GB1576971A - Method and apparatus for quantitative structural analysis of solids - Google Patents

Description

(54) METHOD AND APPARATUS FOR QUANTITATIVE STRUCTURAL ANALYSIS OF SOLIDS (71) We, VSESOJUZNY NEF TYANOI NAUCHNO ISSLEDOVATELSKY GEOLOGORAZ VEDOCHNY INSTITUT (VNIGRI) of USSR Leningrad, Liteiny prospekt, 39 MOSKOVSKY GOSUDARSTVENNY UNIVERSITET IMENI M.V.

LOMONOSOVA of USSR Moscow Leninskie Gory and LENINGRADSKY GOSUDARSTVENNY UNIVERSITET IMENT A.A. ZHDANOVA of USSR Leningrad Universitetskaya naberezhnaya 7/9 all Russian Corporate Bodies do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to structural analysis of porous bodies, and more particularly to a method of and apparatus for quantitative structural analysis of solids, especially solid, porous bodies.

The invention can most advantageously be used in geology, e.g. in estimating oil, gas and water resources or determining the collecting capacity of rocks, as well as in the manufacture of ceramics, catalysts, of sorbents, of constructional and abrasive materials, in powder metallurgy and other fields.

It is an object of the present invention to provide a method for quantitative structural analyses of solids, providing high accuracy and requiring only relatively small specimens.

According to the present invention there is provided a method for quantitative structural analysis of solids specimens, wherein a specimen to be analyzed is cleaved, both parts of the cleaved specimen are placed in a scanning electron microscope, the conjugate specimen cleavage surfaces are scanned to obtain signals representing images thereof, representations of said images are superimposed, and the resulting composite representation is scanned and quantitatively analyzed to determine the structure of the specimen.

The invention also provides an apparatus for quantitative structural analysis of solid specimens according to the above method, comprising a scanning electron microscope with a TV monitor intended for visualization of the images of the conjugate cleavage surfaces of the specimens placed in the microscope and connected both to a video recorder for recording the output signals from the monitor and to an additional TV monitor having a brightness control, the video recorder also being connected to the additional TV monitor whereby the additional TV monitor can simultaneously display the conjugate surface images to be superimposed, a light pen for marking images displayed on the screens of both TV monitors, and an image mixing unit which is connected to the additional TV monitor for matching and super-imposing signals representing said images by matching the marks representing clearly defined conjugate points on the images being superimposed, and is arranged to apply its output signals to an electronic computer arranged for image analysis.

Another advantage of the invention is that it provides a method for quantitative structural analysis of solids, requiring specimens less than 1 cc in volume.

Another advantage of the invention is that it provides a method for quantitative structural analysis of solids, ensuring highaccuracy determination of the porosity and skeleton component of a solid.

Yet another advantage of the invention is that it provides a method for quantitative structural analysis of solids, permitting automation of the process of analysis, which involves substantially nondestructive testing of the materials to be tested.

And, finally, it is an advantage of the present invention that is provides an apparatus ensuring high accuracy of automatic quan titative structural analysis of solids, which would considerably enhance the analysis efficiency in the case of complex structures An advantage of the method of the invention is that superimposition of the images of the conjugate surfaces, producing a composite representation and determination of the structure from such a composite representation permit highly accurate and reliable information on the structure of solids to be obtained, since the superimposition of the images, as has been corroborated by tests and as will be considered in greater detail in what follows, excludes invalid information on porosity.This is due to the fact that the images of imprints of particles, which may be otherwise interpreted as pores, are compensated, as a result of superimposition, by the images of the particles responsible for these imprints, while only the actual pores remain visible.

The method is applicable for determining not only porosity, but also a skeleton component of the structure (with reference to the size and shape of pores, grains, their distribution by these parameters), determining the physical parameters of all types of pores, calculating the frequency of contacts between particles and determining their type.

The high accuracy of analysis obtained by the use of the invention permits the specimen size to be decreased accordingly, whereby analysis is rendered nondestructive, which is particularly essential in the case of expensive materials and enables coreless drilling of prospecting boreholes with drill cuttings being used for analysis.

