  The dynamics of inertial particles in Rayleigh-B\'{e}nard convection, where
both particles and fluid exhibit thermal expansion, is studied using direct
numerical simulations (DNS). We consider the effect of particles with a thermal
expansion coefficient larger than that of the fluid, causing particles to
become lighter than the fluid near the hot bottom plate and heavier than the
fluid near the cold top plate. Because of the opposite directions of the net
Archimedes' force on particles and fluid, particles deposited at the plate now
experience a relative force towards the bulk. The characteristic time for this
motion towards the bulk to happen, quantified as the time particles spend
inside the thermal boundary layers (BLs) at the plates, is shown to depend on
the thermal response time, $\tau_T$, and the thermal expansion coefficient of
particles relative to that of the fluid, $K = \alpha_p / \alpha_f$. In
particular, the residence time is constant for small thermal response times,
$\tau_T \lesssim 1$, and increasing with $\tau_T$ for larger thermal response
times, $\tau_T \gtrsim 1$. Also, the thermal BL residence time is increasing
with decreasing $K$. A one-dimensional (1D) model is developed, where particles
experience thermal inertia and their motion is purely dependent on the buoyancy
force. Although the values do not match one-to-one, this highly simplified 1D
model does predict a regime of a constant thermal BL residence time for smaller
thermal response times and a regime of increasing residence time with $\tau_T$
for larger response times, thus explaining the trends in the DNS data well.
