JP7234537B2 - Determination method of aluminum concentration in aluminum-coated powder - Google Patents

Description

The present invention relates to a method for quantifying aluminum concentration in aluminum-coated powder.

Metal powders are used, for example, as pastes for forming conductive parts of electronic parts. Metal powders can be oxidized in the atmosphere, and the oxidation can impair the inherent properties of the metal powders. Therefore, a coating layer made of aluminum (Al) is sometimes provided on the particle surfaces of the metal powder in order to suppress oxidation. For example, a copper powder containing copper (Cu) has poor weather resistance and tends to decrease in conductivity due to air oxidation. A plated layer containing Al may be formed as a coating layer.

In the production of aluminum-coated powder, it is necessary to form a thin coating layer, so it is important to grasp the thickness of the coating layer with respect to the metal powder, or the aluminum concentration.

As a method for quantifying the aluminum concentration in the aluminum-coated powder, it is conceivable to dissolve the aluminum-coated powder in an acid solution and measure the content of aluminum constituting the coating layer. However, since the coating layer of the aluminum-coated powder is partly oxidized and contains aluminum oxide, it may not be completely dissolved in an acid solution.

Therefore, non-patent documents 1 and 2, for example, disclose methods for quantifying the concentration of aluminum contained in such partially oxidized aluminum-coated powder. Also, generally, first, the aluminum-coated powder is dissolved in an acid solution containing nitric acid. Subsequently, the solution is filtered to recover residues containing aluminum oxide and the like that cannot be completely dissolved in the acid solution. Subsequently, the recovered residue is dried in an electric furnace or the like to be incinerated, and then the incinerated matter is dissolved in an alkali fusion treatment. Then, the concentration of aluminum is measured for each of the solution dissolved in the acid solution and the solution obtained by the alkali fusion treatment. Then, based on these measured values, the aluminum concentration in the aluminum-coated powder is quantified.

JIS H1057 "Method for Determining Aluminum in Copper and Copper Alloys" JIS H1284 "Method for Determining Aluminum in Nickel Alloys"

However, in the above-described quantification method, the aluminum-coated powder and the aluminum oxide contained therein are dissolved by separate methods, and each solution is quantified, which complicates the process. Moreover, the quantification results may vary, and the accuracy of quantification may be low.

The present invention has been made in view of the above problems, and provides a technique for efficiently dissolving aluminum-coated powder with an acid solution without leaving any residue, and for easily and accurately quantifying the concentration of aluminum contained in the aluminum-coated powder. intended to

In order to solve the above problems, the present inventors investigated a method for improving the oxidizing power of an acid solution containing nitric acid. Specifically, since the oxidizing power of nitric acid increases when heated, the solubility of nitric acid was examined by appropriately changing the heating conditions of the acid solution and the concentration of nitric acid in the acid solution. As a result, the inventors have found that it is preferable to add the aluminum-coated powder to an acid solution having a predetermined concentration of nitric acid, and then heat the mixed solution at a predetermined temperature in a sealed state. By heating the acid solution in a sealed state, it is possible to obtain high oxidizing power capable of dissolving aluminum oxide contained in the aluminum-coated powder while suppressing volatilization of nitric acid.

On the other hand, when the aluminum-coated powder is melted in a closed state, gas is generated as the metal melts, and the pressure in the closed container may increase, for example. At this time, it is necessary to set the heating temperature low in order to control the pressure in the sealed container so as not to exceed the withstand pressure of the container. However, if the heating temperature is lowered even in the closed state, not only does it take a long time until the metal melts, but the metal may not be completely melted, leaving a residue. Therefore, in order to raise the heating temperature, further studies were conducted on a method for suppressing the increase in pressure inside the sealed container due to the generation of gas. As a result, after adding the aluminum-coated powder to the acid solution, before heating in a sealed state, the mixed solution should be allowed to stand in an atmosphere of normal temperature and normal pressure in advance to dissolve the soluble components of the aluminum-coated powder. I found out.

As a result, the acid solution can be used to efficiently dissolve the aluminum-coated powder without residue.