For quantitative determination of porosity, one should preferably obtain, in the scanning electron microscope, negative images of the conjugate specimen cleavage surfaces, superimpose them, and quantitatively determine the parameters of porosity from the composite representation.

In order to feed porosity data into a computer, i.e., to digitize the image, the direction of anisotropy of the pore space is advantageously determined by passing a monochromatic light beam through the composite representation of the conjugate surfaces, and the image is scanned in that direction which is found to be the optimum scanning direction.

To investigate a skeleton component of the structure, in the scanning electron microscope a positive composite image is obtained along with negative images of the conjugate cleavage surfaces, which images are then superimposed in pairs, composite images of grain imprints on the cleavage surfaces are obtained, these images are converted to a contour form, the converted images are superimposed, resulting in a contour image of a granular structure component, and the skeleton component of the structure is quantitatively analyzed. The method permits investigation and obtaining a full picture of the structure of a solid, including such binding components as cement, glass, etc.To this end, the image of pores, which is a positive total image, is converted to a contour image superimposed on the contour image of the skeleton component, and the structure of the solid is quantitatively analyzed.

For higher accuracy of matching the images of the conjugate cleavage surfaces and enhancing certain image areas at higher magnification, consecutive images of the conjugate areas are obtained, at increasing magnifications, the first pair of images at minimum magnification being superimposed along the specimen's contour or characteristic morphological features observed on both cleavage surfaces.Then, one of the conjugate images is marked at portions selected for investigation at higher magnification, the marks being transferred on the other conjugate image, the conjugate image areas selected for investigation being detected by visual monitoring, with reference being made to the marks on the conjugate images, and brought to the centre of the field of vision of the scanning electron microscope, the images being recorded with the marks from the preceding small-magnification image being transferred on the resulting image and with visual monitoring being effected with reference to morphological features, the conjugate images being matched with reference to the marks, and said operations being repeated each time an image of greatermagnification is obtained.

Manual implementation of the method of the invention for quantitative structural analysis of solids was found to be a timeconsuming and laborious operation even when instantaneous micrography techniques were used, with many people being involved in the investigation, which involved preparation of the conjugate specimen cleavage surfaces and their micrography, development of the negatives of the conjugate cleavage surfaces, their matching by salient morphological features, obtaining composite negatives, printing of electron micrographs, analysis of porosity with the aid of an image analyzer, obtaining slides (positive images) from the composite negatives, their superimposition on the negative images of the conjugate cleavage surfaces, printing electron micrographs from the matched pictures, subsequent quantitative analysis of the grained structure component with the aid of the image analyzer, and so on.

Speeding up the process of structural analysis of solid specimens, ruling out numerous manual operations involved in carrying out the above method, elimination of subjective errors inevitable in manual operations, hence, enhancing the accuracy of the obtained results, are made possible with the aid of the proposed apparatus.

The invention will now be described in greater detail with reference to preferred embodiments thereof, taken in conjuction with the accompanying drawings, wherein: Figure 1 shows schematically a cleavage surface of a specimen; Figure 2 shows the specimen cleavage surface conjugate with the surface shown in Fig.

1; Figure 3 is a composite image of both conjugate specimen cleavage surfaces; Figure 4 represents an electron micrograph of a cleavage surface of a specimen with low porosity; Figure 5 is an electron micrograph of the specimen cleavage surface conjugate with the surface of Fig. 4; Figure 6 is an electron micrograph of the composite image of both conjugate cleavage surfaces of the specimen of Figures 4 and 5; Figure 7 is an electron micrograph of a cleavage surface of a specimen with high porosity; Figure 8 is an electron micrograph of the specimen cleavage surface conjugate with the surface of Fig. 7; Figure 9 is an electron micrograph of the total image of both conjugate cleavage surfaces of the specimen of Figures 7 and 8; Figure 10 is an electron micrograph of grain imprints on the surface shown in Fig. 7;; Figure 11 is an electron micrograph of grain imprints on the surface shown in Fig. 8; Figure 12 is an electron micrograph of a contour image of the granular component of Fig. 10; Figure 13 is an electron micrograph of a contour image of the granular component of Fig. 11; Figure 14 is an electron micrograph of the total contour image obtained as a result of conversion of the image of Fig. 9; Figure 15 is an electron micrograph of the total image of the complete structure of the specimen; and Figure 16 is a block diagram of an apparatus for carrying out the proposed method.

