JP2615994B2 - Manufacturing method of electrorheological fluid - Google Patents

Description

The present invention relates to a method for producing an electrorheological fluid which becomes viscous when placed in an electric field. Application of the electrorheological fluid to a torque converter, a viscous coupling, an engine mount, and the like of an automobile is being studied.

[Related Art] An electrorheological fluid has a characteristic of having a small viscosity and fluidity when not in an electric field, but has a property of increasing the viscosity when placed in an electric field. There is also a property that the viscosity increases in proportion to the magnitude of the electric field. Therefore, its viscosity can be freely adjusted by applying electricity, and its use is being studied in various fields.

As the electrorheological fluid, a fluid in which dispersoids such as silica gel and organic particles are dispersed in a dispersion medium such as liquid paraffin has been used. For example, JP-A-63-33
No. 459 discloses an electrorheological fluid in which fine particles of an acrylic copolymer are dispersed in oil. In recent years, utilization of a dispersion of silicon dioxide powder in a dispersion medium of silicon oil has been studied. As the silicon dioxide powder, one produced by a sodium silicate method, a gas phase combustion method, a sol-gel method, or the like is used.

[Problems to be Solved by the Invention] By the way, it is common to add water to an electrorheological fluid to assist polarization. However, in the case of an electrorheological fluid to which water is added, there is a phenomenon that when the temperature reaches 70 to 80 ° C., the flowing current increases extremely. As a result, the temperature of the electrorheological fluid further rises, which may cause a thermal runaway in which more current flows.

In addition, in the case of an electrorheological fluid in which silicon dioxide powder is dispersed in silicon oil, the viscosity increases as the amount of silicon dioxide powder added to the silicon oil increases. However, there is a problem that the initial viscosity increases when the temperature is not within the range, the degree of change in the viscosity depending on the magnitude of the electric field is small, and the electrorheological effect is small. It has been found that this phenomenon is remarkable when there are many silanol groups on the surface of the silicon dioxide powder.

By the way, when silicon dioxide is produced industrially, it is usually produced by the above three methods. Of these, the sodium silicate method is also called a wet method, and is produced by reacting an acid or salt with an aqueous solution of sodium silicate. However, silicon dioxide produced by the sodium silicate method has many silanol groups on the surface, is easily aggregated, is difficult to disperse, and is not suitable as a raw material for electrorheological fluid. Further, in the gas phase combustion method, it is produced by burning silicon tetrachloride and hydrogen in air or oxygen. However, the silicon dioxide produced by this method also has a large number of silanol groups and has a disadvantage that the cost is high. The sol-gel method is also referred to as an aerosol method, and is produced by reacting sodium silicate with an acid and an alcohol to form an organogel, and then subjecting it to an oclave treatment. Silicon dioxide produced by this sol-gel method has relatively few silanol groups, but has the disadvantage of being extremely expensive.

The present invention has been made in view of the above circumstances,
An object is to produce an electrorheological fluid having a large electrorheological effect at low cost.

[Means for Solving the Problems] The present applicant discloses a novel method for producing an oxide powder in, for example, JP-A-63-79712. The present inventor has found that an electrorheological fluid having a large electrorheological effect can be obtained by using silicon dioxide powder produced by using this production method, and has completed the present invention.

That is, the method for producing an electrorheological fluid of the present invention comprises: a powder forming step of forming a silicon oxide powder containing silicon dioxide as a main component by burning a silicon powder containing metal silicon as a main component in an oxidizing gas atmosphere; A dispersing step of dispersing the silicon oxide powder formed in the forming step to a content of 5 to 30% by weight in silicon oil.

The powder forming step generally includes a first step of supplying the silicon powder into the reaction vessel, a second step of igniting the silicon powder together with the oxidizing gas in the reaction vessel to form a flame and form the silicon oxide powder, And a third step of collecting the silicon oxide powder thus obtained. To supply the silicon powder in the first step, a carrier gas is usually used. As the carrier gas, any of an inert gas such as a nitrogen gas and an argon gas, a combustible gas such as a propane gas, a hydrogen gas and a methane gas, and an oxidizing gas such as an oxygen gas and air can be used. In some cases, the silicon powder can be supplied by an external force such as gravity without using a carrier gas.

In the second step, the silicon powder contacts the oxidizing gas and is ignited to form a flame. This can be performed by igniting with an ignition source in a state where the silicon powder and the oxidizing gas are mixed. The ignition can be performed by a method such as generating a spark in the reaction vessel. Alternatively, a combustible gas such as propane gas may be supplied to the reaction vessel to form a pilot flame, and the pilot flame may be used. In the second step, by controlling the supply rate of the silicon powder and the like, silicon oxide powders having various particle diameters can be formed. In order to prevent the unreacted metal silicon powder from remaining, it is preferable that the supply amount of the oxidizing gas is larger than the equivalent of the reaction with the metal silicon powder.

