Context : We present a study of the Silicon-bearing species detected in a line confusion limited survey towards Orion KL performed with the IRAM 30-m telescope .

Aims : The analysis of the line survey is organized by families of molecules .
Our aim is to derive physical and chemical conditions for each family taking into account all observed lines from all isotopologues of each species .
Due to the large number of transitions in different vibrationally excited states covered by our data , which range from 80 to 280 GHz , we can provide reliable source average column densities ( and therefore , isotopologue abundances and vibrational temperatures ) for the detected molecules .
In addition , we provide a wide study of the physical properties of the source based on the different spectral components found in the emission lines .

Methods : We have modeled the lines of the detected molecules using a radiative transfer code , which permit us to choose between Large Velocity Gradient ( LVG ) and Local Thermodinamic Equilibrium ( LTE ) approximations depending on the physical conditions of the gas .
We have used appropriate collisional rates for the LVG calculations .
In order to qualitatively investigate the origin of the SiS and SiO emissions in Orion KL we ran a grid of chemical models .

Results : For the v =1 state of SiO we have detected the J =2-1 line and , for the first time in this source , emission in the J =4-3 transition , both of them showing strong masering effect .
For SiO v =0 , we have detected ^ { 28 } SiO , ^ { 29 } SiO , and ^ { 30 } SiO ; in addition , we have mapped the J = 5-4 SiO line .
For SiS , we have detected the main species , ^ { 29 } SiS , and SiS v =1 .
Unlikely other species detected in Orion KL ( IRc2 ) , the emission peak of SiS appears at a velocity of \simeq 15.5 km s ^ { -1 } ; a study of the 5-4 SiO line around IRc2 shows this feature as an extended component that probably arises from the interaction of the outflow with the ambient cloud .
We derive a SiO/SiS column density ratio of \simeq 13 in the plateau component , four times lower than the cosmic O/S ratio \simeq 48 .
In addition , we provide upper limits to the column density of several non-detected Silicon-bearing species .
The results of our chemical models show that while it is possible to reproduce SiO in the gas phase ( as well as on the grains ) , SiS is a product of surface reactions , most likely involving direct reactions of Sulphur with Silicon .

Conclusions :