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Scanning electron microscopy in different fields
In the introduction of various image imaging mechanisms 'signal detection and processing technology, the relationship between contrast and resolution, as well as x-ray spectroscopy, qualitative and quantitative analysis of energy spectrum, some application examples are listed. In recent years, due to the improvement and improvement of the electronic optical properties of probes and scanning electron microscopes and signal detection and processing techniques, the new development of x-ray spectroscopy and energy spectrum technology, as well as the application of various new imaging mechanisms and the improvement of dynamic testing techniques The electron beam instrument has the unique ability to analyze the micro-area structure while analyzing the micro-area. Therefore, it has been extended to some new fields in application, or deepened and expanded in the original field. In this chapter, from the actual reports of domestic and foreign applications, a series of application scopes are summarized and combined with the various principles and application conditions mentioned above, and typical examples in various fields are introduced to the readers.
First, the application of metallography
Castaing introduced the use of electron probe microanalyzers in alloy research very early in his work. The existing electron beam scanning display technology can utilize the sample current image and the reflected electron image in the range of 0.1 um 2 (or smaller) to several square millimeters to exhibit the distribution of sample elements, the composition of the phase regions, and the intergranularity. Segregation and infiltration of interphase elements, as well as diffusion trends. The secondary electron image can reveal the root cause and characteristics of fracture fracture at high and low magnification. The absolute sensitivity of the probe analysis is as high as 10 -15 g, which can accurately determine the chemical composition within 1 um 3 volume. Comprehensive use of these unique skills to study the composition of alloys; explore the effects of various added elements on metallographic structure, micro-segregation, diffusion mechanism and mechanical properties; analyze the improvement of metal structure by heat treatment specifications; This method measures the phase equilibrium diagram of the formulated alloy.
Fracture observation
High-resolution or low-magnification fracture observation was once a problem in metallographic techniques. When a sample with irregularities and undulations on a surface is observed by a transmission electron microscope, the fracture must be replicated. However, it is difficult to remove the film, it requires special skills, and it takes time. Uneven density of the composite material can cause wrinkles, tears, and artifacts, and partial replicas may miss areas of observational value. Grids that support the replica film can also cause missed inspections. As a result, the transmission current can only reach a resolution of 20 to 50 angstroms when observing the fracture. Depth of field is also greatly limited. Optical microscopes do not need to be reshaped, but their flexibility, resolution, depth of field and magnification are limited. Observing the fracture from the secondary electron image of the scanning electron microscope can overcome the above difficulties. As long as the previous introduction, the beam is selected according to the high magnification and low magnification observation conditions, the ideal image can be obtained. In the fracture observation, the depth of field is more important than the resolution. The following observations of the fracture are introduced from different application angles.
(1) Polycrystalline iron fracture observation The photograph is a secondary electron image of a polycrystalline iron fracture of 77k pull-down at different magnifications. The entire field of view of the various magnification magnified images is within the precise focus range. It can be seen from the appearing facets and angled surfaces that the fracture almost always occurs on the intercrystalline cracks. Occasionally, cracks in the cleavage can be seen. The high-resolution function of the SEM allows the observation of tiny particles on the interface. As long as the precise focus is achieved on the high-power image, turning the magnification knob will clearly see the lower magnification images at all levels. This is another feature of SEM. The uneven surface on the port often appears too bright and dark, and the method described in this book can overcome this defect. The inspection of the topographical details of the sample in a wide range also promoted the development of multifunctional scanning electron microscopy.
(2) Observation of inclusions on the fracture The uniformity of MnS inclusions in the steel improves the toughness and fatigue resistance. The photograph reflects the waisting phenomenon caused by MnS addition (X-ray spectroscopy) during the heating of the steel before hot rolling. At 1583K, steel samples with different heat treatment times were pulled in the same direction. After observing the fracture, it was found that the type II MnS patch-like inclusions on the surface of the steel sample heated for 15 hours had been broken into smaller and uniform sulfides. The MnS inclusions on the surface of the steel sample which broke after 100 hours of heat treatment had an increasing tendency. There is a smooth dimple-like area between the sulfides. Uniform treatment improves the performance of the steel and allows accurate interpretation by scanning electron microscopy.
