Ceramic electrical insulation coating
View Patent ↗A coating mixture comprising at least one ceramic powder and a first and second binder that when applied to a substrate and heat treated produces a thin ceramic electrical insulation coating suitable for superconducting magnet applications.
1. A green coated wire for superconducting applications, the green coated wire comprising:
a Bi-2212 wire comprising an Ag-alloy sheath;
a base coat surrounding the Ag-alloy sheath of the Bi-2212 wire, the base coat comprising:
15% by weight TiO 2 powder,
5% by weight polyvinyl butyral,
1% by weight polysilicate sol-gel,
78% by weight xylene ethanol=1:1,
0.5% by weight butyl benzoyl phthalate, and
0.5% by weight polyalkylene glycol; and
a top coat surrounding the base coat, the base coat surrounding the Ag-alloy sheath of the Bi-2212 wire, wherein the top coat comprises a polyacrylic binder, wherein the top coat does not dissolve in the base coat and a decomposing temperature of the top coat is substantially equal to, or lower than, a decomposing temperature of the first binder and the second binder.
2. The green coated wire of claim 1 , wherein the base coat surrounding the Bi-2212 wire is about 10 μm thick and the top coat is about 1 μm thick.
3. The green coated wire of claim 1 , wherein a viscosity of the base coat ranges from about 200 to about 250 cPs at 21° C.
4. The green coated wire of claim 1 , wherein a surface tension of the base coat ranges from about 20 to about 30 mN/m.
5. A green coated wire for superconducting applications, the green coated wire comprising:
a Bi-2212 wire comprising an Ag-alloy sheath;
a base coat surrounding the Ag-alloy sheath of the Bi-2212 wire, the base coat comprising:
at least one ceramic powder;
a first binder comprising polyvinyl butyral, wherein a ratio of the ceramic powder to the first binder is between about 2.5:1 and 3.5:1 by weight;
a second binder comprising a polysilicate;
two plasticizers;
wherein the second binder comprising a polysilicate is non-reactive with the Ag-alloy sheath of the Bi-2212 wire; and
a top coat surrounding the base coat, the base coat surrounding the Ag-alloy sheath of the Bi-2212 wire,
wherein the top coat comprises a polyacrylic binder,
wherein the top coat does not dissolve in the base coat and a decomposing temperature of the top coat is substantially equal to, or lower than, a decomposing temperature of the first binder and the second binder,
wherein the base coat surrounding the Ag-alloy sheath of the Bi-2212 wire is about 10 μm thick and the top coat is about 1 μm thick, and
wherein the base coat surrounding the Bi-2212 wire comprises:
15% by weight TiO 2 powder;
5% by weight polyvinyl butyral;
1% by weight polysilicate sol-gel;
78% by weight xylene ethanol=1:1;
0.5% by weight butyl benzoyl phthalate; and
0.5% by weight polyalkylene glycol.
6. The green coated wire of claim 5 , wherein a viscosity of the base coat ranges from about 200 to about 250 cPs at 21° C.
7. The green coated wire of claim 5 , wherein a surface tension of the base coat ranges from about 20 to about 30 mN/m.
8. A heat treated coated wire for superconducting applications, the heat treated coated wire comprising:
a Bi-2212 wire comprising an Ag-alloy sheath, wherein a diameter of the Bi-2212 wire is 0.8 mm and wherein the Ag-alloy sheath is in contact with the Bi-2212 wire;
a porous coating surrounding the Ag-alloy sheath of the Bi-2212 wire, wherein the porous coating is positioned on top of the Ag-alloy sheath of the Bi-2212 wire, wherein the porous coating exhibits a porosity that provides a pathway for oxygen permeability, wherein the porous coating has a thickness of about 7 μm, and wherein the porous coating comprises;
at least one sintered ceramic powder comprising a plurality of interconnected ceramic powder particles;
a partially decomposed polysilicate, wherein the partially decomposed polysilicate is non-reactive with the Ag-alloy sheath of the Bi-2212 wire; and
silicon dioxide decomposed from the polysilicate,
wherein the porous coating is formed from a base coating composition comprising:
15% by weight TiO 2 powder;
5% by weight polyvinyl butyral;
1% by weight polysilicate sol-gel;
78% by weight xylene ethanol=1:1;
0.5% by weight butyl benzoyl phthalate; and
0.5% by weight polyalkylene glycol.
9. The heat treated coated wire of claim 8 , wherein the porous coating does not degrade the transport critical current of the Bi-2212 wire.