Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Bl\CICGROUND OF Tlll~ INVENTION
_______ ___ _ ~
Eield_of the Inv n tiO n
This invention relates to a method of forminy a colored
oxide film on tl~e surface o~ an ~luminum or aluminum alloy
material (l~ereinafter referred to simply as an aluminum
material), and more particularly to a method of forming a
colored oxide film on the surface of an aluminum material
by electrolyzing the aluminum material in an electrolytic
bath containing a metallic salt to thereby color the oxide
film with a color tone characteristic of the metal in the
metallic salt. ~ `
Descri~tlon of the Prior Art
~lerertofore, a variety of methods have been employed
:i .
Eor ~orming a colored oxide Eilm on the surface of an alumi-
num material by electrolyzing the aluminum material by
applying thereto a predetermined voltage in an electrolytic
., .
bath containing a metallic salt. In one such method an oxide
film is formed first by electrolyzing the aluminum material
used as an anode and then colored by applying an AC voltage to
the aluminum material in an aqueous solution containing a color~
forming metallic salt.
With this method, however, the colored oxide film forming
process is composed of two steps and, further, it is necessary
! that the second step using the AC field be achieved after the
, oxide film formation of the first step. This introduces dis-
-. advantages such as difficulty in bath control, low productivity,
a narrow range of color tone of the colored oxide film and poor
reproducibility of color tone, making it difficult to obtain
i uniform colored oxide films at all times.
SUMMARY OF THE INVENTION ~-
According to the invention there is provided a method of
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; forming a colored oxide film on an aluminum material by
electrolyzing said aluminum material in an aqueous electrolytic
bath containing a metallic salt by supplying said aluminum
material serving as at least one electrode with a pulse voltage
consisting of a plurality of unipotential pu:lses whose polarity
is reversed every 0.2 to 240 seconds.
Various features and advantages of this invention will
become apparent from the following description o~ preferred
embodiments taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a waveform diagram of a pulse voltage which is
obtained by half-wave rectification of a single-phase sinewave
. voltage and whose polarity is periodically inverted;
F:iyure 2 is a waveform dlagram o~ a pulse voltage which
is obtairled by phase-controllincl the waveform oE Fic~ure 1
with a silicon controlled rectifier;
Figure 3 is a waveform diagram of a rectangular-wave
pulse voltage whose polarity is periodically inverted and whose
positive and negative pulses are both of rectangular shape;
Figure 4 is a graph showing the interrelationships of a ~:
pulse period T/a pulse duration ra, a peak voltage and color
tone of the resulting colored oxide film in an electrolysis
which is effected in an electrolytic bath containing a metal-
lic salt by applying a rectangular pulse voltage whose po- ~`
larity is periodically inverted;
Figure 5 is a graph showing the same relationships as
in Figure 4 in the case of using a silver salt as a metallic :
salt; -
Figure 6 shows an equivalent circuit of an aluminum
material electrolytic cell;
Figures 7 and 8 show voltage variations between both
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electrodes cluc to a clischarcle frolll arl electrolytic cell
during an elcctroly~sis elllployin<3 ~sucll a rectangular-wave
pulse voltage as depicted in Figure 3;
Figures 9 and 10 are circuit diagrams :illustratinq
an external impedance in conjunction with electrolytic cell;
Figure 11 shows the mode of a current flowing between ~ -
both electrodes in an electrolytic bath which is caused by
the influence of accessories to an electrolyzing equipment
such as leads or the like during an electrolysis using such
a rectangular-wave pulse voltaye as shown in Figure 3; and
Figure 12 is a waveform diaqram of a rectangular-wave
pulse voltage produced by half-wave rectification and phase
control of a commercial AC.
DESCRIPTION OF T~IE PREFERR~D ~ IMENT~
The present invention will hereinafter be described in detail. ~ ~'
At first, an aluminum material is subjected to pretreat-
ment as is the case of ordinary electrolysis. This pre-
treatment is not related directly -to the present invention and
may be a mechanical or a chemical pretreatment. Further, an alu-
minum material having an oxide film previously formed thereoncan also be used and, in this case, the mechanical or chemi-
cal pretreatment is achieved prior to the formation of the
oxide film, so that such pretreatment need not be effected
again.
Then, in an electrolytic bath containing a color forming - ~
metallic salt, the aluminum material with no oxide film formed ~ -
~3 thereon or the aluminum material with an oxide film previously
formed thereon is electrolyzed by using the aluminum material
as one or both electrodes and applying a voltage of the following
characteristics thereto.
The voltage used in this case is a voltage of pulse waveform
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and the polarity of the pulses is periodically reversed with a
reversal period longer than the period of a single pulse.
Further, this voltage of pulse waveform is desirably one
in which the duration of each pulse is short, in which the
initial and final values of the pulse are equal to each other ;~
and in which the pulse rises up to a predetermined level. This
voltage may be such as shown in Figure 1 which is obtained by
half-wave rectification of a single-phase sine-wave voltage,
such as shown in ~igure 2 which is obtained by phase-
controlling the voltage of Figure 1 with a silicon control-
led rectifier or like rectifier, or such as shown in Figure
3 which is a rectangular-wave voltage, or may be a triangu-
lar-wave, exponential-wave or a partly sine-wave voltage.
Of these voltages, a pulse voltage of rectangular waveform is
the easiest to obtain industrially and, by changing the -
characteristic values of the rectangular-wave as required,
~;
i, oxide films colored over a wide range of color tone can be
obtained. ~-
The characteristic values of the rectangular-wave pulse
voltage are pulse durations T and Ta, pulse periods T and Ta,
peak voltages V and Vpa and pulse polarity reversal periods
(hereinafter referred to as conduction times) t and ta, as
shown in Figure 3. The particular metallic salt, which is
contained in the electrolytic bath, is selected according to
the desired color tone of the resulting colored oxide film and
it may be a sulfate, nitrate or any other salt. Further, the
electrolytic bath is required only to be conductive and an `~
aqueous sulfuric acid solution is the most inexpensive, and
hence economical.
' 30 By electrolyzing the aluminum material under such conditions
as described above, a colored aluminum oxide film is formed
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on the surface of the aluminum material.
