activated gelling materials without aging

The principle of the present invention is as follows: under normal temperature conditions, nanometer _SiO2 particles can be dissolved in strong alkali solution, and NaOH solution is a strong alkaline solution, and nanometer _SiO2 particles can be rapidly dissolved therein under normal temperature conditions. The exothermic rate curve of adding 0.03 g of nanometer SiO ₂ particles to 2.2 g of NaOH solution (containing 0.2 g of Na ₂ O+2.0 g of water) was measured by a microcalorimeter, as shown in FIG. 1 . The results show that there is an obvious long-term exothermic process in the solution at 20 °C, which indicates that there is a certain chemical process between nano-SiO ₂ particles and NaOH solution. According to its exothermic history, the explanation is as follows: the surface of hydrophilic nano-SiO ₂ particles is wetted by water and exothermic, which is manifested as the first stage of intense exotherm lasting tens of minutes _; heat, releasing soluble silicon and forming [SiO _n (OH) _4-n ] ^n- , manifested by a second stage of slow exotherm lasting several hours. The above exothermic behavior confirms that the nano- _SiO2 particles are soluble in NaOH solution. Although the process is long, nano- _SiO2 particles can exert their modification effect whenever the formulated low-modulus sodium silicate solution is used. If it is prepared and used immediately, the nano- _SiO2 particles in the solution are only partially dissolved, and at this time it can simultaneously play the chemical role of providing solubility, the physical filling role of ultrafine particles, and the role of crystal nucleation; if it is used after a long time, the solution will The nano- _SiO2 particles are fully dissolved to maximize the chemistry that provides solubility.

Using a laser particle size analyzer, the dissolution characteristics of nano-SiO ₂ particles in NaOH solution can be further confirmed. The shading degree of the laser particle size analyzer is used to characterize the dissolution characteristics of nano-SiO ₂ particles. The shading degree refers to the optical concentration of the particles in the solution. When the particles are finer and better dispersed, the shading degree of the solution is higher under the premise of adding the same mass of particles. The size of nano-SiO ₂ particles is very small, reaching the nanometer level. When a small amount of it is added to the solution and dispersed by ultrasonic waves, the shading degree of the solution will soon approach 20%. If the nano-SiO ₂ has been dispersed in the solution in the form of particles, the shading degree of the solution will be maintained at about 20%. The change curve of the shading degree of the solution after adding nano- _SiO2 particles in the NaOH solution is shown in Figure 2. The results show that the shading of the solution decreases rapidly within tens of minutes, which means the dissolution of nano-SiO ₂ particles; then the shading decreases slowly, and this trend lasts for hundreds of minutes, which means that the nano-SiO ₂ particles dissolve gradually; After a sufficient time (200 minutes), the shading has been reduced from the initial 20% to about 1%, which shows that most of the nano- _SiO2 particles have been dissolved during this period. The duration of this process is almost the same as the exothermic duration of adding nano- _SiO2 particles into NaOH solution, which shows again the solubility of nano- _SiO2 particles in NaOH solution, that is, nano- _SiO2 particles can indeed play a role in providing The role of soluble silicon.

The dissolution process of nano-SiO ₂ particles is bound to be accompanied by the change of solution viscosity. If nano-SiO ₂ is in a granular state, the viscosity of the solution will increase significantly because of its hydrophilic properties; if it dissolves and becomes a solution component, the viscosity will inevitably decrease significantly. The change curve of solution viscosity after adding nano- _SiO2 particles in NaOH solution is shown in Fig. 3. The results show that the change of viscosity of the solution after adding nano _{- SiO2} at room temperature is in line with the above speculation, and the solution changes from a turbid state to a clear state, and the viscosity is close to the initial solution. Almost no effect.

Based on the above-mentioned dissolvability of nano- _SiO2 particles in NaOH solution at room temperature, the present invention designs a scheme for adding nano- _SiO2 particles to NaOH solution to prepare low-modulus sodium silicate solution. This solution can quickly obtain low modulus sodium silicate solution at normal temperature, and the solution has the characteristics of high activity, low viscosity and high stability.

The present invention will be further described below in conjunction with specific embodiment, but can not be interpreted as the restriction to protection scope of the present invention, some non-essential improvement and adjustment that those skilled in the art make to the present invention according to the content of the above-mentioned present invention still belong to this invention. protection scope of the invention.

