Surface-roughness evolution during the cementation of silver ions on solid copper in aqueous sulfuric acid solution

Article abstract of DOI:10.1002/hlca.200690093

The evolution of the surface roughness during cementation of Ag⁺ conducted either in O₂-free or O₂-saturated aqueous H₂SO₄CuSO₄ was investigated at two different initial concentrations of Ag⁺. The kinetics data of the process determined previously in the rotating cylinder were linked directly with scanning-electron-microscope (SEM) images and surface-height-distribution diagrams calculated for various cementation times. It was found that, at the beginning of the process, the surface roughness decreases due to formation of a flat Ag layer on the top of the surface, independent of the presence or absence of O₂ in the system. With increasing reaction time, an increase in the surface roughness was observed. The rate enhancement of the process is mainly responsible for the increase of the surface roughness in the O ₂-saturated solutions, especially at the higher initial Ag ⁺ concentration (100 mg/dm³). The rate enhancement observed at a latter stage of the process, connected with the increase of the effective surface area of the cathodic sites, was separated from the rate enhancement induced by the competitive chemical process occurring in O ₂-free solution. The difference in the mechanisms of the processes conducted under aerobic and anaerobic conditions was reflected in the surface-heigth distributions calculated from the SEM images.

Full text of DOI:10.1002/hlca.200690093

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Surface-Roughness Evolution During the Cementation of Silver Ions on Solid
Copper in Aqueous Sulfuric Acid Solution
by Grzegorz D. Sulka* and Marian Jaskuła
Department of Physical Chemistry, Faculty of Chemistry, Jagiellonian University, Ingardena 3, PL-30-060
Krakow
(phone: +48-12-663-2266; fax: +48-12-634-0515; e-mail: sulka@chemia.uj.edu.pl)
The evolution of the surface roughness during cementation of Ag+ conducted either in O2-free or O2-
saturated aqueous H2SO4/CuSO4 was investigated at two different initial concentrations of Ag+. The
kinetics data of the process determined previously in the rotating cylinder were linked directly with scan-
ning-electron-microscope (SEM) images and surface-height-distribution diagrams calculated for various
cementation times. It was found that, at the beginning of the process, the surface roughness decreases due
to formation of a flat Ag layer on the top of the surface, independent of the presence or absence of O2 in
the system. With increasing reaction time, an increase in the surface roughness was observed. The rate
enhancement of the process is mainly responsible for the increase of the surface roughness in the O2-satu-
rated solutions, especially at the higher initial Ag+ concentration (100 mg/dm3). The rate enhancement
observed at a latter stage of the process, connected with the increase of the effective surface area of
the cathodic sites, was separated from the rate enhancement induced by the competitive chemical process
occurring in O2-free solution. The difference in the mechanisms of the processes conducted under aerobic
and anaerobic conditions was reflected in the surface-heigth distributions calculated from the SEM
images.
Introduction. – Cementation is an electrochemical process in which a more-electro-
positive metal ion present in solution is reduced by an electronegative solid metal. Due
to the simplicity of the reaction conditions in various industrial processes and due to its
low-energy consumption, cementation is commonly used for recovery of valuable [1–5]
and precious metals [6–11] from the leach liquors and wastewaters. Cementation pro-
cesses are often employed for purification of electrolytes used for electrodeposition of
high-purity metals [12–14] as well as for removal of toxic metal species and soluble
heavy-metal ions presented in aqueous solutions [15–18]. The overall reaction for sil-
ver (Ag) cementation on copper (Cu) is expressed by the following equation:
2 Ag+ +Cu0 !2 Ag0 +Cu2+
(1)
This is a heterogeneous redox reaction involving reduction of Ag+ at cathodic sites
on the Cu surface, and dissolution of Cu at anodic sites on the same metallic surface. It
is generally accepted that this type of cementation follows first-order kinetics, and is
