Preparation method of sintering aid-free calcium oxide crucible and calcium oxide crucible

Abstract

The invention relates to a preparation method of a sintering aid-free calcium oxide crucible and the calcium oxide crucible. The method comprises the following steps: preparing a calcium oxide block by utilizing a pure calcium carbonate raw material; performing electric arc melting and high-pressure air atomization treatment on the calcium oxide block to obtain hollow calcium oxide powder particles; mixing the hollow calcium oxide powder particles with molten paraffin, compacting in a crucible mold, and cooling to obtain a calcium oxide crucible blank; the calcium oxide crucible green body is demolded and then subjected to heating dewaxing, and then sintering is conducted through a two-step method, specifically, sintering is conducted in the air at the temperature of 1400-1650 DEG C to achieve primary forming, and then high-temperature sintering forming is conducted in the vacuum environment at the temperature of 1900-2000 DEG C to obtain the calcium oxide crucible. The sintering aid-free pure calcium oxide crucible is obtained by utilizing two-step high-temperature sintering and the inherent essential properties of low volume expansion coefficient and high heat insulation performance of the hollow material, and the heat insulation capability and the thermal shock resistance of the pure calcium oxide crucible are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of crucibles, and particularly relates to a preparation method of a calcium oxide crucible without a sintering aid and a calcium oxide crucible. Background Art

[0002] Calcium oxide (CaO) is the most stable metal oxide with the lowest free enthalpy of formation. It has the least reaction degree with liquid metal materials, excellent high-temperature stability, and good deoxidation and desulfurization effects. Using it to make crucibles that need to be in direct contact with molten metal can minimize the pollution of molten metal and obtain high-purity alloy materials with low oxygen and low sulfur. It is a promising refractory material for vacuum metallurgy worldwide.

[0003] For highly reactive metal materials such as high-purity metals platinum, rhodium, iridium, uranium, thorium, etc. and alloy products containing relatively high concentrations of metals titanium, chromium, uranium, thorium, etc., vacuum induction melting using calcium oxide refractory products can obtain excellent metal product properties.

[0004] However, CaO materials have two obvious disadvantages: (1) Low purity: Current CaO crucibles are sintered in air. Since the temperature that can be achieved by a conventional air sintering furnace is relatively low (generally less than 1650 °C), the sintering and forming of calcium oxide crucibles cannot be realized. Therefore, for the need of sintering and forming, sintering aids such as magnesium oxide, yttrium oxide, boric acid, calcium fluoride, barium carbonate, etc. are often added to the crucible raw materials, resulting in other impurity elements in the obtained calcium oxide crucibles, and the advantage of high chemical stability of calcium oxide materials cannot be effectively exerted, and it cannot be used for the melting of high-purity materials; (2) High thermal expansion coefficient (~13.8×10 -6 K -1 ), which causes poor thermal shock resistance and significantly lower crucible life of CaO crucible products compared with alumina, silica and other types of crucibles, and it is difficult to prepare large-size products. The above two problems make the current calcium oxide crucibles far from meeting the actual industrial needs. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a preparation method of a calcium oxide crucible without a sintering aid and a calcium oxide crucible, and its solution ideas are as follows: (1) Using hollow calcium oxide particles as raw materials to solve the problems of high thermal expansion coefficient, poor thermal cycling performance and low life of calcium oxide crucibles made of solid raw materials. (2) Solving the sintering and forming problem of the calcium oxide crucible without a sintering aid. A two-step sintering method is adopted: First, sinter at 1400 - 1650 °C in air to burn out trace impurity elements and achieve the preliminary forming of the calcium oxide crucible; then perform high-temperature sintering and forming at 1900 - 2000 °C in a vacuum environment.

