RU2483833C2 - Metal compositions - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to powder metallurgy, particularly, to hard-alloy compositions. Proposed composition comprises, at least, one high-strength material powder and, at least, two powders of binder. Said first powder contains cobalt, pre-alloyed by one or several elements of the fourth period of periodic table 3^rd-8^th groups. At least, one further powder of binder us selected from the group of one-element powders of Fe, Ni, Al, Cr or alloy thereof. Further powders of binder do not contain cobalt in preliminarily unalloyed form. Free corrosion potential between high-strength material and said binder first powder measured in air-saturated water at normal pressure and room temperature makes less than 0.300 V while high-strength material has positive polarity.

EFFECT: lower toxicity.

17 cl, 3 tbl, 2 dwg, 4 ex

Description

Compositions consisting of powdered high-strength materials and powdered binder metals are used in industry to obtain, among other things, sintered hard alloys or sprayed powders for surface coating. As carbide, tungsten carbide is indisputably used as the most common carbide, others, such as titanium carbide, vanadium carbide, chromium carbide, tantalum carbide and niobium carbide or their mixed carbides with each other or with tungsten carbide, are used in most cases only as additives. Nitrides are also used. Cobalt is by far the most commonly used binder metal, and binder systems with 2 or 3 elements of Fe, Co and Ni are also used, in sprayed powders also, for example, Mn, Al, Cr. Metal powders such as tungsten, molybdenum, but also elemental carbon are also used as the following inorganic additives. If the hard alloy contains titanium carbonitride as the main component instead of tungsten carbide, then we speak of cermet. Borides are also used as high strength material.

In the majority of cases, cobalt is used as a binder metal in hard alloys and sprayed powders, but also nickel, or an alloy of Fe, Co, and Ni, is also used. In all cases, the binder phase after sintering or thermal metallization by spraying contains parts due to mass transfer with the carbide phase during sintering of the liquid phase or melting, for example, tungsten, chromium, molybdenum and carbon, which come from high-strength material. As a powdered binder metal, either a single-element powder, such as iron, nickel or cobalt powder, or doped powder is used.

The sprayed powder along with the above elements and inorganic additives in the binder phase also contains other elements, such as aluminum, rare earth elements, yttrium.

For decades, there has been a statistically significant increased occurrence of pulmonary fibrosis in the hard alloy industry with a specific appearance that results from handling a pulverized carbide or handling pulverulent compositions to produce a carbide. The syndrome is also referred to as "pneumoconiosis from dust of hard alloys" and is the subject of numerous epidemiological studies and publications. In the conventional production of hard alloys using powder metallurgical production processes, that is, pressing and sintering the powdered compositions of hard alloys, they release dust caused by the process that can penetrate into the lungs. If sliding treatment is used in the sintered or pre-sintered state of the hard alloy, very fine dust also arises that can penetrate into the lungs (“grinding dust”).

During thermal metallization by spraying with carbide sprayed powders, very fine dust also arises (“excessive spraying”).

For 5 years, it is also known that dust of hard alloys at a sufficiently high concentration after inhalation also has an acutely toxic effect on rats. The exact mechanism of action is still unknown. Both components, tungsten carbide and cobalt, do not take this action only on themselves. Therefore, to improve labor protection, there is a strong interest in clarifying the mechanism of action for substituents who have no acute toxic effect or have a greatly reduced effect.

The objective of the proposed invention is the following: to provide cobalt in a composition that equally reduces toxicity during inhalation both during thermal metallization by spraying and during grinding processing of pre-sintered parts of hard alloys ("gray treatment") and sintered hard alloys. The solution to the problem is a composition that contains at least one powder of high strength material and at least 2 binder metal powder, characterized in that the first binder metal powder contains completely cobalt and it is pre-alloyed with one or more elements of 3- 8 groups of the Periodic Table of the Elements, and contains at least one further binder metal powder from the group of single-element powders Fe, Ni, Al, Mn, Cr or their alloys with each other and further binder metal powders do not contain cobalt in pre-alloyed form.

It was unexpectedly found that the acutely toxic effect of the pulverulent compositions of tungsten carbide with cobalt is based on the electrochemical corrosion phenomenon, which leads to increased bioavailability of cobalt after inhalation.

In addition, it was unexpectedly found that cobalt as a binder metal in hard alloy compositions loses its inhalation toxicity if it is doped with iron or another element of groups 3-8 (subgroups IIIa-VIIIa) of the Periodic Table of Elements, but not if they are represented along with unalloyed cobalt. In principle, all metals that are to the left of cobalt in the Periodic Table of the Elements and preferably in the same period, due to their more base character, reduce the tendency to corrosion, while those elements that are more noble, such as copper, have the opposite effect, which can even be confirmed in the case of alloyed copper, which exists as an extraneous phase.

The preferred alloying component of cobalt in the first binder metal is an element of the fourth period and groups 3-8 of the Periodic table of elements. In particular, the preferred alloying component of cobalt in the first binder metal powder is an element selected from the group consisting of Fe, Ni, Cr, Mn, Ti and Al. The first binder metal powder may also contain further elements, such as aluminum and / or copper.

In addition to the first binder metal powder, in most cases further binder metals are required. Particularly preferred are those selected from the group consisting of iron powder, nickel powder, iron-nickel alloy powder, and pre-alloyed iron-nickel powder.

