JPH042607A - Production of silica balloon - Google Patents

Abstract

PURPOSE:To readily obtain superfine particles having an adjusted particle size by dividing a closed cylindrical oven into a low temperature combustion region and a high temperature combustion region and spraying a water glass aqueous solution in the low temperature combustion region in a silica balloon production method in which the water glass aqueous solution is sprayed in a combustion gas stream passing through the oven. CONSTITUTION:In a method for spraying a water glass aqueous solution in a combustion gas stream passing through a closed cylindrical oven and subsequently staying the resultant glass fine particle intermediates in a high temperature oven for a certain period to convert into silica balloons, the following means are adapted. Namely, the oven is divided into a low temperature combustion region of 200-500 deg.C and a high temperature combustion region of >=1300 deg.C and a water glass is sprayed in the low temperature region. In the above-mentioned method, the co-employment of oxygen gas as a combustion oxidizing agent fed into the low temperature combustion region and/or the feeding of carbon dioxide in the low temperature region through a route different from a route of a fuel hydrocarbon can increase the concentration of CO2 gas in the low temperature combustion region to more homogeneously and efficiently promote the alkali-removing reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing ultrafine, high-quality silica balloons with good operability.

(Prior Art) A single hollow microsphere having an outer diameter on the order of microns is called a balloon, and inorganic microspheres such as alumina, fly ash, glass glass, silica, and silt are already on the market. Among these, those whose constituent material is silica are
Usually called silica balloon, aggregate of fireproof insulation material,
It is useful for applications such as plastic fillers.

Conventional techniques for producing silica balloons include a method in which silicon source material is melted and then exposed to a jet stream of air, inert gas, etc. to cause gas inclusion/hollowing;
A method in which the silicon source raw material is thermally decomposed as it is or mixed with a foaming agent, and then made into hollow particles by gas foaming, or a method in which the alkali silicate raw material is chemically and thermally treated and then foamed into hollow particles in a high-temperature atmosphere. etc. are known.

However, these conventional methods have limitations in making the silica balloons finer and adjusting the particle size.
It has been difficult to efficiently produce sized fine particles of 00 μm or less.

As a means to eliminate these drawbacks, the present inventors sprayed a water glass aqueous solution into a high-temperature combustion gas flow flowing in a closed cylindrical furnace to dealkalize it, and the resulting glass fine particle intermediate was treated for a certain period of time. We have developed a method for producing silica balloons that remains in a high-temperature furnace, and have already filed a patent application for 1991-1.
It was proposed as No. 65009.

(Problems to be Solved by the Invention) When forming silica balloons by heat treatment of water glass-based silicon source raw materials, how can the dealkalization reaction be carried out uniformly and effectively in the process of converting water glass into warp force? This is a major determining factor that controls the purity, particle size distribution, content of irregular shot, etc. of the product.In the invention of the above-mentioned Japanese Patent Application No. 1-165009, as a solution to this problem, hydrochloric acid, nitric acid, etc. A method of introducing an aqueous acid solution without I! has been adopted, but introducing an inorganic acid into the furnace risks causing various troubles in terms of operation, and is problematic as an industrial production process.

The present invention was developed based on the elucidation of an industrially productive dealkalization reaction method, and produces high-quality silica balloons in the ultrafine range with an outer diameter of 10 μm or less with easy particle size adjustment and good operability. The purpose is to provide a method to do so.

(Means for Solving the Problems) A method for manufacturing a silica balloon according to the present invention to achieve the above object is to dealkalize a silica balloon by spraying an aqueous solution of water glass into a combustion gas stream flowing in a closed cylindrical furnace. In this method, the produced glass particle intermediate is retained in a high-temperature furnace for a certain period of time to be converted into a silica balloon.
The structure is characterized in that it is divided into a low-temperature combustion region of 500° C. and a subsequent high-temperature combustion region of 1300° C. or more, and that a water glass aqueous solution is sprayed into the low-temperature combustion region.

The combustion gas flow flowing through the closed cylindrical furnace is formed by injecting fuel hydrocarbons into the furnace together with a combustion oxidizer such as air and completely combusting them. A furnace with a two-stage combustion zone structure is used, which includes a low-temperature combustion zone with a combustion zone and a high-temperature combustion zone with another combustion burner connected thereto.