The present invention has been made based on the above findings.

That is, the first aspect of the present invention is
A preparation step of preparing an aluminum-coated powder in which a coating layer containing aluminum is provided on the particle surface of the metal powder;
a mixing step of mixing the aluminum-coated powder with an acid solution containing nitric acid and having a nitric acid concentration of 5 mol/L or more and 11 mol/L or less to form a mixed solution;
a standing step of leaving the mixed solution in an open state until the generation of gas accompanying dissolution of the aluminum-coated powder ceases;
a heating step of heating the mixed solution after the standing step to a temperature of 200° C. or higher in a sealed state to form a sample solution in which the aluminum-coated powder dissolves;
a quantification step of quantifying the concentration of aluminum contained in the sample solution;
A method is provided for quantifying aluminum concentration in aluminum coated powders.

A second aspect of the present invention is the method for quantifying the aluminum concentration in the aluminum-coated powder of the first aspect,
In the heating step, the mixed solution is heated at a temperature of 200° C. or higher and 240° C. or lower.

A third aspect of the present invention is the method for quantifying the aluminum concentration in the aluminum-coated powder of the first or second aspect,
In the heating step, the mixed solution is heated by microwave irradiation.

A fourth aspect of the present invention is the method for quantifying the aluminum concentration in the aluminum-coated powder according to any one of the first to third aspects,
In the mixing step, the aluminum-coated powder and the acid solution are mixed so that the nitric acid is two to five times the equivalent in the dissolution reaction of the aluminum-coated powder with nitric acid.

A fifth aspect of the present invention is the method for quantifying the aluminum concentration in the aluminum-coated powder according to any one of the first to fourth aspects,
The acid solution contains only nitric acid as mineral acid.

A sixth aspect of the present invention is the method for quantifying the aluminum concentration in the aluminum-coated powder according to any one of the first to fifth aspects,
In the heating step, the mixed solution is placed in a container made of fluororesin, and heated while the container is sealed.

A seventh aspect of the present invention is the method for quantifying the aluminum concentration in the aluminum-coated powder according to any one of the first to sixth aspects,
The metal powder contains at least one of copper and nickel.

According to the present invention, an acid solution can be used to efficiently dissolve aluminum-coated powder without residue, and the concentration of aluminum contained in the aluminum-coated powder can be easily and accurately quantified.

<One embodiment of the present invention>
A method for quantifying the aluminum concentration in the aluminum-coated powder according to one embodiment of the present invention will be described below. The quantification method of this embodiment has a preparation step, a mixing step, a standing step, a heating step and a quantification step. Each step will be described below.

(Preparation process)
First, an aluminum-coated powder to be quantified is prepared.

The aluminum-coated powder is used, for example, as a conductive paste for forming a conductive member, and is configured by providing a coating layer containing aluminum on the particle surface of the metal powder. As this metal powder, for example, a powder containing at least one of copper and nickel can be used. The coating layer contains aluminum (Al) and is formed, for example, by plating metal powder. The coating layer contains aluminum oxide by oxidation of Al. Although the particle size of the aluminum-coated powder is not particularly limited, it is preferably, for example, 0.1 μm or more and 10 μm or less.

(Mixing process)
Subsequently, the aluminum-coated powder and an acid solution for dissolving it are added to the container and mixed. This forms a mixed solution. By mixing with the acid solution, the metal powder and the coating layer of the aluminum coating powder can be dissolved. On the other hand, the aluminum oxide contained in the coating layer remains undissolved in the acid solution at room temperature.

The acid solution contains at least nitric acid and water. In this embodiment, the nitric acid concentration in the acid solution is set to 5 mol/L or more and 11 mol/L or less. By setting the nitric acid concentration to 5 mol/L or more, a desired oxidizing power can be achieved in the heating step described later, and aluminum oxide can be dissolved without leaving any residue. On the other hand, if the concentration of nitric acid is excessively high, the oxidizing power becomes too strong, so that a passivation film is formed on the aluminum-coated powder, and aluminum oxide may remain. In this respect, the oxidizing power of nitric acid can be appropriately maintained by setting the nitric acid concentration to 11 mol/L or less.