The proposed method can be realized as follows: A specimen to be investigated is cleaved (fractured) in any known manner into two pieces having conjugate cleavage surfaces.

By conjugate surfaces are here meant surfaces of two bodies, characterized by the fact that concavities and convexities on one surface correspond with respective convexities and concavities on the other surface, perfectly matching in shape, size and location.

Thus, any cavities occurring in the plane of division constitute deviations from conjugation. Mathematically, conjugate surfaces are those described by functions U(x,y,z) and V(x,y,z) and satisfying the following condi tion.Xt dV; d dU . Referring now to the drawings, Fig. I shows one and Fig. 2 shows the other condjugate surface of the cleaved specimen, in which corresponding to a round particle a (convexity) on the surface shown in Figure 1, there is, on the conjugate surface shown in Figure 2, an imprint b (concavity), while corresponding to an elongate particle c (convexity) on the surface of Fig. 1 there is in Fig. 2 an imprint d (concavity); and corresponding to a pore e on the surface of Fig. 1 there is a porefon the surface of Fig. 2.

The present invention is based on the well known physical phenomenon of optical multiplication or superimposition of images. In the case of multiplication, the transmission factor of the superimposed optical transparencies is equal to the product of the transmission factors of the individual transparencies. When images are superimposed and simultaneously projected on the same screen, the brightness at each point of the screen is equal to the sum of brightnesses of the individual superimposed images. (cf. A.

Rosenfeld, "Image Identification and Processing","Mir"Publishers, Moscow, 1972, p.

67/ in Russian).The procedure of multiplying images is widely used in various photographic processes, particularly, in aerial photography to enhance the quality of irregularly exposed pictures by way of masking (cf. V.Ya. Mikhailov, "The Practice of Using Unsharp Masks in an Inactive Process" in "Geodeziya i kartografiya", No. 1, 1957, pp. 27-32/in Russian/). Therewith, multiplication is achieved by superimposing a transparency of the aerial photograph on that showing the correction mask with the result that the field of the aerial photograph is flattened, and previously unseen features become visible all over the picture. Similar flattening may be achieved by superimposing the aerial photograph and correction mask on the TV screen.

For a better understanding of the proposed method, consider the above procedure as applied to revealing features representative of cavities inside a solid, as well as a skeleton component of the solid's structure, with the aid of electron micrographs of the conjugate specimen cleavage surfaces.

If the solid had no pores, multiplication or superimposition of the images of the conjugate surfaces would result in a field with uniform optical density, for the pictures can be considered as an image-mask pair. Since the solids under investigation are porous, no mutual compensation takes place of the transmission factors or brightness in the porous areas of the conjugate surfaces, and pores manifest themselves as spots against the background of a uniform field. Taken as an example were specimens of two types of solids: one with high porosity (60%) and one with low porosity (15%), respectively.

In the former case, the conjugate surfaces (Figs 7 and 8) differ greatly because of the high porosity, and the composite image (Fig.

9) clearly shows numerous pores, while in the latter case the surfaces are almost completely conjugate (Figs 4 and 5), and the total image (Fig. 6) shows very few pores.

The procedure of optical multiplication of images permits the positive image of pores (Fig. 9) to be used as a correction mask to obtain an image of grain imprints on the micrographs of both conjugate surfaces (Figs 10 and 11).

