Preparation system and method of graphite pipe for high-temperature-resistant spectrum analysis

Abstract

The invention provides a preparation system and method of a graphite pipe for high-temperature-resistant spectral analysis, and belongs to the technical field of spectral analysis, and the preparation system comprises a raw material pretreatment module used for crushing, grading and purifying a graphite raw material and mixing a preparation to form uniform slurry; the isostatic pressing forming module is connected with the raw material pretreatment module, composite sol comprises silica sol, molybdate and phytic acid, and a stirring piece is arranged in the composite sol preparation module; the vacuum-pressurization alternating module is connected with the composite sol preparation module; the high-temperature sintering module is connected with the vacuum-pressurization alternating module; the chemical vapor deposition module is connected with the high-temperature sintering module; and the quality detection module is connected with the chemical vapor deposition module. The silica sol, the molybdate and the phytic acid have a synergistic effect to form a SiC-MoSi composite phase, so that the temperature resistance of the graphite pipe is improved, the thermal stability of the graphite pipe is enhanced, and the service life of the graphite pipe is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of spectral analysis, and in particular relates to a system and method for preparing a high-temperature resistant graphite tube for spectral analysis. Background Art

[0002] The graphite tube, the core component of an atomic absorption spectrometer, operates on the principle of atomic absorption spectroscopy. When light of a specific wavelength emitted by a light source (such as a hollow cathode lamp) passes through the atomic vapor in the graphite tube, the electrons in the atoms absorb the energy of the photons, transitioning from their ground state to an excited state. According to the Lambert-Beer law, the absorbance is proportional to the atomic concentration, allowing the concentration of elements in the sample to be determined by measuring the absorbance.

[0003] Graphite tubes used for spectral analysis have extremely high material performance requirements and are made of high-purity graphite. One of the core characteristics of graphite tubes is their high-temperature resistance. High-purity graphite can withstand extreme temperatures of up to 3000°C in an inert gas or vacuum environment. In practical applications, the high-temperature resistance of graphite tubes is affected by the following factors: Material purity: High-purity graphite (purity ≥99.9%) has higher thermal stability and oxidation resistance, and can maintain structural integrity at high temperatures. Environmental atmosphere: Graphite exhibits excellent high-temperature resistance in an inert gas (such as argon, nitrogen) or vacuum environment and can be used for a long time at 2500-3000°C.

[0004] However, the most common problems with existing graphite tubes are: 1. High-temperature oxidation: When temperatures exceed 600°C, the graphite tube reacts violently with oxygen, producing CO or CO2, leading to rapid tube wear. 2. Thermal shock damage: The instantaneous high temperature during the atomization phase (typically 2000-3000°C) and the rapid temperature fluctuations during the cooling phase cause microcracks in the graphite tube, leading to structural failure. Both of these phenomena shorten the lifespan of the graphite tube. Summary of the Invention

[0005] Based on this, the present invention provides a system for preparing high-temperature resistant graphite tubes for spectral analysis to solve the technical problem in the prior art of shortening the service life of graphite tubes due to high-temperature oxidation and thermal shock damage.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] A system for preparing a graphite tube for high temperature resistant spectral analysis, comprising:

[0008] Raw material pretreatment module, used to crush, classify, purify and mix the graphite raw materials to form a uniform slurry;

[0009] an isostatic pressing module, connected to the raw material pretreatment module, for pressing the slurry into a graphite tube matrix;

[0010] A composite sol preparation module, wherein the composite sol comprises silica sol, molybdate and phytic acid, and a stirring element is provided in the composite sol preparation module for uniformly mixing the silica sol, molybdate and phytic acid;

[0011] a vacuum-pressurization alternating module connected to the composite sol preparation module, the vacuum-pressurization alternating module comprising a vacuum pumping component and a pressurizing component, for infiltrating the composite sol into the graphite tube matrix;

[0012] A high-temperature sintering module is connected to the vacuum-pressure alternating module, and the high-temperature sintering module includes a programmable temperature control component and an atmosphere protection component, and is used to perform a step-by-step temperature increase heat treatment on the graphite tube substrate infiltrated with the composite sol;

[0013] The chemical vapor deposition module is connected to the high-temperature sintering module and is used to deposit a pyrolytic carbon layer on the surface of the graphite tube substrate after sintering.

[0014] Preferably, in the above-mentioned high-temperature resistant graphite tube preparation system for spectral analysis, the raw material pretreatment module includes a primary grinding component and a secondary grinding component, the primary grinding component is used to grind the graphite raw material into 60-120 mesh particles, and the secondary grinding component is used to further grind the particles ground by the primary grinding component to a particle size of 1-10 μm.

[0015] Preferably, in the above-mentioned high-temperature resistant graphite tube preparation system for spectral analysis, the vacuum-pressurization alternating module includes a vacuum pumping unit, which is used to vacuum into a negative pressure state, the vacuum degree of which is -0.08 to -0.1 MPa, and is maintained for 20-40 minutes, and a pressurizing unit, which is used to increase the pressure, the increased pressure is 0.5-1.2 MPa, and is maintained for 1-3 hours.

[0016] Preferably, in the above-mentioned high-temperature resistant graphite tube preparation system for spectral analysis, the high-temperature sintering module is used to perform the following steps to perform a stepwise temperature increase heat treatment on the graphite tube substrate infiltrated with the composite sol:

[0017] The first stage: heating to 400-600℃ at 2-10℃ / min and keeping warm for 0.5-2 hours;

[0018] The second stage: heating to 1200-1400℃ at 1-5℃ / min and keeping warm for 1-3 hours;

[0019] The third stage: heating to 1800-2200℃ at 5-15℃ / min and keeping warm for 0.5-2 hours.

[0020] Preferably, in the above-mentioned high-temperature resistant graphite tube preparation system for spectral analysis, the chemical vapor deposition module uses chemical vapor deposition to deposit a pyrolytic carbon layer on the surface of the sintered graphite tube substrate, wherein the carbon source is methane, acetylene or propane, the deposition temperature is 1600-2000°C, the time is 20-60 minutes, and the thickness of the obtained pyrolytic carbon layer is 10-100 μm.

[0021] Preferably, the above-mentioned high-temperature resistant graphite tube preparation system for spectral analysis further includes a surface coating module for coating the outer surface of the graphite tube with a graphite antioxidant after the step-by-step temperature increase heat treatment, with a coating thickness of 5-20 μm and curing at 300-500°C.

[0022] A method for preparing a high-temperature resistant graphite tube for spectral analysis, using the above-mentioned system for preparing a high-temperature resistant graphite tube for spectral analysis, comprising:

[0023] S1: Grind, classify, purify the graphite raw materials, and add a binder to form a uniform slurry;

[0024] S2: isostatically pressing the slurry into a high-purity graphite tube matrix;

[0025] S3: preparing a composite sol, wherein the composite sol comprises a mixture of silica sol, molybdate and phytic acid;

[0026] S4: infiltrating the composite sol into the graphite matrix using a vacuum-pressure alternating impregnation process;

[0027] S5: performing a stepwise temperature increase heat treatment in an inert environment to form a SiC-MoSi2 composite reinforcement phase;

[0028] S6: Depositing a pyrolytic carbon layer on the inner wall of the graphite tube.