limited by the diffusion of Ag+ to the Cu surface at the initial stage of the process. How-
ever, the structure and morphology of the reaction product formed during the initial
stage have a significant influence on the kinetics of the process in the latter stage, either
enhancing the rate in some cases [19–28] or passivating the surface in others
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[19][26][29]. In nitrate, sulfate, or perchlorate solutions, rate enhancement was
observed, but a passivating effect of the Ag deposit was observed in cyanide or chloride
solutions. The enhanced cementation rate results usually from the enhancing effect of
the growing deposit by increasing the effective surface area [20–26], thus increasing the
roughness of the deposit and the rate of the mass transfer [19][23][26–28]. The
decrease of the overall reaction rate is attributed to the blocking effect of the growing
Ag cement [19], lower diffusion rate of Ag complexes [26], and a chemical, competitive
process [19][26].
It is worth considering that the starting surface area of the metallic Cu can be easily
modified and significantly enlarged by a relatively high concentration of Ag+, as com-
monly used in cementation. In the latter case, especially when the reacting surface area
is small, a separation and determination of the rate-enhancing factor seems to be
impossible.
The cementation of Ag+ on Cu has been studied before in neat H2SO4 solution
[30][31]. Also, the influence of the concentration of Cu2+ and of O2 in the system on
the kinetics of cementation was discussed. The kinetics and mechanism of Ag cemen-
tation on Cu in 0.5M H2SO4 solution containing 0.5M CuSO4 were reported in previous
papers [32][33]. To avoid the unwanted effect of high Ag+ concentrations and small sur-
face areas, the study was performed in a solution containing either 20 or 100 mg/dm3 of
Ag+ in a rotating cylinder system with a relatively large surface area. It was found that
the cementation reaction at the initial stage of the process follows first-order kinetics.
At a latter stage, the kinetics and mechanism strongly depends on the presence of O2 in
the system. Under anaerobic conditions, a competitive reaction between Ag+ and Cu+,
enhancing the kinetics of the process, can occur in bulk solution. Therefore, the initial
Ag+ concentration influences the morphology of the Ag deposit. On the contrary, the
presence of O2 does not affect significantly the morphology of cemented Ag.
In the present study, we have developed a new approach for studying the surface-
roughness evolution during the cementation process. The observed results are linked
with the mechanism of the process.
Experimental. – Reagent-grade chemicals and four times dist. H2O were used to prepare all solns.
Cementation experiments were carried out in a rotating-cylinder system described previously [32].
The rotating cylinder provides similar turbulent mass-transport conditions even if the roughness of the
deposit increases significantly. The working surface area of the rotating cylinder was 27.50 cm2. Before
each run, the rotating steel cylinder was immersed in HNO3/H2O 1:1 (v/v), rinsed with H2O, and
degreased in MeOH. Then, it was covered electrolytically with a fresh, 24-mm thick layer of Cu. The dep-
osition of Cu was carried out at const. current density (36.4 mA/cm2) for 30 min at 208 in an electrolyte
containing 0.5M H2SO4 and 0.5M CuSO4. To obtain a smooth and flat initial reaction surface, the deposited
Cu layer was electropolished in H3PO4/H2O 3 :1 at const. current density (72.7 mA/cm2) for 40 s at 208,
and then chemically polished in 0.5M H2SO4 soln. After polishing, the cylinder was rinsed, dried, and used
for cementation. All pre-treatment procedures have been described in detail in [32][33].
Cementation was investigated in an electrolyte made of 0.5M H2SO4 and 0.5M CuSO4 at 258. The soln.
was stirred at a controlled speed of 500 r.p.m. The initial concentration of Ag+ in soln. was either 20 or 100
mg/dm3, and was determined before the experiment by atomic-absorption spectroscopy (AAS). The vol-
ume of the electrolyte in the cell was 0.2 dm3. Before each run, the electrolyte in the cell was purged by
bubbling with high-purity Ar or O2 gas for 20 min. The O2-free or O2-sat. atmosphere was maintained
over the soln. throughout the whole process by continuously passing Ar or O2.