Example 1

Add nanometer SiO ₂ particles to NaOH solution to prepare low modulus sodium silicate solutions with modulus of 0.15, 0.30, 0.45.

Assuming that the water-cement ratio of the alkali-activated gelling material is 0.5, and the dosage of the activator is 6.813% (based _on the mass percentage of the Na2O content in the powder raw material in the alkali-activated gelling material, the same below), then the preparation meets the requirement of 450g See Table 1 for the parameters of the solution required for powder raw materials.

Table 1 prepares the parameters of low modulus sodium silicate solution with modulus of 0.15, 0.30, 0.45

water/g Required concentration of NaOH solution/(mol/L) Required volume of NaOH solution/L Nano-SiO₂/g modulus 225 4.40 0.225 4.45 0.15 225 4.40 0.225 8.90 0.30 225 4.40 0.225 13.35 0.45

Nano SiO ₂ particles: hydrophilic type, particle size is 7-40nm (D0.5=14nm), specific surface area is 400m ² /g.

Water: 225g, tap water.

NaOH: 39.56g, industrial grade caustic soda.

NaOH solution: dissolve caustic soda in 225g of water, stir, seal, and cool to obtain a NaOH solution with a concentration of 4.40mol/L.

At room temperature, add 4.45g, 8.90g, and 13.35g of nano- _SiO2 particles into the NaOH solution, stir mechanically at a speed of 500r/min for 10min, and then ultrasonically disperse for 5min to obtain a low-modulus sodium silicate solution ,spare.

The role of nano-SiO ₂ particles in providing soluble silicon is illustrated by the results of FTIR spectra. The change curve of FTIR vibration characteristics after adding nano- _SiO2 particles in NaOH solution is shown in Fig. 4. It can be seen from the results that when nano-SiO ₂ particles are added to NaOH solution, the characteristic vibration band of O-Si-O (1108cm ^-1 ) and Si-OH characteristic vibration band (810cm ^-1 ) disappear, which shows that Nano-SiO ₂ particles were dissolved in this solution. The NaOH solution added with nano-SiO ₂ particles has an obvious vibration band at the wave number of 1000cm ^-1 , which is the corresponding O-Si-O after the nano-SiO ₂ particles are dissolved into [SiO _n (OH) _4-n ] ^n- vibration. Comparing the sodium silicate solutions with moduli of 0.15, 0.30, and 0.45, there is almost no significant difference among the three, which shows that no matter how much the nano- _SiO2 particles are added, they can be dissolved in the solution, and there is no difference in the soluble silicon provided.

The above results show that it is feasible to rapidly prepare low-modulus sodium silicate solution by using nano-SiO ₂ particles to "provide soluble silicon".

Using NaOH solution and the above-mentioned sodium silicate solution as activators, a mortar sample of alkali-activated gelling material was prepared. When the amount of NaOH solution and sodium silicate solution is 0.225L, the water-cement ratio of the mortar sample is just 0.5, and the amount of activator is just 6.813%.

Alkali-activated gelling materials were prepared using fly ash and slag powder as raw materials, and NaOH solution and the above-mentioned sodium silicate solution as activators respectively. The ratio of the cementitious material is: 90% fly ash and 10% slag powder (specific surface area 405m ² /kg, the same below) as powder raw materials.

Prepare samples and measure strength according to "Cement Mortar Strength Test Method (ISO Method)" (GB/T 17671), but the curing condition is humid air at normal temperature (RH=95±5%). See Table 2 for the comparison results of NaOH solution and sodium silicate solutions with moduli of 0.15, 0.30, and 0.45 as activators.

For the gelling material with the above ratio, if a low concentration (≤3.0mol/L) NaOH solution is used as the activator, the coagulation is abnormally slow at room temperature, with almost no strength in the early stage, and the strength in the later stage does not exceed 10.0MPa. Therefore, it is necessary to increase the concentration and dosage of NaOH solution. When the NaOH solution is ≥ 4.0mol/L and the dosage is greater than 5%, the sample can coagulate normally at room temperature, and its early and late stages have sufficient strength.