High strength material in most cases is titanium carbide, vanadium carbide, molybdenum carbide, tungsten carbide, or mixtures thereof with each other. In addition, these compounds are known as catalysts for oxygen reduction and as catalysts for reactions occurring in aqueous media according to the oxygen reduction mechanism in the case of metal oxidation:

Co + ½O ₂ + H ₂ O = Co (OH) ₂

In the case of sprayed powders, at least one further additional metal powder in addition to Fe, Ni also contains, for example, the following elements, such as Al, Cr, Mn, Nb, Ta, Ti, but does not contain cobalt, except for inevitable and unintended impurities .

Preferably, the first, containing cobalt and fully alloyed binder metal powder contains from 10 to 50% of the mass. cobalt. Especially preferred is the iron to cobalt content of 1: 1 or more. Suitable are, for example, compositions FeCo 50/50, FeCoNi 90/5/5. This powder along with this may contain even further elements of the iron group.

Further or further binder metal powders not containing cobalt in prealloyed form are preferably based on iron or nickel, i.e. the sum of the iron and nickel contents is at least 50%. The remainder of the powder or powders consists generally of at least 50% iron and nickel. Preferably, a doped powder of the composition can be used as a further binder metal powder: for example, FeNi powder having up to 30% Fe, FeNi 50/50, FeNi 95/5.

The mass ratio of the first binder metal powder to further or further is preferably from 1:10 to 10: 1, particularly preferably from 1: 5 to 5: 1. The person skilled in the art can choose the desired ratio depending on the desired stoichiometry and the presence of doped powders.

Preferably, the following binder metal powders have a BET surface of more than 0.3 m ² / g, preferably more than 0.5 m ² / g, in particular more than 1 m ² / g.

In the industry of hard alloys and sprayed powders, the use of pre-alloyed powders that contain two or more elements from the Fe, Co Ni group and represent the composition of the binder phase relative to these elements is the same as the use of two or three single-element powders to obtain a prior art composition . While the latter option does not reduce toxicity, it is reduced or eliminated due to complete doping of the binder system. Such alloyed powders from hydrogen reduction of oxides or other compounds are commercially available, however, in comparison with single-element powders, they have significant disadvantages, such as the highest oxygen values and poor compressibility. In particular, nickel and iron powders can be obtained by the carbonyl process and achieve very low oxygen values, since the reduction potential of carbon monoxide is greater than that of hydrogen, which is usually used to produce fine doped powders with a specific surface of more than 1 m ² / g.

Therefore, preferred are, for example, compounds which are prepared by a process for preparing a mixture of hard alloys by using a) at least one pre-alloyed powder selected from the group consisting of iron / cobalt and iron / nickel / cobalt; b) at least one single-element powder selected from the group consisting of iron and nickel or one pre-alloyed powder selected from the group consisting of iron / nickel, which is different from components a); c) a powder of high-strength material, the composition of the substance expressed by the gross formula of components a) and b) together contains a maximum of 90% of the mass. cobalt and a maximum of 70% of the mass. nickel. Preferably, the iron content is at least 10% by weight.

In a preferred embodiment of the invention, this is a method for producing a mixture of hard alloys according to claim 1, wherein the composition of the substance, expressed by the gross formula of the binder, is With a maximum of 90% by weight, Ni a maximum of 70% by weight and Fe, at least 10 wt. -%, and the iron content satisfies the inequality

$$\text{Fe}\ge \text{one hundred\%}-\frac{\text{\%}\text{Co}\cdot \text{90\%}}{\text{(\% Co}+\text{\% Ni)}}-\frac{\text{\% Ni}\cdot \text{70\%}}{\text{(\% Co}+\text{\% Ni)}}$$

(where Fe: iron content in% mass.,% Co cobalt content in% mass.,% Ni: nickel content in% mass.),

moreover, at least two binder powders are used, wherein the binder powder has a lower iron content than the composition of the substance expressed by the gross formula of the binder, and other binder powders have a higher iron content than the composition of the substance expressed by the gross formula a binder and at least one binder powder is used, pre-alloyed with at least two elements selected from the group consisting of iron, nickel and cobalt.

Since during thermal metallization by sputtering and also during sintering of the liquid phase of the pressed compositions to obtain sintered hard alloys, a chemical equilibrium arises between the binder phase and the carbide phase, as well as between the molten particles of the binder metal powders, from the point of view of materials this is sufficient for using a single-element powder, while from a toxicological point of view, according to the above examples, only complete preliminary doping of the cobalt content is satisfactory the content of iron, nickel, manganese, chromium or titanium, and the remaining residue of the desired composition of the gross formula of the binder metal phase, which, for example, regulate the iron and / or nickel content or the content of the following metals, are in the form of corresponding single-element powders or FeNi-doped powders. Such new modes of action in the preparation of the compositions make it possible to satisfy both aspects (toxicology and oxygen content or control of carbon content after sintering). Moreover, in addition, it is preferable that only the partial use of pre-alloyed powders significantly improves the compressibility relative to the exclusive use of pre-alloyed powders.

