Method for control of magnetic admixtures content in nanodiamonds of detonation synthesis

FIELD: nanotechnologies.

SUBSTANCE: nanodiamond is placed into installation for annealing, hydrogen is passed through and maintained at the temperature selected from the range of (900÷1100) °C, cooled down to room temperature. X-ray diffraction pattern is taken. Additionally spectrum of electronic paramagnetic resonance (EPR) is registered at room temperature. Availability of metal phases is identified.

EFFECT: invention makes it possible to increase sensitivity of magnetic admixtures content detection in nanodiamonds of detonation synthesis.

2 cl, 6 ex

 

The invention relates to nanotechnology materials, specifically to the processes of production of nanodiamonds by the method of detonation synthesis, and can be used to control the cleaning of magnetic impurities (specifically iron oxide) ultradispersed diamonds produced by the method of detonation synthesis of explosives, and output control (rejection) in their industrial production.

The known method of determination of mineral impurities in diamond /USSR GOST 9206-80. The diamond powders/, which is determined by the availability of inorganic, including magnetic impurities. In accordance with hanging diamond is burned in air atmosphere at 900°C for 6 hours. The result of a measurement is the ratio of the weights of the sample before and after burning.

The method allows to determine the presence and total number of non-combustible impurities in diamond, but does not allow them qualitatively to identify. The sensitivity of this method is about 1×10-4but it does not allow for qualitative identification of impurities.

There is a method of qualitative detection of the presence of iron compounds in carbon materials, in particular in nanodiamonds, by electron paramagnetic resonance (EPR) /Altshuler S.A., Kozyrev BM Electron paramagnetic resonance of compounds of elements of the intermediate groups. The 2nd edition is. M.: Nauka 1972 (672 pages)/. In accordance with register EPR spectrum of the sample material at room temperature, and the presence of a signal in the range of values of g-factor (4.1-4.3) shows the presence of iron compounds.

The sensitivity of the method is less than 1·10-6. The method also allows to determine the presence of Nickel compounds (g-factor 2.1-2.3) and cobalt (g-factor 6.32 or 3.12 depending on the connection type).

A known method of determining the content of relatively large amounts of impurities in the nanopowders is the registration of x-ray diffraction patterns with subsequent identification of the crystalline phases /Weinstein B.K. Modern crystallography (in 4 volumes), volume 1, the symmetry of the crystals. Methods of structural crystallography. M.: Nauka, 1979 (page 383)/.

However, the use of this method to the detonation synthesis nanodiamonds, which passed the standard procedure for chemical cleaning (processing in highly concentrated acids and oxidants /Dolmatov V.Y., Veretennikov M.V., Marchukov, VA, Sushchev V.G. Modern industrial possibilities of synthesis of nanodiamonds. FTT, 2004, volume 46, issue 4, str.596-600 (2004)/), as it was experimentally established, it is not possible to identify the impurity metal compounds. This is due to the lower sensitivity of the method of x-ray diffraction in comparison with the EPR method. B is further, metal compounds in samples of detonation synthesis nanodiamonds, specially alloyed with iron or other metals, also proved impossible to identify the known x-ray method.

The article selected by the prototype of the invention /Aeolianite, Magascene, Ajavon. The intercalation of ultradispersed diamond in aqueous suspensions. FTT, 2004, volume 46, issue 4, str-669 (2004)/, as a way of determining the presence of iron impurity in nanodiamond selected method of registration of x-ray diffraction with the subsequent identification of the crystalline phases formed by iron. It was found that for the detection of the formed crystalline phase of iron compounds in the samples of detonation nanodiamond synthesis of optionally entered by the admixture of iron, you need to register x-ray diffraction to expose the sample nanodiamond annealing (heat treatment in hydrogen at 500°C. However, the sensitivity of the method is insufficient for the detection of iron impurity at a concentration of less than 1%. For example, attempts to identify the impurity metal in the samples of detonation nanodiamond synthesis (without specially introduced impurities of iron) after annealing in hydrogen atmosphere at 500°C did not lead to success.

