Rice husk ash and its manufacturing method, as well as calcium silicate molded body and its manufacturing method

Abstract

This invention provides rice husk ash and a method for producing the same, which are suitable as raw materials for manufacturing xonotlite-based calcium silicate molded articles that have good properties (e.g., good mechanical strength) and excellent non-flammability. [Solution] The rice husk ash of the present invention has a cristobalite (101) peak intensity of 10,000 counts or less in the diffraction spectrum obtained by powder X-ray diffraction, and a loss on ignition of 3% by mass or less. The method for producing the rice husk ash of the present invention comprises a step of burning rice husks, and the burning time is 10 hours or more. The rice husk ash of the present invention is suitable as a raw material for producing xonotlite-based calcium silicate molded articles that have good mechanical strength and excellent non-flammability.

Description

Technical Field

[0001] The present invention relates to rice husk ash, a method for producing the same, a calcium silicate molded body, and a method for producing the same.

Background Art

[0002] Silica raw materials used for producing calcium silicate products generally use inexpensive natural resources (such as silica). A method of substituting this silica raw material with rice husk ash silica to produce calcium silicate products is also being carried out. Such rice husk ash silica can be obtained, for example, by burning rice husks in a biomass boiler. As a method for producing rice husk ash from rice husks, Patent Document 1 discloses a method of burning carbonized rice husks and recovering the combustion ash generated by this combustion as silica, as well as a silica production apparatus. Further, Patent Document 2 discloses an apparatus and a production method for producing vegetable silica by burning biomass fuel or the like at a high temperature of 1000 degrees or more.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, as a result of investigations by the present inventors, it was found that the quality of conventionally obtained rice husk ash (rice husk ash silica) tends to vary. Further, even when producing xonotlite-based calcium silicate using such rice husk ash, it was difficult to synthesize a xonotlite-based calcium silicate molded body having good properties (for example, good mechanical strength).

[0005] The present invention has been made in view of the above, and aims to provide rice husk ash and a method for producing the same, which are suitable as raw materials for producing xonotlite-based calcium silicate molded articles having good properties (for example, good mechanical strength and non-flammability). The present invention also aims to provide calcium silicate molded articles obtained using the aforementioned rice husk ash and a method for producing the same. [Means for solving the problem]

[0006] The inventors of this invention conducted extensive research to achieve the above objectives and discovered that these objectives can be achieved by adjusting the cristobalite (101) peak intensity of rice husk ash to 10,000 counts or less and the ignition loss to 3% by mass or less, thereby completing the present invention.

[0007] In other words, the present invention encompasses, for example, the subject matter described in the following sections. Item 1 In the diffraction spectrum obtained by powder X-ray diffraction, the cristobalite (101) peak intensity is 10,000 counts or less. Rice husk ash with a loss on ignition of 3% by mass or less. Section 2 A method for producing rice husk ash as described in item 1, It includes a process for burning rice husks, A method for producing rice husk ash, wherein the combustion treatment time is 10 hours or more. Section 3 A calcium silicate molded body obtained from the rice husk ash described in item 1. Section 4 A step of obtaining a slurry by hydrothermally treating the raw material containing rice husk ash as described in item 1, The process of forming the slurry and A method for producing a calcium silicate molded article containing [the specified substance]. Section 5 The method comprises the step of obtaining the aforementioned rice husk ash by the manufacturing method described in item 2, The method for producing a calcium silicate molded article according to item 4, wherein the energy generated by burning the aforementioned rice husks is used in the production of a calcium silicate molded article. [Effects of the Invention]

[0008] The rice husk ash of the present invention is suitable as a raw material for producing a xonotlite-based calcium silicate molded body having good mechanical strength and excellent incombustibility.

Brief Description of the Drawings

[0009] [Figure 1] It is a schematic explanatory view showing an example of an apparatus for producing the rice husk ash of the present invention.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described in detail. In this specification, the expressions "contain" and "include" include the concepts of "contain", "include", "consisting essentially of", and "consisting only of".

[0011] 1. Rice husk ash The rice husk ash of the present invention has a cristobalite (101) peak intensity of 10,000 counts or less in the diffraction spectrum obtained by the powder X-ray diffraction method, and the rice husk ash of the present invention has a loss on ignition of 3% by mass or less.

