JP2982602B2 - Method and apparatus for laser vaporization analysis of molten metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for quickly analyzing a molten metal such as a hot-dip galvanizing bath or a metal being melted and refined without being solidified.

[0002]

2. Description of the Related Art In the production process of metal materials, in recent years, there has been a demand for a technique for analyzing metal in a frequently or continuously molten state in real time in order to perform higher-level management. Analytical techniques for responding to this include a sensor method, a direct emission spectroscopy method, and a vaporization transfer method. However, in the sensor method, analytical components are limited and it is difficult to quantify trace elements. In the direct light emission method, the molten metal is excited by discharging, irradiating a laser beam, or exothermic element to excite and emit light, and the excitation light is spectrally analyzed and analyzed. There is a problem with the technique for guiding the emitted light to the spectroscope, and it has not been put to practical use. This problem has been avoided by the vaporization transfer method, which includes a method of blowing an inert gas or a reactive gas into the molten metal and a method of applying high-density energy to the molten metal. In the gas injection method, there is a problem of gaseous component selectivity due to a difference in vapor pressure in the case of an inert gas, and there is a problem that the type of reacting component is limited in the case of a reactive gas.

[0003] Among the high-density energy input methods, there is a laser vaporization analysis method of irradiating a laser beam. For example, Japanese Patent Application Laid-Open No. 60-61657 discloses that a probe is brought into contact with a molten metal, a pulsed laser beam is irradiated to collect a sample to be vaporized, and the sample is conveyed to an analytical instrument located remotely from the probe. A method for analyzing a component is disclosed.

[0004]

However, even in the case of vaporizing by irradiating a pulsed laser beam, the rate of vaporization varies considerably depending on the components, and the components that are easily vaporized are selectively collected or the amount of collection is insufficient. However, there remains a problem that there are components and the like, and satisfactory analysis accuracy cannot be obtained.

[0005] The present invention has been made to solve this problem, and by examining the sampling conditions,
An object of the present invention is to provide a highly accurate analysis technique for molten metal by increasing the sample representativeness of a collected sample and securing an amount necessary for detection.

[0006]

Means for achieving the object are to send an inert carrier gas to a probe, irradiate the molten metal with a pulsed laser beam in the probe, and transport the generated fine particle sample to a detector. In the laser vaporization analysis method in which the elemental analysis is performed, a foreign substance on the surface of the molten metal is removed, and the analytical sample is introduced into a probe in an inert gas atmosphere. the energy density of 0.5GW / cm ² or more 50GW / cm ² or less, to implement a laser vaporization analytical method of molten metal taking a sample by irradiating the oscillation frequency 100Hz or more, the embodiments and the methods of the method In the embodiment, the carrier gas is fed into the probe and exhausted from the sample inlet at the tip, and the sample inlet is connected to the molten metal surface. The laser of the molten metal to introduce the analysis sample by removing the foreign material on the surface layer of the molten metal by bringing the probe into a pressurized state and inserting it into the molten metal by bringing it into contact with the probe and releasing the pressurized state after introducing the analysis sample. It is a vaporization analysis method, the apparatus is a pulse laser light irradiation apparatus,
In a laser vaporization analyzer consisting of a probe having a laser light transmission window, a sample inlet, and a carrier gas inlet / outlet, and a detector connected to the probe and a carrier pipe, a double structure in which the probe has an inner cylinder and an outer cylinder An upper portion of the inner cylinder has an opening through which the molten metal is led out of the lower portion of the transmission window, an inlet for the carrier gas is provided on the transmission window side, and an outlet for the carrier gas leading to the outer cylinder has an opening. Of the molten metal having a mechanism provided on the side of the section for forming a flow path through which the carrier gas flows from the transmission window toward the analysis sample, and having a mechanism for suppressing the flow of the carrier gas at the outlet to the carrier pipe provided in the outer cylinder. It is a laser vaporization analyzer.

[0007]

[Function] Ideally, a sample collected from a molten metal by laser irradiation (hereinafter referred to as a "collected sample") has the same component ratio as the original molten metal. Has a different component ratio. Since this difference is corrected by using the calibration curve, there is no problem if the difference has a certain relationship. Variations from this fixed relationship that occur with each analysis are one of the causes of a decrease in analysis accuracy.

[0008] The factors causing the above fluctuations include the mixing of foreign matter and the conditions of laser beam irradiation. As for foreign matter,
In addition to the cleanliness of the equipment and the purity of the carrier gas, the influence of the surface layer of the molten metal is significant. In the molten metal, undissolved compounds as well as oxides oxidized by oxygen in the atmosphere float on the surface layer. Inclusions in steel and dross in plating baths. These contaminants can be avoided by first removing the surface layer of the molten metal and then collecting an analysis sample.

