Yevamot 24: Converting for the Sake of Marriage

On the mitzvah that is on the eldest of brothers to do yibum. Plus, what is the purpose of yibum?! (Finally?) What does it mean to carry on a dead brother's name? Also, when a man is suspected of having slept with a non-Jewish maidservant or a non-Jewish woman, who is then set free or converts to Judaism (respectively)... He can't marry that woman. What's the rationale and how far does it go? Including when ulterior motives negate the conversion, and when they seem not to.