From the viewpoint of safety, the acid solution preferably contains only nitric acid as a mineral acid. On the other hand, in order to further enhance the oxidizing power of the acid solution, other mineral acids than nitric acid may be included as necessary. Other mineral acids that can be used include, for example, sulfuric acid and hydrochloric acid.

The mixing ratio of the aluminum-coated powder and the acid solution is not particularly limited as long as the amount of the acid solution is sufficient to dissolve the aluminum-coated powder. It is preferable to mix the aluminum coating powder and the acid solution so that the equivalent weight in the dissolution reaction of the coating powder with nitric acid is 2 to 5 times.

The container for containing the mixed solution is not particularly limited as long as it has a sealable structure, is highly resistant to the acid solution, and does not melt and deform in the heating step described later. From the viewpoint of acid resistance and heat resistance, a container made of fluororesin is preferable, and for example, a container made of polyethylene tetrafluoride resin can be used.

(Standing process)
Subsequently, the container containing the mixed solution is left open. As a result, the components of the aluminum-coated powder that are soluble under normal temperature and normal pressure are dissolved. Also, the mixed solution is allowed to stand until the generation of gas due to the dissolution of the aluminum-coated powder ceases. As a result, in the heating step described later, when the mixed solution is sealed, it is possible to suppress the increase in pressure in the sealed container due to the generation of gas, and the heating temperature can be increased accordingly. . The time for leaving is not particularly limited, but is, for example, about 15 minutes to 1 hour.

(Heating process)
Subsequently, the container containing the mixed solution is closed by, for example, covering the opening. Then, by heating the sealed container, the temperature and pressure of the contained mixed solution are increased. As a result, the residue mainly composed of aluminum oxide contained in the mixed solution is dissolved to obtain a sample solution in which the aluminum-coated powder is dissolved. If necessary, a certain amount of water may be added to the obtained sample solution to make it a constant volume.

In the heating step, the mixed solution is heated to a temperature of 200° C. or higher. At a temperature of less than 200°C, the aluminum oxide remaining in the mixed solution cannot be dissolved, but by heating to a temperature of 200°C or higher, the aluminum oxide can be reliably dissolved. The upper limit of the temperature is not particularly limited, and may be appropriately changed according to the heat resistance temperature of the container. For example, among fluororesins, tetrafluoroethylene resin has a heat resistant temperature of about 250° C., so the temperature of the mixed solution is preferably 200° C. or higher and 240° C. or lower, more preferably 200° C. or higher and 220° C. or lower. is more preferable.

Moreover, the method for heating the mixed solution is not particularly limited, and a conventionally known method can be employed. From the viewpoint of shortening the heating time and increasing analysis efficiency, heating by microwave irradiation is preferable. Since the mixed solution can be directly heated by microwaves, the time required for heating the mixed solution can be shortened. The irradiation dose, output, etc. of the microwave may be appropriately adjusted so that the temperature of the mixed solution can be maintained, for example, at 200° C. or higher and at a temperature not higher than the temperature at which the container is not thermally deformed. The heating time is not particularly limited as long as the residue is completely dissolved.

In the heating step, the temperature of the mixed solution in the sealed container may be obtained based on the temperature of the container bottom or the container side measured by a non-contact sensor or the like.

(Quantification process)
Next, the concentration of aluminum contained in the obtained sample solution is quantified. Specifically, among the aluminum-coated powder, the content of each of the metal (e.g., copper, nickel, etc.) contained in the metal powder and the aluminum contained in the coating layer is measured, and the concentration of aluminum in the aluminum-coated powder is quantified. . As the quantification method, conventionally known methods such as ICP emission spectrometry, atomic absorption spectrophotometry, and EDTA titration can be employed, but ICP emission spectrometry is preferred because it can be easily quantified.