[0012] By using the rice husk ash of the present invention, a xonotlite-based calcium silicate molded body can be produced, and the obtained xonotlite-based calcium silicate molded body can have good mechanical strength and is also excellent in incombustibility.

[0013] When the cristobalite (101) peak intensity exceeds 10,000 counts, the mechanical strength of the obtained xonotlite-based calcium silicate molded body decreases.

[0014] The cristobalite (101) peak intensity is preferably 8000 counts or less, more preferably 6000 counts or less, still more preferably 5000 counts or less, and particularly preferably 4000 counts or less. Also, the cristobalite (101) peak intensity is preferably 100 counts or more, more preferably 1000 counts or more, still more preferably 1500 counts or more, and particularly preferably 2000 counts or more.

[0015] The method for adjusting the cristobalite (101) peak intensity to 10000 counts or less is not particularly limited. For example, by adjusting the combustion conditions of rice husks, which are the raw materials when producing rice husk ash, particularly the combustion time (residence time), to an appropriate range, it becomes easy to adjust the cristobalite (101) peak intensity to 10000 counts or less.

[0016] The cristobalite (101) peak intensity can be determined by measuring the rice husk ash of the present invention by the powder X-ray diffraction method. Specifically, in the diffraction spectrum obtained by the powder X-ray diffraction method of the rice husk ash of the present invention, it can be estimated based on the peak intensity (2θ = 21.9° ± 0.5) derived from the crystals of the cristobalite (101) plane. The measuring device uses the powder X-ray diffractometer "MiniFlex600" manufactured by Rigaku Corporation, and the rice husk ash is measured under the conditions of (X-ray source: Cu-Kα ray (wavelength 0.154 nm), tube voltage 35 kV, tube current 10 mA, measurement range 20° to 30°, scan speed 2.0000° / min, step width 0.0200°, slit 0.3 mm), and correction is performed using a standard sample. The standard sample uses SRM-640d of NISI, and measurement is performed under the conditions of X-ray source: Cu-Kα ray (wavelength 0.154 nm), tube voltage 35 kV, tube current 10 mA, measurement range 20° to 40°, scan speed 2.0000° / min, step width 0.0200°, slit 0.3 mm. It is estimated based on the peak intensity (2θ = 28.6° ± 0.5) derived from the crystals of the silicon (111) plane, and the measured value of the rice husk ash is corrected by the following formula using the measured value of the standard sample. Rice husk ash corrected value (counts) = Measured value of rice husk ash × Correction coefficient Correction factor = Standard substance measurement value immediately after bulb replacement ÷ Standard substance measurement value for the current month For the standard sample, the peak intensity at 28.4° based on Si(111) is measured, while for the rice husk ash, the peak intensity at 22.0° based on cristobalite(101) is measured.

[0017] As mentioned above, the ignition loss of the rice husk ash of the present invention is 3% by mass or less. If the ignition loss exceeds 3% by mass, the mechanical strength of the resulting xonotlite-based calcium silicate molded article decreases, and its non-flammability also decreases.

[0018] The ignition loss is preferably 2.9% by mass or less, more preferably 2.8% by mass or less, even more preferably 2.7% by mass or less, and particularly preferably 2.6% by mass or less. Furthermore, the lower limit of the ignition loss is not particularly limited and may be 0% by mass, 0.1% by mass or more, or even 0.5% by mass or more.

[0019] The method for adjusting the ignition loss to 3% by mass or less is not particularly limited. For example, by adjusting the combustion conditions of the rice husks, which are the raw material when producing rice husk ash, particularly the combustion time (residence time), to an appropriate range, it becomes easy to adjust the ignition loss to 3% by mass or less.

[0020] The ignition loss of the rice husk ash of this invention can be measured by the following method. Approximately 5 g of rice husk ash dried at 150°C is weighed and placed in an electric furnace (Nabertherm "Muffle Furnace LT9 / 11 (Germany)"), and the temperature is raised to 1000°C over 150 minutes, followed by a heat treatment at 1000°C for 30 minutes. After the heat-treated rice husk ash is allowed to cool naturally to room temperature (25°C), it is removed from the electric furnace, and the ignition loss is calculated using the following formula. Ignition loss (%) = ((Weight before heating - Weight after heating) / Weight before heating) x 100 Calculate from there.