Therefore, compositions according to table 1 are particularly preferred, wherein the first and further binder metal powder are contained in a 1: 1 ratio:

Table 1 No. The composition of the first binder metal powder The ratio of alloying elements of the first binder metal powder The composition of the further binder metal powder The ratio of alloying elements of the following powder of the binder metals 1.01 FeCo 50:50 FeNi 30:70 1.02 FeCoNi 90: 5: 5 FeNi 30:70 1.03 FeCo 50:50 FeNi 50:50 1.04 FeCoNi 90: 5: 5 FeNi 50:50 1.05 FeCo 50:50 FeNi 95: 5 1.06 FeCoNi 90: 5: 5 FeNi 95: 5 1.07 Crco 50:50 FeNi 30:70 1.08 CrCoNi 90: 5: 5 FeNi 30:70 1.09 Crco 50:50 FeNi 50:50 1.10 CrCoNi 90: 5: 5 FeNi 50:50 1.11 Crco 50:50 FeNi 95: 5 1.12 CrCoNi 90: 5: 5 FeNi 95: 5 1.13 Mnco 50:50 FeNi 30:70 1.14 Mnconi 90: 5: 5 FeNi 30:70 1.15 Mnco 50:50 FeNi 50:50 1.16 Mnconi 90: 5: 5 FeNi 50:50 1.17 Mnco 50:50 FeNi 95: 5 1.18 Mnconi 90: 5: 5 FeNi 95: 5 1.19 TiCo 50:50 FeNi 30:70 1.20 TiCoNi 90: 5: 5 FeNi 30:70 1.21 TiCo 50:50 FeNi 50:50 1.22 TiCoNi 90: 5: 5 FeNi 50:50 1.23 TiCo 50:50 FeNi 95: 5 1.24 TiCoNi 90: 5: 5 FeNi 95: 5 1.25 Alco 50:50 FeNi 30:70 1.26 Alconi 90: 5: 5 FeNi 30:70 1.27 Alco 50:50 FeNi 50:50 1.28 Alconi 90: 5: 5 FeNi 50:50 1.29 Alco 50:50 FeNi 95: 5 1.30 Alconi 90: 5: 5 FeNi 95: 5 1.31 Vco 50:50 FeNi 30:70 1.32 Vconi 90: 5: 5 FeNi 30:70 1.33 Vco 50:50 FeNi 50:50 1.34 Vconi 90: 5: 5 FeNi 50:50

1.35 Vco 50:50 FeNi 95: 5 1.36 Vconi 90: 5: 5 FeNi 95: 5 1.37 FeCoNi 50:50 FeNi 50:50 1.38 FeCoNi 90: 5: 5 Ni one hundred 1.39 FeCoNi 50:50 Fe one hundred 1.40 CrCoNi 90: 5: 5 FeNi 50:50 1.41 CrCoNi 50:50 Ni one hundred 1.42 CrCoNi 90: 5: 5 Fe one hundred 1.43 Mnconi 50:50 FeNi 50:50 1.44 Mnconi 90: 5: 5 Ni one hundred 1.45 Mnconi 50:50 Fe one hundred 1.46 TiCoNi 40:20:40 FeNi 50:50 1.47 TiCoNi 40:20:40 Ni one hundred 1.48 TiCoNi 40:20:40 Fe one hundred 1.49 Alconi 40:20:40 FeNi 50:50 1.50 Alconi 40:20:40 Ni one hundred 1.51 Alconi 40:20:40 Fe one hundred 1.52 Vconi 40:20:40 FeNi 50:50 1.53 Vconi 40:20:40 Ni one hundred 1.54 Vconi 40:20:40 Fe one hundred

Further preferred are the compositions of tables 2 and 3.

Table 2: Table 2 shows 54 compositions with numbers from 2.01 to 2.54, whose first binder metal powders, whose further binder metal powders and the ratio of the doped elements of the first binder metal powder and the further binder metal powder are identical to those from table 1, the first and the further binder metal powder is contained in a ratio of 1: 2. That is, for composition 2.01, the first doped powder is FeCo 50/50, the further doped powder is FeNi 30/70, and the ratio of FeCo to FeNi is 1: 2.

Table 3: table 3 shows 54 compositions with numbers from 3.01 to 3.54, whose first binder metal powders, whose further binder metal powders and the ratio of the alloyed elements of the first binder metal powder and the further binder metal powder are identical to those from table 1, the first and further binder metal powder is contained in a ratio of 2: 1. That is, for composition 3.01, the first doped powder is FeCo 50/50, the next doped powder is FeNi 30/70, and the ratio of FeCo to FeNi is 2: 1.

Therefore, the invention relates to metal compositions that contain at least one powder of high strength material and at least 2 powder of a binder metal, characterized in that the first powder of the binder metal contains cobalt completely and it is pre-alloyed with one or more elements of groups 3-8 of the Periodic table of elements that are elements of the fourth period, and contains at least one further powder of binder metals from the group of single-element powders Fe, Ni, Al, Mn, Cr or their alloys with each other and further binder metal powders do not contain cobalt in a pre-alloyed form;

or

metal compositions containing at least one powder of high strength material and at least 2 binder metal powder, characterized in that the first binder metal powder contains cobalt completely and is pre-alloyed with one or more elements from group 3-8 of the Periodic table of elements, and contains at least one further binder metal powder from the group of single-element powders Fe, Ni, Al, Mn, Cr or their impurities with each other and further binder metal powders do not contain viola in pre-alloyed form, while the free corrosion potential between the high-strength material and the first binder metal powder, measured in air-saturated water at normal pressure and room temperature, is less than 0.300 V (preferably less than 0.280 V), and the high-strength material has a positive polarity ;

