CZ99493A3 - Magnesium hydroxide and process for preparing thereof - Google Patents

Abstract

Magnesium hydroxide Mg/(OH)2 has a crystallite size above 15.0 nm and below 50.0 nm and a spectral ratio from 2 to 5, a maximum deformation of 4.2.10<-3>. 50% of the secondary particles have a diameter below 1.4 micrometers, 100% of the secondary particles have a maximum diameter of 4.0 micrometers and a surface determined by the BET method below 25 m<2>/g. It is prepared by a two-stage synthesis: in the first stage magnesium nitrate is treated with ammonia in an aqueous medium at a 1.5 to 6.0-fold excess at a maximum temperature of 85 degrees C and at atmospheric pressure, producing alkaline magnesium nitrate, which is decomposed in the second stage at a temperature of 110 to 150 degrees C and a pressure up to 1.5 MPa. It is preferably that a 3.0 to 5.0-fold excess of ammonia is used at a temperature of 50 to 75 degrees C and when the decomposition of nitrate is performed at a temperature of 120 to 130 degrees C and a pressure of 0.3 to 1.3 MPa.

Description

BACKGROUND OF THE INVENTION

It is generally known that for the use of magnesium hydroxide in thermoplastic materials, the most suitable is that of magnesium hydroxide, which has developed crystallinity and is chemically inactive. Such magnesium hydroxide has a small specific surface area S, aer, usually less than 20 to 25 m ² / g. It is also important that the incorporation of such magnesium hydroxide into the thermoplastic material results in a uniform distribution of the secondary particles in the volume of the thermoplastic. Therefore, it is important that the secondary particles stick as small as possible and their size distribution. bare as narrow as possible. Magnesium hydroxide which does not have the desired properties, after incorporation into thermoplastic, significantly deteriorates their physical parameters, in particular the shape properties, creating in them locally manifested on the surface of the material as materials sideways and inhomogeneities, with colored spots.

Commercially available magnesium hydroxides do not meet this condition and have a large specific surface area of 5 _{Θ (ΞΤ} - up to .00 nf ^ / g. Most processes which result in the preparation of special types of magnesium hydroxide with small secondary particles and small specific surface area are based on preparation. It is known to add small amounts of citric acid or its salts (CJP 10,784 (1958)) or to remove calcium cations (CJP 10,786 (1958)), thereby ensuring the formation of large crystals. Other CEP procedure 0 189 098

A2) in addition to the magnesium, often with 0 365 347, to form a morphologically different hydroxide having spherical and non-square secondary diameters of 5-500 µm. The process according to EP A1 yields secondary particles with a large particle size

Specific surface area S _Be: -i 20 to 50 m &lt; -1 &gt; / g.

The magnesium hydroxide of U.S. Pat. Nos. 4,098,762 and 4,145,404 is characterized by a crystal size in < 10 > in a direction greater than 800 [deg.] C. and a crystal lattice deformation in < 101 &^gt; The secondary particles formed from such crystals then have a specific surface area Sbet of less than 20 m ² / g.

A common disadvantage of the processes for preparing large magnesium hydroxide crystals is that they have to be treated with dilute solutions, which imposes the energy consumption of such processes. A disadvantage of the process described in U.S. Pat. Nos. 4,098,762 and 4,145,404 is that it produces very large crystals (crystal size in the <101> direction of 800-10,000 A °) which are not shape-defined, i.e. . they can have any ratio of the width of the base to the height of the crystal (the crystal size in <101> direction does not say anything about its shape). Thus, narrow and high crystals, wide and low crystals can be formed, but also crystals having a width and height size of approximately comparable. Aggregation of such shape-diverse crystals leads to the formation of secondary particles with a larger specific surface area Sbet than would be the case when shape-shaped crystals of aggregate of approximately comparable width and height size are aggregated. In order to achieve a minimum specific surface area of the Sbet of secondary particles resulting from the aggregation of shape-diverse crystals, this disadvantage must be compensated by the preparation of large crystals (Examples 1 to 5 US 4,145,404 report crystal size in <101> up to 2250-5260 A ° invention