As described above, the aluminum concentration of the aluminum-coated powder can be quantified. According to the aluminum concentration, it is possible to quantitatively judge how much the coating layer is formed on the metal powder, and it is possible to grasp the formation state of the coating layer such as the thickness and coverage of the coating layer.

<Effects of this embodiment>
According to this embodiment, one or more of the following effects can be obtained.

In the present embodiment, the aluminum-coated powder is added to an acid solution having a nitric acid concentration of 5 to 11 mol/L to prepare a mixed solution, and this mixed solution is left open until gas generation due to dissolution of the aluminum-coated powder ceases. After dissolving under normal pressure, the mixed solution after dissolving under normal pressure is heated at a temperature of 200° C. or higher in a sealed state. By allowing the mixed solution to stand in an open state before heating in a sealed state, components of the aluminum-coated powder that are soluble at normal temperature and normal pressure are dissolved. As a result, when the mixed solution is heated in a closed state, an increase in the internal pressure of the container due to the generation of gas can be suppressed, so that the heating temperature when heated in a closed state can be 200° C. or higher. Further, by heating the mixed solution at a temperature of 200° C. or higher in a sealed state, the oxidizing power can be increased without volatilizing nitric acid. Therefore, when the aluminum-coated powder is added to the acid solution, the aluminum oxide that cannot be completely dissolved and becomes a residue can be dissolved by heating in a sealed state. That is, it is possible to dissolve aluminum oxide using only an acid solution containing nitric acid without subjecting aluminum oxide to residue treatment as in the conventional art. Therefore, according to the present embodiment, the residue treatment can be omitted when the aluminum-coated powder is dissolved, so the aluminum concentration of the aluminum-coated powder can be easily quantified. Moreover, since the aluminum-coated powder and the aluminum oxide contained therein are not dissolved separately, and the aluminum-coated powder can be dissolved without residue in a single operation, the concentration of aluminum contained in the coating layer can be quantified with high accuracy. can. That is, the aluminum concentration in the aluminum-coated powder can be quantified simply and accurately.

Moreover, the temperature for heating the mixed solution in the heating step is preferably 200° C. or higher and lower than the heat-resistant temperature of the container containing the mixed solution. By heating at such a temperature, the aluminum oxide residue in the mixed solution can be reliably dissolved by the acid solution, and melting deformation of the container due to excessive heating can be suppressed. That is, the aluminum-coated powder can be safely and reliably dissolved.

In the heating step, the container containing the mixed solution is preferably a container made of fluororesin, for example, a container made of polyethylene tetrafluoride resin. According to such a container, the mixed solution can be heated at a temperature of 200° C. or higher and 240° C. or lower.

Moreover, in the heating step, the mixed solution is preferably heated by irradiation with microwaves. Microwaves can selectively heat the mixed solution without heating the container or the like. Therefore, the heating efficiency is good, and the time required to dissolve the aluminum oxide by heating can be shortened.

In the mixing step, the aluminum-coated powder and the acid solution are preferably mixed so that the amount of nitric acid is two to five times the equivalent in the dissolution reaction of the aluminum-coated powder with nitric acid. By mixing in such a ratio, the aluminum-coated powder can be dissolved more reliably.

Also, the acid solution preferably contains only nitric acid as the mineral acid. In this embodiment, by heating the acid solution in a sealed state, the oxidizing power is maximized without volatilizing the nitric acid. Therefore, only dilute nitric acid having a nitric acid concentration of 5 to 11 mol/L may be used, and there is no need to add mineral acids other than nitric acid. As a result, the safety in the mixing process, standing process, and heating process can be improved.

In addition, in this embodiment, by omitting the residue treatment, for example, the ashing treatment in an electric furnace and the subsequent alkaline melting treatment can be omitted, so that higher safety can be realized.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be modified in various ways without departing from the gist of the present invention.

The present invention will be described below based on more detailed examples, but the present invention is not limited to these examples.

(Example 1)
First, as the aluminum-coated powder, an Al-coated Cu powder was prepared in which the core metal powder was copper powder and the coating layer was an aluminum layer. Also, as a container, a closed container made of polytetrafluoroethylene resin was prepared.