In order to obtain a contour image of all the structural components of the solid, the images of pores (Fig. 9) and grain imprints (Figs. 10 and 11) are converted to contour forms (Figs 12, 13 and 14) by way of high- frequency image signal filtration mathematically described through differentiation (cf A.

Rosenfeld, "Image Identification and Processing", "Mir"Publishers, Moscow, 1972, pp. 114-123/in Russian/). Individual contour images of the structural components of the solid are superimposed to obtain a complete structural picture. In a further process the two parts of a specimen, having conjugate surfaces, are mounted together on the specimen stage, then placed in the specimen chamber of a scanning electron microscope of any type, e.g., described in the catalogue of "Coates and Welter" ("106A SEM Ultra High Resolution, USA 4/1/75"). To prevent distortion of the shape of the structural components of the specimens, the latter are preferably arranged at right angles to the electron probe. Then, at moderate magnifications (about x100), the two cleavage surfaces of the specimens are examined with a view to finding conjugate portions thereon.

For this purpose, reference is made to salient morphological features of the specimen (clearly visible particles, fissures, pores on one cleavage surface and mating pores on the other). An image of the conjugate portions is obtained, they are photographed on a film or a plate, and negatives are produced prints made from these negatives are shown in Figs 4 and 5). Then, the negative of one conjugate portion is superimposed on that of the other (at the same magnification), the two negatives are properly matched, and a composite negative is obtained which, when printed, produces a composite black-and-white picture (Fig. 6) in which dark spots unambiguously represent pores, while bright spots represent particles. With the aid of any known image analyzer, such as "Quantimet-720", quantitative analysis of the true structure of the specimen's pore space of the specimen is then performed.The basic characteristics are, in this case, total porosity as well as distribution of pores by size and depth (a measure of depth is provided by the optical density of the image of a pore).

However, structural analysis of solids with the aid of special-purpose image analyzers available at present does not permit determining certain important physical properties of specimens, such as perviousness, effective porosity, pore tortuosity factor and distribution of hydraulic radii of pores. The use of an electronic computer permits more flexible and complete calculation of the physical properties of solids on the basis of analysis of electron micrographs. Calculations involve appropriate programes written for each particular case, which are not described herein.

For the electron micrograph data to be fed into the computer, they must be read out and digitized. The readout of an image per se is a well known procedure and is carried out with the aid of any of various conventional devices, for example, the widely used facsimile recorder. We have established, however, that if the anisotropy of a solid's structure is not taken into account, serious errors occur in the course of computation of some parameters, such as perviousness. To determine the optimum image readout direction corresponding to that of anisotropy of the pore space image, the latter is transformed to an image of an optical spatial spectrum.For this purpose, a monochromatic light beam is passed through a transparency which is a composite image of the conjugate specimen cleavage surfaces, and, with the aid of a focusing lens, the light distribution is registered in the back focal plane to provide for a spatial spectrum of the image. A similar procedure can be carried out by means of optical filters, for example, a commercially produced optical filter of the "Coherent-1" type (cf."Catalogue of Geophysical Instrumentation", "Nedra" Publishers, Leningrad, 1973/in Russian/). The resulting image of the optical spectrum is used to define the direction of maximum anisotropy, hence, the direction of image readout on the image of pores. The resolution of readout is determined either by the investigation object or by the capacity of the computer's read/write memory. Thus, after the pore image has been read out, it is digitized forming a matrix fed into the computer. It should be noted that such a digitizing operation aimed at calculation of the physical properties of solids makes sense only in the context of electron micrographs presenting a true picture of porosity, i.e., pictures obtained by the herein-proposed method, and cannot be applied to analysis of an image of a single specimen cleavage surface because of the inital data being invalid.

