- Target preparation time and the cost of each target
- Equipment cost
- Reliability and reproducibility of the process
- Build-up of the required thickness
- Coating material losses
- Coating adhesion, especially at a high operating temperature
- Density of the coating
2. Materials and Methods
- Mo powder, <150 μm, 99.99% trace metals basis, Sigma Aldrich 203823
- Polyvinyl alcohol, Mw 89,000–98,000, 99+% hydrolyzed, Sigma Aldrich 341584
- C10100 oxygen free copper, OnlineMetals, www.onlinemetals.com
- 3M 250 Flatback Masking Tape, 3M Company
- 3M 720 Film Fiber Tape, 3M Company
- Hydrogen sintering oven system, Rapidia Inc., Vancouver, BC, Canada
- The substrates samples, approximately 40 mm × 40 mm, were sheared from a 2 mm thick, C10100, oxygen-free, copper sheet and lightly wet-sanded with #400 silicon carbide paper, followed by a wash with hot water and detergent.
- The metal slurry was deposited on the substrate. This was done with the substrate on a scale and the weight of slurry deposited and evenly spread over an area of a 25 mm diameter circle that corresponded to final molybdenum thicknesses of 3–5 gm/cm2. Figure 1a.
- The sample was dried on a hot plate for one hour at 50 °C.
- The surfaces of the first ten samples were rolled with a silicon carbide ball-bearing (mounted on a handle) using hand pressure. Small rolling mills with steel rollers were used for later samples. The rolling was to consolidate the dry coat and to flatten any small voids that were left as a result of air bubbles. Figure 1b.
- The sample was placed in a hydrogen oven (Figure 2), the temperature was raised to 980 °C with a ramping rate of 8 °C per minute, and it was kept at 980 °C for a number of hours. Various times were employed from 4 to 8 h. There seemed to be no difference in the results after 4 h.
- The hydrogen was at atmospheric pressure, and a flow of 0.3 L/min was maintained throughout the process. Since the temperature was close to the melting point of copper and to avoid any deformation, the samples were place on a flat sheet of 99.8% alumina.
- At the end of the process, samples were allowed to cool while still in the oven (and still under hydrogen atmosphere) to below 100 °C and removed (Figure 3). The cooling time of the oven to this temperature was 12 h, and the cooling was done overnight.
Conflicts of Interest
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