US 2016/0251602 Al  5  Sep.  1, 2016  such as succinic acid, oxydisuccinic acid, carboxymethylox› ysuccinic acid, polymaleic acid, mellitic acid and benzene  1,3,5-tricarboxylic acid, phosphates such as sodium hydro› gen phosphate, sodium dihydrogen phosphate and zinc  hydrogen phosphate, sulphate and sulphite containing com› pounds such as sodium bisulphate, sodium bisulphite, iron  (II) sulphate and iron (III) sulphate, sulphonic acids such as  methane sulphonic acid, phenol sulphonic acid, toluene sul› phonic acid, acrylamido-2-methylpropanesulphonic acid and  polyvinylsulphonic acid, polyacetic acids such as ethylene› diamine tetraacetic acid and nitrilotriacetic acid, weak acids  such as phosphoric acid, carbonic acid and hydrogen perox› ide, and others including ascorbic acid and acidic ion  exchange resins based on sulphonic acids such as acryla› mido-2-methylpropanesulphonic acid and chelating resins  based on dicarboxylic acids such as iminodiacetic acid.  where [H+], etc. represent the concentrations of the respective  species inmol/L.  It follows thatpKa=pH+log [HA]-log [A-],  so a solution with 50% dissociation has pH equal to the pKa  of the acid.  [0113]  In some embodiments of the invention the acids can  have pKa values greater than about -1. 7. In further embodi› ments, the acids can have a pKa between about -1. 7 and about  15.7 (the pKa of water). In still further embodiments, the  acids can have pKa values greater than about 1. In certain  embodiments, the acids can have pKa values between about 1  and about 15.7. In still further embodiments, the acids can  have pKa values between about 1 and about 12. In embodi› ments of the invention containing polyprotic acids, each pKa  value may be in accordance with the ranges specified above  (for example, the acidic compound can contain more than one  pKa value each which is greater than about -1.7). Thus in  some embodiments of the invention, the acids of the cleaning  formulation are weaker than strong acids with pKa values of  less than -1.7 ( e.g. sulphuric acid or hydrochloric acid) that  are commonly employed in methods of the prior art.  [0114]  In some embodiments it is preferred that no acid  present in the cleaning formulation has a pKa ofless than or  equal to about -1.7, more preferably no acids presents in the  cleaning formulation have a pKa outside about -1.7 to about  15.7, even more preferably no acids presents in the cleaning  formulation have a pKa outside about 1 to about 12. In some  embodiments the cleaning formulation does not comprise a  mineral acid ( examples of which include sulphuric acid,  hydrochloric acid, hydrofluoric acid, hydriodic acid, nitric  acid and phosphonic acid)  [0110]  In some embodiments of the invention the cleaning  formulation can comprise at least one base. In some embodi› ments, the cleaning formulation can include bases selected  from, but not limited to, one or more alkali metal containing  compounds and/or salts thereof such as sodium polyacrylate,  sodium  acrylamido-2-methylpropanesulphonate,  sodium  polyvinylsulphonate, sodium carbonate, sodium hydrogen  carbonate, sodium citrate, trisodium citrate, sodium oxalate,  sodium phosphate, sodium phenol sulphonate, sodium tolu› ene sulphonate, sodium methane sulphonate, sodium lactate,  sodium gluconate, sodium glycolate and sodium formate and  others including zinc phosphate, poly (acrylamido-N-propy› ltrimethylammonium chloride), polyethylene amine, zinc  dithiophosphate, benzalkonium chloride, alkylaminophos› phates plus the alkali metal salts of polyphosphates, ammo› nium salts of polyphosphates and alkanolammonium salts of  polyphosphates, alkali metal silicates, alkaline earth and  alkali metal carbonates, aluminosilicates, polycarboxylate  compounds, ether hydroxypolycarboxylates, copolymers of  maleic anhydride with ethylene or vinyl methyl ether, 1,3,5- trihydroxybenzene-2,4,6-trisulphonic acid, and carboxym› ethyl-oxysuccinic acid, alkali metal salts of polyacetic acids,  ammonium salts of polyacetic acids and substituted ammo› nium salts of polyacetic acids such as ethylendiamine tet› raacetic acid and nitrilotriacetic acid, as well as polycarboxy› lates such as mellitic acid, succinic acid, oxydisuccinic acid,  polymaleic acid, benzene 1,3,5-tricarboxylic acid, car› boxymethyloxysuccinic acid and soluble salts thereof and  basic ion exchange resins including those based on quater› nary amino groups such as trimethylammonium groups, for  example, poly (acrylamido-N-propyltrimethylammonium  chloride).  [0115]  As noted above, bases included in some embodi› ments of the invention can have ionization constants within a  specified range. Thus the bases can have particular pKb val› ues in a dilute aqueous solution, wherein the logarithm of the  ionisation constant, pKb, is derived from the reaction:  B+H$_{2}$0~  BH+ +OH-. This is related to Ka by:  [0116]  In some embodiments of the invention bases  included in the cleaning formulation can have pKb values  greater than about -1.7. In further embodiments, the bases  can have pKb between about -1.7 and about 15.7 (the pKb of  water). In still further embodiments, the bases can have pKb  values greater than about 1. In certain embodiments, the bases  can have pKb values between about 1 and about 15 .7. In still  further embodiments, the bases can have pKb values between  about 1 and about 12.  pKa+pKbccp~a<er~14.00 (at 25°  C.).  [0111]  Thus in some embodiments of the invention the  cleaning of the metal substrate can be performed using bases  as opposed to the acidic reagents typically employed in meth› ods of the prior art.  [0112]  In some embodiments of the invention the acids  and/or bases when present in the cleaning formulation can  have dissociation or ionization constants within a specified  range. Thus the acids can have particular pKa values in a  dilute aqueous solution, wherein pKa is defined as the nega› tive of the logarithm of the equilibrium constant Ka for the  reaction:  [0117]  In some embodiments it is preferred that no base  present in the cleaning formulation has a pKb of less than or  equal to about -1.7, more preferably no bases presents in the  cleaning formulation have a pKb outside about -1. 7 to about  15.7, even more preferably no bases presents in the cleaning  formulation have a pKa outside about 1 to about 12.  [0118]  The solid particulate material for use in embodi› ments of the method of the invention can comprise a multi› plicity of polymeric particles or a multiplicity of non-poly› meric particles. In some embodiments, the solid particulate  material can comprise a multiplicity of polymeric particles.  Alternatively, the solid particulate material can comprise a  mixture of polymeric particles and non-polymeric particles.  In such embodiments, the mixture can contain predominantly  polymeric particles. In other embodiments, the solid particu› late material can comprise a multiplicity of non-polymeric  particles. Thus the solid particulate material in embodiments 