Newsgroup: it.scienza.chimica
Titolo: Deposizione rame su tubi in alluminio

Salve a tutti,
vogliate scusarmi se magari ripropongo post gia trattati ma se vi
chiedo è perchè non ho trovato abbastanza, e in piu' perchè sono nuovo
di queste parti:) Beh vado al dunque:la mia domanda nasce da una mera
necessità pratica voglio brasare dei tubi in alluminio di piccolo
diametro 9mm con dei tubi in rame; ne nasce dunque la necessità di
ramare i tubi in alluminio per permetter la brasatura con lo
stagno.Ora quanto questo sia possibile non lo so, ma cmq facendo varie
prove ho ottenuto anke risultati decenti ma non riesco piu' a
ripeterli!!! ecco dunque vi chiedevo un po' tutto tipo: la
concentrazione del solfato di rame che tensione e che trattamenti
eseguire sul pezzo per ottimizzareil processo.
Grazie a tutti in anticipo e scusate se mi sono dilungato... Ciao!

Sembra che Max83 abbia detto :
L'alluminio  si può placcare ma devi pulire in modo adeguato e 
particolare la superficie
Per la placcatura prova  a fare prima lo strike come consigliato per le 
sfere un paio di topic sotto
Potresti (dico potresti) tentare con la soluzione che ho fornito prima 
a 50 grammi litro di solfato di rame
Se ci fossero problemi di eccessivo ribollimento suggerirei di stare a 
pH più neutro (verso il 5-6) in modo da limitare gli effetti 
dell'acido.
Non so se funziona quindi test and try.
Per rendere il rame meno efficace nell'autodeposizione ti conviene 
portare il pH a 5-6 usando ammoniaca diluita che ben complessa il rame.
Poi puoi placcare come ho suggerito prima con la soluzione 
solforico/soltato di rame e anodi in rame.
io poi sono disponibile per suggerimenti
QUANTO ALLA PULIZIA DELL'ALLUMINIO ESISTONO TOMI IN MATERIA quindi ti 
ho trovato quanto sotto che dovrebbe darti indicazioni sufficienti. 
Purtroppo è in inglese ma non credo per te sia un problema
leaning and Etching of Aluminum
Aluminum represents a special cleaning problem. The metal has high 
reactivity; an oxide film of variable thickness is always present; and 
many of the finishing processes for aluminum are sensitive to surface 
residues. The cleaning formulations are therefore somewhat restricted, 
and because of these restrictions, aluminum cleaners are generally 
grouped as a special category. While it is quite true that cleaning 
materials developed for aluminum will work quite well on other 
substrates, the reverse is not always true.
Aluminum cleaners are subdivided into non-etch and etch types.
The non-etch types are generally used for processing buffed parts, or 
parts made from prefinished or pre-rolled stock. They may also be 
required prior to certain sensitive type coatings such as highly 
corrosion resistant chromates.
The etch cleaners are used to produce matte finishes, and in particular 
are widely used to produce finishes which mask surface imperfections 
such as die marks, rolling imperfections, orange peel, score marks, and 
other defects produced during, or as a result of, processing 
procedures. Tonnage figures show the etch cleaners to be by far the 
most widely used. Since etch cleaners are consumed in the process of 
etching, an estimate of the comparative surface area processed in each 
type of cleaner is not possible from this data. However, it does 
indicate that etched finishes possibly predominate.
The non-etch cleaners fall into three general categories:
Acid,
Alkaline inhibited , and
Alkaline non-inhibited.
The acid cleaners are generally based on the fact that strong acids, 
particularly oxidizing acids are capable of removing soils by chemical 
breakdown of the soil. At the same time, the oxidizers present 
passivate the surface of the aluminum. The non-oxidizing acid used must 
have a relatively low rate of attack on aluminum and is generally 
either phosphoric or sulfuric.
A typical formula would be:
    85% Phosphoric acid 40 - 60% by volume
    Nitric acid 20 - 30%
    Water to make 100%
    Temperature 38 - 72oC ( 100 - 160oF)
Sulfuric acid can often be substituted for phosphoric acid. Chromic 
acid at a concentration of 60 - 180 g/L (8 to 24 oz/gal) can be 
substituted for nitric acid, but because of the waste disposal problems 
involved, this change may not be desirable. The use of chromic acid as 
the oxidizing agent may be an important consideration ahead of the 
application of certain chromate coatings, where it seems to improve the 
corrosion resistance of the coating being applied.
The degree of surface attack can be controlled by the water content and 
temperature to produce either a very light etch, or essentially no 
attack at all. Buffed pieces passed through such a solution will often 
suffer some slight loss of lustre, and develop a somewhat milky 
appearance. This is apparently an optical effect due to the formation 
of an oxide film. Plating with a bright nickel for example restores the 
original buffed luster. In general, the use of such solutions is 
limited to plating operations, partly because of the nature of the acid 
solutions, and more importantly because of the appearance change noted.
The alkaline inhibited cleaners utilize the principle that alkaline 
silicates will react with aluminum to form an insoluble aluminum 
silicate. Silicates of various grades are incorporated in the cleaner 
where they act as inhibitors by forming an insoluble silicate film on 
the surface of the work. While this film is invisible, it is extremely 
tenacious and continuous, and provides a barrier to further attack by 
the solution. Chromates may be used in a similar manner, supplying the 
oxidative power necessary to produce a continuous film of aluminum 
