"expounded in" is correct and usable in written English.
It is used to indicate the process of explaining something fully. For example: The research findings were expounded in great detail in the report.
Imagism, Impressionism, and vers libre were expounded in the magazine's pages.
The 10 principles, the backbone of the book, are expounded in the Shackleton saga.
This is our programme, the benefits of which have been expounded in many places recently.
But there is too much remove and it is expounded in too much detail.
It's very much still following the theories that I expounded in my early articles".
The "not fine" is expounded in overwhelming detail; repetitious, perhaps, in light of "Papal Sin".
In the cosmogony as expounded in the Bundahishn, Ormazd (Ahura Mazdā) and Ahriman are separated by the void.
The stories of gods, heroes, Vikings, and ordinary Icelanders were expounded in rímur, or extended chanted tales.
"The crowd was a mixed bag," Scudder expounded in the 1986 thriller "When the Sacred Ginmill Closes".
It was a chapter marked by strong anti-Chinese sentiment and xenophobia, the court expounded in its ruling.
"The Net, though, is different," according to one reasonable-sounding argument that was expounded in Wired magazine in 1996.