or

metal compositions containing at least one powder of high strength material and at least 2 binder metal powder, characterized in that the first binder metal powder contains cobalt completely and is pre-alloyed with one or more elements from group 3-8 of the Periodic table of elements, and at least one further binder metal powder is used selected from the group consisting of iron powder, nickel powder, FeNi-doped powder and pre-FeNi-doped powder and further binder metal powders do not contain cobalt in pre-alloyed form. In all of the three above metal compositions, high strength materials may include, in particular, titanium carbide, vanadium carbide, molybdenum carbide or tungsten carbide, which preferably has a BET surface of more than 0.3 m ³ / g, preferably more than 0.5 m ² / g , particularly preferably greater than 1 m ² / g.

In further embodiments of the invention, in the case of the above metal compositions, the cobalt alloying partner in the first binder metal powder is an element of the fourth period; or in the above metal compositions, the cobalt alloying partner in the first binder metal powder is an element selected from the group consisting of Fe, Ni, Cr, Mn, Ti and Al;

or

in the above metal compositions, the first binder metal powder may contain further alloyed elements, and aluminum and / or copper (Cu) can be used as further elements.

In further embodiments of the invention, in the above metal compositions, along with the first binder metal powder, there is one or more further binder metal powders selected from the group consisting of iron powder, nickel powder, FeNi-doped powder and pre-FeNi-doped powder.

Preferably, in the case of all the above metal compositions, the free corrosion potential between the high strength material and the first binder metal powder, measured in air-saturated water at normal pressure and room temperature, is less than 0.300 V, the high strength material having a positive polarity.

As high-strength material, titanium carbide, vanadium carbide, molybdenum carbide or tungsten carbide, which preferably has a BET surface of more than 0.3 m ³ / g, preferably more than 0.5 m ² / g, particularly preferably more than 1 m ² / g, may be contained. .

In all such metal compositions, the weight ratio of the first binder powder to further or further binder metal powders is preferably from 1:10 to 10: 1.

All such metal compositions may preferably contain: a) at least one pre-alloyed powder selected from the group consisting of iron / cobalt and iron / nickel / cobalt; b) at least one powder element selected from the group consisting of iron and nickel or pre-alloyed powder consisting of iron and nickel, which is different from component a); c) a powder of high strength material, the composition of the substance expressed by the gross formula of components a) and b) together contain a maximum of 90% of the mass. cobalt and a maximum of 70% of the mass. nickel. In the case of such a metal composition, the iron content is preferably at least 10% of the mass. In the case of such a metal composition, the composition of the substance, expressed by the gross formula of the binder, is preferably Co at most 90% by mass., Ni at most 70% by mass. and Fe, at least 10 wt. -%, and the iron content satisfies the inequality

$$\text{Fe}\ge \text{one hundred\%}-\frac{\text{\%}\text{Co}\cdot \text{90\%}}{\text{(\% Co}+\text{\% Ni)}}-\frac{\text{\% Ni}\cdot \text{70\%}}{\text{(\% Co}+\text{\% Ni)}}$$

(where Fe: iron content in% mass.,% Co cobalt content in% mass.,% Ni: nickel content in% mass.),

moreover, at least two binder powders are used, wherein the binder powder has a lower iron content than the composition of the substance expressed by the gross formula of the binder, and the other binder powder has a higher iron content than the composition of the substance expressed by the gross formula a binder, and wherein at least one binder powder is pre-alloyed with at least two elements selected from the group consisting of iron, nickel and cobalt.

Such metal compositions are preferred for various applications and such metal compositions can be used to produce sintered hard alloys, or to obtain porous sintered agglomerates. Such a porous agglomerate is obtained by sintering without pressing one of the above metal compositions.

Further suitable are thermally sprayed powders that contain such a porous agglomerate that can be obtained by sintering without pressing one of the above metal compositions and contains aluminum, yttrium and / or rare earth elements.

Further, the proposed invention relates to a method for controlling the toxic effect of cobalt-containing metal compositions, characterized in that one of the above metal compositions, preferably the metal compositions shown in Tables 1-3, are used to produce sintered hard alloy or porous sintered agglomerates.

In general, the proposed invention provides a method for controlling the toxic effect of cobalt-containing metal compositions, characterized in that in the metal composition, cobalt is pre-alloyed with one or more elements from groups 3-8 from the Periodic table of elements.

Therefore, the proposed invention also relates to a method for controlling the toxic effect of cobalt-containing metal compositions, wherein the metal composition according to the invention, the porous agglomerate according to the invention or the thermally sprayed powder according to the invention are used to produce molded parts or coatings. In a method for controlling the toxic effect of cobalt-containing metal compositions, the toxicological effect includes, in particular, pulmonary fibrosis and / or the syndrome of "pneumoconiosis from dust of hard alloys".