Now, a description will be given of the colored oxide
. .
film forming mechanism mainly in connection with the case
of electrolyzlncl an aluminum matc~rial by applying thereto ..
the rectangular-wave pulse voltage shown in Figure 3. In
the rectangular-wave pulse shown in Figure 3, the positive
and negative pulse waveforms are different from each other :~
but the characteristic values of the bath pulse waveorms,
for example, the peak voltages V ancl Vpa, the pulse periods
T and Ta~ the pulse durations T and I and the conduction
.. .,~,
times t and ta~ can be selected to be identical or symmetrical .
with each other. Accordingly, the rectangular-wave pulse
voltage will hereinafter be described on the assumption that ...
the characteristic values of the both pulse waveforms are
identical with each other. However, this invention is not .. ~.
limited specifically to the above. ~or example, by selecting
the conduction times o~ the positive and negative pulses to ;~
be different from each other, the color tone of the colored .
. . .
oxide film can be changed as required. Furthermore, by
selacting the peak voltage, the period and the duration of the
positive pulse to be different from those of the negative -~
pulse, the color tone of the colored oxide film can be changed
as desired. ` . :
Thus, in the present invention, if alternately sup- .
plied with the positive and negative pulses such as depicted -.
in Figure 3, the aluminum material serving as one or each
of the electrodes ~ecomes positive and negative alternately ; ~`
with the predetermined conduction times t and ta. In this ~
case, while the polarity of the aluminum material remains .~ .
30 positive, the aluminum material is oxidized as the anode ~.
to form an oxide film. Then, when the polarity of the alu-
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392Z8
minum material becomes negative, metallic ions from the
', metallic salt in the electrolytic bath enter into the oxide
film. (The above metall,ic ions will hereinafter be referred
to simply as the metallic salt.) Next, when the polarity of
the aluminum material becomes positive again, an oxide film
` is formed as mentloned above and, in addition, the metallic
salt having entered into the oxide film is also oxidized
and the resulting products are electro-precipitated in the
oxide film when the polarity of the aluminum material be-
comes negative again, thus forming a colored o~ide film.
With such a mechanism, the colored oxide film is form-
1 ed on the aluminum material and the conditions for the above
i~ coloring mechanism are satisfie~ by the electrolysls using
the pulse voltage. The use of such a rectangular-wave volt-
age as shown in Figure 3 Eacilitates fulfilment of-such con-
ditions.
Namely, while the negative rectangular-wave pulse,volt-
age is applied to the aluminum material to electrolyze it,
the metallic salt invades the oxide film formed on the alu-
'`~ 20 minum material during the application of the positive
rectanyular-wave pulse voltage or the oxide film formed ~ ;
previously. Since the applied pulse voltage is of rectan-
l gular waveform, a predetermined amount of energy to cause
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,' invasion is obtained and the metallic salt invades the oxide
,~ film in the vicinity of the bottom of each pore therein.
~, In other words, the pulse voltaye, in particular, the
rectangular-wave pulse voltac~e, has entirely no rise time
as shown in Figure 3 and the negative peak voltage V
acts on the aluminum material with practically no rise time,
30 so that the energy to cause the invasion by the metallic salt
' is provided simultaneously with rising of the pulse voltage.
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~ Q392Z~ ; ~Hence, the metallic salt enters deeply into the pores of the
oxide film, that is, down to the bottoms of -the pores. `
The metallic salt thus driven into the oxide film by
the electrolysis by the application of the negative rectan-
i gular-wave pulse voltage is electrolyzed and oxidized again
by the application of the positive rectangular-wave pulse
voltage. While the positive rectangular-wave pulse voltage
is applied, oxidation of the metallic salt is promoted to
provide an excellent colored oxide film. ~ ~`
When the oxide film into which the metallic salt
has entered is electrolyzed by the application of the ~ ;
positive pulse voltage, the m~tallic salt is oxidized ~
,
but part of the resulting product is eluted from the pores of `
' the oxide film and, further, part of the metallic salt is
¦ eluted before oxidized. During the next application of the
negative pulse voltage, the remaining oxidized metallic salt
is electro-precipitated in the oxide film and serves as a
;~ coloring source. Accordingly, in order that the
colored oxlde film may be of clear and deep color tone
when it is gradually formed by repeatedly effecting the
above processes, it is necessary that electro-precipita- ~ ;
tion and elution of the product are balanced with each
other. The rectangular-wave pulse voltage satisfies
this requirements most easily and, in the electrolysis
using the rectangular-wave pulse voltage, it is easy
to control the voltage to fulfil the requirement.
Namely, the amount of the metallic salt oxidized -~
during electrolysis by the application of the positive ~ ~;
pulse voltage increases in proportion only to the magni-
tude of such an applied voltage Vp as shown in Figure 3.
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The amount of the oxidized product re-elutec~ is in pro-
portion to the product of the value of the applied
voltage and the duration thereof, that is, the amount of - .
. positive charges. For example, in the case of the volt-
`~ age of the waveform of Figure 3, it isin proportion to
(Vpxl) and, at the same time, the oxide film is formed -
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in proportion to the amount of positive charges or
current flowed.
Consequently, for electrolyzing the aluminum
material in such a manner as to oxidize the metallic
salt and to increase the electro-precipitated product
, within a range in which the oxide film can be formed on
the aluminum material and to prevent re-elution of the ~-
product, it is preferred that the value of the applied
voltage is as large as possible and that the amount of
positive charges or the amount of current is small.
~5 In the case of the rectangular-wave pulse voltage,
'¦ it is possible to apply a high voltage instantaneously.
In the case of controlling the amount of positive
charges and the peak voltage at will as described above,
the rectangular-wave pulse voltage shown in Figure 3
~1 is easier to control than the other pulse voltages and
'I has an advantage that a colored oxide film of desired
i color tone can be obtained.
Figure 4 generally shows the relationships of the
pulse durations T and Ta, the pulse periods T and Ta
' and the peak voltages Vp and Vpa to color tone of the
oxide film in the case where an aluminum material A.A6063
was electrolyzed by the rectangular-wave pulse voltage
, of Figure 3 in a sulfuric acid aqueous solution contain-
ing a metallic salt. Figure 5 shows similar relation-
, ships in the case of an electrolysis in a sulfuric acid
aqueous solution containing Ag2SO4. As is apparent
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from the both graphs, the relationships of Figure 4 and
those of Figure 5 employing a special metallic salt
, (Ag2SO4) are substantially the same but there are some
occasions when chemical and physical properties of the
metallic salt used differ a little in accordance with the
kind of metallic salt added. In Figure 5, triangles,
white circles, black circles and crosses indicate yellow,
light reddish orange, reddish orange and unclear reddish
orange colors, respectively.
