Methods for inhibiting corrosion

Abstract

The present disclosure is directed to the methods for identifying a combined corrosion inhibitor formulation comprising at least a first and second corrosion inhibitor formulation for inhibiting corrosion in various substrates, for example in metal substrates. The present disclosure is also directed to compositions for inhibiting corrosion comprising a combined corrosion inhibitor formulation each independently selected from organic heterocyclic compounds and metal salts, metal anions, metal complexes, or any combinations thereof selected from rare earth, alkali earth and transition metals.

1 . A method of identifying a combined corrosion inhibitor formulation for inhibiting corrosion of a metal substrate, wherein the combined corrosion inhibitor formulation comprises at least a first corrosion inhibitor formulation comprising at least one corrosion inhibitor and a second corrosion inhibitor formulation comprising at least one corrosion inhibitor that is different to a corrosion inhibitor in the first corrosion inhibitor formulation, the method comprising the steps of:
 independently applying each of the first and second corrosion inhibitor formulations to the substrate and determining a polarisation resistance value for each of the first and second corrosion inhibitor formulations;   combining the first and second corrosion inhibitor formulations together to provide the combined corrosion inhibitor formulation;   applying the combined corrosion inhibitor formulation to the substrate and determining a polarisation resistance value for the combined corrosion inhibitor formulation, wherein, when said polarisation value for the combined corrosion inhibitor formulation is greater than the sum of the polarisation values for each of the first and second corrosion inhibitor formulation, said combined corrosion inhibitor formulation is categorised as positive;   wherein the corrosion inhibitors are each independently selected from the group consisting of:   a metal cation, metal anion, metal complex, or any combination thereof, wherein the metal is selected from the group consisting of Zn, La, Pr, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Co, Cu, Y, Ca, Sr, Ba, Sc, Mo, W, V and Zr; and   an organic heterocyclic compound according to Formula 1, or complex, or salt or ion thereof:   
       
         
           
           
               
               
           
         
         wherein 
         A is a 5- or 6-membered aryl, heteroaryl or heterocyclic ring, which is optionally substituted with one or more substituents and optionally fused with one or more aryl or heteroaryl rings, wherein a dotted line represents one or more optional double bonds; 
         Y 1  is selected from S, SH, NH 2  or is absent, wherein the dotted line represents a double bond when Y 1  is S or is absent when Y 1  is SH or NH 2 ; 
         X 1 , X 2− , and X 3  are selected from N, NR 5 , O, S, CR 6  and CR 7 R 8 , 
         R 5  is selected from hydrogen, amino, C 1 -C 10 alkyl, C 2 -C 10 alkenyl, C 2 -C 10 alkynyl, aryl and heteroaryl, in which each amino, alkyl, alkenyl, alkynyl, aryl or heteroaryl group may be optionally substituted, and 
         R 6 , R 7  and R 8 , are each independently selected from hydrogen, halogen, carboxyl, sulphide, thiol, amino, C 1 -C 10 alkyl, C 2 -C 10 alkenyl, C 2 -C 10 alkynyl, aryl and heteroaryl, in which each amino, alkyl, alkenyl, alkynyl, aryl or heteroaryl group may be optionally substituted; 
         wherein the combined corrosion inhibitor formulation comprises at least two corrosion inhibitors selected from metal cations, metal anions, metal complexes, or any combinations thereof; and 
         wherein the combined corrosion inhibitor formulation comprises: 
         (i) at least two metal cations and at least one organic heterocyclic compound of Formula 1 or complex, salt or ion thereof; 
         (ii) at least one metal cation, at least one metal anion and at least one organic heterocyclic compound of Formula 1 or complex, salt or ion thereof; 
         (iii) at least two metal complexes; 
         (iv) at least one metal complex and at least one metal anion; 
         (v) at least two metal cations and at least two organic heterocyclic compounds of Formula 1 or complex, salt or ion thereof; 
         (vi) at least one metal cation, at least one metal anion, and at least two organic heterocyclic compounds of Formula 1, or complex, salt or ion thereof; or 
         (vii) at least three corrosion inhibitors selected from metal cations, metal anions, metal complexes, or any combinations thereof, and at least one organic heterocyclic compound of Formula 1, or complex, salt or ion thereof. 
       