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The duration of the experiments was adjusted depending on the initial Ag+ concentration. At 20
mg/dm3 Ag+, samples were analyzed after 7, 14, 21, 30, 40, 50 and 60 min. When the initial Ag+ concen-
tration was 100 mg/dm3, the experiment was terminated after 5, 10, 15, 20, 30, 45, and 60 min. After each
run, the Cu layer with cemented Ag was rinsed carefully, dried, cut, and separated from the cylinder.
Samples of the Cu sheet with cemented Ag were then dissolved in hot HNO3/H2O 1:1, and analyzed
for Ag content by AAS. For each cementation test, the surface of two samples of the Cu sheet with
cemented Ag was inspected with a Phillips XL-30 scanning electron microscope (SEM). SEM Images
were analyzed with the scanning-probe image processor WSxM 3.0 Beta [34].
Results and Discussion. – The surface-roughness evolution during Ag+ cementation
on Cu was investigated under O2-free (anaerobic) and O2-saturated (aerobic) condi-
tions at either 20 or 100 mg/dm3 Ag+. In Fig. 1, the SEM top-view images of the Cu sur-
face with cemented Ag resulting from 20 mg/dm3 Ag+ under O2-free conditions is
shown, together with the corresponding surface-height-distribution diagrams taken at
various time intervals. The analyzed surface area of the samples was ca. 500 mm2. To
better understand the evolution of the surface roughness with cementation time, a
semi-quantitative analysis of the surface–height distribution was performed. The
peak width at half peak height, W1/2, was measured for all histograms (Fig. 1).
At the beginning of the cementation process, some parts of the Cu surface are cov-
ered with metallic Ag, but some parts still remain uncovered. The parts of the surface
with deposited Ag behave as cathodic sites, where the deposition of the noble metal
occurs. The uncovered Cu surface plays the role of the anodic site, where dissolution
of Cu takes place. The dark spots in the SEM image taken after 7 min (Fig. 1,a) repre-
sent anodic sites and/or relatively deep cavities on the surface. These spots are distrib-
uted rather uniformly over the surface area. The distribution histogram of the surface
height calculated from this non-homogeneous surface shows a relatively wide peak
(W1/2 =0.208), with a wide range of surface heights existing on the top of the analyzed
surface. Especially, a negative-height region in the diagram (dark spots in the SEM
image) varies significantly. After 21 min of cementation (Fig. 1,b), the surface is fully
covered with Ag, and the anodic sites are fully developed and spread over the surface
as a net of cracks. It was previously found that anodic sites develop their working sur-
face area in the Cu material just under the deposited Ag, with formation of cavities
under the surface [33]. After 21 min, the Ag crystals found on the surface are tiny, cov-
ering the surface uniformly and compactly. As a result, the surface-height analysis of
the SEM image shows a narrow and intense peak (Fig 1,b; W1/2 =0.168).
The surface roughness changes once again after 40 min (Fig. 1,c). As expected, the
cemented Ag now forms a thicker, less-uniform layer on the top of Cu, and, con-
sequently, a broader peak appears in the surface-height-distribution diagram
(W1/2 =0.243). Further extension of the process duration to 60 min does not change sig-
nificantly the roughness of the Ag deposit (Fig. 1,d). The half-width of the peak
(W1/2 =0.230) is comparable with that obtained after 40 min. This can be attributed
to the percentage of cemented Ag on Cu (relative to the initial Ag content determined
by AAS) remaining almost constant after 30 min under anaerobic conditions at 20
mg/dm3 Ag+. In the distribution diagram of the surface heights presented in Fig. 1,d,
some surface heights, especially in the positive range of the diagram, create an addi-
tional subdiagram. This can be attributed to a rather incidental regularity of the change

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Fig. 1. SEM Top-view images and surface-height-distribution diagrams for Ag cementation in an O2-
free solution. [Ag+]0 =20 mg/dm3, electrolyte: 0.5M H2SO4/0.5M CuSO4, T=258; process time: 7 min
(a), 21 min (b), 40 min (c), 60 min (d).