[0021] The rice husk ash of the present invention is not particularly limited in terms of other physical properties, as long as the cristobalite (101) peak intensity and ignition loss each satisfy the above ranges, and can be, for example, the same as known rice husk ash. Furthermore, the composition of the rice husk ash of the present invention is not particularly limited as long as the cristobalite (101) peak intensity and ignition loss each satisfy the above ranges.

[0022] 2. Method for producing rice husk ash The method for producing the rice husk ash of the present invention is not particularly limited. For example, the rice husk ash of the present invention can be obtained by burning the rice husks used as raw material. Preferably, the method for producing the rice husk ash of the present invention includes a step of burning the rice husks, and the burning time is 10 hours or more. In this case, the rice husk ash of the present invention can be easily produced, and in particular, it becomes easy to adjust the cristobalite (101) peak intensity to 10,000 counts or less and the ignition loss to 3% by mass or less.

[0023] When burning rice husks, the type of rice husk used is not particularly limited; for example, known types of rice husks can be widely applied in this invention.

[0024] The combustion treatment conditions are preferably divided into two stages, namely a first combustion treatment and a second combustion treatment. In this case, it becomes easier to adjust the cristobalite (101) peak intensity and ignition loss of the resulting rice husk ash to a desired range. The combustion treatment is not limited to two stages; it may be one stage or three or more stages.

[0025] In the first combustion treatment, the combustion temperature can be set to 300 to 1100°C, as this makes it easier to adjust the cristobalite (101) peak intensity and the ignition loss to a desired range. The combustion time is preferably 30 to 60 seconds, excluding the heating time (i.e., from the time the desired temperature is reached), as this makes it easier to adjust the cristobalite (101) peak intensity and the ignition loss to a desired range. In the first combustion treatment, it is preferable to burn the rice husks in the presence of air.

[0026] In the second combustion treatment, the combustion temperature can be set to 500-800°C, as this makes it easier to adjust the cristobalite (101) peak intensity and the ignition loss to a desired range. The combustion time is preferably 10-20 hours, excluding the heating time (i.e., from the time the desired temperature is reached), as this makes it easier to adjust the cristobalite (101) peak intensity and the ignition loss to a desired range. In the second combustion treatment, it is preferable to burn the rice husks in the presence of air. The temperature of the first combustion treatment may be higher than the temperature of the second combustion treatment, or the temperature of the first combustion treatment may be lower than the temperature of the second combustion treatment. In either case, the rice husk ash of the present invention can be obtained.

[0027] In the combustion of rice husks, it is preferable that the combustion treatment time (excluding the heating time) be 10 hours or more. In this case, it becomes easier to adjust the cristobalite (101) peak intensity to 10,000 counts or less and the ignition loss to 3 mass% or less. The combustion treatment time referred to here means the total combustion time. Therefore, if the combustion treatment is divided into two stages, a first combustion treatment and a second combustion treatment, as described above, it means the total combustion time of the first and second combustion treatments.

[0028] Based on the above, the present invention's method for producing rice husk ash is preferably characterized by a step of burning the rice husks, and the burning time being 10 hours or more.

[0029] The process of burning the rice husks can be carried out in a boiler, and preferably in a biomass boiler designed to perform the burning process in two or more stages.

[0030] Figure 1 is a schematic diagram illustrating the structure of a biomass boiler that can be used in the process of burning rice husks.

[0031] The biomass boiler B shown in Figure 1 has a first combustion furnace 1 for the first combustion treatment of rice husks M1 and a second combustion furnace 2 for the second combustion treatment of rice husks M1, both located inside the boiler and adjacent to each other separated by a partition wall 3. The first and second combustion furnaces are designed to be heated in order to burn the rice husks M1. The biomass boiler B also has a raw material supply port 4 connected to the first combustion furnace 1 for supplying rice husks M1 to the first combustion furnace 1.

