Corrosion inhibitors for Fe2P structure magnetocaloric materials in water

Abstract

Use of a composition (A) having a pH of at least 8 at 25 C. containing at least 50 wt.-% of water or a water containing solvent mixture, at least 0.1 mol/m3 of at least one water soluble silicate, optionally at least one molybdate, optionally at least one phosphonate, optionally at least one azole, optionally at least one additional freezing point depressing salt, optionally at least one phosphate, and optionally at least one nitrate, as heat carrier medium for magnetocaloric materials of formula (I) (A.sub.yB.sub.1y).sub.2+uC.sub.wD.sub.xE.sub.z (I) where: A is Mn or Co, B is Fe, Cr or Ni, C is Ge, As or Si, D is different from C and is selected from P, B, Se, Ge, Ga, Si, Sn, N, As and Sb, E may be same or different from C and D and is selected from P, B, Se, Ge, Ga, Si, Sn, N, As and Sb.

Claims

1. A method, comprising contacting a magnetocaloric material with a heat carrier medium adapted to transfer thermal energy to or from the magnetocaloric material, wherein: the heat carrier medium comprises a composition (A) having a pH of at least 8 at 25 C. and comprising (a1) at least 50 wt.-% of water or an aqueous solvent mixture comprising at least 90 wt.-% of water based on a total weight of (a1), based on a total weight of composition (A), and (a2) 0.1 mol/m.sup.3 to 10 mol/m.sup.3 of at least one water soluble silicate, (a3) optionally at least one molybdate, (a4) optionally at least one phosphonate, (a5) optionally at least one azole, (a6) optionally at least one additional freezing point depressing salt, (a7) optionally at least one phosphate, and (a8) optionally at least one nitrate, units of mol/m.sup.3 being based on a total volume of the composition (A); the magnetocaloric material comprises a compound of formula (I):
(A.sub.yB.sub.1y).sub.2+uC.sub.wD.sub.xE.sub.z(I); A is Mn; B is Fe; C Si or As; D is P; E is the same or different from C and D and is selected from the group consisting of P, B, Se, Ge, Ga, Si, Sn, N, As and Sb; u is a number in the range from 0.1u0.1; y is number in the range of 0<y<1; w, x are numbers in the range of 0<w, x<1; z is a number in the range of 0z<1; and w+x+z=1.

2. The method according to claim 1, wherein the overall concentration of components (a2), (a3), (a4), (a5), (a6), (a7), and (a8) in composition (A) is at least 150 mol/m.sup.3.

3. The method according to claim 1, wherein the aqueous solvent mixture is a mixture of water with one or more solvent comprising a water miscible C.sub.1-6-alkanol, C.sub.1-6-alkanolamine, C.sub.2-6-alkanediol or polyol having an aliphatic hydrocarbon radical with 3 to 6 hydroxyl groups.

4. The method according to claim 1, wherein the composition (A) has a pH at 25 C. in the range of 9 to 11.

5. The method according to claim 1, wherein the silicate (a2) is selected from the group consisting of Na.sub.2O.nSiO.sub.2, K.sub.2O. nSiO.sub.2, Li.sub.2O.nSio.sub.2,Rb.sub.2O. nSiO.sub.2, and Cs.sub.2O.nSiO.sub.2 with 1n4, in which the silicates may be hydrated.

6. The method according to claim 1, wherein composition (A) comprises at least 0.1 mol/m.sup.3 of at least one molybdate (a3).

7. The method according to claim 6, wherein the at least one molybdate (a3) is selected from the group consisting of Na.sub.2MoO.sub.4, K.sub.2MoO.sub.4, Li.sub.2MoO.sub.4, Rb.sub.2MoO.sub.4, Cs.sub.2MoO.sub.4, MgMoO.sub.4, and an ammoniummolybdate.

8. The method according to claim 1, wherein the composition (A) comprises at least 0.01 mol/m.sup.3 of at least one phosphonate (a4).

9. The method according to claim 8, wherein the at least one phosphonate (a4) is selected from the group consisting of 2-hydroxy phosphonoacetic acid, 2-phosphonobutane-1,2,4-tricarboxylie acid, amino tris(methylene phosphonic acid), and 1-hydroxyethylidene-1,1-diphosphonic acid.

10. The method according to claim 1, wherein the composition (A) comprises at least 0.01 mol/m.sup.3 of at least one azole (a5).

