Adding a metal oxide coating to a metal slab can be achieved through various methods. Here are a few common techniques:

1. **Thermal Oxidation:**

- Subject the metal slab to high temperatures in the presence of oxygen.

- Common for metals like aluminum and titanium.

- Forms a natural oxide layer on the metal surface.

2. **Anodization:**

- Applicable to metals like aluminum.

- Electro-chemically oxidize the metal by immersing it in an electrolyte solution and applying a controlled electric current.

- Produces a controlled, thicker oxide layer with enhanced properties.

3. **Chemical Vapor Deposition (CVD):**

- Introduce a gaseous metal precursor and an oxidizing agent at elevated temperatures.

- Reactants deposit a thin oxide layer on the metal surface.

- Requires specialized equipment.

4. **Electrochemical Deposition:**

- Submerge the metal slab in an electrolyte solution containing metal ions.

- Apply an electric current to induce the reduction of metal ions, forming a metal oxide coating on the slab.

5. **Sol-Gel Method:**

- Prepare a sol (solution) containing metal alkoxide precursors.

- Apply the sol to the metal surface and allow it to undergo gelation and subsequent drying.

- Heat treatment then forms the metal oxide film.

6. **Spray Pyrolysis:**

- Dissolve metal salts in a solvent to create a precursor solution.

- Spray the solution onto the metal slab, and heat it to decompose the precursor, leaving a metal oxide coating.

Choose the method based on the specific metal, desired thickness, and properties of the oxide layer. Each technique has its advantages and limitations, so the selection depends on the application and desired outcome.