Name: quantitative analysis of vacuum induction melting by laser-induced breakdown spectroscopy
Uploaded: 2019-06-10T13:00:00
Description: Watch this Scientific Journal Video about Quantitative Analysis of Vacuum Induction Melting by Laser-induced Breakdown Spectroscopy at JoVE.com

This study was financially supported by the National Key Scientific Instrument and Equipment Development Projects (Grant No. 2014YQ120351), the Youth Innovation Promotion Association of CAS (Grant No. 2014136), and the China Innovative Talent Promotion Plans for Innovation Team in Priority Fields (Grant No. 2014RA4051).

1. Preparation of Standard Samples
NOTE: This step is not essential.
<ol>
	<li>Prepare raw material (Table 1). To make a 100 kg of sample #1, add 12.82 kg of Cr, 3.39 kg of Mo, 4.79 kg of Al, 1.00 kg of Ti, 0.60 kg of Cu, and approximately 77.4 kg of Ni to the crucible. During the melting process, some elements will be burned. The final ingredient is determined by the melting temperature, melting duration, and other working parameters. The ingredient test shows the quantity ...

<ol>
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For elemental analysis, popular methods are X-ray fluorescence (XRF), spark discharge optical emission spectrometry (SD-OES), atomic absorption spectroscopy (AAS), and inductive couple plasma (ICP). These methods are mainly suited for a laboratory and industrial online application for molten alloys, which is determined by the characters of these technologies, is difficult. XRF uses X-rays to shock samples, and SD-OES makes sparks on the samples. The working distance of these two methods are always in the range of several...

Due to its unique features, such as remote sensing, fast analysis, and no need for sample preparation, laser-induced breakdown spectroscopy (LIBS) offers unique capabilities for on-line concentration determination1,2,3. Although the use of the LIBS technique in different fields has been investigated4,5,6, a considerable attempt to develop its capabilities in industrial applications is ongoing.
Analysis of molten material contents during the course of industrial processes can effectively improve the product quality, which is a promising development direction of LIBS. Experimental findings have been reported about the application of LIBS in the industrial field, such as findings about argon oxygen liquid steel7,8,9,10,11, molten aluminium alloy12, molten salt13, and molten silicon14. The majority of these materials exist in the environment of air or an assistant gas. However, vacuum induction melting (VIM) is another good application field of LIBS to realize processing control. A VIM furnace can realize smelting at temperatures higher than 1,700 &#176;C for alloy refining; it is the most popular method for refining high-purity metal and alloys such as iron-base or nickel-base alloys, high purity alloys, and clean magnetic alloys. During the course of melting, the pressure in a furnace is always in the region of 1-10 Pa, and the composition of air in the furnace mainly includes the air absorbed on the sample or the inner wall of the furnace and some vaporous oxide or nitride metal. These working situations induce quite different LIBS measurement situations for smelting in air. Here, we report an experimental investigation of the analysis of molten alloy during the course of VIM by LIBS.
An optical window is added to a furnace for laser ablation and radiant light detection. A silica glass with a diameter of 80 mm serves as the window. An emitting laser and gathering of radiant light employ the same window; it is a co-axial optical structure that focuses on the same point. The working focal length is approximately 1.8 m, and the focusing length of the experimental setup can be adjusted from 1.5 to 2.5 m.
Based on the practicality of industrial online analysis, precision, repeatability and stability is more important than the low limit of detection (LOD) during molten alloy ingredient analysis. The technical route of a four-channel linear CCD spectrometer is chosen, the spectral range of the spectrometer ranges from 190 to 600 nm, the resolution is 0.06 nm, and the wavelength is 200 nm. A laser diode pumped Q-switched laser (constructed in house) is used to ablate molten alloy, with an output energy of 100 mJ, a frequency of 5 Hz, an FWHM pulse width of 20 ns, and a working wavelength of 1064 nm. The remaining part will present the VIM LIBS-analysing process and live measurement, followed by an introduction of the data processing results.

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	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Laser source</td>
			<td style="width:135px;">Gklaser Co.,Ltd.</td>
			<td style="width:119px;"></td>
			<td style="width:229px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Molten alloy to be measured</td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Smelting furnace</td>
			<td style="width:135px;">Tianyu Co.,Ltd.</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Spectrometer</td>
			<td style="width:135px;">Avantes</td>
			<td style="width:119px;"></td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:216px;">standard samples</td>
			<td style="width:135px;"></td>
			<td style="width:119px;"></td>
			<td>Well known of its composition</td>
		</tr>
	</tbody>
</table>

quantitative analysis of vacuum induction melting by laser-induced breakdown spectroscopy

