Title of Invention

A NOVEL COMPOSITION COMPRISING OF NANO ZIRCONIA AND NANO SILICA POWDER AND A PROCESS FOR MAKING THE SAME

Abstract A novel composition comprising of nano zirconia and nano silica powder, having an average particle size in the range of at ieast 2 nm to 70 nm was synthesized effectively utilizing the as received zircon flour. The composition thus obtained compri,§.es predominantly of silica rich and zirconia rich regions wherein the said silica region exists in the range of 40- 60 weight percent and the said zirconia region exists in the range of 40- 60 weight percent. The synthesized composition with improved strength can be effectively utilized in medical applications such as that of dental fillers.
Full Text Related Patents Documents: (US 7,012,036; US 6.982,073; US 6,376,590, US o, i94,48i; US 5,338.713; US 5,958,361 ;CN 1482066, CN 1450124) Title of the Invention:
[1] A novel composition comprising of nano zirconia and nano silica powder and a process for making the same.
Area of the Invention:
[2] The invention relates to a process for the synthesis of a mixture of nano zirconia and nano silica powder from zircon (zirconium ortho silicate) flour.
Object of the Invention:
[3] 1. The primary objective of the present invention is to utilize commercially available zircon flour for synthesizing a mixture of nano zirconia and nano silica by sol-gel method.
2. Yet another objective of the present investigation is to use chemicals such as hydrofluoric acid, hydrochloric acid, sodium hydroxide, ammonium hydroxide of commercial purity. Background of The Invention
[4] Zircon is naturally occurring silicate of zirconium. It is tetragonal, with zirconium and silicon linked through oxygen atoms to form edge-sharing alternating SiO4 (tetrahedra) with ZrO8 (triandodecahedra). Zircon is the most important commercial source of zirconium, its compounds and alloys.
[5] Zircon is an important ceramic material due to its high resistance to thermal shock, low thermal expansion coefficient and high chemical stability. Zircon is widely used in ceramic industry, for example, as an opacifier in ceramic glazes and enamels. A new application of zircon has been proposed as potential host for 239 Pu waste resulting from the dismantling of nuclear weapons
[6] Zircon is valuable mineral used in foundry, ceramics and refractories. Zircon is synthesized by heating a mixture of zirconium oxide and silicon oxide at 1500 deg C for
several hours. Zircon can he thermally dissociated in an arc furnace or an electric reactor when heated above 1750 deg C (followed by rapid cooling to prevent recombination) into its respective oxides (silica fumes). The particle size of the oxides will be in the micron level. Zircon silicate is highly stable. Decomposition is accomplished only by aggressive chemical attack, usually at high temperatures.
[7] Several methods have been adopted for industrial processing of zircon for the production of zirconium dioxide and tetrachloride. These methods include sintering of zircon with sodium carbonate or sodium hydroxide or calcium oxide or calcium carbonate and with potassium fluorosilicate, chlorination of zircon mixture with coal in blast furnace and carbidization of zircon in a mixture of coal in electric arc furnace. All these methods are carried out at high temperatures and have many disadvantages in that the extent of decomposition brought about by various agents vary. Some of the disadvantages are requirement of high degree of grinding of the zircon concentrate, difficulty in equipment design, rapid corrosion of furnaces and their coatings, high temperature and large expense of electrical energy.
[8] There are methods known in the prior art to synthesize stabilized nano zirconia or a mixture of nano zirconia and nano alumina or functionalized zirconia or mixture of nano zirconia and nano silica using either pure raw materials or salts of zirconium or commercially available precursors. The methods reported have numerous steps: utilize high temperatures in the process and some processes also have sintering, grinding and sieving steps.
Miranda Salvado and Fernandez Navarro have synthesized glass systems of the compositions xTi02.(100-x)Si02 ( x= 10, and 30 mol%) and yZr02.(100-y)Si02(y= 10,30 and 55 mol%) using tetra-ethyl-ortho-silicate, titanium isopropoxide and zirconium n- propoxide as starting materials by alkoxide route. They observed bloating and phase separation during drying of the respective gels after subjected to thermal treatment at various temperatures. They have quantified the bloating effect by density measurements. From scanning electron microscopic studied reported the presence of phase separation in these samples with increasing Si02 mol percent and that separated phase to be richer in Zr02.( Phase separation in materials of the systems Ti02-Si02 and Zr02.Si02 prepared by the alkoxide route. (I.M.Miranda Salvado and J.M.Fernandez Navarro, J Mater.Sci.Lett (1990) 9, 173-174.)