To determine a skeleton (granular) structure component, basically the same approach is used as in porosity studies, the difference being that after the composite negative has been obtained, a slide (positive on film or plate) (Fig. 9) is produced therefrom and superimposed successively on a negative of each of the respective cleavage surfaces (similarly to superimposing negatives). As a result, composite negatives are obtained, which are then printed to produce micrographs showing grains on respective specimen cleavage surfaces (Fig 10 and 11).Image analyzers enable evaluation of grain size, shape and distribution by size.Thereafter, photography, video or diffraction microscopy techniques are used to convert the total negative images of grain imprints on each cleavage surface to contour images (Figs. 12 and 13) which, superimposed as described above, produce a contour image of the skeleton component of the solid. If the image of the porous component is also converted to a contour image and the latter is matched with the image of the skeleton component, the resulting composite image offers a complete picture of the solid's structure (Fig. 15). This picture is used for discrimination of the nodal points of the structure, representative of intergranular contacts, as well as for quantitative analysis of the skeleton component of the structure with the aid of any conventional image analyzer.The problems considered above are those related to obtaining a true picture of porosity (total image), however, for more perfect matching of images and enhancing them at higher magnification, one should investigate a specimen in a scanning electron microscope at increasing magnifications, in which case the first pair of images produced at minimum magnification are superimposed following the specimen's contour or salient morphological features observed on both cleavage surfaces. Then, one of the superimposed images is marked at portions selected for examination at higher magnification. The marks are transferred to the other image. The conjugate portions selected for examination at higher magnification are then detected by visual monitoring with reference to the marks on the superimposed images and brought to the centre of the field of vision of the microscope.The portions are photographed, and the marks from the previous small-magnification image are transferred to the resulting images, with visual monitoring being exercised with reference to morphological features. The conjugate portions are matched with reference to the marks, and each time a highermagnification image is produced, the above operations are repeated.

To speed up the process of structural analysis of solids and eliminate numerous manual operations involved in such analysis, an apparatus whose block diagram is shown in Fig. 16 may be used.

The apparatus for quantitative structural analysis of solids, according to the invention, comprises a scanning electron microscope (SEM) 1 which may be of any known type (e.g., SEM'KWIKSCAN-106A", cf.

catalogue of "Coates and Welter", "106A SEM Ultra High Resolution, USA, 4/1/75"), provided with a TV monitor 2 for visualization of the image of the surface of a specimen placed on the specimen stage (not shown). The output of the TV monitor 2 is coupled to the input of a unit 3 intended for video recording of the image; this unit may be any conventional video recorder (e.g.,"Sony AV-3650" manufactured by "Sony" of Japan). The apparatus also comprises an additional TV monitor 4 with brightness control(we used an "auxiliary TV monitor" manufactured by "Coates and Welter", USA), associated through direct coupling and feedback with the video recorder. Images on the screen of the TV monitors are marked by means of a light pen 5.There is also provided a read/write memory module 6 enabling the image scale to be varied (e.g., a "KWICKSTOR" Image Storage System,' module), associated by direct coupling and feedback with the additional TV monitor 4. In addition, the apparatus includes an image mixing unit 7 which may be any known mixing unit widely used in television, e.g., a C12-75-2 unit (cf. "Technical Description of Stationary Color TV Unit "Respublika", USSR, 1975/in Russian/). Inputs of the image mixing unit 7 are connected to the output of the SEM TV monitor 2, to the output of the video recorder 3, and via direct coupling and feedback, to the additional TV monitor 4. The output of the image mixing unit 7 is coupled to the input of the read/write memory module 6 and to the input of an image analyzer 8.

The image mixing unit 7 is intended for matching and superimposition of images with reference to marks representing definite conjugate points of the images being superimposed. The image analyzer 8 (e.g., "Quantimet-720") including a readout device (not shown) has its input connected to an electronic computer 9 and is intended for digitizing images by way of readout of an image in a predetermined direction, as well as for preliminary quantitative structural analysis of the image. The output of the image analyzer 8 is connected to the input of the video recorder 3 and, via the latter, to the image mixing unit 7.

