Dispersion Kinetics of Thin Double Chromium-Silver Films …
449
metallized oxides by brazing or welding by pressure. The quality of the deposited
films was monitored using an XJL-17 metallographic microscope.
Since the solder material is silver, in this case, specimens with metallic films
deposited onto them were annealed in a vacuum chamber at different temperatures
(from 900 to 1000 °C) in a vacuum no worse than 2 × 10
−3 Pa for different times
(from 5 up to 20 min).
Annealed specimens were investigated using scanning electron microscopes JSM6700 F and Superprobe 733 with microphotographs storing. Using these microphotographs, the areas of metal islets on the surface of non-metallic samples were determined by the planimetric weighting method, i.e., by weighing the elements of the
metallized surfaces of samples carved out from the paper microphotograph copy
[11]. The experimental data obtained were processed in the form of graphs showing
the dependence of the surface area of the samples covered with metal nanofilms on
the annealing parameters (temperature, time).
3 Results and Discussion
The initial double films at all three oxide materials surfaces were continuous, without
cracks, pores, and other defects.
The annealing of the initial double chromium–silver film at the leukosapphire
surface at 900 °C made rather small changes in the film morphology after 20-min
of exposure. The film annealing at 950 °C for 5 and 10 min also did not lead to the
film morphology change. After 20-min of exposure at 950 °C, the film had already
broken up into many interconnected fragments of different shapes covering about
85% of the chromium metallization coating surface (Figs. 1a and 2). In this state, the
film is well suited for the formation of joints of metallized leukosapphire samples by
pressure welding. Annealing the film at 1000 °C for 5 min resulted in the slight film
disintegration (Fig. 1b). Further 10-min exposure led to the silver layer melting and
disintegration into separate droplets covering about 75% of the chromium coating
surface (Figs. 1c and 2). After 20-min of annealing, the molten silver droplets occupied only about 70% of the chromium surface area (Figs. 1d and 2). In this state, the
film is also suitable for brazing leukosapphire samples with low load (up to 0.1 MPa).
In Fig. 2, dependence of the leucosapphire surface area covered with double
chromium–silver film on the annealing time at different temperatures (900–1000 °C)
is shown.
The appearance and character of the morphology change of the double chromium–
silver film deposited onto alumina ceramics were initially almost the same as for films
at the leucosapphire surface. Thus, annealing at 900 °C slightly impaired the integrity
of the original continuous film, even after 20-min of exposure, when the area of its
breaks and voids did not exceed 5–10% of the total film area (Figs. 3a and 4). Increase
of the annealing temperature up to 950 °C intensified somehow the film dispersion
process, and yet after 20-min of exposure, the film covered about 90% of the sample
surface area (Figs. 3b and 4) which makes it possible to use this double film for
449
metallized oxides by brazing or welding by pressure. The quality of the deposited
films was monitored using an XJL-17 metallographic microscope.
Since the solder material is silver, in this case, specimens with metallic films
deposited onto them were annealed in a vacuum chamber at different temperatures
(from 900 to 1000 °C) in a vacuum no worse than 2 × 10
−3 Pa for different times
(from 5 up to 20 min).
Annealed specimens were investigated using scanning electron microscopes JSM6700 F and Superprobe 733 with microphotographs storing. Using these microphotographs, the areas of metal islets on the surface of non-metallic samples were determined by the planimetric weighting method, i.e., by weighing the elements of the
metallized surfaces of samples carved out from the paper microphotograph copy
[11]. The experimental data obtained were processed in the form of graphs showing
the dependence of the surface area of the samples covered with metal nanofilms on
the annealing parameters (temperature, time).
3 Results and Discussion
The initial double films at all three oxide materials surfaces were continuous, without
cracks, pores, and other defects.
The annealing of the initial double chromium–silver film at the leukosapphire
surface at 900 °C made rather small changes in the film morphology after 20-min
of exposure. The film annealing at 950 °C for 5 and 10 min also did not lead to the
film morphology change. After 20-min of exposure at 950 °C, the film had already
broken up into many interconnected fragments of different shapes covering about
85% of the chromium metallization coating surface (Figs. 1a and 2). In this state, the
film is well suited for the formation of joints of metallized leukosapphire samples by
pressure welding. Annealing the film at 1000 °C for 5 min resulted in the slight film
disintegration (Fig. 1b). Further 10-min exposure led to the silver layer melting and
disintegration into separate droplets covering about 75% of the chromium coating
surface (Figs. 1c and 2). After 20-min of annealing, the molten silver droplets occupied only about 70% of the chromium surface area (Figs. 1d and 2). In this state, the
film is also suitable for brazing leukosapphire samples with low load (up to 0.1 MPa).
In Fig. 2, dependence of the leucosapphire surface area covered with double
chromium–silver film on the annealing time at different temperatures (900–1000 °C)
is shown.
The appearance and character of the morphology change of the double chromium–
silver film deposited onto alumina ceramics were initially almost the same as for films
at the leucosapphire surface. Thus, annealing at 900 °C slightly impaired the integrity
of the original continuous film, even after 20-min of exposure, when the area of its
breaks and voids did not exceed 5–10% of the total film area (Figs. 3a and 4). Increase
of the annealing temperature up to 950 °C intensified somehow the film dispersion
process, and yet after 20-min of exposure, the film covered about 90% of the sample
surface area (Figs. 3b and 4) which makes it possible to use this double film for