Unburned magnesia-calcia brick and its preparation method

Abstract

This invention provides a non-fired magnesia-calcium brick and its preparation method, belonging to the field of refractory materials. Its raw materials include aggregates, fine powder, graphite, binders and composite additives, wherein the composite additives contain calcium nitrate tetrahydrate. The non-fired magnesia-calcium brick of this invention has the following beneficial properties: (1) The composite additives are uniformly distributed in a network in the non-fired magnesia-calcium brick. Due to the dehydration reaction of calcium nitrate tetrahydrate in the composite additives during the brick drying process, a uniform network crack is formed in the finished brick, thereby improving the thermal shock resistance of the product; (2) The calcium nitrate formed by the dehydration of calcium nitrate tetrahydrate has strong water absorption, effectively protecting the CaO in the brick from hydration and improving the hydration resistance of the product; (3) During the high-temperature use of the finished non-fired magnesia-calcium brick, the calcium nitrate undergoes melting and decomposition to transform into highly active CaO, and reacts with SiO2 introduced in the composite additives to form a combined phase, improving the medium-temperature performance of the non-fired magnesia-calcium brick.

Description

Technical Field

[0001] This invention belongs to the field of refractory materials, and specifically relates to a non-fired magnesia-calcium brick and its preparation method. Background Technology

[0002] Magnesia-calcium bricks possess excellent resistance to alkali erosion and are considered a clean refractory material that minimizes pollution to molten steel during secondary refining in steelmaking, even playing a role in purifying the steel. Currently, widely used magnesia-calcium bricks are typically sintered at high temperatures using heavy oil or natural gas as fuel. Firing magnesia-calcium bricks requires prolonged firing at temperatures exceeding 1600℃, resulting in high energy consumption. Furthermore, the rapid heating in the preheating zone during firing can lead to incomplete fuel combustion, causing significant environmental pollution. In recent years, the government has intensified its efforts to control environmental pollution and promote energy conservation. To adapt to this new situation, the research and promotion of non-fired magnesia-calcium bricks is imperative.

[0003] While unfired magnesia-calcium bricks offer significant energy savings compared to fired products, they still fail to address the long-standing issue of hydration in magnesia-calcium products. Furthermore, because unfired magnesia-calcium products are not fired at high temperatures, their strength decreases sharply under medium-temperature conditions (900–1000℃) after the binder fails, posing a significant risk to their use.

[0004] Currently, the main methods for improving the hydration resistance of magnesia-calcium bricks can be divided into three categories: surface treatment, sealed packaging, and the addition of anti-hydration additives. Surface treatment and sealed packaging essentially involve coating the product to isolate it from the air, but the coating stability is poor. Once the coating layer is uneven or damaged, the product will hydrate rapidly. Currently, the anti-hydration additives used in magnesia-calcium bricks include additives that primarily generate a liquid phase, such as oxides like Al2O3, Fe2O3, and TiO2, as well as salts like CaF2 and MgCl2; and additives that primarily form solid solutions, such as rare earth oxides like CeO2 and La2O3. The mechanism of these additives is mainly to coat the CaO particles inside the brick, thereby isolating them from air. However, the introduction of additives inevitably leads to a decrease in some high-temperature properties of magnesia-calcium materials. Therefore, using the reduction of its excellent high-temperature properties to achieve hydration resistance is clearly not an ideal method.

[0005] To improve the intermediate temperature strength of unburned magnesia-calcium bricks, Chinese invention patent 201611077331.0, "A method for increasing the intermediate temperature strength of unburned magnesia-calcium bricks," proposes introducing 3-10% magnesia-calcium alloy powder into the material and improving the intermediate temperature strength of the product through liquid-phase sintering at 900-1000℃. However, magnesia-calcium alloy powder is expensive, and the safety of high-activity metal powder during use is difficult to guarantee. At the same time, this method does not solve the hydration problem of the product.

