Method of producing molybdenum carbide nanoparticles

FIELD: chemistry.

SUBSTANCE: invention can be used in chemical industry and metallurgy. The method of producing molybdenum carbide nanoparticles involves dissolving molybdenum pentachloride in ethanol in ratio of 1:(1-3). Urea is added to the obtained solution. Annealing is then carried out in two steps. At the first step, heating is carried out in a vacuum at a rate of not more than 5°C/min to temperature of 430-450°C. At the second step, heating is carried out in a nitrogen atmosphere to temperature of 550-600°C, followed by holding at said temperature for 2.5-3 hours.

EFFECT: invention lowers the process temperature and enables to obtain molybdenum carbide particles with size of 5-10 nm.

2 dwg, 2 ex

 

The invention relates to methods for nanoscale materials, in particular to a method for producing a carbide of molybdenum with the morphology of the nanoparticles, which are used in the production of steels, corrosion resistant, heat-resistant and heat-resistant material as a reducing agent, deoxidizer, catalyst.

A method of obtaining nanowires of the molybdenum carbide (patent CN 101367521, IPC C01B 31/34, 2009). The method of obtaining consists of several stages: the corresponding molybdate is dissolved in water, obtaining a solution with a concentration of molybdenum 0.02 to 1.5 M can Then spend the intercalation of organic amine in a ratio of amine : Mo 20÷1:1. To the resulting composite is added dropwise acid to establish a pH environment 3-6. This forms a white precipitate. Then the reaction mixture is heated on an oil bath to a temperature of 30-60°C and maintained at this temperature for 6-24 hours, the Final product is filtered, washed, dried, and then annealed in an inert gas atmosphere at a temperature of 675-750°C for 4-10 hours

The disadvantages of this method are the multistage; impurity carbon content on the surface of the molybdenum carbide, reducing the quality of the final product; not a high yield of target product, which does not exceed 95%.

Closest to the proposed technical re the structure is a method for producing nanoparticles of molybdenum carbide (.Giordano, Segre, W.Yao, .Antonietti "Synthesis of Mo and W carbide and nitride nanoparticles via a simple urea glass" route", Nano Lett, 2008, v.8, p.4659-4663). In the known method as precursors used pentachloride molybdenum MoCl5and urea, CO(NH2)2in the ratio of urea : Mo 5÷7:1. Powder pentachloride molybdenum is dissolved in ethanol, then slowly under stirring for 2 hours, add urea. The obtained gel is placed in a furnace and slowly at a heating rate of 3°C/min is heated in a stream of nitrogen for 4 hours to 800° C and kept at this temperature for additional 3 hours. According to x-ray phase analysis of the composition of the product corresponds to the α-Mo2With the cubic system (JCPDS 15-0457). According to transmission electron microscopy (TEM) particle size of the molybdenum carbide is equal to 15-30 nm. According to x-ray analysis particle size equal to 21.1 and 24.7 nm.

The disadvantage of this method for obtaining a sufficiently high temperature annealing (800°C), leading to the growth of nanoparticles of molybdenum carbide.

Thus, the authors faced the task of developing a method of producing molybdenum carbide, which would help to reduce the annealing temperature and to improve the quality of the final product by reducing the particle size.

The problem is solved in the proposed method of obtaining nanoparticles of molybdenum carbide, including RA is the creation of pentachloride molybdenum in ethanol, adding to the urea solution and subsequent annealing, in which pentachloride molybdenum and ethanol taken in a ratio equal to 1:1÷3, respectively, and annealing are in two stages: at a speed of not more than 5°C/min to a temperature of 430-450°C in vacuum, then to a temperature of 550-600°C. in a nitrogen atmosphere, followed by exposure at this temperature for 2.5-3 hours.

At the present time of patent and technical literature is not a method of obtaining nanoparticles of molybdenum carbide composition of the α-Mo2With the cubic system step annealing reaction gel-like mass initially in the vacuum, and then in a stream of nitrogen.

Experimental studies conducted by the authors led to the development of the two-stage method of producing nanoscale carbide molybdenum. Moreover, when carrying out the process in two stages becomes possible to conduct the process at lower temperatures, resulting in smaller particle size of the obtained product, because there are no conditions sintering of small particles into larger ones. The authors experimentally it was found that significant in the preparation of the starting components is the ratio between pentachloride molybdenum and alcohol, for example ethanol. Observe the value in the interval MoCl5: ethanol =1:(1÷3). Compliance with sootnoshenie is in the specified interval, first, it allows for a shorter time to get the original gel-like product composed of a mixture of pentachloride molybdenum, dissolved in ethanol, and urea (15-20 minutes compared to 2 hours in the prototype), and secondly, to increase the speed of heating the gel-like product (up to 5°C/min compared to 3°C/min). A further increase in the heating rate technologically impractical as it may be foaming of the reaction mass and forced her release from the tank. While the authors found that there is no need for compliance with slow heating during the whole process. The need to slow heating exists only in the first phase when heated to a temperature of 430-450°C. under these conditions, the authors experimentally obtain powdery product, so in the second stage, further heating can be performed with an arbitrary velocity. A set of proposed conditions of the process of obtaining the molybdenum carbide allows annealing at 550-600°C to obtain nanosized carbide molybdenum composition of the α-Mo2C the cubic system.

