DESC:FIELD OF THE DISCLOSURE:
The present disclosure relates to a composite material and a method for its preparation.
BACKGROUND:
Sintered mullite is a very well-known refractory product used for high temperature refractory applications in the form of bricks or castables. Mullite, a rare clay mineral with the chemical composition 3Al2O3.2SiO2 is produced artificially by using different sources of alumina and silica during various melting and firing processes and is used as a refractory material due to its high melting point of 1840 oC. The sources of alumina and silica used for the purpose of manufacturing sintered mullites generally include different types of clays. Sintered corundum grains constitute another important category of refractory products. In terms of properties, corundum possesses a high elastic constant as compared to mullite and therefore has superior properties. However, the disadvantage of obtaining a pure corundum microstructure is that the source raw material has to be highly pure, for example, bauxite which is very expensive. Further, sintering of such pure material requires a considerably high sintering temperature. A disadvantage of the sintered mullite granules is its reduced mechanical properties as compared to pure corundum grains.

Therefore, there is felt need of a composite material that has improved properties as compared to individual sintered mullite granules and sintered corundum grains, and wherein the disadvantages of sintered corundum grains and sintered mullite granules such as cost and high sintering temperature are overcome.

OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a composite material which exhibit improved/enhanced properties such as tensile strength, compression resistance and density.
Another object of the present disclosure is to provide a method for preparing composite material with reduced cost and which can be manufactured at lower sintering temperature and hence is cost effective and energy efficient.
Other objects and advantages of the present disclosure will be more apparent from the following description which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure provides a composite of sintered mullite reinforced corundum granules and process for its preparation. The composite of sintered mullite reinforced corundum granules comprises 30 wt% to 90 wt% of mullite and 10 wt% to 70 wt% of corundum. The composite has an interlocking microstructure. The method for preparing the composite involves the step of admixing fine powders of at least one clay and at least one alumina ore having particle size less than 45 microns to obtain an admixture, granulating the admixture in the presence of at least one binder and at least one additive to obtain a granulated pellets and sintering the granulated pellets in the temperature range of 1300 oC to 1600 oC to obtain a composite comprising sintered mullite reinforced corundum granules. The particle size of the so obtained sintered mullite reinforced corundum granules ranges from 0.25 mm to 1.5 mm.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The process of the present disclosure will now be described with the help of the accompanying drawings, in which:
Figure 1 illustrates an SEM image of rod shaped mullite entangling with corundum grains;
Figure 2 illustrates an SEM image of corundum granules; and
Figure 3 illustrates an SEM image of mullite rods and corundum having interlocking microstructure.

