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  • C04B35/48—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on zirconium or hafnium oxides, zirconates, zircon or hafnates
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Definitions

• the present invention relates to a process for the production of metallic or ceramic moldings from thermoplastic molding compositions comprising powdered metals, powdered metal alloys or powdered ceramics and organic binders.
• the first binders for the powder injection molding process were generally based on blends of polyethylene or polypropylene and wax.
• the green body is first liberated from the wax by melting and the residual binder burned out by a slow pyrolysis.
• the green parts For melting, the green parts must be stored in a powder bed, because the green strength is practically not given by the melting.
• Later binder systems for thermal debinding dispensed with the melting, because the elaborate embedding of the green parts in powder and subsequent excavation are far too time-consuming.
• an improved binder system for complete thermal debindering consists of several components, e.g. in DE 1992 5197. These components are released successively during heating at different temperatures from the molding, so that the usually lower binder component is still present at least 400 ° C and can be seen as a residual binder.
• a purely thermal debinding takes 1 to 3 days and is thus extremely slow.
• a still further improved process is solvent debindering which employs binder systems containing binder components of varying solubility.
• a binder component is first removed by solvent extraction, after which the remaining, not or very poorly soluble in the solvent residual binder component is again removed by a slow thermal decomposition of the molded part (eg US 4,197.1 18 or EP 501 602).
• the melt area of the residual binder is Steps and a plastic deformation of the powder molded part is therefore inevitable.
• WO 201 1/016718 A1 describes a powder injection molding process in which a binder mixture of a polymer, e.g. POM and a non-polymeric solvent (molecular weight ⁇ 300 g / mol, melting point> RT) is used for the polymer. Initially, the aforementioned solvent is dissolved out or evaporated. The remaining polymer is removed by thermal debinding. A disadvantage of this method is that such binders already evaporate the non-polymeric solvent when mixed with powder and during processing on the injection molding machine. The low molecular weight component is sweated out on the green part surface and pollutes the injection mold. In addition, the green part strength is significantly reduced.
• a binder mixture of a polymer e.g. POM and a non-polymeric solvent (molecular weight ⁇ 300 g / mol, melting point> RT)
• a non-polymeric solvent molecular weight ⁇ 300 g / mol, melting point> RT
• Binder Breaths therefore contain 70 to 30% by volume of a major component.
• EP-A 0 413 231 discloses, for example, a process for producing an inorganic sintered molding in which a mixture of a sinterable inorganic powder and polyoxymethylene as a binder is formed into a green body and the binder is then treated by treating the green body in a gaseous, acidic, eg boron trifluoride or HN0 3 , containing atmosphere is removed. Subsequently, the thus treated green body is sintered.
• Examples of sintered powders are both oxide ceramic powders such as Al 2 O 3 , Zr0 2 , Y 2 O 3 and non-oxide ceramic powders such as SiC, S13N4, and metal powder.
• EP-A 0 444 475 describes binder compositions which are suitable for ceramic molded articles and which, in addition to polyoxymethylene, comprise poly-1,3-dioxolane, poly-1,3-dioxane or poly-1,3-dioxepane as additional soluble polymer or as polymer dispersible in POM aliphatic polyurethanes, aliphatic polyepoxides, poly (C 2 -C 6 alkylene oxides), aliphatic polyamides or polyacrylates or mixtures thereof.
• EP 0 465 940 A1 and DE 100 19 447 A1 describe thermoplastic molding compositions for the production of metallic moldings which, in addition to a sinterable pulverulent metal or a pulverulent metal alloy, contain a mixture of polyoxymethylene homopolymers or copolymers and a polymer which is immiscible therewith as binder.
• Suitable additional polymers include polyolefins, in particular polyethylene and polypropylene, as well as polymers of methacrylic esters such as PMMA (EP 0 465 940 A1).
• DE 100 19 447 A1 describes a binder for inorganic material powder for producing metallic and ceramic shaped bodies, said binder copolymers, a mixture of polyoxymethylene homo- or and a polymer system of polytetrahydrofuran and at least one polymer is selected from C 2- 8-olefins, vinylaromatic rule monomers Vinylestern aliphatic Ci -8- carboxylic acids, vinyl-Ci -8 -alkyl ethers or Ci-12-alkyl (meth) acrylates.
• WO 2008/006776 A1 describes a binder for inorganic material powder for producing metallic shaped bodies, said binder copolymers or a blend of polyoxymethylene and a polymer system selected from C 2- 8-olefins and poly-1, 3-dioxepane or poly-1, 3- Dioxolane are.