Since the high bioavailability of cobalt is based on an electrochemical corrosion phenomenon, according to the invention, the free corrosion potential between a high-strength material and the first binder metal powder, measured in air-saturated water at normal pressure and room temperature, is less than 0.380 V, preferably less than 0.330 V, in particular less than 0.300 V and most preferably less than 0.280 V, with tungsten carbide having a positive polarity. The figure 1 schematically represent the applicable test setup. Reference sign 1 denotes positive electrodes of tungsten carbide (or other high-strength material), 2 denotes negative electrodes of a binder metal, for example, consisting of cobalt or a binder metal composition according to the invention, 3 denotes a reaction medium saturated with drinking water.

However, contact stress decreases unexpectedly if cobalt is alloyed with iron, although iron is less noble than cobalt. The reason for this phenomenon is not known. It is easy to see that due to the incident free corrosion stress, the driving force of the corrosion phenomenon is reduced or it proceeds more slowly, and the bioavailability is also reduced. Therefore, the free corrosion stress of the measuring apparatus described in Example 4 can serve as an indicator for the expected inhalation toxicity of a high strength binder metal composition. The next indicator for the expected inhalation toxicity is the dissolved amount of the binder metal, which passes into the solution as soon as the corresponding contact element comes into contact with water in the presence of oxygen after a certain period of time.

The reason for the phenomena of inhalation toxicity, which can only be explained by the intense interaction of the body with inhaled dust, should be responsible for the synergistic effect of both components of cobalt and high-strength material, since both, as proved, do not show this behavior, which is known in the literature. Since, in addition, in the proposed invention, a dependence on the intensity of geometric contacts of both components was found, the increased biological assimilation caused by corrosion suggests itself as an explanatory concept for a toxicological effect.

Carbide has long been known as a contact corrosion element, it is known, for example, that water-based coolants, such as, for example, are used to polish hard alloys, preferably cobalt is removed by dissolution from the hard alloy. In the dissertation, zur Megede (University of Frankfurt, 1985) describes in detail the mechanism: cobalt corrodes in the presence of water and oxygen according to the principle of oxygen reduction and forms a hydroxide layer on the surface that has a passivating effect. Tungsten carbide catalyzes the transition of electrons during the formation of a hydroxide anion, so that corrosion is greatly accelerated and proceeds topotactically. Thus, the passivating effect damages the hydroxide layer. This also clarifies why, when opening a lung subject to pneumoconiosis from hard alloy dust, tungsten carbide is found, but does not detect cobalt, it obviously corrodes and is absorbed rapidly. Thus, the increased bioavailability of cobalt in lower doses / concentrations leads to chronic diseases (pulmonary fibrosis or "pneumoconiosis from dust of hard alloys"), in the case of high concentrations, to acutely toxic phenomena. Biologically assimilable cobalt has still not fully clarified, a negative effect on the body. Explanatory concepts include the deposition of ionic cobalt on DNA or the stabilization of reactive oxygen species, such as, for example, the peroxide oxide by complexation, than cobalt is known for.

In the case of hard alloys and carbide sprayed powders, the corrosion resistance, which is determined by chemical corrosion on a binder, can be improved by the addition of chromium carbide or metallic chromium to the composition. In both cases, chromium after agglomeration or thermal metallization by spraying is partially doped in a binder. With a sufficiently high concentration of chromium in the binder, which is regulated through the carbon balance, the hard alloy or the sprayed layer in this case is much more resistant to corrosion, which suggests that when polishing such hard alloys or over-spraying compared to pure WC-Co be obviously less toxic. The following improvement in corrosion resistance can be further achieved by replacing cobalt with nickel, which in the case of hard alloys is normal industrial practice.

In total, the acutely toxic effect of dust of hard alloys can be explained by the corrosion rate in the presence of water and oxygen. Free corrosion stress can be reduced by alloying cobalt with, for example, iron, as a result of which a composition containing cobalt, and cobalt pre-alloyed with iron, is at least less acutely toxic when breathing. These results are supported by the fact that sintered hard alloys, whose binder phase contains cobalt and iron, in the presence of air have better corrosion resistance against oxidizing acids than those bound by pure cobalt (TU Wien, Dissertation of Wittmann, 2002).

It can be predicted that the intermediates in the preparation of the hard alloy can be especially toxic during inhalation, this includes the polishing of the pre-sintered parts of the hard alloys (“gray treatment”). Here, the composition is pressed and sintered at temperatures within the eutectic of the alloys (“pre-sintering”), thus, bridges of sintered materials form sufficient mechanical stability so that the sintered preform can be processed by polishing. In this state, the sintered preform is still porous, no longer contains organic additives, and the powders used have not yet been equal in composition, so that cobalt is still largely elemental. Therefore, together with the porous structure of grinding dust, very high inhalation toxicity is expected. Also, for the case that metal iron powder is also used along with cobalt metal powder to obtain a composition, it is not necessary to take into account the reduction in toxicity, since during preliminary sintering, practically no interdiffusion (= doping) between cobalt and iron particles occurs.

Because of their size, sintered powders sintered from granular compositions are only difficult to disperse in air, but the fraction of fine fractions that can penetrate into the lungs, which, when the powder is processed, arises due to internal friction, is very toxic (see Example 1e).

Compositions according to the invention can be used, for example, to obtain sintered hard alloy or porous sintered agglomerates, and porous sintered agglomerates can preferably be used in thermally sprayed powders. In particular, carbides with FeCoNi-based binder systems, depending on the composition, in many applications offer technical advantages relative to those bonded with pure cobalt, and are therefore particularly preferred according to the invention.