(3) Scanning electron microscopic observation of several typical fractures Scanning electron microscopy is used to observe the fractures of different materials and fracture types, and the difference between them can be clearly seen.
2. Study on the segregation of oriented alloys
Nickel-based superalloys are important materials for gas turbine engines. It has a high melting point, good corrosion resistance, and can be incorporated into some other elements to enhance the various properties of the alloy, and thus is widely used. In recent years, new casting processes, especially the development of directional solidification technology, have resulted in directional solidified parts replacing the deformed parts, but the composition of the nickel-based alloy is complicated. The oriented alloy DZ-22 contains 10 elements, each of which has its unique role in the alloy, and its distribution significantly affects the structural properties of the alloy. It is important to fully understand the distribution of elements in various parts of the alloy. However, in the casting alloy itself, segregation is large, and it is quite difficult to measure microsegregation by other methods. Domestic Dong Yuxi et al. used the JXA-733 probe to conduct element segregation studies on DX-22 alloy. The main discussion was about the change of element segregation after adding different amounts of Hf, and the influence of different distances of the same plate from different cooling plates. Ren Yunrong of Beijing Iron and Steel Institute studied the segregation of trace elements on grain boundaries by X-ray energy spectrometer on transmission electron microscope. The beam spot and the segmentation integration method along the grain boundary are used to reduce the pollution, and the analysis precision is improved, and a good effect is obtained.
3. Study on the effect of heat treatment process on steel properties
The mechanical properties, microstructure and fracture behavior of OOCr13Ni6MONb and OOCr14Ni6MOTi maraging stainless steels after slow solution cooling at high temperature, intermediate isothermal annealing, subsequent aging and other different heat treatment processes were studied by transmission electron microscopy and scanning electron microscopy. . The results show that the material is fractured along the grain boundary due to the precipitation of Nb and Ti particles along the prior austenite grain boundary during high temperature and slow cooling. The influence of alloying elements is different, and the degree of intergranular fracture is also different. During the aging process, Ti-containing steel occurs. In the quasi-cleavage mode, river-like, feather-like, and tongue-like patterns can be observed on the fracture surface. Ni-containing steel still maintains the characteristics of grain-breaking.
4. Formulation of phase equilibrium diagram
In the Cu-Zn diffusion study, Castaing first applied electron probe micro-analysis. Adda et al. also obtained phase equilibrium diagrams by studying diffusion to explain the formation of binary alloy systems. The two endmembers of the binary alloy diffuse into each other, and a constantly changing alloy is obtained in the range of passing through the solid solution. Abrupt changes in the composition of the phase boundary can be observed in the two-phase region of the phase diagram. These changes use electron probe analysis technology, combined with the scanned image can accurately determine the phase boundary point, and then connect the phase boundary point to draw the phase equilibrium diagram. The square point on the phase boundary in the figure is the probe analysis point. Adda et al. also discussed limitations such as the failure of the dynamic process to achieve phase equilibrium conditions, the failure of phases, or insufficient analysis width. Goldstein and Ogilvie compared the method of drawing a phase equilibrium diagram with a conventional method and obtaining a phase diagram by probe analysis. In a conventional method, the composition of the alloy biphasic zone range is annealed at a suitable temperature and then analyzed for the composition of the resulting phase zone. These components indicate the range of solubility intervals at a given temperature. The method of probe phase-balancing equilibrium is cumbersome, but more accurate, combined with other necessary metallographic techniques for binary and ternary and gold studies. The nature of the diffusion process has been described in detail by Eifert et al. In Heinrich's paper on the study of binary phase diagrams using diffusion couples, 37 related literatures are given. For a discussion of the use of probes in metallology, reference is also made to Golgstein's comments.
