received by the International Bureau on 10 January 2017 (10.01.2017)

An improved process for producing silica aerogel thermal insulation product capable of suppressing radiative heat transport having metal oxide nanoparticles formed in situ in silica aerogel comprising the step of:

(i) preparing an aqueous solution of alcohol selected from methanol, ethanol, isopropanol preferably ethanol, in which an aqueous solution of ammonium fluoride and ammonia solution is added as alkaline catalysts;

(ii) addition of metal oxide precursor of metals selected from iron, manganese, magnesium, zirconium, zinc, chromium, cobalt, titanium, tin, indium or the mixture thereof and dissolve into the solution of step (i) during which metal oxide nanoparticles are precipitated in the solution

(iii) mixing silica precursor comprising alkoxides of silica selected from tetramethylorthosilicate (TEOS), tetraethyl orthosilicate, hexamethyldisiloxisilane, methyl trimethoxisilane (MTMS), sodium silicate, more preferably TEOS and MTMS, individually or in combination, in the dispersion formed in the step (ii);

(iv) stirring the resulting mixture continuously till the total mixture starts becoming viscous;

(v) soaking an individual inorganic fibre mat or a sandwich sheet of desired size, shape and thickness prepared by stitching together two or more layers of inorganic fibre mat with organic sponge sheet placed between the layers in the liquid formed in step (iv). (vi) ageing the resultant product of step (v) for 1-24 hr at room temperature

(vii) immersing the resultant product (vi) in pure solvent preferably ethanol to replace all the original solvent and water mixture used in step (i) for at least 3 days ;

(viii) replacing the solvent and water mixture used in step (i) every day with the fresh batch of said pure solvent till the complete exchange of liquid present in gel is replaced by the solvent;

(ix) subjecting the resultant product to supercritical temperature by keeping the gel in a pressure vessel filled with said solvent used in step (vii) and maintain a temperature of 260 °C to 350 °C, and pressure of 80 bars to 150 bars for 0.2 to 3 hours;

(x) venting out the vapours of the solvent completely at the rate of about 0.5 bar / min from the pressure vessel by opening the release valve and putting off the heater to cool down the pressure vessel and recovering the silica aerogel products from the pressure vessel.

2. An improved process for producing silica aerogel product as claimed in claiml , wherein total silica aerogel granule content in the sheet can be tailored by changing the thickness of organic sponge sheet and its number of layers.

3. An improved process of producing silica aerogel product as claimed in claim 1 or 2, wherein the titanium dioxide is the most preferred metal oxide from the said group of metal oxides of iron, manganese, magnesium, zirconium, zinc, chromium, cobalt, titanium, tin, and indium of step (ii).

4. An improved process for producing silica aerogel product as claimed in any of the preceding claims, wherein dipping the gel formed in step (viii) in metal oxide precursor solution and more preferably in titanium isopropoxide or its solution in alcohol preferably in ethanol to form additional metal oxide in-situ.

5. An improved process for producing silica aerogel product as claimed in any of the preceding claims, wherein said inorganic fibre mat used is from material selected from woven or non woven sheet of ceramic fibres, refractory fibres, glass fibres, e-glass fibres, any other oxide or mixture of oxide fibres of any desired thickness, size and density.

6. An improved process for producing silica aerogel product as claimed in any of the preceding claims, wherein the organic sponge selected has degradation temperature more than or equal to 250 °C so that the organic part of the sponge is completely degraded during the supercritical drying process to releases the aerogel granules trapped in its pores.

7. An improved process for producing siilca aerogel products as claimed in any of the preceding claims, wherein the organic sponge sheet made up of polymeric material selected from polyethylene, polypropylene, polyolefin, polyurethane, polyvinyl chloride more preferably polyurethane.

8. An improved process for producing silica aerogel product as claimed in any of the preceding claims, wherein the thread used for stitching of fibre mat having two or more layers with organic sponge sheet placed in between is preferably made of the fibers or yarn of silica, silica-alumina, zirconia with or without metal threads/ reinforced metal threads for usage at high temperature.

9. An improved process for producing silica aerogel product as claimed in any of the preceding claims, wherein said metal oxide precursor preferably titanium precursor used in step(ii) is diluted with alcohol, preferably ethanol to form less than or equal to 5% solution.

10. An improved process for producing silica aerogel product as claimed in any of the preceding claims, wherein the molar ratio of silica precursor to metal oxide precursor used is in the range of 1: 0.0014 to 1: 0.7 moles

11. An improved process for producing silica aerogel products as claimed in any of the preceding claims, wherein the concentration ratio of silica precursor : solvent used is in between 1 :4 to 1 :50 moles and the ratio of TEOS and MTMS precursors used is in between 5:1 to 5:5.

12. An improved process for producing silica aerogel product as claimed in any of the preceding claims, wherein said catalyst concentration ratio used with respect to silica precursor is in between 1 :0.05 to 1 : 0.1 moles.

13. An improved process for producing silica aerogel product as claimed in any of the preceding claims, wherein the precursor-water molar ratio used is in the range of 1:0.5 to 1: 4 moles.

14. An improved process for producing silica aerogel product as claimed in any of the preceding claims, wherein metal oxide nanoparticles formed in-situ in silica aerogel demonstrate increase in the infra red radiation reflectivity when subjected to heat even if the metal oxide preferably titanium dioxide concentration in silica aerogel≤ 2%.

15. An improved process for producing silica aerogel product as claimed in any of the preceding claims, wherein the silica aerogel content in the sandwiched sheet is up to 90% since by sandwiching silica aerogel granules are in-filtered in the pockets between two silica aerogel in-filtered flexible sheets of inorganic fibre mat or their multilayer structures with increased ability to infrared opacification.

16. An improved process for producing silica aerogel product as claimed in any of the preceding claims, wherein the silica aerogel is having specific surface above 300 m²/g.

17. An improved process for producing silica aerogel product as claimed in any of the preceding claims, wherein said aerogel composite sheet serve as a flexible, durable, light-weight having enhanced suppression of radiative heat transport at high temperatures and increased thermal insulation property.

18. A silica aerogel thermal insulation product comprising silica aerogel dispersed in the individual inorganic fibre mat or in the sandwiched sheet comprising metal oxide nanoparticles formed in situ capable of suppressing radiative heat transport produced by the process as claimed in 1 to 17