JP3986489B2 - Foaming agent for foaming / porous metal production - Google Patents

Description

  The present invention relates to a foaming agent used in the production of foam / porous metal.

  A technique for obtaining a foam metal or a porous metal by adding a foaming agent to a molten metal or a powder metal and gasifying the foaming agent by heating them to form countless holes in the metal is known. . In a narrow sense, foam metal contains gas in a myriad of pores, and porous metal has a difference in releasing gas, but it is the same in that it has innumerable pores. I will call it.

Conventionally, a method for producing a foamable metal body has been proposed (for example, Patent Document 1).
Japanese Patent No. 2898437 (page 5)

  Patent Document 1 describes a specific example of a blowing agent such as “titanium hydride 0.2% by weight” in paragraph 5 [0022] line 5 of the publication and “sodium bicarbonate” in line 19 of the same publication. ing.

  In order to foam aluminum that is strongly bound to oxygen, it is common to use titanium hydride or sodium hydrogen carbonate containing hydrogen having a strong reducing power.

However, titanium hydride and sodium hydrogen carbonate are expensive, and there is a problem of raising the production cost of the foamed / porous metal.
In addition, the generated hydrogen gas is a gas that tends to explode, and sufficient care must be taken in handling, increasing the burden on the operator.

  It is an object of the present invention to provide a foaming agent that is inexpensive and free from the danger of hydrogen explosion.

  The present inventors attempted to re-evaluate sodium carbonate because sodium carbonate, which is a hydrogen-free foaming agent and an inexpensive foaming agent, can be used.

  First, a foamable metal was produced by mixing sodium carbonate powder with molten aluminum. When this foamable metal was cut and observed with a microscope, the pores were large and the number of pores per unit volume was less than expected. This is as expected.

  The large pores are those in which the generated bubbles are coalesced in the molten metal, but sodium carbonate has extremely poor wettability with molten aluminum and does not disperse uniformly. For this reason, a large amount of decomposed bubbles are generated at one place, and it is considered that the bubbles collided and grew.

As a new foaming agent, the use of a material having good wettability with molten aluminum has led to the idea that it can be uniformly dispersed and the coalescence of bubbles can be suppressed.
Therefore, a material with better wettability was sought, and in the process, attention was focused on SiO ₂ , which is an easily available and extremely inexpensive material.

The contact angle was examined to evaluate the runout of the material.
FIG. 1 is an explanatory view of a contact angle.
In (a), the test piece 11 is submerged in the molten metal 10 vertically and gently from above, and the angle formed between the edge of the depression formed on the liquid surface and the vertical line is examined. This angle θ is defined as the contact angle.

In (b), the test piece 11 having good wettability was submerged in the molten metal 10. If the wettability is good, the contact angle θ decreases. That is, when the wettability is poor, the contact angle θ increases as shown in FIG.
Thus, the wettability can be evaluated by examining the contact angle θ.

FIG. 2 is a graph showing the contact angle / wettability by material.
First, the test piece 11 (see FIG. 1) was a piece of CaCO ₃ or SiO ₂ , and the molten metal 10 was molten aluminum, and the contact angle was examined. It was found that CaCO ₃ has a large contact angle and SiO ₂ has a small contact angle. From this, it was confirmed that SiO ₂ has sufficiently better wettability than CaCO ₃ .

Therefore, if Coated ing powder CaCO ₃ in SiO _2, and functions SiO ₂ good wettability in the initial stage of foam to prevent movement of the foam, collision of bubbles, as it can prevent the coalescence As a result, when metal foam metal was produced, good results were obtained. Details will be described later.

Accordingly, claim 1 is a foaming agent used when producing a foamed / porous metal, wherein the foaming agent comprises a foamable powder composed of CaCO ₃ or MgCO _3, and a SiO ₂ coating layer covering the surface of the powder. It is characterized by comprising.

Foaming agent according to claim 1, characterized in that it consists an effervescent powder of CaCO ₃ or MgCO _3, and SiO ₂ coating layer covering the surface of the powder.

Since SiO ₂ has good wettability, the foaming agent obtained by applying this layer to a foamable powder made of CaCO ₃ or MgCO ₃ is well dispersed in the molten metal column and has a good quality with pores dispersed uniformly. A foam / porous metal can be obtained.

Blowing agent, since it is merely coated with SiO ₂ in effervescent powder of CaCO ₃ or MgCO _3, less expensive, and using the foaming powder of CaCO ₃ or MgCO ₃ unexpected contain H group So there is no danger of hydrogen explosion.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.
First, the coprecipitation method which is a foaming agent manufacturing method according to the present invention will be described.
FIGS. 3A to 3E are process charts of the coprecipitation method of the foaming agent according to the present invention.
In (a), the Na ₂ SiO ₃ aqueous solution 11 placed in the container 10 is heated to about 40 ° C. by the heating means 12.

In (b), a strong acid (for example, hydrochloric acid) is mixed in the Na ₂ SiO ₃ aqueous solution 11 and the foamable powder 13 is added. The foamable powder 13 is suitably a carbonate such as calcium carbonate (CaCO ₃ ) or magnesium carbonate (Mg CO ₃ ). This is because carbon dioxide gas (carbon dioxide gas) is generated without risk of explosion.

The magnesium carbonate (MgCO ₃ ) is easily obtained and is produced by subjecting basic magnesium carbonate (4MgCO ₃ · Mg (OH ₂ ) · 5H ₂ O), which is highly stable, to a dehydration treatment or the like. Can do.

