Preparation method of heterogeneous structure medical bone implant based on additive manufacturing

Abstract

The present invention discloses a preparation method of a heterogeneous structure medical bone implant based on additive manufacturing, comprising the following steps: Step 1: Using selective laser melting technology, prepare a titanium alloy scaffold with interconnected pores from TC4 titanium alloy powder according to a suitable printing strategy; Step 2: Place the titanium alloy scaffold in a chemical polishing solution for polishing; Step 3: Take the chemically polished titanium alloy scaffold as the cathode and a pure iron sheet as the anode, and immerse both in an electroplating solution for electroplating; Step 4: Pour the molten zinc-based metal into a square crucible containing the titanium alloy-iron scaffold, and press a heavy block on top. After cooling, cut it. After the formed heterogeneous structure medical bone implant of titanium alloy-iron-zinc is implanted into the human body, over time, the zinc-based metal gradually degrades, and at the same time, new bone forms on the surface. The good biocompatibility of the zinc-based metal ensures the development and growth of cells and avoids the growth of bacteria.

Description

Technical Field

[0001] The present invention relates to a preparation method of a heterogeneous structure medical bone implant based on additive manufacturing, in particular to a preparation method of a titanium alloy-iron-zinc heterogeneous structure medical bone implant that can meet the mechanical property requirements of human bone implants, has a good degradation rate and excellent biological properties, and can reasonably regulate bone repair. Background Art

[0002] With the development of the aging population society, the market demand for bone implants has become increasingly large. Titanium alloy is regarded as a good alternative candidate material for bone implants because it is close to the elastic modulus of bone and has good wear resistance, etc. In recent years, with the development of additive manufacturing technology, people have seen the possibility of using titanium alloy to prepare various interconnected pore structures, and it has become a popular material in the field of processing and preparation of bone implants. However, the biological inertness of titanium alloy has been a problem that has troubled researchers for many years.

[0003] Degradable metals refer to metal materials that can be biodegraded and absorbed by the human body. After being prepared into bone implants, as the metal gradually degrades, it is finally replaced by new bone tissue, and has good biocompatibility. The most representative ones are metal magnesium, zinc, iron and their alloys. Among them, iron-based degradable metal materials have excellent comprehensive mechanical properties, but the degradation rate is too low, and the corrosion products are difficult to be cleared from the bone implant site; the degradation products of magnesium-based degradable metals will be metabolized out of the body, but its relatively fast degradation rate will lead to premature disintegration of the structure, and the hydrogen gas evolved during its degradation will affect the cell attachment of adjacent tissues, resulting in cysts and embolisms; zinc-based degradable metals do not produce bubbles during the degradation process, can promote the generation of new bone cells and have certain antibacterial ability. However, its hardness and mechanical strength are relatively low, unable to meet the mechanical requirements of bone implants, and the degradation rate is slightly slow.

[0004] Therefore, absorbing the advantages of various materials and improving its biological properties as much as possible while meeting the mechanical strength requirements for the preparation of bone implants has become an important trend in current research. At present, some people have studied the combination of titanium alloy and magnesium alloy to prepare a heterogeneous structure bone implant, integrating the mechanical properties of titanium alloy and the biological properties of magnesium alloy. However, as mentioned above, the negative effects generated by magnesium-based metals during the degradation process are a problem that must be faced and urgently solved. The biological properties of zinc are much better than those of magnesium alloy. Replacing magnesium with zinc can not only avoid hydrogen generation, but also further adjust biological properties such as antibacterial performance. However, the slow degradation rate of zinc is also a problem that currently troubles scientific researchers.

[0005] Preparing a heterogeneous structure of titanium alloy - iron - zinc can give full play to the biological properties of zinc - based metal while maintaining the mechanical strength of the titanium alloy skeleton, and reasonably utilize the galvanic corrosion effect to adjust an appropriate degradation rate. During the degradation of zinc, osteoclasts continuously generate new bone tissue, and ultimately form a heterogeneous structure of titanium alloy - bone, which has a great promoting effect on bone repair.

[0006] Therefore, it becomes very necessary to select a suitable process method to prepare a heterogeneous structure bone implant from a titanium alloy and a zinc - based alloy. Summary of the Invention

[0007] (I) Technical problems to be solved

[0008] In order to solve the problem of the difficulty in preparing heterogeneous metal structure bone implants in the prior art, the present invention provides a preparation method of a heterogeneous structure medical bone implant based on additive manufacturing.