[0032] The first combustion furnace 1 and the second combustion furnace 2 are designed to be supplied with air A from the outside from the bottom of the first combustion furnace 1 and the second combustion furnace 2, and an exhaust passage E is provided for exhausting the air introduced from the outside or the gas produced by combustion to the outside. The partition wall 3 is provided with a ventilation passage 5 for supplying high-temperature air generated in the first combustion furnace 1 to the second combustion furnace 2.

[0033] The ventilation passage 5 is a pipe for guiding air A into the rice husks accumulated in the second combustion furnace 2, and is provided to penetrate the partition wall 3. In this embodiment of the biomass boiler B, because the ventilation passage 5 is provided, air A is supplied to the second combustion furnace 2 through the ventilation passage 5, thereby ensuring that sufficient oxygen reaches the inside of the rice husks accumulated in the second combustion furnace 2, and promoting the combustion of the rice husk ash M2. At the same time, since air A is supplied from the bottom, oxygen is supplied to the inside of the rice husks accumulated in the second combustion furnace 2, so that the biomass boiler B of this embodiment can continue burning for more than 10 hours in total.

[0034] Conventional biomass boilers can promote the combustion of the surface of rice husks accumulated in the furnace, but it is difficult to burn the inside of the rice husk deposit for more than 10 hours. For this reason, it has been difficult to produce the rice husk ash of the present invention (rice husk ash with a peak intensity of 10,000 counts or less and a loss on ignition of 3% by mass or less). To overcome this difficulty, it is conceivable to increase the combustion temperature, but when processed at high temperatures, it is not possible to stably adjust the cristobalite (101) peak intensity to 10,000 counts or less. It is also conceivable to burn the entire rice husk uniformly and for a long time by making the combustion furnace longer, but in this case, the equipment becomes large and complex.

[0035] In contrast, the biomass boiler B shown in Figure 1, by having the above-described configuration, can burn the rice husks M1 accumulated in the furnace uniformly, and can burn for more than 10 hours, thus making it easy to obtain the rice husk ash of the present invention.

[0036] The rice husks that have undergone the first combustion treatment in the first combustion furnace 1 are supplied to the second combustion furnace 2 across the partition wall 3, where they undergo a second combustion treatment. This produces the desired rice husk ash M2. The produced rice husk ash M2 can be recovered from the recovery port 7 via the feeder 6.

[0037] The rice husks supplied to the first combustion furnace of the biomass boiler B shown in Figure 1 can be continuously burned by air A supplied from the bottom once they are ignited at the start of operation. The rice husks M1, which have become lighter after combustion, are then lifted up by the airflow caused by the supplied air A and the heat of combustion, and the lifted rice husks M1 are cooled by the water drum 8 and multiple water pipes 10. The temperature and time of this cooling are not particularly limited, and the effects of the present invention are not impaired regardless of the cooling temperature. After cooling, the rice husks M1 fall into the second combustion furnace 2 due to their own heat of combustion and the decrease in airflow (dashed arrow in Figure 1). The second combustion furnace 2 is designed to burn continuously using the heat it has stored, the high-temperature air supplied from the ventilator 5, and the air A supplied from the bottom side.

[0038] The combustion heat can be used (reused) as various energy sources, for example, and the method is not limited. For example, similar to a known water-tube boiler, the combustion heat can be used to heat the water in the water drum 8 and the water in the water tubes 10 to generate steam in the steam-water drum 9. Alternatively, the combustion heat can be used as a heat source for producing hot water. As will be described later, it can also be used as a heat source to obtain steam for manufacturing calcium silicate molded bodies.

[0039] 3. Calcium silicate molded body A calcium silicate molded article can be produced using the rice husk ash of the present invention. Since the rice husk ash of the present invention is adjusted so that the cristobalite (101) peak intensity is 10,000 counts or less and the ignition loss is 3% by mass or less, the calcium silicate molded article obtained using this rice husk ash can have good mechanical strength and also has excellent non-flammability.

[0040] The density of the calcium silicate molded body obtained using the rice husk ash of the present invention is not particularly limited, for example, 120 to 240 kg / m³. 3 This is within the specified range. There are no particular restrictions on the shape or size of the molded product, and it can be designed as appropriate according to the application.