According to the invention, pre-alloyed powder is understood to mean metal powder, which in each powder particle contains a distributed composition of a binder with respect to the content of Fe, Co and Ni already at the atomic level. According to the invention, preferred powders can be obtained from atomized melts or by precipitation and reduction, for example, according to US patent 6554885, European patent application EP 1079950, as well as the references therein obtained doped powders, or by other, in principle suitable, such as carbonyl method, plasma method, chemical vapor deposition method, etc., wherein doped powders obtained by precipitation and reduction, for example, according to US Pat. No. 6,554,885, European Patent Application nt EP 1079950 and references cited therein are preferred. The preparation of carbide sprayed powders corresponds to the production of hard alloys to obtain granular compositions, however, the granules are not pressed, but as such they are sintered at temperatures both lower and slightly higher than the lowest eutectic temperature, and then sieved. The contained organic additives are then removed. The particles thus obtained are still porous and have necks of sintered materials between particles representing the phase of the binder metals and high-strength materials.

The sprayed powders along with the above elements and inorganic additives in the binder phase also contain other elements, such as aluminum, rare earth elements, yttrium.

Compositions for the preparation of hard alloys and sprayed powders along with the above-mentioned inorganic constituents contain in most cases also organic additives such as paraffins, polyethylene glycols, inhibitors, which facilitate further processing and use, but are no longer contained in sintered hard alloys or after firing in the sprayed powder . These compositions may be granulated, for example, by spray drying. Plasticizers, such as those used in continuous casting, for example polyethylenes, along with paraffin waxes, and adhesion enhancers, such as carboxylic acids and dispersants, may also be contained.

Industrial compositions of high-strength material and binding metals always also contain oxygen, since the surface of the powder due to application in air, grinding with stirring in aqueous liquids and subsequent drying is filled with air and hydroxides. In the subsequent heat treatment, the resulting oxygen interacts with the carbon contained in the carbides or in elementary form in the composition to form carbon monoxide and carbon dioxide, and thus interferes with the precisely maintained equilibrium between the metal content and the carbon content of the sintered preform or sprayed powder. It is generally believed that the oxygen content in the composition should be as low as possible so that the metal / carbon balance can be better controlled.

Examples

All examples are carried out in the form of inhalation studies according to EEC (Appendix II.5.23) using Huntington Life Sciences Ltd., Cambridge, GB, on behalf of the applicant. The test powder is sprayed as an aerosol and the chambers containing 10 rats are ventilated. The aerosol concentration is set in mg / l, the average particle size in microns. Share> 7 μm as a percentage; hours in abbreviated hours. The dust concentration, as well as its particle size distribution, is determined in a chamber (Marple Cascade Impactor Mod. 298, manufactured by Graseby Andersen Inc, Atlanta, Georgia). After 4 hours, the number of dead or dying rats is determined and the total mortality rate is indicated.

Example 1) Inhalation Toxicity of WC / Co Compositions

a) a mixture of tungsten carbide / cobalt receive according to international patent application 01/46484. It contains 10% cobalt. This mixture is characterized by a very close contact between cobalt and tungsten particles. The result of an inhalation test at a concentration of 0.25 mg / L was a mortality rate of 100%. The average particle size in the chamber is 2.5 μm with 90% of the particles below 7 μm.

b) get a mixture of tungsten carbide with metal powder of cobalt, which contains 10% of the mass. cobalt, inhalation test is repeated in three concentrations:

Effective concentration Mortality rate Average particle size Share <7 μm 0.24 thirty four 75 0.52 one hundred 4.2 74

c) a mixture of cobalt and tungsten carbide is obtained, which contains 6% cobalt. The results of an inhalation test at effective aerosol concentrations of 0.26 mg / L were: 0%, but 20% 3 days after the end of the chamber loading with an aerosol. The average particle size is 3.8 μm, 79% of all particles <7 μm.

d) grinding with stirring a mixture of tungsten carbide with cobalt containing 10% cobalt is carried out in the form of a dispersion in hexane for 4 hours. After the grinding is finished, paraffin wax is added, so that, based on the solids content, a mass fraction of paraffin of 2% is obtained. in the composition. After 4 hours of grinding with stirring, the hexane is separated by distillation in vacuo, so that a paraffin-containing powder occurs. In this case, an inhalation test is carried out at three concentrations of aerosols with the following results:

Effective aerosol concentration Mortality rate Average particle size Part <7 μm 0.24 0% 3.2 87 1,08 twenty% 4.2 83

e) a porous, sintered powder of tungsten carbide and cobalt with 17% cobalt and an established particle size distribution between 5 and 30 mm was tested in an inhalation study with the following result: the effective concentration of aerosol is limited between 1.01 and 0.93 mg / l, the mortality rate 60%, the average particle size in the chamber is measured between 5.2 and 5.6 microns, about 20% of particles <7 microns.

The results show that the inhalation toxicity of the WC / Co compositions depends on various influencing factors.

The highest toxicity is shown in example a). Due to the production method, there is a maximum of contacts between particles of cobalt and tungsten carbide.

Example b), which in the form of a powder mixture has significantly fewer contacts between particles of cobalt and tungsten carbide, is the least toxic.