oxide which inhibits further attack.
In either case, the protective film has a finite time of formation. 
During this period, reaction of the surface with the solution occurs. 
Thus, when the part is initially immersed, some gassing is evident. 
This rapidly diminishes and stops however, and the resulting etch is 
microscopic and essentially invisible. The slight gassing which does 
occur helps to dislodge solid particles and speed cleaning.
Inhibited alkaline cleaners of this type can be formulated over a wide 
range of composition. In general, they fall into two categories: pH 9.5 
- 11.0, and pH over 11.0. The higher pH materials will develop heavier 
inhibiting films with corresponding problems of removal later. They do 
offer the advantage of being more effective on soils which can be 
removed by saponification. The lower pH materials produce lighter 
inhibiting films more easily removed and are particularly effective on 
sulfurized oils. The time required for film formation is generally 
considerably shorter with low pH materials and the microscopic etch 
during the induction period is correspondingly reduced.
A typical low pH formula would be in the range of
    Sodium bicarbonate 10 - 30%
    Sodium silicate 30 - 50%
    Complex phosphate 15 - 30%
    Complexers 0 - 10%
    Wetting agents 1 - 5 %
This formula is obviously more complicated than many of the older 
formulations listed by Springer; Wernick and Pinner; and others. The 
components are selected not only for their buffering capacity, but also 
for their deflocculating and soil suspension characteristics. Where 
local restrictions on phosphates still exist, it may be necessary to 
eliminate these important constituents. Generally, they are replaced by 
a combination of additional buffers, complexers such as EDTA and its 
homologues, and deflocculants such as ligno sulfonates, resin 
condensates, or condensed tall oil surfactants, making the formulas 
still more complex. These non-etch cleaners will generally be operated 
in the range of 30 - 90 g/l (4 to 12 oz/gal) and from 60 - 90 C (140 - 
180 F). Time of immersion will depend on the soil to be removed but is 
usually in the range of 2 to 10 minutes.
More recent developments have produced cleaners which operate at 
considerably lower temperatures and concentrations - as low as 38oC 
(100oF) and 15 to 30 g/L (2 - 4 oz/gal. The alkaline blend and balance 
in these materials is similar to the standard compounds but the 
surfactant blend is considerably altered. Displacement types are 
generally operated at the lower temperatures and concentrations. Where 
there is a limit on the hexane soluble content of the effluent, the 
displacement types are preferred. The permit the removal of the 
displaced oil by suitable grease traps. The removed oil can frequently 
be reused or beneficially burned. All of these materials require that 
the oil to be removed must be in the liquid state. Therefore the lowest 
operating temperature possible is that at which all the components of 
the oil are liquid. The incorporation of a 49oC (120oF) melt paraffin 
in a forming oil would require an operating temperature of at least 
54oC (130oF). Because of the high melting point of buffing compounds, 
low temperature compounds are not usually suitable for buffing compound 
removal.
As previously indicated, the inhibiting action used in this type of 
cleaner is dependent on the formation of a film of aluminum silicate. 
Unless the preliminary cleaning is to be followed by an etching 
procedure, it is necessary to remove this film in a deoxidizing 
solution before further processing. Such solutions consist of suitable 
acid mixtures augmented with a controlled percentage of fluoride ion.
These deoxidizing solutions are often referred to as "desmutters" since 
the also remove the smut formed by the segregated metals found in the 
alloys and left behind after the removal of even small amounts of 
aluminum by the alkaline cleaner.
A typical deoxidizing solution would be:
    42 Be' Nitric acid 50 - 75% by vol
    Fluoride salt 15 to 120 g/L (2 - 16 oz/gal)
For alloys containing appreciable percentages of magnesium, the 
addition of sulfuric acid may be required:
    42 Be' Nitric acid 50 - 75% by vol
    Conc. Sulfuric acid 10 to 20%
    Water to make 100%
    Fluoride salt 15 - 120 g/L (2 - 16 oz/gal)
A mixture of this type is sometimes referred to as a "universal" acid 
because it is suitable for all alloys.
The activity of the deoxidizing bath is to a large extent controlled by 
the concentrations of nitric acid and fluoride salt. High 
concentrations of readily available fluoride ion gives baths with very 
high activity. For baths of this type, ammonium bifluoride is the 
preferred source of fluoride. For slightly lower activity with an 
appreciable reservoir of fluoride, potassium or sodium fluoride may be 
used. And for low activity, silicofluoride, fluoborate, or another 
slightly ionized complex fluoride may be used.
Mixtures based on chromic acid, chromic-sulfuric, sulfuric acid 
hydrogen peroxide, and sulfuric acid with iron salts are also 
available. Many of these combinations are formulated as dry powdered 
acid salt mixtures by using hexavalent chromium salts, peroxygen salts, 
or iron salts. When iron is used as the oxidizer, the concentration of 
fluoride that can be added is quite limited since with will complex the 
available iron and prevent it from acting as a protective oxidizer for 
the aluminum.
The peroxygen desmutters tend to be unstable and have relatively short 
life in the presence of certain catalysts such as copper and silver. 