     
     
         2 . The method of  claim 1 , wherein the combined corrosion inhibitor formulation is according to (i), and the at least two metal cations are selected from the group consisting of Pr 3+ , Gd 3+ , Tb 3+ , Ce 3+ , Dy 3+ , Sm 3+ , Er 3+ , Lu 3+ , Tm 3+ , Zn 2+ , Co 2+ , Cu 2+ , and the at least one organic heterocyclic compound of Formula 1 is selected from the group consisting of 3-amino-1,2,4-triazole, benzimidazole, 1H-benzotriazole, 5-amino-2-mercapto-1,3,4-thiadiazole, 9H-purine-8-thiol, 1,2,4-triazole, 1,2,4-triazole-3-thiol, and 5-methyl-2-mercapto-1,3,4-thiadiazole. 
     
     
         3 . The method of  claim 1 , wherein the combined corrosion inhibitor formulation is according to (ii), and the at least one metal cation is selected from the group consisting of Pr 3+ , Gd 3+ , Tb 3+ , Ce 3+ , Dy 3+ , Sm 3+ , Er 3+ , Lu 3+ , Tm 3+ , Zn 2+ , Co 2+ , Cu 2+ , the at least one metal anion is selected from the group consisting of MoO 4   2− , VO 4   3− , ZrO 4   2− , WO 4   2− , and the at least one organic heterocyclic compound of Formula 1 is selected from the group consisting of 3-amino-1,2,4-triazole, benzimidazole, 1H-benzotriazole, 5-amino-2-mercapto-1,3,4-thiadiazole, 9H-purine-8-thiol, 1,2,4-triazole, 1,2,4-triazole-3-thiol, and 5-methyl-2-mercapto-1,3,4-thiadiazole. 
     
     
         4 . The method of  claim 1 , wherein the combined corrosion inhibitor formulation is according to (iii), and the at least two metal complexes are selected from the group consisting of zinc molybdate, erbium molybdate, lutetium molybdate, zinc vanadate, zinc benzotriazole, dysprosium benzotriazole, lutetium benzotriazole, gadolinium benzotriazole, gadolinium molybdate, praseodymium benzimidazole, lutetium benzimidazole, zinc benzimidazole, praseodymium molybdate, dysprosium molybdate, erbium benzotriazole, praseodymium benzimidazole, dysprosium benzimidazole, erbium benzimidazole, zinc tungstate, zinc vanadate, praseodymium vanadate, dysprosium vanadate, erbium vanadate, praseodymium tungstate, dysprosium tungstate, erbium tungstate. 
     
     
         5 . The method of  claim 1 , wherein the combined corrosion inhibitor formulation is according to (iv), and the at least one metal complex is selected from the group consisting of zinc molybdate, erbium molybdate, lutetium molybdate, zinc vanadate, zinc benzotriazole, dysprosium benzotriazole, lutetium benzotriazole, gadolinium benzotriazole, gadolinium molybdate, praseodymium benzimidazole, lutetium benzimidazole, zinc benzimidazole, praseodymium molybdate, dysprosium molybdate, erbium benzotriazole, praseodymium benzimidazole, dysprosium benzimidazole, erbium benzimidazole, zinc tungstate, zinc vanadate, praseodymium vanadate, dysprosium vanadate, erbium vanadate, praseodymium tungstate, dysprosium tungstate, erbium tungstate, and the at least one metal anion is selected from the group consisting of MoO 4   2− , VO 4   3− , ZrO 4   2− , WO 4   2− . 
     
     
         6 . The method of any one of  claims 1  to  5 , wherein, when the first corrosion inhibitor formulation comprises at least one corrosion inhibitor providing a delayed inhibitive response and the second corrosion inhibitor formulation comprises at least one corrosion inhibitor providing an immediate inhibitive response, the polarisation response for the combined corrosion inhibitor formulation polarisation resistance response is a continuous inhibitive response. 
     
     
         7 . The method of any one of  claims 1  to  6 , wherein the steps further comprise a component substitution step. 
     
     
         8 . The method of any one of  claims 1  to  7 , wherein the steps further comprise a ratio variation step. 
     
     
         9 . The method of any one of  claims 1  to  8 , wherein ring A is selected from an optionally substituted monocyclic 5 or 6 membered heteroaryl or heterocyclic ring or an optionally substituted bicyclic heteroaryl or heterocyclic ring, wherein the bicyclic ring has two rings independently selected from 5 and 6 membered rings. 
     
