Abstract:
The invention refers to the electrolytic deposit of a tin- and ruthenium-based alloy having good features of corrosion resistance. In particular, the invention refers to an ecologically compatible process to achieve the electrolytic deposit of the alloy and to the operative conditions to make the deposit. Moreover, the invention refers to the electrolytic bath from which the alloy is caused to electro-deposit. In particular, the electrolytic bath is advantageously distinguished by the total absence of toxic metals and cyanides. The invention refers also to the alloy obtained through that process, as well as to the object/manufactured article covered with the alloy obtained through that process.

Description:
TECHNICAL FIELD 
       [0001]    The invention refers to the electrolytic deposit of a substantially tin- and ruthenium-based alloy having optimal features of corrosion resistance. In particular, the invention refers to an ecologically compatible process to realize the electrolytic deposit of said alloy and to the operative conditions to realize said deposit. 
         [0002]    Moreover, the invention refers to the electrolytic bath by which said alloy is made to electro-deposit. In particular, said electrolytic bath is advantageously distinguished by the total absence of toxic metals and cyanides. 
         [0003]    The invention also refers to said alloy obtained through said process, as well as to the object/manufactured article covered with said alloy obtained through said process. 
       BACKGROUND ART 
       [0004]    In the field of electrodeposit, for example in the decorative one, some types of tin-based alloys are known. Among the most commonly used there are those comprising also other metals such as, for example nickel, lead, copper, zinc, etc. This implies that, together with tin, also allergenic or toxic metals are currently co-deposited. Moreover, in order to obtain this result, alkali electrolytic baths that contain cyanides are normally used. All this reflects negatively both from the point of view of toxicity of the baths and of their final products, and from the point of view of toxicity and/or of the eco-compatibility of the entire production process. 
         [0005]    Moreover, a great part of the tin-based alloys known in the field, which are deposited with a level of tin superior to the 50%, have, for example, a scarce resistance to fumes of nitric acid (as well as to acids in general), oxidizing and/or corroding too quickly. 
         [0006]    To sum up what has been explained above, unfortunately said alloys are not sufficiently resistant and contain, as additional components, or also just as traces, metals and/or residues of elaboration that are toxic for the man and the environment. 
       Technical Problem 
       [0007]    It remains alive among the operators of the field the need to have at disposal a tin-based alloy which does not present the inconveniences cited above and that results also advantageous in terms of duration and of aesthetic aspect. Moreover, it is equally felt the need in the field that such an alloy can also be used as a re-enforcing under layer before the application of a final decorative finishing (said finishing is usually constituted by a thin thickness of a precious metal), thus conferring further advantageous physical-chemical performances to the finite object. 
         [0008]    It is the subject of the present invention to overcome all or at least a great part of these inconveniences, thus giving an adequate response to the technical problem described above. 
       DISCLOSURE OF INVENTION 
       [0009]    The applicant has now totally unexpectedly found out that, by electrolytically depositing an appropriate substantially tin- and ruthenium-based alloy by an appropriate electrolytic bath (electrolyte) not containing toxic products and/or metals, it is possible to give an adequate response to the technical problem described before. 
         [0010]    It is therefore the subject of the present invention a process to realize the electrolytic (galvanic) deposit of a substantially tin- and ruthenium-based alloy on a cathode soaked into an appropriate electrolytic bath (electrolytic solution) containing at least an effective amount of tin, and/or of one of its salts, and at least an effective quantity of ruthenium, and/or of one of its salts, as described in the independent claim attached. 
         [0011]    It is another subject of the present invention the electrolytic bath above, as described in the attached independent claim. 
         [0012]    Another subject of the invention is also the substantially tin- and ruthenium-based alloy obtained through the process above, as described in the attached independent claim. 
         [0013]    It is another subject of the present invention an object/manufactured article realized through the electrolytic deposit method of the bath described above. 
         [0014]    Further subjects of the present invention are described in the attached dependent claims. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Definitions 
       [0000]    
       
         
           
             from now onwards, for greater simplicity, by the term “tin” is intended indifferently metal tin (Sn) and/or one or more salts thereof; 
             from now onwards, for greater simplicity, by the term “ruthenium” is intended indifferently metal ruthenium (Ru) and/or one or more salts thereof. 
           