, 10 In Figures 4 and 5, n=pulse period/pulse duration
f (=T/~>l or Ta/Ta>1).
' In Figure 4, the ordinate represents the peak voltage
f and the abscissa represents n. Re~erence characters A, B,
C and D indicates zones o~ color tone of the oxide ~ilm.
I C'o~,~ sO~7
As is seen ~rom _ of Figures 4 and 5, ~or
example, in the case of an electrolysis using the pulse
! voltage in a sulfuric acid aqueous solution containing
f Ag2SO4, the zones A,B and C correspond to yellowish, light
f reddish orange and partly deep reddish orange colors, res-
1 20 pectively, and the zone E is one in which the oxide film
f is destroyed even i~ any kind of metallic salt is employed.
As shown in Figure 4, in the zone E above the line
I-I, the peak voltage is high and a current flows ex
cessively, so that the oxide film is broken and its color ~ `
tone becomes unclear. Hence, it is not preferred to
raise the peak voltage above the line I-I. In the zones
f lower than the line I-I, by electrolyzing with the pulse
voltage at different values of n and the peak voltage,
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colors such as shown in Figure 4 can be obtained with
ease.
Further, the zone below the line II-II is divided
into the zones A,B and C in accordance with the values
`,, S of n and the peak voltage. In each zone, the oxide film
is colored only by the balance between the amount of
, the invaded metallic salt oxidized and electro-precipitated
i~' and its eluted amount. For example, as the value of n
increases, the color tone of the oxide film changes from
; 10 A to B and C one after another. For example, in the zone
A in which the value of n is small, the amount of current
, is
~7~ flowed ~n large and the amount of metallic salt eluted
! is larger than that oxidized and electro-precipitated
and, as a result of this, the color tone of the oxide
film becomes light and, in the case of Figure 5, the oxide
film becomes yellowish. In the zone B in which the value
of n is a little larger than that in the zone A, the
amount of metallic salt eluted is a little smaller than
that in the zone A and the color tone of the oxide film
becomes a little deeper. For example, in the case of
Figure 5, the oxide film becomes of a light reddish orange
color. Further, in the zone C in which the value of n is
~, larger than that in the zone B, the pulse width T iS small
¦ but the quiescent time t is short, so that the amount of
. . .
positive current flowed decreases and the thickness of the
~i oxide film decreases but the peak value remains as it is.
Accordingly, in th~ zone C, since the eluted amount de-
creases as compared with the oxidized and electro-
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precipitated amoun-t, the oxide film becomes deeper
in color than in the other zohes. In the case of Figure
5, the oxide film becomes of a reddish orange color and
is partly in a deep reddish orange color. In Figure 4,
the lines III-III and IV-IV between ad~iacent zones below
the line II-II are inclined upwardly. This indicates that
the amount of current flowed contributes to coloring
of the oxide film.
Moreover, the line II-II separating the zones A, B
and C from the zone D is also inclined upwardly. This
indicates that the line II-II exists in the presence
of a certain energy level, considering that when the
amount of current flowed is decreased by an increase in
n, even if the amount of current flowed is increased
by an increase in the peak voltage Vpa, the overall energy
level is lowered.
I Further, in the zone D above the line II-II in Figure
1 4, the color of the oxide film becomes deep and its thick-
ness greatly increases regardless of the value of n. In
this zone D, the peak voltage is high and the current
density increases, so that the balance between the electro-
precipitation and oxidation and the elution is remarkedly
`j~ different from those in the zones A,B and C. Particularly,
over a wide range of n, in other words, over a wide range
of current density zone, oxide films of generally deep
colors can be obtained and, for example, in the case of
Figure 5, a deep reddish orange color can be obtained.
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; In the foregoing, n and the peak voltaye which are
color control factors have been described in connection
with the pulse voltage.
Namely, the magnitude oE the positive peak voltage
~- 5 Vp is related mainly to oxidation of a metal and the
magnitude of the negative peak voltage V a is related
mainly to invasion of the metallic salt into the oxide
film. Considering that coloring of the oxide fllm in
this invention is achieved by invasion, oxidation and
electro-precipitation of the metallic salt, any peak
voltage, whether it is positive or negative, has a close
relation directly to the depth of color tone of the oxide
film.
Z In the present inventlon, the depth of color tone
~;! 15 of the oxide film is dependent upon the energy balance
Z between the amount of the invaded metallic salt oxidized
and its eluted amount. Whether the pulse voltage is
positive or negative, in the zones below the line II-II
in Figure 4, when the values of the peak voltage, n, etc.
are controlled in such a direction as to decrease the
current, the color of the oxide film becomes deeper
and when the above values are controlled in such a di-
rection as to increase the current, the color of the
Z oxide film becomes lighter.
Z, Z5 As described above, in the present invention, the
aluminum material is electrolyzed by applying between
~e both electrodes, at least one of which is the aluminum
material, positive and negative rectangular-wave pulse
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~392Z~
voltages such, for example, as depicted in Figure 3,
for the predetermined conduction times t and ta ~refer
to Figure 3), respectively, whereby oxide films of various
colors are formed.
In the case of electrolyzing the aluminum material
'~ `r~ as described above, unlike in the conventional ~e~
oxidation or AC electrolysis, the peak voltages V and Vp
' rise in a moment and they are impressed for the durations
`~ T and la' respectively, and stopped for the predetermined
quiescent times (T-la andTa-Ta)~ respectively, and then
impressed again ~refer to Figure 3).
However, even if the rectanyular-wave pulse voltage
of such a characteristic is applied to the aluminum material
from a power souce such, for example, as a pulse generator,
lS there are some occasions when exactly the same voltage as
the rectangular-wave pulse voltage is not applied between
the both electrodes, at least one of which is the aluminum
material, under the influence of the amount of charges
stored in the electrolytic cell. An electrolytic cell 1
for electrolyzing the aluminum material has a predetermined
electric capacitance c and an internal resistance r as
shown in its equivalent circuit diagram of Figure 6.
