Patent Application
20120237687
The present invention relates to a method of manufacturing a surface-modified carbon material.
A carbon material is light in weight and excellent in chemical and thermal stability and has good thermal conductivity and electrical conductivity even though it is a non-metal material. However, problems with the basic characteristics of the carbon material include dust emission and difficulty in adhering to ceramics, metals, and resins.
As a method for improving the adhesivity, for example, Patent Document 1 shows a proposed method including attaching or printing, onto a graphite surface, metal powder that reacts with carbon to form a carbide, heating the resultant article in a non-oxidizing atmosphere to 800° C. to 2000° C. to form a metal carbide layer on the graphite surface, thereafter metal plating a surface of the metal carbide layer to metallize the graphite surface, and further joining the resultant article to another member using soft solder or hard solder.
Patent Documents 2 and 3 describe that a carbon material is buried in an infiltrating agent that produces chromium halide gas and is heat-treated.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. Hei 01(1989)-203209
[Patent Document 2] Japanese Unexamined Patent Application Publication No. Hei 08(1996)-143384
[Patent Document 3] Japanese Unexamined Patent Application Publication No. Hei 08(1996)-143385
However, by merely attaching or printing metal powder and then heating the material as described in Patent Document 1, a portion in which the metal carbide layer is not formed remains in the carbon substrate. Consequently, problems arise that unevenness is produced in the coating film and the adhesivity of the coating film degrades. The method of burying a carbon material in an infiltrating agent and treating the material, as described in Patent Documents 2 and 3, has the problem that a component of the infiltrating agent adheres to the carbon material. In addition, since it is necessary to pass hydrogen gas through the substance that constitutes the infiltrating agent, variations in product quality occur because of temperature unevenness, and a detector is required to enable hydrogen gas to flow through the equipment. Those factors have increased the cost.
The present invention has been accomplished in view of the foregoing problems, and it is an object of the present invention to provide a carbon material that can prevent unevenness in a coating film and degradation of the adhesivity of the coating film by inhibiting a portion in which a metal carbide layer is not formed from forming in a carbon substrate, and that makes it possible to form a metal carbide in a selected portion thereof and to eliminate excessive manufacturing equipment by causing metal powder to adhere thereto.
The present invention provides a method of manufacturing a carbon material, characterized by comprising: a first step of causing metal powder to adhere to a carbon substrate; and a second step of heat-treating the carbon substrate to which the metal powder has adhered in a vessel containing an atmosphere of hydrogen halide gas.
When the metal powder is heat-treated under an atmosphere of hydrogen halide gas as in the above-described manufacturing method, a metal carbide layer is uniformly formed over a surface of the carbon substrate. Therefore, a portion in which the metal carbide layer is not formed is prevented from forming in the carbon substrate. As a result, it is possible to inhibit formation of unevenness in the coating film and degradation in the adhesivity of the coating film.
In addition, when the metal layer or the like is formed by plating, thermal spraying, or the like after the formation of the metal carbide layer, the bonding strength of the metal layer increases. On the other hand, when the carbon material is used as it is after the formation of the metal carbide layer, generation of dust can be prevented.
It is desirable that in the first step, the metal powder be caused to adhere to the carbon substrate by coating a slurry containing the metal powder and a binder onto the carbon substrate or dipping the carbon substrate into the slurry.
The reason is that when the metal powder is coated onto the carbon substrate using the slurry containing a binder, the metal powder can be coated uniformly and smoothly over a surface of the carbon substrate. Preferable examples of the binder include resin components that are soluble in a solvent, and especially include water-soluble resins, which are soluble in water. Preferable examples of the water-soluble resins include ones that can be burned up during the heat treatment so as not to remain in the carbon material and not to cause adverse effects, and polyvinyl alcohol (PVA) is especially preferable because it is easily available and low cost.
It is desirable that in the second step, the hydrogen halide gas be a hydrogen chloride gas.
The reason is that when the hydrogen halide gas is a hydrogen chloride gas, formation of unevenness in the coating film and degradation of the adhesivity of the coating film can further be inhibited, and moreover, the carbon material can be manufactured at low cost.
It is desirable that in the second step, the carbon substrate to which the metal powder has adhered and ammonium chloride be enclosed in one and the same vessel and heat-treated.