In the third step, the formed silicon oxide powder is recovered. This can be performed by collecting the product together with the exhaust gas in a dust collector or the like. As the dust collector, for example, a bag filter, a drum type fine powder collecting device, or the like can be used.

In the powder forming step, it is preferable to supply at least one of sodium compound powder and sodium chloride powder together with the metal silicon powder in the first step. Both can be used together. By simultaneously supplying the metal silicon powder and the sodium compound powder to the reaction vessel, a silicon oxide powder containing a sodium compound and containing silicon dioxide as a main component can be formed. If such a powder is used as a dispersoid of an electrorheological fluid, a high electrorheological effect can be obtained because the dielectric constant increases due to the presence of sodium and the polarization increases.

The sodium compound powder is suitably in the range of 0.5 to 30% by weight of the whole powder. If it is out of this range, the added effect may not be obtained, or a desired electrorheological effect may not be obtained due to a decrease in silicon dioxide content.

Incidentally, the metal silicon powder used in the powder forming step,
It is preferable to use one having a particle diameter of 40 μm or less. When the particle diameter is larger than 40 μm, the surface area decreases, the reactivity becomes poor, and the unreacted metal silicon powder remains.

In the dispersing step, the silicon oxide powder formed in the above-mentioned powder forming step is dispersed in silicon oil so as to be 5 to 30% by weight. Here, the silicone oil is mainly composed of siloxane bonds, and preferably has a viscosity of about 5 to 100 cps at 20 ° C. If the addition amount of the silicon oxide powder is less than 5% by weight, a sufficient electrorheological effect cannot be obtained. If the addition amount is more than 30% by weight, the viscosity in the absence of an electric field becomes too high and cannot be put to practical use. It is particularly desirable to add 15 to 25% by weight. Incidentally, the addition amount of silicon dioxide powder formed by the conventional gas phase combustion method is limited to 5% by weight.

To disperse silicon oxide powder in silicon oil,
As in the conventional case, it can be easily performed simply by stirring. In some cases, a disperser such as a ball mill may be used. In addition, if the dispersion is performed while heating in a vacuum, the dispersion can be performed more quickly and uniformly.

[Operation and Effect of the Invention] In the method for producing an electrorheological fluid of the present invention, silicon oxide powder formed by burning silicon powder containing metal silicon as a main component in an oxidizing gas in a powder forming step is used as a dispersoid. I have. In this powder forming method, the metal silicon powder is burned to be a vapor, then to a droplet, and then to a powder. Therefore, the silicon oxide powder becomes a spherical silicon oxide powder through the state of a droplet. Although the reason is not clear, the surface of the silicon oxide powder formed by this powder forming method has a feature that it has few silanol groups. Due to these two characteristics, the silicon oxide powder formed in the present invention can be dispersed in a large amount of 5 to 30% by weight in silicon oil in a practical viscosity range.

Therefore, according to the electrorheological fluid formed by the manufacturing method of the present invention, the amount of increase in viscosity when placed in an electric field is extremely large, and has a high electrorheological effect. And since it has a high electrorheological effect without adding water, the danger of thermal runaway caused by the presence of water is eliminated. That is, according to the production method of the present invention, such an electrorheological fluid can be produced at low cost and reliably. In addition, it is possible to easily incorporate a sodium compound with high productivity.

[Examples] Hereinafter, specific examples will be described. First, the manufacturing apparatus used to form the silicon oxide powder will be described with reference to FIG.

This manufacturing apparatus includes a heat-resistant reaction vessel 1, a powder supply passage 2, an oxygen gas supply passage 3, a propane gas supply passage 4, and a collection device 5. A powder supply passage 2 is opened in the upper part of the reaction vessel 1, and an oxygen gas supply passage 3 and a propane gas supply passage 4 are opened concentrically around the opening. Air as a carrier gas is supplied from the other end of the powder supply passage 2, and a hopper 20 for temporarily storing raw material powder is provided on the way.

The collection device 5 is a collection passage that opens at the lower end of the reaction vessel 1.
50, a bag filter 51 connected to the other end of the collection passage,
A blower 52 sucks the gas in the bag filter 51. By driving the blower 52, the product in the reaction vessel 1 is sucked into the bag filter 51 together with the exhaust gas, and the solid matter is collected.

In this manufacturing apparatus, propane gas supplied from the propane gas supply passage 4 is ignited in the reaction vessel 1 to form a pilot flame. The powder raw material is ejected from the powder supply passage 2 together with the carrier gas there, mixed with the oxygen gas ejected from the oxygen gas supply passage 3 and ignited by a pilot flame to form a flame 6. The formed oxide powder is sucked together with the exhaust gas from the collection passage 50 into the bag filter 51 and collected.

(Example 1) In the above-described manufacturing apparatus, 350 mesh metal silicon powder is charged into the hopper 20. Then, air as a carrier gas is supplied at a flow rate of 6 m ³ / min, and metal silicon powder is ejected from the powder supply passage 2 into the reaction vessel 1 at a supply rate of 2 g / min. Further, oxygen gas is ejected from the oxygen gas supply passage 3 into the reaction vessel 1 at a flow rate of 5 m ³ / min. The metal silicon powder and oxygen gas are mixed in the reaction vessel 1 and ignited by a pilot flame to form a flame 6.