Next, 0.5 g of Al-coated Cu powder was weighed and added to a container, and a nitric acid solution having a nitric acid concentration of 7 mol/L was added to a 10 ml container as an acid solution to form a mixed solution. Here, the Al-coated Cu powder and the acid solution were mixed so that the equivalent of nitric acid was 3.0 times that of the Al-coated Cu powder. The Al-coated Cu powder was preliminarily dissolved by leaving it in an open state at room temperature for about 30 minutes. After confirming that no gas was generated by dissolution, the container was closed and placed in a microwave thermal decomposition apparatus ("MultiWave 3000" manufactured by AntonPaar Co., Ltd.). Subsequently, the output of the microwave was adjusted to 800 W so that the temperature of the mixed solution was within the range of 200° C. to 220° C., and when the mixed solution reached a predetermined temperature, this state was maintained for 15 minutes. After standing to cool, the solution was collected from the container, transferred to a 100 ml volumetric flask, and water was added to adjust the volume to 100 ml to prepare a sample solution.

It was confirmed that the obtained sample solution had no turbidity and the Al-coated Cu powder was completely dissolved. When this sample solution was measured using an ICP-luminescence spectrometer ("5100" manufactured by Agilent Co., Ltd.), it was confirmed that the aluminum concentration in the Al-coated Cu powder was 4.9%. In this example, the time required for quantifying the aluminum concentration was about 3 hours.

(Example 2)
In Example 2, a sample solution was prepared by dissolving Al-coated Cu powder in the same manner as in Example 1, except that a nitric acid solution having a nitric acid concentration of 5 mol/L was used as the acid solution. In Example 2, the Al-coated Cu powder and the acid solution were mixed so that the equivalent of nitric acid was 2.1 times that of the Al-coated Cu powder.

The resulting sample solution was free of turbidity as in Example 1, and it was confirmed that the Al-coated Cu powder was completely dissolved. When this sample solution was measured using an ICP-luminescence spectrometer, it was confirmed that the aluminum concentration in the Al-coated Cu powder was 4.9%.

(Example 3)
In Example 3, a sample solution was prepared by dissolving Al-coated Cu powder in the same manner as in Example 1, except that the amount of Al-coated Cu powder added was changed from 0.5 g to 0.25 g. In Example 3, the Al-coated Cu powder and the acid solution were mixed so that the equivalent of nitric acid was 6.0 times the Al-coated Cu powder.

The resulting sample solution was free of turbidity as in Example 1, and it was confirmed that the Al-coated Cu powder was completely dissolved. When this sample solution was measured using an ICP-luminescence spectrometer, it was confirmed that the aluminum concentration in the Al-coated Cu powder was 4.9%.

(Comparative example 1)
In Comparative Example 1, 0.5 g of Al-coated Cu powder was weighed and added to a beaker, then pure water and 10 ml of nitric acid were added to the beaker and heated with a heater. After this mixed solution was allowed to cool, it was filtered using a 5B quantitative filter paper in a 100 ml volumetric flask to separate into a filtrate and a residue.

Water was added to the filtrate obtained here to adjust the volume to 100 ml, and then the aluminum concentration was measured using an ICP-luminescence spectrometer. On the other hand, the residue was melted with sodium peroxide and sodium carbonate after being incinerated in an electric furnace by placing a filter paper in a nickel crucible. The solution obtained by the same operation was transferred to a 200 ml volumetric flask, and water was added to adjust the volume to 200 ml. After that, the aluminum concentration was measured using an ICP-luminescence spectrometer.

Finally, the concentration of aluminum contained in the Al-coated Cu powder was obtained from the concentration of each aluminum contained in the filtrate and residue. Three tests were performed and confirmed aluminum concentrations of 4.9%, 4.7% and 4.9%, respectively. In other words, it was confirmed that the aluminum concentration varied in each test and the accuracy of quantification was low. In this comparative example, the time required for one determination of the aluminum concentration was about 9 hours.