     
         10 . The method of  claim 1 , wherein the metal is selected from at least one of Zn, Co, Cu, Mo, W, V, Zr, Sm, Dy, Tb, Pr, Er, Tm, Lu and Gd. 
     
     
         11 . The method of  claim 10 , wherein the metal is selected from at least one of Zn, Co, Cu, Mo, W, V, Zr, Pr, Er, Lu, and Gd. 
     
     
         12 . The method of  claim 1 , wherein the metal cation is selected from at least one of Pr 3+ , Gd 3+ , Tb 3+ , Ce 3+ , Dy 3+ , Sm 3+ , Er 3+ , Lu 3+ , Tm 3+ , Zn 2+ , Co 2+ , Cu 3+ , and wherein the metal is in the form of a chloride, nitrate, sulphate salts or other soluble salts. 
     
     
         13 . The method of  claim 1 , wherein the metal anion is selected from at least one of MoO 4   2+ , VO 4   3+ , ZrO 4   2+ , and WO 4   2+ . 
     
     
         14 . The method of  claim 1 , wherein the metal complex is selected from at least one of zinc molybdate, erbium molybdate, lutetium molybdate, zinc vanadate, zinc benzotriazole, dysprosium benzotriazole, lutetium benzotriazole, gadolinium benzotriazole, gadolinium molybdate, praseodymium benzimidazole, lutetium benzimidazole, zinc benzimidazole, praseodymium molybdate, dysprosium molybdate, erbium benzotriazole, praseodymium benzimidazole, dysprosium benzimidazole, erbium benzimidazole, zinc tungstate, zinc vanadate, praseodymium vanadate, dysprosium vanadate, erbium vanadate, praseodymium tungstate, dysprosium tungstate, erbium tungstate. 
     
     
         15 . The method of  claim 1 , wherein the organic heterocyclic compound of Formula 1, or complex, salt or ion thereof, is selected from at least one of 3-amino-1,2,4-triazole, benzimidazole, 1H-benzotriazole, 5-amino-2-mercapto-1,3,4-thiadiazole, 9H-purine-8-thiol, 1,2,4-triazole, 1,2,4-triazole-3-thiol, and 5-methyl-2-mercapto-1,3,4-thiadiazole. 
     
     
         16 . The method of any one of  claims 1  to  15 , wherein the substrate is selected from the group consisting of steel, zinc, magnesium, copper, brass, and bronze. 
     
     
         17 . The method of  claim 16 , wherein the substrate is steel. 
     
     
         18 . The method of  claim 1 , wherein the combined corrosion inhibitor formulation is according to (v) and the at least two metal cations are selected from the group consisting of Pr 3+ , Gd 3+ , Tb 3+ , Ce 3+ , Dy 3+ , Sm 3+ , Er 3+ , Lu 3+ , Tm 3+ , Zn 2+ , Co 2+ , Cu 2+ , and the at least two organic heterocyclic compounds of Formula 1, or complex, salt or ion thereof, selected from the group consisting of 3-amino-1,2,4-triazole, benzimidazole, 1H-benzotriazole, 5-amino-2-mercapto-1,3,4-thiadiazole, 9H-purine-8-thiol, 1,2,4-triazole, 1,2,4-triazole-3-thiol, and 5-methyl-2-mercapto-1,3,4-thiadiazole. 
     
     
         19 . The method of  claim 1 , wherein the combined corrosion inhibitor formulation is according to (vi) and the at least one metal cation selected from the group consisting of Pr 3+ , Gd 3+ , Tb 3+ , Ce 3+  Dy 3+ , Sm 3+ , Er 3+ , Lu 3+ , Tm 3+ , Zn 2+ , Co 2+ , Cu 2+ , the at least one metal anion selected from the group consisting of MoO 4   2+ , VO 4   3+ , ZrO 2− , WO 4   2− , and the at least two organic heterocyclic compounds of Formula 1, or complex, salt or ion thereof, are selected from the group consisting of 3-amino-1,2,4-triazole, benzimidazole, 1H-benzotriazole, 5-amino-2-mercapto-1,3,4-thiadiazole, 9H-purine-8-thiol, 1,2,4-triazole, 1,2,4-triazole-3-thiol, and 5-methyl-2-mercapto-1,3,4-thiadiazole. 
     