11. The method according to claim 10, wherein the at least one azole (a5) is selected from the group consisting of tolyltriazole; 1,2,3-benzotriazole; 1H-benzotriazole, 6(or 7)-methyl-, sodium salt (1:1); 2-mercaptobenzothiazole; and sodium salt of 2-mercaptobenzothiazole.

12. The method according to claim 1, wherein the composition (A) comprises at least 150 mol/m.sup.3 of at least one freezing point depressing salt (a6).

13. The method according to claim 12, wherein the at least one additional freezing point depressing salt (a6) is selected from the group consisting of sodium acetate, potassium acetate, sodium formate, potassium formate, sodium adipate and potassium adipate.

14. The method according to claim 1, wherein the composition (A) comprises at least 0.1 mol/m.sup.3 of at least one phosphate (a7) selected from the group consisting of an orthophosphate, a pyrophosphate and a polyphosphate.

15. The method according to claim 14, wherein the at least one phosphate (a7) is an orthophosphate selected from the group consisting of Zn.sub.3(PO.sub.4).sub.2, Na.sub.3PO.sub.4, Na.sub.2HPO.sub.4, NaH.sub.2PO.sub.4, K.sub.3PO.sub.4,K.sub.2HPO.sub.4, KH.sub.2PO.sub.4, (NH.sub.4).sub.3PO.sub.4, (NH.sub.4).sub.2HPO.sub.4, (NH.sub.4)H.sub.2PO.sub.4and H.sub.3PO.sub.4, a pyrophosphate selected from the group consisting of sodium pyrophosphate and potassium pyrophosphate, or are sodium hexametaphosphate.

16. The method according to claim 1, wherein the composition (A) comprises at least 0.1 mol/m.sup.3 of at least one nitrate (a8).

17. The method according to claim 16, wherein the at least one nitrate (a8) is selected from the group consisting of LiNO.sub.3, NaNO.sub.3, KNO.sub.3, RbNO.sub.3, NH.sub.4NO.sub.3, Mg(NO.sub.3).sub.2, Ca(NO.sub.3), Sr(NO.sub.3).sub.2, and Zn(NO.sub.3).sub.2.

18. The method according to claim 1, wherein the composition (A) comprises (a1) at least 60 wt.-% of the water or then aqueous solvent mixture comprising at least 90 wt.-% of water based on a total weight of (a1), based on the total weight of composition (A), and (a2) 0.1 mol/m.sup.3 to 10 mol/m.sup.3 of the at least one water soluble silicate, (a3) 0.1 to 100 mol/m.sup.3 of at least one molybdate.

19. The method according to claim 1, wherein the composition (A) comprises (a1) at least 60 wt.-% of the water or then aqueous solvent mixture comprising at least 90 wt.-% of water based on a total weight of (a1), based on the total weight of composition (A), and (a2) 0.1 mol/m.sup.3 to 10 mol/m.sup.3 of the at least one water soluble silicate, (a3) 0.1 to 100 mol/m.sup.3 of at least one molybdate, (a4) 0.01 to 10 mol/m.sup.3 of at least one phosphonate, and (a5) 0.01 to 100 mol/m.sup.3 of at least one azole.

20. A system, comprising a magnetocaloric material of formula (I) and a composition (A) as heat carrier medium being in direct contact with the magnetocaloric material:
(A.sub.yB.sub.1y).sub.2+uC.sub.wD.sub.xE.sub.z(I), wherein: A is Mn; B is Fe; C Si or As; D is P; E is the same or different from C and D and is selected from the group consisting of P, B, Se, Ge, Ga, Si, Sn, N, As and Sb; u is a number in the range from 0.1u0.1; y is number in the range of 0<y<1; w, x are numbers in the range of 0<w, x<1; z is a number in the range of 0z<1; w+x+z=1; and the heat carrier medium comprises a composition having a pH of at least 8 at 25 C. and comprising (a1) at least 50 wt.-% of water or an aqueous solvent mixture comprising at least 90 wt.-% of water based on a total weight of (a1), based on a total weight of composition (A), and (a2) 0.1 mol/m.sup.3 to 10 mol/m.sup.3 of at least one water soluble silicate, (a3) optionally at least one molybdate, (a4) optionally at least one phosphonate, (a5) optionally at least one azole, (a6) optionally at least one additional freezing point depressing salt, (a7) optionally at least one phosphate, and (a8) optionally at least one nitrate, units of mol/m.sup.3 being based on a total volume of the composition (A).