Table 2 Comparison of the effects of NaOH solution and the above-mentioned sodium silicate solution as stimulators

Note: The modulus is 0 means that the activator is NaOH solution

It can be seen from Table 2 that when using sodium silicate solutions with modulus of 0.15, 0.30, and 0.45 as the activator, the 3-day strength and 28-day strength are all higher than when NaOH solution is used as the activator, and with the increase of the modulus increasing gradually. This is precisely due to the role of nano-SiO ₂ particles in providing soluble silicon, which not only promotes the development of early strength, but also significantly improves the later strength. For example, when the sodium silicate solution with a modulus of 0.45 is used as the activator, the compressive strength of the 28-day sample is 17.1MPa higher than that of the sample excited by the NaOH solution, which is a significant increase.

Example 2

Example 1 confirmed the solubility of nano- _SiO2 particles from the aspect of structural characteristics, and confirmed its effectiveness in providing soluble silicon. Example 2 will expand the modulus range, and further verify the modification effect of nano- _SiO2 particles on NaOH solution.

Nano SiO ₂ particles: hydrophilic type, particle size 16-50nm (D0.5=30nm), specific surface area 290m ² /g.

Water: 225g, tap water.

NaOH: 39.56g, industrial grade caustic soda.

NaOH solution: dissolve caustic soda in 225g of water, stir, seal, and cool to obtain a NaOH solution with a concentration of 4.40mol/L.

At room temperature, add 14.83g, 17.80g, 20.77g, 23.74g, 26.70g, 29.67g of nano- _SiO2 particles into 0.225L of the above NaOH solution, mechanically stir for 30min at a speed of 700r/min, and then ultrasonically Disperse for 10 minutes to obtain sodium silicate solutions with modulus of 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 and set aside. Due to the increase in the addition of nano-SiO ₂ particles, the mechanical stirring was properly accelerated, and the duration of stirring and ultrasonication was prolonged.

It should be pointed out that when preparing sodium silicate solutions with moduli of 0.7, 0.8, 0.9, and 1.0, nano- _SiO2 particles are added in two times, as follows:

Sodium silicate solution with a modulus of 0.7: Add 10.77g of nano- _SiO2 particles for the first time, mechanically stir at a speed of 700r/min for 30min, and then ultrasonically disperse for 10min; immediately after obtaining a clear solution, add 10.00g of nano-SiO ₂ Particles were stirred mechanically for 30 minutes at a rotational speed of 700r/min, followed by ultrasonic dispersion for 10 minutes.

Sodium silicate solution with a modulus of 0.8: Add 12.74g of nano- _SiO2 particles for the first time, mechanically stir at a speed of 700r/min for 30min, and then ultrasonically disperse for 10min; immediately after obtaining a clear solution, add 11.00g of nano-SiO ₂ Particles were stirred mechanically for 30 minutes at a rotational speed of 700r/min, followed by ultrasonic dispersion for 10 minutes.

Sodium silicate solution with a modulus of 0.9: Add 13.70g of nano- _SiO2 particles for the first time, mechanically stir at a speed of 700r/min for 30min, and then ultrasonically disperse for 10min; immediately after obtaining a clear solution, add 13.00g of nano-SiO ₂ Particles were stirred mechanically for 30 minutes at a rotational speed of 700r/min, followed by ultrasonic dispersion for 10 minutes.

Sodium silicate solution with a modulus of 1.0: Add 15.67g of nano- _SiO2 particles for the first time, mechanically stir at a speed of 700r/min for 30min, and then ultrasonically disperse for 10min; immediately after obtaining a clear solution, add 14.00g of nano-SiO ₂ Particles were stirred mechanically for 30 minutes at a rotational speed of 700r/min, followed by ultrasonic dispersion for 10 minutes.

When the amount of NaOH solution and the above-mentioned sodium silicate solution is 0.225L, the water-cement ratio of the mortar sample is exactly 0.5, and the dosage of the activator is just 6.813%.

Alkali-activated gelling materials were prepared using fly ash and slag powder as raw materials, and NaOH solution and the above-mentioned sodium silicate solution as activators respectively. The ratio of the cementitious material is: 90% fly ash and 10% slag powder (specific surface area 405m ² /kg, the same below) as powder raw materials. The exothermic process of hydration of the gelled material was observed with a microcalorimeter, and the results are shown in Figure 5. According to the exothermic results of hydration, when NaOH solution was used as the activator, only the first obvious exothermic peak corresponding to wetting and dissolution was observed, while the characteristic exothermic peak (second Exothermic peak) is not obvious, that is, its hydration process is slow, which is the main reason for the low strength of the sample. When the sodium silicate solution with low modulus is used as the activator, the characteristic exothermic peak (second exothermic peak) of the alkali excitation reaction is gradually obvious, which is obviously the promotion of the reaction by the soluble silicon provided by the nano-SiO ₂ particles.

