What rhetorical and persuasive devices does Orwell use to communicate the torture and purification of Winston Smith?

One way that Orwell communicates the torture that Winston goes through is to show, at first, that it all runs together for him. It is all one big painful blur, and one might emphasize that the point of it all was to get into Winston's mind by beating and torturing his body:

How many times he had been beaten, how long the beatings had continued, he could not remember... Their real weapon was the merciless questioning that went on and on, hour after hour, tripping him up, laying traps for him, twisting everything that he said, convicting him at every step of lies and self-contradiction until he began weeping as much from shame as from nervous fatigue.

The most powerful rhetorical device one might use here would be the imagery: Winston trying not to urinate on himself, writhing on the ground, begging for mercy, and so on. These shocking images demonstrate how ruthless and brutal the torture of Winston is. Another image that serves as a central focus for Orwell is his explanation of the future of humanity: "If you want a picture of the future," he tells Winston, "imagine a boot stamping on a human face—for ever." This imagery encapsulates the hopelessness Winston experiences during his torture and reeducation.
In the end, there is much evidence that Winston has been "purified." Almost involuntarily he writes the oxymorons that serve as Party orthodoxy on the slate that they give him: "FREEDOM IS SLAVERY," "TWO AND TWO MAKE FIVE," and "GOD IS POWER." At the end, there is in fact a powerful symbol of Winston's and Julia's torture and purification, one that has not occurred to Winston yet. He hears the line "I sold you and you sold me" from the song "Under the Spreading Chestnut Tree." This is a reminder that he has sold out Julia when he was in Room 101, and that she has done the same. His soul has been destroyed, and all that is left is his love for Big Brother, made explicit in the final line of the book.