• the debindering of the green parts is carried out catalytically using the aforementioned POM binder systems by treating the green part in a gaseous, acidic atmosphere of e.g. Hydrogen halides, formic acid or nitric acid at elevated temperature.
• the Polyoxymethylenhomo- or copolymers are depolymerized residue-free, followed by a slow thermal Restentbind réelle the remaining polymer.
• the melt area of the residual binder is passed through and plastic deformation of the powder molded part is thereby inevitable.
• the residual binder content in the catalytic removal is generally about 10%. Because of the lower residual binder content, the plastic deformation is usually less pronounced than in the solvent debinder, where the residual binder content is usually 30 to 70%.
• powders in which reactions with HNO 3 are not directly apparent are W, V, Mg, Mn and ceramic powders such as AIN and Si 3 N 4 .
• ceramic powders such as AIN and Si 3 N 4 .
• alloys containing reactive metals for example Al- and / or Ti-containing superalloys such as IN713C, MAR 246, GMR 235 and IN 100
• such superficial reactions are not disturbing to the progress of debindering, but the resulting Al - and Ti-containing oxide layers are no longer reducible in the further course of the sintering step and then these alloying elements are not or only partially available for alloying; the material properties of the sintered product are worse or even unusable.
• a catalytic debinding with oxalic acid also for oxidation-sensitive sintered materials such as WC / Co and Cu, described in WO 94/25205.
• the catalytic debinding with oxalic acid is significantly slower in direct comparison with HN0 3 and oxalic acid is problematic as a solid in the dosage, so that it has not yet come to industrial use.
• this residual binder this so-called “backbone”
• the "backbone” must provide for a basic strength in the brown part, in order to transport the brown parts (for example to control measurements, or from the debinding oven into the sintering furnace).
• the residual binder should guarantee the integrity of the molded parts during the early stage of the sintering process, because usually the diffusion processes, which initially lead to contact formation between the powder particles and later to compaction, only at about 600 - 1000 ° C. Below this temperature, a debindered molding without residual binder would correspond to a pure packing of powder particles, quasi a sand castle, ie without any strength.
• the content of the residual binder varies from about 10 to at most 70% by weight of the binder phase, the content being dependent on the primary binder removal method chosen and the type of polymer.
• the residual binder is removed according to the prior art without exception by thermal decomposition.
• the temperature at which the residual binder leaves the brown part is dependent on the polymer chosen and on the choice of furnace protection gas, but is usually in the temperature range 300 to 600 ° C, in particular 400 to 500 ° C.
• thermal Restentbindtation is an additional source of undesirable reactive substances.
• thermal debinding polymer chains are usually cracked and split into shorter chains.
• carbon is produced as a by-product and this carbon is very finely dispersed and reactive. This reactive carbon can in turn be bound by the reactive metals or alloying elements and form further undesirable secondary phases (carbides).
• the residual binder is still of considerable disadvantage for the operation of the sintering furnace, in the heating rate always the thermal decomposition of the residual binder must be taken into account and often there are problems with the control of the carbon content by charring the residual binder.
• the sintering furnace must therefore fulfill a special task in a temperature range (300 to 600 ° C), where the furnace is not easy to control;
• the sintering furnaces are built from the power output for the high temperature range above 1200 ° C. Since sintering furnaces, in particular batch sintering furnaces for MIM, because of the used very expensive, it would be an important cost advantage not to have to take into account the thermal decomposition. The higher heating rate possible without residual binder could reduce the cycle time by 20 to 40%.
• a further disadvantage is that the sintering furnace is burdened by decomposition products of the residual binder, which are led out by elaborate constructions of the furnace and usually must be condensed out, causing considerable maintenance is required.
• the object is achieved in that the debindering takes place in two steps, wherein in a first binder removal step, a first binder fraction is dissolved out of the green parts with a solvent and in a second debinding step the remaining binder fraction is removed by acid catalysis.
• the invention relates to a method for producing a metallic or ceramic molding of a thermoplastic composition containing
• B-i from 50 to 95% by weight of one or more polyoxymethylene homopolymers or copolymers
• B 2 from 5 to 50% by weight of a polymer homogeneously dissolved in Bi) or having a mean particle size of less than 1 ⁇ m in Bi), as binder, and
• the polyoxymethylene homopolymers or copolymers are known as such and are commercially available.