[10] Pedro Tartaj and Lutgard C.De Jonghe prepared nanospherical amorphous precursor particles with a stoichiometric zircon composition, by hydrolysis of mixtures of tetra-ethyl- ortho-silicate and zirconium n-propoxide within the water droplets of water-in-oil micro emulsions. They characterized the powders in terms of phase compositions, morphology (size and shape) and bulk and surface chemical composition. They have also reported the thermal evolution of the nanophase precursor powders up to zircon crystallization. ("Preparation of nanospherical amorphous zircon powders by a micro-emulsion-mediated processes" Pedro Tartaj and Lutgard C.De Jonghe (2000) J Mater.Chem, 10, 2786-2790.)
[11] In another method, radio-opaque Si02 based fillers were produced, containing upto 45 wt % Zr02 by sol-gel process for incorporating Zr02.Si02 powders as filler material in the light cured resins. Pure (99 wt %) tetra-ethoxy-silane (TEOS) Si (OCiHj^ and pure (75 wt %) zirconium tetra-isoproxide (TPZR) Zr[OCH(CH3)2]4 were utilized as the starting materials and Zr02.Si02 glass ceramics were synthesized with 0. 15. 30 and 45 wt % Zr02. The radio- opacity of the composites made from experimental resin and two commercially available light-cured resins containing the Zr02.Si02 glass ceramics nano particles produced by sol- gel method after filling the composites in the extracted human teeth having routine class 111 and class II cavities and light curing was evaluated. The radio-opacity of the composites was found to be dependent on the Zr02 content in the filler particles ( "'Studies on radio-opaque
cornpositcs containing Zr02.Si02 fillers prepared by soi-gei synthesis M. l aira, H.Toyaook. H.Miyawakasi, and M.Yamaki. (May 1993) Dental Materials 9. 167-171) Brief Description of the Drawings:
[12] Figure 1. Process steps in the preparation of mixture of nano Zr02.Si02 from commercial zircon flour.
[13] Figure 2 shows the scanning electron micrographs of as received zircon flour at 450X. The scanning electron micrographs reveal the shape of the constituents of the flour from which it can be seen that particles are irregular in shape and there is a distribution of particle size from about 1 micron to 20 microns. Particle shape also ranges from simple spherical to irregular with sharp corners.
[14] Figure 3 depicts the Energy Dispersion And X-Ray (EDAX) pattern of as received zircon Flour. The diffraction pattern obtained confirms that the elements present are zirconia silicon and oxygen.
[15] Figure 4 shows the scanning electron micrograph of mixture of nano zirconia and nano silica taken at 25,000X. The scanning electron micrograph reveals that the particles are spherical in shape and are highly agglomerated. The average individual particle size is about 80 to 90 nanometers (0.8 to 0.9 microns)
[16] Figure 5 represents the Energy Dispersion And X-Ray (EDAX) of silica rich region of mixture of nano zirconia and nano silica, wherein the said silica is in the range of 40 to 60 weight percent (40-60 wt%)
[17] Figure 6 represents the Energy Dispersion And X-Ray (EDAX) of zirconia rich region of mixture of nano zirconia and nano silica, wherein the said zirconia is in the range of 40 to 60 weight percent (40-60 wt%).
[18] Figure 7 shows the Transmission Electron Micrographs of Nano Mixture of Zirconia and Nano silica. Transmission Electron Micrographs (TEM) of mixture of nano zirconia and
nano silica reveal that the particlcs are spherical in shape and their size is in the range of 2 to 70 nano meters (nm). The particles shown in figure are agglomerated and got arranged in pentagonal or hexagonal shapes.
Detailed Description:
The as received zircon flour was characterized by scanning electron microscopy for the particle size and corresponding EDAX was carried out for identification of the phases present.(Figurel,2).
[20] The present invention differs from the methods stated in the prior art in that the present invention advantageously utilizes the as received zircon flour in its native form for synthesizing a mixture of nano zirconia and nano silica by sol-gel method. Further the present invention also utilizes employment of cost effective chemicals such as hydrofluoric acid, hydrochloric acid, sodium hydroxide, ammonium hydroxide of commercial purity.
❖ The process has following steps namely
(a) Digestion at low temperatures
(b) Filtration
(c) Alkoxylation
(d) Neutralization
(e) Removal of halide ions and
(f) Drying
[21] Each of the above mentioned steps shall be described in detail herein as exemplary steps for achieving the said composition of nano zirconia and nano silica. The process of achieving the said composition is further explained by providing examples for synthesizing the said composition.
Process steps
(a) [0022] Digestion at low temperatures (70-150 deg C),
The mixture of few grams of as received zircon flour (300 mesh) and few ml of hydrofluoric acid are digested in a TEFLON cup secured in a mild steel vessel (after closing the lids of both TEFLON cup and MS reactor) at a temperature of 70-150° C for 24 hours, 48 hours and 72 hours in different experiments involving various concentrations
(b) [0023] Filtration,
The solution, after cooling is filtered off using Whatman Filter Paper (40 size) using a Plastic (Polypropylene) Buchner Funnel.