Therefore, even if the power souce is cut off at the time
of decay of the rectangular-wave pulse voltage, since
, 25 charges are stored in the electrolytic cell 1 at the time
~ of impression of the peak voltages Vp and Vpa, the charges
;1 are discharged even after decay of the pulse voltage and
3 the pulse voltage does not fall from the point 2 to 3 but
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falls from the point 2 to 4, as indicated by the solid and
broken lines, respectively, in Figure 7. Further, the
decay time H of the pulse voltage in this case is longer
than the pulse interval or quiescent time h, so that the
next pulse starts to rise before the preceding pulse
, reaches the zero level. Accordingly, in theory, the pulse
voltage should rise from the zero poten-tial to the peak
voltage Vp but, in practice, the pulse only rises :Erom V
to the peak voltage Vp, so that if the value of Vl is
large, the aforementioned effect resulting from sharp
~ rise of the pulse voltage is lost. Therefore, it is
`~ necessary to select the value of Vl as small as possible.
To this end, it is preferred to control the conditions
~ ~ for ele~trolysis in accordance with the capacitance c and
! 15 the intcr~al resistance ~ of the electrolytic cell 1 so
as to ensure that each pulse starts to rise after the
preceding one falls down to substantially zero potential.
i In this case, however, the capacitance c and the
j internal resistance y of the electrolytic cell 1 do not
remain constant during electrolyzing of the aluminum
material. Especially, the value of the capacitance c is
dependent upon the surface area of the aluminum material
and the thickness of a barrier layer of the o~ide film
and it is almost impossible, in practice, to detect the
instant when the pulse voltage lowers down to substantially
zero potential.
If the time necessary for lowering of the pulse
voltage down to about 1/4 of the peak voltage Vp is
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shorter than 1/3 of the ~s9 ~lnterval h, a suffi.ciently
colored oxide film can be obtained regardless of the value :
of the capacitance c of the electrolytic cell. Further, ~ .
by changing the voltage applied between the both electrodes
in the electrolytic cell ~nder ~ch condition as menti.oned
above, color tone of the colored oxide fi.lm can also be .: :.
controlled as desired~
Such a control of the applied voltage can be effected
only by connecting an impedance between out put terminals
of a pulse generator or like pulse source in the following
manner.
Namely, as illustrated in Figure 9, an impedance 7 is
connected in parallel between output terminals 5 and 6 of a .
pulse generator or like pulse source. With such an arrange- ~:
ment, the impedance 7 is connected in parallel with the
capacitance c and the internal resistance r of the electro-
lytic cell 1.
When the pulse voltage is applied to the electrolytic .; ~:.
cell 1 and the power source is cut off, charges in the electro-
lytic cell 1 pass through the impedance 7, so that the mode of :
voltage drop is changed with a change in the time constant of
the impedance 7. Therefore, only by setting the value of the
impedance 7 such that the time necessary for lowering of the
pulse voltage down to 1/4 of the peak voltage Vp may be shorter
than 1/3 of the pulse interval h, the pulse voltage can be
controlled as described above. The same effect cannot be
obtained if, as shown for comparative purposes in Figure 10,
the impedance 7 is connected in series.
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I~ the above, tile influence of the electric capacitance
; c and the internal resistance r of the electrolytic cell 1 has
been described mainly in connection with the voltage which i9 "
applied or detected between the both electrodes at least one of
which is the aluminum material. The reason therefore is that
even if the influence of the current during electrolyzing is
not considered, it is sufficient, in practice, only to consider
the applied or detected voltage as a coloring control factor
and that, in actual electrolysis, the control by the applied or
detected voltage is the easiest and excellent from the industrial
view point.
However, where the pulse voltage of such a wave form
as shown in Figure 3 is applied to the aluminum material to
electrolyze lt in the presence of a large electrolyzing current,
a large difference occurs between the applied pulse voltage
and the current and it is necessary to achieve the electrolysis
taking this difference into account.
Namely, an equivalent circuit of the electrolytic
cell containing an electrolytic bath containing a metallic salt
is regarded to have the electric capacitance c and the internal
resistance r connected to each other as shown in Figure 6.
Accordlngly, in the case of applying the rectangular-wave pulse
voltage to electrolyze the aluminum material in the presence
of a large electrolyzing current, the influence of the load
of a lead in aadition to the electric capacitance c and the
ineernal
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~ resistance ~ of the electrolytic cell is produced,
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--~ by which although a pulse voltage indicated by the
broken line in Figure 11 is applied, the curren-t rises
as indicated by the solid line and does not reach a peak
value Ip in some cases.
Consequently, before the current I :reaches the peak
- value Ip, the power source is cut off and the pulse
voltage rapidly falls. This appreciably lessens the
effect of the pulse voltage impression.
In the present invention, in the case of the impress-
ed voltage, particularly, in the case of the rectangular-
wave pulse voltage, it is sufficient, in practice, only
to properly control the relationships of the peak voltages
Vp and Vpa to the pulse durations r and T a. Especially,
it is advisable to control the peak voltages Vp and V
in the range of 5 to 150V, preferably 10 to 80V and to
control the pulse durations T and ra of the pulse voltages
to be longer than lOxlO sec. in the presence of a large
electrolyzing current. In the presence of an ordianry
electrolyzing current, it is sufficient that the pulse
durations are shorter than lOxlO 3 sec.
In other words, where the peak voltages Vp and Vpa
and the pulse widths T and Ta of the pulse voltage are
controlled as described above and the aluminum material
is electrolyzed by such pulse voltage in the electrolytic
bath containing a metallic salt, the values of the loads
of the electrolytic cell 1 and the lead need not be
considered and the current rises up to its peak value and
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then falls. Thus, the effec-t of application of the
- pulse voltage, that is, the effect of rapid rise and
fall of the voltage or current can be sufficiently
produced.
As described in detail in the foregoing, according
to this invention, the aluminum material is electrolyzed
in an electrolytic bath containing a metallic salt by
applying to the aluminum material a pulse voltage whose
polarity changes from positive to negative and vice
versa alternately with a predetermined period,thereby
to form a colored oxide film on the surface of the
aluminum material. In this case, lt is preferred from
the industrial point of view to obtain the rectangular-
wave pulse voltage by half-wave rectification and phase
control of individual AC components of, for example,
:1 a three-phase or other commercial AC voltage by means of,
;l for example, a silicon controlled rectifier or the like.
