Regulation mosaic scattering material of high-oriented pyrolytic graphite

 

(57) Abstract:

Usage: to obtain x-ray monochromators with specified characteristics. The technical result of the invention consists in the production of high-oriented pyrolytic graphite (HOPG) with a narrow interval mosaic scattering. The inventive method includes the steps of selecting samples are made from a material having a mosaic scattering, which lies below the desired area of the mosaic scattering, and cold working the selected samples for the application of the stamp surface texture sufficient to shift the mosaic scattering samples in a desired area of the mosaic scattering. The textured surface preferably otiskivayut by pressing the samples between the metal matrix, at least one of which is knurled. 10 C.p. f-crystals, 4 Il.

The invention relates to a method of shifting mosaic scattering of high-oriented pyrolytic graphite (HOPG) in a specified narrow range.

Graphite monochromators are high-oriented forms of pyrolytic graphite of high purity, which giragira x-rays and neutrons with education is erenee characteristics of crystalline materials.

Graphite monochromators are classified in accordance with the characteristics of their mosaic scattering. Mosaic scattering is a measure of the full width of the peak at half maximum intensity of reflection of x-ray beam from the sample of HOPG by tilting the sample in the preferred orientation, as a result, formed is preferably oriented x-ray diffraction curve, known as the "swing curve". The oscillatory curve is a graph of the intensity of the reflected x-rays as a function of angular distance from a reference plane when using the Bragg law for determining the angular deviation. The oscillatory curve is determined for each sample HOPG so that it was possible to classify mosaic scattering by attributing it to various standard intervals mosaic scattering.

When the consumer must purchase a monochromator of HOPG, he can choose the standard variety that matches any of the available intervals mosaic scattering. One of the commercial varieties of material from HOPG has a wide range of mosaic scattering, comprising 3,51,5o. However, the consumer can potrebbe the o.

The implementation of this requirement will adversely affect the output of material from HOPG obtained by traditional technology. In the above example, only about 30% of the material from HOPG obtained in the usual way, to meet the more narrow interval mosaic scattering of 0.25o.

The method proposed in the present invention, allows to increase the output up to 100% of the material of HOPG with mosaic scattering, corresponding to any desired predetermined narrow interval, based on material from HOPG with mosaic scattering, lying in the field, which is below the desired final characteristics of the mosaic scattering.

The method according to the present invention includes the steps of selecting samples are made from a material having a mosaic scattering, which lies below the desired area of the mosaic scattering, and cold processing selected samples with the formation of the imprint surface texture sufficient to shift the mosaic scattering samples in a desired area of the mosaic scattering. The textured surface preferably otiskivayut by pressing the samples between the metal matrix, at least Odo detailed description of the present invention, which is accompanied by drawings.

Fig. 1 is a schematic view of the device for receiving the oscillatory curve for HOPG samples in order to establish their mosaic scattering.

Fig.2 - diagram of the location of metal matrices for the cold processing of samples made according to the present invention.

Fig.3 is another example implementation, similar to the arrangement in Fig.2, for cold treatment of the samples made according to the present invention.

Fig.4 is a graph illustrating the principle of the present invention used to control mosaic scattering within any desired interval above the level of the mosaic scattering to regulation.

Graphite has a layered structure, in the plane of the layers which are hexagonal arrays or networks of carbon atoms. These layers of hexagonal arranged carbon atoms are essentially flat, while they are oriented so that are essentially parallel and equidistant with respect to each other. Essentially flat parallel layers of carbon atoms, called the base planes, associated or connected with each other in groups forming cu is bathing graphite has a high degree of preferred orientation of crystallites. In accordance with this graphite can be described as a laminated structure of carbon atoms with two main axis of rotation, the axis "C" which is generally defined as the axis or the direction perpendicular to the carbon layers and the axis or the direction parallel to the carbon layers and perpendicular to the axis "C". Graphite materials are characterized by a high degree of orientation, include natural graphite and synthetic or pyrolytic graphite. Pyrolytic graphite is produced by pyrolysis of carbon-containing gas on a suitable substrate at an elevated temperature. In short, the pyrolitic deposition can be performed in a heating furnace at a temperature above 1500oWith and up to 2500oWith and at the proper pressure. In furnace carbon-containing gas, such as methane, natural gas, acetylene, etc., and subjected to thermal decomposition on the surface of a substrate of a suitable composition, such as graphite, having any desired shape. The substrate can be removed or separated from pyrolytic graphite. Next pyrolytic graphite can be subjected to thermal annealing at high temperature to produce high-oriented graphite, commonly called HOPG or the practical graphite, which was subjected to annealing at a high temperature essentially equal to 3000oC or higher. The HOPG samples are usually obtained in the form of plates or once or twice folded forms. Structure and preferred orientation of the samples of records from HOPG determined by x-ray diraction processes.

