WO2021154174A1

WO2021154174A1 - A method to produce crystal nano boron oxide grains

Info

Publication number: WO2021154174A1
Application number: PCT/TR2020/050653
Authority: WO
Inventors: Salih Ugur BAYCA; Haydar ALTINOK; Mehmet Latif OGUREL
Original assignee: Bayca Salih Ugur
Priority date: 2020-01-31
Filing date: 2020-07-24
Publication date: 2021-08-05

Abstract

This invention relates to a nano boron oxide grain production method. A method enabling nano boron oxide grains to be obtained by non-isothermal heating of the aqueous solution of solid boric acid has been developed with the present invention. Controlling the shape and size of the nano boron oxide grains is also explained.

Description

A METHOD TO PRODUCE CRYSTAL NANO BORON OXIDE GRAINS

Technical Field

This invention relates to a nano boron oxide grain production method. Prior Art

Boron oxide (B2O3) is also known as boron trioxide and anhydride boric acid in literature. Boron oxide is produced in two different structures in micrometer grain size as vitreous and crystal. The molecular weight of the crystalline boron oxide is 69.62 g/mol, its density in the hexagonal crystal structure is 2.4 g/cmB, the density in the monoclinic crystal structure is 2.9 g/cmB, the melting temperature in the hexagonal crystal structure is 450⁰ C, and the melting temperature in the monoclinic crystal structure is 510⁰ C, monoclinic structured boron oxide is more resistant to boron oxide water and diluted HF than boron oxide in a hexagonal crystal structure. Molten boron oxide is corrosive for most metals and alloys at temperatures above 1000 °C. This is due to the flux property of boron oxide. In the literature, there are publications on the use of many different boron sources such as ammonium pentaborate, boric acid, ammonium tetraborate tetrahydrate in the production of B2O3.

Boron oxide is used in many ways in the optical industry. Production of specific glass types, including optical and telescope lenses, medical glasses (ampuls), electronic glasses, and glass-ceramic composites requires pure B2O3. High resistance to water and chemicals, enhanced thermal resistance and mechanical strength, reduced melting temperature are the general benefits of using B2O3 in glass formulations. Boron oxide is used in many different ways in the ceramic industry. It is used in the production of various high strength and heat resistant ceramic products such as boron carbide, boron nitride, titanium and zirconium diborides, and elemental boron. Boron oxide has versatile uses in the refractory industry. It is used for producing chemically bonded firebricks and crates that require high temperature, abrasion, and corrosion resistance. Boron oxide is used as a stabilizer for dolomite refractory bricks and as a binder for magnesia-based refractory bricks commonly used in steel melting furnaces. Boron oxide is also used in many different ways in the metallurgy industry. Boron oxide is a perfect solvent for metal oxides at high temperatures. Boron oxide is used for preparing specific welding and soldering fluxes, in chemically bonded refractories, in hardening of steel and in the production of iron, nickel, or manganese alloys in metallurgy. It is also used for producing amorphous metal and rare earth magnets.

In the industry, pure boron oxide is produced by heating boric acid. Etimaden produces boric acid by heating solid boric acid in a fluid bed furnace. Etimaden produces an average of 312 pm glassy and amorphous boron oxide with 98.00% B2O3 content.

The molecular weight of crystal boron oxide is 61,83 g/mol, B2O3 content is %56.36, density is 1.517 g/cr , the chemical formula is H3BO3, HBO3 or B203-3H20, melting point is 170,9 °C, and crystal structure is triclinic. Crystal boron oxide is found in three structures as orthoboric acid, metaboric acid, tetraboric acid. However, only orthoboric acid has a commercial value.

While the water solubility of boric acid is 5.4 g / 100 mL at 25 ⁰ C, it increases to 27.5 g / 100 mL at 100 ° C.

Table 1. The water solubility of boric acid.

when boric acid dissolves in water B(OH) 4 ¹ ion and H proton is released.

H3BO3 + H2O = B(0H)₄ ¹ + H⁺¹ Boric acid is weak compared to other acids. Boric acid can be found as sasollite mineral in nature. Boric acid in Turkey is produced via leaching colemanite mineral, which is a boron mineral, in sulfuric acid solution.

Boric acid dehydration The chemical formula of boric acid is H₃BO₃ or B₂0₃-3/2H₂0. Solid boric acid involves 1.5 mol chemically bonded water. Boric acid loses its chemically bonded water when heated and transforms into metaboric acid (HB0₂). B₂O₃ crystals form as an end product if the heating continues. A mixture of metaboric acid (HBC>₂-(III)) and boric acid crystals form when boric acid is heated at temperatures above 130 °C. (HBC>₂-(II)) crystals form when the mixture of (HBC>₂-(III)) and boric acid crystals are heated at 150 °C. (HBC>₂-(I)) + B₂O₃ crystals form when

(HBC>₂-(II)) crystals are heated at 170 °C.