     
         20 . The method of  claim 1 , wherein the combined corrosion inhibitor formulation is according to (vii) and the at least three corrosion inhibitors selected from metal cations, metal anions, metal complexes, or any combinations thereof, are selected from the group consisting of Pr 3+ , Gd 3+ , Tb 3+ , Ce 3+ , Dy 3+ , Sm 3+ , Er 3+ , Lu 3+ , Tm 3+ , Zn 3+ , Co 2+ , Cu 2+ , MoO 4   2− , VO 4   3− , ZrO 4   2− , WO 4   2− , zinc molybdate, lutetium molybdate, zinc benzotriazole, lutetium benzotriazole, gadolinium benzimidazole, gadolinium molybdate, praseodymium molybdate, dysprosium molybdate, erbium benzotriazole, praseodymium benzimidazole, dysprosium benzimidazole, erbium benzimidazole, zinc tungstate, zinc vanadate, praseodymium vanadate, dysprosium vanadate, erbium vanadate, praseodymium tungstate, dysprosium tungstate, erbium tungstate, and the at least one organic heterocyclic compound of Formula 1, or complex, salt or ion thereof, selected from the group consisting of 3-amino-1,2,4-triazole, benzimidazole, 1H-benzotriazole, 5-amino-2-mercapto-1,3,4-thiadiazole. 
     
     
         21 . The method according to any one of  claims 1  to  20 , wherein the combined corrosion inhibitor formulation is a film forming formulation. 
     
     
         22 . A combined corrosion inhibitor formulation as defined according to any one of  claims 1  to  21 . 
     
     
         23 . A combined corrosion inhibitor formulation for inhibiting corrosion of a metal substrate, wherein the combined corrosion inhibitor formulation comprises at least a first corrosion inhibitor formulation comprising at least one corrosion inhibitor and a second corrosion inhibitor formulation comprising at least one corrosion inhibitor that is different to a corrosion inhibitor in the first corrosion inhibitor formulation;
 wherein the corrosion inhibitors are each independently selected from the group consisting of:   a metal cation, metal anion, metal complex, or any combination thereof, wherein the metal is selected from the group consisting of Zn, La, Pr, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Co, Cu, Y, Ca, Sr, Ba, Sc, Mo, W, V, and Zr; and   an organic heterocyclic compound according to Formula 1, or complex, salt or ion thereof:   
       
         
           
           
               
               
           
         
         wherein 
         A is a 5- or 6-membered aryl, heteroaryl or heterocyclic ring, which is optionally substituted with one or more substituents and optionally fused with one or more aryl or heteroaryl rings, wherein a dotted line represents one or more optional double bonds; 
         Y 1  is selected from S, SH, NH 2  or is absent, wherein the dotted line represents a double bond when Y 1  is S or is absent when Y 1  is SH or NH 2 ; 
         X 1 , X 2− , and X 3  are selected from N, NR 5 , O, S, CR 6  and CR 7 R 8 , 
         R 5  is selected from hydrogen, amino, C 1 -C 10 alkyl, C 2 -C 10 alkenyl, C 2 -C 10 alkynyl, aryl and heteroaryl, in which each amino, alkyl, alkenyl, alkynyl, aryl or heteroaryl group may be optionally substituted, and 
         R 6 , R 7  and R 8 , are each independently selected from hydrogen, halogen, 
         carboxyl, sulphide, thiol, amino, C 1 -C 10 alkyl, C 2 -C 10 alkenyl, C 2 -C 10 alkynyl, aryl and heteroaryl, in which each amino, alkyl, alkenyl, alkynyl, aryl or heteroaryl group may be optionally substituted; 
         wherein the combined corrosion inhibitor formulation comprises: 
         (i) at least two metal cations and at least one organic heterocyclic compound of Formula 1, or complex, salt or ion thereof; 
         (ii) at least one metal cation, at least one metal anion and at least one organic heterocyclic compound of Formula 1, or complex, salt or ion thereof; 
         (iii) at least two metal complexes; 
         (iv) at least one metal complex and at least one metal anion; 
         (v) at least two metal cations and at least two organic heterocyclic compounds of Formula 1, or complex, salt or ion thereof; 
         (vi) at least one metal cation, at least one metal anion, and at least two organic heterocyclic compounds of Formula 1, or complex, salt or ion thereof, or 
         (vii) at least three corrosion inhibitors selected from metal cations, metal anions, metal complexes, or any combinations thereof, and at least one organic heterocyclic compound of Formula 1, or complex, salt or ion thereof, 
         wherein the organic heterocyclic compound of formula 1, or complex, salt or ion thereof, is selected from the group consisting of 3-amino-1,2,4-triazole, benzimidazole, 1H-benzotriazole, 5-amino-2-mercapto-1,3,4-thiadiazole, 9H-purine-8-thiol, 1,2,4-triazole, 1,2,4-triazole-3-thiol, and 5-methyl-2-mercapto-1,3,4-thiadiazole; the metal cation is selected from of Pr 3+ , Gd 3+ , Tb 3+ , Ce 3+ , Dy 3+ , Sm 3+ , Er 3+ , Lu 3+ , Zn 2+ , Co 2+ , Cu 2+ ; the metal anion is selected from MoO 4   2− , VO 4   3− , ZrO 4   2− , WO 4   2− ; and metal complexes zinc molybdate, erbium molybdate, lutetium molybdate, zinc vanadate, zinc benzotriazole, dysprosium benzotriazole, lutetium benzotriazole, gadolinium benzotriazole, gadolinium molybdate, praseodymium benzimidazole, lutetium benzimidazole, zinc benzimidazole, praseodymium molybdate, dysprosium molybdate, erbium benzotriazole, praseodymium benzimidazole, dysprosium benzimidazole, erbium benzimidazole, zinc tungstate, zinc vanadate, praseodymium vanadate, dysprosium vanadate, erbium vanadate, praseodymium tungstate, dysprosium tungstate, erbium tungstate; and 
         wherein the combined corrosion inhibitor formulation is categorised as positive when tested in a method according to any one of  claims 1  to  22 . 
       