Example c) also shows in the form of a mixture of powder, but with a reduced cobalt content, again the smallest action.

Example d), carried out with 2 concentrations, shows once again a reduced toxic effect. Since the contact between cobalt particles and tungsten carbide can be very intense due to grinding in a fine grinding mill, the reduced toxicity is explained by the paraffin wax contained (2% of the mass corresponds to 25% of the volume).

Example e) shows the toxicity of a typical thermal spray metallization powder. It is observed here that lung permeability due to relatively large particles is only partially reduced, and yet significant mortality occurs.

If examples a) -f) are compared, then it is recognized that, along with the passage of the lungs and the possible content of water-repellents, the intensity of contacts between Co and WC is the magnitude of the main effect on the level of inhalation toxicity.

Example 2) Inhalation Toxicity of WC / FeCo Compositions

a) industry-standard grinding dust of hard alloys, such as obtained from irrigation finishing, with a content of 70.6% tungsten carbide, 14.8% cobalt and 12.2% iron, shows an mortality rate of 70% during an inhalation test. In this case, the effective concentration of aerosol is 0.28 mg / L, the average particle size is 4.3 μm, 76% of all particles <7 μm.

b) a mixture of 90% tungsten carbide, 5% iron powder and 5% cobalt metal powder is ground in a fine mill, as described in example 1d), but no paraffin is added. Iron and cobalt due to grinding acting deformation are contaminated with each other, and partially mechanically contaminated with each other, but not alloyed with each other. The results of 2 inhalation tests are listed below:

Effective aerosol concentration Mortality rate Average particle size Share <7 μm 0.25 0% 2,8 86 1,03 thirty% 3.2 85

c) the mixture obtained according to international patent application WO 01/46484 contains 5% iron and cobalt, as well as 90% tungsten carbide. In this case, iron and cobalt are completely alloyed with each other. In an inhalation test, the following results are obtained:

Effective aerosol concentration Mortality rate Average particle size Share <7 μm 0.988 0 3 94 5.03 0 3,7 84

Example a) shows a comparatively very high toxicity in the form of grinding dust from the final processing of carbide, which is common in industrial grinding. The iron content of 12% is due to the removal of the grinding disc and other contaminants, but not the final processing of hard alloys with an iron-containing binder system. The iron content is thus not prealloyed with the cobalt content. This grinding dust according to the invention does not need to be considered as a composition, since it is not obtained intentionally, and the cobalt content is not previously alloyed with iron.

Example b) was obtained using single-element powders of Fe and Co and shows toxicity, which could lie on a similar scale, as well as the composition with 5% Co, ground in a fine grinding mill, without further additives.

Example c) does not show any toxicity, not even at 5 mg / l, despite the fact that here the contact between WC particles and pre-doped FeCo particles is exactly as intense as in example 1a), and it is obtained in the same way.

Example 3) Inhalation Toxicity of WC / FeNi Compositions

An inhalation test is carried out with a mixture of 10% pre-alloyed FeNi 50/50 with 90% tungsten carbide, in which case at an effective aerosol concentration of 0.53 and 5.22 mg / l, a mortality rate of 0% is also found.

An example shows that no acute inhalation toxicity is detected, due to the absence of cobalt.

Example 4) free corrosion stress of contact elements WC / FeCo

The tungsten carbide powder is hot pressed at a temperature of 2200 ° C to obtain dense bodies with a density of 15.68 g / cm ³ , which corresponds to the theoretical density. In addition, cobalt metal powder and pre-alloyed cobalt-iron metal powder (cobalt content of 50%) are completely pressed at a temperature of 1000 ° to obtain dense bodies with almost theoretical density. In the first test, the contact voltage of the tungsten carbide / cobalt carbide galvanic circuit is measured by the fact that two suitably dense products are provided with diverting electrodes for measuring the contact voltage, and this device is partially dipped in air saturated with drinking water. Without flipping both dense bodies to the opposite side, a difference of 0.330 V was measured, with cobalt relative to tungsten carbide having a negative polarity. This difference represents free corrosion stress. When turning solid bodies on the back side (short circuit), a difference of 0.04 mV was measured, and polarity reversal was observed.

The measurement was repeated, with the cobalt portion being replaced by the portion derived from FeCo. The measured value for the free corrosion potential was now 0.240 V while maintaining polarity. During the inversion of dense bodies of FeCo and tungsten carbide, a difference of 0.007 mV was measured, and the polarity reversed.

If examples 1) -3) are compared with each other, it is obvious that the presence of elemental cobalt in contact with tungsten carbide is a necessary prerequisite to cause inhalation toxicity, that the required concentration, however, is at least equal to a factor of 20 or more if cobalt is pre-alloyed with an equal part of iron.

Example 4) shows that the contact voltage or free contact voltage between tungsten carbide and cobalt, which according to the laws of electrochemistry known to a person skilled in the art, finally depends on the concentration of molecular oxygen in water, is significant. Thus, the measured 0.33 V compares well with the value of Mori et al. from 0.301 to 0.384 V (R&HM 21, 135 (2003)) obtained from potentiometric measurements on hard alloys.

