Stabilized hydrogen peroxide solutions

Aqueous hydrogen peroxide solutions used in metal dissolution processes are effectively stabilized against decomposition caused by metal ion contaminants by addition of saccharin or an alkali-metal salt of saccharin to the solutions.

BACKGROUND OF THE INVENTION 
Hydrogen peroxide containing solutions are used in various processes for 
the dissolution of metals and metal oxides. Examples of such processes 
included pickling, bright dipping, pre-etching, etching, manufacture of 
filaments for light bulbs etc. Hydrogen peroxide, which is added to the 
acid treatment solutions for the purpose of promoting the disolution 
and/or to prevent the formation of toxic fumes during the dissolution, is 
consumed in these processes and has to be replenished at least on a 
periodic basis to maintain its concentration in the treatment solution 
within the effective range. Some of the heavy metals, most notably iron 
and copper, cause an instability of the hydrogen peroxide in solution, 
expecially as these heavy metal ions accumulate during use. A rapid 
catalytic decomposition of the hydrogen peroxide not related to its 
consumption during processing occurs, resulting in excessive quantities of 
hydrogen peroxide being lost from the processing solution. In the past, 
various stabilizers have been added to hydrogen peroxide to protect it 
from decomposition in storage and shipping from trace quantities of these 
metals. Other stabilizers have been formulated to stabilize the hydrogen 
peroxide content of metal processing solutions. Compounds such as low 
molecular weight carboxylic acids and alcohols have been shown to have a 
retarding effect of hydrogen peroxide composition. Other known inhibitors 
include glycerine, glycols, polyglycols, phenol, p-methoxy phenol, alkyl 
and aryl sulphonic acids, sulfathiazole, phenacetin, 9-hydroxy quinoline, 
urea and amino pyridine. In general, the above mentioned hydrogen peroxide 
stabilizers have not been entirely satisfactory, for various reasons, such 
as insufficient stability at elevated process temperatures, obnoxious 
odors, excessive volatility, problems of undesirable side reactions with 
metal ions causing the formation of insoluble by-products, high costs, 
toxicity, etc. 
It is therefore a primary object of the present invention to provide a new 
and improved metal dissolution process solution containing hydrogen 
peroxide stabilized against decomposition by the dissolved heavy metals 
contained therein. Another object is to provide a method for stabilizing 
hydrogen peroxide solutions against the degrading effect by heavy metal 
ions. Still another object is to provide a novel process for the pickling 
of copper and copper alloys. 
Other objects will become readily apparent from a reading of the 
specification and appended claims. 
THE INVENTION 
According to the present invention it has been found that aqueous hydrogen 
peroxide solutions are effectively stabilized against decomposition by 
heavy metal ion contaminants if the solutions contain saccharin or an 
alkali metal salt of saccharin in quantities ranging from about 0.2g/l to 
the saturation of the solution. It should be understood that in this 
context the term "solution" applies to the various aqueous metal treating 
solutions which are prepared in situ by the user and are based on hydrogen 
peroxide and acids and mixtures of acids. The concentrations given 
throughout this specification are therefore based on the total amount of 
the hydrogen peroxide containing solution. 
In an acid-hydrogen peroxide metal treatment solution the saccharin 
stabilizer is incorporated in amounts broadly ranging from about 0.2 
grams/liter to the solubility of the stabilizer in the system. Solubility 
will depend on the make-up of the processing solutions and temperature. 
Higher dissolved salt and/or acid content depresses solubility while 
higher temperature increases solubility. Preferably at least about 0.5 
grams/liter is used, most preferably at least about 1 gram/liter. It 
should be understood that it is also within the scope of this invention to 
add the saccharin compound in amounts which are in excess of its 
solubility, to provide a self regulating reservoir of stabilizer in the 
system. The stabilizer is advantageously provided in the form of a 
concentrated aqueous solution of an alkali metal salt of saccharin, such 
as sodium saccharin, which is converted in situ to saccharin by the action 
of the acid. 
The hydrogen peroxide concentration of the metal treatment solution 
generally may vary over a wide range, e.g. from about 5 to 200 grams/liter 
on a free basis. Pickling solutions for the cleaning of metals such as 
copper, brass, aluminum, steel and the like usually contain between about 
5 and about 50 grams of hydrogen peroxide per liter. In bright dipping of 
copper and copper alloys a concentration of from about 5 to about 
40g/liter is commonly used, while in chemical milling of steel the 
concentration is generally between about 10 and about 50 grams per liter. 
In copper etching processes usual concentrations are in the range of 
50-200 g/l. 
Similarly, the acid component or components and the concentrations thereof 
in the solution may vary considerably depending upon the particular 
application for which the solution is intended. However, they are not 
variables affecting the stabilization of the hydrogen peroxide component. 
Thus, the solutions can be based on any of the acids and mixtures of acids 
used in metal dissolution processes including sulfuric acid, nitric acid, 
phosphoric acid, hydrochloric acid, hydrofluoric acid, fluoroboric acid 
and the like, and their acid concentrations usually range between about 2 
to about 400 grams/liter (free aid basis), although even higher 
concentrations may also be employed. For instance low acid concentrations 
typically in the range of about 2 to about 100 grams/liter are used in the 
cleaning of steel, copper, zinc, etc. while relatively high acid 
concentrations up to about 300-400 grams/liter are used in the etching 
processes. In the pickling of copper and alloys of copper the acid 
concentration typically amounts to between about 100 to about 400 
grams/liter. 
Various other additives may of course be added to these solutions in 
suitable quantities for achievement of certain desired results, including 
catalysts and promoters for increase of metal dissolution rates, 
brighteners, passivating agents, leveling agents, etc. 
The stabilized metal treatment solutions of this invention are used with 
advantage in any metal dissolution process resulting in the accumulation 
in the solution of metal ions which have degrading effect on the hydrogen 
peroxide stability. Examples of such processes include etching, chemical 
milling, pickling, bright dipping and polishing of metals as well as 
processes for the manufacture of tungsten filaments for light bulbs and 
others. Metals dissolved in these processes include copper and alloys of 
copper, iron, steel, nickel, cadmium, zinc, aluminum, molybdenum, lead and 
the like. 
The saccharin additives used in this invention have an excellent 
stabilizing effect upon aqueous hydrogen peroxide solutions, thereby 
extending their usefulness to a remarkable degree in the processes where 
they are employed. In addition, they exhibit other qualities which are 
highly desirable in that they are readily available, stable, non-volatile, 
non-toxic, odor-free compounds, which do not form undesirable by-proucts 
with metal ions in use.