[0006] Improving hydration resistance and mid-temperature strength are the main development directions for non-fired magnesia-calcium bricks, and also the key technological bottlenecks limiting their widespread use. Therefore, developing non-fired magnesia-calcium bricks with simple processes, low costs, and excellent hydration resistance and mid-temperature strength is of great significance. Summary of the Invention

[0007] This invention provides a non-fired magnesia-calcium brick and its preparation method. By introducing a composite additive containing calcium nitrate tetrahydrate, the product's resistance to hydration and its medium-temperature strength are greatly improved.

[0008] The technical solution adopted in this invention is as follows:

[0009] A non-fired magnesia-calcium brick, the raw materials of which include aggregate, fine powder, graphite, binder and composite additive, wherein the composite additive contains calcium nitrate tetrahydrate.

[0010] Furthermore, the aggregate is magnesium calcium sand, the fine powder is fused magnesium sand, and the binder is anhydrous resin or paraffin wax.

[0011] Furthermore, the composite additive contains one or more of refined quartz powder, high-purity quartz powder, silica powder, and silica fume, as well as calcium nitrate tetrahydrate.

[0012] In one embodiment of the present invention, the raw materials of the unburned magnesia-calcium brick include aggregate, fine powder, graphite, binder and composite additive, wherein the aggregate is magnesia-calcium sand; the fine powder is fused magnesia sand; the binder is anhydrous resin or paraffin wax; and the composite additive contains calcium nitrate tetrahydrate, as well as one or more of refined quartz powder, high-purity quartz powder, silica fume and silica ash.

[0013] Furthermore, the aggregates have particle sizes of 5-3 mm, 3-1 mm, and 1-0.088 mm, respectively. Using aggregates of different particle sizes for reasonable particle gradation can improve the density of the brick body; the fine powder has a particle size of ≤ 0.088 mm.

[0014] Furthermore, taking the total mass fraction of the aggregate, fine powder, graphite, and composite additive as 100 parts, the mass fraction of aggregate with a particle size of 5-3 mm is 10-30 parts, the mass fraction of aggregate with a particle size of 3-1 mm is 15-40 parts, and the mass fraction of aggregate with a particle size of 1-0.088 mm is 10-20 parts; the mass fraction of fine powder is 15-30 parts; the mass fraction of graphite is 0.5-10 parts; and the mass fraction of composite additive is 3-10 parts. Based on this, the amount of binder is 0.5%-5% of the total mass of the aggregate, fine powder, graphite, and composite additive.

[0015] Furthermore, the composite additive contains 80%-95% calcium nitrate tetrahydrate by mass. Since the composite additive mainly contains SiO2 and CaO after heating, the aforementioned amount of calcium nitrate tetrahydrate allows them to react and form C2S (see reaction formula 4). Excessive SiO2 content will form low-melting-point compounds, affecting the strength of the magnesia-calcium brick. Moreover, SiO2 is an impurity phase in magnesia-calcium bricks and should not be excessive. Insufficient SiO2 content will leave only CaO in the composite additive, failing to improve its intermediate-temperature strength.

[0016] The preparation method of the non-fired magnesia-calcium brick as described above includes the following steps:

[0017] (1) Weigh the aggregate, fine powder, graphite, binder and composite additive according to the proportion;

[0018] (2) Bake calcium nitrate tetrahydrate until it melts, and mix the molten calcium nitrate tetrahydrate with one or more of refined quartz powder, high-purity quartz powder, silica powder, and silica fume and stir evenly to obtain composite additive mud.

[0019] (3) Mix the mud material in step (2) with the aggregate, graphite and binder in step (1), and put it into a wet mill for 5-10 minutes to knead. Then add fine powder, knead again for 10-20 minutes, and press it into brick blanks.

[0020] (4) The brick blank is placed in a drying oven for drying treatment to obtain the unfired magnesium-calcium brick.

[0021] Furthermore, in step (2), calcium nitrate tetrahydrate is baked until it melts because liquid-phase mixing results in better uniformity. If the additives are all in powder form, it is difficult to mix them uniformly. Regardless of the additives added, they are all impurities in the material, and excessive amounts will affect the high-temperature performance of the brick. Therefore, the ideal situation is to distribute them as evenly as possible, so as to reduce the amount added while achieving the best performance.