[0009] (II) Technical solutions

[0010] In order to achieve the above - mentioned purpose, the main technical solutions adopted by the present invention include: a preparation method of a heterogeneous structure medical bone implant based on additive manufacturing, comprising the following steps:

[0011] Step 1: Using selective laser melting technology, prepare a titanium alloy scaffold with interconnected pores from TC4 titanium alloy powder according to a suitable printing strategy;

[0012] Step 2: Place the titanium alloy scaffold in a chemical polishing solution for polishing;

[0013] Step 3: Take the chemically polished titanium alloy scaffold as the cathode, and a pure iron sheet as the anode, and immerse both in an electroplating solution for electroplating;

[0014] Step 4: Pour the molten zinc - based metal into a square crucible containing the titanium alloy - iron scaffold, press a heavy block on it, and cut it after cooling.

[0015] Preferably, the titanium alloy scaffold in Step 1 is a rhombic dodecahedron scaffold.

[0016] Preferably, the design method of the rhombic dodecahedron scaffold is: first, draw a two - dimensional structure of a star - shaped honeycomb according to the radian angle r, the cell side length a, and the concave side length b of the star - shaped honeycomb inside; then set curved beams outside each concave side of the star - shaped honeycomb to obtain a two - dimensional structure of curved beams, and the governing curve of the curved beam is , rad is the unit of radian, x is the abscissa of the point on the curved beam, y is the ordinate of the point on the curved beam, and four curved beams are connected end to end through a rectangular block with a side length of h; the star-shaped honeycomb and the curved beam are thickened inward, with thicknesses of 0.75h and 0.25h respectively. Subsequently, the convex vertices of the star-shaped honeycomb are connected to the rectangle, and the concave vertices of the star-shaped honeycomb are connected to the top of the curved beam through a rectangle with a width of h, thereby combining the two-dimensional structure of the star-shaped honeycomb and the two-dimensional structure of the curved beam to generate a two-dimensional modified star-shaped negative Poisson's ratio structure; the two-dimensional modified star-shaped negative Poisson's ratio structure is stretched along the X-axis, and the stretching length is h; the center of the stretched two-dimensional modified star-shaped negative Poisson's ratio structure is restricted to the origin, and it is replicated along the XY plane and the ZX plane respectively to obtain a single-cell modified star-shaped negative Poisson's ratio structure; finally, the single-cell modified star-shaped negative Poisson's ratio structure is arrayed along the X, Y, and Z axes in sequence once to obtain 2 2 2 Array of modified star-shaped negative Poisson's ratio structures.

[0017] Preferably, the chemical polishing solution in the second step includes nitric acid, hydrofluoric acid, and deionized water, and the volume ratio of nitric acid, hydrofluoric acid, and deionized water is (3~8):(1~2):(5~10), the concentration of nitric acid is: 1~8mol / L, and the concentration of hydrofluoric acid is: 1~22.5mol / L.

[0018] Preferably, the polishing time in the second step is: 1min~3min.

[0019] Preferably, the electroplating solution in the third step is prepared from ferrous chloride particles and deionized water, and its concentration ratio is 200~400g / L, and the pH value is 1.5.

[0020] Preferably, the electroplating conditions in the third step are: the electroplating solution is placed in a water bath at 60°C, the current magnitude is 100~500mA, and the duration is 10~50min.

[0021] Preferably, the molten zinc-based metal is obtained by placing the zinc-based metal in a cylindrical crucible and simultaneously heating it to 500~800°C in a sintering device.

[0022] (III) Beneficial effects

[0023] The present invention can uniformly remove the stepped effect caused by processing inside and outside the titanium alloy stent and the adhered powder, ensure the fitting effect of the electroplated iron layer, ensure the fluidity of the zinc-based metal during subsequent casting, and the preparation of the iron layer can avoid element diffusion caused by the good mutual solubility between the zinc-based metal and titanium elements, ensuring the good forming of the heterogeneous structure medical bone implant of titanium alloy-iron-zinc. At the same time, titanium alloy-iron-zinc forms a three-electrode galvanic couple, with the titanium alloy as the cathode and zinc as the anode. The galvanic corrosion rate generated by the three-electrode galvanic couple is much higher than that of the two-electrode galvanic couple of titanium alloy-zinc and pure zinc, and the corrosion rate can be effectively increased to improve the problem of the relatively low degradation rate of zinc;