;1 In Figure 12, a six-phase commercial AC voltage is
shown by broken lines and voltages obtained by half-wave
rectification and phase control of its individual AC
components are shown by solid lines. The rectangular
pulse voltage depicted in Figure 12 has six ripple
components in the unit period T, Ta or the unit pulse
duration T ~ ~a and the ripple components are saw-tooth
~ 25 in wave form. Consequently, when a positive pulse is
il applied to the aluminum material, the applied voltage on
the aluminum material rises from zero level to the peak
voltage Vp in a moment and, by the impulsive energy
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3~03~ZZ~ ~
resulting from this abrupt rise o~ the voltage, the metallic
salt is oxidized and electro-precipitated. Since the six r~pple
components of the saw-tooth wave form are intermlttently applied
to the aluminum material, the impulse energy is intermittently
; provided, by which oxidation and electro-precipitation of the
metallic salt is further promoted. However, while the electro- ~
precipitation proceeds, the metal is eluted but, in the case 1`
of such a wave form as shown in Figure 12, the oxidation and
electro-precipitation are promoted by the presence of the ripple
; components, so that the pulse width T need not be so large.
Therefore, the amount of positive charges applied to the aluminum
material can be decreased and the amount of the metal eluted `
can be lnevitably held small, with the result that the balance
between the electro-precipitation and the elution can be well
ma intained.
Then, in the negative conduction time ta after the
positive one t, a negative pulse voltage having the same
characteristics as the positive pulse voltage is applied. This
negative pulse voltage also rises from the æero level up to the
peak value Vpa in a moment as is the case with the positive
pulse voltage and the energy for the invasion by the metallic
' salt is applied and, Eurther, by the presence of the six saw-
tooth ripple components, invasion of the metallic salt into
the oxide film is promoted, thereby to further enhance the
coloring effect.
.~ .
,,~, ,
, -21-
.; .
`
~39~
~, Further, in the case of rectifying the commercial
- AC as shown in Figure 12, it is preferred that the pulse
interval or the quiescent time (T-r or Ta-Ta) is deter-
j mined based on the unit period of the commercial AC.
For example, in the waveform shown in Figure 12, its
unit period is used as the pulse period.
In the case of applying the rectangular-wave pulse
'~ voltage, the following values are appropriate.
' V /V / .......... 5 to 150 (10 to 80V)
a T ~ fa T ) 5 to 500Hz (5 to 150HZ)
a
~4O
t~ ta ........... 0.2 to ~T4~ sec. (3 to 50 sec.
In the above, the bracketed values indicate
optimum ranges. The time for electrolysis is usually
sufficient to be about 60 minutes.
The reason why the above values are proper is as
follows:
For example, where the peak voltages are lower
than 5V, coloring is deteriorated and where they are
higher than 150V, it is difficult to control the rate of
forming the oxide film.
From the viewpoint of the coloring effect, it is
preferred, in general, to select the values of the peak
! voltages Vp and Vpa as large as possible. However, the
values of the peak voltages Vp and Vpa are determined
dependent upon the kind of the metallic salt in the
electrolytic bath selected in accordance with color tone
.1 . .
~~
~L~3~2;~8
which is desired to be ultimately obtained. For example t
in the case of the silver salt, optimum values of the
peak voltages Vp and Vpa for Eorming an oxide film of
clear and deep color tone are about 20V or more and,
in this case, the electrolysis can be ac:hieved at rela-
tively low peak voltages Vp and Vpa.
For convenience' sake, the foregoing description
has been given mainly in connection with the case of
applying the rectangular-wave pulse voltage that the
characteristic values of its positive and negative
waveforms are partly or entirely equal to each other.
With the method of this invention however, even if the
~' characteristic values of the positive and negative
~ waveforms are entirely different from each other, a
l 15 colored oxide film can be formed by electrolyzing an
aluminum material and, in addition, the color of the
' oxide film can also be changed as desired. Especially,
1 by increasing the amount of charges of the negative
.~ waveform component in the case of electrolyzing the
. 20 aluminum material in the sulfuric acid aqueous solutioncontaining a metallic salt, degreasing or the like of
:1 I the aluminum material (except the aluminum material
~ v ~,zec/
3~ previously a*~7~e~) can also be achieved.
Further, the foregoing description has been made
~ ' .
1, 25 mainly with regard to the case where the electrolytic
j bath is one containing only sulfuric acid but, even
if one or more of malonic acid, malic acid, maleic acid,
sulfosalicylic acid, sulfamic acid, tartaric acid and
:` ~ z3
:, .
.. .
. ~ ' ~ . . . ....
. ., . . . . . .:
;
. . . . .. .
~39ZZ~
oxalic acid are contained in the electrolytic bath, the
effect does not change. The electrolytic bath may be
- any aqueous solution containing any of the above acids
other than sulfuric acid, so long as it is conductive.
In Figures 1, 2, 3, 7, 8, 11 and 12, the abscissa
represents time and the ordinate represents the peak
voltage.
Now, this invention will be further described by
-1 the following Examples.
EXAMP~E 1
Aluminum materials 1100, degreased and rinsed with
water in usual manner, were electrolyzed in an electro-
, lytic bath composed of 150g of H2SO~ per liter of
water and 60mg of AgNO3 per liter of water, with
aluminum material used as both electrodes. Pulse volt-
ages of rectangular-waveform having a duration of 2 msec.
shown in the following Table 1 were applied, by which
~ colored oxide films of such color tone as shown in Table
! 1 were formed on the aluminum materials. In the cases
shown in Table 1, the time for electrolysis was 60
minutes and the positive and negative waveforms of the
pulse voltages were the same.
,, ~ z~/
. -- ~ _
1~39~28
Table 1.
Conditions for electrolysis Fo:rmed oxide film
Frequency Peak Mean Conduction Film Color tone
f-l or 1 Voltage current Time of thickne.ss
T Ta Vp,V a density Positive (Color indication
f , ~ 2 and of the Munsel
~HZJ (V) (A/dm ) negative(~) solid)
pulses
,...
. 30 1.2 11.3 1-4Y 5.6/7.2
20 0.6 5 3.9 5.6YR
' 10 0.2 . . .1.3 2Y 4.1/5.1
30 1.1 10.3 5.2/4.8
_ 5
20 0.5 3.0 4.1/6.9
, 30 10.6 7.1 2-5Y 5.7/7.9
.j 30 20 O.S 5 3.0 3.4/0.1
~'' 10 6.16 1.0 1.5Y 4.2/4
! _ _
1.0 4.2 0-9Y 5.3/8.7
_ _ 5
20 0.5 2.5 3.8/8.7
. 30 0.8 3.3 3.9/8.7
, 10 5
.3 20 0.4 2.0 2.4YR
;,
1,
~3~1~Z~
The relationships between the pulse durations T and T
of the positive and negative pulse voltages obtained (a)
based on the results given in Table 1 are shown in the
following Table 2. Further, (b) by our experiments
in which the aluminum material was electrolyzed under the
same conditions as those in Table 1, with the aluminum
- being used as one electrode and a carbon electrode as the
counter electrode, it was found that substantially the
same colored oxide films as shown in Table 1 could be
obtained. In the both cases (a) and (b), the time for
electrolysis was also 60 minutes.
