Silicon nitride protective coatings for silvered glass mirrors

• US 4,780,372 A
• Filed: 06/04/1986
• Issued: 10/25/1988
• Est. Priority Date: 07/20/1984
• Status: Expired due to Fees

• Current Assignee: United States Department of Energy
• Original Assignee: United States Department of Energy
• Inventors: Tracy, C. Edwin, Benson, David K.
• Primary Examiner(s): Kittle, John
• Assistant Examiner(s): Schwartz, P. R.
• Application Number:
  US06/873,069
• Time in Patent Office: 874 Days
• Field of Search: 428/428, 428/912.2, 428/434, 428/433, 428/450, 428/451, 428/458, 428/460-463, 428/698, 428/912.2, 428/469, 428/448, 428/472, 428/472.1, 427/94, 427/419.7, 427/397.7, 350/641, 350/642
• US Class Current: 428/428
• CPC Class Codes: C03C 17/36 at least one coating being a metal
• CPC Class Codes: C03C 17/3605 Coatings of the type glass/metal/inorganic compound
• CPC Class Codes: C03C 17/3626 one layer at least containing a nitride, oxynitride, boronitride or carbonitride
• CPC Class Codes: C03C 17/3644 the metal being silver
• CPC Class Codes: C03C 17/3652 the coating stack containing at least one sacrificial layer to protect the metal from oxidation
• CPC Class Codes: C03C 17/3663 specially adapted for use as mirrors
• CPC Class Codes: C03C 17/3697 one metallic layer at least being obtained by electroless plating
• CPC Class Codes: G02B 5/0808 having a single reflecting layer G02B5/0883, G02B5/0891 take precedence
• CPC Class Codes: G02B 5/0858 the reflecting layers comprising a single metallic layer with one or more dielectric layers

Abstract

A protective diffusion barrier for metalized mirror structures is provided by a layer or coating of silicon nitride which is a very dense, transparent, dielectric material that is impervious to water, alkali, and other impurities and corrosive substances that typically attack the metal layers of mirrors and cause degradation of the mirrors'"'"' reflectivity. The silicon nitride layer can be deposited on the substrate before metal deposition to stabilize the metal/substrate interface, and it can be deposited over the metal to encapsulate it and protect the metal from corrosion or other degradation. Mirrors coated with silicon nitride according to this invention can also be used as front surface mirrors.

Claims

1. A mirror, comprising:

a substrate comprising glass;

a first diffusion barrier comprising silicon nitride deposited on said substrate; and

a reflective layer of metal deposited on said first silicon nitride diffusion barrier such that said first silicon nitride diffusion barrier is positioned between the substrate and the metal for preventing leaching and diffusion of substances from and through the substrate to the metal and for avoiding metal contact and chemical reaction with the substrate.

2. The mirror of claim 1, including a second diffusion barrier comprising silicon nitride deposited on the side of said reflective metal layer that is opposite said first silicon nitride diffusion layer for sandwiching said metal layer between silicon nitride diffusion barriers while keeping said first silicon nitride diffusion barrier between the substrate and the metal.

3. The mirror of claim 2, wherein said metal layer comprises silver.

4. The mirror of claim 3, wherein said first silicon nitride diffusion barrier is in contact with the entire surface of the silver that faces said substrate and said second silicon nitride diffusion barrier covers the entire surface of the silver that faces opposite the substrate as well as covering the entire peripheral edge of the silver layer such that the entire silver layer is hermetically sealed in silicon nitride and not exposed directly to either the substrate or the atmosphere.