Metaboric acid transforms into boron oxide (B2O3) and loses 0.5 mol water when heated at this range (Table 2).

Table 2. Types and properties of metaboric acid

Metaboric acid types Formula Density g/cm³ Melting temperature °C

Orthorhombic metaboric acid HBO2 - III 1,78 176

Monoclinic metaboric acid HBO2 - II 2,04 201

Cubic metaboric acid HBO2 - I 2,49 236

Kocaku§ak et al. (1996) researched micrometer-sized boron oxide production by heating solid boric acid in fluidized bed furnace. They used Etimaden 56,36% B2C>3and 315 pm grain sized solid boric acid as starting material. They produced boron oxide by heating for 210 minutes at 130 °C in the first phase, 270 minutes at 180 °C in the second phase, and 360 minutes at 250 °C in the third phase. They produced 99,6% B2O3 and 405 pm grain-sized boron oxide from solid boric acid withthese three-phased heating. Sevim et al. (2006) examined the thermal degradation of solid boric acid kinetically by TGA (thermogravimetric analysis). Etimaden solid boric acid is heated at a temperature between 20-600 °C in platinum crucible in TGA device. It is identified in the TGA analysis that the solid boric acid lost 43.68% of its weight. This value is compatible with theoretical chemically bound water (43.67%) value in boric acid (B203-3H20). in this study they calculated the activation energy for the first phase as 79,85 kJ/mol and for the second area as 4,79 kJ/mol.Balci et al. (2012) studied boron oxide production by heating boric acid in a muffle furnace. They obtained boron oxide at 99.93% purity by heating the solid boric acid at 130 °C for 30 minutes in the first phase and then at 330 °C for 60 minutes. The article did not indicate the grain size of the boron oxide produced. However, the grain size of the boron oxide produced can be approximately 315 pm as the grain size of the Etimaden solid boric acid used is 315 pm with the medium. Tore and Ay (2004) studied B2O3 production by gradual heating of the boric acid product of Etimaden. They indicated that amorphous boron oxide containing 99.4% B2O3IS obtained as a result of heating boric acid at the speed of 3 °C/minute and at a temperature of 500 °C.

The grain size of the boron oxide obtained by heating boric acid depends on the initial grain size of the boric acid. On the other hand, boric acid solutions are not suitable to produce boron oxide with the preferred grain size due to their high agglomeration tendency. The document numbered CN100551824C explains the use of boric acid dissolved in organic solvents to produce boron oxide at the nanometer level. However, using aqueous solutions of boric acid to produce boron oxide at the nanometer level is not known in the art. Brief Description and the Aim of the Invention

The invention aims to obtain nano boron oxide grains by the dehydration of boric acid.

A method enabling nano boron oxide grains to be obtained by non-isothermal heating of the aqueous solution of solid boric acid has been developed with the present invention. Descriptions of the Figures Explaining the Invention

The figures and the related descriptions to explain the nano boron oxide production method developed with this invention can be found below.

Figure 1 - The graph showing the TGA result of a solid boric acid sample. Figure 2 - The graph showing the derivative of the TGA curve in Figure-1.

Figure 3 - The graph showing the DSC (differential scanning calorimetry) analysis result of a solid boric acid sample.

Figure 4 - The SEM (scanning electron microscope) image of a boron oxide sample obtained according to the invention.

Figure 5 - The SEM (scanning electron microscope) image of a boron oxide sample obtained according to the invention.

Figure 6 - The SEM (scanning electron microscope) image of a boron oxide sample obtained according to the invention. Figure 7 - The SEM (scanning electron microscope) image of a boron oxide sample obtained according to the invention.

Figure 8 - The graph showing the XRD (X-ray diffraction) analysis result of a boron oxide sample obtained according to the invention.

Detailed Description of the Invention The temperature and weight loss of the Etimaden product boric acid is analyzed by TGA device. TA brand model Q500 TGA device, TA brand model Q2000 DSC device and nitrogen gas as the analysis medium, gas flow rate 50 mL/min, and heating rate 2 °C/min were used in this experiment.

B2O3 analysis of solid crystals are performed by the titrimetric method. The phase analysis of the solid crystals are performed by the XRD device, grain size and grain shape are determined by the SEM device.

Figure - 1 presents the TGA analysis of solid boric acid. The weight loss started at approximately 80 °C with the heating of the boric acid. 31.66% weight loss is observed between 80 - 138 °C in the first area. 12.68% weight loss is observed between 138 - 450 °C in the second area. The total weight loss between 80-400 °C has been determined to be

44.34%. Theoretically boric acid consists of 43.69% H2O. The remaining 0.65% H2O is because of the moisture content of the boric acid. Figure - 2 presents the derivative of the TGA curve. A peak is observed at 107,53, 123,42, and 151,56 "C.