Prepare samples and measure strength according to "Cement Mortar Strength Test Method (ISO Method)" (GB/T 17671), but the curing condition is humid air at room temperature (RH=95±5%), and the results are shown in Table 3.

Table 3 Comparison of the effects of NaOH solution and sodium silicate solution with a modulus of 0.5-1.0 as activators

Note: The modulus is 0 means that the activator is NaOH solution

It can be seen from Table 3 that as the modulus increases, the 3-day strength and 28-day strength of the sample gradually increase, indicating that the soluble silicon provided by nano-SiO ₂ particles has an increasingly obvious effect on the strength growth, which shows that using the It is feasible to prepare low modulus sodium silicate solution by dissolving nano SiO ₂ particles in NaOH solution.

Example 3

In order to further verify the effectiveness of the method of the present invention, the excitation effect of the sodium silicate solution obtained by comparing the water glass solution obtained by the traditional method with the sodium silicate solution obtained by the present invention is proposed, and parameters such as viscosity and pH value are compared.

(1) The traditional method obtains the water glass solution of low modulus

The modulus is adjusted from high to low by adding caustic soda for cooking.

Initial water glass solution: the modulus is 2.4, the solid content is 45.7%, the pH value is 12.8, and the viscosity is 345mPa·s.

In 100g of the initial water glass solution with a modulus of 2.4, add 24.84g of caustic soda and 102.5g of water, stir, seal, boil, cool and age for 24 hours. After adjustment, the solid content of the water glass solution is 28.6%, and the modulus is 1.0. When the adjusted water glass solution is used as the activator of the alkali-activated gelling material, when the addition amount is 20% (in terms of the mass percentage of its solids in the powder; converted to Na ₂ O, the dosage is 10.16%) , the water-cement ratio of the cementitious mortar sample is exactly 0.5.

(2) the inventive method obtains the water glass solution of low modulus

Add nano- _SiO2 particles in NaOH solution to increase the modulus from zero.

Nano SiO ₂ particles: hydrophilic type, the particle size is 150-200nm (D0.5=185nm), and the specific surface area is 120m ² /g.

Water: 225g, tap water.

NaOH: 58.99g, industrial grade caustic soda.

NaOH solution: dissolve caustic soda in 225g of water, stir, seal, and cool to obtain a NaOH solution with a concentration of 6.55mol/L.

At room temperature, add 22.25g of nano- _SiO2 particles for the first time, mechanically stir for 30min at a speed of 900r/min, and then ultrasonically disperse for 10min; immediately after obtaining a clear solution, add 22.00g of nano- _SiO2 particles, Under the condition of 1/min, mechanically stir for 30min, followed by ultrasonic dispersion for 10min. Obtain a clear solution and set aside.

The alkali-activated gelling material is prepared by using fly ash and slag powder as raw materials, and using the above-mentioned water glass solution obtained by the traditional method and the above-mentioned sodium silicate solution obtained by the method of the present invention as activators respectively. The ratio of the cementitious material is: 90% fly ash and 10% slag powder (specific surface area 405m ² /kg, the same below) as powder raw materials. 450g powder (including 360g fly ash, 90g mineral powder), according to the "cement mortar strength test method (ISO method)" (GB/T 17671) to prepare samples, measure the strength, but the curing condition is humid air at normal temperature ( RH=95±5%).

When being mixed with 314.7g by the water glass solution that the modulus that traditional method obtains is 1.0, the alkali amount that brings is 45.84g (in Na ₂ O), the silicon amount that is brought in is _44.26g (in SiO ), The water brought in was 225g, and the water-cement ratio of the sample was just 0.5.

When being mixed with 0.225L the sodium silicate solution that the modulus obtained by the inventive method is 1.0, the amount of alkali that is brought in is 45.72g (in Na ₂ O), and the amount of silicon that is brought in is _44.25g (in SiO ) , the water brought in is 225g, and the water-cement ratio of the sample is just 0.5.

It can be seen that the two different activators have a consistent liquid phase environment, which sets a reliable boundary condition for the effect comparison of this example.

NaOH solution, modulus is the initial water glass solution of 2.4, modulus is 1.0 cooking water glass solution and sodium silicate solution of the present invention when as activator effect contrast and solution parameter, see Table 4.