The above-mentioned disadvantages are overcome by the magnesium hydroxide according to the invention of formula Mg (OH > 2), characterized in that it has a crystal size in <101> direction greater than 150 A ° and less than 500 A °, , a deformation in <004> up to a maximum of 4.2.10 ^-3 and a deformation in <110> up to a maximum of 3.0.10 ^-3 , said magnesium hydroxide further having 50% secondary particle diameters less than 1.4 µm and 100% secondary particle diameters at most 4.0 µm and the specific surface area, determined by BET, is less than 25 m ² / g. The subject magnesium hydroxide is prepared according to the process according to the invention in two stages, which consists in the first stage being converted to magnesium nitrate an alkaline compound, in particular ammonia, in an aqueous medium at a temperature of max. 85 ° C, at atmospheric pressure, to form a basic magnesium nitrate. The reaction is carried out with an ammonia in a 1.5 to 6.0-fold excess, preferably a 3.0 to 5.0-fold excess, at a temperature of 50 to 75 ° C. The resulting basic magnesium nitrate is decomposed in a second step, in a hydrothermal manner, at a temperature of 110 to 150 ° C, preferably 120 to 130 ° C and a pressure of up to 1.5 MPa, preferably 0.3 to 1.3 MPa. The slurry from the first stage is heated in the pressure apparatus, whereby the pressure and temperature stages are maintained at a desired value of about 1 hour, and the pressure is then gradually reduced by discharging ammonia gas from the pressure apparatus so that it remains at 0.3 MPa at the end. After the pressurization is complete, the suspension is cooled to 50-60 ° C, filtered and, after washing with demineralized water, dried or, if necessary, before being dried in demineralised water and treated with a suitable surfactant. The magnesium hydroxide of the present invention, when incorporated into thermoplastic materials, improves their properties, but in particular their resistance to fire.

It has been found that the Mg (OH> 2) crystal characteristics, in particular its crystal lattice shape, size and deformation, have a decisive influence on these and other properties of magnesium hydroxide. Individual crystals aggregate to form secondary particles of angular shape, characterized by specific The characteristics of the secondary particles are equally important, but these are already dependent on the shape and size of the crystal and the deformation of the crystal lattice. dimensions and a heavier specific surface.

An important finding from the results is that the dominant crystal parameter, which decisively affects the specific surface area of the Sbet, is the shape of the crystal lattice induced by the surface crystal, expressed by the aspect ratio AR, where AR = D / H, and H is the height of the crystal, calculated as the crystal size in the <004> direction. It has been found that if magnesium hydroxide crystals with an aspect ratio of not less than 2 and not more than 5 are prepared, these crystals may not switch to the largest possible condition, but it is sufficient if the crystal size in <004> direction is greater than 150 A ° and less than 500 A °.

Yet! both the shape and the size of the crystal are the necessary geometric conditions for bonding the crystals into the secondary particles, the deformation characterizes the tendency of the crystals, by the forces, to bond to form the secondary particles. The smaller the crystal lattice deformation value is, the lower the likelihood of large secondary particles being formed. From the measurements performed, it follows that, if the previous crystal shape and size conditions are met, it is sufficient that the deformation in <004> direction is not more than 4.2.10 ^-3 and the deformation in <110> is not greater than 3.0.10 ^-3 . The magnesium hydroxide of the present invention typically has deformation values in the <004> direction between 1.0.10 ^-3 to 3.0.10 ^-3 and in the <110> direction between 0.5.10 ^-3 to 2.5.10 ^-3 .

The magnesium hydroxide according to the invention has new characteristics which can be determined by the X-ray powder diffraction method and which differ from the other known magnesium hydroxides, namely a crystal size in the <004> direction of 150 to 500 A °, an aspect ratio of 2 to 5 , deformation in <004> direction max. 4.2-10 ^-3 and deformation in <110> direction max. 3,0.10 ^-3 .

In view of the incorporation of the magnesium hydroxide into the thermoplastic materials and the desired properties of the materials thus obtained, it is important that the secondary particles formed by agglomeration of the magnesium hydroxide crystals have an even particle size distribution. Conventionally produced magnesium hydroxide has 50 secondary particle diameters from 3 to 20 μη and 90% of the diameters from 8 to 40 μιη. Magnesium hydroxide according to EP 0 365 347 has 50% of the secondary particle diameters not more than 1.5 µm and 90% of the diameters not more than 4.0 µm. However, it is used for purposes other than the magnesium hydroxide of the present invention.