[0022] Furthermore, in step (3), the mixing temperature is 40-50℃. Since the fundamental function of the binder is to bond the aggregate together to give the brick strength, the clay is first mixed with the aggregate, graphite and binder, and then fine powder is added after mixing for 5-10 minutes.

[0023] Further, in step (4), the drying temperature is 200℃, and the drying time is 15-24 hours. Preferably, a method of continuous airflow and slow temperature increase is used during drying. The drying curves are: 100℃ for 2 hours; 100℃-200℃ for 5 hours; 200℃ for 15-24 hours. Slow temperature increase is used to allow the calcium nitrate tetrahydrate to dehydrate slowly; if dehydration is too rapid, water vapor will damage the internal structure of the material.

[0024] The melting point of calcium nitrate tetrahydrate is 44℃. During the drying process in step (4), the molten calcium nitrate tetrahydrate will dehydrate and transform into solid calcium nitrate at 130℃ (corresponding to reaction formula 1 below, the melting point of the product calcium nitrate is 561℃). In step (2), the molten calcium nitrate tetrahydrate is premixed with fine powder containing SiO2 (such as refined quartz powder, high-purity quartz powder, silica fume, silica ash) to obtain the composite additive mud, thus realizing the uniform network distribution of the composite additive in the brick.

[0025] Compared to ordinary additives that are distributed in a dotted pattern in bricks, the composite additives in the unburned magnesia-calcium bricks produced by this invention, which are uniformly distributed in a network pattern, have the following advantages:

[0026] (1) Because the dehydration of calcium nitrate tetrahydrate will cause volume shrinkage, a uniform mesh gap will be formed in the dried finished brick, which helps to improve the thermal shock stability of magnesium calcium brick.

[0027] (2) In the finished brick, the calcium nitrate formed after the dehydration of tetrahydrate calcium nitrate has a strong water absorption capacity. The calcium nitrate distributed in a network in the product can preferentially absorb water, protecting the CaO in the brick from hydration. The volume shrinkage caused by the dehydration of tetrahydrate calcium nitrate leaves room for its volume expansion after water absorption. Furthermore, the volume expansion of calcium nitrate after absorbing water will block the channels for water vapor to enter the brick, preventing further water vapor intrusion.

[0028] (3) During the high-temperature use of unfired magnesia-calcium bricks, calcium nitrate undergoes melting and decomposition to transform into highly active CaO (corresponding to reaction formulas 2 and 3 below), and further reacts with the surrounding SiO2 to form a C2S (2CaO·SiO2) composite phase (corresponding to reaction formula 4), thereby improving the medium-temperature physical properties of the finished bricks.

[0029] Ca(NO3)2·4H2O→Ca(NO3)2(1)

[0030] Ca(NO3)2→Ca(NO2)2(2)

[0031] Ca(NO2)2→CaO (3)

[0032] CaO + SiO2 → 2CaO·SiO2 (4)

[0033] This invention provides a non-fired magnesia-calcium brick with a composite additive containing calcium nitrate tetrahydrate, which has good medium-temperature strength and excellent hydration resistance without surface treatment or vacuum packaging.

[0034] This invention, by adding a composite additive containing calcium nitrate tetrahydrate to unburned magnesia-calcium bricks, has the following beneficial effects:

[0035] (1) Calcium nitrate tetrahydrate has a melting point of only 44℃. The composite additive containing calcium nitrate tetrahydrate participates in the mixing of raw materials for unburned magnesia-calcium bricks in the form of mud, thus achieving a uniform network distribution in the brick body.

[0036] (2) Calcium nitrate tetrahydrate decomposes into calcium nitrate at 130℃. After drying, the volume shrinkage caused by the dehydration of calcium nitrate tetrahydrate in the magnesia-calcium brick forms a uniform network of gaps, which helps to improve the thermal shock stability of the magnesia-calcium brick.

