What additives are there in gypsum?

Gypsum is a widely used material in the construction and industrial fields. Its main component is calcium sulfate (CaSO₄). In order to improve the performance of gypsum or give it specific functions, various additives are often added. The following is a detailed discussion of common additives in gypsum and their functions.

1. **Cement Clinker**

Cement clinker is one of the most common additives in gypsum. Its main function is to adjust the hardening time of gypsum. By reacting with gypsum, cement clinker can effectively control the setting time of cement and prevent gypsum from hardening too fast or too slow during construction. This additive is particularly important in gypsum-based composite materials to ensure that the final product has good operability and stability during construction.

### 2. **Dispersants**

Dispersants such as polymers and surfactants are used to improve the fluidity and uniformity of gypsum slurry. This type of additive improves the dispersibility of gypsum slurry by reducing the interaction between particles, making it more uniform during mixing and application. Common dispersants include polycarboxylates and polyvinyl alcohol.

### 3. **Water Retention Agents**

The function of water retention agents is to reduce the loss of water in the gypsum during the hardening process, thereby avoiding surface cracking and reducing shrinkage. Commonly used water retention agents include hydroxypropyl methylcellulose (HPMC), hydroxyethyl cellulose (HEC), etc. These additives can significantly improve the construction performance and final strength of gypsum.

### 4. **Water Reducers**

Water reducers can improve the strength and density of gypsum by reducing the moisture content in the gypsum mixture. Water reducers are usually high-efficiency polymers that can reduce the amount of water without changing the workability of gypsum, thereby optimizing the performance of the material.

### 5. **Expanding Agents**

Expanding agents are mainly used to control the expansion of gypsum. Common expansion agents include aluminum powder and calcium aluminate. These additives can produce gas during the hardening process of gypsum, thereby causing the volume of gypsum to expand. The use of expansion agents can effectively reduce the shrinkage rate of gypsum and improve its crack resistance.

### 6. **Accelerators**

Accelerators are used to accelerate the setting and hardening process of gypsum. Commonly used accelerators include calcium chloride, ammonium chloride, etc. This type of additive changes the crystal structure of gypsum, shortens the hardening time, and improves construction efficiency. Especially in low temperature environments, the effect of accelerators is more significant.

### 7. **Retarders**

Retarders are used to extend the setting time of gypsum to ensure sufficient operating time during construction. Retarders usually include lignin sulfonates, sugars, etc. These additives can effectively slow down the initial setting time of gypsum and are suitable for large-scale construction or complex processes.

### 8. **Fillers**

Fillers such as talcum powder and quartz powder are often used to increase the volume of gypsum and reduce costs. At the same time, they also have a certain effect on the mechanical properties and surface smoothness of gypsum. The type and amount of fillers need to be selected according to actual needs to ensure that the performance of the final product meets the requirements.

### 9. **Fire Retardants**

Fire retardants can improve the fire resistance of gypsum. Common fire retardants include phosphates, borates, etc. Such additives can improve the fire resistance of gypsum and increase its stability and safety in high temperature environments.

### 10. **Antimicrobials**

Antimicrobials are used to improve the antimicrobial properties of gypsum and prevent the growth of mold and bacteria. Such additives include silver ions, copper ions, etc., which can effectively inhibit the growth of microorganisms and improve the service life and hygienic properties of gypsum.

### Summary

Additives in gypsum affect its performance and application areas in many ways. Selecting the right additives and optimizing their dosage can significantly improve the working performance, hardening characteristics and quality of the final product of gypsum. Understanding the characteristics and mechanisms of action of various additives is of great significance for the production of high-performance gypsum products.