Second, the application of materials science
1. Analysis of composite failure
In order to enhance the mechanical strength of the aluminum while maintaining a light weight, the boron-silicon carbide thin rods (d = 0.1 mm) were arranged in a square matrix, which was wrapped by aluminum spray by plasma sputtering to form a composite material. The density is only 3 g/cm 3 , but its strength-to-weight ratio is greatly improved. The photograph is a micrograph of a sample of the destruction test taken with a secondary electron image of the scanning electron microscope. It can be seen that although these thin pins of 01.mm are sprayed with aluminum by sputtering, the thin rods are not wetted before the aluminum is sprayed, and the aluminum is slightly shrunk after cooling to be separated from the thin rods. In the composite structure thus formed, the thin rod is placed in a hole slightly larger than the rod diameter, and the bond with the aluminum matrix is ​​weakened, and the mechanical properties of the composite material are greatly reduced. It can also be seen from the photograph that the aluminum matrix is ​​loose.
The cause of failure of this composite material can hardly be found under an optical microscope. Because this thin rod protrudes from the base body by 0.5mm, it is twisted. An optical microscope with a small depth of field is powerless to the above-mentioned microscopic stereoscopic scene. Scanning electron microscopy can quickly identify the cause of strength failure.
Similar composite materials, such as thermoplastic polyesters with glass fibers as reinforcing ribs, can also be finely observed for their bonded microstructures under scanning electron microscopy.
2. Observation of deep etched surface
3. Bonding properties of diamond bond materials
The microstructure of the interface between copper-titanium alloy and stone or diamond can also be studied by scanning electron and electron probe analysis techniques. The mechanism of wetting and bonding of copper-titanium alloy to stone or diamond surface has been revealed, which proves that it has good adhesion to diamond and is a promising material for bonding diamond.
4. Application in high temperature ceramics and refractory research
The application of scanning electron microscopy and probe analysis techniques in the field of ceramics and refractories is relatively late. In recent years, the microstructure and crystal morphology of LaCrO3, ZrO2 high temperature ceramics and Mg-Cr2O3, MgO-C alkaline refractories and AL2O3-SiO2 refractory fibers have been observed by scanning electron microscopy. The relationship between the fiber structure and the instability of the material, as well as the crystallization temperature of the refractory fiber and the composition of the refractory material were discussed.
5. Research on the mechanism of antioxidant coating
The Nb-10Hf-1.0Ti-0.7Zr alloy plate sample sprayed with 3Si-15Cr-10Ti-10Zr slurry was placed in a vacuum and melted at different temperatures such as 1280 ° C, 1300 ° C, 1350 ° C, 1380 ° C, and 1400 ° C. It burns and spreads to form a five-layer structure of different thickness and different intermetallic compounds, and then statically burns in air at 1600 ° C for 8 hours. Scanning electron microscopy showed that the most resistant to oxidation was the calcined layer at 1300 °C. Compared with other thin layers formed at the temperature of melting, except for the outer layer of 1600 ° C, the outer layer forms an oxide layer. Although the layers are all resistant to NbSi2, they have high antioxidant capacity, but at 1600 ° C. When the air is statically burned, the NbSi2 phase of each diffusion layer tends to decrease, and the oxidation resistance decreases. The NbSi2 phase formed by the 1300 degree Celsius diffusion layer remains unchanged at high temperatures, which not only enhances the antioxidant capacity, but also The interdiffusion of materials has also slowed down.
3. Applications in geology and mineralogy
Mineral refers to a crystalline phase with a defined composition and crystal structure. Data on early mineral components were obtained using physical separation and chemical methods. False results are often obtained due to imperfect separation and the effects of cross-growth fine phases. Using probe analysis and scanning image observation, it has a prominent role in mineralogical research. It can use the composition contrast and characteristic x-ray image distribution of electronic images to observe the element distribution and phase composition in minerals, and guide the probe to fixed point. Zone analysis to determine the exact composition of the microdomain composition in the mineral. In recent years, the following significant effects have been exerted in mineralogical research.
1. Rapid inspection of phase and composition of mineral samples
On polished mineral flakes, the difference in sample current of the constituent phases reveals the distribution of the phases. The sample current image of the photo reflects the composition phase number and phase difference of the basalt ore sample. Since the incident electron backscattering coefficient η monotonously increases with the atomic number Z and is complementary to the sample current I, the lowest phase region of the average Z is the brightest in the sample current image, and the phase region with the highest average Z is the darkest. There are significant differences in the composition of the four phase regions in which the gray scales are significantly different. Mineralogists usually know the basic composition of basalt. Therefore, it can be quickly determined that the bright area A in the image is a useful mineral, the grayish white area B is a pyroxene, the light black area C is an plagioclase, and the dark black area D is an altered mineral. By using the configured X-ray spectrum and energy spectrum, all the characteristics of the basalt can be more accurately detected. Trained mineralogists can use a scanning electron image to determine the phase number, microstructure characteristics, and native marking of a mineral sample in minutes.
2. Identification of difficult minerals and discovery of new minerals
For example, Mackinac mines, which usually appear as small aggregates, have distinct non-mean characteristics. It was mistaken for a long time as an ink copper mine. It was found by electron probe analysis to be an iron sulfide containing a small amount of Co, Ni and a trace amount of Cu.
In recent years, most of the platinum group minerals have been discovered by electron probe analysis. It was previously believed that platinum group minerals in the South African platinum group deposits were only produced by metals. Through probe analysis, it was found that there are minerals with very small contents such as PtAs2, PtSb2, Pt(Sb, Bi), Pd3Sb, Pd3CuSb and Pd(Sb, Bi). Later, many new types of platinum group deposits were discovered abroad. The Institute of Geochemistry of the Chinese Academy of Sciences also found Pd(Te1.165Bi0.866)2.031 and arsenic platinum ore using electron probes.
3. Research on mineral solid solution series
The mineral solid solution composition has an uncertain amount. It is impossible to directly obtain the chemical composition of each phase of the solid solution by optical microscopy. It is convenient and accurate to use probe analysis.
Ratamani and Prewit analyzed the pentlandite produced in the Frood mine in Ontario, Canada and the Quakumpu mine in Finland, which was found to be a nickel-rich and cobalt-rich nickel pyrite solid solution. And their chemical formulas are Fe3.97Ni4.84C0.007 and Fe1.63Ni1.82Co5.60S8.
Ren Yingjun and Deng Yuren used the electron probe analysis to study the PdS-PtS mineral series, which they considered to be two types in structure. One is thioplatin ore and the other is sulphur platinum palladium ore. The two types are discontinuous, and each class is itself a series of homogeneous in-phase.
4. Study on trace elements and inclusions in minerals
This kind of research is of great significance to explore the genesis of mineral deposits, the relationship between mineralization and surrounding rock, and the physical and chemical conditions of mineralization. Trace elements often exist in minerals in a micro-aggregation state, and such aggregation may also be present in the inclusions. The microstructure of the inclusion body can be examined by scanning electron microscopy image, and the probe element can be used to detect trace elements directly from the inclusion microdomain of the sample without using separation. Therefore, it plays an important role in the study of inclusions.
The Institute of Geochemistry of the Chinese Academy of Sciences has analyzed trace elements such as Mn, Cr, Co, Ni and Zn in magnetite in the surrounding rock, intrusion and ore body of an iron ore mine. The results provide evidence for the study of the genesis of the mine. Reference.
The analysis of micro-envelopes in minerals can also be used to study the characteristics of mineral phenotypes. ЛOCEBA and other probes studied zircons in various tungsten-containing and rare-metal granites in several mining areas of the Soviet Union. Zircon inclusions in tin-containing granites were also found to contain cassiterite inclusions. The fluorine-rich magmatic rock zircon contains fine fluorine minerals and a very small amount of Sn, Nb, W, Y, Ce, La, which are rich in rare earth elements, and can be seen in zircon. To the small inclusions containing brown stone. Obviously, the different inclusions in zircon reflect the geochemical characteristics of granite.