For a better understanding of the invention, the following examples are 
provided. 
EXAMPLES 1 AND 2 
These comparative examples demonstrate the excellent stabilizing effect 
obtained by addition of sodium saccharin to a copper pickling solution 
containing appreciable quantities of copper ions. Solutions were prepared, 
each having a volume of 400 ml and containing 265 grams/liter H.sub.2 
SO.sub.4 and 30.6 grams/liter of copper ion (added as equivalent amount of 
copper sulfate pentahydrate). These solutions were placed in a constant 
temperature bath maintained at 120.degree. F and additions were made of 
hydrogen peroxide and sodium saccharin in the concentrations shown in 
Table I. After 21.5 hours, the two solutions were analyzed for hydrogen 
peroxide, the results being shown in the table. 
Table 1 
______________________________________ 
Sodium H.sub.2 O.sub.2 conc. - g/l 
Rate of 
Ex. Saccharin After H.sub.2 O.sub.2 loss 
No. g/l Initial 21.5 hrs. 
g/l/hr. 
______________________________________ 
1 0 12.19 0.0 -- 
2 1.0 12.72 11.10 0.075 
______________________________________ 
EXAMPLES 3-5 
In these examples, an investigation was made regarding the effect on 
stability of varying amounts of sodium saccharin additions to copper 
pickling solutions. The procedure of the previous examples was followed 
except that the duration of the experiments were now 29.5 hours. The 
results are shown in Table II below. 
Table II 
______________________________________ 
Sodium H.sub.2 O.sub.2 Conc. - g/l 
Rate of 
Ex. Saccharin After H.sub.2 O.sub.2 loss 
No. g/l Initial 29.5 hrs. 
g/l/hr 
______________________________________ 
3 0.2 11.05 7.23 0.13 
4 0.5 11.41 8.33 0.10 
5 3.0.sup.(1) 
11.35 10.17 0.04 
______________________________________ 
.sup.(1) Initially not completely soluble; complete solution achieved in 
4-5 hours. 
EXAMPLES 6-8 
When excessive hydrogen peroxide instability develops in a copper pickling 
system, it is often found that iron contamination of the pickling bath is 
an additional source of the problem. This is a common condition, because 
of many of the pickling tanks are made of stainless steel as are the 
chains, hooks and rails. The following comparative examples demonstrate 
the excellent ability of sodium saccharin to alleviate the detrimental 
effect of soluble iron on the peroxide stability. The procedures of 
Example 1 were followed in making up the bath solutions except that each 
of these also contained 500 mg/l of soluble iron, added as an equivalent 
amount of ferrous sulfate, and the tests were carried out for a period of 
21 hours. The results are tabulated in TABLE III 
Table III 
______________________________________ 
Sodium H.sub.2 O.sub.2 conc. - g/l 
Rate of 
Ex. Saccharin After H.sub.2 O.sub.2 loss 
No. g/l Initial 21 hrs. g/l/hr. 
______________________________________ 
6 0 12.36 0.0 -- 
7 1.0 12.29 8.74 0.17 
8 3.0 12.17 9.28 0.14 
______________________________________ 
It is obvious to those skilled in the art that many variations and 
modifications can be made to the specific embodiments discussed above. All 
such departures from the foregoing specification are considered within the 
scope of this invention as defined by this specification and the appended 
claims.