Special maintenance procedures must be followed if the alloys being 
processed contain these metals. Recent work on the stabilization of 
hydrogen peroxide has resulted in at least one grade that is suitable 
for use in desmutting and deoxidizing solutions to replace the 
peroxygen salts.
As previously mentioned, some processes such as chemical polishing and 
certain chromating solutions are particularly susceptible to the 
presence of silicate films remaining after the used of inhibited 
alkaline cleaners. For these operations a deoxidizer operated to 
provide complete removal of the silicate film would result in 
noticeable etching of the surface. If such an etch cannot be tolerated, 
consideration must be given to the use of the so-called non-silicated, 
non-etch cleaners.
Non-silicated, Non-etch Aluminum Cleaners
These compounds are not in the strictest sense truly non-etching. They 
are carefully buffered, mild etchants operated under controlled 
conditions to hold the etch to a microscopic level. A typical mixture 
would contain:
    Alkali buffer mix for pH 9.0 90%
    Complexers and deflocculants 5%
    Wetting agents 5%
Occasionally, additional insurance against noticeable attack will be 
provided by alkaline chromates. However, this practice is somewhat 
dangerous since improper balance (sometimes resulting from aging of the 
solution) can result in the development of an appreciable oxide coating 
similar to that produced by the Alroc process. Waste disposal 
conditions also limit this approach.
These solutions are usually operated in the range of 23 - 60 g/l (3 - 8 
oz/gal) at 60 - 62oC (140 - 180oF). At the lower concentrations and 
temperatures the etch will be essentially unnoticeable. Under the more 
severe conditions, a definite "frosting" will usually occur, although 
the etch will not be so severe that it cannot be eliminated by chemical 
polishing or a bright plating operation. Careful attention to 
operational conditions is a must with these solutions. Exceeding the 
upper limits of concentration and temperature will result in excessive 
etching. Falling below the lower limit can result not only in the 
possibility of poor cleaning, but the possible development of a film of 
undissolved aluminum salts on the surface.
While these cleaners, properly operated will leave the surface 
generally free from any film, it is common practice to follow their use 
with a simple nitric acid deoxidizing step - 25 - 75% by vol 42 deg Be' 
nitric acid - to insure the removal of any trace of alloying elements 
from the surface.
These cleaners may also be formulated for low temperature operation 
with the same limitations previously mentioned. There is the further 
advantage, that at the lower temperature, chemical attack is even more 
limited.
Etching Cleaners
Etching cleaners for aluminum are based on the rapid reaction of 
aluminum with alkalies according to the reaction:
1.     2 Al + 2 OH- + 4 H2O ---> 2 H2AlO3- + 3 H2
        and
2.     Al (OH)3 << ----->> H+ + H2AlO3 - which can also be written as
        Al(OH)3 << ----- >> H+ + AlO2- + H2O
Additional alkali leads to
3.     Al(OH)3 + 3 NaOH ------> Na3AlO2 + 3 H2O
and
4.     Al(OH)3 + NaOH ------> NaAlO2 + 2H2O or NaAl(OH)4
The fact that sodium aluminate can be precipitated only from 
concentrated solutions as well as the wide variety of forms in which it 
appears, suggest the possibility that,  at least in dilute solution, it 
is not a true compound but a peptized hydroxide, or a colloidal 
dispersion of the hydroxide. Furthermore, freshly precipitated material 
is gelatinous and very absorptive, both characteristics of the 
hydroxide. Sodium aluminate solutions also show abnormal viscosity. 
This fact can explain many of the problems encountered with etching 
baths.
The earliest etching solutions for aluminum consisted of sodium 
hydroxide, occasionally modified with other alkalies. Maintaining a 
uniform etch with these solutions was a difficult proposition. 
Similarly, the baths would orm heavy deposits on coils, tank bottoms, 
etc. which had to be removed by brute force.
In the early 1950's several patents were issued on additives, 
principally sugar acids such as gluconic and glucoheptonic acids, for 
the prevention of tank scaling and operation of the solutions became 
somewhat easier. At the same time that the scaling problem was 
overcome, it was noted that the etching action became more uniform, and 
etching rates increased. In addition, gas tracking (the production of 
etched grooves in parts as a result of gas following a fixed path along 
the part to the surface) was almost eliminated, and rinsing was 
simplified.
In extensive unpublished research at the time, the author noted that 
not only acids, but the corresponding primary and secondary amines, as 
well as some of the simple sugars in some cases, were effective for 
this purpose. While it was generally noted that effective scale 
prevention materials were capable of forming complexes, or chelate 
links, with aluminum, the stability constant of the complex could not 
be too high or the material would not perform well. Additionally, the 
materials had to be highly hydroxylated and exhibit effective 
performance in other applications where the deflocculating action was 
the determining factor. From this data, it was concluded that a 
possible function of these materials was a deflocculating action. If we 
examine reactions 2 and 3 above, it is readily noted that to prevent 
formation of the aluminum hydroxide, massive amounts of alkali are 
required. However, if the reaction is not prevented, but the 
precipitated hydroxide is deflocculated or peptized sufficiently, it 