Liquid fuel oils such as light oil, heavy oil, creosote oil, and ethylene bottom oil can be used as the fuel hydrocarbon oil, but gases such as propane, methane, butane, etc. can be used in order to impart high purity to the silica balloons produced. It is desirable to use hydrocarbons.

As a combustion oxidizer that is supplied simultaneously with fuel hydrocarbons,
Air, oxygen or a mixture thereof is used.

The temperature inside the furnace is controlled so that a low-temperature combustion zone of 200 to 500° C. and a subsequent high-temperature combustion zone of 1300° C. or higher are formed separately, and a water glass aqueous solution is sprayed into the low-temperature combustion zone. This step is a major requirement of the present invention in order to proceed with the smooth dealkalization reaction of the water glass component. If carbon dioxide gas is introduced through a route different from that of fuel hydrocarbons, or if both of these methods are implemented simultaneously, the concentration of carbon oxide in the low-temperature combustion zone becomes excessive, promoting the dealkalization reaction more uniformly and efficiently. becomes possible.

The water glass aqueous solution sprayed into the low-temperature combustion zone may be, for example, an inexpensive industrial water glass dissolved in water to an appropriate viscosity, and the water glass solution sprayed into the low-temperature combustion zone may be made by dissolving inexpensive industrial water glass in water to an appropriate viscosity. Introduce into the furnace in a sprayed state.

The concentration of the water glass aqueous solution is preferably in the range of 20 to 80% by weight. The reason for this is that when the concentration is less than 20% by weight, the auxiliary stage where the combustion heating lid is consumed for water evaporation becomes larger and the residence time in the furnace required for dealkalization becomes longer.On the other hand, when the concentration exceeds 811% This is because the viscosity of the aqueous solution increases, making it difficult to feed it into the furnace and resulting in larger spray droplets.

The aqueous water glass solution sprayed into the furnace is thermally decomposed in two speeds to cause a dealkalization reaction and is converted into an intermediate consisting of fine silicic acid glass particles with high purity. The glass fine particle intermediate produced in this manner foams and is converted into ultrafine silica balloons while remaining in the high temperature furnace for a certain period of time. The formed silica balloon is water-cooled in the latter stage of the furnace, cooled to below its melting point, and then sent to a collection process and recovered.

In addition, by introducing hydrocarbons into the combustion gas stream at the same time as the water glass aqueous solution or through a separate route, a carbon blank is generated and coexisted in the furnace, thereby preventing silica balloons widely dispersed in the furnace from adhering to each other. can be done.

In the process of the present invention, the particle size of the produced silica balloons can be adjusted by appropriately controlling conditions such as the viscosity (dissolution concentration) of the water glass aqueous solution and the residence time of the glass fine particle intermediate in the furnace. For example, in order to make the particles larger, it is effective to increase the viscosity of the water glass aqueous solution and to increase the residence time of the glass fine particle intermediate in the furnace.

[For production]

Generally, the sodium in water glass is Naz 01Na
It is contained in the form of OH, and when it comes into contact with carbon dioxide, it becomes sodium carbonate through the reactions of formulas (1) and (2) below.

Naz O + CO□−+Na2CO3−<1)2NaO
H+CO, -+Na2Co, +H,0.=(2) These reactions are clear from thermodynamic calculations, and proceed faster at low temperatures.

In the present invention, the water glass aqueous solution sprayed into the low-temperature combustion zone of 200 to 500°C undergoes a catalytic reaction with carbon dioxide present in large amounts in the combustion zone at the same time as the solvent water evaporates, and the sodium component turns into sodium carbonate. It is dealkalized to produce silicic acid hydrate. This dealkalization is carried out by using oxygen gas as a combustion oxidant introduced into the low-temperature combustion zone, or by introducing carbon dioxide gas into the low-temperature combustion zone through a route other than that of the fuel oil. It is further promoted by increasing the partial pressure and progresses uniformly and rapidly.

In addition, since the water glass aqueous solution is sprayed into the low-temperature combustion region of 200 to 500°C, the phenomenon of coagulation and adhesion caused by sodium glass, silica, etc. at the tip of the spray nozzle, which occurs when directly spraying into the high-temperature combustion region of over 1300°C, does not occur. .