     
     
         24 . The combined corrosion inhibitor formulation of  claim 23 , wherein the combined corrosion inhibitor formulation is according to (i), and the at least two metal cations are selected from the group consisting of Pr 3+ , Gd 2+ , Tb 3+ , Ce 2+ , Dy 3+ , Sm 3+ , Er 3+ , Lu 3+ , Tm 3+ , Zn 2+ , Co 2+ , Cu 2+ , and the at least one organic heterocyclic compound of formula 1, or complex, salt or ion thereof, is selected from the group consisting of 3-amino-1,2,4-triazole, benzimidazole, 1H-benzotriazole, 5-amino-2-mercapto-1,3,4-thiadiazole, 9H-purine-8-thiol, 1,2,4-triazole, 1,2,4-triazole-3-thiol, and 5-methyl-2-mercapto-1,3,4-thiadiazole. 
     
     
         25 . The combined corrosion inhibitor formulation of  claim 23 , wherein the combined corrosion inhibitor formulation is according to (ii), and the at least one metal cation is selected from the group consisting of Pr 3+ , Gd 3+ , Tb 3+ , Ce 3+ , Dy 3+ , Sm 3+ , Er 3+ , Lu 3+ , Zn 2+ , Co 2+ , Cu 2+ , the at least one metal anion is selected from the group consisting of MoO 4   2− , VO 4   3− , ZrO 4   2− , WO 4   2− , and the at least one organic heterocyclic compound of Formula 1, or complex, salt or ion thereof, is selected from the group consisting of 3-amino-1,2,4-triazole, benzimidazole, 1H-benzotriazole, 5-amino-2-mercapto-1,3,4-thiadiazole, 9H-purine-8-thiol, 1,2,4-triazole, 1,2,4-triazole-3-thiol, and 5-methyl-2-mercapto-1,3,4-thiadiazole. 
     
     
         26 . The combined corrosion inhibitor formulation of  claim 23 , wherein the combined corrosion inhibitor formulation is according to (iii), and the at least two metal complexes are selected from the group consisting of zinc molybdate, erbium molybdate, lutetium molybdate, zinc vanadate, zinc benzotriazole, dysprosium benzotriazole, lutetium benzotriazole, gadolinium benzotriazole, gadolinium molybdate, praseodymium benzimidazole, lutetium benzimidazole, zinc benzimidazole, praseodymium molybdate, dysprosium molybdate, erbium benzotriazole, praseodymium benzimidazole, dysprosium benzimidazole, erbium benzimidazole, zinc tungstate, zinc vanadate, praseodymium vanadate, dysprosium vanadate, erbium vanadate, praseodymium tungstate, dysprosium tungstate, erbium tungstate. 
     
