Claims:WE CLAIM:

1. Nano spinel (magnesium alluminate) coated magnesia grains.

2. Nano spinel coated magnesia grains as claimed in claim 1, wherein the grains are coated with upto 2% alumina.

3. Nano spinel coated magnesia grains as claimed in claims 1 and 2, wherein the size of the coat above magnesia grains surface varies from 100-900 nm.

4. Nano spinel coated magnesia grains as claimed in claims 1 to 3, wherein the chemistry of the coating with 2% alumina solution taken from inca software is as follows:

Element O K 41.85 wt%, 55.05 atomic% Element Mg K 29.42 wt%, 25.47 atomic% Element Al K 17.27 wt%, 13.47 atomic% Element Ca K11.46 wt%, 6.02 atomic% Total 100.00

5. Nano spinel coated magnesia grains as claimed in claims 1 to 4,when fired at elevated temperatures.

6. Nano spinel coated magnesia grains as claimed in claims 1 to 5 show varying textures when alumina content of the coat is increased.

7. Alumina coated magnesia grains as a precursor to nano spinel coated magnesia grains as claimed in claims 1 to 6.

8. A process for manufacturing alumina coated magnesia grains comprising treating magnesia grains with a composition containing Aluminium hydroxide powder
1-4%, Carbon black ( N220 ) 0.1-0.5%, Dispersant 0.05-0.2%, Polyvinyl alcohol

0.05-0.1% and water 95-98%.

9. A process for manufacturing nano spinel (magnesium alluminate) coated magnesia grains comprising treating magnesia grains with a composition containing Aluminium hydroxide powder 1-4%, Carbon black ( N220 ) 0.1-0.5%, Dispersant
0.05-0.2%, Polyvinyl alcohol 0.05-0.1% and water 95-98% and firing the alumina coated magnesia grains to elevated temperatures.

10. A process for manufacturing nano spinel coated magnesia grains as claimed in claim 9 wherein the coated grains are fired at 1550 deg. C.

11. A process of coating magnesia grains with alumina/nano spinel as claimed in claims 8 to 10.

Dated: this 31st day of January, 2017

(N. K. Gupta)
Patent Agent
Of NICHE
For SAIL

To,
The Controller of Patents,
The Patent Office, Kolkata.
, Description:ALUMINA COATED AND NANO SPINEL COATED MAGNESIA GRAINS AND A PROCESS FOR MANUFACTURING THE SAME

FIELD OF THE INVENTION

This invention relates to alumina coated and nano spinel coated magnesia grains. This invention particularly relates to MgAl2O4 coated magnesia grain used in refractory/steel industry. The invention also relates to a process for manufacturing the same.

BACKGROUND OF THE INVENTION

Magnesia is widely used in the steel industry as a refractory brick often impregnated with carbon (tar, pitch, graphite) to give optimum properties for corrosion resistance in environments of basic slags, particularly in BOF furnaces or slag lines of treatment ladles. Magnesia bricks often in combination with spinel or chrome are also used in ferroalloy, non-ferrous, glass and cement industries. Castables and sprayables based on magnesia are widely used for basic refractory linings for steel transfer applications. Since magnesia grains are the major component of the magnesia content refractories, the purity, density, crystal size etc of magnesia grains affect enormously the overall properties of the brick. The quality of magnesia grains has a significant effect on the physical properties like density and porosity, mechanical parameters e.g. elastic modulus, strength and fracture toughness. The idea is to provide a coating of MgAl2O4 to decrease the hydration characteristics of MgO and to reduce the open porosity as well as surface purity. This coating may also helps in improving the mechanical properties of the MgO grains and reaction characteristics with basic slag.

The idea behind this coating is that the coated alumina will react on the surface of the grain and form spinel above the surface. The hydrated alumina first break and react with the surface of the magnesia grain and form nano to micro magnesium aluminate spinel on to the surface of magnesia.

Some non-patent literature on the related subject is found to have been reported. These include:

1. Sol-gel synthesis of magnesium aluminum spinel from a heterometallicalkoxide (Materials Research Bulletin, May 1994, Vol 29(5) 479-488) by Olivier Varnier et al.

In this article MgAl2O4 spinel powder of 5 to 20 nm particle size was prepared by the hydrolysis-condensation reaction of a heterobimetallic aluminum magnesium n- butoxide modified by polyethylene glycol.

2. Influence of nano boehmite on solid state reaction of alumina and magnesia – Journal of Alloys and Compounds 507 (2010) 443-447 by H R Zargar et al

In this article effect of nano boehmite on formation ofalumina-magnesia spinel via solid state reaction is reported. Various amounts of nano boehmite were added to Al2O3-MgO mixtures and the mixtures were heated at different temperatures ranging from 800-1500 deg.C for 2h. The results were explained with emphasis on the importance of low temperature spinel formation in refractory materials.

3. Synthesis of magnesium aluminate spinel nano-powders by co-precipitation method—Journal Materials Research Innovations Vol 19, 2015 p S9-20-S9-23 by H Li, Y Q Liu.

In this article magnesium aluminate spinel nano-powders were synthesized by the wet chemical co-precipitation method. First, the gel-like precursors were obtained by dropping ammonia into the mixed solution magnesium chloride hexahydrate and aluminium chloride hexahydrate with different Mg2+/Al3+ molar ratios and concentrations. After drying, the precursors were calcined at different high temps.

In the prior art there has been no report of making alumina coated and nano spinel coated magnesia grains. Thus, there is a need for the same which can be used in the refractory/steel industry.

The object of the invention is to provide for alumina coated and nano spinel coated magnesia grains.