In the preparation of the magnesium hydroxide of the present invention, its crystals are combined into secondary particles having 50% diameters less than 1.4 µη and 100% diameters less than 4.0 µm, the BET specific surface area being less than 25 m ² / g.

Measurement of crystal size and crystal lattice deformation in directions <110> and <004>

The crystal size was calculated according to the relationship

D = K. Á / (i. Cos Θ and crystal lattice deformation according to e = β / 4. Tan Θ where X is the wavelength of the X-ray radiation used (in this case Cu-Kcc with wavelength 1,5406 A ° l, Θ is Bragg angle) , β is the actual peak width of the sample at half the height in radians and K is the instrumental constant (here K = 0,9).

The β value given in the relationships was determined as follows:

- diffraction profiles in the <110> direction and the <004> direction were also measured by CuKa radiation,

- conditions of measurement: voltage 40 kV, current 30 mA, gonioraetra speed 0,001 ° / s, spiner on, divergence diaphragm automatic, output diaphragm 0,2 mm, graphite monochromator,

The width of the profile at half height above Και, after subtracting the background value, gives the value Bs - widening of the measured material profile.

Diffraction profiles corresponding to instrument profiles were also measured using high purity silicon (99.999 r- &gt;

WHAT

-Η

Ο

4> ·· <Χ>

ο ο cx r— Ο

--J

OO with the same measurement conditions *

The half-width of the profile for Koci _lr, after subtracting the value of the seat, gives a value of B _{for the} instrument extension of the profile. In the articulation, the value of B _{o is} for <11D> direction 0, 133 2Θ and for <004> direction 0.141 2Θ.

From the above, the spread of the diffraction profiles caused by the measured material was calculated according to the relation & (crystal size) - B <3 - B _o β (deformation) ~ B _{C of the} particle size rieranle

The particle size was measured with a laser analyzer (CPRO-7000) operating on the principle of Fraurihof Fair Diffraction, supplemented in part by 1% of the theoretical, valid for particles smaller than 1 µm. The device is controlled by a computer system. Samples were measured in an aqueous medium, dispersed by ultrasound at max. 150 s.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

1 of a 2 mol / l aqueous magnesium nitrate solution in a 2.5 L reaction vessel equipped with heating and stirrer. heated to 70 ° C. With vigorous stirring, 0.9 l of 11.9 mol / l ammonia water is added uniformly over 5 minutes. 1 L of the suspension thus obtained is poured into a 1.5 L pressure apparatus which is sealed and heated to 130 ° C. At this temperature, the suspension is maintained for 1 h, with the pressure exiting! to 0.6 l * IPa. After 1 h, the reaction mixture is cooled, the suspension is filtered, washed with demineralized water and dried.

The obtained product was analyzed by X-ray powder diffraction method and measured crystal size in <004> direction 315 A °, aspect ratio 2.81, deformation in <004> direction 2.12.10 ^-3 and deformation in <1.10> direction 1.52.10 ^{- 3} .

The procedure was as in Example 1, except that the ammonia water concentration was 15.7 moles / l, resulting in a pressure of 11 bar.

The obtained product had a crystal size in <004> direction 315 fl °, an aspect ratio of 3.53, a deformation in <004> direction

2.18.10 ^{- 3} and deformation in <110> direction 1.45.10 ^-3 .

50% of the particle diameters less than 1.1 µm were measured and all particle diameters were less than 4 µm. The specific surface area determined by BET was 9.9 m ² / g.

Example 3

The procedure is as in Example 1 except that the pressurizing time is prolonged to 4 h.

The product obtained had a crystal size in <004> direction of 309 ft °, an aspect ratio of 5.38, a deformation in <004> direction

2.19.10 ^{- 3} and deformation in <110> direction 1.31.10 ^-3 .

50% of particle diameters less than 1.0 µm were measured and all particle diameters were less than 4 µm. The BET specific surface area was 6.57 m ² / g.

