Crystalline niobium silicide preparation method
FIELD: powder metallurgy.
SUBSTANCE: starting powders of silicon, 40 to 400 mcm, and niobium, below 63 mcm, are taken in proportion (1.33-1.38):1 to form monophase product and in proportion (1.44-1.69):1 to form multiphase product. Powders are subjected to mechanical activation in inert medium for 0.5 to 2 min, ratio of powder mass to that of working balls being 1:20. Resulting powder is compacted and locally heated under argon atmosphere to initiate exothermal reaction producing niobium silicide under self-sustaining burning conditions. Process may be employed in metallurgy, chemistry, mechanical engineering, space, nuclear, and semiconductor engineering, and in electronics.
EFFECT: found conditions for monophase and multiphase crystalline niobium silicide preparation.
The present invention relates to powder metallurgy, in particular to methods for silicides in the mode of self-propagating high temperature synthesis.
The silicides are widely used in metallurgy, chemistry, mechanical engineering, aerospace, nuclear, semiconductor equipment, energy. They differ in many technically important properties - electrical, fireproof, anti-corrosion, wear resistance, which makes them promising inorganic materials for various engineering fields associated with the use of high temperatures, velocities, pressures, corrosive environments.
The known method (patent RF №2076065, 6 Μl. 01 In 33/06, 1997) obtain a silicide of refractory metals comprising preparing a mixture consisting of powders of refractory metals and silicon. According to this method, a mixture is prepared in the following ratio of the components of Mo, W, TA, Ti, or Fe - 23-38 at.% and Si - 62-77 at.% in mechanochemical reactor 20-40 minutes at a centrifugal acceleration of 400-1000 m/s2and the degree of filling of the reactor 0,3-0,6 volume of the reactor. This method of obtaining silicides does not include obtaining niobium silicide.
Also known method (U.S. patent No. 5213730, 6 Μl. From 04 To 35/65, 1995) obtain a composite material consisting of a silicide of a transition metal, including niobium. This way of getting in is cancel the following steps: mixing the starting components, adding a reducing agent, re-mixing, adding a reinforcing filler, forming in raw, coating protective atmosphere, ignition.
Its disadvantages are the complexity and the multi-stage process, and, consequently, large energy and labor.
The closest the result achieved by the declared object is a method of producing niobium silicide by mechanical activation of powders of silicon and niobium in a planetary mill (B.Li, L.Liu and X.M. Ma Amorphization in the Nb - Si system by mechanical alloying/ Journal of allows and compounds, 202, 1993, 161-163). After 150 hours of activation was obtained amorphous powder composition of Nb50Si50.
The disadvantages of this method include the duration of the activation process and the impossibility of obtaining them crystalline product.
The technical result of the present invention is to provide a method for obtaining both multiphase and single-phase crystalline disilicide niobium.
The technical result is achieved by the fact that the source components (powders of silicon dispersion 40-400 μm and niobium particle size less than 63 µm), taken in the ratio of Si:Nb=1,33-1,38:1 for single-phase product and Si:Nb=1,44 was 1.69:1 for multiphase product is subjected to mechanical activation in a planetary mill in argon at a ratio of mass of powder is ka to the weight of the balls, equal to 1:20, for 0.5-2 minutes, followed by pressing, local heating in an inert atmosphere (argon), initiating an exothermic reaction of formation of the crystalline disilicide niobium in the mode of self-sustaining combustion.
Significantly, the ratio of powders of silicon and niobium. When the mixing ratio of Si:Nb less of 1.33:1 and more 1,38:1 it is impossible to get adenopathy product, because with a smaller ratio of the mixture does not burn, but at a higher begins the formation of various phases of the silicides. When the ratio is less than 1.44MB product obtained contains related phase silicide. There is no need to increase the ratio Si:Nb more 1,69:1, since it has already received a multiphase product.
For implementing the method is an important source dispersion powders. When using larger powder particles will require a longer activation time, for smaller - particle powders will not have sufficient surface that is activated by a manual activation.