Vacuum induction melting is a popular method for refining high purity metal and alloys. Traditionally, standard process control in metallurgy involves several steps, include drawing samples, cooling, cutting, transport to the laboratory, and analysis. The whole analysis process requires more than 30 minutes, which hinders on-line process control. Laser-induced breakdown spectroscopy is an excellent on-line analysis method that can satisfy the requirements of vacuum induction melting because it is fast and noncontact and does not require sample preparation. The experimental facility uses a lamp-pumped Q-switched laser to ablate melted liquid steel with an output energy of 80 mJ, a frequency of 5 Hz, a FWHM pulse width of 20 ns, and a working wavelength of 1,064 nm. A multi-channel linear charge coupled device (CCD) spectrometer is used to measure the emission spectrum in real time, with a spectral range from 190 to 600 nm and a resolution of 0.06 nm at a wavelength of 200 nm. The protocol includes several steps: standard alloy sample preparation and an ingredient test, smelting of standard samples and determination of the laser breakdown spectrum, and construction of the elements concentration quantitative analysis curve of each element. To realize the concentration analysis of unknown samples, the spectrum of a sample also needs to be measured and disposed with the same process. The composition of all main elements in the melted alloy can be quantitatively analyzed with an internal standard method. The calibration curve shows that the limit of detection of most metal elements ranges from 20-250 ppm. The concentration of elements, such as Ti, Mo, Nb, V, and Cu, can be lower than 100 ppm, and the concentrations of Cr, Al, Co, Fe, Mn, C, and Si range from 100-200 ppm. The R2 of some calibration curves can exceed 0.94.

Ten nickel-based alloy samples (#1-#10) are used to construct internal-standard calibration curves. The compositions of all samples are listed in Table 1. The elemental concentrations of these samples are orthogonally designed to avoid signal interference. The concentration of each element in all samples is measured with chemical analysis methods.
Nickel is the internal standard element. The calibration curves o...

Watch this Scientific Journal Video about Quantitative Analysis of Vacuum Induction Melting by Laser-induced Breakdown Spectroscopy at JoVE.com

Quantitative Analysis of Vacuum Induction Melting by Laser-induced Breakdown Spectroscopy

During vacuum induction melting, laser-induced breakdown spectroscopy is used to perform real-time quantitative analysis of the main-ingredient elements of a molten alloy.

Vacuum induction melting is a popular method for refining high purity metal and alloys. Traditionally, standard process control in metallurgy involves ...

We have realized industrial online monitoring of the molten alloys component by laser-induced breakdown spectroscopy. By this technology, main and trace elements of the molten alloys can be analyzed in realtime. A vacuum induction smelting furnace can smelt for alloy refining, and this is the most popular method for refining alloys.Analysis of the molten material components during the course of industrial processes can effectively improve the production quality. LIBS has the advantages of fast and long-distance analysis. It is a good method to realize online ingredient analysis for industrial application.Demonstrating the procedure will be Xin Li and Shenghai Zhao, a PhD student and a technician from my laboratory. To begin this procedure, analyze the standard samples and construct the calibration curve of the quantitative analysis as outlined in the text protocol. Then put the unknown sample into the smelting system.Next open the laser generator and realize the pulsed laser output using a pulse width of 20 nanoseconds, a frequency of five hertz, and an energy of 90 millijoules for each pulse. Open the spectrometer and the spectrum deposit software, and determine the spectrum using a spectral range of 190 to 600 nanometers, a resolution of 0.06 nanometers at a wavelength of 200 nanometers, and an integration time of 10 milliseconds. After this, adjust the laser focusing position, and optimize it until the strongest spectrum signal is attained.Determine the laser breakdown spectrum, taking note that each laser pulse generates a frame of the spectrum and that 20 frames of the spectrum are obtained and averaged for the analysis. Intensity of plasma spectral signal is an important factor to get good precision of quantitative analysis. In our experiments, the value of the highest peak should exceed 10, 000.For spectrum pretreatment, perform background correction, such as deleting the background effect caused by breaking radiation, to perform spectrum fitting. Then perform analysis elemental concentration by the internal standard method from the calibration curve. In this study, 10 nickel-based alloy samples are used to construct internal standard calibration curves.Nickel is the internal standard element, and the calibration curves for copper, titanium, molybdenum, aluminum, and chromium are shown here. The calibration curves all show a near-linear relationship between the concentration of the element and the peak intensity. All signal peaks are filtered by the signal intensity, the central wavelength, and the Lorentz fitting effect.The limit of detection for each element is calculated according to the standard of International Union of Pure and Applied Chemistry. Experimental results have shown that this technology can be used on industrial vacuum melting production, and this major components of molten alloys can be quantitatively analyzed.

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