Butterman, William. "Equilibrium phase relations among oxides in the systems GeO₂, GeO₂-B₂O₃, HfO₂-B₂O₃, ZrO₂-SiO₂-B₂O₃, and ZrO₂-SiO₂ /." Doctoral dissertation, Ohio State University, 1965. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486566908027119Chicago Manual of Style (17th edition)