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Impurities such as SiO2 , metal silicates and alkali metal oxides that form glassy grain boundary phases must be minimized to less than 0.1 wt % , since the in vivo degradation of such glassy phases leads to the appearance of stress concentration sites where cracks can be initiated , leading to the catastrophic failure of the component .
 machanical property: Impurities; material: as; material: metal silicates; material: alkali metal oxides; concept or principle: grain boundary; material: be; concept or principle: degradation; process characterization: stress concentration; material: be; concept or principle: failure; machine or equipment: component
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: 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:
 machanical property: Impurities; material: as; material: metal silicates; material: alkali metal oxides; concept or principle: grain boundary; material: be; concept or principle: degradation; process characterization: stress concentration; material: be; concept or principle: failure; machine or equipment: component