However, contact stress decreases unexpectedly if cobalt is alloyed with iron, although iron is less noble than cobalt. The basis of this phenomenon is not known. It is easy to see that due to the incident free corrosion stress, the driving force of the corrosion phenomenon is reduced or it proceeds more slowly, and the bioavailability is also reduced. Therefore, the free corrosion stress of the measuring device described in Example 4 serves as an indicator for the expected inhalation toxicity of a high strength binder metal material composition. The next indicator for the expected inhalation toxicity is the dissolved amount of the binder metal, which passes into the solution as soon as the corresponding contact element comes into contact with water in the presence of oxygen after a certain period of time.

In figure 2, aerosol concentrations are applied in accordance with the death rate and the examples are categorized.

Claims (17)

1. Carbide composition containing at least one powder of high strength material and at least 2 powder of a binder metal, characterized in that the first powder of the binder metal contains completely cobalt and it is pre-alloyed with one or more elements from group 3-8 of the periodic table of elements , which are elements of the fourth period, and contains at least one further powder of a binder metal from the group of single-element powders of Fe, Ni, Al, Mn, Cr or their alloys with each other and far pure binder metal powders that do not contain cobalt in a pre-alloyed form. 2. Carbide composition containing at least one powder of high-strength material and at least 2 powder of a binder metal, characterized in that the first powder of the binder metal contains fully cobalt and it is pre-alloyed with one or more elements from group 3-8 of the Periodic table of elements and contains at least one further binder metal powder from the group of single-element powders of Fe, Ni, Al, Mn, Cr or their alloys with each other, and further binder metal powders not containing Balta in not pre-alloyed form and the free corrosion potential between the high strength material and a first binder metal powder, measured in air-saturated water at normal pressure and room temperature is less than 0,300 V, wherein the high strength material has a positive polarity. 3. Carbide composition containing at least one powder of high strength material and at least 2 powder of a binder metal, characterized in that the first powder of the binder metals contains cobalt completely and it is pre-alloyed with one or more elements from group 3-8 of the Periodic table of elements and contains at least one further binder metal powder selected from the group consisting of iron powder, nickel powder, FeNi-doped powder and pre-doped FeNi-powder and binder metal powders further contain cobalt in not pre-alloyed form. 4. The carbide composition according to claim 2, in which the cobalt alloying element in the first binder metal powder is an element of the fourth period. 5. The carbide composition according to one of claims 1 to 3, in which the cobalt alloying element in the first binder metal powder is an element selected from the group consisting of Fe, Ni, Cr, Mn, Ti and Al. 6. The carbide composition according to one of claims 1 to 3, in which the first binder metal powder may contain further alloyed elements. 7. The carbide composition according to claim 6, in which Al and / or Cu is used as an additional alloying element. 8. The carbide composition according to claim 1 or 2, in which, along with the first binder metal powder, one or more further binder metal powders selected from the group consisting of iron powder, nickel powder, FeNi-doped powder and pre-doped FeNi- can be used powder. 9. The carbide composition according to claim 1 or 3, in which the free corrosion potential between the high-strength material and the first binder metal powder, measured in air-saturated water at normal pressure and room temperature, is less than 0.300 V, and the high-strength material has a positive polarity. 10. The carbide composition according to one of claims 1 to 3, in which the high-strength material contains titanium carbide, vanadium carbide, molybdenum carbide or tungsten carbide. 11. The carbide composition of claim 10, in which the powder of high strength material has a BET surface of more than 0.3 m ² / g, preferably more than 0.5 m ² / g, particularly preferably more than 1 m ² / g 12. The carbide composition according to one of claims 1 to 3, in which the mass ratio of the first binder powder to further powder or binder metal powders is from 1:10 to 10: 1. 13. The carbide composition according to one of claims 1 to 3, which contains a) at least one pre-alloyed powder selected from the group consisting of iron / cobalt and iron / nickel / cobalt; b) at least one single-element powder selected from the group consisting of iron and nickel or pre-alloyed powder consisting of iron and nickel, which is different from component a); c) a powder of high strength material, the composition of the substance expressed by the gross formula of components a) and b) together containing a maximum of 90 wt.% cobalt and a maximum of 70 wt.% nickel. 14. The carbide composition of claim 13, wherein the iron content is at least 10 wt.%. 15. The carbide composition according to claim 1, in which the composition of the substance, expressed by the gross formula of the binder, is With a maximum of 90 wt.%, Ni a maximum of 70 wt.% And Fe, at least 10 wt.%, And the iron content satisfies the inequality
$$Fe\ge \mathrm{one\; hundred}\%-\frac{\%Co\cdot 90\%}{(\%Co+\%Ni)}-\frac{\%Ni\cdot 70\%}{(\%Co+\%Ni)}$$

,
where Fe is the iron content in wt.%,% Co is the cobalt content in wt.%,% Ni is the nickel content in wt.%,
wherein at least two binder powders are used, wherein one binder powder has a lower iron content than the composition of the substance expressed by the gross formula of the binder, and the other binder powder has a higher iron content than the composition of the substance expressed by gross a binder formula, and at least one binder powder preliminarily doped with at least two elements selected from the group consisting of iron, nickel and cobalt is used. 16. The use of carbide composition according to one of claims 1 to 15 to obtain a sintered hard alloy. 17. The use of carbide composition according to one of claims 1 to 15 for obtaining porous sintered agglomerates.

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