Another object of the invention is to provide a process for manufacturing the same.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1 represents XRD of Q mag magnesia grain

Figure 2 represents XRD of Aluminium hydroxide

Figure 3 represents pictures of uncoated and alumina coated magnesia grains

Figure 4 represents X ray diffraction of uncoated and alumina coated magnesia grain with 1 and 2% alumina solutions

Figure 5 represents SEM of magnesia grain (a) Uncoated (b) 1% alumina coating (c)

2% alumina coating

Figure 6 represents pictures of Uncoated and coated magnesia grain fired at 1550 deg.C/ 3h

Figure 7 represents XRD of Uncoated and coated magnesia grains fired at 1550 deg.C/ 3h

Figure 8(a) – (b) shows microstructure of 1% and 2% alumina coated magnesia grains fired at 1550 deg.C for 3h

Figure 9 shows EDAX of 2% alumina solution coated magnesia grains

Figure 10 shows grain size of spinel from SEM of 2% alumina coated magnesia grain fired at 1550 degC/3h.

According to the invention there is provided Nano spinel coated magnesia grains. The Magnesia grains are initially coated with alumina and then the alumina coated magnesia grains are fired at elevated temperatures to get the desired nano spinel coated magnesia grains.

Nano spinel coated magnesia grains have the size of the coat above magnesia grains surface vary from 100-900 nm.

Nano spinel coated magnesia grains have the chemistry of the coating with 2%

alumina solution taken from inca software as follows- Element O K 41.85 wt%, 55.05 atomic%
Element Mg K 29.42 wt%, 25.47 atomic% Element Al K 17.27 wt%, 13.47 atomic% Element Ca K 11.46 wt%, 6.02 atomic% Total 100.00
Nano spinel coated magnesia grains when fired at elevated temperatures show different textures and show varying textures when alumina content of the coat is increased.

The invention includes a process for manufacturing alumina coated magnesia grains which comprises treating magnesia grains with a composition containing Aluminium hydroxide powder 1-4%, Carbon black ( N220 ) 0.1-0.5%, Dispersant 0.05-0.2%, Polyvinyl alcohol 0.05-0.1% and water 95-98%.

The invention also includes a process for manufacturing nano spinel coated magnesia grains which comprises treating magnesia grains with a composition containing Aluminium hydroxide powder 1-4%, Carbon black (N220) 0.1-0.5%, Dispersant 0.05-0.2%, Polyvinyl alcohol 0.05-0.1% and water 95-98% and firing the

alumina coated magnesia grains to elevated temperatures viz, 1200deg.C,1400 deg. C preferably at 1550 deg C.

The invention further includes a process of coating magnesia grains with alumina/nano spinel in the manner as described herein.

In this development magnesia grain of 0.5 - 1mm were taken whose chemistry is

(MgO- 94.62%, SiO2 – 1.81%, CaO – 2.69%, Al2O3 – 0.28%, Fe2O3- 0.25% & Cr2O3

– 0.14%) ) which was confirmed by XRD also. The base material of coating of alumina was taken a very fine chemical grade aluminium hydroxide which was also confirmed by XRD which shows only aluminium hydroxide phase as shown in Figure
1 of the accompanying drawings.

The base material of coating of alumina was taken a very fine chemical grade aluminium hydroxide, whose purity is 99.5%, melting point - 300oC and bulk density -
2.42 g/cm3 ,which was confirmed by XRD as shown in Figure 2 of the drawings.

Different solutions were prepared in which fine aluminum hydroxide was dispersed with some nano carbon and light dispersing media. Poly vinyl alcohol in the range of
0.05 to 0.1 % was also added in the solution for better coating of alumina. The Q mag magnesia grains of 0.5 – 1.00mm size were taken for coating with this solution. Alumina content in the solution was varied from 0.5 to 2 %. The composition of the solution shown in Table 1

Table 1

Aluminium hydroxide powder: 1 - 4% Carbon black (N220) 0.1 – 0.5% Dispersant 0.05 - 0.2% Poly vinyl Alchohol 0.05 - 0.1% Water 95 – 98%

The grains were poured into this solution and mix for 5 to 10 minutes with a stirrer. After that grains were taken out from the solution. Now the grains were coated with alumina which was put up in air for drying for 24 hours. The magnesia grains coated with alumina are shown in Figure 3.

The X ray diffraction of uncoated and coated with 1 and 2 % alumina solutions were taken and shown in Figure 4. It was observed that the grains with 2% alumina fully coated with the solution.

The SEM of uncoated and coated grains were taken that are shown in Figure .5(a-c) which also confirm the coating but the texture of the coating with 1% and 2% alumina have different. In 2% alumina coating it was observed a needle like formation above the grains.

The coated grains were fired in a muffle furnace at different temperature at 1200,

1400 and 1550oC for three hours in normal atmosphere. The magnesia grains with and without coating fired at 1550oC for 3 hours are shown in Figure.6. It was observed that the grains with alumina coating have different texture than uncoated grains. Increase in alumina content in coating varies in texture of the grains.

The microstructure of 1% and 2% alumina coated magnesia grains fired at 1550oC for 3 hours were also taken and shown in Figure.8(a-b) which confirms the coating of alumina but the formation of spinel above the magnesia grains was confirmed with coating of 2% alumina solution as shown in Figure 8(b) .

The Chemistry of the coating was also taken from inca software of the coating with

2% alumina solution which is shown in Figure 9.

The size of the coated spinel were also measured on the microstructure of this 2% alumina coated magnesia grains fired at 1550oC/3hrs and shown in Fig.10. It was observed that coated spinel size vary from 100 to 817nm.

The invention has prospects for utilization/commercialisation at Steel plants, Refractory bricks, castables and coating making.

From the above disclosure of the invention it is apparent that several additional embodiments beyond those disclosed herein are possible which can be carried out by a person skilled in the art and the same are included within the broad ambit of the invention claimed herein.