[0037] (3) Calcium nitrate has strong water absorption. The uniformly distributed network of calcium nitrate in the finished unburned magnesia-calcium bricks can preferentially absorb water, protecting the CaO in the brick from hydration. The volume shrinkage caused by the dehydration of tetrahydrate calcium nitrate leaves room for its volume expansion due to water absorption. Furthermore, the volume expansion of calcium nitrate due to water absorption will block the channels for water vapor to enter the brick, preventing further water vapor intrusion and improving the material's resistance to hydration.

[0038] (4) During the high-temperature use of unburned magnesia-calcium bricks, calcium nitrate undergoes melting and decomposition to transform into highly active CaO, and further reacts with SiO2 in the composite additives to form a C2S (2CaO·SiO2) composite phase, thereby improving the medium-temperature physical properties of the material. Detailed Implementation

[0039] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be described in detail below with reference to specific embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of the invention.

[0040] Example 1

[0041] Taking the mass percentage of unfired magnesia-calcium bricks as 100%, 4.5% calcium nitrate tetrahydrate was baked until melted, and then 0.2% silica powder and 0.3% high-purity quartz powder were added and mixed evenly to form a mud. The mud was then mixed with 24% 5-3mm magnesia-calcium sand, 30% 3-1mm magnesia-calcium sand, 12% 1-0.088mm magnesia-calcium sand, 3% graphite, and 3.5% anhydrous resin binder for 10 minutes. Then, 26% fused magnesia powder was added and the mixture was mixed for another 20 minutes. After mixing, the material was pressed into shape and quickly placed in a drying oven for drying for 15 hours to obtain unfired magnesia-calcium bricks.

[0042] The resulting unfired magnesia-calcium bricks, after testing, had a bulk density of 2.95 g / cm³. 3 The compressive strength at room temperature is 79.1 MPa, the apparent porosity is 6.5%, and the hydration weight gain is 0.7%. The flexural strength of the sample after firing at 1000℃ is 8.9 MPa.

[0043] Example 2

[0044] Taking the mass percentage of unfired magnesia-calcium bricks as 100%, 4.5% calcium nitrate tetrahydrate is baked until melted, and then 0.1% silica fume and 0.4% high-purity quartz powder are added and mixed evenly to form a mud. The mud is then mixed with 22% 5-3mm magnesia-calcium sand, 32% 3-1mm magnesia-calcium sand, 12% 1-0.088mm magnesia-calcium sand, 3% graphite, and 3.5% paraffin binder for 5 minutes. Then, 26% fused magnesia powder is added and the mixture is mixed for another 10 minutes. The mixed material is pressed into shape and quickly placed in a drying oven for 24 hours. After drying, the product is vacuum sealed to obtain unfired magnesia-calcium bricks.

[0045] The resulting unfired magnesia-calcium bricks, after testing, had a bulk density of 2.94 g / cm³. 3 The compressive strength at room temperature is 78.5 MPa, the apparent porosity is 7.1%, and the hydration weight gain is 0.5%. The flexural strength of the sample after firing at 1000℃ is 7.8 MPa.

[0046] Compared to Example 1, Example 2 underwent vacuum sealing, a traditional method for improving hydration resistance, reducing the hydration weight gain rate from 0.7% to 0.5%. This demonstrates that the unfired magnesia bricks prepared according to this invention have a hydration weight gain rate of only 0.7% even without sealing, and the increase after sealing is only 0.2%. Comparing with Comparative Examples 1 and 2, the hydration weight gain rate decreased from 5.9% to 1.2% before and after sealing, indicating that this product does not require sealing and also possesses excellent hydration resistance.

[0047] Example 3

[0048] Taking the mass percentage of unfired magnesia-calcium bricks as 100%, 8% calcium nitrate tetrahydrate is baked until melted, and then 1.5% refined quartz powder is added and mixed evenly to form a mud. The mud is then mixed with 26% 5-3mm magnesia-calcium sand, 30% 3-1mm magnesia-calcium sand, 12% 1-0.088mm magnesia-calcium sand, 0.5% graphite, and 3% anhydrous resin binder for 10 minutes. Then, 22% fused magnesia powder is added and the mixture is mixed for another 10 minutes. After mixing, the material is pressed into shape and quickly placed in a drying oven for 18 hours to obtain unfired magnesia-calcium bricks.