The apparatus of the present invention operates as follows: A small -magnification image F of one of the conjugate specimen cleavage surfaces is obtained on the screen of the TV monitor 2 of the scanning electron microscope 1. Primary marks Ml are applied on this image with the aid of the light pen 5 to produce an image FM which is fed to the video recorder 3 and displayed on the screen of the additional TV monitor 4. Then, the image F of the other conjugate surface is produced on the screen of the TV monitor 2 with primary marks also being applied thereon with the aid of the light pen 5, and the resulting image FM is recorded by the video recorder 3. The images FM and FM, are superimposed with reference to the marks Ml by means of the image mixing unit 7.The result of the superimposition is visualized on the screen of the TV monitor 4 and, at the same time, fed from the image mixing unit 7 to the image analyzer 8, then to the computer for further processing.

Thereafter, secondary marks M2 are applied on the image FM, displayed on the screen of the TV monitors 2 and 4 with the aid of the light pen 5, resulting image FM1,2 is recorded by the video recorder 3. This image is fed to the read/write memory module 6 wherein it is varied in scale (magnified) to the next required magnification, whereby an image F"M2 is produced. Therewith, the primary marks Ml go beyond the frame of the picture, and only the magnified image with the secondary marks M2 is displayed on the screen.Thereafter, there is produced on the screen of the TV monitor 2 of the scanning electron microscope 1 is an image of the first conjugate specimen cleavage surface on the same scale as the image F"M" which is then marked with secondary marks by means of the light pen 5, and an image F"M, is obtained. This image is recorded by the video recorder 3, then the images FM,,, and FM, are called from the video recorder 3 and dis played on the TV monitor 4.By manipulat ing the brightness control, the image F is removed from the image FM"2 (with only the primary and secondary marks being left), and the remaining primary and secondary marks Ml,2 are matched, with the aid of the image mixing unit 7, with the image FM, to produce a composite image of the second conjugate specimen cleavage surface together with the primary and transferred secondary marks.By means of the read/write memory module 6, this image is magnified to form an image F"M2. Displayed on ths screen of the TV monitor 2 of the scanning electron microscope 1 is an image of the second conjugate surface to the same scale, and the secondary marks from the image F"M2 are transferred thereto with the aid of the light pen 5 and by way of visual monitoring on the screen of the TV monitor 4, as a result of which an image F*"M"2 is obtained. Then, with the aid of the image mixing unit 7, the images FIIMII2 and F M1,2 are superimposed, and a composite image is obtained, which is displayed on the screen of the TV monitor 4 and fed to the image analyzer 8; this sequence is repeated for each new magnification and for new marks.

From the image analyzer 8, data pertain ing to each image are fed into the computer 9, wherein the parameters of the pore space of the solid are fully calculated with the aid of programs which are written for each specific task and which are not described here.

In structural skeleton component investigation, individual images of conjugate cleavage surfaces (Figs 7 and 8) and the corresponding pore images (Fig 9) available in the video recorder 3 are fed to the image mixing unit 7 in which, for each magnification and each pair of images of the conjugate surfaces (Figs 7 and 8), and the corresponding pore images (Fig. 9) are superimposed with the result that half-tone pictures of granular structure components Figs 10 and 11) are produced, which, just as in the case of pore images, are converted to a contour form (Figs 12 to 14) with the aid of the image analyzer 8 and fed, via the video recorder 3, to the image mixing unit 7 wherein they are superimposed. Thus, a complete contour image of the structure of the solid (Fig. 15) is obtained.This image is first analyzed by the image analyzer 8, then, according to a respective program, by the computer 9.

The advantage of the present invention is that it enables the accuracy of determining parameters of solids to be increased severalfold, at least by one order of magnitude, as well as permitting automation of the process of structural analysis of solids, which, in turn, substantially improves the efficiency of investigation and provides a rapid solution to problems arising in connection with the structure of solids WHAT WE CLAIM IS: 1.A method for quantitative structural analysis of solid specimens, wherein a specimen to be analyzed is cleaved, both parts of the cleaved specimen are placed in a scanning electron microscope, the conjugate specimen cleavage surfaces are scanned to obtain signals representing images thereof, representations of said images are superimposed, and the resulting composite representation is scanned and quantitatively analyzed to determine the structure of the specimen.

