Title of Invention	A PROCESS FOR PREPARATION OF HIGH TEMPERATURE COATING MATERIALS FROM FLY ASH
Abstract	The present invention relates to a process for preparation of high temperature coating materials from fly ash. This invention will be useful for high temperature coating on mild steel and stainless steels components such as tube spacers and hangers, platen super heater in power generating system and like.

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The present invention relates to a process for preparation of high temperature coating materials from fly ash. This invention will be useful for high temperature coating on mild steel and stainless steels components such as tube spacers and hangers, platen super heater in power generating system and like. Fly ash which is one of the by-product of pulverised coal fired thermal power plants in India, poses environmental problems and needs proper utilization .There are 82 such thermal power plants in India . Although 15-25% of the total fly ash produced in our country is effectively utilized yet huge amount of this industrial waste (around 200 million tons annually) are unutilized. Fly ash is available at a very cheap rate around Rs.30-357. per tonne and an efficient fly ash utilization programme will prevent/minimize environmental pollution to a great extent. The high temperature coating materials involve use of phosphates, borates, silicates, silicates-chromate and oxides. Oxide coating such as aluminide or alumina coating on nickel/cobalt base super alloys work at high temperature & under corrosive environments. However, high temperature coatings on alloys, especially iron-base alloys need attention as they find many applications in chemicals plants, petroleum refineries, thermal power units, coal gasification plants etc. Coatings for this purpose are generally prepared from oxides of aluminium, silicon, chromium, zirconium, titanium, or transitional metal carbides, silicides, borides, nitrides, silicates and borates. The major drawbacks of the above processes are either lengthy or uneconomic or resources are not cheap. Some of the demerits of these coating materials are: (i) although aluminide coatings are suitable under ordinary oxidising conditions on steels, under hot corrosive environment ,i.e., power generating units using low grade fossil fuel, these coating materials do not show satisfactory results because of formation of non-protective NaAlC and alkali tri-ironsulphate (A.U.Malik and Sharif Ahmed, Anti-Corrosion, September, 1984, p4), (ii) silicon based coatings find limited applications due to impairment of the coatings by formation of low melting Fe-Si-O compounds and poor mechanical stability (P.Felin and E.Prdoes, Werkstoff Korros, 23, 627 (1972). Further, these coatings sometimes have excessive swelling effect, poor spreadability and compatibility. Coating based on aluminium phosphate have poor adherance to the substrate. Oxides such as A12O3 and ZrO2 have limited protection efficiency(45-75%) at 500°C-700°C. In other words, efficiency decreases at temperatures more than 600°C. Other oxides such as ZnO, Cobalt oxide and Kaoline do not provide sufficient protection. Moreover the above said coatings for high temperature applications are costly from economic as well as processing point of view. Reference may be made to an U.S. patent No. 012514, wherein a fire retardant coating composition has been made consisting of fly ash up to 50 percent using costly chemicals like vinyl acrylic type emulsion polymer, plasticiser, preservative, fungicide, fiber glass flakes, inorganic pigment, amorphous silica, colloidal silica and surfactant. The application has not mentioned about high temperature oxidation resistance properties of the coating as well as metal surface on which it will be applied. The above process is non-economic and time consuming. The present invention provides an easy and economic process for development of a high temperature coating materials from fly ash which can be suitably used on the mild steel as well as 304 grade stainless steel for protection from high temperature oxidation. The main objective of the present invention is to provide a process for preparation of high temperature coating materials from fly ash which obviates the drawbacks as detailed above. Another objective of the present invention is to utilize the fly ash, an industrial waste, for preparation of high temperature coating material and thereby reducing the industrial pollution. Accordingly, the present invention provides a process for the preparation of high temperature coating materials from fly ash, the said process comprising the steps of: (i) mixing the fly ash powder with water and filtering to remove carbon particles, (ii) mixing the above said filtered material with dilute inorganic acid of strength ranging between 0.5 - 4.ON and stirring the mixture for a period of 30-40 minutes and washing with water, (iii) filtering the above said mixture and adding a mixture of alkali oxide and alkali solution of alkali carbonate or alkali hydroxide to the resultant solution and stirring for a period of 20-30 minutes at a temperature of 80°- 120°C followed by cooling at temperature of 20-30°C, (iv) mixing 0.1-5% rare earth salt solution to above said mixture under stirring for a period of 20-30 minutes, (v) mixing binder material to the above said resultant mixture to obtain the desired coating slurry. In an embodiment of the present invention the fly ash powder used have the following composition: SiO2 60-65 wt% A12O3 25-30 wt% Fe2O3 2-5 wt % TiO2 1-2 wt% CaO 1-4 wt% MgO 0.2-1.0wt% Na2O trace Na2O2 0.1-0.5wt% K2O trace K2O2 0.5-2.0 wt% P2O5 0.1-0.5wt% Sulphates : 0.1-0.5 wt% Loss on Ignition: 1-3 wt% In an another embodiment the inorganic acid used is selected from the group consisting ofH2S04,HCland HNO3. In yet another embodiment the alkali oxide used is selected from the group consisting of sodium oxide, calcium oxide and potassium oxide. In yet another embodiment the alkali solution used is alkali carbonate or alkali hydroxide selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate. In yet another embodiment the rare earth salt solution is selected from rare earth chloride and rare earth nitrate salt. In yet another embodiment the rare earth element used is selected from Ce, La and Zr. In still another embodiment the binder material used is selected from the group consisting of aluminium phosphate, sodium silicate, sodium hexametaphosphate and sodium phosphate. The novelty of the present invention is use of fly ash which is an industrial waste for high temperature coating material for protection of steel from high temperature and the process is novel, easy and economic for preparation of high temperature coating materials having protection efficiency of about 80-95%. The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention. EXAMPLE-1 About 500 gm. of fly ash collected from the thermal power boiler station was mixed with 100 ml of distilled water and stirred and filtered. The mass was treated with 20ml of dilute hydrochloric acid of 2N concentration for 30 minutes and again washed with distilled water and filtered 30 gm. of CaO was added to the filtered mass and then digested with l.ON calcium hydroxide solutions for 30-60 minutes and allowed to cool to room temperature. Then 5 ml of 2% solution of rare earth chloride was added to the above slurry and stirred again. 