In (c), the Na ₂ SiO ₃ aqueous solution 11, hydrochloric acid (HCl), and the foamable powder 13 are sufficiently stirred by the stirring means 14. The following reaction occurs by this stirring.

(Liquid) indicates a liquid (aqueous solution), and (solid) indicates a solid (powder or film).
Hydrochloric acid (HCl), which is a strong acid, is added to an aqueous Na ₂ SiO ₃ solution, and SiO ₂ (solid) is produced by utilizing the colloidal silicic acid production reaction that occurs when the solution is made weakly acidic. This SiO ₂ (solid) covers the powder surface of CaCO ₃ .

Note that SiO ₂ is likely to be in the form of silica gel (SiO ₂ .nH ₂ O).
Therefore, silica gel is included in SiO ₂ constituting the SiO ₂ coating layer.

In (d), the mixed solution is filtered with a filter medium 15 such as filter paper. At this time, suctioning is facilitated by a filtering operation.
In (e), the desired foaming agent 20 is obtained by drying.

FIG. 4 is a model diagram of a foaming agent according to the present invention. The foaming agent 20 includes a foamable powder 13 made of CaCO ₃ powder or MgCO ₃ powder, and a SiO ₂ coating layer 21 covering the surface of the foamable powder 13. Consists of.

Next, a method for producing a foamed / porous metal using the foaming agent 20 having the above-described structure will be described.
5 (a) to 5 (e) are production process diagrams of a foam / porous metal using the foaming agent of the present invention.
In (a), Si-based aluminum alloy 32 containing 7% silicon is put in crucible 31 and heated to about 700 ° C. by heater 33 to melt the metal. In addition, although this process and subsequent processes are implemented in a vacuum furnace when melting in vacuum, the vacuum furnace is omitted here.

In (b), while stirring the molten metal 35 with the stirring means 34, the viscosity adjusting agent 36 of Ca or Mg is added to the molten metal 35 to adjust the viscosity.
In (c), an appropriate amount of the blowing agent 20 is further added to the molten metal 35.

(D) shows that the amount of the molten metal 35 was increased because the foaming agent 20 was gasified. In this state, cooling is started.
In (e), the foam / porous metal 37 is obtained by removing from the crucible at an appropriate temperature and further cooling.

In addition to the coprecipitation method described in FIG. 3, the foaming agent of the present invention can be produced by the evaporation method described below.
FIGS. 6A to 6C are process diagrams for the method of evaporating the foaming agent according to the present invention.
In (a), the strong acid and the foamable powder 13 are put into the Na ₂ SiO ₃ aqueous solution 11 put in the container 10.
In (b), the Na ₂ SiO ₃ aqueous solution 11, the strong acid, and the foamable powder 13 are stirred while being heated by the heating means 12. The following reaction occurs by this stirring.

The details of the reaction have been described above and will be omitted.
In (c), the container 10 is continuously heated by the heating means 12 to evaporate the moisture, and as a result, the foaming agent 20 is obtained. The cross-sectional structure of the foaming agent 20 is as described in FIG.

  The foam / porous metal is basically an aluminum alloy, but any metal (including alloy) may be used, and examples thereof include magnesium alloy, iron-based alloy, and stainless steel.

Also, although using hydrochloric acid as the strong acid, sulfuric acid, may be a nitric acid, the kind of strong acid is not limited.

Next, experimental examples according to the present invention will be described. The present invention is not limited to this experimental example.
A: Conditions for producing a foaming agent Production method: Coprecipitation method Na ₂ SiO ₃ (liquid): 2.0% by mass
CaCO ₃ (solid) / Na ₂ SiO ₃ (liquid) = 0.21 g / g
pH: 6.87
Drying temperature: 100 ° C

B: Conditions for producing foam metal Metal to be melted: Si-based aluminum alloy containing 7% silicon Melting equipment: Vacuum melting furnace Melting temperature: 700 ° C
Viscosity modifier: Ca, Mg

FIG. 7 is a graph showing foam / porous metal density.
The density of the example (SiO ₂ coating layer + CaCO ₃ ) was about 1.0 g / cm ³ .
The density of Comparative Example 1 only CaCO ₃ as a blowing agent to which was about 1.8 g / cm ^3.
Further, the density of Comparative Example 2 was about 1.0 g / cm ^{3 using} TiH ₂ conventionally employed as a foaming agent.

As indicated by the white arrow on the left of the vertical axis, the smaller the density, the greater the foamability.
The example is sufficiently smaller in density and larger in foamability than Comparative Example 1.
Moreover, an Example can obtain the foamable metal of a density comparable as the comparative example 2.

  The present invention is suitable for a filler that fills the hollow portion of the vehicle body frame.

It is explanatory drawing of a contact angle. It is a graph showing the contact angle / wettability according to material. It is a coprecipitation method process drawing of the foaming agent concerning the present invention. It is a model figure of the foaming agent which concerns on this invention. It is a manufacturing-process figure of the foaming / porous metal using the foaming agent of this invention. It is an evaporation method process drawing of a foaming agent concerning the present invention. It is a graph which shows a foaming / porous metal density.

Explanation of symbols

13 ... effervescent powder, 20 ... foaming agent, 21 ... SiO ₂ coating layer, 37 ... foam / porous metal.

Claims (1)

In the foaming agent used in producing a foamed / porous metal, the blowing agent is characterized in that it consists an effervescent powder of CaCO ₃ or MgCO _3, and SiO ₂ coating layer covering the surface of the powder Foaming agent for foaming / porous metal production.

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