Absorber coated with TiOxNy was cut in a hexagonal shape. The edge of the plate was hooked by small metal pin. Then, the plate was maintained at just the center of the mold. The silica sol was poured into the polyethylene mold and the plate was immersed in the sol. Thickness of the mold was 20 mm. After the gelation took place, the gel was removed from the mold and supercritical drying was done.

Analysis

Analysis of the obtained selectively solar-absorbing coatings and silica aerogel was carried out by TG-DTA (SII, TG-DTA), ESCA (Kratos, Axishs), UV-VIS (Jasco, UV-570), Emission and FT-IR (PerkinElmer,

SpectrumOne), XRD (Rigaku, RV-200)

SHAPE * MERGEFORMAT

Results and discussion Selectively solar-absorbing coatings

TGA curve of the precursor is shown in Fig. 3. The rapid weight decreasing occurred below 200 °C by evaporation of solvent such as IPA, DMF, piperidine, and so on. Above 200 °C, the weight decreased gradually.

FT-IR spectra of selectively solar-absorbing coatings which heat-treated at 500, 600, 700 and 800 °C were measured. These spectra are shown in Fig. 4. The O-H bonds at 3300 cm-1 disappeared at 700 °C. When selectively solar-absorbing coatings was heated at 800 °C, new peak appeared

Wavenumber (cm-1)

Fig. 4 FT-IR spectra of selectively solar-absorbing coatings treated at 500 (a), 600 (b), 700 (c) and 800 °C (d).

about 700 cm-1. The peak was a signed to Ti-O-Ti stretching vibration. The result of XRD at 700 °C was shown broad hallo pattern. Then, the selectively solar-absorbing coatings heated up to 700 °C remained as amorphous state. The ESCA result showed N/O ratios of the coatings changed according to the heat treatment temperature. The N/O ratios of coatings heat-treated at 500 °C and 700°C was 0.29 and 0.94, respectively. The result was in good agreement with reduction of the O-H bonds by FT-IR measurement.

UV-VIS spectrum of selectively solar-absorbing coatings heat-treated at 700 °C was measured. The result is shown in Fig. 5. The reflectance remained below 1 % for wide rage of wavelength.

The emission spectra of the selectively solar-absorbing coatings were measured at 100 °C. The emission of the selectively solar-absorbing coatings heat-treated at 700 °C was 3%. Therefore, the selectively

solar-absorbing coatings with reflectance lower than 1% and emission of 3 %.