The produced silicic acid hydrate enters the subsequent high-temperature combustion zone of 1300'C, where it is further dehydrated and becomes highly pure silicic acid 1j (
Converts to SiO□). At this time, the particles are foamed by the moisture released at the same time to form a balloon.

With the above i-structure, the water glass aqueous solution undergoes a series of dehydration, dealkalization, and foaming in the combustion gas of the closed cylindrical furnace controlled at low and high temperatures, so that the desired ultrafine silica balloon can be produced. This makes it possible to consistently produce with good operability and stability.

〔Example〕

Hereinafter, the present invention will be specifically explained based on each example.

Examples 1 to 4 Horizontal sealed structure consisting of a low-temperature combustion zone with a diameter of 300 mm and a length of 500 mm with a combustion burner attached to the furnace head, and a high-temperature combustion zone with a diameter of 300 IllI and a length of 1200 av with a combustion burner connected thereto. In a cylindrical furnace, the tip of the spray nozzle for the water glass aqueous solution is located 5 minutes from the furnace head.
Set along the furnace axis so that it is located 0mm downstream,
A cooling water injection nozzle was installed at the rear of the high-temperature combustion area to stop the reaction.

Using this furnace, silica balloons were produced under various production conditions shown in Table 1. As a raw material, 5i0236-3
8%, NazO17-18%, Nano: 5i02
Commercially available industrial water glass 1 with a composition of molar ratio l:2.1
The number was used.

The characteristics of the obtained silica balloon are shown in Table 1 in comparison with the production conditions.

In addition, the DCF method was applied to measure the particle size and flow rate distribution of the produced silica balloon, and the disk rotation speed was 1100 O.
rp, sample concentration 100mg/100ml. so+,,
The conditions were that the sample injection volume was 0.5 ml and the buffer solution was 10.0 ml. This measurement is in good agreement with the results obtained by scanning electron microscopy. Further, the Na content of the produced silica balloon was quantitatively measured by atomic absorption spectrometry and fluorescent X-ray spectrometry.

The results in Table 1 indicate that according to the present invention, silica balloons with high quality properties and an outer diameter of 10 II gA or less can be continuously produced with good operability.

Comparative Example From a combustion chamber (diameter 200ffil, length 500 mm) with a combustion burner and raw material injection nozzle attached to the furnace head, and a wide-diameter reaction chamber (diameter 1201, length 2000 mm) coaxially connected to the combustion chamber. A closed cylindrical furnace having a cooling water spray hole provided at a predetermined position of the wide-diameter reaction chamber was installed. Using this furnace, silica balloons were manufactured under the conditions shown in Table 1.

The characteristics and properties of the obtained silica balloons are listed in Table 1 in comparison with the production conditions.

As can be seen from the results in Table 1, the silica balloon according to the comparative example does not spray water glass aqueous solution into the low-temperature combustion zone, so the dealkalization reaction is inferior to that of the example, the specific gravity in water is high, the purity is low, and the operability is poor. It was something.

(Effects of the Invention) As described above, according to the present invention, ultrafine silica balloons having excellent purity and grain properties can be continuously produced with always stable operability.

Therefore, the manufactured silica balloons are made of metal, plastic, ceramic fillers, sintered filters, etc.
In addition to being a raw material for lightweight heat insulating materials, it is expected to be useful as a material for semiconductor encapsulation and white pigments that take advantage of its ultra-fine grain size and optical properties that suppress translucency.

Applicant: Tokai Carbon Co., Ltd. Agent: Patent Attorney Masaya Takahata

Claims (1)

[Claims] 1. A water glass aqueous solution is sprayed onto a combustion gas flow flowing in a closed cylindrical furnace to dealkalize it, and the resulting glass fine particle intermediate is retained in a high temperature furnace for a certain period of time to form a silica balloon. In the method for converting the silica balloon, the inside of the furnace is divided into a low-temperature combustion zone of 200 to 500°C and a subsequent high-temperature combustion zone of 1300℃ or higher, and a water glass aqueous solution is sprayed into the low-temperature combustion zone. manufacturing method. 2. Claim 1, in which oxygen gas is also used as a combustion oxidant introduced into the low-temperature combustion zone, and/or carbon dioxide gas is introduced into the low-temperature combustion zone through a route different from that of fuel hydrocarbons.
The method for producing the described silica balloon.