Conception of New Thermal Insulation Coatings – CITOYEN

Syntheiss of nano-material with crystalline structure.
Soft chemistry routes as sol-gel or coprecipitation processes are developped.
Structural characterization is mainly performed by X-ray diffraction and TEM microscopy.
Chemical characterization by ICP and EDX spectroscopies.
Optical properties are characterized via UV-visible-IR spectroscopies in transmission mode through films or suspensions and with diffuse reflexion mode on powder beds.

-Optimization of infrared absobance of Ga3+, In3+ doped zinc oxides. Results were fully interpreted and were submitted for publication.

-Synthesis and characterization of core@shells as new ZnO@MgF2 with improved visible transparency for thin films shaping. Obtaining of other core@shells composition as ZnO@SiO2 and ZnO@ZnF2.

-Obtaining of suspensions ethanol - doped-ZnO monocrystalline nanoparticles (with 35-40 nm diameter) with visible transparent near the final requirements.

-Synthesis and characterization of n doped ZnF2
-Coating on glass substrate of films or varnishes within our nano-powder with best optical properties. Insulating tests on such coated glasses.
-Publications or patents on whole progresses and innovative results. Research of industrial partners for future collaboration.

3 submitted publications in peer-reviewed international journals.
1. “Encapsulation of ZnO particles by metal fluorides: towards an application as transparent insulating coatings for windows”; Isabelle Trenque et al. submitted at Optical Materials (Elsevier Ed.)
2. “Discussion on the structural anisotropy of würtzite-type compounds.” Isabelle Trenque et al. submitted at Solid State Science (Elsevier Ed.)
3. “Establishment of the correlation law between electron density, infrared absorption and doping concentration in A3+-doped ZnO”; Isabelle Trenque et al. submitted at Material Research Bulletin (Elsevier Ed.)
1 oral conference : workshop : NanoTCMs, Grenoble (14 et 15 Juin 2011) ; 2 posters

The windows are permeable skin to the light for buildings. Unfortunately, the visible permeability is accompanied by a “double heat strainer effect”. Actually, the glazed surfaces well constitute the weak point besides thermal insulation of the buildings. Indeed, the glazed surfaces are responsible at the same time of “greenhouse” effect (in the summer time) and a large loss of heat (in winter).
The CITOYEN project aims at understanding and developing a new generation of windows coating for thermal insulation. It deals with the aim assigned to the buildings conception for saving energy by the “Grenelle de l’environnement”.
The solution proposed by CITOYEN is based on the use of large gap semi-conductors (as transparent conductive oxides: TCOs or transparent conductive fluorides). Currently, the TCOs as example are not applied on large window areas because of the high cost of deposition as transparent films. Thin monocrystalline film is the indispensable shaping which preserves transparency. On the contrary to metallic films which are more largely used, large gap semi-conductors could selectively absorbed the Infra-red part of the spectrum, i.e. without absorption of an important amount of the visible light. The solution proposed here is to develop a technology based on large gap semi-conductors as nanoparticles dispersed in a enamel, a paint or a polymeric film (as a polyester sheet). The transparency of the proposed systems can only be achieved by matching very finely the refractive indexes of the nanoparticles and the dispersing matrix. This target can be achieved only from two competitive breakthroughs:
(i) succeeding in the preparation of new large-gap semiconductors with very low refractive index as fluorides –but currently, no such fluorides with the satisfying electrical conductivity for Infra-red absorption are known; Furthermore, they are already specialized on optical properties characterization and a PhD doctorate on doped ZnO and ZnF2 particles for magneto-optical properties has just been achieved,
(ii) succeeding in the synthesis of complex structures as particles coated with multiple shells or refractive index grade shells in order to get -as an antireflection films here transferred on each individual dispersed particles- a significant enhancement of the transparency in comparison to simple dispersions of the transparent oxides currently used (doped ZnO, In2O3…).
For succeeding in such tasks, the members of the CITOYEN project have already a large experimental experience on the synthesis and characterization of doped fluorides, doped ZnO, core@shell architectures, dispersion in polymeric matrix.
Briefly, the CITOYEN project focuses on opening new technological solutions for the thermal insulation improvement of building windows, with a breakthrough besides the current technologies. This breakthrough expected is ambitious and self-consistent. Hence, the project is original in the way that it has no vocation to multiply simultaneously several solutions for several problems. However, the project just proposes seriously the amelioration of the glazed surface thermal insulation.