[0006] The technical problems to be solved by the present invention are realized through the following technical solutions:

[0007] The present invention provides a method for preparing a calcium oxide crucible without a sintering aid, comprising:

[0008] Step 1: Sintering a calcium carbonate raw material with a purity of not less than 99% in air to obtain a pure calcium oxide bulk;

[0009] Step 2: Arc melting the pure calcium oxide bulk to obtain a pure calcium oxide melt;

[0010] Step 3: Preparing pure hollow calcium oxide powder particles by subjecting the pure calcium oxide melt to high-pressure air atomization treatment;

[0011] Step 4: Mixing the pure hollow calcium oxide powder particles with molten paraffin, vibrating and compacting the mixture in a crucible mold, and obtaining a calcium oxide crucible blank after the paraffin cools and solidifies;

[0012] Step 5: Demolding the calcium oxide crucible blank, placing it in a sand box, wrapping magnesium oxide sand around the calcium oxide crucible blank, performing a dewaxing treatment by heating the calcium oxide crucible blank, and performing a two-step sintering treatment on the dewaxed calcium oxide crucible blank to obtain a calcium oxide crucible.

[0013] The present invention also provides a calcium oxide crucible prepared by using the method for preparing a calcium oxide crucible without a sintering aid described in the above embodiment.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] The method for preparing a calcium oxide crucible without a sintering aid of the present invention utilizes the inherent essential attributes of a hollow powder material, namely, a low volume expansion coefficient and high heat insulation performance. By preparing pure calcium oxide into hollow spherical particles or powder, and then forming the hollow particle powder and sintering it in two steps without a sintering aid to make a pure calcium oxide crucible without a sintering aid. This calcium oxide crucible has extremely high heat insulation ability and extremely high thermal shock resistance, can give full play to the advantage of high chemical stability of calcium oxide, and can be used for the melting of ultra-pure metals or alloys.

[0016] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly, it can be implemented in accordance with the content of the specification. And in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the following specific preferred embodiments are given and described in detail in conjunction with the accompanying drawings as follows. Brief Description of the Drawings

[0017] Figure 1 is a flowchart of a method for preparing a calcium oxide crucible without a sintering aid provided by an embodiment of the present invention. Detailed Embodiments

[0018] In order to further elaborate on the technical means and effects adopted by the present invention to achieve the intended invention purpose, the following provides a detailed description of a preparation method of a calcium oxide crucible without a sintering aid and the calcium oxide crucible according to the present invention in combination with the accompanying drawings and specific embodiments.

[0019] The foregoing and other technical contents, features, and effects of the present invention can be clearly presented in the following detailed description in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and specific understanding of the technical means and effects adopted by the present invention to achieve the intended purpose can be obtained. However, the attached drawings are only for reference and explanation, and are not used to limit the technical solution of the present invention.

[0020] In the first aspect, an embodiment of the present invention provides a preparation method of a calcium oxide crucible without a sintering aid. Please refer to Figure 1 , Figure 1 which is a flowchart of a preparation method of a calcium oxide crucible without a sintering aid provided by an embodiment of the present invention. As Figure 1 shown, the preparation method of the calcium oxide crucible without a sintering aid in this embodiment includes:

[0021] Step 1: Sinter calcium carbonate raw materials with a purity of not less than 99% in air to obtain pure calcium oxide blocks.

[0022] In an optional embodiment, calcium carbonate raw materials with a purity of not less than 99% can be sintered in air to obtain pure calcium oxide blocks, wherein the temperature exceeds 800 °C.

[0023] Step 2: Arc melt the pure calcium oxide blocks to obtain an arc-melted calcium oxide melt.

[0024] In an optional embodiment, the pure calcium oxide blocks can be melted in a three-phase arc furnace with a capacity of 500 - 1500 kVA. After the pure calcium oxide blocks are completely melted, they are refined for 10 - 60 minutes to obtain a pure calcium oxide melt.

[0025] Optionally, the three-phase power supply voltage during melting is 100 - 230 V, the current is 200 - 5000 A, and the electrode distance between the graphite electrode and the pure calcium oxide blocks is 0.01 - 0.1 m.

[0026] Step 3: Perform high-pressure air atomization treatment on the pure calcium oxide melt to prepare pure hollow calcium oxide powder particles.

[0027] In this embodiment, a high-pressure air atomizer is used to perform high-pressure air atomization treatment on the calcium oxide melt. The high-pressure air atomizer includes a tundish and a ceramic nozzle arranged below the tundish. The ceramic nozzle can be made of ceramics such as zirconia and boron nitride. The high-pressure air ejected from the ceramic nozzle performs two-fluid high-pressure air atomization on the calcium oxide melt flowing through the tundish to obtain hollow calcium oxide powder particles.