. ' .
:, .
:,,
',
,.
: ~ Z ~
.` . . , , :
.
1~392~3
Table 2.
Conditlons for electrolysis Formed oxide film
Duration Frequency Peak Mean Conduction Film Color Tone
. T ~ 1 voltage current time of thick- (Color indica-
: ~ a f= T or V , V density positivenesstion of the
(m sec) 1 P pa 2 and Munsel Solid)
~; _ (V)(A/dm ) negative
:~ (Hz) pulses
: (sec) (~)
:' .. .
40 1.9 22.64.6/5.4 .
2 30 1.6 5 17~2 g.9YR
_ 100 20 0.6 3. a 6.9/1/5
:~ 40 3.6 28.3 3.4Y
, . 5.8/2.9
`~ 3 30 2.1 5 12.88-9Y 5.2/5.8
0.7 5.95Y 7.4/6.1 _
1.4 13.54.5/8~.5
. 2 30 1.2 5 11.3_ 5 6/7.2
0.6 3.95 6YR4/8.8
. 50 40 2.0 20.0 2.7G
;l. 4.9/5.6
!, 3 30 1 3 5 6.86.1/5.6
. _ _ _ 20 0.6 4.3 5Y 6.3/2.4
,",
~ 7
' "
. . , . , ~ .
.. . . . . . .
39~
It appears from Table 2 that color tone of the
colored oxide film can also be changed only by changing
the pulse duration as required.
EXAMPLE 2
Aluminum materials 6063, degreased and rinsed with
water in usual manner, were electrolyzed by applying
the same rectangular pulse voltage as that used in
Example 1 under such conditions as shown in the following
Table 3, with the aluminums being used as both electrodes.
As a result of this, colored oxide films such color tone
as shown in Table 3 were formed on the aluminum materials.
The for each electrolysis was 60 minutes. In Table 3,
additive components in the electrolytic bath are shown in
their weights per liter of wate~.
"
~ z~
~,.. I _ ~ _
.
~ , .
:. ~. ,.. ~ . , . - , . . ..
1~39~221~
~ Table 3.
, .
BathConditions for electrolysis Formed oxide film
Compos Ltion
Basic Added Duration Frequency Peak Mean Conduc- Film Color
liquid Metalic T, T 1 1 Volt- cur- tion thick tone
. Salt af=T or T- age rent time of ness (Color
: (msec) dens- positive indica-
., (Hz) Vp~ ity and tion of
V r.egative the
pa pulses Munsel
, (A/2 t, ta Solid)
1 (V) dm ) (sec) (~)
.
H2So4 HAuCl4 3.5RP
~ 2 50 25 0.98 5 6
J150 100 4.2/
lg/Q mg/~ 7.1
:~ _
~;H2SO4Na3SeO3 2 25 0.6 5 4.6 ly
6.7/
2.4
5 g/Q 6;2~ 11.0 51( 4 ~ 8YR
~.
i1 .
.' .
.
.. .. . .
~ ~39~z~
EXAMPLE 3
Aluminum materials of the same kind as employed in
Example 1, similarly degreased and rinsed with water,
were electrolyzed in the electrolytic bath of the same
S composition as that in Example 1, with the aluminum
materials being used as both electrodes. In this case,
a voltage obtained by half-wave rectification of a
single-phase sine-wave, shown in Eigure 1, and a voltage
obtained by controlling the above voltage with a silicon
controlled rectifier (refer to Figure 2), were applied
.1 as positive and negative pulse voltages to the aluminum
, materials. The electrolysis was achieved under the
', conditions shown in the following Tahle 4.
Colored oxide films of such color tone as shown in
L5 Table 4 were formed on the aluminum materials. The
, time for each electrolysis was 60 minutes and the
` frequency used was 60 Hz.
;,
:;, .
.~, ,,, . : , : .
:.............. , , . , , , :
Table 4.
, .
Formed oxide
` Conditions for electrolysis film
:`, _
Kind of Duration Peak Mean Conduction Film Color
. applied T, T Volt- current time of thick- tone
.~ voltage a age density positive ness (Color indica- :~
V ,V and tion of the
p pa pulses Munsel solid)
t, ta
(msec) (Y) (A/dm2) (sec) (~ _ _ _
i Voltage 2.9Y .
obtained 30 2.4 5 15.0 6.2/8.2
by half- 3.0Y
rectification 5.7 20 1.14 5 _4 8 5.9/7.6
. single-phase 4.lY
Fi . 1) 10 0.64 5 1.5 5.7/3.5
lq
Voltage 9.4YR
, obtained by 2.6 30 1.8 5 14.8 5.2/8.8: controlling 3.lYR
. the above 1.4 20 0.24 5 1.5 3.8/7.4
voltage ::
with SCR 8.5YR :
(Fig. 2) 1.6 10 0.30 5 0.8 4.1/6.3
,~ .
.;i . :,
'~' :' `
, ! ,:
: '.
~Z '-
,:1
::
,.,
~Z ~I g/
-- _
:`
'': : , ' ' ` ~ `. ' ' . ` ' :
3~Z~I
-
EXAMPLE 4.
Aluminum materials A.A6063, subjected to pretreat-
ment in known manner, were electrolyzed in an electrolytic
~` bath containing 150g of H2SO4 per liter of water and 50mg
of Ag2SO4 (at a bath temperature 23C~ under -the conditions
shown in Table 5 for 60 minutes. The puls~ width used was
' ~ ~ 16 msec. By changing the ~t~ of the peak voltage and
. ~.
- n(=T/T) during electrolyzing, colored oxide films shown in
Table 5 were formed.
By rearranging the results in relation to the peak
` voltage and n(=T/T), the relation-ships shown in Figure
5 were obtained.
Further, when the aluminum materials were electrolyzed
under the conditions shown in Table 6 with different pulse
! 15 durations, such colored oxide films shown in Table 6 were
~ obtained.
. ~ .
The distribution of the depth of color tone of the
I colored oxide films obtained in this case was substantially
j! the same as shown in Figure 5. Even when the pulse dura-
i 20 tion was changed based on the above, the variation in the
depth of color tone of the oxide films was substantially
the same as the basic tendency shown in Figure 4.
