Hi,

to fillup all free space of a ntfs partition with zero’s

use sysinternals sdelete

D:> sdelete.exe -z d:  -accepteula
Copyright (C) 1999-2019 Mark Russinovich
Sysinternals - www.sysinternals.com

SDelete is set for 1 pass.
Purging MFT files 0% complete

Michael