[0029] Preferably, in the above-mentioned method for preparing a high-temperature resistant graphite tube for spectral analysis, the composite sol comprises, by weight:

[0030] 40-60 parts of the silica sol,

[0031] 3-10 parts of the molybdate,

[0032] 2-8 parts of phytic acid,

[0033] 30-50 parts of alcohol solvent.

[0034] Preferably, in the above-mentioned method for preparing a high-temperature resistant graphite tube for spectral analysis, the SiO2 content in the silica sol is ≥30wt%; the molybdate is ammonium molybdate or sodium molybdate, wherein the content of ammonium molybdate or sodium molybdate is ≥99wt%; and the purity of the phytic acid is ≥50%.

[0035] Preferably, in the above-mentioned method for preparing a graphite tube for high temperature resistant spectral analysis, the density of the graphite tube matrix is ​​1.7-2.2 g / cm 3 , carbon content ≥ 99.9wt%, and the surface of the substrate is surface activated by plasma treatment or acid pickling activation.

[0036] Compared with the prior art, the present invention has at least the following advantages:

[0037] 1. The silica sol, molybdate, and phytic acid interact synergistically to form a SiC-MoSi2 composite phase. The phytic acid prevents molybdate aggregation and promotes SiC whisker growth during heat treatment, raising the graphite tube's oxidation resistance temperature. Simultaneously, the phytic acid catalyzes the reconstruction of the graphite matrix edge, forming a unique "toothed interlaced interface." This improves the graphite tube's structural strength, reducing its oxidation weight loss rate from >10% to <3%, thereby enhancing its temperature resistance. Repeated heating and rapid temperature changes reduce microcracks on the graphite tube's surface, enhancing its thermal stability. This enhanced temperature resistance and thermal stability ultimately significantly increase the number of uses for the graphite tube, extending its service life.

[0038] 2. The vacuum-pressure alternating impregnation process accelerates the penetration of the composite sol into the graphite matrix, solving the problem of high-density graphite matrix being difficult to penetrate, achieving a combination of internal matrix reinforcement and surface modification, and realizing overall protection "from the inside out".

[0039] 3. The deposited pyrolytic carbon layer reduces the reaction or penetration of the measured elements with graphite at high temperatures, reduces cross contamination, and reduces the memory effect of the graphite tube by 70%, while traditional pyrolytic graphite tubes can only reduce it by 30-40%. It is particularly suitable for the analysis of high melting point elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the graphite tube preparation system for high-temperature resistant spectral analysis.

[0041] Figure 2 Schematic diagram of the raw material pretreatment module.

[0042] In the figure: raw material pretreatment module 100, primary grinding assembly 110, secondary grinding assembly 120, isostatic pressing module 200, composite sol preparation module 300, vacuum-pressurization alternating module 400, high-temperature sintering module 500, chemical vapor deposition module 600, quality inspection module 700. DETAILED DESCRIPTION

[0043] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The following will further describe the technical solution of the present invention in conjunction with the drawings of the embodiments of the present invention, and the present invention is not limited to the following specific embodiments.

[0044] It should be understood that the same or similar numbers in the drawings of the embodiments correspond to the same or similar parts. In the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "front", "back", "left", "right", "top", "bottom" and the like indicating an orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as a limitation of this patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to the specific circumstances.

[0045] Please see Figure 1 , a high temperature resistant graphite tube preparation system for spectral analysis, including

[0046] The raw material pretreatment module 100 is used to crush, classify, purify and prepare the graphite raw material to form a uniform slurry; the graphite raw material is flake graphite, wherein the grinding equipment used for crushing grinds the flake graphite into graphite powder of a preset particle size, and the classification uses a centrifugal classifier, using a multi-stage separation box (one to three stages) to separate the graphite powders of different particle sizes according to the gradient by centrifugal force. For example, the diameter of the grading holes of the three-stage separation box decreases step by step (such as the first stage > the second stage > the third stage) to achieve precise control of the particle size. Purification uses acid-base purification equipment, continuous gas-powder mixing purification equipment and high-temperature roasting furnaces. The acid-base purification equipment includes an alkali melting furnace (high-temperature melting of sodium hydroxide) and an acid immersion tank (hydrofluoric acid or sulfuric acid treatment) to remove silicates and metal impurities, which can increase the purity of graphite to more than 99.8%. The continuous gas-powder mixing purification equipment uses a spiral rod to mix graphite powder with process gas (such as chlorine) at high temperature to remove volatile impurities and achieve continuous production. The purity can reach 99.9%, and then the impurities are gasified in a high-temperature roasting furnace at 2700-3000℃ to make the graphite purity reach ≥99.9%.

[0047] The isostatic pressing module 200 is connected to the raw material pretreatment module 100 and is used to press the slurry into a graphite tube matrix; the isostatic pressing module includes an isostatic press, which gradually increases the pressure through a booster system and transmits pressure through liquid so that each surface of the object is subjected to equal pressure and is formed into a graphite tube matrix, such as a transverse graphite tube matrix, under the restriction of the mold.

[0048] The composite sol preparation module 300 includes silica sol, molybdate and phytic acid. A stirring element is provided in the composite sol preparation module for uniformly mixing the silica sol, molybdate and phytic acid.

[0049] The alternating vacuum-pressurization module 400 is connected to the composite sol preparation module 300 and includes a vacuum unit and a pressurization unit for infiltrating the composite sol into the graphite tube substrate. The vacuum unit is used to evacuate to a negative pressure state, with a vacuum degree of -0.08 to -0.1 MPa maintained for 20-40 minutes, and the pressurization unit is used to increase the pressure to 0.5-1.2 MPa for 1-3 hours. This alternating vacuum-pressurization method allows the composite sol to infiltrate the graphite substrate, solving the problem of high-density graphite substrates being difficult to penetrate.

[0050] The high-temperature sintering module 500 is connected to the vacuum-pressurization alternating module 400. The high-temperature sintering module includes a programmable temperature control component and an atmosphere protection component, which are used to perform a step-by-step temperature increase heat treatment on the graphite tube substrate infiltrated with the composite sol; the programmable temperature control component increases the temperature in a step-by-step manner, and the atmosphere protection component introduces argon gas during the heating process to isolate the air and prevent high-temperature oxidation.

[0051] The chemical vapor deposition module 600 is connected to the high-temperature sintering module and is used to deposit a pyrolytic carbon layer on the surface of the graphite tube substrate after sintering.

[0052] The quality inspection module 700 is connected to the chemical vapor deposition module and includes a spectrum analyzer and an electron microscope for performing structural characterization and performance testing on the finished product.

[0053] In a possible embodiment, the raw material pretreatment module 100 includes a primary grinding component 110 and a secondary grinding component 120. The primary grinding component 110 is used to grind the graphite raw material into 60-120 mesh particles. The primary grinding component 110 adopts a honeycomb mill. The secondary grinding component 120 is used to further grind the particles ground by the primary grinding component 110 to a particle size of 1-10 μm. The secondary grinding component 120 adopts a cell mill.

[0054] In a possible embodiment, the quality detection module 700 also includes a laser thermal conductivity meter, a four-probe resistance tester and an atomic absorption spectrometer. The laser thermal conductivity meter is used to test thermal conductivity, the four-probe resistance tester is used to test resistivity, and the atomic absorption spectrometer is used to test element content.

