Electric melting manufacturing method of yttrium ytterbium silicate

Abstract

The invention provides an electric melting manufacturing method of yttrium ytterbium silicate, and belongs to the technical field of inorganic non-metallic materials. Silica sand, yttrium oxide and ytterbium oxide which are easy to obtain are adopted as raw materials and put into an electric arc furnace in batches to be smelted, furnace charge is smelted into high-temperature melt through segmented melting-refining heat preservation homogenization, the raw materials are subjected to high-temperature chemical reaction, and melt with the porosity smaller than 2% is obtained through high-temperature refining heat preservation exhaust; and finally preparing yttrium ytterbium silicate with high density and low porosity. According to the preparation method, an electric arc furnace melting process is adopted, powder prepared through a high-temperature chemical reaction of an electric arc furnace is higher in density and lower in porosity compared with powder prepared through a solid-phase sintering method, and the environment barrier coating prepared through cooperation of the prepared yttrium ytterbium silicate and an atmospheric plasma spraying technology is high in density and lower in porosity; the requirements on oxidation failure resistance and high-temperature water vapor corrosion resistance of the ceramic-based composite material in a use environment can be met.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic materials technology, and in particular to an electrofusion manufacturing method for yttrium silicate. Background Technology

[0002] Yttrium silicate is a rare-earth disilicate, composed of two phases: yttrium silicate and ytterbium silicate, with the molecular formula Y. 2- x Yb x Si2O7. Yttrium silicate possesses properties such as high melting point, low coefficient of thermal expansion, low oxygen permeability, low modulus, low thermal conductivity, and good chemical and thermal stability. It is a C... f / C and C f One of the best candidates for anti-oxidation coatings of SiC composite materials. f / C and C f SiC composites exhibit excellent properties such as high specific strength and specific modulus, high temperature resistance, high damage tolerance, and corrosion resistance, making them strategic thermal structural materials that influence the development of hypersonic vehicles and high-performance engines. However, oxidation failure is one of the key challenges that must be addressed in the process of expanding the application of these two composite materials.

[0003] Ceramic matrix composites (CMCs), such as SiC f Ceramic matrix composites (CMC), characterized by low density, high-temperature strength, and high fatigue limit, are considered a leading candidate material for hot-section components of next-generation high thrust-to-weight ratio aero-engines. However, during long-term service in aero-engines, CMC is threatened by high-temperature water vapor corrosion, leading to a sharp decline in material properties. Therefore, improving the structural and performance stability of CMC in the engine operating environment is crucial. Research indicates that depositing environmental barrier coatings (EBCs) on the surface of the matrix material can effectively address this challenge. Rare earth silicates, with their high melting point, coefficient of thermal expansion matching that of CMC, low thermal conductivity, and good corrosion resistance, have become the most promising environmental barrier coating materials.

[0004] Continuous SiC fiber reinforced SiC ceramic matrix composites (SiC f SiC possesses excellent high-temperature mechanical properties, oxidation resistance, and radiation resistance, making it a superior material to C. f / C and C fFollowing SiC composites, they are considered the ideal next-generation high-temperature structural materials for aerospace and nuclear energy fields. To address the challenges of oxidation failure and high-temperature water vapor corrosion in the operating environment, which lead to a sharp decline in material performance, it is essential to develop a rare-earth silicate material—electrominated yttrium silicate—to meet the environmental barrier coating requirements of aerospace and nuclear energy fields. Currently, the main method for preparing rare-earth silicate materials is solid-state sintering, which produces powders with low density. Environmental barrier coatings prepared using atmospheric plasma spraying technology also exhibit low density and high porosity, failing to meet the requirements for oxidation resistance and high-temperature water vapor corrosion resistance in the operating environment of ceramic matrix composites. Summary of the Invention

[0005] The purpose of this invention is to provide an electrofusion manufacturing method for yttrium silicate. The method provided by this invention produces yttrium silicate powder with high density and low porosity. The environmental barrier coating prepared by using the prepared yttrium silicate in conjunction with atmospheric plasma spraying technology has high density and low porosity, which can meet the requirements of ceramic matrix composites for oxidation resistance and high-temperature water vapor corrosion resistance in the service environment.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides an electric melting manufacturing method for yttrium silicate, comprising the following steps: mixing 22-35 parts of silica sand, 1-66 parts of yttrium oxide and 1-77 parts of yttrium oxide by mass to obtain furnace charge, and then feeding it into an electric arc furnace in batches for melting to obtain yttrium silicate;

[0008] The smelting process involves segmented melting, refining, heat preservation, and homogenization.