(Comparative example 2)
In Comparative Example 2, a sample solution was prepared by dissolving Al-coated Cu powder in the same manner as in Example 1, except that the nitric acid concentration of the nitric acid solution was changed from 7 mol/L to 3 mol/L. In Comparative Example 2, the Al-coated Cu powder and the acid solution were mixed so that the equivalent of nitric acid was 1.3 times that of the Al-coated Cu powder.

It was confirmed that the sample solution obtained in Comparative Example 2 contained residues due to incomplete dissolution of aluminum oxide. This is probably because the concentration of nitric acid was too low, and even if the mixed solution was heated in a sealed state, an oxidizing power capable of dissolving aluminum oxide could not be obtained. The concentration of aluminum contained in the sample solution was not measured because it contained residues.

(Comparative Example 3)
In Comparative Example 3, a sample solution was prepared by dissolving Al-coated Cu powder in the same manner as in Example 1, except that the mixed solution was heated by irradiating microwaves so that the temperature reached 170°C to 190°C.

It was confirmed that the sample solution obtained in Comparative Example 3 contained residues due to incomplete dissolution of aluminum oxide. This is probably because the temperature of the mixed solution was low and the oxidizing power for dissolving aluminum oxide was not obtained. The concentration of aluminum contained in the sample solution was not measured because it contained residues.

As described above, the aluminum-coated powder is added to an acid solution having a predetermined concentration of nitric acid, the mixed solution is left open at normal temperature, and then heated at a predetermined temperature in a sealed state to remove nitric acid. Since the oxidizing power can be improved while suppressing volatilization, the aluminum-coated powder can be dissolved without residue (aluminum oxide, etc.). This makes it possible to quantify the aluminum concentration in the aluminum-coated powder simply and accurately.

Claims (8)

A preparation step of preparing an aluminum-coated powder in which a coating layer containing aluminum and aluminum oxide is provided on the particle surface of the metal powder;
a mixing step of mixing the aluminum-coated powder with an acid solution containing nitric acid and having a nitric acid concentration of 5 mol/L or more and 11 mol/L or less to form a mixed solution;
a standing step of leaving the mixed solution in an open state until the generation of gas accompanying dissolution of the aluminum-coated powder ceases, and dissolving a component of the aluminum-coated powder that is soluble under normal temperature and normal pressure;
By heating the mixed solution after the standing step to a temperature of 200° C. or higher in a sealed state, the residue containing the aluminum oxide that is not dissolved in the standing step is dissolved, forming a sample solution in which the aluminum-coated powder dissolves. a heating step of
a quantification step of quantifying the concentration of aluminum contained in the sample solution;
Method for quantifying aluminum concentration in aluminum-coated powder. In the heating step, the mixed solution is heated at a temperature of 200° C. or higher and 240° C. or lower.
A method for quantifying the aluminum concentration in the aluminum-coated powder according to claim 1. In the heating step, the mixed solution is heated by microwave irradiation.
A method for quantifying the aluminum concentration in the aluminum-coated powder according to claim 1 or 2. In the mixing step, the aluminum-coated powder and the acid solution are mixed so that the nitric acid is two to five times the equivalent in the dissolution reaction of the aluminum-coated powder with nitric acid.
A method for quantifying the aluminum concentration in the aluminum-coated powder according to any one of claims 1 to 3. In the leaving step, leave for 15 minutes or more and 1 hour or less,
A method for quantifying the aluminum concentration in the aluminum-coated powder according to any one of claims 1 to 4. The acid solution contains only nitric acid as a mineral acid,
A method for quantifying the aluminum concentration in the aluminum-coated powder according to any one of claims 1 to 5 . In the heating step, the mixed solution is placed in a container made of fluororesin, and the container is sealed and heated.
A method for quantifying the aluminum concentration in the aluminum-coated powder according to any one of claims 1 to 6 . the metal powder comprises at least one of copper and nickel;
A method for quantifying the aluminum concentration in the aluminum-coated powder according to any one of claims 1 to 7 .