Research conducted by the authors, has led to the conclusion that the particles grain size of 5-10 nm of the molybdenum carbide α-Mo2With the cubic system can only be obtained subject to the pairs of the m process, claimed in the proposed method. Thus, when the temperature of the first stage below 430°C, and the second stage below 550°C in the final product there is the appearance of impurity phases (metallic molybdenum, molybdenum oxide, carbon). When the temperature of the first stage above 450°C, and the second stage above 600°C in the final product appears carbide molybdenum another modification of the morphology of the microparticles.

The proposed method can be implemented as follows. Pentachloride molybdenum MoCl5dissolved in ethanol at a ratio of MoCl5: ethanol =1:(1÷3). Add urea, CO(NH2)2in the ratio of urea: Mo=5÷7:1 and stirred until the formation of gel (approximately 15-20 minutes). Then a gel-like mass loaded into an oven, heated in vacuum at a speed of not more than 5°C/min to a temperature of 430-450°C, and then continue heating in nitrogen atmosphere with an arbitrary velocity to a temperature of 550-600°C and maintained at this temperature for 2.5-3 hours. The resulting product is cooled to room temperature. Certification obtained product is carried out using an x-ray phase analysis (XRD) and transmission electron microscopy (TEM). According to XRD the resulting gray powder is molybdenum carbide composition of the α-Mo2With the cubic system. According to transmission electron microscopy of the particles is of Armida molybdenum have the morphology of nanoparticles with a diameter of 5-10 nm. The particle size calculated from x-ray data analysis using the sherrer equation, does not exceed 10 nm.

The proposed method is illustrated by the following examples.

Example 1. Take 1 g of pentachloride molybdenum MoCl5, dissolved in 1 ml ethanol at a ratio of MoCl5: ethanol =1:1. Added 1.10 g of urea (in the ratio of MoCl5: urea =1:5), was incubated for 20 minutes until its complete dissolution and formation of gel-like mass. Then a gel-like mass loaded into an oven, heated in vacuum at a speed of 5°C./min to a temperature of 430°C, and then continue heating in nitrogen atmosphere with an arbitrary velocity to a temperature of 550°C and maintained at this temperature for 2.5 hours. The resulting product is cooled to room temperature. According to XRD and TEM resulting product has a composition of α-Mo2With the cubic system with lattice parameter a=4,225Å and consists of nanoparticles with a diameter of 5-10 nm. Figure 1 shows the radiograph of α-Mo2C. figure 2 shows an image of the nanoparticles of the molybdenum carbide, obtained with a transmission electron microscope high resolution.

Example 2. Take 1 g of pentachloride molybdenum MoCl5, dissolved in 3 ml of ethanol at a ratio of MoCl5: ethanol =1:3. Add 1.54 g of urea (in the ratio of MoCl5: urea =1:7), soak in ECENA 20 minutes to complete dissolution and formation of gel-like mass. Then a gel-like mass loaded into an oven, heated in vacuum at a speed of 5°C./min to a temperature of 450°C, and then continue heating in nitrogen atmosphere with an arbitrary velocity to a temperature of 600°C and maintained at this temperature for 3 hours. The resulting product is cooled to room temperature. According to XRD and TEM resulting product has a composition of α-Mo2With the cubic system with lattice parameter a=4,225Å and consists of nanoparticles with a diameter of 5-10 nm.

Thus, the authors propose a method for production of nanoparticles of molybdenum carbide, lowering the process temperature and improving the quality of the final product by reducing particle size distribution.

Method for producing nanoparticles of molybdenum carbide, including the dissolution of pentachloride molybdenum in ethanol, adding to the urea solution and subsequent annealing, characterized in that pentachloride molybdenum and ethanol taken in a ratio equal to 1:(1÷3), respectively, and annealing are in two stages: at a speed of not more than 5°C/min to a temperature of 430-450°C in vacuum, then to a temperature of 550-600°C in nitrogen atmosphere, followed by exposure at this temperature for 2.5-3 hours



 

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