[0009] Preferably, the SiO2 content in the silica sand is >99%; the purity of the yttrium oxide is >4N; and the purity of the ytterbium oxide is >4N.

[0010] Preferably, it includes the following steps:

[0011] (1) Silica sand, yttrium oxide and ytterbium oxide are mixed in a mixer to obtain furnace charge;

[0012] (2) The furnace charge obtained in step (1) is fed into the electric arc furnace in batches for smelting, and the electrodes in the electric arc furnace are gradually raised. The above operation is repeated until the requirements are met or the furnace is full.

[0013] The smelting process is segmented melting, refining, heat preservation, and homogenization. After the last smelting of each furnace, the furnace is held for 1-2 hours and then shut down for 12 hours. The furnace shell is removed, and the melt is allowed to cool naturally to below 80°C. The melt is then subjected to a first crushing and a first sorting process to remove the shavings, thus obtaining the material.

[0014] (3) The material obtained in step (2) is subjected to a second crushing and a second sorting to obtain dense block material;

[0015] (4) The dense block material obtained in step (3) is crushed and reprocessed, iron is removed, and the material is tested to obtain yttrium silicate.

[0016] Preferably, when the electric arc furnace in step (2) is a fixed three-phase electric arc furnace, the molten state of the mixture inside the electric arc furnace during operation is a melt of solid outside and liquid inside.

[0017] Preferably, when the electric arc furnace in step (2) is an inclined three-phase electric arc furnace, the mixture inside the electric arc furnace is in a molten state during the working process, and the molten liquid is cast into the desired product.

[0018] Preferably, the melting voltage in step (2) is 180~320V and the current is 3000~10000A.

[0019] Preferably, the melting voltage in step (2) is 220V and the current is 5000~8000A.

[0020] Preferably, the ratio of melting time to refining time in step (2) is 1:1.

[0021] Preferably, in step (3), the second crushing is to crush the material to a particle size ≤ 4 mesh, or to the particle size required for use; the second sorting is to remove loose material blocks.

[0022] Preferably, in step (4), the material is crushed and reprocessed to a particle size that meets the requirements for use.

[0023] This invention provides an electrofusion manufacturing method for yttrium silicate. It utilizes readily available silica sand, yttrium oxide, and yttrium oxide as raw materials, which are fed into an electric arc furnace in batches for melting. Through segmented melting, refining, and heat-holding homogenization, the furnace charge is melted into a high-temperature molten liquid, causing a high-temperature chemical reaction between the raw materials. After high-temperature refining, heat holding, and venting, a melt with a porosity of less than 2% is obtained, ultimately producing yttrium silicate with high density and low porosity. This invention employs an electric arc furnace melting process, and the yttrium silicate produced through the high-temperature chemical reaction in the electric arc furnace has a higher density and lower porosity than yttrium silicate powder produced by solid-state sintering. Furthermore, the prepared yttrium silicate, in conjunction with atmospheric plasma spraying technology, forms an environmental barrier coating with high density and low porosity, meeting the requirements for oxidation resistance and high-temperature water vapor corrosion resistance in ceramic matrix composites during use. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the process for preparing yttrium silicate in Examples 1-3 of the present invention. Detailed Implementation

[0025] This invention provides an electric melting manufacturing method for yttrium silicate, comprising the following steps: mixing 22-35 parts of silica sand, 1-66 parts of yttrium oxide and 1-77 parts of yttrium oxide by mass to obtain furnace charge, and then feeding it into an electric arc furnace in batches for melting to obtain yttrium silicate;

[0026] The smelting process involves segmented melting, refining, heat preservation, and homogenization.

[0027] Unless otherwise specified, all raw materials used in this invention are commercially available products in the art.