• the homopolymers are usually prepared by polymerization of formaldehyde or trioxane, preferably in the presence of suitable catalysts.
• Polyoxymethylene copolymers which are preferred in the context of the invention also contain trioxane and other cyclic or linear formals or other formaldehyde sources as main monomers.
• the term main monomers is intended to express that the proportion of these monomers in the total amount of monomers, ie the sum of main and comonomers, is greater than the proportion of comonomers in the total amount of monomers.
• POM polymers have at least 50 mole percent of recurring units -CH 2 O- in the polymer backbone.
• Suitable polyoxymethylene copolymers are described in EP-A 0 446 708 (page 3, lines 39 to page 4, line 31).
• the proportion of component B-i) is preferably 50 to 95 wt .-%, particularly preferably 70 to 90 wt .-%, based on the total amount of the binder B).
• the proportion of component B 2 ) is preferably from 5 to 50% by weight, particularly preferably from 10 to 30% by weight, based on the total amount of binder B).
• component B 2 are in principle polymers which are homogeneously soluble in Polyoxymethylenhomo- or copolymers Bi) or dispersible therein in the required particle size.
• Preferred polymers B 2 ) of this type are polyolefins, aliphatic polyurethanes, aliphatic uncrosslinked polyepoxides, polyethers, aliphatic polyamides and polyacrylates, and mixtures thereof.
• the abovementioned preferred polymers B 2 ) are likewise described in EP-A 0 446 708 (page 4, line 34 to page 7, line 12).
• polyethers in particular poly (C 2 -C 6 ) -alkylene oxides, such as polyethylene oxide (PEO), polypropylene oxide, poly-1,3-dioxepane (PDP), poly-1, 3 Dioxolane and polytetrahydrofuran or mixtures thereof, preferably with mean molecular weights (weight average) in the Range of 600 to 50 000 g / mol, more preferably 2000 to 30 000, most preferably 5000 to 20 000 g / mol.
• PEO polyethylene oxide
• PDP polypropylene oxide
• PDP poly-1,3-dioxepane
• Dioxolane polytetrahydrofuran or mixtures thereof
• mean molecular weights weight average
• Corresponding products are commercially available or the corresponding production processes are known to the person skilled in the art, so that further details are unnecessary here. It is also possible to use mixtures of different polyethers and / or polyethers of different molecular weights.
• the inorganic sinterable powder A can be selected from all known suitable inorganic sinterable powders, in particular also reactive and / or oxidation-sensitive powders. Preferably, it is selected from metal powders, metal alloy powders, metal carbonyl powders, ceramic powders, and mixtures thereof, with metallic powders being particularly preferred.
• metals which may be present in powder form are aluminum, iron, in particular carbonyl iron powder, chromium, cobalt, copper, nickel, silicon, titanium, tungsten and rare earths such as Nd, Sm and Y.
• powdery metal alloys are high or low alloy steels and metal alloys based on aluminum, iron, titanium, copper, nickel, tungsten or cobalt. Both powder of finished alloys and powder mixtures of the individual alloy components can be used.
• the metal powders, metal alloy powders and metal carbonyl powders may also be used in admixture.
• Suitable inorganic powders are also oxide ceramic powders such as Al 2 O 3 , Zr0 2 , Y 2 O 3 but also non-oxide ceramic powders such as SiC, S13N4, and more complex oxide powders such as NiZnFe 2 0 4 , and inorganic color pigments such as C0AI2O4.
• the reactive and oxidation-sensitive powders are in particular those of copper, cobalt, Ti, W, V, Mg, Mn, Nd, Sm, Y and their alloys, ceramic powders such as AIN and Si 3 N 4 and alloys of aluminum and / or titanium, so-called superalloys such as IN713C, MAR 246, GMR 235 and IN 100 and to name the alloys known from the magnet technology with the main components Nd-Fe-B and Sm-Co.
• the particle sizes of the powders are preferably from 0.1 to 50 ⁇ m, more preferably from 0.3 to 30 ⁇ m.
• the metal powders, metal alloy powders, metal carbonyl powders, ceramic powders can also be used in a mixture.
• the optionally present as component C) dispersing agent may be selected from known dispersing aids.
• dispersing aids are oligomeric polyethylene oxide having an average molecular weight of 200 to 600, stearic acid, stearic acid amide, hydroxystearic acid, fatty alcohols, fatty alcohol sulfonates and block copolymers of ethylene oxide and propylene oxide, and also polyisobutylene.
