  Fe/MgB2 tapes have been prepared starting with pre-reacted binary MgB2
powders. As shown by resistive and inductive measurements, the reduction of
particle size to a few microns by ball milling has little influence on Bc2,
while the superconducting properties of the individual MgB2 grains are
essentially unchanged. Reducing the particle size causes an enhancement of Birr
from 14 to 16 T, while Jc has considerably increased at high fields, its slope
Jc(B) being reduced. At 4.2K, values of 5.3*10^4 and 1.2*10^3 A/cm^2 were
measured at 3.5 and 10 T, respectively, suggesting a dominant role of the
conditions at the grain interfaces. A systematic variation of these conditions
at the interfaces is undertaken in order to determine the limit of transport
properties for Fe/MgB2 tapes. The addition of 5% Mg to MgB2 powder was found to
affect neither Jc nor Bc2. For the tapes with the highest Jc values, very high
exponential n factors were measured: n = 148, 89 and 17 at 3.5, 5 and 10T,
respectively and measurements of critical current versus applied strain have
been performed. The mechanism leading to high transport critical current
densities of filamentary Fe/MgB2 tapes based on MgB2 particles is discussed.