will not adhere to the aluminum surface to cause non-uniform etching, 
nor to the tank walls to cause caking, but will undergo the 
transformation
    2 Al(OH)3 ---> Al2O3H2O + 2 H2O
in the body of the solution resulting in a granular precipitate easily 
flushed from the tank. The additional deflocculating action also tends 
to reduce the viscosity previously noted accounting thereby for the 
elimination of gas tracking.
It was quickly noted that even with this type of solution, production 
of specific etch patterns required modification and control. It became 
common practice for example to discard only part of the etching 
solution at a time since freshly made baths initially produced brighter 
etches and required "aging" by dissolving some aluminum before reaching 
a stable condition. The presence of other alkalies such as carbonate, 
or phosphate could influence the appearance of the etch. In one 
particular case where a highly characteristic etch pattern had to be 
maintained with unusual uniformity, success was attained only by 
frequent analysis and close control of 1. free alkalinity, 2. carbonate 
concentration, 3. complexer concentration, and 4. concentration of 
dissolved aluminum.
Where the etching solutions were used to dissolve aluminum mandrels 
from electroformed parts, the rates were quickly be pushed to the point 
where the gas involved in the reaction limited the access of the 
solution to the interface and therefore limited the rates obtainable. 
Oxidizers such as chlorate, chlorite, mixed nitrate/nitrite etc. were 
added and still higher rates were obtained since the oxidizer reduced 
hydrogen evolution and allowed better contact of the solution with the 
surface. It was also noticed in this work that the oxidizer had a 
pronounced effect on the appearance of the etch - in some cases 
producing a more matte finish; in others, brightening almost in the 
manner of a chemical polishing bath. Stock removal however was far too 
high to allow such baths to be used for either purpose.
In general, etching solutions of this type are relatively poor 
cleaners. The amount of gas evolved limits the amount and type of 
surfactant which can be employed without developing excessive foaming. 
This is particularly true since the finely divided aluminum hydroxide 
present stabilizes foam readily.causing foam problems even with the 
so-called non-foaming surfactants and even in the absence of surfactant 
materials. Additionally, they are operated at relatively high pH and 
therefore give poor performance on many soils such as sulfonated oils. 
Variable etch patterns delineating the oil distribution can occur 
easily.
It is common practice therefore to preclean critical parts in a 
non-etch cleaner prior to etching. The non-silicated materials are 
preferred for this purpose since they offer no possibility of 
subsequent non-uniform etching as a result of adsorbed silicate.
All of these etching solutions have relatively high rates of attack and 
leave the surface covered with a "smut" consisting of undissolved 
alloying elements. The degree of smut formation naturally varies with 
the alloy, and the depth of etch - from barely discernable to heavy 
black - but can be removed in one of the acid deoxidizers previously 
described.
With these formulations, one particular form of non-uniform etching 
known as "spangling" still occurred periodically, particularly with 
extruded alloys. One patent attributes this to the presence of 
dissolved zinc in the etching solution and controls the problem with a 
special additive to maintain the zinc concentration below a critical 
level. As a corrollary advantage, it is claimed that the bath is free 
from caking and never has to be discarded. In observing operational 
baths it is noted that the baths show a rapid and marked increase in 
viscosity as aluminum is dissolved, with a corresponding increase in 
dragout. It is possible that the additive, in addition to controlling 
the zinc, in some way stabilizes the aluminum in the NaAlO{2} form 
accounting for the increased viscosity. The dragout might then 
stabilize the aluminum content at a level below the precipitation point 
preventing caking. The point has not been resolved. Considerable 
amounts of precipitated hydroxide are visible in the rinse, however, so 
the stabilization is apparently reversible on dilution. Very similar 
results can be obtained by the addition of small amounts of sodium 
sulfide to the etching solution instead of the proprietary addition 
agent.
Acid Etching
One particularly fine etch with remarkable defect hiding power is an 
acid etch using a fluoride acid salt at slightly elevated temperature. 
The etch produced is extremely fine, non-reflective and uniform. Stock 
removal is very low. Hiding power is exceptional.
The etch uses ammonium bi-fluoride at concentrations of 15 - 60 g/L (2 
- 8 oz/gal) at temperatures from 20 to about 38 - 48oC (70 to about 100 
- 120oF.).
Variations on this etch can be produced by modifying the fluoride with 
other powdered acids to vary the attack rate. Sodium bisulfate, 
sulfamic acid, and citric acid are among the acids that have been used. 
Nitric acid or oxidizers must be avoided however since these act as 
inhibiters and prevent the proper operation of the etch.
All etched finishes regardless of the method of development are 
extremely susceptible to finger marking and staining unless protected 
by an auxiliary coating of wax or clear coating of some type. Great 
care has to be used in drying and handling prior to application of the 
finish coating to avoid problems from this source.