• the dispersing aid in an amount of 1 to 5% by volume, based on the components A), B) and C) is used.
• thermoplastic compositions may also contain conventional additives and processing aids which favorably influence the rheological properties of the mixtures during shaping.
• the preparation of the thermoplastic composition used in the process according to the invention can be carried out in a conventional manner in a kneader or extruder at temperatures of 150 to 200 ° C (see, EP-A-0413231). After cooling the mass, it can be granulated.
• the preparation of the thermoplastic mass to be formed by melting the components B) and mixing the components A) and optionally C) take place.
• component B) can be melted in a twin-screw extruder at temperatures of preferably 150 to 220 ° C., in particular 170 to 200 ° C.
• Component A) is then metered at temperatures in the same range in the required amount to the melt stream of component B).
• component A) contains on the surface the dispersant (s) C).
• the preparation of the thermoplastic compositions can also be carried out by melting the components B) and C) in the presence of component A) at temperatures of 150 to 220 ° C.
• thermoplastic molding composition by injection molding
• the usual screw and piston injection molding machines can be used.
• the molding is generally carried out at temperatures of 175 to 200 ° C and pressures of 3,000 to 20,000 kPa in molds having a temperature of 60 to 140 ° C.
• the demolded green compacts are then treated by the process according to the invention according to step a) with a solvent.
• a solvent The choice of solvent depends on the chemical nature of the binder component B 2 ). Solvents for some binder components B 2 ) are given below by way of example only; the solvents for other binder components B 2 ) should be known to the person skilled in the art. Mixtures of suitable solvents can also be used.
• Polyolefins are preferably dissolved in apolar solvents such as pentane, hexane, cyclohexane, octane or benzene, and also in aromatic solvents such as benzene.
• apolar solvents such as pentane, hexane, cyclohexane, octane or benzene
• aromatic solvents such as benzene.
• Polyacrylates (eg PMMA) and polyamides are generally soluble in the following solvents: ethers such as diethyl ether or tetrahydrofuran, ketones such as Methyl ethyl ketone or acetone, esters such as butyrolactone and CrC 4 alcohols such as ethanol.
• Polyethers such as polytetrahydrofuran, poly-1, 3-dioxepane, poly-1,3-dioxolane, polyethylene oxide or polypropylene oxide can be dissolved, for example, in solvents such as tetrahydrofuran or acetone and in CrC 6 -alcohols such as ethanol and isopropanol; Polyethylene oxide could also be dissolved in water.
• water can be used as the solvent for the binder component B 2 ), it is particularly preferred because water provides much easier and more environmentally friendly handling because of its incombustibility.
• this is preferably a conventional corrosion inhibitor, for example modified phosphonates such as amino-tris (methylenephosphonic acid), hydroxyethylamino-di (methylenephosphonic acid) or phosphonobutane-1,2,4-tricarboxylic acid , available eg from Zschimmer & Schwarz.
• modified phosphonates such as amino-tris (methylenephosphonic acid), hydroxyethylamino-di (methylenephosphonic acid) or phosphonobutane-1,2,4-tricarboxylic acid , available eg from Zschimmer & Schwarz.
• Extremely reactive sintering powders A are preferably mixed with aprotic organic solvents such as ethers, esters, amides or ketones, e.g. Tetrahydrofuran, diethyl ether, butyrolactone, dimethylformamide, methyl ethyl ketone or preferably acetone.
• aprotic organic solvents such as ethers, esters, amides or ketones, e.g. Tetrahydrofuran, diethyl ether, butyrolactone, dimethylformamide, methyl ethyl ketone or preferably acetone.
• step a) of the process according to the invention can be carried out in commercially available systems with closed solvent circuit for the purification of machined, contaminated with lubricants workpieces, described by way of example in DE-A 4337129.
• step a) at elevated temperature, d, h. a temperature above room temperature to the boiling point of the solvent, in particular at a temperature of 40 to 120 ° C.
• step a) takes place at the boiling point of the solvent under reflux.
• polyoxymethylene homopolymers and copolymers (POM) used as binder component B -I) or secondary binder for step a) of the process according to the invention are resistant to virtually all common solvents up to 120 ° C. and still guarantee a very high temperature of up to 120 ° C. high strength.
• component B2) in the molding and the solvent can be achieved by replacing the loaded solvent often with fresh solvent and / or the dissolved extract is quickly carried away, for example by a circulation of the surface of the extraction material.