[0024] After the formed heterogeneous structure medical bone implant of titanium alloy-iron-zinc is implanted into the human body, as time goes by, the zinc-based metal gradually degrades, and at the same time, new bone is formed on the surface. The good biocompatibility of the zinc-based metal ensures the development and growth of cells and avoids the growth of bacteria; the addition of the iron layer makes titanium alloy-iron-zinc form a three-electrode galvanic couple, which greatly promotes the degradation of zinc acting as the anode. The appropriate degradation rate ensures the healing of the new bone tissue. At the same time, the skeleton of the titanium alloy provides good mechanical properties to avoid the failure of the bone implant. Brief Description of the Drawings

[0025] Figure 1 is the preparation flow chart of the present invention;

[0026] Figure 2 is the schematic diagram of the forming principle of the electroplated iron layer;

[0027] Figure 3 is the schematic diagram of casting the molten zinc-based metal on the rhombic dodecahedron stent in Example 1;

[0028] Figure 4 is the design flow chart of the modified star-shaped negative Poisson's ratio structure array in the present invention;

[0029] Figure 5 is the schematic diagram of the preparation of the heterogeneous structure of titanium alloy-iron-zinc; wherein (a) is: the schematic diagram of the titanium alloy-iron stent, and (b) is: the schematic diagram of the heterogeneous structure of titanium alloy-iron-zinc;

[0030] Figure 6 is the schematic diagram of the accelerated degradation of the three-electrode galvanic corrosion of titanium alloy-iron-zinc;

[0031] Figure 7 is the comparison chart of the degradation rates of pure zinc, the heterogeneous structure of titanium alloy-zinc, and the heterogeneous structure of titanium alloy-iron-zinc;

[0032] Figure 8 is the comparison chart of the test results of the antibacterial experiment;

[0033] Figure 9Comparison diagram of mechanical properties of titanium alloy scaffolds, titanium alloy-zinc heterostructures, and titanium alloy-iron-zinc heterostructures: Among them, (a) is the stress-strain curve, and (b) is the bar chart of elastic modulus analysis and comparison;

[0034] In the figure, 1: titanium alloy scaffold; 2: pure iron sheet; 3: electroplating solution; 4: water bath; 5: square crucible; 6: titanium alloy-iron scaffold; 7: molten zinc-based metal; 8: cylindrical crucible; 9: heavy block. Specific implementation method

[0035] In order to better explain the present invention for easy understanding, the present invention will be described in detail below in conjunction with the accompanying drawings and through specific implementation methods.

[0036] Example 1 of the present invention:

[0037] A preparation method of a heterogeneous structure medical bone implant based on additive manufacturing includes the following steps:

[0038] Step 1: Using selective laser melting technology, prepare a titanium alloy scaffold 1 with interconnected pores from TC4 titanium alloy powder according to a suitable printing strategy. Here, the titanium alloy scaffold 1 is a rhombic dodecahedron scaffold; the design method of the rhombic dodecahedron scaffold is as follows: First, according to the radian angle r, the edge length a of the unit cell, and the inner concave edge length b of the star-shaped honeycomb, draw the two-dimensional structure of the star-shaped honeycomb, as shown in Figure 4 (a); Then, set curved beams outside each inner concave edge of the star-shaped honeycomb to obtain a two-dimensional structure of the curved beams. The governing curve of the curved beams is , where rad is the radian unit, x is the abscissa of the point on the curved beam, y is the ordinate of the point on the curved beam, and the four curved beams are connected end to end through a rectangular block with a side length of h, as shown in Figure 4 (b); The star-shaped honeycomb and the curved beams are thickened inward, with thicknesses of 0.75h and 0.25h respectively. Subsequently, the outer convex vertices of the star-shaped honeycomb are connected to the rectangle, and the inner concave vertices of the star-shaped honeycomb are connected to the top of the curved beams through a rectangle with a width of h. Thus, the two-dimensional structure of the star-shaped honeycomb and the two-dimensional structure of the curved beams are combined to generate a two-dimensional modified star-shaped negative Poisson's ratio structure, as shown in Figure 4 (c); Stretch the two-dimensional modified star-shaped negative Poisson's ratio structure along the X-axis, with a stretching length of h, as shown in Figure 4 (d); Limit the center of the stretched two-dimensional modified star-shaped negative Poisson's ratio structure at the origin and replicate it along the XY plane and the ZX plane respectively to obtain a unit cell modified star-shaped negative Poisson's ratio structure, as shown in Figure 4 (e); Finally, the unit cell modified star-shaped negative Poisson's ratio structure is arrayed once along the X, Y, and Z axes in sequence to obtain a 2 2 2 modified star-shaped negative Poisson's ratio structure arrays, as shown in Figure 4 (f);