DETAILED DESCRIPTION:
The present disclosure envisages a composite material and a method for its preparation. The composite material in accordance with the present disclosure is a sintered mullite reinforced corundum granule which demonstrates improved properties such as higher density and compression resistance as compared to the individual counterparts, sintered mullite granules and sintered corundum grains.
The composite of sintered mullite reinforced corundum granules comprises 30 wt% to 90 wt% of mullite and 10 wt% to 70 wt% of corundum. The mullite and the corundum in the composite have interlocking microstructure. In the composite of the present disclosure, the mullite is obtained from Kaolin and the corundum is obtained from alumina ore.
In accordance with the present disclosure, the process for the preparation of the composite material is described below.
To carry out the process, the raw materials are obtained and ground in a pulverizer and a classified mill to obtain ground raw material. The raw material is selected from clay and alumina ore. The method comprises the steps of preparing an admixture of pre-determined weight proportions of the clay and the alumina ore. The clay and the alumina ore are ground in a grinder separately to obtain fine powders of clay and alumina ore.
In accordance with one of the embodiments of the present disclosure, the particle size of the fine powder obtained after the step of grinding is less than 45 microns.
The obtained fine powder of clay and fine powder of alumina ore are mixed to form an admixture. The mixing is carried out in Eirich RV-02 granulator to obtain desired admixture.
The amount of clay used in the admixture ranges from 20 wt% to 80 wt%. The clay is selected from the group consisting of Kaolin, Dickite, Halloysite and the like. In one embodiment the clay is Kaolin.
The amount of alumina ore used in the process for preparing the admixture ranges from 10 wt% to 75 wt%. In an exemplary embodiment, the alumina ore is selected from bauxite and aluminum trihydroxide.
After the formation of an admixture, the process of granulation is carried out. The granulation is carried out in the presence of at least one binder and at least one additive to obtain granulated pellets.
The binder employed in the process of the present disclosure may be selected from the group of organic binders and inorganic binders. The non-limiting examples of binders suitable for the process of the present disclosure include bentonite and the like.
The additive employed in the process of the present disclosure typically includes, but is not limited to, a fluxing agent, a sintering aid and the like. The non-limiting examples of fluxing agent suitable for the process of the present disclosure include ceramic fluxing agents such as iron-ore slime or other source which supplies fluxing oxides. The non-limiting examples of sintering aid suitable for the process of the present disclosure include mineral Attapulgite, Olivine or any other source of MgO.
The binder and the additive are typically added in amounts ranging from 1 wt% to 5 wt% and 1 wt% to 10 wt%, respectively.
The granulated admixture undergoes sintering in the temperature range of 1300 oC to 1600 oC to obtain a composite material comprising sintered mullite reinforced corundum granules having the particle size ranging from 0.25 mm to 1.5 mm.
In accordance with one of the embodiments of the present disclosure, the clay and alumina ore are added in a pre-determined weight proportion so as to obtain the sintered mullite reinforced corundum granules having alumina content varying from 50 wt% to 85 wt%. The obtained admixture is then subjected to sintering at a pre-determined temperature to obtain a composite material comprising sintered mullite reinforced corundum granules. In accordance with one of the embodiments of the present disclosure, sintering is typically carried out in the temperature range of 1300 oC to 1600 oC.
The composite material comprising the sintered mullite reinforced corundum granules obtained in accordance with the process of the present disclosure is characterized by various improved physicochemical properties including bulk density, specific gravity, crush resistance, acid solubility, roundness, and the like.
Sintered mullite has elongated rod shaped grains (Figure 1) and therefore, advantageously utilized by the inventors of the present disclosure to reinforce or contribute to enhance the tensile strength of the composite material wherein long mullite crystals entangle with the hexagonal corundum grains (Figure 2) which increases the compressive strength of the composite. Further, the raw material used in the process of the present disclosure is commonly available in the form of minerals and combinations thereof and is cost effective. Also the use of such combination of raw materials requires a considerably lower sintering temperature as compared to the sintering temperature required for the sintering of pure corundum granules. The sintered mullite reinforced corundum granules obtained from the method of the present disclosure have an interlocking microstructure (Figure 3). The mullite rods entangle with the hexagonal shaped corundum granules which helps in delaying fracture by arresting crack propagation during rigorous mechanical loading.
The composite material obtained in accordance with the process of the present disclosure finds extensive applications including, but not limited to, their uses in proppants, foundry, filter bed for molten metals and the like.
The present disclosure is further illustrated herein below with the help of the following experiments. The experiments used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of embodiments herein. The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. These laboratory scale experiments can be scaled up to industrial/commercial scale.
Experimental details
Experiment 1:
The raw ingredients were crushed and ground to the desired particle size. The ground material was then fed into a Eirich RV-02 granulator and thoroughly mixed for duration of 2 minutes. Post mixing was done by adding 1% PVA (Polyvinyl alcohol as a binder) in the granulator to initiate and aid in granulation and binding of the individual particles. This binder forms an interface between the particles and aids in better compacted pellets. With time, an entire coalescence of particle takes place, resulting in fine spherical granules. The granules were then sintered at 1600 oC to obtain the composite of sintered mullite reinforced corundum granules. The results are tabulated in Table 1.
• Raw Materials & their ratio: Kaolin clay: Bauxite (85:15)
• Particle size: d90 - 35 microns
• Process: Granulation using Eirich RV-02 mixer and 1% PVA binder
• Sintering temperature: 1600 °C

Table 1: Sintered pellet composition:
S.no % Al2O3 % Mullite % Corundum Fired Density % Breakage % Wt loss*
1 61 70 10 1.5 <10 6
*Weight loss refers to the differenece in weight of the pellets before and after acid treatment.