[0028] Optionally, step 3 may include:

[0029] Step 3.1: Pour the pure calcium oxide melt into the preheated tundish in the high-pressure air atomizer. The preheating temperature of the tundish is 1400 - 1600 °C.

[0030] In this implementation, preheating the tundish is to ensure that the pure calcium oxide melt poured into the tundish remains in a molten state.

[0031] Step 3.2: Use the ceramic nozzle below the tundish to perform two-fluid high-pressure air atomization on the pure calcium oxide melt flowing through the tundish to obtain pure hollow calcium oxide powder particles. Among them, the gas pressure of the high-pressure air atomization is 0.1 - 1.0 MPa.

[0032] In this embodiment, the particle size of the pure hollow calcium oxide powder particles prepared by high-pressure air atomization is 0.01 - 3 mm, and the proportion of the pure hollow calcium oxide powder particles is 60 - 70%.

[0033] Step 4: Mix the pure hollow calcium oxide powder particles with molten paraffin, vibrate the mixture in a crucible mold, and obtain a calcium oxide crucible blank after the paraffin cools and solidifies.

[0034] Optionally, the pure hollow calcium oxide powder particles can be mixed with solid paraffin particles. The volume fraction of the solid paraffin particles is 0.1 - 5 vol.%, and then the temperature is raised to 80 - 90 °C to mix the pure hollow calcium oxide powder particles and the molten paraffin evenly; vibrate the mixture in a crucible mold, and obtain a calcium oxide crucible blank after the paraffin melt cools.

[0035] Exemplarily, the mixture can be vibrated in a 25 kg model crucible mold, and a 25 kg type calcium oxide crucible blank can be obtained after the paraffin cools; considering that calcium oxide will shrink during the subsequent high-temperature sintering process, the male mold of the crucible mold is 2 mm smaller than the standard size, and the female mold is 5 - 6 mm larger than the standard size.

[0036] It should be noted that in this embodiment, the molten paraffin and the pure hollow calcium oxide powder particles are used for integral molding, rather than directly pressing the pure hollow calcium oxide powder particles using traditional cold isostatic pressing or cold pressing processes, in order to avoid damaging the hollow structure of the hollow calcium oxide powder particles by the traditional cold isostatic pressing or cold pressing processes.

[0037] Step 5: After demolding the calcium oxide crucible blank, place it in a sand box, wrap magnesium oxide sand around the calcium oxide crucible blank, perform a dewaxing treatment by heating the calcium oxide crucible blank, and perform a two-step sintering treatment on the dewaxed calcium oxide crucible blank to obtain a calcium oxide crucible.

[0038] In an optional embodiment, Step 5 includes:

[0039] Step 5.1: After demolding the calcium oxide crucible blank, place it in a sand box, and wrap magnesium oxide sand around the calcium oxide crucible blank.

[0040] In this embodiment, the reason for wrapping the calcium oxide crucible blank with magnesium oxide sand is that the strength of the hollow calcium oxide formed by the paraffin method is insufficient, and the magnesium oxide sand plays a role in supporting and protecting the calcium oxide crucible blank. The sand box can be composed of oxide ceramics such as magnesia bricks.

[0041] Step 5.2: Heat the sand box to 120 - 350 °C to heat the calcium oxide crucible blank for dewaxing.

[0042] Step 5.3: After the calcium oxide crucible blank is heated for dewaxing, continue to heat the sand box to 1400 - 1650 °C to sinter and form the dewaxed calcium oxide crucible blank to obtain a preliminarily formed calcium oxide crucible.

[0043] Step 5.4: After the preliminarily formed calcium oxide crucible is cooled to room temperature, place it in a vacuum sintering furnace, heat it to 1900 - 2000 °C in a vacuum (<100 Pa) or an inert gas protection atmosphere, and perform a secondary ultra-high temperature sintering on the preliminarily formed calcium oxide crucible blank to obtain a calcium oxide crucible.

[0044] In this embodiment, the prepared calcium oxide crucible is used for the melting of CuCr25 contacts. The service life of the calcium oxide crucible in this embodiment is 15 furnace times, which is significantly higher than the case where the service life of a conventional calcium oxide crucible is not higher than 5 furnace times. The comparison of the performance of the calcium oxide crucible prepared by the embodiment of the present invention for vacuum melting CuCr25 contacts with the national standard performance of CuCr25 contacts is shown in Table 1.