[0049] The resulting unfired magnesia-calcium bricks, after testing, had a bulk density of 2.96 g / cm³. 3 The compressive strength at room temperature is 74.5 MPa, the apparent porosity is 5.9%, and the hydration weight gain is 0.5%. The flexural strength of the sample after firing at 1000℃ is 9.8 MPa.

[0050] Example 4

[0051] Taking the mass percentage of unfired magnesia-calcium bricks as 100%, 3% calcium nitrate tetrahydrate was baked until melted, and then 0.2% silica powder was added and mixed evenly to form a mud. The mud was then mixed with 24% 5-3mm magnesia-calcium sand, 33% 3-1mm magnesia-calcium sand, 12% 1-0.088mm magnesia-calcium sand, 5.8% graphite, and 3.5% paraffin binder for 10 minutes. Then, 22% fused magnesia powder was added and the mixture was mixed for another 10 minutes. After mixing, the material was pressed into shape and quickly placed in a drying oven for 20 hours to obtain unfired magnesia-calcium bricks.

[0052] The resulting unfired magnesia-calcium bricks, after testing, had a bulk density of 2.94 g / cm³. 3 The compressive strength at room temperature is 77.5 MPa, the apparent porosity is 8.5%, and the hydration weight gain is 1.2%. The flexural strength of the sample after firing at 1000℃ is 5.5 MPa.

[0053] In Example 3, the amount of composite additive added was close to the upper limit of the content. The hydration weight gain was slightly lower than that in Example 1, and the flexural strength after firing at 1000℃ was slightly improved. This was because the content of the generated C2S bound phase increased, resulting in increased strength. In Example 4, the amount of composite additive added was close to the lower limit of the content. The hydration weight gain rate was greater than that in Example 1, but the flexural strength was lower than that in Example 1.

[0054] Comparative Example 1

[0055] Taking the mass percentage of unfired magnesia-calcium bricks as 100%, 26% magnesia-calcium sand of 5-3mm, 32% magnesia-calcium sand of 3-1mm, 12% magnesia-calcium sand of 1-0.088mm, 6% graphite, and 3.5% anhydrous resin binder are mixed together for 10 minutes. Then, 24% fused magnesia powder is added and the mixture is mixed for another 20 minutes. After mixing, the material is pressed into shape and quickly placed in a drying oven for drying for 15 hours to obtain unfired magnesia-calcium bricks.

[0056] The resulting unfired magnesia-calcium bricks, after testing, had a bulk density of 2.96 g / cm³. 3 The compressive strength at room temperature is 79.5 MPa, the apparent porosity is 5.9%, and the hydration weight gain is 5.9%. The flexural strength of the sample after firing at 1000℃ is 1.5 MPa.

[0057] Comparative Example 2

[0058] Taking the mass percentage of unfired magnesia-calcium bricks as 100%, 26% magnesia-calcium sand (5-3mm), 32% magnesia-calcium sand (3-1mm), 12% magnesia-calcium sand (1-0.088mm), 4% graphite, and 3.5% paraffin binder are mixed together for 10 minutes. Then, 26% fused magnesia powder is added and the mixture is mixed for another 20 minutes. After mixing, the material is pressed into shape and quickly placed in a drying oven for 18 hours. After drying, the product is vacuum sealed to obtain unfired magnesia-calcium bricks.

[0059] The resulting unfired magnesia-calcium bricks, after testing, had a bulk density of 2.97 g / cm³. 3 The compressive strength at room temperature is 78.7 MPa, the apparent porosity is 5.5%, and the hydration weight gain is 1.2%. The flexural strength of the sample after firing at 1000℃ is 1.3 MPa.