[0055] In a possible embodiment, the vacuum-pressurization alternating module includes a vacuum unit, which is used to vacuum into a negative pressure state, the vacuum degree of which is -0.08 to -0.1 MPa, and is maintained for 20-40 minutes, and a pressurization unit, which is used to increase the pressure, the increased pressure is 0.5-1.2 MPa, and is maintained for 1-3 hours.

[0056] In a possible embodiment, the high-temperature sintering module is used to perform the following steps to perform a step-by-step temperature increase heat treatment on the graphite tube matrix infiltrated with the composite sol:

[0057] The first stage: heating to 400-600℃ at 2-10℃ / min and keeping warm for 0.5-2 hours;

[0058] The second stage: heating to 1200-1400℃ at 1-5℃ / min and keeping warm for 1-3 hours;

[0059] The third stage: heating to 1800-2200℃ at 5-15℃ / min and keeping warm for 0.5-2 hours.

[0060] In a possible embodiment, the chemical vapor deposition module uses chemical vapor deposition to deposit a pyrolytic carbon layer on the surface of the sintered graphite tube substrate, wherein the carbon source is methane, acetylene or propane, the deposition temperature is 1600-2000°C, the time is 20-60 minutes, and the thickness of the obtained pyrolytic carbon layer is 10-100 μm.

[0061] In a possible embodiment, a surface coating module is further included, which is used to coat the outer surface of the graphite tube with a graphite antioxidant after the step-by-step temperature increase heat treatment, with a coating thickness of 5-20 μm and curing at 300-500°C.

[0062] A method for preparing a high-temperature resistant graphite tube for spectral analysis, comprising:

[0063] S1: The graphite raw material is crushed, graded, purified, and a binder is added to form a uniform slurry; the crushing is first processed by a primary grinding (honeycomb mill), the deagglomeration wheel speed is 1500rpm, and the grinding is carried out for 30 minutes to obtain 60-80 mesh particles; then it enters the secondary grinding (cell mill) for fine grinding, the medium is zirconia balls, the ball-to-material ratio is 5:1, and the time is 2 hours to obtain graphite powder with an average particle size of 3μm; the graphite powder is added to a centrifugal classifier for gradient separation to obtain a primary graphite powder; the primary graphite powder is sequentially added to an acid-base purification equipment, a continuous gas-powder mixing purification equipment, and a high-temperature roasting furnace to remove impurities to obtain 99.95% purified graphite powder; the purified graphite powder is mixed with a binder, the binder is a mixture of 1.5wt% white graphene (hexagonal boron nitride nanosheets) and 15wt% high-temperature phenolic resin (residual carbon rate ≥60%), and an appropriate amount of ethanol is added as a dispersant. The mixture was premixed at 800 rpm for 30 minutes using a high-speed shear mixer, and then ground three times using a three-roll mill (roller spacing of 50 μm) to obtain a uniform slurry.

[0064] S2: isostatically pressing the slurry into a high-purity graphite tube matrix; the slurry is loaded into a special rubber mold (such as a transverse graphite tube mold), and maintained at an isostatic pressure of 220 MPa for 15 minutes. The graphite tube matrix is ​​a transverse graphite tube matrix.

[0065] S3: Prepare a composite sol, which is a mixture of silica sol, molybdate and phytic acid; the silica sol is a colloidal solution, which is a dispersion of nano-scale silica particles in water or solvent, and contains a large amount of silicon dioxide SiO2; the molybdate is an inorganic chemical substance, which can be reduced and reacts with graphite to form molybdenum silicide MoSi2 under high temperature environment, and the molybdenum silicide forms a high-temperature resistant coating on the graphite tube. For example, the invention patent No. CN116023157A discloses the high-temperature coating characteristics formed by molybdenum silicide; the phytic acid is also known as inositol hexaphosphate C6H 18 O 24 P6, Traditionally, phytic acid has only been used as a metal ion chelating agent.

[0066] S4: The composite sol is infiltrated into the graphite matrix by a vacuum-pressure alternating impregnation process; that is, the graphite matrix is ​​immersed in the composite sol, and the composite sol is infiltrated into the graphite matrix by alternating vacuum-pressure, thereby solving the problem that the high-density graphite matrix is ​​difficult to penetrate.

[0067] S5: Perform step-by-step temperature increase heat treatment in an inert environment. Argon gas is introduced into the inert environment to isolate oxygen, prevent oxygen from reacting with the graphite tube and graphite in a high-temperature environment, and reduce the generation of CO or CO2. Step-by-step temperature increase means increasing the preset temperature within a preset time, stopping / keeping the temperature for a preset time, and then increasing the preset temperature again within a preset time to achieve the effect of step-by-step temperature increase to form a SiC-MoSi2 composite reinforcement phase. The SiC-MoSi2 composite reinforcement phase system is composed of a matrix phase (MoSi2) and a dispersed reinforcement phase (SiC), with molybdenum disilicide (MoSi2) as the matrix and silicon carbide (SiC) as the reinforcement phase.

[0068] S6: Depositing a pyrolytic carbon layer on the inner wall of the graphite tube. Chemical vapor deposition is a method for depositing a thin film on a substrate through the gas phase. The carbon-containing precursor gas is dissociated at high temperature, causing carbon atoms to be deposited on the substrate, that is, on the inner wall of the graphite tube. The pyrolysis method is to prepare pyrolytic carbon by pyrolyzing hydrocarbon gases (such as propane, methane, etc.) at high temperature. This is carried out in a high-temperature furnace, and carbon atoms are deposited on the inner wall of the graphite tube through processes such as pyrolysis and polycondensation.

[0069] In a possible embodiment, the composite sol comprises, by weight:

[0070] The silica sol is 40-60 parts. The silica sol is a dispersion of nano-sized silicon dioxide particles with a high specific surface area and active hydroxyl groups. It can form a dense silicon-oxygen network structure (-Si-O-Si-), enhancing the mechanical strength and high temperature resistance of the coating (resistant to 1500-1600°C). The amount of 40-60 parts ensures sufficient film-forming material and coverage while avoiding brittleness or cracking caused by excessive use.

[0071] The molybdate is 3-10 parts. Molybdate (such as sodium molybdate) forms a molybdenum oxide passivation film by oxidizing the metal surface to inhibit electrochemical corrosion. It is particularly effective when replacing toxic chromate. The concentration of 3-10 parts balances cost and performance. Excessive use may affect coating uniformity due to solubility limitations or crystallization precipitation.

[0072] The phytic acid molecule contains 12 phosphate groups and can react with metal ions (such as Fe 3+ 、Al 3+ ) forms a stable chelate, generates a dense monomolecular film on the metal surface, blocks the corrosion path, and 2-8 parts are sufficient to cover the metal surface and form a continuous film. Excessive use may cause the film to be too thick and brittle.

[0073] The alcohol solvent is 30-50 parts. Alcohols (such as ethanol and ethylene glycol) are used as solvents to promote the uniform dispersion of silica sol, molybdate and phytic acid and prevent particle agglomeration. 30-50 parts ensures the full dissolution of each component and process operability. Excessive amounts may delay curing or reduce coating hardness.