[0028] In this invention, the SiO2 content in the silica sand is preferably >99%; the purity of the yttrium oxide is preferably >4N; and the purity of the ytterbium oxide is preferably >4N. This invention ensures that the purity of the obtained yttrium silicate is greater than 99% by controlling the purity of the above raw materials, thus meeting the quality requirements of environmental barrier coatings. During the smelting process in this invention, the reaction between the above raw materials is: 2SiO2 + {(2-X) / 2}Y2O3 + (X / 2)Yb2O3 = Y 2-x Yb x Si2O7, where X = 0.1~1.9.

[0029] In this invention, the method for electro-melting yttrium silicate preferably includes the following steps:

[0030] (1) Silica sand, yttrium oxide and ytterbium oxide are mixed in a mixer to obtain furnace charge;

[0031] (2) The furnace charge obtained in step (1) is fed into the electric arc furnace in batches for smelting, and the electrodes in the electric arc furnace are gradually raised. The above operation is repeated until the requirements are met or the furnace is full.

[0032] The smelting process is segmented melting, refining, heat preservation, and homogenization. After the last smelting of each furnace, the furnace is held for 1-2 hours and then shut down for 12 hours. The furnace shell is removed, and the melt is allowed to cool naturally to below 80°C. The melt is then subjected to a first crushing and a first sorting process to remove the shavings, thus obtaining the material.

[0033] (3) The material obtained in step (2) is subjected to a second crushing and a second sorting to obtain dense block material;

[0034] (4) The dense block material obtained in step (3) is crushed and reprocessed, iron is removed, and the material is tested to obtain yttrium silicate.

[0035] This invention mixes silica sand, yttrium oxide, and ytterbium oxide in a mixer to obtain furnace charge.

[0036] In this invention, the silica sand is preferably quartz sand.

[0037] After obtaining the furnace charge, the present invention feeds the furnace charge into the electric arc furnace in batches for melting, and gradually raises the electrodes in the electric arc furnace, repeating the above operation until the requirements are met or the furnace is full.

[0038] The smelting process is segmented melting, refining, heat preservation, and homogenization. After the last smelting of each furnace, the furnace is held at a temperature of 1-2 hours and then shut down for 12 hours. The furnace shell is then removed, and the melt is allowed to cool naturally to below 80°C. The melt is then subjected to a first crushing process, followed by a first sorting process to remove the outer skin and obtain the final material.

[0039] In this invention, when the electric arc furnace is a fixed three-phase electric arc furnace, the molten state of the mixture inside the furnace during operation is preferably a melt with a solid outer layer and a liquid inner layer. In this invention, when the electric arc furnace is an inclined three-phase electric arc furnace, the molten state of the mixture inside the furnace during operation is preferably a molten liquid, which is then cast into the desired product.

[0040] In this invention, the segmented melting-refining and heat-holding homogenization is preferably performed as follows: after the previous batch of furnace charge is fed into the electric arc furnace, melting and refining heat-holding homogenization are performed sequentially, and then the next batch of furnace charge is fed into the electric arc furnace, and the same process is repeated. This invention, through segmented melting-refining and heat-holding homogenization, ensures that each batch of furnace charge is fully melted and uniformly refined and heat-held, allowing the furnace charge to undergo a full high-temperature chemical reaction during the melting process. In this invention, the melting voltage is preferably 180~320V, more preferably 220V, and the current is preferably 3000~10000A, more preferably 5000~8000A. By controlling the melting voltage and current within the above ranges, this invention ensures that the electric arc furnace has sufficient power to melt the furnace charge. In this invention, the ratio of melting time to refining time is 1:1. This invention controls the ratio of melting time to refining time within the aforementioned range to ensure that the furnace charge is fully melted and undergoes a high-temperature chemical reaction. The molten metal is then refined at high temperature, held for heat preservation, and vented to obtain a melt with a porosity of less than 2%. This invention does not impose any special restrictions on the first crushing method; it facilitates subsequent first sorting to remove the slag. This invention uses first sorting to remove the slag, thus clearing away unmelted furnace charge adhering to the furnace shell and obtaining a melt with uniform density.

[0041] After obtaining the material, the present invention performs a second crushing and a second sorting on the material to obtain dense block material.

[0042] In this invention, the second crushing is preferably performed to crush the material to a particle size ≤ 4 mesh, or to the required particle size; the second sorting is preferably performed to remove loose material lumps. This invention removes loose material lumps through the second sorting process to ensure the acquisition of dense lumps, thus obtaining a qualified yttrium silicate product.