[0060] Comparative Examples 1 and 2 are ordinary unfired magnesia-calcium brick products currently in production. Their test data show that: (1) the hydration gain is greater than that of the unsealed bricks, and the sealing effect is obvious, but it is still higher than that of the example products; (2) the flexural strength after firing at 1000℃ is much lower than that of the example products.

[0061] Comparative Example 3

[0062] Taking the mass percentage of unfired magnesia-calcium bricks as 100%, 5% calcium nitrate tetrahydrate is baked until melted and then mixed with 26% magnesia-calcium sand (5-3 mm), 32% magnesia-calcium sand (3-1 mm), 10% magnesia-calcium sand (1-0.088 mm), 3% graphite, and 3% anhydrous resin binder for 5 minutes. Then, 24% fused magnesia powder is added and the mixture is continued to be mixed for 20 minutes. After mixing, the material is pressed into shape and quickly placed in a drying oven for drying for 18 hours to obtain unfired magnesia-calcium bricks.

[0063] The resulting unfired magnesia-calcium bricks, after testing, had a bulk density of 2.95 g / cm³. 3 The compressive strength at room temperature is 78.6 MPa, the apparent porosity is 6.8%, and the hydration weight gain is 0.9%. The flexural strength of the sample after firing at 1000℃ is 1.9 MPa.

[0064] Compared with Example 1, the proportion of calcium nitrate tetrahydrate in the composite additive in Comparative Example 3 increased to 100%. Due to the inability to form a C2S binding phase, the flexural strength after firing at 1000°C was significantly reduced in its test results.

[0065] Comparative Example 4

[0066] Taking the mass percentage of unfired magnesia-calcium bricks as 100%, 3% calcium nitrate tetrahydrate is baked until melted, and then 0.8% silica powder and 1.2% high-purity quartz powder are added and mixed evenly to form a mud. The mud is then mixed with 22% 5-3mm magnesia-calcium sand, 32% 3-1mm magnesia-calcium sand, 12% 1-0.088mm magnesia-calcium sand, 3% graphite, and 3.5% anhydrous resin binder for 10 minutes. Then, 26% fused magnesia powder is added and the mixture is mixed for another 15 minutes. After mixing, the material is pressed into shape and quickly placed in a drying oven for 24 hours to obtain unfired magnesia-calcium bricks.

[0067] The resulting unfired magnesia-calcium bricks, after testing, had a bulk density of 2.95 g / cm³. 3The compressive strength at room temperature is 79.6 MPa, the apparent porosity is 6.2%, and the hydration weight gain is 1.9%. The flexural strength of the sample after firing at 1000℃ is 3.9 MPa.

[0068] Compared with Examples 1 and 3, Comparative Example 4 showed that the proportion of calcium nitrate tetrahydrate in the composite additive was reduced to 60%. The test results showed that the hydration weight gain rate increased due to the reduced calcium nitrate tetrahydrate content, and the flexural strength after firing at 1000°C decreased due to excessive addition of silicon-containing raw materials.

[0069] Comparative Example 5

[0070] Taking the mass percentage of unfired magnesia-calcium bricks as 100%, 4.9% calcium nitrate tetrahydrate was baked until melted, and then 0.1% high-purity quartz powder was added and mixed evenly to form a mud. The mud was then mixed with 26% 5-3mm magnesia-calcium sand, 30% 3-1mm magnesia-calcium sand, 10% 1-0.088mm magnesia-calcium sand, 3% graphite, and 3.5% anhydrous resin binder for 10 minutes. Then, 26% fused magnesia powder was added and the mixture was mixed for another 20 minutes. After mixing, the material was pressed into shape and quickly placed in a drying oven for drying for 15 hours to obtain unfired magnesia-calcium bricks.

[0071] The resulting unfired magnesia-calcium bricks, after testing, had a bulk density of 2.95 g / cm³. 3 The compressive strength at room temperature is 78.8 MPa, the apparent porosity is 6.7%, and the hydration weight gain is 1.0%. The flexural strength of the sample after firing at 1000℃ is 4.8 MPa.

[0072] Compared with Example 1, the proportion of calcium nitrate tetrahydrate in the composite additive in Comparative Example 5 was increased to 98%. Due to the reduced amount of C2S bound phase, the flexural strength after firing at 1000°C was slightly lower in the test results.

[0073] Comparative Example 6

[0074] Taking the mass percentage of unfired magnesia-calcium bricks as 100%, 4.5% calcium nitrate tetrahydrate was baked until melted, and then 0.2% silica powder, 0.3% high-purity quartz powder, 3% graphite, and 26% fused magnesia powder were added and mixed together for 20 minutes to make a mud. The mud was then mixed with 24% 5-3mm magnesia-calcium sand, 30% 3-1mm magnesia-calcium sand, and 12% 1-0.088mm magnesia-calcium sand, plus 3.5% anhydrous resin binder, and mixed together for 10 minutes. After mixing, the material was pressed into shape and quickly placed in a drying oven for drying for 15 hours to obtain unfired magnesia-calcium bricks.

[0075] The resulting unfired magnesia-calcium bricks, after testing, had a bulk density of 2.94 g / cm³. 3 The compressive strength at room temperature is 63.4 MPa, the apparent porosity is 6.3%, and the hydration weight gain is 1.5%. The flexural strength of the sample after firing at 1000℃ is 4.8 MPa.

[0076] Compared to Example 1, Comparative Example 6 first involved mixing composite additives, graphite, and fine powder together to form a clay, which was then mixed with aggregates and binders. The test results showed a slightly higher hydration weight gain and a slightly lower flexural strength after firing at 1000°C.

[0077] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this invention, and these modifications or substitutions should all be covered within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the scope defined in the claims.

Claims

1. A not-burned magnesia-calcia brick, characterized by, Its raw materials include aggregates, fine powder, graphite, binders and composite additives, wherein the composite additives contain calcium nitrate tetrahydrate; The aggregate is magnesium calcium sand, the fine powder is fused magnesium sand, and the binder is anhydrous resin or paraffin. The composite additive contains one or more of high-purity quartz powder, silica powder, and silica fume, as well as calcium nitrate tetrahydrate. Based on a total mass fraction of 100 parts, the aggregate, fine powder, graphite, and composite additives are as follows: aggregate with a particle size of 5-3 mm comprises 10-30 parts; aggregate with a particle size of 3-1 mm comprises 15-40 parts; aggregate with a particle size of 1-0.088 mm comprises 10-20 parts; fine powder comprises 15-30 parts; graphite comprises 0.5-10 parts; and composite additives comprises 3-10 parts. Furthermore, the amount of binder is 0.5%-5% of the total mass of the aggregate, fine powder, graphite, and composite additives. The composite additives contain 80%-95% calcium nitrate tetrahydrate by mass. The method for preparing the unfired magnesia-calcium brick includes the following steps: (1) Weigh the aggregate, fine powder, graphite, binder and composite additive according to the proportion; (2) Bake calcium nitrate tetrahydrate until it melts, mix the molten calcium nitrate tetrahydrate with one or more of high-purity quartz powder, silica powder, and silica fume and stir evenly to obtain composite additive mud. (3) Mix the mud material in step (2) with the aggregate, graphite and binder in step (1), and put it into a wet mill for 5-10 minutes to knead. Then add fine powder, knead again for 10-20 minutes, and press it into brick blanks. (4) The brick blank is placed in a drying oven for drying treatment to obtain the unfired magnesia-calcium brick; In step (4), the drying temperature is 200℃ and the drying time is 15-24 hours. The drying method is to continuously ventilate the drying air and slowly increase the temperature. The drying curve is: 100℃ for 2 hours; 100℃-200℃ for 5 hours; 200℃ for 15-24 hours.

2. The dead burned magnesium calcium brick according to claim 1, characterized by The particle size of the fine powder is ≤ 0.088 mm.

3. The dead burned magnesium calcium brick according to claim 1, characterized by, In step (3), the mixing temperature is 40-50℃.