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CVD coatings
Published in Kwang Leong Choy, Chemical Vapour Deposition (CVD), 2019
Tungsten has the highest melting temperature of all refractory metals (3422°C). It tends to be difficult to form due to its high hardness, and the most common manufacturing technique is powder metallurgy. However, W can be easily deposited with CVD using the common gaseous precursor tungsten hexafluoride, WF6. CVD-deposited W coatings have high purity, density, and thermal conductivity with a fine, well controlled structure and thickness (µm to mm) required to meet the challenging coating requirements for fusion applications such as abrasion resistance to particle bombardment, high thermal load, high operating temperatures and high thermal conductivity. Other applications of pure W include electronic switches, filaments of incandescent light bulb, and elements to produce X-rays. For X-ray anodes manufacturing, tungsten is mixed with rhenium to improve alloy’s ductility, high temperature resistance, corrosion resistance and tensile strength. Such X-ray anodes are used in medical imaging devices and they are integrated into angiography, mammography, computed tomography, and cardiology equipment, as well as for other non-medical applications such as non-destructive inspection and security checks. In addition, thick metal coatings such as W and Re have been also deposited by CVD onto graphite or composites for fusion applications. Figure 6.13a shows a CVD reactor for the deposition of W-Re coatings and Figure 6.13b shows CVD deposited W layers with Re interlayers to reduce the thermal stress and for crack resistance [44]. Tungsten-rhenium deposits can range from 1 µm to 1 mm. In order to deposit a tungsten-rhenium alloy, two precursors are used: tungsten hexafluoride (WF6) and rhenium hexafluoride (ReF6) with dihydrogen being the carrier gas. The chemical reactions which occur on the substrate surface are as follows:
CVD coatings
Published in Kwang Leong Choy, Chemical Vapour Deposition (CVD), 2019
Tungsten has the highest melting temperature of all refractory metals (3422°C). It tends to be difficult to form due to its high hardness, and the most common manufacturing technique is powder metallurgy. However, W can be easily deposited with CVD using the common gaseous precursor tungsten hexafluoride, WF6. CVD-deposited W coatings have high purity, density, and thermal conductivity with a fine, well controlled structure and thickness (µm to mm) required to meet the challenging coating requirements for fusion applications such as abrasion resistance to particle bombardment, high thermal load, high operating temperatures and high thermal conductivity. Other applications of pure W include electronic switches, filaments of incandescent light bulb, and elements to produce X-rays. For X-ray anodes manufacturing, tungsten is mixed with rhenium to improve alloy’s ductility, high temperature resistance, corrosion resistance and tensile strength. Such X-ray anodes are used in medical imaging devices and they are integrated into angiography, mammography, computed tomography, and cardiology equipment, as well as for other non-medical applications such as non-destructive inspection and security checks. In addition, thick metal coatings such as W and Re have been also deposited by CVD onto graphite or composites for fusion applications. Figure 6.13a shows a CVD reactor for the deposition of W-Re coatings and Figure 6.13b shows CVD deposited W layers with Re interlayers to reduce the thermal stress and for crack resistance [44]. Tungsten-rhenium deposits can range from 1 µm to 1 mm. In order to deposit a tungsten-rhenium alloy, two precursors are used: tungsten hexafluoride (WF6) and rhenium hexafluoride (ReF6) with dihydrogen being the carrier gas. The chemical reactions which occur on the substrate surface are as follows:
Studying propagation of wave of metal foam rectangular plates with graded porosities resting on Kerr substrate in thermal environment via analytical method
Published in Waves in Random and Complex Media, 2022
One of the rarest elements in Earth's crust is Rhenium. Rhenium is a silvery-white metal with very great melting and boiling points and because of this fact, it can be used in various technological applications such as nuclear reactors, semiconductors, thermocouples, mass spectrometer filaments, cathode cups and grid heaters. Also, it can be added to other resistant metals as it amplifies the ductility, tensile and creep strengths and wear resistance of the alloys. Particularly, Rhenium is added to high-temperature super-alloys which are utilized to manufacture jet engine parts and another main application of it, is in platinum–rhenium catalysts and also Rhenium hexafluoride (ReF6) is utilized in the electronics industry for rhenium's depositing films [34–36].