The DSC device analyzed endothermic and exothermic reactions of Etimaden product solid boric acid at different temperatures. The first endothermic peak is observed at 122,87 °C in the DSC analysis presented in Figure - 3. The second endothermic peak is observed at 155,74 "C.

The chemically bound water is separated by evaporation as a result of heating the solid boric acid. This dehydration reactions occur in two phases.

First Phase The reaction occurs when the boric acid ( B₂0₃-3H₂0 ) is heated at a temperature range of 130°C.

B₂0₃·3H₂0 + ISI = B₂0₃·H₂0 + 2H₂0

The boric acid loses 2 mol chemically bound water and transforms into metaboric acid (HBO2) when heated at this temperature. This reaction is reversible. Second Phase

The following reaction occurs when the metaboric acid (B₂0₃-H₂0 or HB0₂) is heated at temperatures lower than ISO °C.

B₂0₃-H₂0 + ISI = B₂0₃ + H₂0

The metaboric acid (HBO2) loses 1 mol chemically bound water and transforms into boron oxide (B₂0₃) when heated at the temperatures lower than 130 °C.

Above, the weight change and endothermic and exothermic reactions of Etimaden product solid boric acid as a result of the change in temperature are given.

Crystalline boron oxide grains were synthesized by the crystallization method from the aqueous solution of Etimaden product solid boric acid. The production method subject to the invention involves the steps below, respectively: preparing an aqueous solution of boric acid,

• adding hydrazine (N₂H₄) to the solution,

• drying the solution temperatures below 80 °C,

• dehydration of the obtained precipitate at temperatures of 115 °C and above. The problem of not being able to obtain a nanoscale boron oxide from the aqueous solution due to the high agglomeration tendency of the boron oxide encountered in the prior art is overcome by obtaining boric acid from an aqueous solution which also contains hydrazine prior to dehydration. Agglomeration was prevented during the separation of hydrazine and boron oxide from the aqueous solution, and nanoscale grains were obtained. When hydrazine is added to the aqueous boric acid solution, a boric acid aqueous solution containing a hydrazine concentration between 0.5 and 7 M is obtained. Hydrazine is preferably added in an amount such that concentrations less than 7 M are obtained.

Nano boron oxide at high purity can be produced when the hydrazine evaporates (the evaporation temperature of hydrazine is 114 °C) during the dehydration of the precipitate. The dehydration of the precipitate is performed in phases, each of which is at a higher temperature than the previous one.

In a preferred embodiment of the invention, dehydration process takes place at temperatures between 120 and 170° C, in particular at 130° C for 2 to 48 hours, and at temperatures above 160 °C, in particular at temperatures between 270 and 280 ° C, for 1 to 72 hours.

The shape and sizes of boron oxide grains can be controlled through the method that is subject to the invention. In order to obtain such a result, the pH value and boric acid concentration of the solution is controlled. As the boric acid concentration of the solution is increased or the pH of the solution is decreased, the sizes of the boron oxide grains become bigger, and the grains become spherical. In an embodiment of the invention, at least one acidity regulator is added to the solution to control the pH value.

To assess the efficiency of the invention, experiments are performed using a solid boric acid sample obtained from Etimaden company. A boric acid solution is prepared and heated at different temperatures in two phases in non-isothermal conditions within this scope. To this end, the following steps are done respectively:

• A boric acid solution is obtained by stirring solid boric acid in 200 mL water at 90°C for 30 minutes in a three-necked flask.

Hydrazine was dripped into the boric acid solution with the dropping roller.

• The prepared solution was taken into the beaker.

• The solution in the beaker is heated until it is dried at 70 °C in a drying oven.

• The precipitation consisting of dried boric acid is heated in a muffle furnace at 130 °C with a heating rate of 5 °C/minute for 12 - 48 hours. · The precipitation is heated in a muffle furnace at 270 °C with a heating rate of 5

°C/minute for 12 - 72 hours.

The effect of pH on the shape, grain size and the purity of boron oxide grains

The effect of pH is analyzed in the SEM analysis of the samples obtained from boron oxide synthesis experiments. It is determined that the grain size of the boron oxide samples varies between 1440 - 2130 nm in low pH levels (pH=2). It is determined that boron oxide grains have a spherical morphology. Figure - 4 presents the SEM image at a low pH level.