20 gm. of sodium silicate was added to this slurry . Mechanically polished mild steel plate specimens (10x5x0.3 cm.) were cleaned, degreased with acetone and dried. Slurry made as above was coated on the surface of these plates by hand brush and allowed to dry in air. The coated plates were warmed for 20 minutes and put in a muffle furnace at 600°C for 6hrs.and then allowed to cool in air at room temperature. Surface deterioration, loss in weight and efficiency of protection has been observed and determined respectively. It has been found that protection efficiency of coating obtained from fly ash is 85% where as case of uncoated specimen, scale formation was 40%. EXAMPLE-2 750 gm of fly ash collected as above was treated with water, stirred and filtered. The filtered mass was added to 50 ml of dilute hydrochloric acid of strength 3N and 100 ml of distilled water was then added to it and stirred for 10 minutes and filtered. 50 gm of calcium oxide was then added to the filtered mass and mixed properly. 10ml of 2.5% cerium nitrate salt solution was added to this mix and digested with 50 ml of calcium hydroxide solution of strength 2N for 45minutes and 150ml of distilled water was then added and again stirred for 30 minutes. 45 gm of binding material then added and slurry was obtained. Mild steel plates (10cmx5cmx0.3cm) were polished up to 600 grit finish, degreased with acetone, cleaned and dried. Slurry prepared as above was then applied over these plates by hand brush and dried. These coated and uncoated mild steel plates were initially warmed 25 minutes before heating in a muffle furnace at 800°C for 4-6 hrs and then air cooled. Scale formation, surface deterioration of coated as well as uncoated plates were noted. Loss in weight was determined. Protection efficiency was found to be 75-80% for fly ash coated plates where as scale formation in case of uncoated plates was 50-70% respectively. EXAMPLE-3 600 gm of fly ash was used for slurry preparation and treated with water, stirred and filtered. Then 30ml of hydrochloric acid of strength 2.5N was added to the mass and stirred for 30 minutes and filtered. 30 gm of calcium oxide was added to the mass and then digested for 20 minutes and then cooled. 40ml of calcium hydroxide solution was then added and again stirred. 6ml of 4% cerium chloride salt was added and stirred again. 20 gm of sodium silicate was added to this slurry. Stainless steel like 304 grade plates (3cmxlcmxx0.3cm) were mechanically polished up to 600 grit finish and degreased with acetone, cleaned and dried. Slurry made from fly ash was applied by hand brush over these plates and dried in air. The coated and uncoated stainless steel plates were then warmed for 10-20 minutes and heated in a muffle furnace at 800°C for 2-4 hrs and air cooled. Surface deterioration and scale formation were noted. Loss in weight and protection efficiency was determined. Protection efficiency of coated material was 80- 95% and scale formation in uncoated materials was 30-50% respectively as shown in(Table Removed) We claim: 1. A process for the preparation of high temperature coating materials from fly ash, the said process comprising the steps of: (vi) mixing the fly ash powder with water and filtering to remove carbon particles, (vii) mixing the above said filtered material with dilute inorganic acid of strength ranging between 0.5 - 4.ON and stirring the mixture for a period of 30-40 minutes and washing with water, (viii) filtering the above said mixture and adding a mixture of alkali oxide and alkali solution of alkali carbonate or alkali hydroxide to the resultant solution and stirring for a period of 20-30 minutes at a temperature of 80°- 120°C followed by cooling at temperature of 20-30°C, (ix) mixing 0.1-5% rare earth salt solution to above said mixture under stirring for a period of 20-30 minutes, (x) mixing binder material to the above said resultant mixture to obtain the desired coating slurry. 2. A process as claimed in claim 1, wherein the fly ash powder used have the % 3. A process as claimed in claims 1&2, wherein the inorganic acid used is selected from the group consisting of H2SO4, HC1 and 4. A process as claimed in claims 1-3, wherein the alkali oxide used is selected from the group consisting of sodium oxide, calcium oxide and potassium oxide. 5. A process as claimed in claims 1-4, wherein the alkali solution used is alkali carbonate or alkali hydroxide selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate. 6. A process as claimed in claims 1-5 wherein the rare earth salt solution is selected from rare earth chloride and rare earth nitrate salt. 7. A process as claimed in claims 1-6, wherein the rare earth element used is selected from Ce, La and Zr. 8. A process as claimed in claims 1-7 wherein the binder material used is selected from the group consisting of aluminium phosphate, sodium silicate, sodium hexametaphosphate and sodium phosphate. 9. A process for the preparation of high temperature coating materials from fly ash substantially as herein described with reference to the examples.

Documents:

1228-del-2002-abstract.pdf

1228-del-2002-claims.pdf

1228-DEL-2002-Correspondence-Others-12-12-2008.pdf

1228-del-2002-correspondence-others.pdf

1228-del-2002-correspondence-po.pdf

1228-del-2002-description (complete).pdf

1228-DEL-2002-Form-1-12-12-2008.pdf

1228-del-2002-form-1.pdf

1228-del-2002-form-18.pdf

1228-del-2002-form-2.pdf

1228-del-2002-form-3.pdf

1228-DEL-2002-Petition-137-(12-12-2008).pdf