Hi, I am also learning English grammar. From what I have understood, I would say that the word interested used in your example is an adjective. Adjectives are used with nouns to: i) describe or point out the person, animal or things which the noun names.
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AnonymousI am interested in that article.The fact that the preposition 'in' rather than 'by' is used would suggest that we are dealing with BE plus adjective rather than a passive form. However, as the adjective is identical in form to the past participle, it doesn't really make any difference.