Final answer:
Sodium citrate and borax are additives used to prevent the setting time of gypsum materials, providing more workability. These ingredients have been chosen for their effectiveness and lower environmental impact compared to some traditional materials.
Step-by-step explanation:
Sodium citrate and borax are used to modify the setting time and characteristics of gypsum materials. Gypsum materials, such as calcium sulfate dihydrate (also known as gypsum) and calcium sulfate hemihydrate (also known as plaster of Paris), are widely used in various applications, including dental molds and construction. By adding sodium citrate and borax to gypsum, it is possible to slow down the setting reaction, allowing for more workable time when using these materials.
The earliest additives to modify gypsum materials were sodium carbonate and sodium silicate. With time, these were replaced by more effective compounds such as phosphates and polycarboxylates. However, due to environmental concerns, there has been a shift towards more environmentally friendly additives like sodium citrate, which belongs to the citrates group. The use of sodium citrate and borax, therefore, improves the usability of gypsum products without causing significant environmental harm.