17341
The chromogenic array used eight sensing materials ( based on aluminium oxide and silica gel ) containing pH indicators , Lewis acids and an oxidation - reduction indicator .
 Chemical: aluminium oxide; Chemical: silica gel; Chemical: Lewis acids
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: aluminium oxide; Chemical: silica gel; Chemical: Lewis acids