         
       
     
         [0017]    The present invention is directed to a process for electrolytically depositing a layer of a substantially tin- and ruthenium-based alloy on a cathode soaked into an aqueous electrolytic bath containing at least effective amounts of tin, ruthenium, conductor salts, complex-forming salts, alkali metal hydroxides, in which said process is characterized in that in said aqueous electrolytic bath:
       tin (under the form of metal or one or more of its salts) is present in an amount comprised between 1 and 100 g/L pro litre of electrolytic bath; preferably, between 5 and 50 g/L; still more preferably, of about 15 g/L;   ruthenium (under the form of metal or one or more of its salts) is present in an amount comprised between 0.030 and 10 g/L pro litre of electrolytic bath; preferably, between 0.1 and 5 g/L; still more preferably, of about 0.8 g/L;   the conductor salts, taken alone or in a mixture thereof, are present in an overall amount comprised between 5 and 100 gr/L pro litre of electrolytic bath; preferably, between 10 and 50 gr/L; still more preferably, of about 30 gr/L;   the complex forming salts are present in an overall amount comprised between 10 and 100 g/L pro litre of electrolytic bath; preferably, between 20 and 50 gr/L; still more preferably, between 30 and 40 gr/L;   the alkali metal hydroxides are present in an amount comprised between 0.2 and 10 gr/lt pro litre of electrolytic bath; preferably, between 1 and 3.5 g/L; still more preferably, of about 3 g/L;       
 
         [0023]    with the proviso that, in said electrolytic bath cyanides and toxic and allergenic metals or metalloids, such as Be, Ni, Cd, As, Tl, are absent. 
         [0024]    In the method of the present invention:
       the tin salts according to the invention are preferably selected from tin (II) salts and tin (IV) salts;       
 
         [0026]    examples of tin salts (II) comprise: sulphate, chloride, bromide, iodide, oxide, phosphate, pyrophosphate, acetate, citrate, gluconate, tartrate, lactate, succinate, sulphamate, phormiate; 
         [0027]    examples of tin (IV) salts comprise: sodium stannate, potassium stannate, nitrate, chloride and sulfide;
       ruthenium salts according to the invention are preferably selected from ruthenium (III) salts and ruthenium (IV) salts;       
 
         [0029]    examples of ruthenium salts comprise the groups: sulfide, carboxylate, chlorides, bromides, oxalate, sulphamate, composed nitrile, oxydryl;
       the conductor salts are preferably selected from the group consisting of: phosphates, carbonates, citrates, sulphates, tartrates, oxalates, sulphamates, gluconates, phosphonates, acetates and pyrophosphates;   the complex forming salts are preferably selected from the group consisting of: sulphates, carboxylates, chlorides, oxalates, pyrophosphates, citrates, sulphamates, gluconates, tartrates, phosphates, phosphonates;   the hydroxides of the alkali metals are selected from sodium hydroxide and potassium hydroxide.       
 