21. The system according to claim 20, wherein the overall concentration of components (a2), (a3), (a4), (a5), (a6), (a7), and (a8) in composition (A) is at least 150 mol/m.sup.3.

Description

EXAMPLES

Example 1

(1) The corrosion of MnFePSi was tested in different heat carrier media. Platelets (size ca. 1 to 2 cm.sup.2, total mass ca. 1 to 2 g) of Mn.sub.1.24Fe.sub.0.71P.sub.0.48Si.sub.0.52 were fully immersed in 50 mL of the following fluids: a) deionized water (non-inventive), pH=6.5 to 7.0 b) 0.533 mol/m.sup.3 tolyltriazole in deionized water (non-inventive), pH=9.8, c) 2.271 mol/m.sup.3 sodium silicate in deionized water (inventive), pH=10.4, d) 0.802 mol/m.sup.3 sodium molybdate dihydrate in deionized water (non-inventive), pH=8, e) 0.673 mol/m.sup.3 2-hydroxy phosphonoacetic acid in deionized water (non-inventive), pH=8.6.

(2) After 13 days of immersion of the platelets in the different fluids at room temperature, all platelets except for the ones in 2.271 mol/m.sup.3 sodium silicate (inventive example 1c)) showed discoloration on the platelet surface. The discolorations on the other platelets ranged from light brown to brown to dark brown and black as well as a dark blue appearance. In all non-inventive examples 1a), b), d) and e) a mixture of different discolorations was observed.

Examples 2-1 to 2-8

(3) The corrosion of MnFePSi was tested in different heat carrier media. Granulates (particle size 300-425 m, total mass 2 g per sample) of Mn.sub.1.26Fe.sub.0.69P.sub.0.48Si.sub.0.52 were fully immersed in 30 mL of different heat carrier media consisting of deionized water and different additives. The immersed samples were kept on a plate vibrator for 12 days at room temperature. The concentration of Fe, Mn, P and Si in the heat carrier media after the twelve days was determined via inductively coupled plasma optical emission spectrometry (ICP-OES). The concentrations of the different additives in the deionized water and the concentration of Fe, Mn, P and Si determined in the heat carrier media after twelve days are shown in Table 1.

(4) TABLE-US-00001 TABLE 1 Fe Mn P Si [mg/ [mg/ [mg/ [mg/ Additives kg] kg] kg] kg] 2-1 2.3 mol/m.sup.3 sodium inventive <1 <1 <3 90 orthosilicate pH: 11.38 2-2 0.8 mol/m.sup.3 sodium non- <1 4 3 4 molybdate dihydrate inventive pH: 9.6 2-3 2.3 mol/m.sup.3 sodium non- <1 1 65 14 phosphate inventive pH: 9.65 2-4 2.3 mol/m.sup.3 sodium non- <1 4 9 4 nitrate inventive pH: 9.65 2-5 2.3 mol/m.sup.3 sodium inventive <1 <1 <3 95 orthosilicate + 0.8 mol/m.sup.3 sodium molybdate dihydrate pH: 11.5 2-6 2.3 mol/m.sup.3 sodium inventive <1 1 55 95 orthosilicate + 2.3 mol/m.sup.3 sodium phosphate pH: 10.3 2-7 2.3 mol/m.sup.3 sodium inventive <1 <1 <3 85 orthosilicate + 2.3 mol/m.sup.3 sodium nitrate pH: 11.6 2-8 2.3 mol/m.sup.3 sodium inventive <1 <1 55 85 orthosilicate + 0.8 mol/m.sup.3 sodium molybdate dihydrate + 0.5 mol/m.sup.3 1H- benzotriazole + 2.3 mol/m.sup.3 sodium phosphate pH: 11.6 The sign < means, that the concentration was below the limit of detection.

(5) The results in Table 1 show that sodium orthosilicate is more effective in reducing the leaching of Mn, Fe and P from the magnetocaloric material than sodium molybdate dihydrate, sodium phosphate and sodium nitrate alone. The inventive heat carrier media containing sodium orthosilicate and additional additives like sodium molybdate dihydrate, sodium phosphate and sodium nitrate show better results than compositions containing the additional additives alone, too. This is a very beneficial effect, since in a magnetocaloric cooling device the heat carrier medium usually flows through a tube and pumping system which is made from different materials than the magnetocaloric material. The inventive heat carrier media for magnetocaloric materials allow the adjustment of their composition to the materials of the pump and piping system if needed without detrimental effect on the magnetocaloric materials.