[0041] For example, a calcium silicate molded body has a bending strength of 20 N / cm. 2 Preferably 30 N / cm² 2 More preferably 40 N / cm 2 That's all.

[0042] The linear shrinkage rate (heating linear shrinkage rate) of a calcium silicate molded body when heated at 1,000°C for 3 hours is, for example, 2% or less, preferably 1% or less.

[0043] The method for producing a calcium silicate molded article using the rice husk ash of the present invention is not particularly limited, and known methods can be broadly applied to the present invention. For example, it is preferable to obtain a calcium silicate molded article by a production method comprising step A, in which a raw material containing the rice husk ash of the present invention is hydrothermally treated to obtain a slurry, and step B, in which the slurry is molded.

[0044] In step A, a slurry is obtained by hydrothermally treating the raw material containing the rice husk ash of the present invention. The raw material containing the rice husk ash may contain calcareous components and water.

[0045] Examples of the aforementioned calcareous components include quicklime (calcium oxide), slaked lime (calcium hydroxide), carbide slag, and calcium chloride.

[0046] The raw materials may include other siliceous components along with the rice husk ash of the present invention, such as silica, silica sand, silica gel, white carbon, diatomaceous earth, ferrosilicon dust, and shirasu (volcanic ash). The siliceous component included in the raw materials may consist solely of the rice husk ash of the present invention.

[0047] The aforementioned raw materials may also contain other components, to the extent that they do not impair the effects of the present invention. Examples of other components include gypsum, aluminosilicates such as kaolin, organic acids, and the like.

[0048] In the aforementioned raw materials, the content of the rice husk ash of the present invention is preferably 40% by mass or more, more preferably 45% by mass or more, and more preferably 70% by mass or less, and more preferably 60% by mass or less, based on the total amount of solids contained in the raw materials.

[0049] In the raw materials, the content of the calcareous component is preferably 40% by mass or more, more preferably 45% by mass or more, and more preferably 60% by mass or less, and more preferably 55% by mass or less, based on the total amount of solids contained in the raw materials.

[0050] In the raw materials, the total amount of the rice husk ash and the calcareous components of the present invention is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the total amount of solids contained in the raw materials.

[0051] The amount of water contained in the raw materials is not particularly limited and can be adjusted, for example, to be 3 to 10% by mass in terms of solid content concentration.

[0052] The conditions for hydrothermal treatment of the raw materials are not particularly limited; for example, the temperature can be 150 to 260°C, preferably 160 to 250°C. The hydrothermal treatment time can be set appropriately according to the temperature, etc., preferably 2 to 10 hours, and more preferably 3 to 7 hours. The hydrothermal treatment of the raw materials can be carried out, for example, in a known pressure vessel.

[0053] By hydrothermally treating the raw materials, an aqueous slurry containing xonotlite-based calcium silicate is obtained. The resulting xonotlite-based calcium silicate can take the form of a hydrate, for example. The xonotlite (xonotlite-based calcium silicate) in the slurry can form secondary particles. The particle size of the secondary particles is not limited, and is, for example, about 5 to 150 μm.

[0054] In step B, the slurry obtained in step A is molded. The molding method is not particularly limited; for example, dehydration molding can be employed. The dehydration molding method is not particularly limited; for example, a wide range of known dehydration molding methods can be employed.

[0055] When forming the slurry, various additives can be added to the slurry as needed. Examples of additives include fibrous materials, cement, fillers, pigments, dyes, polymers (resins), flocculants, and water repellents.

[0056] Examples of fibrous materials include known organic and inorganic fibers such as pulp, glass fibers, cotton, ceramic fibers, vinylon fibers, aramid fibers, nylon fibers, polyester fibers, polyethylene fibers, polypropylene fibers, steel fibers, and carbon fibers. Examples of cement include Portland cement, white cement, alumina cement, blast furnace cement, fly ash cement, and blended cement. Examples of fillers include clay, bentonite, talc, and calcium carbonate.

[0057] The fibrous material content can be, for example, 20% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less, relative to the total mass of solids in the slurry. The cement content can be, for example, 5 to 30% by mass, relative to the total mass of solids in the slurry.