         [0033]    In the method of the present invention, the cathode is constituted, on the basis of the realization needs and of the applicative field, by an appropriate metal object/manufactured article, for example made of brass, zama, iron or aluminium, preferably, previously covered with deposits of electrolytic copper, nickel, bronze, gold, palladium and the alloys thereof, and the like. 
         [0034]    In the method of the present invention, the anode or the anodes is/are generally made of titanium coated with platinum, ruthenium, iridium or alloys from these metals. 
         [0035]    The process of electro-deposit of the present invention is made at pH values comprised between 10 and 14; preferably, between 11 and 13; still more preferably, of about 12. 
         [0036]    The process of electro-deposit of the present invention is made at a temperature comprised between 30° C. and 75° C.; preferably, between 35° C. and 70° C. In a preferred embodiment of the invention, the temperature is comprised between 40° C. and 60° C. 
         [0037]    Moreover, the process of electro-deposit of the present invention is made at a density/intensity of current comprised between 0.5 and 5 Amp/dm 2 ; preferably, between 1 and 4 Amp/dm 2 . 
         [0038]    Moreover, during the realization of the method of the present invention, it is necessary to maintain constant a cathodic agitation and of the electrolyte. 
         [0039]    The duration of the process of electro-deposit of the present invention is variable on the basis of the size of the object (the cathode) that wants to be coated with the tin-ruthenium alloy of the invention; of the intensity/density of the current employed; and of the thickness of the layer of alloy that wants to be deposited. In any case, the time of electro-deposit is on average variable between 1 and 10 min; preferably, between 2 and 6 min. 
         [0040]    The electrolytic bath of the present invention can further comprise one or more additional components selected from the group consisting of wetting agents, depolarizing agents, rinse-aid/brightness giving agents, other metal traces, organometallic compounds, stabilizing agents. 
         [0041]    For example, in a preferred embodiment of the invention, the bath can comprise one or more among the following additional additives, eventually an appropriate mixture of them. 
         [0042]    (i) Between 1 and 20 mL/L of at least a wetting agent; preferably between 2 and 10 mL/L; still more preferably, of about 5 mL/L. 
         [0043]    Said at least one wetting agent is selected from all those known that are compatible with alkali environments. 
         [0044]    Preferably, the wetting agent is selected from the non-ionic surfactants. For example, it is selected from the group consisting of: polyoxyethylene β-naphtol ether, polyoxyethylene alkyl ether, polyoxyethylene phenylether, polyoxyethylene alkylamino ether, polyethylene glycol. 
         [0045]    The wetting agent can also be selected from one or more cationic surfactants, anionic surfactants or amphoteric surfactants. 
         [0046]    Examples of cationic surfactants comprise: dodecyltrimethyl ammonium salt, hexadecyltrimethyl ammonium salt, octadecyltrimethyl ammonium salt, dodecyldimethyl ammonium salt, cetyltrimethyl ammonium salt, dodecyldimethyl ammonium betaine, octadecyldimethyl ammonium betaine, dimethylbenzyldodecyl ammonium salt, trimethylbenzyl ammonium salt, octacecylamino acetate and dodecilamino acetate. 
         [0047]    Examples of anionic surfactants comprise: alkyl sulphates, sodium dodecyl sulphate, lauryl sulphate, lauryl sulphonate, dodecyl sulphate, octadecyl sulphate, polyoxyethylene alkylether sulphates, sodium polyoxyethylene (EO12) nonyl ether sulphate, polyoxyethylene alkylphenylether sulphates, alkylbenzensulphonates. 
         [0048]    Examples of amphoteric surfactants comprise betaine and sulphobetaine. 
         [0049]    (ii) Between 0.1 and 20 g/L of a depolarizing agent; preferably, da 1 a 10 g/L; still more preferably, of about 5 g/L. 
         [0050]    Preferably, said depolarizing agents are selected from the group consisting of: salts of alkali tartrates and alkali sulphites. 
         [0051]    (iii) Between 0.010 and 5 mL/L of at least a rinse-aid/brightness giving agent; preferably between 0.050 and 3 mL/L; still more preferably, of about 0,100 mL/L. 
         [0052]    Preferably, said rinse-aid/brightness giving agents are selected from the group consisting of: butyndiol derivatives, di-thiocarboxylic acids, rhodium salts, silver salts and saccharinates. 
         [0053]    (iv) Modest amounts or traces, in any case not superior to 5% in weight, with respect to the overall amount of the salts constituting the bath; preferably, not superior to 3%; of the following metals: Zn, Rh, Pd, Au, Ga, Bi, Ag, Ta, In, Fe. 
         [0054]    The examples that follow have the only subject of illustrating the invention in detail, in particular, the composition of the electrolytic bath from which it is possible to obtain/deposit the alloy that is the subject of the present invention and are absolutely not limiting of the wide applicative potential of the same. 
       Example 1 
       [0055]    Composition of an aqueous electrolytic bath according to the invention and its application 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Sn 
                 15 g/L 
               