[0045] Comparison of the basic performance after vacuum melting of CuCr25 contacts

[0046]

[0047] The preparation method of the calcium oxide crucible without a sintering aid according to the embodiments of the present invention utilizes the inherent essential properties of the hollow powder material, namely low volume expansion coefficient and high heat insulation performance. By preparing pure calcium oxide raw materials into hollow spherical particles or powders, and then forming the hollow particle powders and sintering them twice without a sintering aid to produce a pure calcium oxide crucible without a sintering aid, the calcium oxide crucible has ultra-high heat insulation ability and extremely high thermal shock resistance, can give full play to the advantage of high chemical stability of calcium oxide, and can be used for the melting of ultra-pure metals or alloys.

[0048] Furthermore, the preparation method of the calcium oxide crucible without a sintering aid is described through specific embodiments.

[0049] Example 1. Preparation of a calcium oxide crucible by high-temperature sintering in a vacuum environment

[0050] Step i: Roast calcium carbonate raw materials with a purity of 99% at 900 - 950 °C to obtain pure calcium oxide blocks.

[0051] Step ii: Melt the pure calcium oxide blocks in a three-phase arc furnace. After the materials are completely melted, refine them for 60 min to obtain a pure calcium oxide melt. During melting, the three-phase power supply voltage is 100 V, the current is 200 A, and the electrode distance between the graphite electrode and the pure calcium oxide blocks is 0.01 m.

[0052] Step iii: Pour the pure calcium oxide melt into a tundish that has been preheated in a high-pressure air atomizer. The preheating temperature of the tundish is 1400 °C.

[0053] Step iv: Use a ceramic nozzle below the tundish to perform two-stream high-pressure air atomization on the pure calcium oxide melt flowing through the tundish to obtain pure hollow calcium oxide powder particles. Among them, the gas pressure of the high-pressure air atomization is 0.1 MPa.

[0054] Step v: Mix the pure hollow calcium oxide powder particles with molten paraffin, vibrate the mixture in a crucible mold, and obtain a calcium oxide crucible blank after the paraffin cools. Among them, the volume fraction of paraffin is 0.1 vol.%.

[0055] Step vi: After demolding the calcium oxide crucible blank, place it in a sand box, wrap the calcium oxide crucible blank with magnesia sand, heat the sand box to 120 °C to raise the temperature of the calcium oxide crucible blank to remove the wax. After the calcium oxide crucible blank completes the wax removal, continue to heat the sand box to 1400 °C to sinter and form the wax-removed calcium oxide crucible blank to obtain a preliminarily formed calcium oxide crucible with a certain strength.

[0056] Step vii: After slowly cooling the preliminarily formed calcium oxide crucible to room temperature, place it in a vacuum sintering furnace heated by graphite resistance. Evacuate the air until the air pressure is less than 10 Pa, then increase the temperature in the furnace to 1900 °C at a rate of 5 °C / min. After holding at 1900 °C for 2 hours, stop heating and let the sintered calcium oxide crucible in the furnace cool naturally to room temperature to obtain the calcium oxide crucible.

[0057] Example 2. Calcium oxide crucible sintered at high temperature in an argon protection environment

[0058] Step i: Roast calcium carbonate ore with a purity of 99% at 950 - 1000 °C to obtain pure calcium oxide lumps.

[0059] Step ii: Melt the pure calcium oxide lumps in a three-phase arc furnace. After the mixed materials are completely melted, refine for 10 min to obtain pure calcium oxide melt. The three-phase power supply voltage during melting is 230 V, the current is 5000 A, and the electrode distance between the graphite electrode and the pure calcium oxide lumps is 0.1 m.

[0060] Step iii: Pour the pure calcium oxide melt into a tundish that has been preheated in a high-pressure air atomizer. The preheating temperature of the tundish is 1600 °C.

[0061] Step iv: Use a ceramic nozzle below the tundish to perform two-stream high-pressure air atomization on the pure calcium oxide melt flowing through the tundish to obtain pure hollow calcium oxide powder particles. Among them, the gas pressure of the high-pressure air atomization is 1.0 MPa.

[0062] Step v: Mix the pure hollow calcium oxide powder particles with molten paraffin, vibrate and compact the mixture in a crucible mold. After the paraffin cools, obtain a calcium oxide crucible blank, where the volume fraction of paraffin is 5 vol.%.

[0063] Step vi: After demolding the calcium oxide crucible blank, place it in a sand box, wrap the calcium oxide crucible blank with magnesia sand around it, and heat the sand box to 350 °C to raise the temperature of the calcium oxide crucible blank to remove the wax. After the calcium oxide crucible blank has been heated to remove the wax, continue to heat the sand box to 1650 °C to sinter and form the calcium oxide crucible blank after dewaxing treatment to obtain a preliminarily formed calcium oxide crucible with a certain strength.

[0064] Step vii: After slowly cooling the preliminarily formed calcium oxide crucible to room temperature, place it in a vacuum box furnace. Evacuate the air until the air pressure is less than 100 Pa, then fill the vacuum chamber with argon to 0.03 MPa. Then increase the temperature in the furnace to 1950 °C at a rate of 2 °C / min. After holding at 1950 °C for 1 hour, stop heating and let the sintered calcium oxide crucible in the furnace cool naturally to room temperature to obtain the calcium oxide crucible.

[0065] Example 3. Calcium Oxide Crucible Sintered at High Temperature in a Nitrogen Protection Environment

[0066] Step i: Calcinate calcium carbonate ore with a purity of 99% at 850 - 900 °C to obtain pure calcium oxide lumps.

[0067] Step ii: Melting the pure calcium oxide lumps in a three - phase arc furnace. After the mixed materials are completely melted, refine for 40 min to obtain a pure calcium oxide melt. The three - phase power supply voltage during melting is 150 V, the current is 1000 A, and the electrode distance between the graphite electrode and the pure calcium oxide lumps is 0.05 m.

[0068] Step iii: Pour the pure calcium oxide melt into a tundish that has been pre - heated in a high - pressure air atomizer. The pre - heating temperature of the tundish is 1500 °C.

[0069] Step iv: Use a ceramic nozzle below the tundish to perform two - stream high - pressure air atomization on the pure calcium oxide melt flowing through the tundish to obtain pure hollow calcium oxide powder particles. Among them, the gas pressure of the high - pressure air atomization is 0.5 MPa.

[0070] Step v: Mix the pure hollow calcium oxide powder particles with molten paraffin, vibrate and compact the mixture in a crucible mold. After the paraffin cools and solidifies, obtain a calcium oxide crucible blank. The volume fraction of paraffin is 2.5 vol.%.

[0071] Step vi: After demolding the calcium oxide crucible blank, place it in a sand box, wrap the calcium oxide crucible blank with magnesia sand, heat the sand box to 200 °C to make the calcium oxide crucible blank rise in temperature to remove wax. After the calcium oxide crucible blank rises in temperature to remove wax, continue to heat the sand box to 1500 °C to sinter and form the wax - removed calcium oxide crucible blank to obtain a preliminarily formed calcium oxide crucible.

[0072] Step vii: After slowly cooling the preliminarily formed calcium oxide crucible to room temperature, place it in a vacuum box furnace, evacuate to a pressure less than 10 Pa, then fill the vacuum chamber with nitrogen to 0.05 MPa, and then heat the furnace temperature to 2000 °C at a rate of 10 °C / min. After holding at 2000 °C for 1 hour, stop heating and let the sintered calcium oxide crucible in the furnace cool naturally to room temperature to obtain a calcium oxide crucible.

[0073] In the second aspect, the embodiments of the present invention provide a calcium oxide crucible, which is prepared by using the preparation method of the calcium oxide crucible without a sintering aid provided in the first aspect above. Detect the basic performance of the calcium oxide crucible prepared in Example 1. For the test results, please refer to Table 1. It can be seen from Table 1 that the linear change rate of this calcium oxide crucible is relatively low, and it has good pressure resistance and refractory strength.

[0074] Table 1. Basic Performance of Calcium Oxide Crucible

[0075]

[0076] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant is intended to cover non-exclusive inclusion, so that an article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the article or device comprising the element. Words such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The orientation or positional relationship indicated by "above", "below", "left", "right", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation on the present invention.