The current density values given in Tables 5 and 6
~, ~ are all those obtained with a moving-coil ammeter.
:!
;!
:1 -- 3~S --
-.-; .. . . . ~ . . ` ~ . . .
,.,;. . ~ . . . . ..... .. ; . ... .
.-.. ~ , .. ..
.
- ~392~8
. Table S.
..... _ _
: Conditions for electrolysis Formed oxide Film,, ..... _ _
., peak Voltage Period Mean curren-t Film thick- Color tone
Vp ' n T 2 ness
(V) (A/dm ) (~)
.. , . . ._ _
, 10 lO0 0.32 1.7Reddish orange
. 8 80 0.37 2.0
: 20 6 60 0.44 2.5 ll
4 40 0.64 4.0Right reddish
orange
~, 2 20 1.18 7.8 Yellow
_
lO lO0 0.54 4.0Reddish orange
'~ 8 80 0.60 5.0 . "
, 25 6 60 0.80 5.2Ligh-t reddish
li . orange
4 40 1 1.12 6.7 ,.
2 20 2.04 15.0 Yellow -
j ,
l 8 80 0.88 6 Light reddish
:~ orange :.
27.5 4 40 1.60 11.5 Yellow :
~' 2 20 2.52 19 I. :
:7
I lO lO0 0.88 6.7LicJht reddish
¦ orange
8 80 0.98 7.5 .
6 60 1.32 10.7 ..
~ 4 40 1.64 15.1Reddish orange
.~ 2 20 2.46 21.7 ..
l .. . .__ .
:1 6 60 1.16 ll Unclear reddish
orange
~, 32.5 4 40 3.04 24 ..
.j 2 20 3.28 30 Reddish orange
.1 .
.l lO lO 1.50 17.8 ..
- 8 80 2.28 24.4 ,l
6 60 2.86 28.2 Unclear reddish
orange
i 4 40 3.08 29 .,
.~
~ 3~3 _
i .,
: ~ ' ':: , ,:, . ., ~ :
1~39~2~
.
Table 6.
. . I
Conditions for electrolysis :Formed oxide film
Pulse Peack Frequency Mean Film Color tone
:l width voltage n T current thickness
Tp Vp density
(msec~ (V) (msec) (A/dm2) (~)
15V 2 lO 0.7 3.9 Yellow
8 40 0.5 2.2 Reddish orange
4 20 1.4 10.5 Light reddish
2 lO 3.0 25.7 Reddish orange
1.52 21.5 ..
~, .
:, 25 3 48 0.69 5.5 Yellow
, 25 7 118 0.4 2.5 Light reddish
; orange
16 30 2 32 2.3 11.5 Reddish orange
33 2 32 2.2 22.0 ..
_ 33 4 64 1.8 lO.0 ll
',1,
.. .
~ , .
:.~
~ .
:
.
'~'
:~ ~ 3~
.,' "
.
,' ~. : ' ' . ' ' ' ' ' ' ' ~'
~0392Z8
When metallic salts such as HAuCl4, Na2SeO3, CuSO4,
SnSO4, NiSo4 and CoSO4 were added in a H2SO~ aqueous
solution in place of the aforesaid metallic salt and the
peak voltage Vp and n were changed, colors shown in the
following Table 7 were obtained.
- Table 7.
.,,
, No. Coloring metal Metallic Salt Color of oxide film
~ 1 Au HAucl~l Purple
l 2 Se ~a2SeO3 Cream
i lO 3 Cu CuSO4 Deep red to brown
' 4 Sn SnSO4 White to dark
.~ brown
~ 5 Ni NiSO4 Amber to black
6 Co CoSO4
,~ .
When aluminum materials A.A1099, 1100, 2011, 2014,
1 2024, 3003, 4043, 5005, 5086, 5357 6061 and 7075 other
-~ than 6063 were electrolyzed during which the peak voltage
~' Vp and n were controlled, substantially the same results
,, as those in Figures 4 and 5 were obtained, although
,;j 20 colors of the oxide films formed were a little different
from one another because these aluminum materials were
of different compositions and because their electrical
properties differed in accordance with the contents and
kinds of alloy elements contained in them.
~,
. ~,
~ 3~
., ., ~ .
.,
., .
39~Z~
The relationships of the peak voltage and the value
n to the distribution of color tone showed the same
tendency as shown in Figure 4, though a little affected
by such factors as the power source, voltaye ad~usting
means and the geometrical shape of the electrolytic
cell used (for example, distance between electrodes,
capacitance, etc.) used, a leakage current, etc. in
addition to the quality of each aluminum material and
,
the kind of each metallic salt used.
For example, when one or more of the above factors
j .
were changed, there were some occasions when the sizes
; and shapes of the zones A, B and C in Figure 4 were
~; changed, or the zone D became so narrow that it was
not necessary kodistinguish the zone D between the zones
;
- lS A, B and C and the zone E in actual electrolysis, or
the width of the zone D increased. Further, the afore-
! said factors had relation to at least some of the condi-
tions for electrolysis, so that when one or more of the
factors were altered, the levels of the lines I-I and
II-II became higher or changed in inclination in some
cases.
~, In any case, however, according to the method of
this invention the basic tendency shown in Figure~ can
; ~ 7 be maintained, in which one of the features of the
.~
method of this invention resides.
!
EXAMPLE 5
Aluminum materials 1100, degreased and rinsed with
water and then neutralized in known manner, were electro-
, .,
~ j .
-~
,;~ 76
~;
~':
g~2
lyæed by applying the rectangular pulse voltage shown
in Figure 3 is an electrolytic ba-th containing 150g of
H2SO4 per liter of water and 50mg of Ag2SO4 per liter
of water (at a bath temperature of 25C), with the
-~ 5 aluminum materials being used as both electrodes.
,~ In this case, an impedance was connected as shown
. `~j!
'( in Figure 9 and the impedance used was a resister.
~ By changing its resistance value, the by-pass current
., .
was changed. The results shown in the following Table
; 10 8 were obtained.
; !'j
, ~,
'.:;
''`.l,
, i
... , .
:;'j
,
~'
'``,''
".
...j
".,i
,., ~
:.'
.,
. .,
''`'
: `
~.
'
. .