[0074] In a preferred embodiment, the composite sol comprises, by weight: 40 parts of the silica sol, 3 parts of the molybdate, 2 parts of the phytic acid, and 30 parts of the alcohol solvent.

[0075] In a preferred embodiment, the composite sol comprises, by weight: 50 parts of the silica sol, 6 parts of the molybdate, 5 parts of the phytic acid, and 40 parts of the alcohol solvent.

[0076] In a preferred embodiment, the composite sol comprises, by weight: 60 parts of the silica sol, 10 parts of the molybdate, 8 parts of the phytic acid, and 50 parts of the alcohol solvent.

[0077] In a possible embodiment, the SiO2 content in the silica sol is ≥30wt%; the molybdate is ammonium molybdate ((NH4)2MoO4) or sodium molybdate (Na2MoO4), wherein the content of ammonium molybdate ((NH4)2MoO4) or sodium molybdate (Na2MoO4) is ≥99wt%; and the purity of the phytic acid is ≥50%.

[0078] In a preferred embodiment, the SiO2 content in the silica sol is 30wt%; the molybdate is ammonium molybdate ((NH4)2MoO4) or sodium molybdate (Na2MoO4), wherein the content of ammonium molybdate ((NH4)2MoO4) or sodium molybdate (Na2MoO4) is 99.5wt%, that is, the purity is 99.5%; the purity of the phytic acid is 50%.

[0079] It is important to further clarify that, while conventional wisdom holds that heat treatment of silica sol only produces SiO₂, the present invention demonstrates a synergistic effect between the silica sol, molybdate, and phytic acid. The silica sol provides a skeletal structure, while the molybdate fills the pores, synergistically enhancing corrosion resistance. The chelation effect of the phytic acid complements the oxidative passivation of the molybdate, enhancing comprehensive metal protection. The presence of molybdate and phytic acid promotes the in-situ formation of a unique structure of SiC whiskers and MoSi₂ nanoparticles at temperatures between 1600 and 1800°C. Electron microscopy analysis reveals that this structure effectively pins the graphite matrix grain boundaries, inhibiting crack propagation at high temperatures. Furthermore, while phytic acid has traditionally been used only as a metal ion chelator, the present invention demonstrates for the first time that it can catalyze the reconstruction of the graphite matrix edges at high temperatures (>1200°C), forming a unique "toothed interdigitated interface" that increases the coating-substrate bond strength by more than three times.

[0080] In a possible embodiment, the composite sol further includes 0.1-3 parts of graphene or graphene oxide. The quantum effect of graphene or graphene oxide and the interface bonding force of SiC are synergistically optimized, which can improve the strength of the graphite tube and the thermal conductivity of the graphite tube.

[0081] In a preferred embodiment, the amount of graphene or graphene oxide is 0.5 parts.

[0082] In a preferred embodiment, the amount of graphene or graphene oxide is 2 parts.

[0083] In a possible embodiment, the vacuum-pressure alternating impregnation process includes:

[0084] Vacuum stage: vacuum degree -0.08 to -0.1 MPa, maintained for 20-40 minutes;

[0085] Pressurization stage: pressure 0.5-1.2MPa, maintained for 1-3 hours;

[0086] The number of dipping cycles is 2-4 times.

[0087] The composite sol can penetrate the graphite tube matrix, facilitating the in-situ formation of a unique structure of SiC whiskers and MoSi2 nanoparticles during heating. This solves the problem of high-density graphite matrix penetration, achieving a combination of internal matrix reinforcement and surface modification, providing comprehensive protection from the inside out.

[0088] In a preferred embodiment, during the vacuum stage, the vacuum degree is -0.08 MPa and maintained for 30 minutes; during the pressurization stage, the pressure is 1.2 MPa and maintained for 2 hours; and the number of immersion cycles is 2 times.

[0089] In a preferred embodiment, during the vacuum stage, the vacuum degree is -0.04 MPa and maintained for 30 minutes; during the pressurization stage, the pressure is 0.8 MPa and maintained for 2 hours; and the number of immersion cycles is 2 times.

[0090] In a preferred embodiment, during the vacuum stage, the vacuum degree is -0.02 MPa and maintained for 30 minutes; during the pressurization stage, the pressure is 0.5 MPa and maintained for 2 hours; and the number of immersion cycles is 4 times.

[0091] In a possible embodiment, the stepwise temperature-increasing heat treatment includes:

[0092] The first stage: heating to 400-600℃ at 2-10℃ / min and keeping warm for 0.5-2 hours;

[0093] The second stage: heating to 1200-1400℃ at 1-5℃ / min and keeping warm for 1-3 hours;

[0094] The third stage: heating to 1800-2200°C at 5-15°C / min and keeping at this temperature for 0.5-2 hours. That is, the high temperature sintering module is used to perform the above steps to perform a step-by-step temperature treatment on the graphite tube matrix infiltrated with the composite sol.

[0095] In a preferred embodiment, the step-by-step temperature increase heat treatment includes: the first stage: heating to 500°C at 2°C / min and keeping warm for 1 hour; the second stage: heating to 1300°C at 2°C / min and keeping warm for 1 hour; the third stage: heating to 2000°C at 5°C / min and keeping warm for 1 hour.

[0096] In a preferred embodiment, the step-by-step temperature increase heat treatment includes: the first stage: heating to 500°C at 5°C / min and keeping warm for 1 hour; the second stage: heating to 1300°C at 3°C / min and keeping warm for 1 hour; the third stage: heating to 2000°C at 8°C / min and keeping warm for 1 hour.

[0097] In a preferred embodiment, the step-by-step temperature increase heat treatment includes: the first stage: heating to 500°C at 10°C / min and keeping warm for 1 hour; the second stage: heating to 1300°C at 5°C / min and keeping warm for 1 hour; the third stage: heating to 2000°C at 15°C / min and keeping warm for 1 hour.

[0098] In one possible embodiment, the pyrolytic carbon layer is deposited using chemical vapor deposition, that is, the chemical vapor deposition module uses chemical vapor deposition to deposit a pyrolytic carbon layer on the surface of the sintered graphite tube substrate, with the carbon source being methane, acetylene, or propane, the deposition temperature being 1600-2000°C, the time being 20-60 minutes, and the resulting pyrolytic carbon layer having a thickness of 10-100 μm. At high temperatures, the carbon-containing methane, acetylene, or propane gas is dissociated, and carbon atoms are deposited on the substrate, i.e., on the inner wall of the graphite tube. Chemical vapor deposition can control the film thickness, uniformity, and carbon layer structure. During high-temperature operation, the inner wall pyrolytic carbon layer is selectively consumed to form a dense glassy carbon film. The adaptive protection mechanism enables the graphite tube to maintain stable analytical performance under extreme conditions, reduces the reaction or penetration of the measured element with the graphite at high temperatures, reduces cross-contamination, and reduces the memory effect of the graphite tube by 70%, while traditional pyrolytic graphite tubes can only reduce it by 30-40%, making it particularly suitable for the analysis of high-melting-point elements.

[0099] In a preferred embodiment, the pyrolytic carbon layer is deposited by chemical vapor deposition, with methane as the carbon source, a deposition temperature of 1600° C., and a deposition time of 45 minutes. The resulting pyrolytic carbon layer has a thickness of 50 μm.

[0100] In a preferred embodiment, the pyrolytic carbon layer is deposited by chemical vapor deposition, the carbon source is acetylene, the deposition temperature is 1800° C., the deposition time is 45 minutes, and the obtained pyrolytic carbon layer has a thickness of 50 μm.

[0101] In a preferred embodiment, the pyrolytic carbon layer is deposited by chemical vapor deposition, the carbon source is propane, the deposition temperature is 2000° C., the time is 45 minutes, and the obtained pyrolytic carbon layer has a thickness of 50 μm.

[0102] In a possible embodiment, the graphite tube substrate is isostatic graphite or pyrolytic graphite with a density of 1.7-2.2 g / cm 3 , carbon content ≥99.9wt%, and the substrate surface is plasma treated or acid-activated.

[0103] In a preferred embodiment, the graphite tube substrate is isostatically pressed graphite with a density of 1.82 g / cm 3 The carbon content is 99.95wt%, and the substrate surface is activated by acid pickling, ultrasonically cleaned in 5% nitric acid solution for 30 minutes, rinsed with deionized water and then dried at 120℃.

[0104] In a preferred embodiment, after the step-by-step heat treatment, the outer surface of the graphite tube is coated with RLHY-305 graphite antioxidant to a thickness of 5-20 μm and cured at 300-500°C. Specifically, the aforementioned system for preparing a high-temperature resistant graphite tube for spectral analysis further includes a surface coating module for coating the outer surface of the graphite tube with a graphite antioxidant to a thickness of 5-20 μm and curing at 300-500°C after the step-by-step heat treatment.

[0105] In a preferred embodiment, the RLHY-305 graphite antioxidant is coated with a thickness of 10 μm and cured at 400° C.

[0106] Comparative Example 1

[0107] Matrix preparation: flake graphite is selected and processed through primary grinding (honeycomb mill) with a deagglomeration wheel speed of 1500 rpm for 30 minutes to obtain an average of 60 mesh particles; then it is processed through secondary grinding (cell mill) with a medium of zirconia balls, a ball-to-material ratio of 5:1, and a time of 2 hours to obtain graphite powder with an average particle size of 3 μm and a purity of 99.95%; then after classification and purification, 1.5 wt% white graphene (hexagonal boron nitride nanosheets) and 15 wt% high-temperature phenolic resin (residual carbon rate ≥ 60%) are added and mixed, and an appropriate amount of ethanol is added as a dispersant; first premixed at 800 rpm for 30 minutes in a high-speed shear mixer, and then ground three times in a three-roll mill (roller spacing 50 μm) to obtain a uniform slurry. The slurry was loaded into a transverse graphite tube mold and formed into a standard transverse graphite tube with a maximum length of 55 mm, a maximum width of 30 mm, and a maximum thickness of 12 mm using an isostatic pressing machine. The surface was polished with 200-mesh silicon carbide sandpaper, ultrasonically cleaned in a 5% nitric acid solution for 30 minutes, rinsed with deionized water, and dried at 120°C.

[0108] Performance test: 1. Oxidation weight loss: use a graphite tube, heat it in air at 2800℃ for 10 minutes, cool it down, heat it again, repeat the heating 10 times, calculate the weight loss rate, weight loss rate % = (weight before heating - weight after heating) / weight before heating. 2. Microcracks: after the weight loss rate is calculated, observe the outer surface of the graphite tube under a microscope to see if there are microcracks. 3. Service life: use another graphite tube, continuously measure aluminum samples (atomization temperature 2500℃), and record the total number of times the graphite tube is used before failure (graphite tube failure specifically refers to an abnormal increase in absorbance value or obvious cracks or deformation on the surface of the graphite tube. Either of the two can be considered as graphite tube failure). See Table 1 below for details.

[0109] Comparative Example 2

[0110] Matrix preparation: flake graphite is selected and processed through primary grinding (honeycomb mill) with a deagglomeration wheel speed of 1500 rpm for 30 minutes to obtain an average of 60 mesh particles; then it is processed through secondary grinding (cell mill) with a medium of zirconia balls, a ball-to-material ratio of 5:1, and a time of 2 hours to obtain graphite powder with an average particle size of 3 μm and a purity of 99.95%; then after classification and purification, 1.5 wt% white graphene (hexagonal boron nitride nanosheets) and 15 wt% high-temperature phenolic resin (residual carbon rate ≥ 60%) are added and mixed, and an appropriate amount of ethanol is added as a dispersant; first premixed at 800 rpm for 30 minutes in a high-speed shear mixer, and then ground three times in a three-roll mill (roller spacing 50 μm) to obtain a uniform slurry. The slurry was loaded into a transverse graphite tube mold and formed into a standard graphite tube with a maximum length of 55 mm, a maximum width of 30 mm, and a maximum thickness of 12 mm using an isostatic pressing machine. The surface was polished with 200-mesh silicon carbide sandpaper, ultrasonically cleaned in a 5% nitric acid solution for 30 minutes, rinsed with deionized water, and dried at 120°C.

[0111] Preparation of composite sol: 40 parts of silica sol (SiO2 content 30wt%), 3 parts of phytic acid (purity 70%), and 42 parts of ethanol were stirred and mixed in a 40°C water bath for 2 hours to obtain a uniform and stable composite sol No. 1.

[0112] Impregnation treatment: 1. Place the graphite tube in a vacuum tank and evacuate to -0.08 MPa for 30 minutes. 2. Slowly inject the composite sol until the tube is completely immersed, then pressurize to 1.2 MPa and maintain for 2 hours. 3. Perform two immersion cycles. 4. Remove the tube and centrifuge at 3000 rpm to remove excess sol from the surface.

[0113] Heat treatment: 1. Dry at 80℃ for 12 hours; 2. Raise the temperature to 500℃ at 5℃ / min under argon protection and keep warm for 1 hour; 3. Continue to raise the temperature to 1300℃ at 3℃ / min and keep warm for 1 hour; 4. Finally, raise the temperature to 2000℃ at 8℃ / min, keep warm for 1 hour, and cool with the furnace.

[0114] Performance test: 1. Oxidation weight loss: use a graphite tube, heat it in air at 2800℃ for 10 minutes, cool it down, heat it again, repeat the heating 10 times, calculate the weight loss rate, weight loss rate % = (weight before heating - weight after heating) / weight before heating. 2. Microcracks: after the weight loss rate is calculated, observe the outer surface of the graphite tube under a microscope to see if there are microcracks. 3. Service life: use another graphite tube, continuously measure aluminum samples (atomization temperature 2500℃), and record the total number of times the graphite tube is used before failure (graphite tube failure specifically refers to an abnormal increase in absorbance value or obvious cracks or deformation on the surface of the graphite tube. Either of the two can be considered as graphite tube failure). See Table 1 below for details.

[0115] Comparative Example 3

[0116] Matrix preparation: flake graphite is selected and processed through primary grinding (honeycomb mill) with a deagglomeration wheel speed of 1500 rpm for 30 minutes to obtain an average of 60 mesh particles; then it is processed through secondary grinding (cell mill) with a medium of zirconia balls, a ball-to-material ratio of 5:1, and a time of 2 hours to obtain graphite powder with an average particle size of 3 μm and a purity of 99.95%; then after classification and purification, 1.5 wt% white graphene (hexagonal boron nitride nanosheets) and 15 wt% high-temperature phenolic resin (residual carbon rate ≥ 60%) are added and mixed, and an appropriate amount of ethanol is added as a dispersant; first premixed at 800 rpm for 30 minutes in a high-speed shear mixer, and then ground three times in a three-roll mill (roller spacing 50 μm) to obtain a uniform slurry. The slurry was loaded into a transverse graphite tube mold and formed into a standard graphite tube with a maximum length of 55 mm, a maximum width of 30 mm, and a maximum thickness of 12 mm using an isostatic pressing machine. The surface was polished with 200-mesh silicon carbide sandpaper, ultrasonically cleaned in a 5% nitric acid solution for 30 minutes, rinsed with deionized water, and dried at 120°C.

[0117] Preparation of composite sol: 40 parts of silica sol (SiO2 content 30wt%), 5 parts of ammonium molybdate (purity 99.5%), and 42 parts of ethanol were stirred and mixed in a 40°C water bath for 2 hours to obtain a uniform and stable composite sol No. 2.

[0118] Impregnation treatment: 1. Place the graphite tube in a vacuum tank and evacuate to -0.08 MPa for 30 minutes. 2. Slowly inject the composite sol until the tube is completely immersed, then pressurize to 1.2 MPa and maintain for 2 hours. 3. Perform two immersion cycles. 4. Remove the tube and centrifuge at 3000 rpm to remove excess sol from the surface.

[0119] Heat treatment: 1. Dry at 80℃ for 12 hours; 2. Raise the temperature to 500℃ at 5℃ / min under argon protection and keep warm for 1 hour; 3. Continue to raise the temperature to 1300℃ at 3℃ / min and keep warm for 1 hour; 4. Finally, raise the temperature to 2000℃ at 8℃ / min, keep warm for 1 hour, and cool with the furnace.

[0120] Performance test: 1. Oxidation weight loss: use a graphite tube, heat it in air at 2800℃ for 10 minutes, cool it down, heat it again, repeat the heating 10 times, calculate the weight loss rate, weight loss rate % = (weight before heating - weight after heating) / weight before heating. 2. Microcracks: after the weight loss rate is calculated, observe the outer surface of the graphite tube under a microscope to see if there are microcracks. 3. Service life: use another graphite tube, continuously measure aluminum samples (atomization temperature 2500℃), and record the total number of times the graphite tube is used before failure (graphite tube failure specifically refers to an abnormal increase in absorbance value or obvious cracks or deformation on the surface of the graphite tube. Either of the two can be considered as graphite tube failure). See Table 1 below for details.

[0121] Comparative Example 4

[0122] Matrix preparation: flake graphite is selected and processed through primary grinding (honeycomb mill) with a deagglomeration wheel speed of 1500 rpm for 30 minutes to obtain an average of 60 mesh particles; then it is processed through secondary grinding (cell mill) with a medium of zirconia balls, a ball-to-material ratio of 5:1, and a time of 2 hours to obtain graphite powder with an average particle size of 3 μm and a purity of 99.95%; then after classification and purification, 1.5 wt% white graphene (hexagonal boron nitride nanosheets) and 15 wt% high-temperature phenolic resin (residual carbon rate ≥ 60%) are added and mixed, and an appropriate amount of ethanol is added as a dispersant; first premixed at 800 rpm for 30 minutes in a high-speed shear mixer, and then ground three times in a three-roll mill (roller spacing 50 μm) to obtain a uniform slurry. The slurry was loaded into a transverse graphite tube mold and formed into a standard graphite tube with a maximum length of 55 mm, a maximum width of 30 mm, and a maximum thickness of 12 mm using an isostatic pressing machine. The surface was polished with 200-mesh silicon carbide sandpaper, ultrasonically cleaned in a 5% nitric acid solution for 30 minutes, rinsed with deionized water, and dried at 120°C.

[0123] Preparation of composite sol: 5 parts of ammonium molybdate (purity 99.5%), 3 parts of phytic acid (purity 70%), and 42 parts of ethanol were stirred and mixed in a 40°C water bath for 2 hours to obtain a uniform and stable composite sol No. 3.

[0124] Impregnation treatment: 1. Place the graphite tube in a vacuum tank and evacuate to -0.08 MPa for 30 minutes. 2. Slowly inject the composite sol until the tube is completely immersed, then pressurize to 1.2 MPa and maintain for 2 hours. 3. Perform two immersion cycles. 4. Remove the tube and centrifuge at 3000 rpm to remove excess sol from the surface.

[0125] Heat treatment: 1. Dry at 80℃ for 12 hours; 2. Raise the temperature to 500℃ at 5℃ / min under argon protection and keep warm for 1 hour; 3. Continue to raise the temperature to 1300℃ at 3℃ / min and keep warm for 1 hour; 4. Finally, raise the temperature to 2000℃ at 8℃ / min, keep warm for 1 hour, and cool with the furnace.

[0126] Performance test: 1. Oxidation weight loss: use a graphite tube, heat it in air at 2800℃ for 10 minutes, cool it down, heat it again, repeat the heating 10 times, calculate the weight loss rate, weight loss rate % = (weight before heating - weight after heating) / weight before heating. 2. Microcracks: after the weight loss rate is calculated, observe the outer surface of the graphite tube under a microscope to see if there are microcracks. 3. Service life: use another graphite tube, continuously measure aluminum samples (atomization temperature 2500℃), and record the total number of times the graphite tube is used before failure (graphite tube failure specifically refers to an abnormal increase in absorbance value or obvious cracks or deformation on the surface of the graphite tube. Either of the two can be considered as graphite tube failure). See Table 1 below for details.

[0127] Example 5

[0128] Matrix preparation: flake graphite is selected and processed through primary grinding (honeycomb mill) with a deagglomeration wheel speed of 1500 rpm for 30 minutes to obtain an average of 60 mesh particles; then it is processed through secondary grinding (cell mill) with a medium of zirconia balls, a ball-to-material ratio of 5:1, and a time of 2 hours to obtain graphite powder with an average particle size of 3 μm and a purity of 99.95%; then after classification and purification, 1.5 wt% white graphene (hexagonal boron nitride nanosheets) and 15 wt% high-temperature phenolic resin (residual carbon rate ≥ 60%) are added and mixed, and an appropriate amount of ethanol is added as a dispersant; first premixed at 800 rpm for 30 minutes in a high-speed shear mixer, and then ground three times in a three-roll mill (roller spacing 50 μm) to obtain a uniform slurry. The slurry was loaded into a transverse graphite tube mold and formed into a standard graphite tube with a maximum length of 55 mm, a maximum width of 30 mm, and a maximum thickness of 12 mm using an isostatic pressing machine. The surface was polished with 200-mesh silicon carbide sandpaper, ultrasonically cleaned in a 5% nitric acid solution for 30 minutes, rinsed with deionized water, and dried at 120°C.

[0129] Preparation of composite sol: 40 parts of silica sol (SiO2 content 30wt%), 5 parts of ammonium molybdate (purity 99.5%), 3 parts of phytic acid (purity 70%), and 42 parts of ethanol. The above components were stirred and mixed in a 40°C water bath for 2 hours to obtain a uniform and stable composite sol No. 4.