• the treatment with a solvent according to step a) of the process according to the invention is preferably carried out until the binder component B 2 ) is at least 75%, preferably 85%, particularly preferably 90%, removed from the molded part. This condition is generally reached after 4 to 30 hours.
• the required duration of treatment depends on the treatment temperature, on the quality of the solvent for the binder component B 2, the molecular weight of the component B 2, as well as the size of the molding.
• the green parts which are now porous and saturated with solvent, have to be dried according to step b) of the process according to the invention.
• the drying takes place in a conventional manner, for example with the aid of a vacuum drying oven or a heating cabinet.
• the drying temperature is based on the boiling point of the solvent, but should be chosen slightly lower, in order to avoid the risk of a sudden or too fast drying process with possible negative consequences for the quality of the green part.
• the drying is completed in 0.5 to 8 h.
• the acid treatment in step c) of the process according to the invention is preferably carried out at temperatures in the range from 80 to 180 ° C. over a period of preferably 0.1 to 24 hours, more preferably 0.5 to 12 hours.
• the required treatment time depends on the treatment temperature, the concentration and the type of acid in the treatment atmosphere as well as on the size of the molding. Under the usual conditions, generally results in an acid concentration of about 4 to 5% by volume in the atmosphere (i.a., Nitrogen).
• Nitrogen i.a., Nitrogen
• Suitable acids for the treatment in step c) of the process according to the invention are, for example, inorganic gases which are already gaseous at room temperature but at least evaporable at the treatment temperature. Examples are hydrohalic acids and nitric acid. Suitable organic acids are formic acid, acetic acid, or trifluoroacetic acid. Also suitable as acid are BF 3 or its adducts of organic ethers. If a customary carrier gas (inert gas, for example nitrogen) is used for the abovementioned acids, this is generally conducted beforehand through the acid and charged with it. The thus loaded carrier gas is then brought to the treatment temperature, which is suitably higher than the loading temperature in order to avoid condensation of the acid. Preferably, the acid is admixed to the carrier gas via a metering device and the mixture is heated to such an extent that the acid can no longer condense.
• inorganic gases which are already gaseous at room temperature but at least evaporable at the treatment temperature. Examples are hydrohalic acids and n
• suitable and preferred acids for the treatment in step c) of the process according to the invention are those acids which are solid at room temperature and sublimate or melt and evaporate at higher temperatures, including preferably those with a sublimation or melting point between 80 and 200 ° C.
• Particularly preferred are oxalic acid, preferably anhydrous oxalic acid, or oxalic acid dihydrate. It is preferably used a solution of anhydrous oxalic acid in formic acid, acetic acid or mixtures thereof.
• glyoxylic acid is suitable.
• the acids used generally reach the debinding temperature initially in the gas phase, act from here on the remaining binder and desublimate or solidify after cooling on the walls of the binder removal device. In a subsequent debinding process, they return to the gas phase, i. the acid practically does not leave the device.
• the abovementioned acids which are solid at room temperature and sublimate or melt and evaporate at higher temperatures, as a solution in polar solvents, preferably having boiling points below 200 ° C to use.
• polar solvents preferably having boiling points below 200 ° C to use.
• especially acetone, dioxane, ethanol and acetonitrile are suitable, but especially organic acids such as formic acid and / or acetic acid.
• the acid treatment in step c) of the process according to the invention is carried out in the variant with acids which are solid at room temperature and sublimate at higher temperatures or melt and evaporate, preferably at temperatures in the range of 100 to 160 ° C.
• the acid treatment in step c) of the process according to the invention is preferably carried out until the residual binder content in the molding is less than 0.5% by weight, preferably less than 0.3% by weight, very particularly preferably less than 0.2% by weight .-% is.
• step c) of the process according to the invention is often also referred to as catalytic debinding and can likewise be carried out in commercially available plants which function according to the principles described in EP-A 0 413 231.
• the product thus freed from the binder by the process according to the invention can be converted in a customary manner by sintering into the desired shaped body, in particular metallic or ceramic shaped body.
• the sintering may optionally be carried out at an accelerated heating rate of 5 to 10 ° C / min in the temperature range of 200 to 600 ° C. respectively.
• test compounds were homogenized in a cone mixer and homogenized and granulated in a laboratory extruder heated to 190 ° C.