(c) [0024] Alkoxylation at low temperatures (70-120 deg C),
The filtered digested solution of zircon flour is mixed with isopropyl alcohol in 1:1 to 1:3 volume ratio. The mixture is heated in TEFLON cup secured in a mild steel vessel (after closing the lids of both TEFLON cup and MS reactor) at a temperature of 70-120° C for 24 and 48 hours in various different experiments.
(d) [0024] Neutralization (with either ammonia or sodium hydroxide solution).
The pH of the solution was brought to the near neutral range by neutralizing it w ith dilute sodium hydroxide solution and by or with dilute ammonia solution. In another experiment Neutralization was carried out in a sonicator.
(e) [0025] Removal of halide ions by washing with distilled water
The precipitate so obtained was washed with distilled water several times to obtain a fluoride ion free solution. The supernatant liquid was discarded after decanting.
(f) [0026] Drying the mixture of nano zirconia and nano silica at low temperatures.
The resulting precipitate was dried at room temperature, dried under fan at room temperature and at low temperature ( Characterization Of The Novel Composition:
[27] The dried Zio2, sio2 composition was characterized by Scanning Electronic Microscope(SEM) and Energy Dispersion and X-Ray Analysis(EDAX), for the particle morphology and size and the corresponding phases present, respectively.(Figures 4,5 and 6) The particle size of the composition was characterized by TEM(Figure 7).
[28] The method for obtaining the nano zirconia and nano silica composition has been explained in detail. Further the employment of the said method to achieve the synthesis of the nano zirconia and nano silica composition is best understood by the following examples: Example 1:
[29] To few grams of as received zircon flour (300 mesh) taken in Teflon cup few ml of (60-wt %) hydrofluoric acid is carefully added. Teflon cup with its lid secured in position is then inserted in the mild steel cup having lid with matching threads (Mild Steel (MS) reactor). The mixture is digested at temperature of 70-150°C by placing the MS reactor (containing Teflon cup) over an electrically heated hot plate. The MS reactor is removed from the hot plate after 24 hours. The solution, after cooling, is filtered off and mixed with isopropyl alcohol in 1:1 to 1:3 volume ratio. The mixture is heated in TEFLON cup secured in a mild steel vessel (after closing the lids of both TEFLON cup and MS reactor) at a temperature of 70-120°C for 24 hours. The solution was cooled. The pH of the solution was adjusted to the near neutral range by neutralizing it with dilute sodium hydroxide or with dilute ammonia solution.
Example 2:
[30] To few grams of as received zircon flour (300 mesh) taken in Teflon cup few ml of (40-wt %) hydrofluoric acid is carefully added. Teflon cup with its lid secured in position is then inserted in the mild steel cup having lid with matching threads (MS reactor). The mixture is digested at tempeiaiure of 70-i50"C by piacing the MS reactor (containing Teflon cup) over an electrically heated hot plate. The MS reactor is removed from the hot plate after 48 hours. The solution, after cooling, is filtered off and mixed with isopropyl alcohol in 1:1 to 1:3 volume ratio. The mixture is heated in TEFLON cup secured in a mild steel vessel (after closing the lids of both TEFLON cup and MS reactor) at a temperature of 70-l20"C for 24 hours. The solution was cooled. The pH of the solution was adjusted to the near neutral range by neutralizing it with dilute sodium hydroxide or with dilute ammonia solution. Example 3:
[31] To few grams of as received zircon flour (300 mesh) taken in Teflon cup few ml of (30-wt %) hydrofluoric acid is carefully added. Teflon cup with its lid secured in position is then inserted in the mild steel cup having lid with matching threads (MS reactor). The mixture is digested at temperature of 70-I50°C by placing the MS reactor (containing Teflon cup) over an electrically heated hot plate. The MS reactor is removed from the hot plate after 72 hours. The solution, after cooling, is filtered off and mixed with isopropyl alcohol in 1:1 to 1:3 volume ratio. The mixture is heated in TEFLON cup secured in a mild steel vessel (after closing the lids of both TEFLON cup and MS reactor) at a temperature of 70-120°C for 24 hours. The solution was cooled. The pH of the solution was adjusted to the near neutral range by neutralizing it with dilute sodium hydroxide or with dilute ammonia solution.
The nano zirconia and nano silica composition obtained by a method described in detail earlier and illustrated effectively by providing examples has improved mechanical properties. The presence of predominantly rich zircon and silica regions in the nano zirconia and nano silica composition enhances properties such as micro hardness and compressive strength of the composite material. The increase in mechanical properties of the composition finds it use as an inorganic filler material in commercially available light cured dental restorative composite resin as an additional phase.