In Fig.1 shows a device for producing oscillatory curve. The x-ray source 101 with a small divergence angle of the source, usually 1oor less, directs the monochromatic x-ray beam 103 on the sample 105. The detector 107 is placed in position 2 for detection beam 5 x-rays 109 reflected from the sample. The reflected beam 109 has peaks intensities at the corners of the sample), the corresponding Bragg reflection (002) of the base planes of the crystal lattice of the sample. Angle 2, which is reflected x-ray beam, calculated using the Bragg law ( = 2dsin) where is the wavelength of the monochromatic x-ray beam, d is the interplanar distance of the crystal is the Bragg angle. In the present invention the x-ray emission was obtained using an x-ray source CuK (with a wavelength of Sample 105 rotate the th peak intensity, the corresponding Bragg reflection from a reference plane 002, resulting in the received oscillating curve dependence of the intensity of the reflected x-ray beam angle () of the sample rotation. The oscillatory curve is a graph of x-ray intensity as a function of angular distance from the plane of reflection, which in the case of pyrolytic graphite is a plane of deposition. Therefore, the peak at 0oindicates the reference plane (002), parallel to the plane of deposition defined by the substrate. Parameter PSPM peak oscillatory curve represents the full width of the peak at half its maximum intensity. Figure PSPM characterizes the degree of preferred orientation plane 002, with high-oriented crystalline structure have a low value PSPM (narrow peak) and slaboorganizovannaja crystal structure is of great importance PSPM (broad peak). Mosaic scattering is a measure PSPM intensity of reflection of x-ray beam from the HOPG sample and varies from sample to sample and changing conditions in the furnace.

High-oriented pyrolytic graphite (HOPG) with interval mosaic scattering 3,according to the present invention interval mosaic scattering traditionally received HOPG, which is below the desired interval can be increased so that he fell to the desired area by cold treatment of the samples at room temperature.

One of the options for implementing the present invention, shown in Fig. 2, includes a cylinder and two metal matrix, respectively 13 and 14 with knurling. A sample of 10 of HOPG with a lower than desired, mosaic scattering is placed between the dies 13 and 14 within the cylinder 12 and is subjected to pressures up to 34.5 MPa using a hydraulic press. After soaking for 5-30 s at this pressure the pressure down and remove the HOPG sample. For best results, having a knurled surface 15 and 16 of the matrices 13 and 14 fit one to another in the cylinder 12 so that the projections of one surface of the matrix coincide with the recesses in the other matrix, i.e., the surface with knurling form an interdigital structure, the grooves made in the surface, preferably intersect crosswise. Dimensions with knurled surfaces 15 and 16 with the grooves shown with an increase of 10-20x in Fig.2 and 3, comprise up to 0.127 0,254 mm in depth from 0,381 to 0,762 mm in width. You can use the matrix from brass and stainless is CLASS="ptx2">

In Fig. 3 shows a variant implementation of the invention in Fig.2. In this case, the HOPG sample was pressed between the matrix 20 having a knurled, and the plate 21 of the deformable material (for example, paper thickness 0,254-0,508 mm), installed on a smooth flat matrix 22. This method also leads to the formation of a seal with surface texture, and to achieve the desired texture throughout the thickness of HOPG, which increases the mosaic scattering. In this system, the matrix 20 having a knurled, does not require adjustment of the cylinder 12 because it does not require special orientation with respect to the flat matrix 22.

Mosaic scattering HOPG measured after pressing between matrices with knurling 13 and 14. If mosaic scattering is too high, the HOPG sample is placed between the smooth flat die (not shown) and pressed again usually at a lower pressure than during pressing between matrices with knurling, preferably at a pressure of from 3.45 to 34.5 MPa. In some cases multiple pressing between matrices knurled smooth matrices to obtain a mosaic distribution in dense (very narrow) interval.

In Fig.4 shows 55 examples to illustrate traditionally samples is 1,52-2,34o. Suppose that you want to get mosaic scattering, comprising 2,50-3,00o. This scattering was obtained for 25 samples by single or multiple extrusion using matrices with knurling. Mosaic scattering other 30 samples, as shown, is in the range 3,03-4,13oafter pressing between matrices with knurling. The area is a mosaic of scattering these 30 samples was then reduced to 2,50-3,00oby single or multiple pressing between flat and smooth matrices. Because mosaic scattering can easily be expanded by pressing between matrices with knurling and decrease by pressing between the smooth matrices, it is obvious that by repeated pressing, you can achieve much smaller deviations mosaic scattering, for example 0,05o.