When using ammonium chloride as a hydrogen chloride generating agent, ammonium chloride is easy to handle since ammonium chloride is a solid substance. In addition, the hydrogen chloride gas that is generated from ammonium chloride by heating can change the interior of the vessel into a hydrogen chloride gas atmosphere. As a result, the method of the present invention can be performed easily.
It is desirable that the amount of the ammonium chloride that is contained in the vessel be 1.00×10−4 g/cm3 or more with respect to the volume of the vessel.
The reason is that if the amount of ammonium chloride per unit volume is less than 1.00×10−4 g/cm3, it becomes difficult to form a coating film with good quality. On the other hand, when the amount of ammonium chloride is too large, the resulting advantageous effects do not exceed a certain level, and moreover, the production cost of the carbon material substantially rises. For these reasons, it is desirable that the amount of the ammonium chloride be 1.00×10−2 g/cm3 or less.
It is desirable that the metal powder be chromium powder.
However, the metal powder is not limited to the chromium powder, and it is possible to use a particulate material of an alloy containing chromium, such as stainless steel.
The method of manufacturing a carbon material according to the present invention makes it possible to inhibit a portion in which a metal carbide layer is not formed from forming in a carbon substrate. As a result, it becomes possible to inhibit formation of unevenness in the coating film and degradation in the adhesivity of the coating film.
D3 in which surface unevenness is formed.
Hereinbelow, the present invention will be described in detail.
In a method of manufacturing a carbon material according to the present invention, metal powder is caused to adhere to a carbon substrate, and thereafter, the carbon substrate to which the metal powder has adhered is heat-treated in a vessel containing an atmosphere of hydrogen halide gas. This manufacturing method makes it possible to form a metal carbide layer on a surface of the carbon substrate in a simple manner.
Here, it is preferable that the heat treatment be performed at a temperature of from 800° C. to 1200° C. If the temperature of the heat treatment is too low, it is possible that the formation of the metal carbide layer (for example, chromium carbide) may be slow, and also the layer may not desirably be formed. On the other hand, if the temperature is too high, it is possible that the powder that has not reacted in the heat treatment may be bonded to the carbon substrate.
In addition, it is preferable that the duration of the heat treatment be from 10 to 24 hours. If the treatment duration is too short, the metal carbide layer may not uniformly be formed. On the other hand, if the treatment duration is too long, the formation of the layer will not take place any longer, and moreover, the heat energy required for heating will be correspondingly larger, increasing the production cost.
An example of the method for causing the metal powder to adhere to the carbon substrate is a method of coating a slurry containing metal powder and polyvinyl alcohol (PVA) serving as the binder, as described above, onto the carbon substrate by, for example, printing, screen coating, spin coating, and dip coating. In this case, it is preferable that the amount of the metal powder (for example, chromium) to be attached to the carbon substrate (i.e., the amount of chromium per unit area of the carbon substrate) be from 2.0×10−2 g/cm2 to 8.0×10−2 g/cm2. In addition, it is preferable that the amount of the binder to be attached to the carbon substrate be from 1.0×10−3 g/cm2 to 7.0×10−3 g/cm2.
This will be discussed with reference to
a) to 1(d) are illustrative diagrams showing a manufacturing process of a carbon material in the case where the amount of PVA coated onto the substrate is too large.
First, in the case where the amount of the PVA coated on the substrate is too large, bumps and crevices form on the surface as illustrated in
On the other hand, in the case where the amount of the chromium coated on the substrate is too large, bumps and crevices do not form on the surface as illustrated in
It should be noted that in order to obtain the above-described amount of metal powder per unit area of the carbon substrate, it is possible to repeat the coating process a plurality of times to adjust the coating amount of the slurry.
It is preferable that the amount of the binder be from 1 wt % to 5 wt % with respect to the total amount of the slurry, in order to improve the coatability to the substrate so that the amount of the metal powder can be adjusted easily.
An example of the above-mentioned vessel is a vessel made of carbon, such as a graphite crucible. When such a vessel made of carbon is used, a metal carbide layer can be formed on the carbon substrate within a short time. The reason is believed to be that, by using a vessel made of carbon, the materials contained in the powder, such as the metal particles, can be utilized efficiently for the surface treatment of the carbon substrate, so the necessary heat amount can be reduced.