The product is collected in the bag filter 51 and the bag filter
From inside 51, a silicon dioxide powder was obtained. The obtained silicon dioxide powder had a particle size of 0.01 to 0.02 μm, was almost spherical, and had a specific surface area of 105 m ² / g.

The obtained silicon dioxide powder was stirred and dispersed in silicon oil so as to be 17% by weight. The viscosity of the used silicone oil at 20 ° C. is 20 cps. As a result, an electrorheological fluid having a viscosity of 100 cps at 20 ° C. was obtained. The yield stress when this electrorheological fluid was placed in electric fields of various strengths was measured, and the results are shown in FIG.

(Example 2) As a raw material powder, the same metal silicon powder 80 as in Example 1 was used.
A silicon oxide powder containing silicon dioxide as a main component and containing sodium oxide was obtained in the same manner as in Example 1 except that silicon powder which was a mixed powder of 20 parts by weight of sodium oxide powder and 20 parts by weight of sodium oxide was used. The specific surface area of this silicon oxide powder was 101 m ² / g, and contained 5% by weight of sodium. Using this silicon oxide powder, an electrorheological fluid was produced in the same manner as in Example 1. As a result, an electrorheological fluid having a viscosity at 20 ° C. of 95 cps was obtained. The yield stress when the obtained electrorheological fluid was placed in an electric field of various strengths was measured, and the results are shown in FIG.

(Example 3) As a raw material powder, the same metal silicon powder 80 as in Example 1 was used.
A silicon oxide powder containing silicon dioxide as a main component and sodium chloride was obtained in the same manner as in Example 1 except that silicon powder which was a mixed powder of 20 parts by weight of sodium oxide powder and 20 parts by weight of sodium oxide was used. The specific surface area of this silicon oxide powder was 95 m ² / g, and contained 3% by weight of sodium. Using this silicon oxide powder, an electrorheological fluid was produced in the same manner as in Example 1. Thus, an electrorheological fluid having a viscosity at 20 ° C. of 90 cps was obtained. Measure the yield stress when the obtained electrorheological fluid is placed in an electric field of various strengths,
The results are shown in FIG.

(Comparative Example) A silicon dioxide powder formed by a gas phase combustion method of burning silicon tetrachloride and hydrogen gas in oxygen was prepared. The specific surface area of this silicon dioxide powder is 100 m ² / g, and does not contain sodium. Using this silicon dioxide powder, an electrorheological fluid was produced in the same manner as in Example 1. Viscosity almost equal to that of the electrorheological fluid obtained in Example 1 (20 ° C.
The addition amount required to obtain 100 cps) was 3% by weight. The yield stress when the obtained electrorheological fluid was placed in an electric field of various strengths was measured, and the results are shown in FIG.

(Evaluation) As shown in FIG. 2, the electrorheological fluid obtained in the example increases the yield stress as the electric field strength increases, and shows a high electrorheological effect. It is also clear that the one using the silicon dioxide powder containing sodium shows a higher electrorheological effect. On the other hand, in the comparative example using the conventionally used silicon dioxide powder, the electrorheological effect of the obtained electrorheological fluid is extremely small.

Note that the electrorheological fluid itself obtained in Example 1 was
With respect to the electrorheological fluid obtained in Comparative Example to which 10% by weight of water was added, the relationship between temperature and current density was examined under the condition of electric field strength of 3 kv / min. FIG. 3 shows the results. As shown in FIG. 3, in the case of the one containing water, the amount of current becomes extremely large with the temperature. On the other hand, the water-free electrorheological fluid obtained by the production method of the present invention shows a substantially constant current density even when the temperature rises. That is, the electrorheological fluid obtained by the production method of the present invention can be used even at a high temperature, and is extremely useful for automobiles.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a manufacturing apparatus for manufacturing silicon oxide powder used in one embodiment of the present invention, FIG. 2 is a graph showing a relationship between electric field strength and yield stress, and FIG. It is a graph which shows a relationship. DESCRIPTION OF SYMBOLS 1 ... Reaction container, 2 ... Powder supply passage 3 ... Oxygen gas supply passage 4 ... Propane gas supply passage 5, ... Collection device 20 ... Hopper, 50 ... Collection passage 51 ... Bag filter, 52 …… Blower

Continued on the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical display location C10M 125: 26) C10N 40:16

Claims (1)

(57) [Claims] A powder forming step of burning a silicon powder containing silicon metal as a main component in an oxidizing gas atmosphere to form a silicon oxide powder containing silicon dioxide as a main component; A dispersion step of dispersing the silicon oxide powder in a silicon oil so as to have a content of 5 to 30% by weight, a method for producing an electrorheological fluid, comprising: