Phase observation method of reactive sintering silicon carbide

Abstract

The invention discloses a reaction sintered silicon carbide phase observation method which comprises the following steps: S1, grinding an observation surface of a reaction sintered silicon carbide sample to form a rough surface with microstructure difference; s2, coating the observation surface with an oily coloring agent; s3, after standing for a preset time, wiping the observation surface by using a wiping tool wetted by a polar solvent so as to selectively remove the oily coloring agent which is not firmly adhered; and S4, observing the treated sample under an optical microscope, and distinguishing a silicon carbide phase and a free silicon phase based on color contrast generated by selectively retaining the coloring agent. The method can quickly, simply and conveniently distinguish each phase of the reactive sintering silicon carbide at low cost, and is particularly suitable for scenes with high requirements on timeliness and simplicity, such as a production field and the like.

Description

Technical Field

[0001] This invention relates to the field of materials microanalysis technology, and in particular to a method for observing the phase composition of reaction-sintered silicon carbide. Background Technology

[0002] Reactive sintered silicon carbide (RBSiC) is a high-performance multiphase ceramic composed of a high-hardness silicon carbide framework phase, a relatively soft free silicon filling phase, and pores. Due to its combination of high hardness, high wear resistance, excellent high-temperature stability, and chemical inertness, it is widely used in many industrial fields such as mechanical seals, wear-resistant components, and high-temperature structural parts. The distribution morphology of the silicon carbide framework and the filling state of the free silicon within RBSiC materials directly determine the core performance characteristics of the material, such as its mechanical properties and sealing performance. Therefore, characterizing its internal phases is a crucial step in evaluating material quality and analyzing the causes of failure.

[0003] Among various characterization methods, handheld optical microscopes offer advantages such as ease of operation and rapid in-situ analysis. However, in scenarios such as rapid inspection and preliminary failure analysis in production environments, limited by testing conditions, samples often only undergo conventional grinding processes and cannot be precision polished, resulting in high surface roughness. When such high-roughness samples are observed under a bright-field optical microscope, the scratches generated during the grinding process create a strong contrast between light and dark areas. This contrast masks the natural contrast differences between the silicon carbide phase and the free silicon phase, making it impossible to effectively distinguish the distribution and morphology of each phase within the field of view. This severely restricts the application of optical microscopes in relevant scenarios.

[0004] To enhance phase contrast, existing technologies employ chemical etching, which uses specific etchants to induce differentiated chemical reactions between different phases, creating morphological or compositional differences on the phase surfaces for differentiation. However, this technology is complex, has a long reaction cycle, requires precise control of reaction conditions, and often demands a high degree of sample surface smoothness to eliminate interference from surface morphology on dyeing uniformity, making it unsuitable for the time-sensitive requirements of on-site immediate testing. Summary of the Invention

[0005] The purpose of this invention is to provide a method that enables clear differentiation of phases, is easy to operate, and is suitable for rapid on-site observation using a handheld optical microscope.

[0006] To achieve the above objectives, the present invention provides a method for phase observation of reaction-sintered silicon carbide, comprising the following steps: S1. Grind the observation surface of the reaction-sintered silicon carbide sample to form a rough surface with microscopic morphological differences. S2. Apply the oil-based colorant to the observation surface; S3. After standing for a preset time, use a wiping tool moistened with a polar solvent to wipe the observation surface to selectively remove any oily colorant that has not adhered firmly. S4. Place the treated sample under a handheld optical microscope for observation. The color contrast produced by the selective retention of the colorant distinguishes the silicon carbide phase and the free silicon phase.

[0007] This invention actively utilizes and controls the natural micromorphological differences (hard phase protrusion, soft phase depression) formed during the grinding process due to the hardness difference between silicon carbide and free silicon. By applying an oily colorant to this rough surface and then selectively wiping it, the colorant is selectively retained on the surface of the protruding silicon carbide phase based on the difference in physical contact and adhesion, while being effectively removed from the depression of the free silicon phase. This principle eliminates the need for complex and dangerous chemical corrosion (such as corrosion by a mixed solution of nitric acid and hydrofluoric acid), transforming the surface roughness that interferes with observation in traditional methods into a powerful tool for phase differentiation. This achieves the technical effect of quickly, safely, easily, and cost-effectively separating the various phases of reaction-sintered silicon carbide, making it particularly suitable for scenarios with high requirements for timeliness and simplicity, such as production sites.

[0008] Furthermore, in step S1, the surface roughness Ra value of the observed surface after grinding is 0.1 μm to 1.0 μm. By limiting the surface roughness, it is ensured that sufficiently significant and controllable microscopic morphological differences can be produced after grinding; if the roughness is too low, the unevenness caused by the hardness difference will not be obvious, affecting the selective staining effect; if it is too high, the scratches will be too deep and large, which will interfere with microscopic observation.

[0009] Furthermore, in step S1, a diamond grinding disc or pad with a grit size of 800 to 2000 mesh is used for grinding. This grit size range of abrasive can efficiently and stably produce a defined surface roughness, while ensuring the uniformity and reproducibility of the surface morphology after grinding.

[0010] Furthermore, in step S1, the polished observation surface has a specific microstructure, with the silicon carbide phase forming a network of protrusions and the free silicon phase distributed in the gaps and depressions of the network of protrusions. The specific surface morphology formed based on the material hardness differences provides a structural guarantee for achieving a highly selective coloring effect that clearly reflects the distribution of the silicon carbide framework.

[0011] Furthermore, in step S2, an oil-based colorant is applied to the observation surface using a marker pen in a smearing motion, with no more than two smears. The marker pen, being an extremely common and inexpensive tool, makes this method easy to implement and promote; the limited number of smears avoids overfilling of the recessed areas with colorant, thus helping to maintain clear contrast.

[0012] Furthermore, in step S2, the oily colorant is red or blue. These two colors, together with the natural colors of silicon carbide and free silicon, create the strongest visual contrast, resulting in a vivid and easily distinguishable color contrast under an optical microscope, thus improving the accuracy and intuitiveness of phase identification.

[0013] Furthermore, in step S3, the preset time is 3 to 15 seconds. This time window is sufficient to allow the solvent in the oily colorant to evaporate, increasing its viscosity and thus better anchoring it to the raised silicon carbide phase, but without completely drying and curing it. This ensures that the colorant in the depression can still be easily removed, which is a key control parameter for achieving selective removal.

[0014] Furthermore, in step S3, the observation surface is wiped once in a single direction at an angle of 0° to 45° to the final grinding direction and with a pressure of less than 5 kPa. This wiping method ensures that the wiping tool follows the direction of the microstructure, effectively removing the colorant from the depressions, while using extremely light pressure to reduce the removal of the colorant already anchored in the protrusions, thereby achieving highly selective coloring.

[0015] Furthermore, in step S3, the solvent is one of ethanol, acetone, and isopropanol. These solvents have good dissolving power for oily colorants, which facilitates the removal of colorants from the depressions.

[0016] Furthermore, in step S3, the wiping tool is selected from one of the following: non-woven fabric, degreased cotton, filter paper, and sponge block. These materials are soft, do not easily shed lint, and have moderate liquid absorption, enabling effective wiping.

[0017] In summary, compared with the prior art, the present invention has the following beneficial effects: (1) This invention realizes a paradigm shift from chemical etching to physical selective coloring, solving the fundamental problem of the invisible phases in unfinished reaction-sintered silicon carbide samples. Traditional methods rely on the complex differences in chemical reactions between phases, while this invention cleverly utilizes the hardness-morphology differences naturally generated during grinding. Through the simple physical-mechanical action of coating and selective wiping, the colorant is precisely marked on the silicon carbide skeleton. This not only eliminates the reliance on hazardous chemicals and precision polishing steps, but also transforms scratches that interfere with observation into a favorable factor for enhancing contrast. Ultimately, images with vivid colors, clear contrast, and intuitively visible phase distribution are obtained under an optical microscope.

[0018] (2) This invention transforms complex laboratory analysis techniques into a rapid testing method that can be performed on the production site, greatly reducing the technical threshold and time cost. The entire process requires no special equipment; only conventional grinding tools, oil-based markers, and solvents are needed to complete it in a short time, and operators can quickly master it without professional training. This method has low requirements for sample surface finish, making it particularly suitable for rapid sampling inspection of products on the production line and on-site failure analysis of workpieces, where fine polishing is not possible. This greatly expands the application scope of optical microscopes in the field of silicon carbide material quality control.

[0019] (3) This invention achieves professional-grade characterization results at extremely low cost and has a significant technology spillover effect. This method replaces expensive consumables (precision polishing equipment, chemical reagents) with inexpensive markers and shortens the long processing time (chemical etching takes tens of minutes to several hours) to less than one minute, greatly reducing the detection cost. This simple method makes it easy to carry out professional microstructure analysis even in production workshops and teaching laboratories with limited resources. Attached Figure Description

[0020] Figure 1 This is a flowchart of the phase observation method for reaction-sintered silicon carbide according to the present invention.

[0021] Figure 2 These are photographs of the reaction-sintered silicon carbide samples after grinding and selective coloring in Example 1 of this invention, taken under an optical microscope.

[0022] Figure 3 These are photographs of the reaction-sintered silicon carbide samples after grinding and selective coloring in Example 2 of this invention, taken under an optical microscope.

[0023] Figure 4 These are photographs of the reaction-sintered silicon carbide samples after grinding and selective coloring in Example 3 of this invention, taken under an optical microscope.

[0024] Figure 5 These are photographs of the reaction-sintered silicon carbide samples after grinding and selective coloring in Example 4 of this invention, taken under an optical microscope. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0026] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0028] The specific embodiments of the present invention provide a method for observing the phases of reaction-sintered silicon carbide. By utilizing the hardness-morphology differences generated by grinding, the differential adhesion and selective removal of physical colorants, the method solves the problem that the phases of high-roughness reaction-sintered silicon carbide samples are difficult to distinguish under an optical microscope, and finally achieves rapid, simple and low-cost on-site observation.

[0029] Combination Figure 1 As shown, the above-mentioned phase observation method specifically includes the following steps: S1, sample surface morphology preparation; S2, selective physical staining; S3, selective removal of staining agent; S4, optical microscopy observation. The specific implementation process of each step is as follows: S1. Sample surface morphology preparation This step aims to create a specific microstructure on the observation surface based on phase hardness differences through controlled grinding, laying the structural foundation for subsequent physical selective coloring. First, the reaction-sintered silicon carbide component to be tested, or its accompanying furnace sample, is locally ground and polished. A diamond grinding wheel or disc with a mesh size of 800 to 2000 is selected as the grinding tool. The observation surface of the sample is placed tightly against the grinding wheel or disc, and grinding is performed in a single, fixed direction, maintaining a consistent final grinding direction. Uniform pressure is applied during the grinding process. After grinding, the observation surface is cleaned in an ultrasonic cleaner using anhydrous ethanol or acetone to remove residual abrasive, and then dried in an oven at 60°C to 80°C to ensure a clean and dry surface. After this step, the surface roughness Ra value of the observation surface is controlled within the range of 0.1 μm to 1.0 μm, preferably 0.15 μm to 0.25 μm. Since the silicon carbide phase (Mohs hardness of about 9.5) is much harder than the free silicon phase (Mohs hardness of about 6.5), under consistent grinding conditions, more of the softer free silicon is removed, thus forming a network of protrusions of silicon carbide phase at the microscale, with the free silicon phase distributed in the depressions between the network protrusions in a specific morphology.

[0030] S2, Selective Physical Coloring This step utilizes the principle that oil-based colorants preferentially adhere to microscopic raised surfaces through physical contact to achieve preliminary marking of the silicon carbide phase. Take a red or blue oil-based marker and bring the tip to the dried observation surface treated with S1. Apply the ink with gentle, quick strokes, ensuring the ink covers the entire observation surface. The oil-based ink of the marker has moderate viscosity and thixotropy, making it easy to spread during application and rapidly thickening when left to stand, reducing flow into recessed areas. The key to this operation is to apply the ink no more than twice to avoid overfilling of recessed areas; a single application is preferred.

[0031] S3, Selective removal of colorant This step is crucial for achieving selective phase coloring. By wiping within a specific time window, the colorant in the recessed areas is removed, while the colorant in the raised areas is retained. After completing the S2 coating, allow it to stand for a preset time of 3 to 15 seconds. This time window allows some of the solvent in the ink to evaporate, increasing its viscosity and thus better anchoring it to the raised silicon carbide phase surface, but the entire ink layer is not yet completely dry and cured. Next, take a clean piece of non-woven fabric, absorbent cotton, filter paper, or sponge, dip it in a small amount of a polar solvent such as ethanol, acetone, or isopropanol, and squeeze out the excess liquid. Gently press the moistened wiping tool onto the observation surface, applying very light pressure (less than 5 kPa) to ensure full contact between the tool and the observation surface. Then, perform a single, unidirectional translational wiping along a direction at an angle of 0° to 45° to the final grinding direction. This wiping method ensures that the tool follows the direction of the microstructure, effectively removing the free silicon phase in the depressions and the ink that is not firmly adhered in the pores. At the same time, due to the small contact area and adhesion, the ink anchored on the surface of the raised silicon carbide phase is retained to the greatest extent, thus achieving selective removal.

[0032] S4. Observation under an optical microscope This step involves observing the processed sample to clearly distinguish phases based on color contrast. After the S3-treated surface dries, it is observed using a portable handheld optical microscope. The microscope lens is brought close to and aligned with the observation area, and the focus is adjusted until the image is clear. At this point, in the microscope's field of view, the silicon carbide phase network selectively adhering to red or blue ink clearly displays the color of the colorant; the relatively recessed free silicon phase, where most of the colorant has been removed, appears bright white. The distinct contrast between the silicon carbide and free silicon phases due to color and brightness differences is sufficient for effective discrimination under a handheld microscope. This method eliminates the reliance on large tabletop metallurgical microscopes, enabling rapid preliminary identification and distribution assessment of phases without moving the sample in production environments, laboratory workbenches, and other settings.

[0033] The technical effects of the present invention will be described below with reference to specific embodiments. Unless otherwise specified, the raw materials used in the embodiments of this application were all purchased through commercial channels.

[0034] Example 1 In this embodiment, the phase composition of reaction-sintered silicon carbide is observed using a handheld optical microscope. The steps are as follows: (1) Sample preparation and grinding: A 10mm × 10mm sample of the reaction-sintered silicon carbide component was locally ground. An 800-mesh diamond grinding wheel was used to grind the observation surface under cooling conditions, maintaining a consistent grinding direction. After grinding, the surface roughness Ra of the sample was 0.15μm. The sample was then placed in an ultrasonic cleaner and cleaned with anhydrous ethanol for 5 minutes, then dried with compressed air for 15 minutes. The sample was observed under a handheld optical microscope (magnification: 200x), as shown in the attached figure. Figure 2 As shown in a, the silicon carbide phase and the silicon phase cannot be clearly distinguished.

[0035] (2) Selective physical coloring: Take a red oil-based marker, put the tip of the marker into contact with the dried observation surface, and quickly apply it once with even pressure so that the observation surface is covered with red ink.

[0036] (3) Selective removal of colorant: After coating, let stand for 5 seconds. Take a clean non-woven paper wipe, dip it in a small amount of anhydrous ethanol and squeeze it until it is slightly damp. Gently press the non-woven paper onto the observation surface, apply slight pressure (about 3-4 kPa), and wipe at a uniform speed in a single stroke along a direction parallel to the final grinding direction at an angle of 0° to 45°.

[0037] (4) Observation and Results: After the surface solvent has evaporated, the sample was observed under a handheld optical microscope (magnification: 200x). (See attached image) Figure 2 As shown in b, the continuous three-dimensional network composed of silicon carbide phase is dyed deep red, while the free silicon phase appears bright white, filling the spaces between the red network. The contrast between the two is striking, effectively suppressing the visual interference of the original polishing scratches, and the phase distribution is clearly visible.

[0038] Example 2 In this embodiment, the phase composition of reaction-sintered silicon carbide is observed using a handheld optical microscope. The steps are as follows: (1) Sample preparation and grinding: The sample was ground using a 1000-mesh diamond grinding disc to obtain an observation surface with Ra≈0.2μm. After ultrasonic cleaning with acetone, it was dried at 80℃. The sample was observed under a handheld optical microscope (magnification: 200x), as shown in the attached figure. Figure 3 As shown in a, the silicon carbide phase and the silicon phase cannot be clearly distinguished.

[0039] (2) Selective physical coloring: Use a blue oil-based marker to apply a single coat to cover the surface.

[0040] (3) Selective removal of colorant: After standing for 3 seconds, use a cotton ball soaked in isopropyl alcohol to apply slight pressure (about 3-4 kPa) and wipe at a uniform speed once along a direction parallel to the final grinding direction at an angle of 0° to 45°.

[0041] (4) Observations and Results: Under a handheld microscope (200x), a cool-toned, high-contrast image was observed between the blue silicon carbide framework and the bright white free silicon phase, as shown in the attached image. Figure 3 As shown in b, the phase boundaries are clear.

[0042] Example 3 In this embodiment, the phase composition of reaction-sintered silicon carbide is observed using a handheld optical microscope. The steps are as follows: (1) Sample preparation and grinding: A local area of ​​the reaction-sintered silicon carbide component was ground using a 2000-mesh diamond grinding disc and a handheld electric grinding tool to obtain an observation surface with Ra≈0.25μm. The surface was wiped with ethanol and then allowed to air dry. A handheld optical microscope was placed at the ground observation area (magnification: 200x) for observation, as shown in the attached figure. Figure 4 As shown in a, the silicon carbide phase and the silicon phase cannot be clearly distinguished.

[0043] (2) Selective physical coloring: Quickly apply red marker twice to cover the surface.

[0044] (3) Selective removal of colorant: After standing for 10 seconds, use filter paper dipped in acetone to apply slight pressure (about 3-4 kPa) and wipe once at a uniform speed along a direction parallel to the final grinding direction at an angle of 0° to 45°. The above process takes less than 1 minute.

[0045] (4) Observations and Results: Under a handheld microscope (200x), a deep red silicon carbide phase and a light red free silicon phase were visible, as shown in the attached figure. Figure 4 As shown in b, the phase distribution can still be observed.

[0046] Example 4 (1) Sample preparation and grinding: The sample was ground with a 900-mesh diamond grinding disc to obtain an observation surface with Ra≈0.3μm, and then cleaned and dried. The sample was observed under a handheld optical microscope (magnification: 200x), as shown in the attached figure. Figure 5 As shown in a, the silicon carbide phase and the silicon phase cannot be clearly distinguished.

[0047] (2) Selective physical coloring: Use a red oil-based marker to apply a single coat to cover the surface.

[0048] (3) Selective removal of colorant: After standing for 15 seconds, use a microfiber sponge dipped in ethanol to apply very slight pressure (<2kPa) and wipe at a uniform speed once along a direction parallel to the final grinding direction at an angle of 0° to 45°.

[0049] (4) Observations and Results: Under a handheld microscope (200x), a deep red silicon carbide phase and a light red free silicon phase were visible, as shown in the attached figure. Figure 5 As shown in b, the phase boundaries are clear.

[0050] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the scope of protection of this invention.

Claims

1. A method for observing the phase composition of reaction-sintered silicon carbide, characterized in that, Includes the following steps: S1. Grind the observation surface of the reaction-sintered silicon carbide sample to form a rough surface with microscopic morphological differences. S2. Apply the oil-based colorant to the observation surface; S3. After standing for a preset time, use a wiping tool moistened with a polar solvent to wipe the observation surface to selectively remove any oily colorant that has not adhered firmly. S4. Place the treated sample under an optical microscope for observation. The color contrast produced by the selective retention of the colorant distinguishes the silicon carbide phase and the free silicon phase.

2. The method for phase observation of reaction-sintered silicon carbide according to claim 1, characterized in that, In step S1, the surface roughness Ra of the ground observation surface is 0.1 μm to 1.0 μm.

3. The method for phase observation of reaction-sintered silicon carbide according to claim 2, characterized in that, In step S1, a diamond grinding disc or grinding wheel with a mesh size of 800 to 2000 is used for grinding.

4. The method for phase observation of reaction-sintered silicon carbide according to claim 2, characterized in that, In step S1, the ground observation surface has a specific micromorphology, with silicon carbide phase forming a network of protrusions and free silicon phase distributed in the gaps and depressions of the network of protrusions.

5. The method for phase observation of reaction-sintered silicon carbide according to claim 1, characterized in that, In step S2, an oil-based colorant is applied to the observation surface using a marker pen in a smearing manner, with no more than two smears.

6. The method for phase observation of reaction-sintered silicon carbide according to claim 5, characterized in that, In step S2, the color of the oily colorant is red or blue.

7. The method for phase observation of reaction-sintered silicon carbide according to claim 1, characterized in that, In step S3, the preset time is 3 to 15 seconds.

8. The method for phase observation of reaction-sintered silicon carbide according to claim 7, characterized in that, In step S3, the observation surface is wiped once in one direction at an angle of 0° to 45° to the final grinding direction and with a pressure of less than 5 kPa.

9. The method for phase observation of reaction-sintered silicon carbide according to claim 1, characterized in that, In step S3, the solvent is one of ethanol, acetone, and isopropanol.

10. The method for phase observation of reaction-sintered silicon carbide according to claim 1, characterized in that, In step S3, the wiping tool is selected from one of the following: non-woven fabric, degreased cotton, filter paper, and sponge block.

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