How can I remove this piece of metal from my garbage disposal?
(newbie, so can't comment)

It is unclear whether you can turn the "tooth" with respect to the rotor--it seems like you can turn the rotor around with the hex nut on the bottom.  Instead of whacking them with a hammer, I'd try holding the rotor with a wrench on the hex bolt and trying to rotate the 'tooth' with respect to the rotor with a wooden bar or something that can fit between the wings of the tooth. Think of holding the hex bolt in a vice while using a crowbar-end as an extra-big screwdriver to rotate the tooth. On my old disposal we used to use an old 4' long broom handle chunk to pry things around in situ.  

Silicone should be OK, but if you are worried, normal cooking oil should do the same job and be compatible with anything in the garbage disposal can normally choke down.