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in Ag grain size. As will be seen later, the surface-roughness evolution with cementa-
tion time is closely connected with the mechanism of this process.
In Fig. 2, the SEM top-view images of the Cu surface with Ag deposit formed under
aerobic conditions at 20 mg/dm3 Ag+ ion are shown. In the presence of O2, besides the
cementation reaction occurring on the Cu surface, corrosion of Cu takes place. Com-
parison of the corresponding SEM images presented in Figs. 1 and 2 for the same
time intervals shows that the presence of O2 does not modify significantly the morphol-
ogy of Ag cement formed on the top of the surface. The only difference is the degree of
corrosion of Cu and the formation of anodic sites seen as a dense net of cracks (Fig.
2,d). Anodic sites are also clearly visible on the top of the sample obtained after
7 min, when carried out in O2-saturated solution (Fig. 2,a). Due to the enhanced Cu
corrosion, the surface-height distribution calculated from the SEM image shown in
Fig. 2,a shows a broader peak compared to that presented in Fig. 1,a.
After 21 min of cementation, a flattening effect of the Ag deposit appears (Fig.
2,b), and the value of W1/2 decreases. Now, the Ag deposit covers granular Cu crystals
with a uniform layer. As a result, a narrow and intense peak in the surface-height-dis-
tribution diagram appears. Anodic sites, visible as cracks on the surface, are already
fully developed. Further cementation of Ag on the Cu surface leads to an increase in
the thickness of the Ag deposit and its roughness. Larger Ag crystals on the surface
appear, and the peak in the distribution diagram broadens a little (Fig. 2,c). Finally,
after 60 min, the narrow peak in the surface-height-distribution diagram (Fig. 2,d) indi-
cates, in a qualitative fashion, another flattening effect of the Ag deposit.
To better understand the surface-roughness evolution during Ag+ cementation on
Cu (Figs. 1 and 2), deeper insight into the kinetics data and mechanism of the process
is necessary. The Table below shows the average percentage of cemented Ag as a func-
tion of cementation time for both O2-free and O2-saturated conditions, and for initial
Ag+ concentrations of 20 or 100 mg/dm3. As can be seen, at 20 mg/dm3 initial Ag+,
the difference in cemented Ag gets more pronounced after 21 min of process duration
for the aerobic vs. anaerobic systems. This is in agreement with the observation that,
after 21 min, there are smooth Ag deposits on the Cu surface, with a narrow peak in
the surface-height-distribution diagram, in both cases (Figs. 1,b and 2,b). This can be
attributed to the Cu surface being covered with tiny, uniform Ag crystals and a some-
what flattened surface roughness. This result is consistent with kinetics data obtained
previously [32]. There, we had reported that the presence or absence of O2 does not
modify the kinetics of the process at the initial stage of cementation, i.e., during the
first 10–12 min. At a latter stage, a rate enhancement had been observed, mainly for
cementation conducted in O2-free solution. For the later stage, the enhancement factor,
defined as the ratio of actual to initial reaction rate, was estimated at ca. 1.08 and 1.02
for the O2-free and O2-saturated solutions, respectively [32].
During cementation, the surface roughness increases due to the observed slight rate
enhancement, which induces an increase in the size of the Ag crystals, as well as due to
the increasing depth of the anodic sites. The increase in surface roughness is indicated
by peak broadening in the distribution diagrams (Figs. 1,c and 2,c).
Two questions arise after examination of the Table. Why does the smaller rate
observed under aerobic conditions at 20 mg/dm3 Ag+ lead to a higher percentage of
cemented Ag after 40 min? And, vice versa, why is there a lower percentage of

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907
Fig. 2. SEM Top-view images and surface-height-distribution diagrams for Ag cementation in an O2-
saturated solution. [Ag+]0 =20 mg/dm3, electrolyte: 0.5M H2SO4/0.5M CuSO4, T=258; process time:
7 min (a), 21 min (b), 40 min (c), 60 min (d).

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Table. Percentage of Cemented Silver on Copper Determined by AAS under Oxygen-Free and Oxygen-
Saturated Conditions as a Function of Process Time. T=258, f=500 minꢀ1. For details, see Experimental.
t [min]
[Ag]0 =20 mg/dm3 a
)
t [min]
[Ag]0 =100 mg/dm3 a
)
O2-free
O2-sat.
O2-free
O2-sat.
7
14
21
30
40
50
60
17.0ꢁ1.0
28.8ꢁ0.6
40.1ꢁ0.8
46.5ꢁ1.9
45.2ꢁ4.4
40.9ꢁ2.8
48.2ꢁ5.0
15.2ꢁ0.4
28.5ꢁ0.3
39.3ꢁ0.9
53.0ꢁ0.8
61.3ꢁ1.6
66.4ꢁ2.7
72.9ꢁ0.8
5
10
15
20
30
45
60
12.6ꢁ0.6
33.6ꢁ0.2
55.8ꢁ0.3
64.9ꢁ0.6
73.5ꢁ2.9
72.1ꢁ0.9
77.8ꢁ0.4
13.7ꢁ0.2
31.9ꢁ1.9
54.3ꢁ0.4
66.8ꢁ1.7
91.4ꢁ0.4
92.2ꢁ0.1
93.7ꢁ1.1
a) Initial Ag+ solution concentration.
cemented Ag after the same period of time for the higher-rate enhancement found
under anaerobic conditions? As can be seen from the Table, the percentage of
cemented Ag, calculated for the O2-saturated solutions, gradually increases with
cementation time, but quickly reaches a plateau for the O2-free solutions (41–48%
after 30 to 60 min). These results are in very good agreement with a mechanism we
had proposed previously [33]. The mechanism of Ag+ cementation on Cu in aqueous
H2SO4 solution depends on the presence of O2, and consists of two reaction stages.
In the first step, and independent of the presence of O2, adsorbed Cu+ (Cuaþd) is gener-
ated directly on the Cu surface according to the following reaction:
Ag+ +Cu0 !Ag0 +Cuaþd
(2)
The second step of the cementation reaction, however, strongly depends on the
presence or absence of O2. In an O2-saturated solution, the adsorbed Cu+ species either
react with Ag+ (Eqn. 3) or are immediately oxidized by O2 (Eqn. 4).
Cuaþd +Ag+ !Cu2+ +Ag0
(3)
(4)
4 Cuþad +4 H+ +O2 !4 Cu2+ +2 H2O
The front of the reaction is strictly located at the reaction surface. For the O2-free
solution, the generated Cuþad ions can react immediately with Ag+ (Eqn. 3) or diffuse
into the bulk solution to react as dissolved (soluble) Cuþsol ions with Ag+. The latter
process is represented by the following equations:
Cuþad !Cuþsol (via diffusion)
Cusþol +Ag+ !Cu2+ +Agc0olloid
(5)
(6)
The front of the above reaction can move from the surface towards the bulk of the
solution. The progress of the competitive reaction (Eqn. 6) consuming additional Ag+ is