[0039] Step 2: Prepare a chemical polishing solution with 2 mol / L nitric acid, 22.5 mol / L hydrofluoric acid and deionized water, where the volume ratio of nitric acid, hydrofluoric acid and deionized water is 4:1:5; Place the titanium alloy stent 1 in the chemical polishing solution, polish for 2 minutes, take it out, wash and dry it;

[0040] Step 3: Prepare an electroplating solution 3 with ferrous chloride particles and deionized water, with a concentration ratio of 300 g / L of the solution and a pH value of 1.5; Use the titanium alloy stent 1 as the cathode and a pure iron sheet 2 as the anode, immerse both in the electroplating solution 3, place the electroplating solution 3 in a water bath 4 at 60 °C, with a current magnitude of 200 mA and a duration of 20 minutes; After electroplating, take out the obtained titanium alloy-iron stent 6, clean the surface debris, and place it in alcohol for ultrasonic cleaning and drying;

[0041] Step 4: Place the zinc-based metal in a cylindrical crucible 8 and simultaneously heat it to 700 °C in a sintering device to ensure the melting of the zinc-based metal; Pour the molten zinc-based metal 7 into a square crucible 5 containing the titanium alloy-iron stent 6, and press a weight 9 on top; After cooling to below the melting point of the zinc-based metal, quickly cool it with water, take it out and cut it to obtain a heterogeneous structure of titanium alloy-iron-zinc.

[0042] The printing parameters adopted in the "suitable printing strategy" in Step 1 can be a laser power of 125 w, a scanning speed of 600 mm / s, a scanning spacing of 80 μm, and a scanning layer thickness of 30 μm. These printing parameters have been proven to have good forming accuracy in previous studies.

[0043] Example 2 of the present invention:

[0044] It only includes Step 1, Step 2 and Step 4 of Example 1, that is: Obtain a heterogeneous structure of titanium alloy-zinc.

[0045] Example 3 of the present invention:

[0046] It only includes Step 1 and Step 2 of Example 1, that is: Obtain a rhombic dodecahedron stent with interconnected pores prepared from polished TC4 titanium alloy powder.

[0047] Example 4 of the present invention:

[0048] A polished TC4 titanium alloy solid block.

[0049] Comparative Example 1:

[0050] A pure zinc block.

[0051] Experimental Example 1 Degradation rate determination:

[0052] Determine the degradation rates of Examples 1 and 2 and Comparative Example 1. The degradation rates of each group are shown in Table 2.

[0053] Detection method: Prepare the simulated body fluid according to Table 1. Suspend the sample in the center of the beaker with a thread and conduct a 28-day immersion test. After the immersion is completed, take out the sample, measure the mass change, and calculate the degradation rate. Five parallel samples are tested for each group of samples.

[0054] Table 1 Proportion of simulated body fluid preparation

[0055] Component Concentration (g / L) NaCl 8.00 KCl 0.40 <![CDATA[NaHCO 3 > 0.35 <![CDATA[CaCl 2 > 0.14 <![CDATA[KH 2 PO 4 > 0.10 <![CDATA[MgSO 4 ·H 2 O]]> 0.20 <![CDATA[C 6 H 12 O 6 > 1.00 <![CDATA[NaHPO 4 > 0.06

[0056] Sample specifications: 10mm * 10mm * 10mm

[0057] Test steps: ① Conduct the mass test before immersion and calculate the surface area; ② Prepare the simulated body fluid; ③ Conduct the immersion test; ④ Conduct the mass calculation; ⑤ Conduct the degradation rate calculation.