 QUANTO ALLA PULIZIA DELL'ALLUMINIO ESISTONO TOMI IN MATERIA quindi ti.....
managgia sapevo che l'alluminio era un pò particolare ma qui si fà
dura non ce le ho mica tutte quelle sostanze e nemmeno le
conoscenze...altro che dritta qui mi devi proprio dare uno spassionato
quanto pratico consiglio a modi guida dalla a alla z!
mi sa che mi devi proprio fare una ricetta su misura. Ah altra
curiosità: i modesti risultati che io ho ottenuto praticamente per
caso erano possibili solo se attuavo una agitazione esasperata del
pezzo di alluminio nella soluzione, cosa che non potrei permettermi
nel lavoro che devo fare; quindi mi domando è possibile fare la
deposizione tenedo la soluzione e i pezzi fermi!

 ha scritto nel messaggio 
news:895adf4b-79f8-4fde...@p69g2000hsa.googlegroups.com...
 non riesco a reperire nemmeno l'acido
solforico ...mannaggia nemmeno na batteria al piombo!! quindi sto un
pò messo male per quanto riguarda anke la preparazione della
superficie
Per l'acido solforico prova a cercare
in ferramenta o simili un disgorgante
per scarichi denominato "Disgorgante
idraulico" della ditta SAI spa di Roccabianca PR
contiene H2SO4 al 96%
ciao a tutti.
Paolo