Table 4 Effect comparison and solution parameters of NaOH solution and above-mentioned sodium silicate solution as stimulator

Note: "/" means that the concentration of ^OH- exceeds the characteristic range of pH value, and it is strongly alkaline. The water-cement ratio of all samples is 0.5, and the reduction brought by the activator is consistent, so as to compare the activating effect.

As can be seen from Table 4, compared with the low modulus water glass solution (the former) that adopts cooking method to obtain, the low modulus sodium silicate solution (the latter) that the present invention obtains has more excellent excitation effect: the latter excites sample The strength of the 3-day and 28-day samples is much higher than that of the former excitation sample. The viscosity of the latter is lower, because the former is adjusted from high modulus to low modulus, and the silicon contained in it retains a high polymerization state, while the latter is obtained by dissolving nano- _SiO2 particles, mainly with high activity monomer ([ SiO _n (OH) _4-n ] ^n- ) exists. In addition, the OH ^- concentration in the latter has exceeded the range that can be characterized by the pH value, that is, the solution exists in an ionic state, which can provide stronger alkalinity, which is obviously beneficial to the alkali-induced reaction; while the former still retains the characteristics of the polymeric state, so Its alkalinity can be characterized by pH value, that is, its alkalinity is weaker than that of the latter, and correspondingly its excitation effect is worse than that of the latter, and the intensity of each age of the sample is on the low side. In addition to the influence factor of alkalinity, the latter can also provide more highly active monomers ([SiO _n (OH) _4-n ] ^n- ), while the former still retains high polymerization characteristics so that its single The ability to provide body is limited, which is also another reason for the low intensity of the stimulated samples at different ages.

Compared with the initial water glass solution (the former) that the modulus is 2.4, the low modulus sodium silicate solution (the latter) that the present invention obtains, although the compressive strength of the excited sample is lower than the former excited sample, but The flexural strength is higher, which is the result of some undissolved nano-SiO ₂ particles filling the matrix and playing a toughening role. It can be seen that the method of the present invention can not only play the chemical role of providing highly active silicon, but also the physical filling role can not be ignored. It should be noted that the reason why the former excited sample has higher compressive strength than the latter excited sample is that although the former is characterized by high polymerization, it can provide more soluble silicon on the whole, after all, its silicon content is lower than that of the latter 2.4 times.

Compared with the NaOH solution (the former), the low modulus sodium silicate solution (the latter) obtained by the present invention not only exhibits a stronger excitation effect, but also has similar solution properties such as viscosity.

The above comparison results have confirmed the feasibility of the method of the present invention, and confirmed that the low modulus sodium silicate solution obtained by the present invention has high activity, low viscosity and strong alkalinity.

Example 4

This example will illustrate the effect of aging time on the excitation effect and solution characteristics of the low modulus sodium silicate solution obtained in the present invention.

Nano SiO ₂ particles: hydrophilic type, the particle size is 40-100nm (D0.5=72nm), and the specific surface area is 275m ² /g.

Water: 225g, tap water.

NaOH: 39.56g, industrial grade caustic soda.

NaOH solution: dissolve caustic soda in 225g of water, stir, seal, and cool to obtain a NaOH solution with a concentration of 4.40mol/L.

At room temperature, add 14.83g of nano- _SiO2 particles, mechanically stir at a speed of 500r/min for 10min, and then ultrasonically disperse for 5min to obtain a clear solution with a modulus of 0.5, which is ready for use.

When the dosage of the above-mentioned sodium silicate solution is 0.225L, the water-cement ratio of the mortar sample is just 0.5, and the dosage of the activator is just 6.813%.

The solution aging time is 0min, 60min, 120min, 240min, 480min, 960min, 1920min, 3840min, 7680min, 259200min.

Alkali-activated gelling materials were prepared using fly ash and slag powder as raw materials and the above-mentioned sodium silicate solutions aged for different times as activators. The ratio of the cementitious material is: 90% fly ash and 10% slag powder (specific surface area 405m ² /kg, the same below) as powder raw materials. Prepare samples and measure strength according to "Cement Mortar Strength Test Method (ISO Method)" (GB/T 17671), but the curing condition is humid air at normal temperature (RH=95±5%). See Table 5 for the comparison of the excitation effect and the change of the solution parameters of the sodium silicate solution with a modulus of 0.5 aged for different periods of time.