It is determined that the grain size of boron oxide changes between 210 - 840 nm in high pH value. It has been observed that nano boron oxide grains have a complex morphology. Figure 5 presents the SEM image at a high pH level (pH=10) The effect of boric acid concentration on the shape, size, and purity of boron oxide grains

The effect of boric acid concentration is also analyzed in the SEM analysis of samples obtained from oxide synthesis experiments. It has been determined that the grain size of boron oxide samples change between 166 - 1540 nm in a low boric acid concentration (0,01 M). It has been determined that nano boron oxide grains have a complex morphology. Figure - 6 presents the SEM image in low boric acid concentration. It has been determined that the grain size of boron oxide samples change between 444 - 4840 nm in high boric acid concentration (0,5 M). It has been determined that the grains of nano boron oxide have a partially spherical morphology. Figure - 7 presents SEM image in high boric acid concentration. Figure - 8 presents the XRD analysis of the produced boron oxide samples. The peaks of the phases H3BO3, HBO2, B2O3 in the XRD analysis of the obtained boron oxide sample.

In another experiment to assess the efficiency of the invention, 0.6183 g boric acid is stirred into 200 ml pure water with a magnetic stirrer at 90 °C with 300 rpm. 25 mL hydrazine is dripped into this solution. Nitrogen gas is passed through this solution in 1 bar for 3 hours. The solution put into the beaker at the end of this duration is heated for 24 hours at 130 °C at the heating rate of 1 °C/min in a drying oven, and the dried material is heated for 24 hours at 280 °C at the heating rate of 1 °C/min.

The B2O3 sample obtained as a result of the experiment above is analyzed by the titration method. This analysis reveals that 94% of B2C>3nano boron oxide is synthesized.

References

Beker, Cl. G.; Recepoglu, O.; Bulutcu, N. Identification of the Thermal Decomposition Behaviour of Ammonium Pentaborate. Thermochim. Acta 1994, 235, 211. Beker, LI. G.; Bulutcu, N. A New Process to Produce Granular Boric Oxide by High Temperature Dehydration of Boric Acid in a Fluidized Bed. Chem. Eng. Res. Des. 1996, 74, 133.

Kocakusak, S.; Akcay, K.; Ayok, T.; Koroglu, H. J.; Koral, M.; Savasci, O. T.; Tolun, R. Production of Anhydrous, Crystalline Boron Oxide in Fluidized Bed Reactor. Chem. Eng. Process. 1996, 35, 311.

Kocakusak, S.; Koroglu, H. J.; Tolun, R. Drying of Wet Boric Acid by Microwave Heating. Chem. Eng. Process. 1998, 37, 197. Demir, H.; §ahin, O.; izgi, M. S.; Firatoglu, H. Production of Granular Boron Oxide by Calcinations of Ammonium Tetraborate Tetrahydrate. Thermochim. Acta 2006, 445, 1.

Sevim, F.; Demir, F.; Bilen, M.; Okur, H. Kinetic Analysis of Thermal Decomposition of Boric Acid from Thermogravimetric Data. Korean Journal of Chemical Engineering, 2006, 23, 736. Mergen, A. Properties of Boron Oxide Synthesized from Boric Acid in Fluidized Bed on Pilot Scale. Ind. Ceram. 2004, 24, 23.

Smith, R.A. and McBroom, R.B., Boron Compounds, Kirk othmer Encyclopedia of Chemical Technology vol 4, John Wiley and Sons, New York, 1992.

Tore, I. Ay, N. The Characterization and Production of Amorphous Boron Oxide, Uluslararasi Bor Sempozyumu, 23-25 Eylul 2004 Eski§ehirTurkiye. https://www.borax.com/BoraxCorp

S. Guo, Method for preparing modified nano boron oxide, Patent CN100551824C, 2009

Claims

1. A nano boron oxide production method comprising the following steps to produce boron oxide grains at a nano-level:

• preparing an aqueous boric acid solution, · drying the solution at temperatures below 80 °C,

• dehydrating the precipitation obtained at 115 °C and above and characterized by adding hydrazine to the solution before drying.

2. A nano boron oxide production method according to claim 1, characterized by adding hydrazine to the solution to obtain a concentration between 0.5 - 7 M.

3. A nanoboron oxide production method, according to claim 1, characterized in that the dehydration of the precipitate is carried out in steps, each of which is at higher temperatures than the previous one.

4. A nano boron oxide production method, according to claim 3, characterized by carrying out the dehydration in two steps, at temperatures between 120 and 170 °C for 2 and 48 hours, and at temperatures above 160 °C for 1 to 72 hours.

5. A nano boron oxide production method, according to claim 4, characterized by carrying out the dehydration in two steps, one at 130 °C and the other one at temperatures between 270 and 280 °C

6. A nano boron oxide production method, according to claim 1, characterized by drying the solution at 70 °C.

7. A nano boron oxide production method, according to claim 1, characterized by controlling the shape and size of the boron oxide grains by adjusting the boron oxide concentration of the solution.

8. A nano boron oxide production method, according to claim 1, characterized by controlling the shape and size of the boron oxide grains by adjusting the pH value of the solution.

9. A nano boron oxide production method, according to claim 8, characterized by adding at least one acidity regulator into the solution to adjust the pH value.