 deposizione tenedo la soluzione e i pezzi fermi!
DIREI CHE PER COMINCIARE PULIRLO CON UN PO DI ACQUA SAPONATA CON UN 
POCHINA (MA MOLTO POCA SODA CAUSTICA) A CALDO (70-90°c) E POI LAVARLO 
CON ACQUA DISTILLATA BENE PIU' VOLTE E POI DECAPARLO CON ACIDO 
MURIATICO AL 5% POTREBBE ESSERE UN INIZIO, TI SUGGERIREI DI TAGLIARE UN 
PEZZETTO DI TUBO E FARE DELLE PROVE IN PICCOLO PRIMA DI SCATENARTI 
INDUSTRIALMENTE

 INDUSTRIALMENTE
ecco temo un pò la reattività dell'allumino sia con sostanze basiche
sia acide.... si insomma bolle dentro a ste sostanze di solito vabbè
ci vado leggero con le concentrazioni!
Ti faccio sapere, tu dammi conferma!
grazie ankora ciao!

ehm ho fatto una prova con 0,1 l di soluz di solfato di rame a 50g/l e
ho aggiunto 1ml ammoniaca come dicevo prima diluita al 5-15% la
soluzione è diventata torbida ed opaca con un colore piu chiaro sembra
quasi che sedimenti ..anzi forse lo fa ho messo il tubetto circa 0.5A/
dm2 facendo i conti (solo della sup. ext. del tubo  quindi al limite è
metà) e il risultato è pessimo si attaca in modo disomogeneo lo strato
è poroso anzi direi polverulento e sopratutto non ha adesione!
Aiutooo!

 ho aggiunto 1ml ammoniaca come dicevo prima diluita al 5-15% la
erano 5ml di ammoniaca! 1ml è la prova che sto facendo ora!
Ciao!

 ci vado leggero con le concentrazioni !
anche i tempi regolali di conseguenza. Se l'attacco, magari a 
caldo, è potente, i tempi di pulizia vanno accorciati
ciao
Soviet


Scriveva Soviet_Mario mercoledì, 09/01/2008:

Presumo che i profumanti dell'ammoniaca siano precipitati, soviet come 
sempre ha centrato il problema nel senso che il complesso diamminorame 
placca più lentamente (infatti si usano densità di corrente basse) che 
permettono di dare il primo strato alla nostra tubazione. Poi si placca 
realmente con una soluzione solforico/solfato di rame standard sopra 
questo straterello aderente.
CApisco che con mezzi di fortuna è difficile placcare, se riesce ok se 
no ho la soluzione alternativa che è più laboriosa ma da risultati 
diciiamo accettabili.