[0058] Table 2 Results of degradation rate determination

[0059] Example 1 Example 2 Comparative Example 1 Component Titanium alloy - iron - zinc Titanium alloy - zinc Zinc Degradation rate (Mm / year) 0.4236±0.0490 0.2234±0.0098 0.0279±0.0029

[0060] Experimental conclusion: The heterogeneous structure of titanium alloy - iron - zinc can significantly improve the degradation rate of zinc, providing an idea for reasonably regulating the degradation rate of zinc in the human body.

[0061] Experimental example 2 In vitro antibacterial experiment:

[0062] Take Examples 1, 2, and 4, and Comparative Example 1 to measure the in vitro antibacterial rate against common infectious bacteria (Escherichia coli, Staphylococcus aureus). The in vitro antibacterial rates of each group are shown in Table 3. According to relevant standards such as "JISZ2801 - 2000 Antibacterial processed products - Test methods for antibacterial properties and antibacterial effects" and "GB / T2591 - 2003 Test methods for antibacterial properties and antibacterial effects of antibacterial plastics".

[0063] The calculation formula for the antibacterial rate is as follows:

[0064] ;

[0065] where Cs is the antibacterial rate, A is the number of cells in the test group, B is the number of cells in the blank group, and C is the number of cells in the control group.

[0066] Detection method: Use mouse embryonic osteoblast precursor cells MC3T3 - E1 for in vitro biocompatibility testing. Mouse embryonic osteoblast precursor cells MC3T3 - E1 are cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% fetal bovine serum (FBS), 100 μg / mL streptomycin, and 100 U / mL penicillin, and in 5% CO 2Cultured in a humid atmosphere at 37°C. The culture medium was changed every other day, and the third-generation cells were used for the experiment. Cell viability and alkaline phosphatase (ALP) activity were evaluated by extraction assays. The sample extracts were prepared according to the guidelines of ISO10993-5. Briefly, the samples were immersed in the medium at 37°C for 24 hours (sample area / media volume = 1.25 cm 2 / mL). Cell viability was evaluated using the CCK-8 method. Mouse embryonic osteoblast precursor cells MC3T3-E1 (2×10^ 3 cells / well) were seeded in 96-well plates and incubated at 37°C and 5% CO 2 for 24 hours. Subsequently, the growth medium was replaced with the sample extracts (100 μL) for further culture. DMEM was used as a negative control. CCK-8 solution (10 μL) was added to each well on days 1, 3, and 5, and then incubated for 2 hours. The optical density (OD) value at a wavelength of 450 nm was measured using a microplate spectrophotometer (Biotek, USA).

[0067] Test steps: ① Cultivate bacteria; ② Inoculate the bacteria into the sample immersion solution; ③ Calculate the number of surviving cells; ④ Calculate the antibacterial rate.

[0068] Table 3 Antibacterial rate results

[0069] Example 1 Example 2 Example 4 Comparative Example 1 Component Titanium alloy - iron - zinc Titanium alloy - zinc Titanium alloy Zinc Inhibitory rate against Staphylococcus aureus (%) 99.69±1.36 97.35±1.02 18.89±2.70 90.45±2.10 Inhibitory rate against Escherichia coli (%) 98.34±0.94 91.26±1.95 17.06±3.10 89.04±1.40

[0070] Test conclusion: The heterogeneous structure of titanium alloy-iron-zinc has a significant antibacterial effect compared with titanium alloy materials.

[0071] Experimental example 3 Mechanical property determination:

[0072] The elastic modulus and strain of Examples 1-3 were determined. The results of the elastic modulus determination for each group are shown in Table 4 and Figure 9 (b) of, and the results of the strain determination are shown in Figure 9 (a) of.

[0073] Elastic modulus determination detection method: Use a universal testing machine to perform compression tests on the samples. After converting the compression data into stress-strain curves, measure the slope of the linear elastic stage, and the result is the elastic modulus.

[0074] Sample specifications: 10 mm * 10 mm * 10 mm

[0075] Test steps: ① Compression test; ② Data processing; ③ Measurement of the elastic modulus in the linear elastic stage.

[0076] Table 4 Elastic modulus determination results

[0077] Example 1 Example 2 Example 3 Component Titanium alloy - iron - zinc Titanium alloy - zinc Titanium alloy Elastic modulus (GPa) 2.23±0.06 2.42±0.05 0.94±0.05

[0078] Test conclusion: The mechanical properties of the heterogeneous structure of titanium alloy-iron-zinc are significantly improved compared with those of the titanium alloy stent, and still within the range of mechanical property requirements of natural human bone (1-35 GPa).

