HYDROXYAPATITE POWDER AND METHOD FOR PRODUCING SAME

Abstract

In order to provide a hydroxyapatite that can be used without reservation in the food industry, a hydroxyapatite powder is provided composed of primary particles. The median size of the primary particles from which the powder is made is >0.10 μm and the aspect ratio of the primary particles is <5. The specific surface area of the hydroxyapatite powder is ≤10 m.sup.2/g, and the bulk density is >550 g/l. Also disclosed is a method with which such a hydroxyapatite powder can be obtained.

Claims

1. A hydroxyapatite powder composed of primary particles, wherein the median size of the primary particles is >0.10 and the aspect ratio of the primary particles is <5, wherein the specific surface area of the hydroxyapatite powder is ≤10 m.sup.2/g and the bulk density is >550 g/l.

2. The hydroxyapatite powder according to claim 1, wherein the hydroxyapatite, consists of at least 95 wt % Ca.sub.5(PO.sub.4).sub.3OH.

3. The hydroxyapatite powder according to claim 1, wherein the hydroxyapatite is calcium-saturated hydroxyapatite with the formula Ca.sub.5(PO.sub.4).sub.3OH or is calcium-deficient hydroxyapatite with the formula Ca.sub.10-x(PO.sub.4).sub.x-6(HPO.sub.4).sub.x(OH).sub.2-x, wherein 0<x≤2.

4. The hydroxyapatite powder according to claim 1, wherein, the primary particles of the powder are agglomerated to form secondary particles, wherein the median size of the secondary particles is >1.0 μm.

5. A method for producing a hydroxyapatite powder, in which a reaction mixture is created in which milk of lime is reacted with phosphoric acid to form hydroxyapatite, wherein a method cycle comprising the following method steps is carried out: a) providing a suspension of hydroxyapatite starter particles in water, b) adding milk of lime and phosphoric acid to the suspension, c) reacting the milk of lime with the phosphoric acid in the suspension to form hydroxyapatite at a temperature in the range of >20° C. and <105° C. and at a pH in the range from 6.0 to 13.0, d) separating at least a portion of the hydroxyapatite particles out of the suspension, e) repeating method steps a) to d) at least once, wherein either the hydroxyapatite particles separated in method step d) or the hydroxyapatite particles remaining in the suspension in method step d) are used as the hydroxyapatite starter particles in method step a), and f) removing the hydroxyapatite particles which, in the dried state, have a median size of the primary particles of >0.1 μm from the method cycle.

6. The method according to claim 5, wherein, in said method, the method steps a) to d) are repeated at least 3 times.

7. The method according to claim 5, wherein the method is carried out either in semicontinuous operation, wherein the portion of the hydroxyapatite particles separated in method step d), which, in the dried state, has a median size of the primary particles of >0.10 μm, is always removed from the process, while the remaining portion is resuspended in water in method step a) to provide a suspension of hydroxyapatite starter particles in water, or in fully continuous operation, wherein, in method step d), the portion of hydroxyapatite particles which, in the dried state, has a median size of the primary particles of >0.10 μm is continuously separated and removed from the method cycle while the remaining portion remains in the method cycle.

8. The method according to claim 5, wherein the milk of lime and the phosphoric acid are added at the same time in step c).

9. The method according to claim 5, wherein the phosphoric acid is diluted phosphoric acid with a concentration of 5-25 vol % of phosphoric acid in water.

10. The method according to claim 5, wherein the oxide-based milk of lime has a concentration of 2-20 wt %.

11. A method comprising adding the hydroxyapatite powder according to claim 1 to foodstuffs to fortify with calcium and/or as a free flowing agent to improve the flow properties of said foodstuffs.

12. A method comprising adding the hydroxyapatite powder according to claim 1 plastics and ceramics as a filler, to toothpaste as an abrasive, or to brake linings as a hard material.

Description

EXAMPLES

[0053] Examples 1.1-1.4 describe different production methods for hydroxyapatite powder (HAP).