Table 5 Comparison of excitation effect and solution parameter changes after aging for different time

Note: "/" means that the concentration of ^OH- exceeds the characteristic range of pH value, and it is strongly alkaline. The duration of 259200min is 180 days.

As can be seen from Table 5, even if the solution is aged for a long time (7680min, about 5 days), no stratification or turbidity is found, and it is still a clear solution. The longest aging of this solution is 259200min (180 days), and its outward appearance characteristic still does not change. The above phenomenon shows that the low modulus sodium silicate solution obtained by the present invention has excellent stability and can be stored for a long time. Typically, cementitious materials such as cement have a shelf life of no more than six months. Therefore, the low modulus sodium silicate solution obtained by the present invention meets the requirements of the material preparation period of the construction industry.

From the results in Table 5, it can be seen that no matter how long the solution is stored, the properties such as its excitation effect and viscosity do not change significantly. When stored for a short period of time, although the nano- _SiO2 particles cannot be completely dissolved, that is, they cannot be completely converted into soluble silicon, but the undissolved particles play the role of physical filling and crystal nucleation of ultra-fine particles, which can compensate for the chemical effect to a certain extent. Insufficiency that failed to fully play, so the sample still shows the strength equivalent to the sample excited by the long-term aging solution; when the long-term aging, the nano- _SiO2 particles are almost completely dissolved, and the chemical effect of providing soluble silicon is fully obtained. Play, correspondingly the sample shows a sufficiently high strength. Just because there are some undissolved nano- _SiO2 particles in the short-term aging solution, the viscosity of the solution is larger than that of the long-term aging solution. With the prolongation of aging time, the nano-SiO ₂ particles gradually dissolve, and the viscosity of the solution decreases gradually and remains at a considerable level.

The above results show that the low modulus sodium silicate solution obtained by the present invention has excellent stability, and the shelf life can be as long as 6 months.

In the foregoing embodiments, the descriptions of each embodiment have their own emphases, and for parts not described in detail in a certain embodiment, reference may be made to relevant descriptions of other embodiments.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention still belong to this invention. within the scope of the technical solution of the invention.

Claims (10)

1. A method for preparing a low modulus sodium silicate solution, comprising:

And (3) adding nano SiO2 particles into the NaOH solution at normal temperature, stirring and dispersing to obtain the low-modulus sodium silicate solution with the set modulus.

2. The method for preparing a low modulus sodium silicate solution according to claim 1,

The addition amount of the nano SiO2 particles satisfies formula (1):

m＝30×c×V×n (1)

In the formula (1), the reaction mixture is,

m is the addition amount of nano SiO2 particles in NaOH solution, unit g;

c is the concentration of NaOH solution, unit mol/L;

V is the volume of NaOH solution, unit L;

n is a set modulus, where 0< n <1.

3. The method for preparing a low modulus sodium silicate solution according to claim 1,

The specific surface area of the nano SiO2 particles is 120-400 m2/g, and the particle size D0.5 is 7-200 nm.

4. The method for preparing a low modulus sodium silicate solution according to claim 1,

The nano SiO2 particles are hydrophilic nano SiO2 particles.

5. the method for preparing a low modulus sodium silicate solution according to claim 1,

The stirring is mechanical stirring, the rotating speed of the stirring is 500-900 r/min, and the time is 10-30 min; the dispersion is ultrasonic dispersion, which is carried out after mechanical stirring, and the dispersion time is 5-10 min.

6. The method for preparing a low modulus sodium silicate solution according to claim 1,

When the modulus n is set to be more than or equal to 0.6, the nano SiO2 particles are divided into two parts with similar mass and added in two times, so as to avoid the problem that stirring cannot be carried out due to one-time addition.

7. A low modulus sodium silicate solution, characterized in that it is prepared by the method of any one of claims 1 to 6.

8. The low modulus sodium silicate solution according to claim 7, wherein the viscosity of said low modulus sodium silicate solution is 10 to 20 mPa-s.

9. An alkali-activated cementitious material, characterised in that it uses as alkali activator the low modulus sodium silicate solution according to claim 7 or 8.

10. The alkali-activated cementitious material of claim 9, wherein the low modulus sodium silicate solution is a clear solution that can be used immediately to prepare the alkali-activated cementitious material without the need for aging after mechanical agitation and ultrasonic dispersion.