As a method for removing the surface layer, in the case of a general probe for temperature measurement or the like, the probe is inserted through the surface layer while the opening is closed with a lid or plug, and the lid or plug is melted by molten metal. Methods for analyzing invading metals are well known. However, in the laser vaporization analysis, it is not necessary to contaminate the molten metal with a lid or stopper, and since the inside of the probe is always filled with an inert carrier gas, the probe may be contaminated when the opening is in contact with the molten metal surface. The inside of the probe can be pressurized by narrowing or stopping the gas flow path. Thus, when the probe is inserted into the molten metal, the surface layer does not enter the probe. If the pressurized state is released after the opening has passed through the surface layer containing foreign matter, only the molten metal from which the surface layer has been removed is introduced into the probe as an analysis sample.

Next, a sample is collected by irradiating the introduced molten metal with a pulse laser. Regarding the conditions of laser beam irradiation, the inventors first examined solid samples, and in Japanese Patent Application No. 5-159416, the influence of pulse half-width, energy density, oscillation frequency, irradiation point moving speed, etc. on analysis accuracy was examined. Revealed. That is, in order to enhance the analysis accuracy, the vaporization amount is ensured even for the component having a small vapor pressure, and the ratio between the concentration in the mother sample and the concentration in the collected sample (hereinafter, referred to as a selective collection rate) is set to 1. Bringing it closer has an effect.
After that, the inventors of the present invention have studied the molten sample in detail, and have reached the present invention.

[0011] Even in the case of molten metal, the vaporization rate has a large effect on the analysis accuracy. FIG. 2 shows the results obtained by irradiating the hot dip galvanizing bath with a pulsed laser beam and changing the energy density to change the vaporization rate and the analysis accuracy.

Regarding Al and Fe mixed in Zn,
It shows the relative standard deviation of the analysis value when the measurement is repeated 10 times with respect to the vaporization rate.

When the vaporization rate of both Al and Fe increases, the relative standard deviation decreases and the analysis accuracy increases. Also, in the case of molten metal, the influence of the selective sampling rate on the analysis accuracy is large. FIG. 3 shows the results obtained by irradiating the molten steel with a pulsed laser beam and changing the half-width of the pulse to change the selective sampling rate and the analysis accuracy. About C, Si, Mn in steel,
The relative standard deviation of the analysis when the measurement is repeated is shown with respect to the selective collection rate.

As the selective sampling rate approaches 1, the relative standard deviation decreases and the analysis accuracy increases. In a molten metal, unlike a solid metal, a considerable amount of a component having a high vapor pressure is vaporized without irradiating a laser. This state is a state where the selective collection rate is most apart from one. By reducing the pulse half width, the vaporization rate is reduced, but selective evaporation is prevented, and the selective evaporation rate approaches 1. For molten metal,
The range of the appropriate half width of the pulse is narrower than that of the solid.

If the half width of the pulse is less than 50 nsec, the vaporization rate is low, and the amount of trace components and components having a low vapor pressure is insufficient, resulting in a decrease in analysis accuracy. Also, 500nsec
If it is larger, the tendency of selective evaporation increases, which also lowers the analysis accuracy.

Even if the half width of the pulse is 50 nsec or more,
If the energy density of the pulse is less than 0.5 GW / cm ² , the amount of vaporization is insufficient and high analysis accuracy cannot be obtained. The larger the energy density is, the larger the amount of vaporization is, and the selective sampling rate approaches 1, which has a synergistic effect on the analysis accuracy. However, there is an upper limit to the energy density. If the energy density exceeds 50 GW / cm ² , a phenomenon occurs in which the atmospheric gas is turned into plasma by the electromagnetic or thermal action of the laser light, and the energy is consumed and the amount of vaporization is extremely reduced.

If the oscillation frequency is too low, the vaporization rate is inferior, and the amount of the sample introduced into the detector cannot be regarded as being constant, so that the analysis accuracy decreases. To prevent this decrease, it is sufficient that the oscillation frequency is 100 Hz or more.

In order to carry out this analysis method, the probe is not damaged by the molten metal, the inside of the probe can be easily pressurized or depressurized, and the laser beam does not fluctuate on the molten metal surface. Irradiated devices are suitable.

Factors that cause fluctuations in laser light irradiation include vapor from molten metal. When this adheres to the laser light transmission window, not only does the amount of transmitted light decrease, but also the energy density may decrease.

Since the surface of the molten metal is a horizontal plane, the energy density becomes maximum when a laser beam is irradiated from above. For this purpose, a transmission window is provided on the upper surface of the probe, and an opening through which the molten metal is guided is provided below the probe. When the introduction part of the carrier gas is provided on the transmission window side and the outlet part is provided on the opening side to form a flow path in which the carrier gas flows from the transmission window toward the analysis sample, vaporized substances from the molten metal surface pass through the transmission window. Before it reaches the outlet by the carrier gas,
Adherence to the transmission window is avoided.

Further, if the probe has a double structure having an inner tube and an outer tube, a lead-out portion can be provided around the periphery of the molten metal. This can be derived without drifting inside.