• the molding compound 1 had the following composition:
• the molding compound 2 had the following composition:
• the molding compound 3 had the following composition:
• the molding composition had the following composition:
• the molding compound 5 had the following composition:
• the molding compound 6 had the following composition:
• Figure 1 above shows a view of the component
• Figure 1 below shows a plan view of the component, wherein the position 1 marks the sprue and the position 2 the breaking point by its own weight.
• the length of the component was 100 mm, the weight of the obtained sintered part was about 34 g in the metal powder examples 1 to 5; in Example 6 about 26 g.
• the molding compositions 1 to 5 were melted in the cylinder of the injection molding machine at 190 ° C, the injection mold was heated to 135 ° C.
• the ceramic molding compound 6 was processed at 175 ° C cylinder temperature.
• the required injection pressure was about 1900 bar, only molding compound 3 with a high PEO content and the lower molecular weight 2000 could be processed with 1 100 bar.
• the molding compositions 1 to 6 differed in the cooling time required before demolding.
• the molding compositions with a higher proportion of secondary binders (20% and higher) were somewhat softer and required a longer cooling time in order to be able to demold the green part intact.
• the green parts produced from the molding compositions 1 to 6 were pretreated in a solvent, then subjected to catalytic debinding and sintering. For solvent debinding, the green parts were refluxed in a three-necked flask with a boiling solvent and stirred. Green parts of Examples 1 to 4 were removed after 7 h, 14 h, 21 h and 28 h storage in the solvent, dried and weighed. The green parts of Examples 5a and 6 were reweighed only at the end of storage (28 hours).
• Table 1 shows the results in terms of weight loss as a percent of theory for the solvent primary debinding with acetone:
• Example 3 with the highest PEO content in the molding composition is no longer significantly faster with respect to the solution process. Even at 10% by weight of component B 2 ) in the molding composition (Example 1), the removal is still surprisingly rapid.
• the percent weight loss was based on the total amount of poly-1,3-dioxepane plus dispersant.
• Table 2 shows that the removal of the PEO binder fraction contained in the molded part is also successful in boiling water, albeit at a slower rate than in acetone.
• Catalytic acid debinding carried out after solvent debinding was carried out with the components of Examples 1 to 6 in a 50 L laboratory oven at 110 ° C. It was purged for inerting with 500 L / h of nitrogen, after 1 h 30 ml / h HN0 3 were dosed into it and further purged with 500 l / h of nitrogen oven and evaporated. After 6 h debindering time of all components of the polyacetal portion was at least 98% removed.
• the sintering curve was as follows:
• Example 6 The powder molded articles of Example 6 obtained after the two-stage debindering were sintered in air in a commercial ceramic sintering furnace.
• the sintering curve was as follows and also without holding steps:
• the obtained sintered parts were completely intact, free of defects and had a good sintering density of 6.05 g / cm 3.
• Examples 1 to 6 show that it is possible to produce intact sintered parts without the presence of a residual binder. Due to the now possible abandonment of the usual, slow Ausbrennprogramme a much shorter sintering cycle can be achieved.
• the molding compound 7 had the following composition:
• the tensile bars were conventionally catalytically debinded in a 50-liter oven with 4% by volume HN0 3 in 500 l / h of nitrogen (technically pure) at 140 ° C for 10 h. After binder removal, small, bead-like outgrowths appeared on the surface of the debonded tensile specimens, presumably due to the reaction of magnesium with HN0 3 .
• Example 7 Oxygen content 0.30% 0.24%
• the sintered parts of Comparative Example 1 had as a result of the outgrowths a significantly rougher surface than the sintered parts according to Example 7.
• the sintered parts obtained in Example 7 in comparison to the sintered parts of Comparative Example 1 have a reduced carbon and oxygen content and a higher sintering density. As a result, less brittle materials can be produced from the sintered parts produced according to Example 7, which can be processed more easily.
• the molding compound 8 had the following composition:
• the tensile bars were conventionally catalytically debinded in a 50-liter oven with 4% by volume HN0 3 in 500 l / h of nitrogen (technically pure) at 140 ° C for 6 h.
• the sintered parts according to the invention obtained in Example 8 have in comparison to the sintered parts of Comparative Example 2 a reduced carbon and oxygen content and a higher sintering density.
• the sintered part obtained according to Comparative Example 2 corresponds in the elements C and O only the standard DIN 3.7065, while the sintered part obtained according to the invention according to Example 8 still meets the much stricter standard DIN 3.7035.

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