It is preferable that the heat treatment be performed under normal pressure. Since the treatment can be performed under normal pressure, the equipment such as a vacuum pump is unnecessary, and the time required for reducing the pressure is also unnecessary. As a result, the treatment becomes simpler, and the treatment time reduces.
Although it is possible to perform the treatment under reduced pressure, it may become difficult to cause an efficient reaction of hydrogen halide since the pyrolytic hydrogen halide generating agent may undergo violent decomposition at low temperature, and also, it is possible that the powder may scatter.
Hereinbelow, the components and members used in the present invention will be described.
Examples of the carbon substrate include, but not particularly limited to, isotropic graphite materials, anisotropic graphite materials, and carbon fiber composite materials. It is preferable that the carbon substrate have a bulk density of from 1.0 g/cm3 to 2.1 g/cm3 and a porosity of 40% or less.
In order to allow the vessel to contain an atmosphere of hydrogen halide gas, a pyrolytic hydrogen halide generating agent should be used. The pyrolytic hydrogen halide generating agent is such a substance that is kept in a solid state under room temperature and normal pressure but is decomposed by heating to generate a hydrogen halide, such as hydrogen chloride, hydrogen fluoride, and hydrogen bromide. It is preferable that the heat decomposition temperature of the pyrolytic hydrogen halide generating agent be 200° C. or higher, so that the handling before the heating can be easy. The hydrogen halide generated from the pyrolytic hydrogen halide generating agent reacts with the metal particles during the heat treatment and produces a metal halide gas. By treating the carbon substrate with the metal halide gas, the metal carbide layer can be formed on a surface of the carbon substrate. Since the treatment of the carbon substrate is conducted with gas as described above, the metal carbide layer can be formed substantially uniformly on the carbon substrate even when the carbon substrate has a complicated shape with, for example, holes and grooves.
It is preferable that the pyrolytic hydrogen halide generating agent be ammonium chloride from the viewpoint of availability.
Examples of the metal particles include a powder of a transition metal, a mixture powder of a transition metal and another metal, and an alloy powder of a transition metal and another metal. Examples of the transition metal include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, and Ta, but the transition metal is not particularly limited as long as it reacts with the hydrogen halide and produces a metal halide gas. The produced metal halide gas reacts with the carbon on a surface of the carbon substrate and produces a metal carbide. It is preferable that Cr be contained in the transition metals from the viewpoint of its high reactivity. A preferable example of the metal particles is an alloy powder containing Cr, such as that of stainless steel.
Especially when using metal particles comprising stainless steel, which is an alloy containing Cr, Ni, and Fe, a layer containing Ni, Fe, and chromium carbide is formed at one time of the heat treatment. Therefore, an improvement in handleability and cost reduction can be achieved.
Hereinbelow, the present invention will be described in further detail based on examples thereof. However, the present invention is not limited thereto.
First, chromium powder and a PVA aqueous solution containing 10 wt % of polyvinyl alcohol (PVA), which is a binder, are mixed at a weight ratio of 71.5:28.5 to prepare a slurry, and thereafter, the resultant slurry was coated on a surface of a carbon substrate (20 mm×20 mm) in an amount of 0.4 g. Next, the carbon substrate coated with the slurry was dried at 80° C. until almost all the moisture was eliminated. Next, in a graphite crucible (the crucible was made by Toyo Tanso Co., Ltd, and the volume of the crucible was 351.68 cm3), 0.5 g of ammonium chloride (NH4Cl) (the amount thereof per unit volume of the graphite crucible, which is the vessel, is 1.42×10−3 g/cm3) and the carbon substrate coated with the slurry were placed, and a heat treatment was conducted at 1200° C. for 0.5 hours, whereby a carbon material was fabricated. In the heat treatment, nitrogen was introduced from a gas inlet port, and the gas was discharged naturally from a gas exhaust port.
The carbon material fabricated in this manner is hereinafter referred to as present invention material A1.
Carbon materials were fabricated in the same manner as described in Example 1 above, except that the heat treatment duration was set at 3 hours and 10 hours, respectively.
The carbon materials fabricated in these manners are hereinafter referred to as present invention materials A2 and A3, respectively.
