Galaxy clusters are very important giant astrophysical laboratories in
which one can study many interesting physical phenomena on giant scales.
X-ray spectroscopy and analysis of the Sunyaev-Zeldovich effect play a
crucial role to study interesting phenomena such as non-equilibrium
ionization, non-thermal particle populations in galaxy clusters. The
influence of high energy electron populations on measurements of metal
abundances and on the He-like to H-like iron line ratio is considered.
Measurements of the spectral slope of the Sunyaev-Zeldovich effect are
proposed to obtain unbiased information about the specific properties of
various electron distributions. It will be shown that the non-equilibrium
ionization of iron can occur in galaxy clusters if the baryonic
over-density is smaller than 11.0/tau, where tau<<1 is the ratio of the
hydrodynamic structure age to the Hubble time.