Thus, the disadvantage of the prototype is the low sensitivity of the op is adelene content of magnetic impurities in nanodiamonds of detonation synthesis, because magnetotactic materials, including the resulting developed by the authors method /Alexinsky AU, vul YA, jagovkina M.A. "Method of cleaning nanolab.", Russian Federation patent for the invention №2322389, priority from 13.10.2006/ for example the level of impurities is not more than 1·10-5.

The present invention solves the problem of increasing the sensitivity of the determination of the content of magnetic impurities in nanodiamonds of detonation synthesis.

The task is solved by a method of controlling the content of magnetic impurities in nanodiamonds detonatsionnogo synthesis, comprising annealing the sample detonation synthesis nanodiamonds in hydrogen atmosphere and then cooled to room temperature, the registration of x-ray diffraction and the identification of metallic phases in which the said annealing is carried out at a temperature selected from the interval (900÷1100)°C.

The authors experimentally found that the sensitivity of the determination of contents of metallic (magnetic) impurities can be greatly increased by changing the conditions of the annealing of the sample of nd, namely the increase of treatment temperature to a temperature in the interval (900÷1100)°C. Rise in temperature above 1100°C leads to a graphitization nd (irreversible changes in properties of the sample), when the annealing temperature less than 900°C, it was found that not p is oshodi significant aggregation of metallic impurities, leading to the formation of crystalline phases detected by x-ray diffraction.

Thus, by changing the conditions of annealing (heat treatment) it was possible to increase the sensitivity to a level that ensures the detection of the background (not made on purpose, and obtain in the process of detonation synthesis) of the impurity metal in nanodiamond.

To improve quality control, by increasing the reliability of determination of the content of magnetic impurities, after the identification of metallic phases additionally carry out the registration of the spectrum of electron paramagnetic resonance at room temperature with subsequent identification of the presence of metal impurities.

This effect is achieved due to the higher sensitivity of the EPR method compared with the method of x-ray diffraction, but manifests itself only after preliminary heat treatment of the sample nd when the annealing temperature corresponding to any value from the interval (900÷1100)°C.

Control of the concentration of magnetic impurities is produced as follows.

Sample nd placed in a special unit for annealing, pass a stream of hydrogen and the set temperature of the interval (900÷1100)°Spoke this temperature decrease to room, remove the sample from the unit for annealing and removing the Ute x-ray diffraction pattern, which is judged on the presence of magnetic impurities (metal phase).

In the absence of the diffraction pattern of trace metals advanced shooting range electron paramagnetic resonance (EPR) at room temperature. In case of absence in the spectrum of the EPR signals with values of g-factors of the corresponding magnetic impurities concludes the magnetic cleanliness of the investigated material.

As shown by the study authors, for process optimization - full aggregation of metal impurities at these temperatures is sufficient delivery time t annealing to the value determined from the relation t=t0-b ΔT, where

t0the time interval of 3 hours;

b - factor of 1.25·10-2h/°C;

ΔT is a value exceeding the minimum temperature of the temperature range of annealing (900°C), °C.

Examples

For the control experiments for the determination of magnetic impurities were prepared three test samples.

Sample 1 prepared from industrial nd (obtained by detonation synthesis in water, purified by the oxidation of non-diamond phase 50% nitric acid at 230°C) with ash 0.7%, during the registration of x-ray diffraction pattern showed the presence of impurities in titanium dioxide (non-magnetic impurity) and the absence of impurities of other crystalline phases.

Sample 2 prepared the C industrial nd (obtained by detonation synthesis in aqueous medium, purified by the oxidation of non-diamond phase 50% nitric acid at 230°C) with ash 0.7%, during the registration of x-ray diffraction pattern showed the presence of impurities in titanium dioxide (non-magnetic impurity) and the absence of impurities of other crystalline phases. The sample is optionally washed with 30% hydrochloric acid and distilled water. It can be expected that the number of magnetic impurities in the sample 2 is smaller than in sample 1.