     
         27 . The combined corrosion inhibitor formulation of  claim 23 , wherein the combined corrosion inhibitor formulation is according to (iv), and the at least one metal complex is selected from the group consisting of zinc molybdate, erbium molybdate, lutetium molybdate, zinc vanadate, zinc benzotriazole, dysprosium benzotriazole, lutetium benzotriazole, gadolinium benzotriazole, gadolinium molybdate, praseodymium benzimidazole, lutetium benzimidazole, zinc benzimidazole, praseodymium molybdate, dysprosium molybdate, erbium benzotriazole, praseodymium benzimidazole, dysprosium benzimidazole, erbium benzimidazole, zinc tungstate, zinc vanadate, praseodymium vanadate, dysprosium vanadate, erbium vanadate, praseodymium tungstate, dysprosium tungstate, erbium tungstate, and the at least one metal anion is selected from the group consisting of MoO 4   2− , VO 4   3− , ZrO 4   2− , WO 4   2− . 
     
     
         28 . The combined corrosion inhibitor formulation of  claim 23 , wherein the combined corrosion inhibitor formulation is according to (v) and the at least two metal cations are selected from the group consisting of Pr 3+ , Gd 3+ , Tb 3+ , Ce 3+ , Dy 3+ , Sm 3+ , Er 3+ , Lu 3+ , Tm 3+ , Zn 2+ , Co 2+ , Cu 2+ , and the at least two organic heterocyclic compounds of Formula 1, or complex, salt or ion thereof, are selected from the group consisting of 3-amino-1,2,4-triazole, benzimidazole, 1H-benzotriazole, 5-amino-2-mercapto-1,3,4-thiadiazole, 9H-purine-8-thiol, 1,2,4-triazole, 1,2,4-triazole-3-thiol, and 5-methyl-2-mercapto-1,3,4-thiadiazole. 
     
     
         29 . The combined corrosion inhibitor formulation of  claim 23 , wherein the combined corrosion inhibitor formulation is according to (vi) and the at least one metal cation selected from the group consisting of Pr 3+ , Gd 3+ , Tb 3+ , Ce 3+ , Dy 3+ , Sm 3+ , Er 3+ , Lu 3+ , Tm 3+ , Zn 2+ , Co 2+ , Cu 2+ , the at least one metal anion selected from the group consisting of MoO 4   2− , VO 4   3− , ZrO 4   2− , WO 4   2− , and the at least two organic heterocyclic compounds of Formula 1, or complex, salt or ion thereof, selected from the group consisting of 3-amino-1,2,4-triazole, benzimidazole, 1H-benzotriazole, 5-amino-2-mercapto-1,3,4-thiadiazole, 9H-purine-8-thiol, 1,2,4-triazole, 1,2,4-triazole-3-thiol, and 5-methyl-2-mercapto-1,3,4-thiadiazole. 
     
     
         30 . The combined corrosion inhibitor formulation of  claim 23 , wherein the combined corrosion inhibitor formulation is according to (vii) and the at least three corrosion inhibitors are selected from metal cations, metal anions, metal complexes, or any combinations thereof, selected from the group consisting of Pr 3+ , Gd 3+ , Tb 3+ , Ce 3+ , Dy 3+ , Sm 3+ , Er 3+ , Lu 3+ , Tm 3+ , Zn 2+ , Co 2+ , Cu 2+ , MoO 4   2− , VO 4   3− , ZrO 4   2− , WO 4   2− , zinc molybdate, lutetium molybdate, zinc benzotriazole, lutetium benzotriazole, gadolinium benzotriazole, gadolinium molybdate, praseodymium molybdate, dysprosium molybdate, erbium benzotriazole, praseodymium benzimidazole, dysprosium benzimidazole, erbium benzimidazole, zinc tungstate, zinc vanadate, praseodymium vanadate, dysprosium vanadate, erbium vanadate, praseodymium tungstate, dysprosium tungstate, erbium tungstate, and at least one organic heterocyclic compound of Formula 1, or complex, salt or ion thereof, is selected from the group consisting of 3-amino-1,2,4-triazole, benzimidazole, 1H-benzotriazole, 5-amino-2-mercapto-1,3,4-thiadiazole.