[0130] Impregnation treatment: 1. Place the graphite tube in a vacuum tank and evacuate to -0.08 MPa for 30 minutes. 2. Slowly inject the composite sol until the tube is completely immersed, then pressurize to 1.2 MPa and maintain for 2 hours. 3. Perform two immersion cycles. 4. Remove the tube and centrifuge at 3000 rpm to remove excess sol from the surface.

[0131] Heat treatment: 1. Dry at 80℃ for 12 hours; 2. Raise the temperature to 500℃ at 5℃ / min under argon protection and keep warm for 1 hour; 3. Continue to raise the temperature to 1300℃ at 3℃ / min and keep warm for 1 hour; 4. Finally, raise the temperature to 2000℃ at 8℃ / min, keep warm for 1 hour, and cool with the furnace.

[0132] Performance test: 1. Oxidation weight loss: use a piece of graphite tube, heat it in air at 2800℃ for 10 minutes, cool it down, heat it again, repeat the heating 10 times, calculate the weight loss rate, weight loss rate % = (weight before heating - weight after heating) / weight before heating. 2. Microcracks: after the weight loss rate is calculated, observe the outer surface of the graphite tube through a microscope to see if there are microcracks. 3. Service life: use another piece of graphite tube, continuously measure the aluminum sample (atomization temperature 2500℃), and record the total number of uses before the graphite tube fails (graphite tube failure specifically refers to an abnormal increase in the absorbance value or obvious cracks or deformation on the surface of the graphite tube. Either of the two can be considered as graphite tube failure. The number is the approximate number of uses). See Table 1 below for details.

[0133] Example 6

[0134] Matrix preparation: flake graphite is selected and processed through primary grinding (honeycomb mill) with a deagglomeration wheel speed of 1500 rpm for 30 minutes to obtain an average of 60 mesh particles; then it is processed through secondary grinding (cell mill) with a medium of zirconia balls, a ball-to-material ratio of 5:1, and a time of 2 hours to obtain graphite powder with an average particle size of 3 μm and a purity of 99.95%; then after classification and purification, 1.5 wt% white graphene (hexagonal boron nitride nanosheets) and 15 wt% high-temperature phenolic resin (residual carbon rate ≥ 60%) are added and mixed, and an appropriate amount of ethanol is added as a dispersant; first premixed at 800 rpm for 30 minutes in a high-speed shear mixer, and then ground three times in a three-roll mill (roller spacing 50 μm) to obtain a uniform slurry. The slurry was loaded into a transverse graphite tube mold and formed into a standard graphite tube with a maximum length of 55 mm, a maximum width of 30 mm, and a maximum thickness of 12 mm using an isostatic pressing machine. The surface was polished with 200-mesh silicon carbide sandpaper, ultrasonically cleaned in a 5% nitric acid solution for 30 minutes, rinsed with deionized water, and dried at 120°C.

[0135] Preparation of composite sol: 50 parts of silica sol (SiO2 content 30wt%), 6 parts of ammonium molybdate (purity 99.5%), 5 parts of phytic acid (purity 70%), and 42 parts of ethanol. The above components were stirred and mixed in a 40°C water bath for 2 hours to obtain a uniform and stable composite sol No. 5.

[0136] Impregnation treatment: 1. Place the graphite tube in a vacuum tank and evacuate to -0.08 MPa for 30 minutes. 2. Slowly inject the composite sol until the tube is completely immersed, then pressurize to 1.2 MPa and maintain for 2 hours. 3. Perform two immersion cycles. 4. Remove the tube and centrifuge at 3000 rpm to remove excess sol from the surface.

[0137] Heat treatment: 1. Dry at 80℃ for 12 hours; 2. Raise the temperature to 500℃ at 5℃ / min under argon protection and keep warm for 1 hour; 3. Continue to raise the temperature to 1300℃ at 3℃ / min and keep warm for 1 hour; 4. Finally, raise the temperature to 2000℃ at 8℃ / min, keep warm for 1 hour, and cool with the furnace.

[0138] Performance test: 1. Oxidation weight loss: use a graphite tube, heat it in air at 2800℃ for 10 minutes, cool it down, heat it again, repeat the heating 10 times, calculate the weight loss rate, weight loss rate % = (weight before heating - weight after heating) / weight before heating. 2. Microcracks: after the weight loss rate is calculated, observe the outer surface of the graphite tube under a microscope to see if there are microcracks. 3. Service life: use another graphite tube, continuously measure aluminum samples (atomization temperature 2500℃), and record the total number of times the graphite tube is used before failure (graphite tube failure specifically refers to an abnormal increase in absorbance value or obvious cracks or deformation on the surface of the graphite tube. Either of the two can be considered as graphite tube failure). See Table 1 below for details.

[0139] Example 7

[0140] Matrix preparation: flake graphite is selected and processed through primary grinding (honeycomb mill) with a deagglomeration wheel speed of 1500 rpm for 30 minutes to obtain an average of 60 mesh particles; then it is processed through secondary grinding (cell mill) with a medium of zirconia balls, a ball-to-material ratio of 5:1, and a time of 2 hours to obtain graphite powder with an average particle size of 3 μm and a purity of 99.95%; then after classification and purification, 1.5 wt% white graphene (hexagonal boron nitride nanosheets) and 15 wt% high-temperature phenolic resin (residual carbon rate ≥ 60%) are added and mixed, and an appropriate amount of ethanol is added as a dispersant; first premixed at 800 rpm for 30 minutes in a high-speed shear mixer, and then ground three times in a three-roll mill (roller spacing 50 μm) to obtain a uniform slurry. The slurry was loaded into a transverse graphite tube mold and formed into a standard graphite tube with a maximum length of 55 mm, a maximum width of 30 mm, and a maximum thickness of 12 mm using an isostatic pressing machine. The surface was polished with 200-mesh silicon carbide sandpaper, ultrasonically cleaned in a 5% nitric acid solution for 30 minutes, rinsed with deionized water, and dried at 120°C.

[0141] Preparation of composite sol: 60 parts of silica sol (SiO2 content 30wt%), 10 parts of ammonium molybdate (purity 99.5%), 8 parts of phytic acid (purity 70%), and 42 parts of ethanol. The above components were stirred and mixed in a 40°C water bath for 2 hours to obtain a uniform and stable composite sol No. 6.

[0142] Impregnation treatment: 1. Place the graphite tube in a vacuum tank and evacuate to -0.08 MPa for 30 minutes. 2. Slowly inject the composite sol until the tube is completely immersed, then pressurize to 1.2 MPa and maintain for 2 hours. 3. Perform two immersion cycles. 4. Remove the tube and centrifuge at 3000 rpm to remove excess sol from the surface.

[0143] Heat treatment: 1. Dry at 80℃ for 12 hours; 2. Raise the temperature to 500℃ at 5℃ / min under argon protection and keep warm for 1 hour; 3. Continue to raise the temperature to 1300℃ at 3℃ / min and keep warm for 1 hour; 4. Finally, raise the temperature to 2000℃ at 8℃ / min, keep warm for 1 hour, and cool with the furnace.