5. Examination of mineral chemical formula
6. Study on the luminescence properties of minerals under electron beam bombardment
Under the electron beam bombardment, many minerals emit cathode fluorescence, which can be visually observed by optical microscopy, or the emission spectrum can be recorded by a monochromator or a photomultiplier tube. At the same time as the observations are made, probe analysis can also be performed to correlate the luminescence effect with the composition of the mineral microdomains. Studies have shown that the color and intensity of mineral cathode fluorescence are related to mineral types, trace elements and crystal defects. Therefore, the probe operator can quickly distinguish the minerals by the luminescence characteristics and observe the characteristics. For example, the application of cathodic fluorescence technology can distinguish between samarium ore and rutile in pigments, and can also be used to study the location of submicroscopic microcracks in hailstones and sediments. Usually, the pyroxene emits red or blue light, quartz emits orange light, and calcite emits orange red light.
Knisely et al. used sample luminescence to determine the amount of trace elements, which is often much lower than the detection limit of typical electron probes. For example, in La2O2 and Y2O3, the detection limit of rare earth elements can be as low as 50 ppm by cathode fluorescence spectroscopy.
Through the study of mineral luminescence, it can also help to understand the environment of mineral generation and compare the types of mineral deposits.
7. Application in petroleum geology
Scanning electron microscopy provides a new means for understanding the fine structure of large paleontology and bioclastics in rocks and the understanding of micro-organisms such as sporopollen and algae ultrastructure. Many ultra-fine fossils can also be found from a large number of observations of paleontology, which provide new information for microbiology in terms of stratigraphic comparison and determination of stratigraphic age.
In the history of the earth, the characteristics of the sedimentary environment often remain on the surface of the mineral particles. Scanning electron microscopy is one of the most effective tools for studying the surface characteristics of mineral particles. Therefore, the observation by scanning electron microscopy combined with the energy spectrum can help us understand the characteristics of sedimentary facies and sedimentary environment. For example, the observation of the glauconite can clarify the difference in shape and composition between the Tertiary glauconite and the Sinian glauconite, and infer the source of the glauconite. Combined with other phase features, the characteristics of the sedimentary environment and sedimentary facies can be inferred.
In addition, scanning electron microscopy plays an important role in studying micropores in reservoirs and improving formation evaluation. Reservoir rocks can be divided into two major categories: clastic rocks and carbonate rocks. The micropores in these two types of reservoir rocks play a large role in the migration and storage of petroleum. Their development and connectivity are often carbonate reservoirs and clastic rocks that are good reservoirs. The micro-pores are small, about um up and down, and can be observed in detail at a high magnification of 500-5000 times. Specific application examples in this regard include the use of scanning electron microscopy to study the Ordovician oil sands of a certain oil well in China, and found that they are composed of coarse powdered limestone and granulated limestone. The intergranular gap between the development of the grain and the calcite calcite, the size of 1~2um, is connected to each other. The crystal cavity is developed in the coarse-grained limestone, and the size is larger than 100u. It can be seen that the mesoporous gap is formed and connected to the crystal gap. The cracks develop, most of which are structural joints, 2um wide, and straight and interconnected, and also communicate with the crystal gap. Through observation, the following conclusions are obtained: the layer of the oil sand is pore development, the various crystal gaps are connected to each other, and the crystal holes are connected with the crystal gap. The crack cuts the rock and communicates the crystal gap, thus making it have good storage. Set performance. Later, the well became a high-yield well with a daily output of more than 1,000 tons, confirming that the observations were correct.
Fourth, moon rock research
Since the arrival of Apollo-11 in 1968, more than 100 research institutions around the world have studied the moon rock isotopic age and material.
Extensive research has been carried out on ingredients, surface morphology and physical properties. This is an important theoretical and scientific value for understanding the physico-chemical conditions of moonstone, lunar soil and its formation, deriving the early formation and evolution of the moon, and exploring the origin, formation and evolution of the Earth and the solar system.
Li Wenzhong, Wang et al. conducted the following systematic study on the Apollo-17 moon rock using a scanning electron microscope equipped with x-ray energy spectrum.