[0033] More particularly an application of the embodiment of the present invention with commercially available light cured dental restorative resin containing a mixture of nano zirconia and nano silica obtained by sol-gel process, as an additional phase, is to fill in extracted human teeth, particularly upper and lower molar teeth, having routine class 111 and class II cavity preparations.





We claim:
1. A novel composition comprising of nano zirconia and nano silica powder
having an average particle size in the range of atleast 2 nm to 70 nm wherein the preferred range of the said powder is between 2 and 50 nm and comprising predominantly of silica rich and zirconia rich regions wherein the said silica region exists in the range of 40- 60 weight percent and the said zirconia region exists in the range of 40- 60 weight percent.
2. A process for making the composition in Claim 1 wherein the said process for production of the above composition from zircon flour comprises of
Digestion Filtration Alkoxylation Neutralization
3. A process of Claim 2 wherein the said zircon flour comprises of zirconium dioxide, silicon dioxide and ferric oxide and wherein the percentage of the said constituents of the chemical composition has 50- 70 weight percent of zirconium dioxide. 30- 45 weight percent of silicon dioxide and 2- 5 weight percent of ferric oxide.
4. A process of Claim 2 wherein the said digestion is made by using atleast 2- 20 gms of zircon flour in 50- 70 ml of hydrofluoric acid in the concentration range of 20- 60 percent with a solid to liquid ratio in the range of 0.5 to 15.
5. A process of Claim 2 wherein the digestion of the said zircon flour is carried out at a temperature of atleast 70 degree Celsius and in the preferred range of 70 degree Celsius to 150 degree Celsius with a preferred period range for heating of 24 hrs to 72 hrs under pressure of 1 to 2 atmospheres.
I I
6. A process of Claim 2 wherein the digested zircon flour/ hydrofluoric acid liquor is mixed with alcohol having the formula R-OH wherein R may be alkyls or isoalkyls in the ratio of 1:1 to 1:3 volume/ volume for a time period range of 12 to 48 hours.
7. A process of Claim 2 wherein the zircon digested liquor mixed with alcohol is removed off excess alcohol by distillation.
8. A process of Claim 2, wherein the produce of Claim 7 is neutralized by metal/ non metal hydroxides in the range 2 to 5 percent to yield sol and gel forms of zirconium hydroxide and silicon hydroxide.
9. A process of Claim 2 wherein the hydroxide ions of Claim 8 is evaporated either by heating in the temperature range of 20 to 40 degree Celsius to yield nano zirconia and nano silica.
10. A nano zirconia and nano silica powder composition as substantially herein described and a process for making the same as illustrated in the examples.

Documents:

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Patent Number 269807
Indian Patent Application Number 1899/CHE/2006
PG Journal Number 46/2015
Publication Date 13-Nov-2015
Grant Date 06-Nov-2015
Date of Filing 13-Oct-2006
Name of Patentee M. VISVESVARYA INSTITUTE OF TECHNOLOGY
Applicant Address SIR M. VISVESVARYA INSTITUTE OF TECHNOLOGY, HUNASAMARANAHALLI, (VIA) YELAHANKA BANGALORE-562157.
Inventors:
# Inventor's Name Inventor's Address
1 A.J.K.PRASAD SENIOR LECTURER, DEPARTMENT OF MECHANICAL ENGINEERING, SIR M. VISVESVARYA INSTITUTE OF TECHNOLOGY, HUNASAMARANAHALLI, (VIA) YELAHANKA BANGALORE-562157, INDIA
2 DR. GOPINATHA GARGESA PROFESSOR AND HEAD, DEPARTMENT OF MECHANICAL ENGINEERING, SIR M. VISVESVARAYA INSTITUTE OF TECHNOLOGY, HUNASAMARANAHALLI, YELAHANKA, (VIA) BANGALORE-562157, INDIA
3 DR. VIRESH K.BASALALLI PRINCIPAL, SIR M.VISVESVARAYA INSTITUTE OF TECHNOLOGY, HUNASAMARANAHALLI, YELAHANKA, (VIA) BANGALORE-562 157,INDIA
4 DR. B.K.MURALIDHARA PROFESSOR, DEPARTMENT OF MECHANICAL ENGINEERING, UNIVERSITY VISVESVARAYA COLLEGE OF ENGINEERING, K.R.CIRCLE, BANGALORE-560 001, INDIA
5 MR. K.R.KANNAN SENIOR SCIENTIFIC OFFICER, SOLID STATE AND STRUCTURAL CHEMISTRY UNIT, INDIAN INSTITUTE OF SCIENCES, BANGALORE- 560 001, INDIA
PCT International Classification Number A61K06/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA