High-quality vanadium nitride alloy and method for preparing the same

Abstract

This invention belongs to the field of metallurgical materials and discloses a high-quality vanadium nitride alloy and its preparation method. The method includes the following steps: S1: pressing a square pyramidal raw material block to obtain a raw material block; S2: breaking the raw material block into multiple irregular small blocks, and drying them in a 110℃ oven to constant weight; S3: placing the material in a high-temperature tube furnace and maintaining it in a high-purity nitrogen atmosphere, using a carbothermic reduction nitriding one-step reaction for a set time, first heating to a high-temperature zone, then holding at that temperature, and then naturally cooling down, thus obtaining high-quality vanadium nitride with a nitrogen content higher than 18wt%. This invention, by preparing irregular small blocks, combining the agglomeration method and the reduction method, controlling the size and shape of the material, and controlling various other process conditions to stabilize the nitrogen yield, improves the vanadium-nitrogen microalloying effect, and makes the nitrogen content of the product higher than 18%, possessing excellent properties such as uniform microstructure, stable quality, and high nitrogen content.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical materials, specifically relating to a high-quality vanadium nitride alloy and its preparation method. Background Technology

[0002] Vanadium nitride, a typical transition metal nitride, possesses excellent properties such as high hardness, strong corrosion resistance, and good thermal, chemical, and thermal stability. In my country, its most widespread application is in alloying it with steel to improve its overall mechanical properties, including wear resistance, corrosion resistance, strength, ductility, hardness, and resistance to thermal fatigue. Vanadium-nitrogen alloys are highly efficient additives for steel. When added to construction steel, nitrogen precipitates as vanadium nitride grains, significantly improving the steel's strength and toughness by strengthening the ferrite matrix and saving approximately 15% of steel usage. Studies have found that for every 10 ppm increase in nitrogen content in steel, the yield strength increases by 5–6 MPa. Therefore, increasing the nitrogen content of vanadium-nitrogen alloys and maintaining it above 18% has significant technical and economic implications.

[0003] In existing technologies, the synthesis methods for vanadium nitride mainly include the high-temperature vacuum method and the high-temperature non-vacuum method. While the high-temperature non-vacuum method eliminates the tedious process of repeated vacuuming compared to the high-temperature vacuum method, allowing for continuous production and offering advantages such as shorter reaction cycles, higher production efficiency, and lower costs, it still suffers from drawbacks such as cumbersome operation and long reaction times. As a good microalloying additive, the introduction of nitrogen into vanadium nitride can optimize various properties while promoting vanadium precipitation, thus reducing alloying costs. Therefore, the higher the nitrogen content in vanadium nitride, the higher the quality of the resulting product. However, currently, there is no technology that effectively balances the two crucial aspects of simplified preparation processes and high nitrogen content to obtain high-quality vanadium nitride alloys at low cost.

[0004] In the prior art, Chinese patent document CN 116004987 A discloses a method for producing vanadium-nitrogen alloys using vanadium nitride. This method employs novel raw materials and innovates in process parameters such as batching methods, temperature control, and calcination time, achieving the goals of reducing carbon content and emissions, lowering reaction temperature and energy consumption, and increasing single-kiln throughput. However, its preparation process is complex, and the nitrogen content of the vanadium nitride alloy is less than 15%. Chinese patent CN1212416, using vanadates or vanadium oxides as raw materials, is the first to employ a carbonization-nitridation process under normal pressure to prepare vanadium-nitrogen alloys, providing the possibility for continuous production of vanadium nitride. However, its reduction nitriding time is 0.5–8 hours, the total residence time of the sample in the furnace is 3–15 hours, and the nitrogen content of the product is only 11%–16%. Chinese patent CN114606432 describes a preparation process for a high-density vanadium-nitrogen alloy. It solves the problem of sphere adhesion during firing by spraying a modifying liquid onto the surface of the raw material spheres. However, the firing process requires four stages of segmented heat preservation, with the heat preservation time alone exceeding eight hours, and the nitrogen content of the product is only 14%–15.29%. Chinese patent CN112919433 obtains high-purity vanadium carbonitride products through solid-phase nitriding based on high-purity vanadium carbide. This method yields products with lower impurities, but still suffers from a long production cycle, and the carbon content in the product is much higher than the nitrogen content. Chinese patent CN115522092 discloses a production method for a high-nitrogen, low-carbon vanadium-nitrogen alloy. Using aluminum as a reducing agent, it utilizes an aluminothermic reaction to obtain vanadium melt, followed by a reduction nitriding reaction. Although the nitrogen content of the final vanadium nitride alloy can be controlled above 19%, the preparation process involves multiple processes such as aluminothermic reaction, atomization, annealing, and nitrogen fixation, making the operation complex, the reaction cycle long, and the overall cost high. Summary of the Invention

[0005] The purpose of this invention is to provide a new high-quality vanadium nitride alloy and its preparation method. The new process steps can solve the problems of low nitrogen content and cumbersome operation and long reaction time in the preparation of vanadium nitride. On the other hand, it can solve the problem of steadily increasing the nitrogen content, so that the nitrogen content in the final vanadium nitride alloy is stably greater than 18%.

[0006] This invention provides the following technical solution:

[0007] A method for preparing high-quality vanadium nitride, characterized by comprising the following steps:

[0008] S1: Vanadium oxide powder, graphite powder, ferric oxide powder and an appropriate amount of binder are thoroughly mixed in proportion and pressed into square pyramid-shaped raw material blocks, which are then dried to obtain raw material blocks;

[0009] S2: Crack and break the raw material block into multiple irregular small blocks, and dry the irregular small blocks in a 110℃ oven to remove the moisture from the material;

[0010] S3: The irregular small lumps of material after removing all moisture are placed in a high-temperature tube furnace and kept in a high-purity nitrogen atmosphere. The irregular small lumps of material are reacted in a one-step carbothermic reduction nitridation process for a set time. First, the temperature is directly raised to the high-temperature zone of 1400℃~1600℃ according to the set heating rate. After reaching the highest temperature of the high-temperature zone, it is held for 0.5~2h and then cooled naturally to obtain high-quality vanadium nitride with a nitrogen content of more than 18wt%.

[0011] A high-quality vanadium nitride is prepared using the aforementioned method.

[0012] Compared with the prior art, the present invention has at least the following beneficial effects:

[0013] 1. The method for preparing high-quality vanadium nitride provided by this invention combines the agglomeration method and the reduction method. Small-scale, irregularly shaped materials are placed in a high-temperature tube furnace. The optimal preparation conditions are obtained by adjusting the reaction temperature range of 1400-1600℃ and the reaction time of 0.5-2h. This method combines the agglomeration method and the reduction method, stabilizes the nitrogen yield, and improves the vanadium-nitrogen microalloying effect, thereby obtaining high-quality vanadium nitride. Furthermore, the prepared vanadium nitride meets the highest quality standard VN-19 (GB / T20567-2020 Vanadium-Nitrogen Alloy), and the nitrogen content in the vanadium nitride is stably greater than 18%.

[0014] 2. The method for preparing high-quality vanadium nitride provided by the present invention involves reacting small-scale, irregularly shaped materials in a high-temperature tube furnace to directly obtain high-quality vanadium nitride products through a one-step carbothermic reduction nitridation method. The reaction process is simple to operate and does not require pre-reduction and staged reduction processes. At the same time, vanadium nitride products with high nitrogen content can be produced under conditions of low nitrogen gas rate.

[0015] 3. The method for preparing high-quality vanadium nitride provided by the present invention adopts new process steps, which can solve the problems of low nitrogen content and cumbersome operation and long reaction time in the preparation process of vanadium nitride. On the other hand, it can solve the problem of steadily increasing nitrogen content, so that the nitrogen content in the final vanadium nitride alloy is stably greater than 18%.

[0016] 4. The preparation method described in this invention uses vanadium trioxide as raw material, graphite powder as reducing agent, and adds a small amount of ferric oxide and binder to obtain high-quality vanadium nitride. It also has the advantages of simple operation, economy and environmental protection.

[0017] 5. This invention features simple process, short production cycle, and environmental friendliness, resulting in significant economic benefits; the nitrogen content of the obtained products is all higher than 18%, meeting the VN-19 standard, and possesses excellent properties such as stable quality and high nitrogen content. Attached Figure Description

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0019] Figure 1 This is a scanning electron microscope image of the high-quality vanadium nitride prepared according to an embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram of the XRD phase composition of the high-quality vanadium nitride prepared according to an embodiment of the present invention.

[0021] Figure 3 This is a schematic diagram of the process for preparing high-quality vanadium nitride according to an embodiment of the present invention. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, so that those skilled in the art can implement it based on the description.

[0023] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0024] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0025] Example

[0026] The method for preparing high-quality vanadium nitride provided by this invention generally includes the following steps:

[0027] S1: Vanadium oxide powder, graphite powder, ferric oxide powder and an appropriate amount of binder are thoroughly mixed in proportion and pressed into square pyramid-shaped raw material blocks, which are then dried to obtain raw material blocks;

[0028] In the aforementioned dried raw material block, the mass ratio of each raw material is as follows: vanadium trioxide powder 100, graphite powder 18-25, ferric oxide powder 0.6-2, and binder 3-5.

[0029] S2: Crack and break the raw material block into multiple irregular small blocks. Place 13-18g of irregular small blocks in a 110℃ oven and dry for 2-3 hours until the material quality no longer changes. Stop drying to remove all moisture from the material.

[0030] S3: The irregular small lumps of material, after removing all moisture, are placed in a high-temperature tube furnace and kept in a high-purity nitrogen atmosphere (high-purity nitrogen with a purity of 99.9999% is introduced at a flow rate of 150-240 ml / min). The irregular small lumps of material are reacted in a one-step carbothermal reduction nitridation process for the set time. First, the temperature is raised directly to the high-temperature section of 1400-1600℃ at the set heating rate of 3-5℃ / min. After reaching the highest temperature of the high-temperature section, the temperature is held for 0.5-2 hours and then allowed to cool naturally. This produces high-quality vanadium nitride with a nitrogen content of more than 18wt%.

[0031] The high-quality vanadium nitride preparation method provided in this embodiment focuses on greatly simplifying the carbothermic reduction nitride process by combining the agglomeration method and the reduction method. Under a reducing and inert atmosphere, the temperature is directly raised to a high temperature (1400℃~1600℃) at a certain heating rate, held at that temperature for a certain time (0.5~2h), and then naturally cooled to obtain high-quality vanadium nitride. There are no segmented heating and segmented holding stages, and no specified cooling rate operation.

[0032] Specifically, the multiple irregular small lumps are made from vanadium trioxide as raw material, graphite powder as reducing agent, and a small amount of ferric oxide and binder. After being fully mixed and evenly mixed in a certain proportion, the raw material blocks are pressed into shape. After being completely dried and crushed, they are placed in a high-temperature tube furnace and heated to 1400℃ or above at a heating rate of 3℃ / min under a high-purity nitrogen atmosphere. A reasonable holding time is set (0.5~2h). During the reaction, the nitrogen flow rate is maintained at 150~240ml / min. After the raw material undergoes a carbothermic reduction nitridation reaction on lumps of a specific size, high-quality vanadium nitride can be obtained.

[0033] The following provides a detailed explanation using several specific implementation plans.

[0034] Example 1:

[0035] See appendix Figure 1-3 The method for preparing high-quality vanadium nitride alloy provided by the present invention, based on the foregoing embodiments, specifically includes the following steps:

[0036] (1) The material supplied by Panzhihua Iron and Steel Group (V2O3 powder, graphite powder, and appropriate amount of Fe2O3 powder and binder are fully mixed in a certain proportion and pressed into a square pyramid shape. The material is specifically provided by Panzhihua Iron and Steel Group Vanadium Products Factory) is crushed into multiple irregular small blocks and dried at 110°C for several hours to completely remove the moisture on the surface of the material.