[0054] The analysis results of the thus produced materials are shown below in tables.

[0055] 1.1 Conventional Method

[0056] An aqueous suspension of Ca(OH).sub.2 (calculated content of 10% CaO) is heated to 80° C. in a boiler. Then the appropriate quantity of 20% H.sub.3PO.sub.4 is added slowly until a pH of 7 is reached. The suspension is stirred for another 15 min. Then filtered off, washed and dried.

[0057] 1.2 Method According to the Invention (Precipitation on Hydroxyapatite)

[0058] An aqueous suspension of HAP (material from 1.1) with a solids content of 13% is heated to 90° C. in a boiler; the batch quantity of HAP is 10% of the desired target quantity. Milk of lime with a calculated content of 10% CaO and 20% phosphoric acid are then added at the same time while maintaining a specific pH in the range of 7.0 to 9.0. The suspension is stirred for another 15 min. 90% of the suspension is then filtered off, washed and dried. The experiments for simultaneous precipitation were repeated seven more times (V2-V8) after the first precipitation (V1), in each case the remaining 10% served as the batch for the next precipitation according to said method.

[0059] 1.3. Comparison Method (Precipitation on Ca(OH).sub.2)

[0060] 100 mL milk of lime is provided in a 2 L reactor and measured with a pH electrode. The milk of lime (content: 10% CaO) is then added at 20 rpm via a peristaltic pump. Phosphoric acid (20%) is added at the same time via a process control system, such that a specific pH is present during precipitation. After reaching the >11 filling mark, 400 ml of the preparation was removed and the remainder (in the PCS) was set to a pH of 7 with phosphoric acid. The tests were carried out with precipitation pH values of 10, 9, 8, 7 (V1-V8).

[0061] 1.4 Comparison Method (Sintering Process)

[0062] Material from 1.1 is sintered together using a thermal treatment. To do this, the material was heated in Alusint crucibles to 300, 500 and 900° C. for 12 h respectively (V1-V3).

[0063] Analysis Methods and Results

[0064] The materials produced according to Examples 1.1-1.4 were analyzed using the following methods: [0065] X-ray diffraction (XRD, Bruker D8 Advance, CuKα, 40 kV; 40.0 mA; A 1.5406 Å; Lynxeye detector), [0066] particle size distributions (PSD) by means of dynamic light scattering (“Horiba”) based on both volume and particle size, [0067] specific surface area according to the BET method using N.sub.2 absorption (DIN ISO 9277), [0068] shape and size using scanning electron microscope images (SEM).

[0069] 1. Physical Specifications

[0070] A compilation of the experimentally determined analysis values for the materials produced according to the examples is provided in the following Tables 1 and 2.

TABLE-US-00001 TABLE 1 Overview of the analysis values from Experiments 1.1-1.2. D10 D10 Median Median Saturation D90 D90 BET Bulk density (determined (Volume- (Number- Test no. XRD m.sup.2/g g/l experimentally) based) based 1.1 HAP 65.8 not not determined not determined not determined determined 1.2 (V0) HAP 16.7 260 3.33 not determined not determined 1.2 (V1) HAP 14.7 530 3.23 15.29684(μm) 0.24896(μm) 4.90018(μm) 0.13929(μm) 0.68476(μm) 0.09582(μm) 1.2 (V2) HAP 10.0 570 3.27 11.70868(μm) 0.22861(μm) 5.42478(μm) 0.13090(μm) 0.32242(μm) 0.08679(μm) 1.2 (V3) HAP 8.0 620 3.27 11.56829(μm) 0.22601(μm) 5.89078(μm) 0.13107(μm) 0.32429(μm) 0.08693(μm) 1.2 (V4) HAP 7.4 630 3.28 11.92629(μm) 0.23763(μm) 6.19286(μm) 0.13482(μm) 0.35308(μm) 0.08784(μm) 1.2 (V5) HAP 7.4 640 3.27 11.94827(μm) 0.23467(μm) 6.25612(μm) 0.13396(μm) 0.35594(μm) 0.08767(μm) 1.2 (V6) HAP 6.5 660 3.27 11.94827(μm) 0.23523(μm) 6.25612(μm) 0.13436(μm) 0.35594(μm) 0.08780(μm) 1.2 (V7) HAP 6.0 670 3.27 10.95516(μm) 0.22858(μm) 6.09562(μm) 0.13270(μm) 0.43992(μm) 0.08754(μm) 1.2 (V8) HAP 6.2 650 3.26 11.19130(μm) 0.22947(μm) 6.09160(μm) 0.13279(μm) 0.36278(μm) 0.08750(μm)