The ratio of the mass of powder to the weight of the balls determines energyproject process (at constant number of revolutions of the planetary mill). When the decrease in the ratio of mechanical activation will be less intensive and will take a long time grinding for the implementation of the combustion reaction, which is economically the end of LeSabre. When the magnification ratio decreases free volume of mechanoactivation, thereby reducing energyproject process of mechanical activation and, consequently, violated the mode of combustion of a mixture of powders, moving from a stationary surface. Reduced depth conversion and the yield of the final product, there is a strong heating of the drums.
It is important to realize mechanical activation of a mixture of niobium and silicon in the range of 0.5 to 2 minutes. With less duration of activation of the no formation of layered agglomerates and thus it is impossible to make subsequent self-propagating high-temperature synthesis (SHS). Increasing the duration of mechanical activation above 2 minutes later SHS inhibited mechanosensitivity the niobium silicides. Their number increases with the duration of mechanical activation.
The method is illustrated by the following examples.
Example 1. Obtaining single-phase crystalline niobium silicide
The powder of silicon of a purity of 99.7%, the dispersion of 40-400 μm and powder of niobium particle size less than 63 μm is dried from adsorbed moisture at a temperature of 90-120°With (at a lower temperature, the moisture will not evaporate, the greater will be the processes of interaction between particles of silicon and niobium) in a vacuum Cabinet for 2-3 hours (this time is enough and for to which the moisture has evaporated).
Dosing initial components: for single-phase product (NbSi2) the ratio of initial components is Nb - 57 wt.%, Si - 42 wt.%. Loading weight in one drum 30, Therefore, Nb - 17,4 g, Si - 12,6, the Ratio of the mass of powder to the weight of the balls is 1:20. The mass of the powder mixture is 30 g, the mass of steel balls - 600, Environment activation - argon. The time of mechanical activation is 1 minute. The activated powder mixture is pressed into a cylindrical mold to the initial porosity of 30-35%. When using a lower porosity of the extruded samples are fragile and they work hard next, it is likely that they will be destroyed when removed from the mold, using higher density of samples possible other modes of combustion.
Next, the extruded sample is put on a special stand and placed in a bomb constant pressure, the upper end of the sample fall asleep burn the powder mixture (1-2 g) and brought into contact with the originating tungsten spiral. Bomb the constant pressure seal and after twice blowing filled with argon to a pressure of 1 atmosphere. After that elektrospiral serves current 10 a within 1-3 seconds. After the passage of the combustion front, the sample stand to cool and is removed after pressure relief argon is.
The upper surface of the sample are cleaned from combustion products burn the mixture. Obtain 18 g of the synthesized product. The composition of the obtained product was determined by x-ray phase analysis on the installation of the DRONE. According to the results of the analysis of the obtained single-phase crystalline niobium silicide.
Example 2. Getting multiphase crystalline product
All operations carried out analogously to example 1. To obtain the multi-phase product, the ratio of initial components is Nb - 59 wt.%, Si - 13 wt.%. Loading weight in one drum 30 g, i.e. Nb and 17.7 g, Si - 3,9, the Mass of steel balls 600, the Time of mechanical activation for 2 minutes. After the process SHS analogously to example 1 the resulting product analyzed. The result of x-ray phase analysis showed that the resulting multiphase (NbSi2, Nb5Si3, Nb5Si2) crystalline niobium silicide.
The method of obtaining crystalline niobium silicide, including mechanical activation source powders of silicon and niobium in energyprogram apparatus, characterized in that the starting powders of silicon dispersion 40-400 μm and niobium particle size less than 63 μm take in a ratio of 1.33-1,38:1 for single-phase product, and 1.44-1.69 in:1 to obtain a multiphase product, mechanical activation is carried out in an inert atmosphere at a ratio of mA the si powder to the weight of the balls, equal to 1:20, for 0.5-2 min, the resulting powder is pressed, locally heated in an argon atmosphere, initiating an exothermic reaction in the formation of niobium silicide in the mode of self-sustaining combustion.