[0037] (2) When the mass of irregular small lumps remains constant, take 15.6g of raw material to participate in the reaction. Place the weighed material in an Al2O3 corundum crucible. To prevent the Al2O3 corundum crucible from sticking to the material and the tube wall of the tube furnace at high temperature, a layer of graphite paper should be placed inside and outside the crucible. Place the Al2O3 corundum crucible in the center of the tube furnace to ensure sufficient heating. At the same time, keep the furnace in a high-purity nitrogen atmosphere. Start heating at room temperature with a heating rate of 3℃ / min. The working temperature of the tube furnace is 1400℃ and the nitrogen flow rate is 200ml / min.

[0038] (3) When the working temperature of the tube furnace reaches the target temperature of 1400℃, it is held for 2 hours, followed by natural cooling to obtain a high-quality vanadium nitride product; the XRD diffraction results of the obtained product are shown in the figure. Figure 2 The results showed that only VN diffraction peaks were present, with no other impurity peaks, indicating that the product was relatively pure VN; its electron microscopy results are shown in [Figure number missing]. Figure 1 The product is nanoscale VN with a diameter between 0.5 and 2 nm, a uniform microstructure, and good vanadium-nitrogen microalloying effect. The nitrogen content of the product was found to be 18.98% by a nitrogen-oxygen-hydrogen analyzer, which far exceeds the 18% nitrogen content in VN-19, the highest national standard for vanadium-nitrogen alloys (GB / T 20567-2020 vanadium-nitrogen alloys).

[0039] In this embodiment, the mass ratio of each raw material in the dried raw material block is as follows: 100 parts vanadium trioxide powder, 18 parts graphite powder, 0.6 parts ferric oxide powder, and 3 parts binder.

[0040] In this embodiment, the raw material selection was based on a comparison of vanadium, carbon, and nitrogen sources.

[0041] a. Vanadium Source Selection: Commonly used vanadium raw materials are mostly mixtures of V₂O₅ and V₂O₃. V₂O₅ is in liquid form at high temperatures (>1200K), which easily binds the reducing agent and partially pre-reduced VO₂ (melting point T = 1545℃) and V₂O₃ (melting point T = 1970℃) together, compromising the permeability of the powdered solid material, obstructing airflow, and affecting synthesis efficiency. Therefore, this invention selects V₂O₃ as the raw material for synthesizing VN.

[0042] b. Selection of Reducing Agent: Under standard conditions, C, CO, NH3, CH4, and H2 all have the ability to reduce V2O5 to V2O3. However, to achieve a high proportion of V2O3 reduction in irregularly shaped small materials, the inventors found that only C, CO, and H2 can do so. Elemental C is a solid-phase reducing agent, which achieves the reduction objective while also being inexpensive and easy to control in dosage. In contrast, it is difficult to prepare high-density vanadium-nitrogen microalloying additives using gas-phase reducing agents. Therefore, this invention selects elemental C (graphite powder) as the reducing agent.

[0043] c. Nitrogen source selection: N2 or NH3 can be selected as the nitrogen source. However, the inventors found that N2 has a better penetration effect on irregular small lumps than NH3. Furthermore, NH3 is prone to causing pollution and has special requirements for equipment and exhaust gas treatment. N2 does not cause pollution. Therefore, N2 was selected as the nitrogen component raw material.

[0044] This invention adds an appropriate proportion of ferric oxide powder. Due to its large specific surface area, it can adsorb more reactant molecules, reduce the activation energy of the reaction, and act as a catalyst. At the same time, it can generate reducing substances Fe at high temperatures, which reacts with V2O3 to make the reduction and nitridation of V2O3 more thorough and the reaction can proceed fully, thereby stably obtaining vanadium-nitrogen alloy products with high nitrogen content.

[0045] Implementation Method 2

[0046] The method for preparing high-quality vanadium nitride alloy provided in this embodiment is an improvement on the aforementioned Embodiment 1, and specifically includes the following steps:

[0047] The material, broken into numerous irregular small pieces, was dried to a constant weight. 13.23g was weighed and placed in a corundum crucible lined with graphite paper. Wrapped in graphite paper, the crucible was placed in a high-temperature tube furnace and heated to 1400℃ at a rate of 3℃ / min, holding for 2 hours. After holding, it was allowed to cool naturally to room temperature. The product was then removed. Throughout the reaction process, high-purity nitrogen gas was continuously introduced at a flow rate of 200ml / min. Analysis using a nitrogen, oxygen, and hydrogen analyzer revealed a nitrogen content of 18.86% in the product, far exceeding the 18% nitrogen content in VN-19, the highest national standard for vanadium-nitrogen alloys (GB / T 20567-2020).

[0048] In this embodiment, the mass ratio of each raw material in the dried raw material block is as follows: vanadium trioxide powder 100, graphite powder 20, ferric oxide powder 0.8, and binder 3.5.

[0049] Implementation Method 3

[0050] The method for preparing high-quality vanadium nitride alloy provided in this embodiment, based on the aforementioned embodiments one and two, specifically includes the following steps:

[0051] The irregularly shaped small pieces of material, already broken into irregular blocks, were dried to constant weight. 17.73g was weighed and placed in a corundum crucible lined with graphite paper. Wrapped in graphite paper, the crucible was placed in a high-temperature tube furnace and heated to 1450℃ at a rate of 3℃ / min, holding for 2 hours. After holding, it was allowed to cool naturally to room temperature. The product was then removed. Throughout the reaction process, high-purity nitrogen gas was continuously introduced at a flow rate of 200ml / min. Analysis using a nitrogen, oxygen, and hydrogen analyzer revealed a nitrogen content of 19.06% in the product, far exceeding the 18% nitrogen content in VN-19, the highest national standard for vanadium-nitrogen alloys (GB / T 20567-2020).

[0052] In this embodiment, the mass ratio of each raw material in the dried raw material block is: 100 parts vanadium trioxide powder, 22 parts graphite powder, 1 part ferric oxide powder, and 4 parts binder.

[0053] Implementation Method 4

[0054] The method for preparing high-quality vanadium nitride alloy provided in this embodiment, based on the aforementioned embodiments one to three, specifically includes the following steps:

[0055] The irregularly shaped small pieces of material, already broken into irregular blocks, were dried to constant weight. 15.54g was weighed and placed in a corundum crucible lined with graphite paper. Wrapped in graphite paper, the crucible was placed in a high-temperature tube furnace and heated to 1500℃ at a rate of 3℃ / min, holding for 0.5h. After holding, it was allowed to cool naturally to room temperature. The product was then removed. Throughout the reaction process, high-purity nitrogen gas was continuously introduced at a flow rate of 200ml / min. Analysis using a nitrogen, oxygen, and hydrogen analyzer revealed a nitrogen content of 19.26%, far exceeding the 18% nitrogen content in VN-19, the highest national standard for vanadium-nitrogen alloys (GB / T 20567-2020).

[0056] In this embodiment, the mass ratio of each raw material in the dried raw material block is as follows: vanadium trioxide powder 100, graphite powder 23, ferric oxide powder 1.5, and binder 4.2.

[0057] Implementation Method 5

[0058] The method for preparing high-quality vanadium nitride alloy provided in this embodiment, based on the aforementioned embodiments one to four, specifically includes the following steps:

[0059] The irregularly shaped small pieces of material, already broken into irregular blocks, were dried to constant weight. 13.69g was weighed and placed in a corundum crucible lined with graphite paper. Wrapped in graphite paper, the crucible was placed in a high-temperature tube furnace and heated to 1550℃ at a rate of 3℃ / min, holding for 1 hour. After holding, it was allowed to cool naturally to room temperature. The product was then removed. Throughout the reaction process, high-purity nitrogen gas was continuously introduced at a flow rate of 200ml / min. Analysis using a nitrogen, oxygen, and hydrogen analyzer revealed a nitrogen content of 19.36% in the product, far exceeding the 18% nitrogen content in VN-19, the highest national standard for vanadium-nitrogen alloys (GB / T 20567-2020).

[0060] In this embodiment, the mass ratio of each raw material in the dried raw material block is as follows: vanadium trioxide powder 100, graphite powder 24, ferric oxide powder 1.8, and binder 4.5.

[0061] Implementation Method Six

[0062] The method for preparing high-quality vanadium nitride alloy provided in this embodiment, based on the aforementioned embodiments one to five, specifically includes the following steps:

[0063] The irregularly shaped small pieces of material that have been broken into irregular blocks are dried to a constant weight.

[0064] 16.07g of raw material, broken into irregular lumps and dried to constant weight, was weighed and placed in a corundum crucible lined with graphite paper. Wrapped in graphite paper, the crucible was placed in a high-temperature tube furnace and heated to 1600℃ at a rate of 3℃ / min, and held at that temperature for 1 hour. After holding, it was allowed to cool naturally to room temperature. The product was then removed. Throughout the reaction process, high-purity nitrogen gas was continuously introduced at a flow rate of 200ml / min. Analysis using a nitrogen, oxygen, and hydrogen analyzer revealed a nitrogen content of 19.3% in the product, far exceeding the 18% nitrogen content in VN-19, the highest national standard for vanadium-nitrogen alloys (GB / T 20567-2020).

[0065] In this embodiment, the mass ratio of each raw material in the dried raw material block is: 100 parts vanadium trioxide powder, 25 parts graphite powder, 2 parts ferric oxide powder, and 5 parts binder.

[0066] The embodiments of the present invention, on the one hand, solve the problems of low nitrogen content and cumbersome operation and long reaction time in the preparation of vanadium nitride; on the other hand, they solve the problem of stabilizing and increasing nitrogen content, ensuring that the nitrogen content in the final vanadium nitride alloy is consistently greater than 18%. The key is to stabilize nitrogen yield and improve vanadium-nitrogen microalloying effect by preparing a constant amount of irregular small-sized material, combining the agglomeration method and the reduction method, controlling the size and shape of the material, and controlling various process conditions such as the deoxidation alloying sequence in the high-temperature range and the nitrogen addition method. This allows the material to undergo a carbothermic reduction nitridation reaction, resulting in high-quality vanadium nitride with a stable nitrogen content higher than 18%. The present invention features simple process, short production cycle, and environmental friendliness, resulting in significant economic benefits. The nitrogen content of the obtained products is consistently higher than 18%, meeting the VN-19 standard, and exhibits excellent properties such as uniform microstructure, stable quality, and high nitrogen content.

[0067] It should be noted that other technical solutions obtained by making specific selections within the range of components, proportions and process parameters described in this invention can all achieve the technical effects of this invention, and therefore will not be listed one by one.

[0068] Meanwhile, other technical solutions obtained by using other components similar to the precious metals and solvents described in this invention are included within the protection scope of this invention.

[0069] In the description of this invention, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this invention, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing high-quality vanadium nitride, characterized in that, It includes the following steps: S1: Vanadium oxide powder, graphite powder, ferric oxide powder and appropriate amount of binder are mixed thoroughly in the following mass ratio: 100 parts vanadium oxide powder, 22-25 parts graphite powder, 1-2 parts ferric oxide powder and 4-5 parts binder. The mixture is then pressed into a square pyramidal raw material block and dried to obtain a raw material block. S2: Crack and break the raw material block into multiple irregular small blocks. Place the irregular small blocks in a 110℃ oven and dry for 2-3 hours until the quality of the irregular small blocks no longer changes and the moisture in the irregular small blocks is removed. S3: The irregular small lumps of material after removing all moisture are placed in a high-temperature tube furnace. High-purity nitrogen gas with a purity of 99.9999% is introduced at a flow rate of 150~240ml / min to maintain the atmosphere inside the furnace. The irregular small lumps of material are reacted by a one-step carbothermic reduction nitridation method. First, the temperature is directly raised to the high-temperature section of 1400℃-1600℃ at a heating rate of 3-5℃ / min. After reaching the highest temperature of the high-temperature section, the temperature is held for 0.5~1h and then cooled naturally to obtain high-quality vanadium nitride with a nitrogen content higher than 18wt%. In step S3, the mass of the irregular small lumps of material placed in the high-temperature tube furnace is 13-18 g.

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