TABLE-US-00002 TABLE 2 Overview of the analysis values from Experiments 1.3-1.4 D10 D10 Saturation Median Median Bulk determined D90 D90 BET density experi- (Volume- (Number- Test no. XRD m.sup.2/g g/l mentally) based) based 1.3 (V1) HAP 102.1 not 3.07 not not pH 10 determined determined determined 1.3 (V2) HAP 104.1 not 2.94 not not pH 10 determined determined determined 1.3 (V3) HAP 89.5 not 3.04 not not pH 9 determined determined determined 1.3 (V4) HAP 103.9 not 2.98 not not pH 9 determined determined determined 1.3 (V5) HAP 80.6 not 3.04 not not pH 8 determined determined determined 1.3 (V6) HAP 66.6 not 2.96 not not pH 8 determined determined determined 1.3 (V7) HAP 75.9 not 3.01 not not pH 7 determined determined determined 1.3 (V8) DCP-D 15.7 410 2.11 not not pH 5 determined determined 1.4 75.5 7.46947 3.51947 Un- (μm) treated* 4.03874 1.81696 (μm) 2.01859 1.08566 (μm) 1.4 (V1) HAP 70.3 not not not not 300° C. determined determined determined determined 1.4 (V2) HAP 49.6 not not not not 500° C. determined determined determined determined 1.4 (V3) HAP 10.9 not not not not 900° C. determined determined determined determined *granulated product

[0071] 2. Investigation of Free Flow Properties

[0072] Hydroxyapatite powder produced according to the invention was used as free flowing agent for two different coffee whiteners (VB 30A and VG 80C) and compared with other free flowing agents (B-TCP=beta-tricalcium phosphate; E551=nano-SiO.sub.2).

[0073] The maximum achievable angle of slope of the heaped material was determined and the results are summarized below in Table 3.

[0074] An angle of 31-40° represents good flow properties, an angle of 41 to 45° represents acceptable flow properties, and an angle of 46-55° represents poor flow properties.

TABLE-US-00003 TABLE 3 Overview of angles of repose of the free flow tests Proportion of free Free Angle Test Test flowing flowing of slope no. substance agent [wt %] agent [°] 1 VB 30A 0.0 — 54.1 2 VB 30A 1.0 B-TCP (C73-13) 49.2 19 VB 30A 1.0 1.2 V8 44.4 20 VB 30A 2.0 1.2 V8 44.4 17 VB 30A 1.0 1.4 V3 38.7 18 VB 30A 2.0 1.4 V3 35.8 6 VB 30A 0.3 E551, nano-SiO.sub.2 31.8 7 VG 80C 0.0 — no information 15 VG 80C 2.0 B-TCP (C73-13) 51.6 21 VG 80C 1.0 1.4 V3 49.7 11 VG 80C 0.5 E551, nano-SiO.sub.2 48.7 9 VG 80C 1.0 1.2 V8 46.7 22 VG 80C 2.0 1.4 V3 45.0 16 VG 80C 2.0 1.2 V8 43.8

[0075] The test results show that the addition of hydroxyapatite powder according to the invention imparts good flow properties to the various coffee whiteners.