.`j ~
`,`.,.'` ' ~ .' ' :': :' ' ' " ,'`,' ' '; .,
39ZZ8
Table 8
: Sample Pulse Pulse Peak Surface Resistance
No. duration interval voltage area of Value
T = Ta h=ha Vp=¦Vpa¦ sample
(sec) (sec) (V) (cm ) (Q)
., -3 -3
. 1 2xlO 18xlO 20V 50 10
2 ll ll ll ll 40
3 ll ll ll ll 54
4 ll ll ll ll 100
ll ll ll ll 150
6 ll ll ll ll 220 .
.~ 7 ll ll ll ll 500
8 ll ll ll 100 10
., 9 ll ll ll ll 150
ll ll ll ll 500
~ Sample Mean current Time for lowering Color of
.;, No. Electrolytic By-pass to - V or V film :
cell circuit 4 p pa
(A) (A) (sec)
~ 1 0.21 0.22 0.3xlO 3 Dark brown
i 2 0.23 0.07 0.85x10-3
Jf 3 0.20 0.06 l.lxlO- ll
4 0.22 0.04 2.0xlO A little dark
0.25 0.03 2.5x10-3 ll
i 6 0.23 0.03 4.3xlO Brown
, 7 0.23 0.02 9xlO 3 Light dark
3 yellow
8 0.44 0.27 0.5x13- Dark brown
f 9 0.39 0.04 5xlO Light brown
1 10 0.41 0.015 14.5xlO Light drak
. yellow
... :f.' _ ~ _
~ - ~
`:
~L039~:2
`: The frequency of the applied voltage was 50Hz.
;~ As seen from the above Table, when the resistance
- value was changed, especially in the case of the .
; surface area of the specimen being 50cm , when the resis-
- tance value was 500Q, the time for lowering of the
applied voltage to l/4 of the peak voltage was longer
`5 than 1/3 of the pulse duration and the coloring mode of
the oxide film was not good. The same was true of the
case of the specimen surface area being lOOcm2.
, EXAMPLE 6
~ . Aluminum materials A.A6036, chemically pretreated,
,l in known manner were electrolyzed in an aqueous solution
'~ containing 150g of sulfuric acid per liter of water and
..
50mg of Ag2SO4 per liter of water, with the aluminum
~ materials being used as both electrodes. In this case,
:'
a pulse voltage, obtained by half-wave rectification of
a six-phase AC of the waveform shown in Figure 12 was
applied.
..~
i The results shown in the following Table 9 were
~i obtained.
..
;~ :
.,~
.4l
'~
' ~
"1
!~
' ~
,~,
~.'. ~ ~ 3 ~
;~
392~
; Table 9.
: ..... _ . . .
Characteristics of pulse voltag~ MeanColor of
No Peak Pulse PulseConduction Current ox'de
. Voltage width period time
Vp=Vpa I = I T = Tat = ta
. (V) (sec) (sec) (sec) (A/dm2)
.. 1 25 16x10 48x10 5 0.63 A little
.~.,,i . ydeleleoPw
~. 2 25 33x10-3 132x10-3 ll 0.62 ll ::
'":
,, 3 20 16Xlo 3 48x10 3 .l 0.44 ~ little
4 20 33x10 3 132x10 3 .. 0.43 ye11owt
i~ :''
33 16x10 16x10 ll 1.50Deep
. orange
~, 6 ll 33x10-3 33x10-3 . 1.40
7 ll 50x10 50x10--3~l 1.50
:i
~i~ 8 20 16x10 3 64x10 3 n 1.20Light
i 9 ll 33x10-3 132x10-3 ll 1.00 ..
~! 10 ll 50x10 3 200x10 3ll 1.30 .
.~
s 11 25 16 lD-3 64x10 3 D0 Orange
.',, '
~ . .
.... ~: , ;,, . . : . ' : .
~03922Ei ; ~
It appears from Table 9 that an increase in the
values of the peak voltages Vp and Vpa causes the color
` of the oxide film to become deeper and that, in the case
`d of the same frequency, that is, when the pulse periods
; 5 T and Ta are equal to each other, an increase in the
~' pulse widths land Ta causes the color of the oxide film
to become lighter.
EXAMPLE 7
'' Aluminum materials 1100 were degreased and rinsed
with water and then neutralized to clean the surfaces
i of the aluminum materials. These aluminum materials
were electrolyzed in an aqueous solution containing
150g of H2SO4per liter of water and 50mg of Ag2SO4 per
liter of water, with the aluminum materials being used
as both electrodes. The pulse voltage shown in Figure
3 was applied and the electrolysis was effected with a
i ~ current of ~0e~ for 60 minutes.
J. The results shown in the following Table 10 were
y obtained. The positive and negative waveforms of the
applied voltages were the same and the peak voltages
and the pulse widths were all the same in their absolute
values, respecti.ely.
~, - .
.j .
',~
.~....... . . . . . . .
-
Z~
Table l0.
. ' _ _ _ _ _ !
Conditions for electrolysis
Color of
~ f-1 cr ~ Peak ~oItage Pu1se w1dth fi1m
--(Hz) (V) (sec)
20xl0 Yellow
40xl0 Light Orange
3 30 60xl0 3 A little
~` light orange
l 30 200x10 3 Deep orange
l0In all cases of the above Table, the currents all
reached the peak values and sufficiently colored oxide
films were formed.
"
In the method of this invention, the frequency used
is determined in relation to the pulse width but it was
sufficient to be lower than l00Hz.
, Although the foregoing description has been given
mainly, in connection with the cases in which the aluminum
materials A.All00 and A.A6063 are employed, the present
~- invention can also be easily applied to other aluminum
materials.
However, a change in the composition and electrical
properties of the aluminum materials used causes a change
in the color of the oxide film. For example, under the
~,~
~ Z
~; -- 43 --
:, .
:,
:.: ~ , ,. : . .
: - ~0392;~b~
conditions for electrolysis that when the aluminum
` material A.AllO0 is electrolyzed in the sulfuric acid .
. aqueous solution, an oxide film of an o:range color is
j formed, when the aluminum materials A.A3003, A.A4043,
-. 5 A.A5052, A.A6061 and A.A6063 are electrolyzed in the -:
'~.
; above electrolytic ba-th, oxide films of grayish orange,
dark orange, light orange, dark reddish orange and orange
~, colors are formed, respectively. :~
It will be apparent that many modifications and : ;
.
variations may be effected without departing from the
scope of the novel concepts of this invention.
.1
:i l
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, 1,
: , ,
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