 diciiamo accettabili.
Dimmi pure poi ti dico io se per me è impossibile oppure no!!!
Ah Soviet questa è per te non ti so dire se la concentrazione è
proprio quella, io direi di si, nel senso che il tizio mi ha dato una
tanichetta mezza piena di sto acido solforico (intendiamoci era gia
stata usata) e sull'etichetta è riportata la composizione (36%) nonche
nomenclatura dell'acido solforico quindi boh!!
Ciao

 Ciao

 Ah, l'ammoniaca deve essere in forte eccesso alla fine...........
allora l'ho fatto ho aggiunto un sacco di ammoniaca (direttamente su
una bottiglia che avevo preparato ieri con acqua e 50g/l di solf.di
rame) mi sa che avevo contaminato il bagno nelle prove
precedenti...ieri diveniva torbida e molto chiara (tipo poltiglia
bordolese, quella per le piante) oggi invece è diventata un blu fort
moooolto scuro! pero per quanta ammoniaca aggiungessi non depositava
nulla restava limpida.. boh è normale!
Cmq poi ho provato l'elettrolisi a bassisima corrente per ora sembra
funzionare il dep è abbastanza omogeneo anche se mi pare di vedere dei
punti scuri quasi dei buchi nel deposito vediamo..
ciao!

bene bene...
come vi ho detto sopra ho fatto il primo strato con la soluzione che
mi avete suggerito e poi ho messo il pezzo in una soluzione a piu di
100g/l di solfato di rame e un po di solfato di rame non so quanto :
( e fatto deporre per svariate ore a 2 A/dm^2 e poi in una ultima fase
ho dimezzato la corrente.Risultati:
superfice satinata come da sabbiattura, ma molto fine, colore omogeneo
arancione molto chiaro quasi rosa; ho lucidato la superfice con pasta
diamantata  e poi ho fatto la prova di resistenza del deposito: ci ho
saldato un bel filo di rame e ho tirato....si spezzata la saldatura
lasciando tutto intatto, si ovvio intendo che si è rotto lo stagno non
che questo sia venuto via in toto come se fosse stato attaccato con lo
sputo.
Quindi sostanzialmente sono soddisfatto, ma sono ugualmente curioso
circa l'altro metodo, e inoltre volevo chiedervi:
1) quali sono le concentrazioni ottime di solfato di rame, acido
solforico nella soluzione per la deposizione finale?
2) il pezzo da rivestire è meglio se ha superfice piu lucidata
possibile oppure no?

L'acido per batterie ha una concentrazione di circa il 30% che è quella 
dove la conducibilità è massima. Dovrebbe essere abbastanza puro e 
quindi adatto allo scopo eletrogalvanico.
Quanto alla soluzione di rame alcalinizzata io sono sempre partito da 
soluzioni acide concentrate e le ho neutralizzate step by step con 
ammoniaca. Non ho visto grandi precipitati e quei pochi si sono 
ridisciolti con l'aggiunta di ammoniaca.
Quanto ai tentativi è ovvio che se non si ha capito si va 
sperimentalmente e che quindi il risultato segue una legge 
probabilistica ovvero col c... viene al primo colpo oppure dopo un set 
di tentativi più o meno mirati.
Suggerivo di seguire la sequeza che ho indicato perchè basata sui 
fallimenti di altri ed anche miei poi corretti e fatta storia.

 ciao!
E RICIAO

 possibile oppure no?
si certo sgrassata e decapata.
attenzione alla sensibilità dell'alluminio agli acidi e basi, potresti 
pulirlo con una soluzione a pH 5 di acido citrico/citrato di ammonio 
(basta neutralizzare l'acido citrico parzialmente con ammoniaca fino a 
pH 5)

Ok molto bene ho fatto altre prove e devo dire che sono soddisfatto
quindi vi ringrazio tutti per l'aiuto e la pazienza!
solo un'altra curiosità:
il fatto di neutralizzare con ammoniaca la soluzione è cosa buona
anche se il metallo da placcare è semplice acciaio oppure è una cura
particolare solo per l'alluminio?
Ciao!!

Sembra che Max83 abbia detto :
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Con l'acciaio vale lo stesso discorso, anche più delicato a seconda del 
contenuto di carbonio