[0058] Examples of dehydration molding methods include press dehydration molding, papermaking, roll dehydration molding, and centrifugal molding. The dehydration molding conditions are not particularly limited, and known conditions can be widely adopted in this invention.

[0059] After molding the slurry, drying treatment can be performed as needed. Known drying methods can be employed, including air drying, heat drying, hot air drying, vacuum drying, freeze drying, vacuum freeze drying, humidity-controlled drying, atmosphere-controlled displacement drying, and supercritical drying. The drying temperature and degree of dryness (moisture content) should be appropriately set according to the composition, purpose, and application of the molded product.

[0060] The molding process in step B yields the xonotlite-based calcium silicate molded article of the present invention. The content of xonotlite-based calcium silicate in the calcium silicate molded article is, for example, 50% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more.

[0061] Here, the method for producing the calcium silicate molded body described above can be combined with the method for producing rice husk ash according to the present invention. Specifically, the method for producing rice husk ash according to the present invention involves combustion treatment of rice husks, and the energy contained in such a manufacturing method can be used in step A and / or step B. In particular, the combustion energy in the method for producing rice husk ash according to the present invention can be used in the method for producing the calcium silicate molded body.

[0062] For example, the combustion energy used in the rice husk ash production method can be used to generate steam, which can then be used in the hydrothermal treatment performed in step A. Alternatively, the combustion energy used in the rice husk ash production method can be used to generate steam, which can then be used to dry the calcium silicate molded body obtained in the molding process of step B.

[0063] In other words, the present invention can provide a new manufacturing system for producing a calcium silicate molded body, and more specifically, it can provide a manufacturing method that comprises a step of obtaining rice husk ash by the method for producing rice husk ash of the present invention, and uses the energy generated by burning the rice husks to produce a calcium silicate molded body.

[0064] In the above manufacturing system (manufacturing method), in addition to using silica obtained from rice husk ash as a raw material for manufacturing molded products, the combustion energy of rice husks can be used in the production process of calcium silicate products, thereby enabling energy conservation and reduction of carbon dioxide emissions.

[0065] In identifying the inventions contained herein, the components (properties, structures, functions, etc.) described in each embodiment of this disclosure may be combined in any way. That is, this disclosure encompasses all subject matter consisting of any combination of the combinatable components described herein. [Examples]

[0066] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to the embodiments of these examples.

[0067] (Example 1A) Rice husks were prepared as the raw material, and a two-stage combustion treatment was carried out using a biomass boiler (see Figure 1) equipped with a first combustion furnace for the first combustion treatment and a second combustion furnace for the second combustion treatment of the rice husks. Specifically, the rice husks were supplied to the first combustion furnace and subjected to a first combustion treatment at a temperature of 800°C for 34 seconds. Subsequently, the rice husks that had undergone the first combustion treatment were supplied to the second combustion furnace and subjected to a second combustion treatment at a temperature of 700°C for 12.1 hours. Therefore, the total time for the combustion treatment of the rice husks (sum of the time for the first and second combustion treatments) was 12.1 hours. The rice husk ash obtained in this way was crushed and used as rice husk ash 1a, which was used as a raw material for calcium silicate molded bodies.

[0068] (Examples 2B-2L) As shown in Table 1, rice husk ash was obtained in the same manner as in Example 1A, except that the time of the first combustion treatment of rice husks, the second combustion treatment, and the total length of the combustion treatments were changed.

[0069] (Comparative Examples 1A-1D) As shown in Table 1, rice husk ash was obtained in the same manner as in Example 1A, except that the time of the first combustion treatment of rice husks, the second combustion treatment, and the total length of the combustion treatments were changed.

[0070] (Results of rice husk ash production) Table 1 shows the production conditions (combustion conditions) for rice husk ash in each example and comparative example, as well as the measurement results of the cristobalite (101) peak intensity (Cri peak intensity), ignition loss (Ig. Loss), and BET specific surface area of ​​the obtained rice husk ash. From Table 1, it can be seen that the rice husk ash obtained in each example had a peak intensity of 10,000 counts or less and an ignition loss of 3% by mass or less.

