You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Phosphate bonded investment should be completely carbon free, otherwise: and explain in detail?
Carbon is often added to the powder to produce clean castings and facilitate the divesting of the casting from the investment mold. This addition is appropriate when the casting alloy is gold, but there is disagreement regarding the effects of carbon in phosphate investments used for casting silver-palladium alloys, palladium-silver alloys, or base metal alloys. It is believed that carbon can embrittle the alloys, even though the investment is heated to temperatures that burn out the carbon. Some evidence indicates that palladium reacts with carbon at temperatures above 1504 °C. Thus, if the casting temperature of an alloy with high palladium content exceeds this critical point, a phosphate investment without carbon should be used.
Ref: Phillip’s 12th edition page 208