[0077] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A preparation method of a calcium oxide crucible without a burning aid, characterized in that, Including: Step 1: Sinter calcium carbonate raw materials with a purity of not less than 99% in air to obtain pure calcium oxide blocks; Step 2: Arc melt the pure calcium oxide blocks to obtain a pure calcium oxide melt; Step 3: Prepare pure hollow calcium oxide powder particles by subjecting the pure calcium oxide melt to high-pressure air atomization treatment; Step 4: Mix the pure hollow calcium oxide powder particles with molten paraffin, vibrate the mixture in a crucible mold, and obtain a calcium oxide crucible blank after the paraffin cools and solidifies; Step 5: Demold the calcium oxide crucible blank and place it in a sand box, wrap magnesium oxide sand around the calcium oxide crucible blank, perform a temperature-raising dewaxing treatment on the calcium oxide crucible blank, and perform a two-step sintering treatment on the dewaxed calcium oxide crucible blank to obtain a calcium oxide crucible.

2. The preparation method of the lime crucible without a burning aid according to claim 1, wherein, In Step 1, the sintering temperature of the calcium carbonate raw materials with a purity of not less than 99% in air exceeds 800 °C.

3. The preparation method of the calcium oxide crucible without a combustion aid according to claim 1, characterized in that, Step 2 includes: Melt the pure calcium oxide blocks in a three-phase electric arc furnace with a capacity of 500 - 1500 kVA. After the pure calcium oxide blocks are completely melted, refine them for 10 - 60 min to obtain the pure calcium oxide melt.

4. The preparation method of the lime crucible without a burning aid according to claim 3, characterized in that, During melting, the three-phase power supply voltage is 100 - 230 V, the current is 200 - 5000 A, and the electrode distance between the graphite electrode and the pure calcium oxide blocks is 0.01 - 0.1 m.

5. The preparation method of the lime crucible without a burning aid according to claim 1, characterized in that Step 3 includes: Step 3.1: Pour the pure calcium oxide melt into a tundish that has been preheated in a high-pressure air atomizer, and the preheating temperature of the tundish is 1400 - 1600 °C; Step 3.2: Use a ceramic nozzle below the tundish to perform two-stream high-pressure air atomization on the pure calcium oxide melt flowing through the tundish to obtain pure hollow calcium oxide powder particles. Among them, the gas pressure for high-pressure air atomization is 0.1 - 1.0 MPa.

6. The preparation method of the lime crucible without a combustion aid according to claim 5, characterized in that, The particle size of the pure hollow calcium oxide powder particles prepared by high-pressure air atomization is 0.01 - 3 mm, and the proportion of the pure hollow calcium oxide powder particles is 60 - 70%.

7. The preparation method of the lime crucible without a burning aid according to claim 1, characterized in that Step 4 includes: Mix the pure hollow calcium oxide powder particles with solid paraffin particles, and the volume fraction of the solid paraffin particles is 0.1 - 5 vol.%. Then, raise the temperature to 80 - 90 °C to make the pure hollow calcium oxide powder particles and the molten paraffin mix evenly; vibrate the mixture in a crucible mold, and obtain the calcium oxide crucible blank after the paraffin cools.

8. The preparation method of the lime crucible without a burning aid according to claim 1, characterized in that Step 5 includes: Step 5.1: Demold the calcium oxide crucible blank and place it in a sand box, and wrap magnesium oxide sand around the calcium oxide crucible blank; Step 5.2: Raise the temperature of the sand box to 120 - 350 °C to make the calcium oxide crucible blank undergo temperature-raising dewaxing; Step 5.3: After the calcium oxide crucible blank undergoes temperature-raising dewaxing, continue to raise the temperature of the sand box to 1400 - 1650 °C to sinter and form the dewaxed calcium oxide crucible blank to obtain a preliminarily formed calcium oxide crucible; Step 5.4: After the preliminarily formed calcium oxide crucible is cooled to room temperature, it is placed in a vacuum sintering furnace and heated to 1900-2000 °C in a vacuum or an inert gas protection atmosphere to perform secondary ultra-high temperature sintering on the preliminarily formed calcium oxide crucible blank to obtain the calcium oxide crucible.

9. A calcium oxide crucible, characterized in that, It is prepared by using the preparation method of the calcium oxide crucible without a sintering aid according to any one of claims 1-8.

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