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the main reason why the percentage of cemented Ag remains low and almost constant
between 30 and 60 min (Table). These results are confirmed by the broad peak in the
surface-height-distribution diagram observed after 60 min (Fig. 1,d). The roughness
of the deposit does not change significantly between 40 and 60 min under O2-free con-
ditions. On the contrary, the narrow peak in the diagram (Fig. 2,d) is obtained after 60
min of cementation in O2-saturated solution. This suggests a development of a denser,
more-packed Ag deposit on Cu in the cementation process conducted in O2-saturated
solution. And it is consistent with the kinetics data showing that there is a slight
decrease of the enhancement factor after 30 min of reaction [32]. Taking into account
that the front of the cementation reaction cannot move from the surface towards the
bulk of the solution, the formation of a compact Ag deposit can be expected in the pres-
ence of O2.
In Fig. 3, higher-magnification SEM top-view images of the surface with Ag deposit
are shown for 60 min of cementation for the O2-free (a) and O2-saturated (b) solutions.
The initial Ag+ concentration in solution was 20 mg/dm3. Additionally, a SEM line-scan
analysis of the anodic sites was performed, and the intensity profile along the direction
indicated in the SEM images are presented. Profile analysis shows that there is no sig-
nificant difference in the breadth of cracks on the surface. The average breadth of the
cracks is 0.33 and 0.58 mm for the O2-free and O2-saturated solutions, respectively. This
suggests that the anodic sites develop their surface area under the surface towards the
basic Cu material, as observed in a previous study [33]. Further, it can be seen from Fig.
3 that the Ag cement exhibits a granular structure with small-and medium-sized crys-
tals on the surface, independent of the presence or absence of O2. However, the profile
analysis performed from the SEM images exhibits an interesting, but small difference in
the deposit morphology. Under aerobic conditions, more peaks are recorded in the pro-
file than for the anaerobic system. This can be rationalized in terms of a slightly differ-
ent rate enhancement of the process, and by deposition of finer Ag crystals on the sur-
face during the cementation conducted in the presence of O2.
In Figs. 4 and 5, the SEM images of the sample surface and their surface-height dis-
tributions are shown for an initial Ag+ concentration of 100 mg/dm3 at various reaction
times for O2-free and O2-saturated solutions, respectively. The measured peak half-
width is also shown. The surface area used for the surface-height analysis was ca. 0.7
mm2. A general examination of the SEM images shown in Figs. 4 and 5 leads to the con-
clusion that the presence of O2 does not influence the morphology of the Ag deposit. At
this particular magnification, the dendrites look similar under both aerobic and anae-
robic conditions. The rate enhancement of the process can be expected to be significant
only in the latter stage of the process, based on the increasing surface area of cathodic
sites. Indeed, the enhancement factor for the latter-stage process was estimated at ca.
2.2 and 3.6 for O2-free and O2-saturated solutions, respectively [32]. The increasing sur-
face roughness with cementation time is clearly visible from the SEM images.
As can be seen from Figs. 4,a and 5,a, both taken after 10 min, relatively huge den-
drites appear on the surface. At this stage, the Cu surface is completely covered with a
Ag layer, and cathodic sites start their growth from the surface protrusions developing
significantly their surface area. The surface is highly heterogeneous, and the calculated
distribution histogram of the surface height shows peaks with a significant contribution
of various dendrite heights in the range of positive values (Figs. 4,a or 5,a). The surface