Sample 3 prepared from industrial nd (obtained by detonation synthesis in water, purified by the oxidation of non-diamond phase 50% nitric acid at 230°C) with ash 0.7%, during the registration of x-ray diffraction pattern showed the presence of impurities in titanium dioxide and the absence of impurities of other crystalline phases. The product of this party washed with 30% hydrochloric acid under ultrasonic irradiation and distilled water in accordance with the patent of the Russian Federation No. 2322389, according to which the resulting nanodiamond should not contain magnetic impurities.

Studies of x-ray diffraction was performed on the diffractometer "Geigrflex D/max-RC, firms Rigaku (Japan), with the following instrument settings: radiation α With (λ-1,A) monochromatization; step scan; accumulation time of the signal at one point 2 seconds; a registration step of 0.02°; current and accelerating voltage x-ray tube 70 mA, 40kV; scan interval - (3÷10) degrees 2θ; divergentional slit (DS)=1°; Salerosa slit (SS)=0,15°; receiving slit (RS)=1°.

EPR spectra were obtained on a device company Varian model R160. The generator frequency was 9.45 GHz, in the range of magnetic fields (0÷500) MT, the additional frequency modulation 100 kHz, the experiment was conducted at room temperature. The signal with the specified g-factor was observed when the magnetic field strength in the range (136÷150) MT.

Example 1

Sample 1 was annealed in order in hydrogen at a temperature of 1000°C, which meets specified in the claims of the temperature interval, for 1.75 hours. X-ray diffraction pattern of a sample of registered diffraction peaks identified as the crystalline phase of iron.

Example 2

Same as in example 1, but the temperature of 900°C, which corresponds to that specified in the claims of the temperature interval, the duration of annealing was 3 hours. X-ray diffraction pattern of a sample of registered diffraction peaks identified as the crystalline phase of iron.

Example 3

Same as in example 1, but the temperature was 1100°C, which corresponds to that specified in the claims of the temperature interval, the duration of annealing was 30 minutes On the x-ray diffraction pattern of a sample of registered diffraction peaks, identified as phase Cree is metallic iron.

Example 4

Same as in example 1, but the temperature was 1200°C, while the temperature is beyond the scope specified in the claims of the interval, the duration of annealing was 20 minutes X-ray diffraction pattern of the sample has a complex and uninterpreted character due to graphitization nd. The sample lost consumer properties.

Example 5

Sample 2 was annealed in order in hydrogen at a temperature of 1000°C, which corresponds to that specified in the formula of the invention according to claim 1 temperature interval within 1.75 hours. But x-ray diffraction pattern of the sample was not registered diffraction peaks corresponding to crystalline iron. However, the EPR spectrum showed the presence of a signal in the range of field values (136÷142) MT, the corresponding g-factor of 4.3 characteristic of the iron valence state of Fe+3. Thus, the application of the method according to claim 2 allowed to register the presence of traces of iron, which shows the increase in the reliability of the method.

Example 6

Sample 3 was annealed in order in hydrogen at a temperature of 1000°C for 1.75 hours, which corresponds to that specified in the claims of the temperature interval. X-ray diffraction pattern of the sample the presence of crystalline iron is not detected. Range of EPR shows no signals in the range of field values (136÷142) MT that meet the observed g-factor 4.3, characteristic of the iron valence state of Fe+3. Thus, the control method confirmed the absence in the sample of detonation nanodiamond synthesis of iron impurity, when the cleaning method according to the invention by the patent RF №2322389.

1. The method of controlling the content of magnetic impurities in nanodiamonds detonatsionnogo synthesis, comprising annealing the sample detonation synthesis nanodiamonds in hydrogen atmosphere and then cooled to room temperature, the registration of x-ray diffraction and the identification of metallic phases, characterized in that the annealing is carried out at a temperature selected from the interval (900÷1100)°C.

2. The method according to claim 1, characterized in that after the identification of metallic phases additionally carry out the registration of the spectrum of electron paramagnetic resonance at room temperature with subsequent identification of the presence of metal impurities.



 

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