  WASP-18b is an utra-hot Jupiter with a temperature difference of upto 2500K
between day and night. Such giant planets begin to emerge as planetary
laboratory for understanding cloud formation and gas chemistry in well-tested
parameter regimes in order to better understand planetary mass loss and for
linking observed element ratios to planet formation and evolution. We aim to
understand where clouds form, their interaction with the gas phase chemistry
through depletion and enrichment, the ionisation of the atmospheric gas and the
possible emergence of an ionosphere on ultra-hot Jupiters. We utilize 1D
profiles from a 3D atmosphere simulations for WASP-18b as input for kinetic
cloud formation and gas-phase chemical equilibrium calculations. We solve our
kinetic cloud formation model for these 1D profiles that sample the atmosphere
of WASP-18b at 16 different locations along the equator and in the
mid-latitudes and derive consistently the gas-phase composition. The dayside of
WASP-18b emerges as completely cloud-free due to the very high atmospheric
temperatures. In contrast, the nightside is covered in geometrically extended
and chemically heterogeneous clouds with disperse particle size distributions.
The atmospheric C/O increases to $>0.7$ and the enrichment of the atmospheric
gas with cloud particles is $\rho_{\rm d}/\rho_{\rm gas}>10^{-3}$. The clouds
that form at the limbs appear located farther inside the atmosphere and they
are the least extended. Not all day-night terminator regions form clouds. The
gas-phase is dominated by H$_2$, CO, SiO, H$_2$O, H$_2$S, CH$_4$, SiS. In
addition, the dayside has a substantial degree of ionisation due to ions like
Na$^+$, K$^+$, Ca$^+$, Fe$^+$. Al$^+$ and Ti$^+$ are the most abundant of their
element classes. We find that WASP-18b, as one example for ultra-hot Jupiters,
develops an ionosphere on the dayside.