               
                   
                 Ru 
                 0.8 g/L  
               
               
                   
                 KOH 
                  4 g/L 
               
               
                   
                 Wetting agent 
                 0.01 g/L     
               
               
                   
                 Potassium oxalate 
                  5 g/L 
               
               
                   
                 Potassium citrate 
                 30 g/L 
               
               
                   
                   
               
             
          
         
       
     
         [0056]    In the present example, the wetting agent can be indifferently any one of those described above, preferably the cetyltrimethylammonium chloride or the sodium dodecyl sulfate. 
         [0057]    In the present example the pH of the bath is =12; the exercise temperature is =50° C. and the density of current employed is =2 Amp·dm 2 . 
       Example 2 
       [0058]    Composition of an aqueous electrolytic bath according to the invention and its application 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Sn 
                 25 g/L 
               
               
                   
                 Ru 
                 0.9 g/L  
               
               
                   
                 KOH 
                  4 g/L 
               
               
                   
                 Wetting agent 
                 0.01 g/L     
               
               
                   
                 Potassium oxalate 
                  2 g/L 
               
               
                   
                 Sodium and potassium tartrate 
                 50 g/L 
               
               
                   
                   
               
             
          
         
       
     
         [0059]    In the present example, the wetting agent can be indifferently any one of those described before, preferably the cetyltrimethylammonium chloride or the sodium dodecyl sulfate. 
         [0060]    In the present example the pH of the bath is =12; the exercise temperature is =45° C. and the density of current employed is =1 Amp·dm 2 . 
         [0061]    Moreover, in the present example the electrolytic bath is contained in a polypropylene bath (PVC) and can be thermostatated by means of heater in quartz, PTFE, porcelain or steel. 
         [0062]    The present invention is not limited by the examples illustrated; many variants and alternatives are in fact possible that will result easily realizable by the experts in the field in the light of the teaching of the present description and of the claims attached. 
         [0063]    Some of the advantageous features of the present invention are represented, among others, by the following aspects:
       the electro-deposited alloy results provided with an optimal resistance to oxidation and to acid agents;   the electro-deposited alloy is exempt from toxic and allergenic metals or metalloids;   the electrolyte of the bath is totally exempt from cyanides and from other toxic and polluting substances;   the performance of the deposit process is at least equal, when not superior, to those of traditional processes;   the layer deposited is provided with a good brightness and resistance to oxidation;   great homogeneity of the distribution of the alloy to the different densities of current has been found also on cathodes of complex shapes and not linear;   the colour of the alloy is comprised between white and grey.       
 
         [0071]    The advantages obtained with the method of the present invention derive in particular also from the type of electrolytic bath employed. 
         [0072]    As a consequence, also said bath, as described in the preceding description, is one of the subjects of the present invention. 
         [0073]    Substantially tin- and ruthenium-based alloys, deposited electrolytically on an object (cathode) in accordance with the method of the present invention, are not known until now as per the knowledge of the applicant. 
         [0074]    As a consequence, also said Sn—Ru alloy, as described in the preceding description, is one of the subjects of the present invention. 
         [0075]    In the light of all the above, it is a further subject of the present invention also a manufactured product/an article coated with said Sn—Ru alloy realized through the method of electrolytic deposit from the electrolytic bath of the present invention. 
         [0076]    It is also a further subject of the present invention a substantially tin- and ruthenium-based alloy obtained with the process as described. 
         [0077]    It is also a further subject of the present invention an article/manufactured article coated with a substantially tin- and ruthenium-based alloy obtained as described above.