Experiment 2:
The composite of sintered mullite reinforced corundum granules is prepared by the method as described in experiment 1 by altering the raw material and the amount of ratio of raw material.
• Raw Materials and their ratio: Kaolin Clay + ATH (70:30)
• Particle size: d90 - 33 microns
• Process: Granulation using Eirich RV-02 mixer and 1 % PVA binder
• Sintering temperature: 1600 °C.
Table 2: Sintered pellet composition:
S.no % Al2O3 % Mullite % Corundum Fired Density % Breakage % Wt loss
1 67 76 17 1.4 <10 5.3

Experiment 3:
The composite of sintered mullite reinforced corundum granules is prepared by the method as described in experiment 1 by altering the raw material and the amount of ratio of raw material. The experiment is carried out in the presence of an additive (Feldspar).
• Raw Materials and their ratio: Kaolin Clay + ATH + Feldspar (60:30:10)
• Particle size: d90 - 37 microns
• Process: Granulation using Eirich RV-02 mixer and 1 % PVA binder
• Sintering temperature: 1350 – 1450 °C
Table 3: Sintered pellet composition:
S.no % Al2O3 % Mullite % Corundum Fired Density % Breakage % Wt loss
1 59 70 13 1.35 <10 7

Experiment 4:
The composite of sintered mullite reinforced corundum granules is prepared by the method as described in experiment 1 by altering the raw material and the amount of ratio of raw material. The experiment is carried out in the presence of a binder (Bentonite) and additive (Iron ore slime).
• Raw Materials and their ratio: Kaolin Clay + ATH + Bentonite + Iron ore slime (21:72:1.4:5.6)
• Particle size:d90 < 45 microns
• Process: Granulation using Eirich RV-02 mixer and 1% PVA binder
• Sintering temperature: 1350 °C
Table 4: Sintered pellet composition:
S.no % Al2O3 % Mullite % Corundum Fired Density % Breakage % Wt loss
1 82 33 67 1.5 <10 6.5

In the above experiments, processing conditions in terms of, granulation, sintering temperature have been closely controlled to achieve the desired properties. The quality of the pellets are predominantly governed by the granulation process.

TECHNICAL ADVANCEMENTS:
The process of the present disclosure described herein above has several technical advantages including but not limited to the realization of:
1. A composite material comprising sintered mullite reinforced corundum granules with improved properties including, but not limited to, density and compression resistance.
2. A simple and cost-efficient process for manufacturing a composite material comprising sintered mullite reinforced corundum granules.
3. A very simple and effective way of enhancing the resistance to crack propagation of the granules under load by way of reinforcing mullite grains in a matrix of corundum of very high elastic constant.
The exemplary embodiments herein quantify the benefits arising out of this disclosure and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein has been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Any discussion of documents, acts, materials, devices, articles and the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other modifications in the nature of the disclosure or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation. ,CLAIMS:1. A composite of sintered mullite reinforced corundum granules comprising 30 to 90 wt% of mullite and 10 to 70 wt% of corundum, wherein the mullite is obtained from clay and corundum is obtained from alumina ore;
wherein the mullite and the corundum in the composite have interlocking microstructure; and the composite is characterized by particle size ranging from 0.25 mm to 1.5 mm.
2. The composite as claimed in claim 1, wherein the clay is Kaolin.
3. The composite as claimed in claim 1, wherein the alumina ore is selected from the group consisting of bauxite and aluminum trihydroxide.
4. A method for preparing a composite of sintered mullite reinforced corundum granules comprising the following steps:
a) grinding a raw material comprising at least one clay and at least one alumina ore, separately to obtain ground raw material having a particle size less than 45 microns;
b) admixing the ground raw material to obtain an admixture;
c) granulating the admixture in the presence of at least one binder and at least one additive to obtain granulated pellet; and
d) sintering the granulated pellet in the temperature range of 1300 oC to 1600 oC to obtain the composite comprising sintered mullite reinforced corundum granules.
5. The method as claimed in claim 4, wherein the binder is selected from the group consisting of bentonite and polyvinyl alcohol.
6. The method as claimed in claim 4, wherein the additive is a fluxing agent selected from potash feldspar and iron ore slime.