2. A method as claimed in claim 1, wherein negative images of the conjugate cleavage surfaces are obtained in the scanning electron microscope, and the resulting composite negative representation is used for quantitative analysis of the porosity of the specimen.

3. A method as claimed in claim 2, wherein, with a view to feeding data into an electronic computer, the composite representation is scanned and the resulting signal is applied to a digitizer and, for determining the optimum scanning direction, a monochromatic light beam is passed through the total image to obtain an image of a spatial spectrum required to determine the direction of anisotropy of the pore space represented in the image, said direction corresponding to the optimum scanning direction.

4. A method as claimed in claim 4, wherein a positive composite representation

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   of the TV monitor 2 with primary marks also being applied thereon with the aid of the light pen 5, and the resulting image FM is recorded by the video recorder 3. The images FM and FM, are superimposed with reference to the marks Ml by means of the image mixing unit 7. The result of the superimposition is visualized on the screen of the TV monitor 4 and, at the same time, fed from the image mixing unit 7 to the image analyzer 8, then to the computer for further processing.

   Thereafter, secondary marks M2 are applied on the image FM, displayed on the screen of the TV monitors 2 and 4 with the aid of the light pen 5, resulting image FM1,2 is recorded by the video recorder 3. This image is fed to the read/write memory module 6 wherein it is varied in scale (magnified) to the next required magnification, whereby an image F"M2 is produced. Therewith, the primary marks Ml go beyond the frame of the picture, and only the magnified image with the secondary marks M2 is displayed on the screen.Thereafter, there is produced on the screen of the TV monitor 2 of the scanning electron microscope 1 is an image of the first conjugate specimen cleavage surface on the same scale as the image F"M" which is then marked with secondary marks by means of the light pen 5, and an image F"M, is obtained. This image is recorded by the video recorder 3, then the images FM,,, and FM, are called from the video recorder 3 and dis played on the TV monitor 4.By manipulat ing the brightness control, the image F is removed from the image FM"2 (with only the primary and secondary marks being left), and the remaining primary and secondary marks Ml,2 are matched, with the aid of the image mixing unit 7, with the image FM, to produce a composite image of the second conjugate specimen cleavage surface together with the primary and transferred secondary marks.By means of the read/write memory module 6, this image is magnified to form an image F"M2. Displayed on ths screen of the TV monitor 2 of the scanning electron microscope 1 is an image of the second conjugate surface to the same scale, and the secondary marks from the image F"M2 are transferred thereto with the aid of the light pen 5 and by way of visual monitoring on the screen of the TV monitor 4, as a result of which an image F*"M"2 is obtained. Then, with the aid of the image mixing unit 7, the images FIIMII2 and F M1,2 are superimposed, and a composite image is obtained, which is displayed on the screen of the TV monitor 4 and fed to the image analyzer 8; this sequence is repeated for each new magnification and for new marks.

   From the image analyzer 8, data pertain ing to each image are fed into the computer 9, wherein the parameters of the pore space of the solid are fully calculated with the aid of programs which are written for each specific task and which are not described here.

   In structural skeleton component investigation, individual images of conjugate cleavage surfaces (Figs 7 and 8) and the corresponding pore images (Fig 9) available in the video recorder 3 are fed to the image mixing unit 7 in which, for each magnification and each pair of images of the conjugate surfaces (Figs 7 and 8), and the corresponding pore images (Fig. 9) are superimposed with the result that half-tone pictures of granular structure components Figs 10 and 11) are produced, which, just as in the case of pore images, are converted to a contour form (Figs 12 to 14) with the aid of the image analyzer 8 and fed, via the video recorder 3, to the image mixing unit 7 wherein they are superimposed. Thus, a complete contour image of the structure of the solid (Fig. 15) is obtained.This image is first analyzed by the image analyzer 8, then, according to a respective program, by the computer 9.