[0071] [Table 1]

[0072] (Example 2) A slurry was prepared by mixing 100 parts by mass of raw materials (the remainder being additives such as clay) containing 49.4 parts by mass of rice husk ash and 48.2 parts by mass of quicklime obtained in Example 1A, with 1600 parts by mass of water, according to the formulation table shown in Table 2. The slurry was then autoclaved at a pressure of 14 kgf / cm². 2 Hydrothermal treatment (hydrothermal synthesis reaction) was carried out for 5 hours while stirring under conditions of 200°C. This yielded a molding slurry (CaO / SiO2 molar ratio = 1.050). To 74.5 parts by mass of this molding slurry (calculated in terms of solid content, i.e., the amount of the raw materials), 2.6 parts by mass of pulp, 18.5 parts by mass of cement, and 4.4 parts by mass of glass fiber were added to obtain a molding slurry, which was then poured into a mold and heated at 150 kgf / cm². 2 Dehydration molding was performed under pressure. By drying the resulting molded body, a xonotlite-based calcium silicate molded body was obtained.

[0073] (Example 3) A xonotlite-based calcium silicate molded body was obtained in the same manner as in Example 2A, except that the rice husk ash obtained in Example 1A was replaced with the rice husk ash obtained in Example 1L.

[0074] (Comparative Example 2) A xonotlite-based calcium silicate molded body was obtained in the same manner as in Example 2A, except that the rice husk ash obtained in Example 1A was replaced with the rice husk ash obtained in Comparative Example 1B.

[0075] (Comparative Example 3) A xonotlite-based calcium silicate molded body was obtained in the same manner as in Example 2A, except that the rice husk ash obtained in Example 1A was replaced with the rice husk ash obtained in Comparative Example 1C.

[0076] (Comparative Example 4) A xonotlite-based calcium silicate molded body was obtained in the same manner as in Example 2A, except that the rice husk ash obtained in Example 1A was replaced with the rice husk ash obtained in Comparative Example 1D.

[0077] (Manufacturing results of calcium silicate molded products) Table 2 shows the results of the bending strength, heat shrinkage rate, and non-flammability tests for the calcium silicate molded articles obtained in each example and comparative example.

[0078] [Table 2]

[0079] Table 2 demonstrates that calcium silicate molded articles obtained from rice husk ash with a cristobalite (101) peak intensity of 10,000 counts or less and a loss on ignition of 3% by mass or less possess good mechanical strength, excellent heat resistance due to their low thermal shrinkage rate, and also excellent non-flammability.

[0080] (Evaluation method) The BET specific surface area (m²) of the rice husk ash obtained in each example and comparative example. 2 The peak intensity and ignition loss (Ig.Loss) of cristobalite (101) ( / g), as well as the flexural strength, thermal shrinkage rate, and non-flammability of the calcium silicate molded articles, were evaluated using the following procedure.

[0081] [BET specific surface area] The BET specific surface area of ​​rice husk ash was measured using nitrogen adsorption, with samples pre-treated by vacuum heating at 150°C for 8 hours under reduced pressure of 40 mm Torr. The measurement device used was the Quantachrome "QUADRASORB SI".

[0082] [Cristobalite (101) Peak Intensity (Cri(101))] The cristobalite peak intensity of rice husk ash was estimated based on the peak intensity (2θ = 21.9° ± 0.5) originating from the cristobalite (101) plane crystals in the diffraction spectrum obtained by powder X-ray diffraction. The measurement instrument used was Rigaku's powder X-ray diffractometer "MiniFlex600," and rice husk ash was measured under the following conditions (X-ray source: Cu-Kα rays (wavelength 0.154 nm), tube voltage 35 kV, tube current 10 mA, measurement range 20°~30°, scan speed 2.0000° / min, step width 0.0200°, slit 0.3 mm), and correction was performed using a standard sample. Standard samples were measured using NISI's SRM-640d under the following conditions: X-ray source: Cu-Kα rays (wavelength 0.154 nm), tube voltage 35 kV, tube current 10 mA, measurement range 20°~40°, scan speed 2.0000° / min, step width 0.0200°, slit 0.3 mm. The peak intensity (2θ = 28.6° ± 0.5) originating from the silicon (111) plane crystal was estimated, and the measured values ​​of the rice husk ash were corrected using the measured values ​​of the standard sample with the following formula. Rice husk ash correction value (counts) = Rice husk ash measurement value × Correction coefficient Correction factor = Standard substance measurement value immediately after bulb replacement ÷ Standard substance measurement value for the current month For the standard sample, the peak intensity at 28.4° based on Si(111) was measured, while for the rice husk ash, the peak intensity at 22.0° based on cristobalite(101) was measured.