Respective carbon materials were fabricated in the same manner as described in Examples 1 through 3 above, respectively, except that in preparing the slurry, the weight ratio of the PVA aqueous solution and the chromium powder was set at 33.3:66.7.
The carbon materials fabricated in these manners are hereinafter referred to as present invention materials B1 to B3, respectively.
A carbon material was fabricated in the same manner as described in Example 4 above, except that the amount of the ammonium chloride added was set at 0.1 g (the amount thereof per unit volume of the graphite crucible, which is the vessel, was 2.84×10−4 g/cm3).
The carbon material fabricated in this manner is hereinafter referred to as present invention material C.
Respective carbon materials were fabricated in the same manner as described in Examples 1 through 3 above, respectively, except that in preparing the slurry, the weight ratio of the PVA aqueous solution and the chromium powder was set at 83.3:16.7.
The carbon materials fabricated in these manners are hereinafter referred to as present invention materials D1 to D3, respectively.
A carbon material was fabricated in the same manner as described in Example 4 above, except that no ammonium chloride was added.
The carbon material fabricated in this manner is hereinafter referred to as comparative material Z.
The appearance of each of the present invention materials A1 to A3, B1 to B3, C, and D1 to D3 as well as the comparative material Z was observed. The results are shown in Table 1 below.
As clearly seen from Table 1 above, it was observed that in each of the present invention materials A1 to A3, B1 to B3, C, and D1 to D3, a film of chromium carbide (Cr3C2) was formed on a surface of the carbon material, although some of them show slight unevenness. In contrast, in the comparative material Z, chromium particles were confirmed by visual observation. This indicates that the comparative material Z is in such a condition that chromium is firmly attached to the carbon material.
The relationship of the quality of the chromium carbide with the amount of chromium and the heat treatment time was studied. The results are discussed with reference to
The X-ray diffraction was determined using an X-ray diffractometer RINT2000 made by Rigaku Corp., and the surface was observed using SEM. The film thickness of the chromium carbide was 10 μm or less for all the samples.
In the case where the amount of the chromium in the slurry is 66.7 wt % (i.e., the amount of PVA per unit area of the carbon substrate is 3.33×10−3 g/cm2, and the amount of Cr per unit area of the carbon substrate is 6.85×10−2 g/cm2) In the present invention material B1, surface unevenness (bumps and crevices) is observed (see reference numeral 9 in
In the case where the amount of the chromium in the slurry is 16.7 wt % (i.e., the amount of PVA per unit area of the carbon substrate is 8.33×10−3 g/cm2, and the amount of Cr per unit area of the carbon substrate is 1.67×102 g/cm2)
In the present invention material D1, surface unevenness (bumps and crevices) is slightly observed (see
Moreover, as clearly seen from
When taking into consideration the above-described results of the experiments, it is preferable that the concentration of the chromium in the slurry be 10 wt % or higher, that the concentration of the PVA in the slurry be 8 wt % or less, and that the heat treatment time be 10 hours or longer. In addition, it is preferable that the amount of chromium per unit area of the carbon substrate be 3.00×10−2 g/cm2 or greater and that the amount of PVA per unit area of the carbon substrate be 8.00×10−3 g/cm2 or less.
In the foregoing examples, the heat treatment is carried out under the presence of ammonium chloride after coating the slurry containing PVA and metal powder onto a carbon substrate. However, it is possible to carry out the heat treatment after coating a slurry containing ammonium chloride in addition to the PVA and the metal powder onto a carbon substrate. In this case as well, the carbon substrate is treated under an atmosphere of hydrogen halide gas. However, when NH4Cl is added to the slurry, there are cases in which NH4Cl may be separated. For this reason, it is desirable that the treatment be carried out in the manners described in the foregoing examples.
The method of manufacturing a carbon material according to the present invention makes it possible to modify a surface of a carbon substrate by a very simple treatment, by simply heat-treating the carbon substrate to which metal powder has adhered in a vessel containing an atmosphere of hydrogen halide gas.
1—Carbon substrate
2—PVA
3—Chromium
4—Carbonized PVA
5—Chromium carbide
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-274640 | Dec 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/066393 | 9/22/2010 | WO | 00 | 6/4/2012 |