The following examples from Fig.4 in more detail to explain and illustrate the invention. For each sample the following conditions: the sample had a size 34,5x27,1x1,5 mm; used matrix of brass and steel with a diameter 50,8 mm Mosaic neutron scattering in reflection from the plane (002) HOPG measured on SPINS with neutron guide 5 when 4,15 at N. I. S. T., GaitherUP> subjected to pressing between matrices stainless steel with grooves, the depth of 0.127 mm and a width of 0,381 mm, arranged crosswise, at a pressure of 34.5 MPa within 15 sec. After pressing the mosaic scattering was 2,97o.

Example 2 (Sample 2)

The HOPG sample with the original mosaic neutron scattering 2,24osubjected to pressing between matrices brass grooves depth 0,254 mm and width 0,762 mm, arranged crosswise, at a pressure of 34.5 MPa within 15 sec. After pressing the tile neutron scattering was 3.52othat was higher than the desired interval 2,50-3,00o. The HOPG sample then again opressively between the smooth matrix at a pressure of 34.5 MPa for 15 sec. In the result of this operation mosaic scattering was 2,64o.

Example 3 (Sample 3)

The HOPG sample with the original mosaic neutron scattering 2,03osubjected to pressing between matrices brass grooves depth 0,254 mm and width 0,762 mm, arranged crosswise, at a pressure of 34.5 MPa for 15 sec. Extruded sample was investigated and again opressively at a pressure of 34.5 MPa within 15 sec. After two operations pressing mosaic scattering stood at 2.52oo. In the third pressing operation using a flat brass matrices under pressure 17,24 MPa for 15 mosaic neutron scattering decreased to 2.57o.

Example 5 (Sample 35)

The HOPG sample with the original mosaic neutron scattering 2,12osubjected to pressing between two matrices brass grooves depth 0,254 mm and width 0,762 mm, arranged crosswise, at a pressure of 34.5 MPa for 15 C. After this operation, pressing the tile neutron scattering sample HOPG was 3,57o. The HOPG sample then again opressively between the smooth brass matrices at a pressure of 19.3 MPa for 15 sec. In the result of this operation mosaic scattering was 3.14o. Then the sample HOPG double-extruded using a flat brass matrices at a pressure of 34.5 MPa for 15 C. the Final value of a mosaic of russiantearoom 2,31osubjected to pressing between matrices stainless steel with knurling grooves, the depth of 0.127 mm and a width of 0,381 mm, arranged crosswise, at a pressure of 34.5 MPa within 15 sec. After the operation of pressing the tile neutron scattering was 3,11o. Then the HOPG sample was subjected to extrusion using a flat matrix of stainless steel at a pressure of 20.7 MPa for 15 C. the Final mosaic neutron scattering HOPG was 2,60o.

1. The method of shifting mosaic scattering of high-oriented pyrolytic graphite (HOPG) in the specified area mosaic scattering, including the selection of samples of HOPG with mosaic scattering, which lies below the specified area mosaic scattering, and the cold processing of selected samples with the formation of a seal having a surface texture sufficient to shift the mosaic scattering samples subjected to cold working, in the specified area mosaic scattering.

2. The method according to p. 1, characterized in that the cold treatment is carried out by pressing samples between matrices, at least one of which is knurled.

3. The method according to p. 2, characterized in that Chapter is .3, wherein the deformable material is paper.

5. The method according to p. 2, characterized in that each matrix has a knurled.

6. The method according to p. 5, characterized in that for forming a textured surface using two metal matrix, while the surface of the knurled one matrices relative to the surface with knurling another matrix in such a way that they form an interdigital structure.

7. The method according to p. 6, wherein the metal matrix is made of stainless steel, the surface of the knurled each matrix forms a groove with a cross-section of a depth in the range of from up to 0.127 0,254 mm and a width of 0,371 to 0,762 mm

8. The method according to p. 2, characterized in that the HOPG samples are compressed when the first relatively high pressure equal to or greater than the second pressure.

9. The method according to p. 8, characterized in that the mosaic scattering of these samples are subjected to re-regulation, downward with respect to the mosaic dispersion obtained in the first operation of pressing, by further pressing of the samples at the second pressure that is equal to or smaller than the first pressure is AMI, having a flat smooth surface.

11. The method according to p. 10, characterized in that the second pressing operation using a matrix made of brass.

 

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