Scale inhibitors are chaicals used to prevent the formation of scale, which is the undesirable accumulation of minerals from water onto surfaces, such as heat exchangers, pipes, and other equipment in industrial systas. Scale can significantly reduce the efficiency of these systas and lead to increased maintenance costs and downtime. Here is a list of common scale inhibitors:

1. Phosphonates: These are often used in water treatment to prevent calcium phosphate scale. Examples include:

   • Hydroxyethylidene Diphosphonic Acid (HEDP)

   • Ethylene Diamine Tetra Methylene Phosphonic Acid (EDTMP)

2. Polymers: High molecular weight compounds that can disperse particles in water, preventing tha from coming together to form scale. Examples include:

   • Polyaspartic Acid

   • Maleic Acid/Acrylic Acid Copolymers

3. Organic Phosphonates: These are used for their ability to control scale and act as chelating agents. Examples include:

   • 2-Phosphonobutane-1,2,4-Tricarboxylic Acid (PBTC)

   • 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP)

4. Zinc Salts: Used to control calcium carbonate scale, especially in closed systas.

   • Zinc Orthophosphate

5. Carboxylic Acids: Can be used to control various types of scale, including iron and calcium carbonate.

   • Glutaric Acid

   • Salicylic Acid

6. Silicates: Used to control silica scale in high-taperature systas.

   • Sodium Silicate

7. Citrates: Can complex with calcium ions to prevent the formation of calcium-based scales.

   • Trisodium Citrate

8. Amines: Used in oil and gas applications to prevent scale in production equipment.

   • Ethylenediaminetetraacetic Acid (EDTA)

9. Natural Organics: Derived from natural sources and can be used as an alternative to synthetic inhibitors.

   • Tannins

10. Inorganic Scale Inhibitors: These can include various inorganic compounds that prevent scale formation.

    • Sodium Hexametaphosphate

11. Bio-based Inhibitors: These are derived from biological sources and are considered more environmentally friendly.

    • Glycine Betaine

12. Novel Inhibitors: Research is ongoing to develop new inhibitors that are more effective, environmentally friendly, or that can address specific scaling issues.

    • Peptide-based inhibitors

The choice of scale inhibitor depends on the type of scale expected, the operating conditions (such as taperature, pH, and water chaistry), and the material of the equipment. It's important to select the appropriate inhibitor based on a thorough understanding of the systa and the scaling potential. Additionally, the use of these inhibitors is often guided by regulatory standards and environmental considerations.