The reason why the mechanism for suppressing the flow of the carrier gas is provided at the outlet to the carrier pipe provided in the outer cylinder is to easily increase the pressure in the probe or return it to a constant pressure.

[0023]

EXAMPLE A molten metal such as a molten steel, a galvanizing bath, and an aluminum plating bath was analyzed, and the analysis accuracy was examined.

FIG. 1 shows an outline of the apparatus used. The probe 1 has a double structure consisting of an inner cylinder 2 and an outer cylinder 3,
An inlet 5 for the carrier gas was provided near the transmission window 4, and an outlet 6 was provided below. The transmission window 4 is made of quartz. The lowermost end of the probe 1 becomes an opening 7 and the molten metal 8 enters and exits. Outlet 9
A cock 11 is provided between the probe and the transfer pipe 10 so that the pressure in the probe can be adjusted. The transfer pipe 10 is connected to the detector 12. The laser light 13 is emitted from the laser light irradiation device 14 and passes through the transmission window 4 to irradiate the analysis sample introduced into the probe 1.

The laser beam irradiator 14 adjusts the optical path of the laser beam from the laser oscillator with a reflecting mirror and focuses the laser beam on the surface of the sample to be analyzed with a condenser lens. The laser oscillator has an Nd: YAG with an ultrasonic Q switch. A laser was used. A high frequency inductively coupled plasma emission spectrometer was used as the detector 12.

The probe 1 was slowly immersed in the molten metal while the cock 11 was closed and exhausted from the opening 7 after the carrier gas was flown into the analysis system to purify the inside. After immersion to a depth of about 20 mm, the cock was opened and only the molten metal was introduced.

Table 1 shows laser irradiation conditions and analysis accuracy. The analysis accuracy was evaluated based on the relative standard deviation of the analysis values repeatedly measured 10 times under the same conditions.

[0028]

[Table 1]

In the embodiment of the present invention, molten steel, Zn bath, A
The relative standard deviation was 3% or less for all the components in each of the 1 baths. However, in the comparative example, the relative standard deviation was 4% for all the molten metals.
The above components were found.

[0030]

According to the present invention, the conditions for irradiating the pulsed laser beam are arranged so that the selective sampling rate is close to 1, a sufficient amount of sampling is ensured, and measures are taken to prevent foreign matter from being mixed. Therefore, the molten metal can be directly analyzed with high analysis accuracy. As a result, strict control of the manufacturing process becomes possible, and the effect of the present invention which contributes to the efficient production of high quality materials is great.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a laser vaporization analyzer used in an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a vaporization rate and a relative standard deviation.

FIG. 3 is a diagram showing a relationship between a selective sampling rate and a relative standard deviation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Probe 2 Inner cylinder 3 Outer cylinder 4 Transmission window 5 Inlet 6 Outlet 7 Opening 8 Molten metal 9 Outflow port 10 Conveyance pipe 11 Cock 12 Detector 13 Laser beam 14 Laser irradiation device.

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Akiko Sakashita 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-58-102137 (JP, A) JP-A-63 -30746 (JP, A) JP-A-5-99916 (JP, A) JP-A-60-122354 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 1/28 G01N 21/73 G01N 33/20

Claims (3)

(57) [Claims] 1. A laser vaporization analysis method for sending an inert carrier gas to a probe, irradiating the molten metal with a pulse laser beam in the probe, and transporting a generated fine particle sample to a detector for elemental analysis. An analysis sample is introduced into the probe in an inert gas atmosphere except for foreign substances on the surface layer, and a pulse laser beam having a half width at half maximum of 50 nsec to 500 nsec is applied to the analysis sample at an energy density of 0.5 GW / cm ^2.
A laser vaporization analysis method for molten metal, comprising irradiating at a rate of 50 GW / cm ² or more at an oscillation frequency of 100 Hz or more and collecting a fine particle sample. 2. A sample carrier is fed into the probe and exhausted from the sample inlet at the tip of the probe. The sample inlet is brought into contact with the surface of the molten metal to pressurize the inside of the probe and insert the sample into the molten metal. 2. The method for laser vaporization analysis of molten metal according to claim 1, wherein the pressurized state is released after introducing the sample to remove the foreign matter on the surface layer of the molten metal to introduce the analysis sample. 3. A laser vaporization analyzer comprising: a pulse laser beam irradiation device; a probe having a laser beam transmission window, a sample inlet, and a carrier gas inlet / outlet; and a probe and a detector connected by a carrier tube. The probe has a double structure having an inner cylinder and an outer cylinder, and has an opening through which a molten metal is led into and out of the upper surface of the inner cylinder at a lower portion of the transmission window, and an introduction port for the carrier gas is provided on the transmission window side; An outlet for the carrier gas leading to the outer cylinder is provided on the opening side to form a flow path for the carrier gas to flow from the transmission window toward the analysis sample, and the carrier gas is provided to an outlet to a carrier pipe provided in the outer cylinder. A laser vaporization analyzer for molten metal, comprising a mechanism for suppressing the flow of gas.