   The advantage of the present invention is that it enables the accuracy of determining parameters of solids to be increased severalfold, at least by one order of magnitude, as well as permitting automation of the process of structural analysis of solids, which, in turn, substantially improves the efficiency of investigation and provides a rapid solution to problems arising in connection with the structure of solids WHAT WE CLAIM IS: 1.A method for quantitative structural analysis of solid specimens, wherein a specimen to be analyzed is cleaved, both parts of the cleaved specimen are placed in a scanning electron microscope, the conjugate specimen cleavage surfaces are scanned to obtain signals representing images thereof, representations of said images are superimposed, and the resulting composite representation is scanned and quantitatively analyzed to determine the structure of the specimen.
2. 2. A method as claimed in claim 1, wherein negative images of the conjugate cleavage surfaces are obtained in the scanning electron microscope, and the resulting composite negative representation is used for quantitative analysis of the porosity of the specimen.
3. 3. A method as claimed in claim 2, wherein, with a view to feeding data into an electronic computer, the composite representation is scanned and the resulting signal is applied to a digitizer and, for determining the optimum scanning direction, a monochromatic light beam is passed through the total image to obtain an image of a spatial spectrum required to determine the direction of anisotropy of the pore space represented in the image, said direction corresponding to the optimum scanning direction.
4. 4. A method as claimed in claim 4, wherein a positive composite representation

   is obtained together with negative images of the conjugate cleavage surfaces, said composite representation is superimposed on each of said negative images so as to obtain images representing the grain structure of the cleavage surfaces, the representations of the grain structure are converted to images representing grain contours, the converted images are superimposed, resulting in a contour image of the grain structure of the sample which is quantitatively analyzed.
5. 5. A method as claimed in claims 1 to 4, wherein, for perfect matching of the images of the conjugate cleavage surfaces of the specimen and for enhancing certain image areas at high magnificiation, consecutive images of the conjugate areas are obtained, from small to high magnification, the first pair of images at minimum magnification being superimposed along the contour or characteristic morphological features of the specimen observed on both cleavage surfaces, the image of one of the conjugate surfaces being marked at portions selected for investigation at higher magnification, the marks being transferred on to the other one of the conjugate images, the conjugate image areas selected for investigation being detected by visual observation of the marks on the conjugate images, and brought to the centre of the field of vision of the scanning electron microscope and scanned at increased magnification, said images being recorded with the marks from the preceding smaller magnification image being transferred onto the resulting images and with visual monitoring being exercised with reference to morphological features, the conjugate images being matched with reference to the marks, and said operations being repeated each time a greater-magnification image is obtained.
6. 6. An apparatus for quantitative structural analysis of solid specimens according to the method of claim 1, comprising a scanning electron microscope with a TV monitor for visualization of the images of the conjugate cleavage surfaces of the specimens placed in the microscope and connected both to a video recorder for recording the output signals from the monitor and to an additional TV monitor having a brightness control, the video recorder also being connected to the additional TV monitor whereby the additional TV monitor can simultaneously display the conjugate surface images to be superimposed, a light pen for marking images displayed on the screens of both TV monitors, and an image mixing unit which is connected to the additional TV monitor for matching and superimposing signals representing said images by matching the marks representing clearly defined conjugate points on the images being superimposed, and is arranged to apply its output signals to an electronic computer arranged for image analysis.
7. 7. An apparatus as claimed in claim 6, wherein the output signal from the image analyzer is applied to the input of the video recorder.
8. 8. An apparatus as claimed in claim 6, wherein the additional TV monitor is provided with a means for varying the scale of the image on its screen, which means is essentially a read/write memory module associated through direct coupling and feedback with the additional TV monitor and intended for storing the scale of a preceding image and further magnification thereof.
9. 9. An apparatus as claimed in claim 6, wherein the output of the image mixing unit is connected to the input of the read/write memory module for storing and varying the image scale.
10. 10. A method for quantitative structural analysis of solids, substantially as described hereinabove.
11. 11. An apparatus for quantitative structural analysis of solids, substantially as described hereinabove with reference to Fig.