6945
Since , for a given alloy , powder cost is proportional to its purity , choosing a less expensive powder or reusing powders is interesting for economical and environmental reasons .
 alloy, powder, powder, powders
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 alloy, powder, powder, powders