Example 4

The procedure is as in Example 1 except that 1.3 l of ammonia water at a concentration of 15.7 moles / l are added uniformly over a period of 20 min, the pressure time is 4 h, the pressure is 1.3 MPa.

The product obtained, had a crystal size in <004> direction 355 µ °, an aspect ratio of 3.73, deformation in <004> direction

2.12.10 ^{- 3} and deformation in <110> direction 1.43.10 ^-3 .

50% of particle diameters less than 1.1 µm were measured and all particle diameters were less than 4 µm. The BET specific surface area was 8.83 m ² / g.

Example 5 (Comparative)

1 liter of 2.0 mol / l magnesium nitrate solution is heated in a 2.5 L Cs reaction vessel, and

With vigorous stirring, 0.9 l of ammonia water is added and the suspension thus formed is heated to 70 ° C with a stirrer. over a period of 20 min with a concentration of 4.0 mol / l. 11 is transferred to a pressure apparatus which is sealed and heated to a temperature of 130 ° C. At this temperature, the suspension is maintained for 1 hour, the pressure of the step at 0.25 MPa. After 1 h, the reaction mixture is cooled, the suspension is filtered, washed with demineralized water and dried.

The product obtained had a crystal size in <004> direction 259 A °, an aspect ratio of 8.5, a deformation in <004> direction

2.98.10 ^{- 3} and deformation in <110> direction 1.08.10 ^-3 .

50% of the particle diameters less than 2.1 µm and 90% of the particle diameters less than 4 µm were measured. The BET specific surface area was 26.39 m ² / g.

Example 6 (comparative)

The procedure is as in Example 5, except that the concentration of ammonia water at precipitation is 11.9 mol / l, the hydrothermal treatment temperature is 100 ° C and the pressure is 0.6 MPa.

The product obtained had a crystal size in < 1004 > 111 °, an aspect ratio of 9.6, deformation in < 004 >

6.11.10 ^{- 3} and deformation in <110> direction 1.63.10 ^-3 .

50% of the particle diameters smaller than 3.7 µm and 90% of the particle diameters smaller than 5.4 µm were measured. The BET specific surface area was 32.68 m ² / g.

Example 7 (comparative)

The procedure is as in Example 5 except that the aqueous magnesium nitrate solution is only heated to 15 ° C and the ammonia water at a concentration of 14.7 mol / l is added uniformly over a period of 5 minutes. The suspension is pressurized for 4 hours (at a pressure of 0.8 MPa and a temperature of 130 ° C).

The product obtained had a crystal size in <004> direction of 512 A °, an aspect ratio of 1.62, a deformation in <004> direction

1.94.10 ^{- 3} and deformation in <110> direction 1.88.10 ^-3 .

50% of particle diameters less than 3.1 µm and% of particle diameters less than 6.3 µm were measured. The specific BET surface area was 29.42 m ² / g.

Claims (6)

Magnesium hydroxide of the formula MgCOH> 2, having a crystallite size in <004> direction greater than 150 A ° and less than 500 A °, an aspect ratio ranging from 2 to 5, a deformation in <004> direction of maximum 4.2. 10 ^-3 and a deformation in <110> in the direction of maximum 3.0. 10 ~ ³ . Magnesium hydroxide according to claim 1, having 50% secondary particle diameters less than 1.4 µη and 100% secondary particle diameters of not more than 4.0 µm. Magnesium hydroxide according to claim 2, having a BET specific surface area of less than 25 m ² / g. A process for the preparation of magnesium hydroxide according to claims 1 to 3, characterized in that in the first stage magnesium nitrate is treated with an alkali compound, in particular ammonia, in an aqueous medium, at a maximum temperature of 85 ° C, at atmospheric pressure. to form a basic magnesium nitrate which decomposes in the second stage at a temperature of 110 to 150 ° C and a pressure of up to 1.5 MPa. 5. The process according to claim 4, wherein in the first step the ammonia is treated in an excess of 1.5 to 6.0 times, preferably 3.0 to 5.0 times, at a temperature of 50 to 75 [deg.] C. 6. The process according to claim 5, wherein the basic magnesium nitrate decomposes at a temperature of 120 to 130 [deg.] C. and a pressure of 0.3 to 1.3 MPa.