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Fig. 3. SEM Top-view images with anodic sites and line-scan analysis along the marked direction for
Ag cementation after60 min in a) O2-free and b) O2-saturated solution. [Ag+]0 =20 mg/dm3, electro-
lyte: 0.5M H2SO4/0.5M CuSO4, T=258.
area occupied by dendrites and, consequently, the area of cathodic sites, increase with
increasing reaction time under both O2-free and O2-saturated conditions. The increas-
ing number of dendrites formed on the reaction surface and their size and height evo-
lutions result in a peak broadening in the surface-height-distribution diagram with
increasing cementation time (cf. W1/2 in Figs. 4,a–4,c or 5,a–5,c).
From SEM images taken at identical reaction times, e.g., after 10 or 20 min (Figs.
4,a and 5,a, or Figs. 4,b and 5,b), it can be seen that the number of dendrites on the
surface is similar, independent of the presence or absence of O2. These results are con-
sistent with the percentage of cemented Ag found on the reaction surface for an initial
Ag+ concentration of 100 mg/dm3 (Table). There is no observable difference in the per-
centage of Ag on the reaction surface found after the cementation test conducted in the
presence or absence of O2 for reaction times not exceeding 30 min. The difference in
the percentage of cemented Ag calculated for the aerobic and anaerobic processes is
clearly visible for the range of cementation time between 30 and 60 min. In all of
these experiments, the percentage of cemented Ag does not exceed 78% and 94%,
respectively, for the anaerobic and aerobic solutions. The lower value (78%) is closely
related to the mechanism of the process, and especially to the competitive reaction pre-

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Fig. 4. SEM Top-view images and surface-height-distribution diagrams for cementation at high Ag+
concentration in an O2-free solution. [Ag+]0 =100 mg/dm3, electrolyte: 0.5M H2SO4/0.5M CuSO4,
T=258; process time: 10 min (a), 20 min (b), 45 min (c), 60 min (d).

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Fig. 5. SEM Top-view images and surface-height-distribution diagrams for cementation at high Ag+
concentration in an O2-saturated solution. [Ag+]0 =100 mg/dm3, electrolyte: 0.5M H2SO4/0.5M CuSO4,
T=258; process time: 10 min (a), 20 min (b), 45 min (c), 60 min (d).

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913
sented in Eqn. 6 occurring in bulk solution. The contribution of this reaction to the
overall kinetics of the process was estimated at ca. 40% [32]. This difference in the per-
centage of cemented Ag is indicated also in the distribution diagrams of the surface
height. For O2-free conditions, a narrower peak is observed (W1/2 in Figs. 4,c or 4,d)
in comparison to the one obtained for the same time period it the presence of O2
(Figs. 5,c or 5,d).
Conclusions. – The surface roughness varies during Ag+ cementation on solid Cu.
At the beginning of the process, a decrease in surface roughness is observed in both
O2-free and O2-saturated solutions. The flattening effect of Ag cement deposited on
the Cu surface is responsible for this decrease. Further on, an increase in surface rough-
ness appears. Under aerobic conditions, the effective surface area of cathodic sites is
mainly responsible for the increase of the surface roughness. This effect is especially
pronounced in solutions with a high initial Ag+ concentration (100 mg/dm3). Under
anaerobic conditions, the surface roughness does not change significantly from a certain
moment on, and the observed rate enhancement is induced mainly by a competitive
chemical process between Ag+ and Cu+ ions.
Our study clearly shows that distribution diagrams of surface heights can provide
useful information on the surface roughness at various stages of Ag-deposit formation,
and, consequently, can be related to the kinetics of cementation. Qualitative data on
surface roughness obtained for O2-free and O2-saturated solutions can be linked with
the influence of the presence of O2 on the mechanism of the process. Especially, sur-
face-height-distribution diagrams provide unique information in systems with a very
low concentration of the noble metal, where formation of dendrites does not occur.
The method can be employed successfully to study the evolution of surface roughness
during cementation.
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Received January 13, 2006