[0083] [Ignition loss (Ig.Loss)] Approximately 5g of rice husk ash dried at 150°C was weighed and placed in an electric furnace (Nabertherm "Muffle Furnace LT9 / 11 (Germany)"), and the temperature was raised to 1000°C over 150 minutes, followed by a heat treatment at 1000°C for 30 minutes. After the heat-treated rice husk ash was allowed to cool naturally to room temperature (25°C), it was removed from the electric furnace, and the loss on ignition was calculated using the following formula. Ignition loss (%) = ((Weight before heating - Weight after heating) / Weight before heating) x 100 It was calculated from the above.

[0084] [Bending strength] A 150mm x 37mm x 25mm test specimen was cut from the calcium silicate molded body, and a three-point bending test was performed on this specimen to calculate the bending strength of the calcium silicate molded body.

[0085] [Heat shrinkage rate] A 150mm x 37mm x 25mm test specimen was cut from a calcium silicate molded body, placed in an electric furnace, and heated to 1000°C over 150 minutes, followed by a heat treatment at 1000°C for 3 hours. After the heat-treated molded body was cooled to room temperature (25°C), it was removed from the electric furnace, and the linear shrinkage rate in the length direction was calculated using the following formula. Linear shrinkage rate (%) = ((Dimensions before heating - Dimensions after heating) / Dimensions before heating) × 100 The thermal shrinkage rate of the calcium silicate molded body was calculated from the above and defined as the thermal shrinkage rate of the molded body.

[0086] [Non-flammability test] A cylindrical test specimen measuring Φ45mm x 50mm was cut from a calcium silicate molded body, cured at 60°C for 24 hours, and then allowed to cool in a desiccator for 1 hour. After confirming that the furnace temperature of 750°C was stably maintained for 10 minutes, the test specimen was placed in the furnace and heated for more than 30 minutes until equilibrium was reached. The temperature difference between the surface temperature and core temperature of the test specimen and the furnace temperature is calculated using the following formula. Center temperature (℃) = Maximum temperature at the center of the test piece - Initial temperature in the furnace Surface temperature (℃) = maximum temperature on the surface of the specimen - initial temperature in the furnace Based on the calculations, if both the core temperature and surface temperature are 30°C or lower, it is judged to have excellent non-flammability and is marked with a "○". If either the core temperature or surface temperature exceeds 30°C, it is judged to have poor non-flammability and is marked with a "×". [Explanation of Symbols]

[0087] B: Biomass boiler 1: First Combustion Reactor 2: Second Combustion Reactor 3: Partition wall 3 4: Raw material supply port 5: Ventilation channel 6: Feeder 7: Collection port A: Air E: Exhaust duct M1: Rice husks M2 rice husk ash

Claims

1. In the diffraction spectrum obtained by powder X-ray diffraction, the cristobalite (101) peak intensity is 10,000 counts or less. Rice husk ash with a loss on ignition of 3% by mass or less.

2. A method for producing rice husk ash according to claim 1, It includes a process for burning rice husks, A method for producing rice husk ash, wherein the combustion treatment time is 10 hours or more.

3. A calcium silicate molded body obtained from rice husk ash according to claim 1.

4. A step of obtaining a slurry by hydrothermally treating a raw material containing rice husk ash as described in claim 1, The process of forming the slurry and A method for producing a calcium silicate molded article containing [the specified substance].

5. The method comprises the step of obtaining the aforementioned rice husk ash by the manufacturing method described in claim 2, The method for producing a calcium silicate molded article according to claim 4, wherein the energy generated by burning the aforementioned rice husks is used in the production of a calcium silicate molded article.

Images