Claims

1. A method for preparing a heterogeneous structure medical bone implant based on additive manufacturing, characterized in that: The following steps are involved: Step 1: Using the selective laser melting technology, TC4 titanium alloy powder is prepared into a titanium alloy stent with interconnected pores according to a suitable printing strategy (1); Step 2: placing the titanium alloy stent (1) in a chemical polishing solution for polishing; Step 3: The chemically polished titanium alloy bracket (1) is used as a cathode, and the pure iron sheet (2) is used as an anode, and both are immersed in an electroplating solution (3) for electroplating; Step 4: Cast the molten zinc-based metal (7) into a square crucible (5) with a titanium alloy-iron support (6), and place a weight block (9) on top, and cut after cooling.

2. The method for preparing a heterogeneous structure medical bone implant based on additive manufacturing according to claim 1, characterized in that: The titanium alloy stent (1) in step 1 is a rhombic dodecahedron stent.

3. The method for preparing a heterogeneous structure medical bone implant based on additive manufacturing according to claim 2, characterized in that: The design method of the rhombus dodecahedron bracket is as follows: first, a star-shaped honeycomb two-dimensional structure is drawn according to the arc angle r, the cell side length a, and the concave side length b of the star-shaped honeycomb; then, a curved beam is set outside each concave side of the star-shaped honeycomb to obtain a curved beam two-dimensional structure. The law curve of the curved beam is , rad is the unit of radians, x is the horizontal coordinate of the point on the curved beam, y is the vertical coordinate of the point on the curved beam, and the four curved beams are connected end to end through a rectangular block with a side length of h; the star-shaped honeycomb and the curved beam are thickened inwardly, with thicknesses of 0.75h and 0.25h respectively, and then the convex vertex of the star-shaped honeycomb is connected to the rectangle, and the concave vertex of the star-shaped honeycomb is connected to the top of the curved beam through a rectangle with a width of h, thereby combining the star-shaped honeycomb two-dimensional structure and the curved beam two-dimensional structure to generate a two-dimensional modified star-shaped negative Poisson's ratio structure; the two-dimensional modified star-shaped negative Poisson's ratio structure is stretched along the X-axis, and the stretching length is h; the center of the stretched two-dimensional modified star-shaped negative Poisson's ratio structure is restricted to the origin, and replicated along the XY plane and the ZX plane respectively to obtain a unit-cell modified star-shaped negative Poisson's ratio structure; finally, the unit-cell modified star-shaped negative Poisson's ratio structure is arrayed once along the X, Y, and Z axes in turn to obtain 2 2 2 Modified star-shaped negative Poisson's ratio structure array.

4. The method for preparing a heterogeneous structure medical bone implant based on additive manufacturing according to claim 1, characterized in that: The chemical polishing solution in step 2 includes nitric acid, hydrofluoric acid and deionized water, and the volume ratio of nitric acid, hydrofluoric acid and deionized water is (3-8): (1-2): (5-10), the concentration of nitric acid is 1-8 mol / L, and the concentration of hydrofluoric acid is 1-22.5 mol / L.

5. The method for preparing a heterogeneous structure medical bone implant based on additive manufacturing according to claim 1, characterized in that: The polishing time in step 2 is 1 min to 3 min.

6. The method for preparing a heterogeneous structure medical bone implant based on additive manufacturing according to claim 1, characterized in that: The electroplating solution (3) in step 3 is prepared from ferrous chloride particles and deionized water, with a concentration ratio of 200-400 g / L and a pH value of 1.

5.

7. The method for preparing a heterogeneous structure medical bone implant based on additive manufacturing according to claim 6, characterized in that: The electroplating conditions in step three are as follows: the electroplating solution (3) is placed in a 60° C. water bath (4), the current is 100-500 mA, and the duration is 10-50 minutes.

8. The method for preparing a heterogeneous structure medical bone implant based on additive manufacturing according to claim 1, characterized in that: The molten zinc-based metal (7) is obtained by placing the zinc-based metal in a cylindrical crucible (8) and simultaneously heating the mixture to 500-800° C. in a sintering device.

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