[0144] Performance test: 1. Oxidation weight loss: use a piece of graphite tube, heat it in air at 2800℃ for 10 minutes, cool it down, heat it again, repeat the heating 10 times, calculate the weight loss rate, weight loss rate % = (weight before heating - weight after heating) / weight before heating. 2. Microcracks: after the weight loss rate is calculated, observe the outer surface of the graphite tube under a microscope to see if there are microcracks. 3. Service life: use another piece of graphite tube, continuously measure the aluminum sample (atomization temperature 2500℃), and record the total number of times the graphite tube is used before failure (graphite tube failure specifically refers to an abnormal increase in the absorbance value or obvious cracks or deformation on the surface of the graphite tube. Either of the two can be considered as graphite tube failure). See Table 1 below for details.

[0145]

[0146]

[0147] Table 1

[0148] It can be seen from Table 1 above and the records of this application that the silica sol, the molybdate and the phytic acid have a synergistic effect to form a SiC-MoSi2 composite phase. Phytic acid can prevent molybdate aggregation and promote the growth of SiC whiskers during heat treatment, thereby increasing the oxidation resistance temperature of the graphite tube. At the same time, phytic acid can catalyze the reconstruction of the edge of the graphite matrix to form a unique "toothed staggered interface". On the basis of realizing spectral analysis of the graphite tube, the structural strength of the graphite tube is improved, and the oxidation weight loss rate of the graphite tube is reduced from >10% to <3%, thereby achieving improved temperature resistance of the graphite tube. After repeated heating, after rapid temperature changes, the microcracks on the surface of the graphite tube are The thermal stability of the graphite tube is enhanced by reducing the cracks. By improving the temperature resistance and thermal stability of the graphite tube, the number of uses of the graphite tube is greatly increased. In addition, the vacuum-pressure alternating impregnation process accelerates the penetration of the composite sol into the graphite matrix, solving the problem that the high-density graphite matrix is ​​difficult to penetrate, combining the internal reinforcement of the matrix with the surface modification, and realizing an overall protection "from the inside out". The deposited pyrolytic carbon layer reduces the reaction or penetration of the measured elements with the graphite at high temperatures, reduces the cross contamination phenomenon, and reduces the memory effect of the graphite tube by 70%, while the traditional pyrolytic graphite tube can only reduce it by 30-40%, which is particularly suitable for the analysis of high-melting-point elements.

[0149] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A system for preparing a graphite tube for high temperature resistant spectral analysis, characterized in that: include Raw material pretreatment module, used to crush, classify, purify and mix the graphite raw materials to form a uniform slurry; an isostatic pressing module, connected to the raw material pretreatment module, for pressing the slurry into a graphite tube matrix; A composite sol preparation module, wherein the composite sol comprises silica sol, molybdate and phytic acid, and a stirring element is provided in the composite sol preparation module for uniformly mixing the silica sol, molybdate and phytic acid; a vacuum-pressurization alternating module connected to the composite sol preparation module, the vacuum-pressurization alternating module comprising a vacuum pumping component and a pressurizing component, for infiltrating the composite sol into the graphite tube matrix; A high-temperature sintering module is connected to the vacuum-pressure alternating module, and the high-temperature sintering module includes a programmable temperature control component and an atmosphere protection component, and is used to perform a step-by-step temperature increase heat treatment on the graphite tube substrate infiltrated with the composite sol; The chemical vapor deposition module is connected to the high-temperature sintering module and is used to deposit a pyrolytic carbon layer on the surface of the graphite tube substrate after sintering.

2. The system for preparing a high-temperature resistant graphite tube for spectral analysis according to claim 1, wherein: The raw material pretreatment module includes a primary grinding assembly and a secondary grinding assembly. The primary grinding assembly is used to grind the graphite raw material into 60-120 mesh particles, and the secondary grinding assembly is used to further grind the particles ground by the primary grinding assembly to a particle size of 1-10 μm.

3. The system for preparing a high-temperature resistant graphite tube for spectral analysis according to claim 2, wherein: The vacuum-pressurization alternating module includes a vacuum unit, which is used to vacuum into a negative pressure state, with a vacuum degree of -0.08 to -0.1 MPa and maintained for 20-40 minutes, and a pressurization unit, which is used to increase the pressure, with the increased pressure being 0.5-1.2 MPa and maintained for 1-3 hours.

4. The system for preparing a high-temperature resistant graphite tube for spectral analysis according to claim 3, wherein: The high-temperature sintering module is used to perform the following steps to perform a step-by-step temperature increase heat treatment on the graphite tube matrix infiltrated with the composite sol: The first stage: heating to 400-600℃ at 2-10℃ / min and keeping warm for 0.5-2 hours; The second stage: heating to 1200-1400℃ at 1-5℃ / min and keeping warm for 1-3 hours; The third stage: heating to 1800-2200℃ at 5-15℃ / min and keeping warm for 0.5-2 hours.

5. The system for preparing a high-temperature resistant graphite tube for spectral analysis according to claim 4, wherein: The chemical vapor deposition module uses chemical vapor deposition to deposit a pyrolytic carbon layer on the surface of the sintered graphite tube substrate, wherein the carbon source is methane, acetylene or propane, the deposition temperature is 1600-2000°C, the time is 20-60 minutes, and the obtained pyrolytic carbon layer has a thickness of 10-100 μm.

6. The system for preparing a high-temperature resistant graphite tube for spectral analysis according to claim 5, wherein: The invention also comprises a surface coating module for coating the outer surface of the graphite tube with a graphite antioxidant after the step-by-step temperature increase heat treatment, with a coating thickness of 5-20 μm and curing at 300-500°C.

7. A method for preparing a high-temperature resistant graphite tube for spectral analysis, using the system for preparing a high-temperature resistant graphite tube for spectral analysis according to claim 6, characterized in that: include S1: Grind, classify, purify the graphite raw materials, and add a binder to form a uniform slurry; S2: isostatically pressing the slurry into a high-purity graphite tube matrix; S3: preparing a composite sol, wherein the composite sol comprises a mixture of silica sol, molybdate and phytic acid; S4: infiltrating the composite sol into the graphite matrix using a vacuum-pressure alternating impregnation process; S5: performing a stepwise temperature increase heat treatment in an inert environment to form a SiC-MoSi2 composite reinforcement phase; S6: Depositing a pyrolytic carbon layer on the inner wall of the graphite tube.

8. The method for preparing a high-temperature resistant graphite tube for spectral analysis according to claim 7, wherein: The composite sol comprises, by weight: 40-60 parts of the silica sol, 3-10 parts of the molybdate, 2-8 parts of phytic acid, 30-50 parts of alcohol solvent.

9. The method for preparing a high-temperature resistant graphite tube for spectral analysis according to claim 8, wherein: The SiO2 content in the silica sol is ≥30wt%; the molybdate is ammonium molybdate or sodium molybdate, wherein the content of ammonium molybdate or sodium molybdate is ≥99wt%; and the purity of the phytic acid is ≥50%.

10. The method for preparing a high-temperature resistant graphite tube for spectral analysis according to claim 7, wherein: The graphite tube matrix has a density of 1.7-2.2 g / cm³ and a carbon content of ≥99.9 wt %, and the surface of the matrix is ​​subjected to surface activation treatment, such as plasma treatment or acid pickling activation.

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