[0043] After obtaining the dense block material, the present invention sequentially crushes and reprocesses the dense block material, removes iron, and tests it to obtain yttrium silicate.

[0044] In this invention, the crushing and reprocessing is preferably carried out to a particle size that meets the usage requirements. This invention does not impose any special limitations on the methods for iron removal and qualification testing; well-known technical solutions in the art can be used.

[0045] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0046] Unless otherwise specified, all experiments were repeated three times, and the results are expressed as averages.

[0047] Figure 1 The flowchart of the preparation of yttrium silicate in Examples 1-3 of the present invention is shown. Specifically, the furnace charge or mixture is prepared first, then the material is melted by electric arc and refined (i.e., melting, segmented melting-refining and heat preservation homogenization), then kept warm and naturally cooled, then crushed and sorted for the first time, then crushed and sorted for the second time, and finally crushed and processed, iron removed, and tested to obtain the finished yttrium silicate product.

[0048] Example 1

[0049] An electrofusion manufacturing method for yttrium silicate comprises the following steps:

[0050] (1) By mass fraction, 30 parts of silica sand with SiO2 content > 99wt%, 37 parts of yttrium oxide with purity > 4N, and 33 parts of ytterbium oxide with purity > 4N are loaded into a mixer and mixed evenly to form furnace charge;

[0051] (2) The furnace charge is fed into a fixed three-phase electric arc furnace in batches for melting, and the electrodes in the electric arc furnace are gradually raised to melt, refine and heat-hold homogenize in 15 sections until the requirements are met or the furnace is full.

[0052] The segmented melting-refining and heat-holding homogenization process is as follows: after the previous batch of furnace charge is put into the electric arc furnace, it is successively melted and refined and heat-holding homogenized, and then the next batch of furnace charge is put into the electric arc furnace, and then successively melted and refined and heat-holding homogenized.

[0053] During operation, the electric arc furnace contains a mixture in a molten state that is solid on the outside and liquid on the inside.

[0054] After the last smelting of each furnace, the furnace is held at the temperature for 1 hour, and after the furnace is shut down for 12 hours, the furnace shell is removed and the melt is allowed to cool naturally. When the temperature drops below 80°C, the melt is first crushed and then sorted to remove the sludge to obtain the material.

[0055] (3) The material obtained in step (2) is crushed to below 4 mesh or crushed according to user requirements, and then sorted to remove loose material blocks and obtain dense material blocks.

[0056] (4) The dense block material obtained in step (3) is crushed, reprocessed and graded to the particle size required by the user, with a particle size of 10~90μm. After iron removal, it is tested and qualified to obtain the finished product yttrium silicate.

[0057] In Embodiment 1 of the present invention, when the furnace charge is in a molten state, its color is red. As the temperature decreases, its color becomes lighter, especially when it is naturally cooled to below 80°C, the color becomes grayish-white. When the temperature of the molten furnace charge is below 2200°C, it begins to solidify.

[0058] Example 2

[0059] An electrofusion manufacturing method for yttrium silicate comprises the following steps:

[0060] (1) By mass fraction, 29 parts of silica sand with SiO2 content > 99wt%, 33 parts of yttrium oxide with purity > 4N, and 38 parts of ytterbium oxide with purity > 4N are loaded into a mixer and mixed evenly to form furnace charge;

[0061] (2) The furnace charge obtained in step (1) is fed into a fixed three-phase electric arc furnace in batches for smelting, and the electrodes in the electric arc furnace are gradually raised to perform 5-stage melting-refining and heat preservation homogenization until the requirements are met or the furnace is full.

[0062] The segmented melting-refining and heat-holding homogenization process is as follows: after the previous batch of furnace charge is put into the electric arc furnace, it is successively melted and refined and heat-holding homogenized, and then the next batch of furnace charge is put into the electric arc furnace, and then successively melted and refined and heat-holding homogenized.

[0063] During operation, the electric arc furnace contains a mixture in a molten state that is solid on the outside and liquid on the inside.

[0064] After the last smelting of each furnace, the furnace is held at the temperature for 2 hours. After the furnace is shut down for 12 hours, the furnace shell is removed and the melt is allowed to cool naturally. When the temperature drops below 80°C, the melt is first crushed and then sorted to remove the sludge, thus obtaining the material.

[0065] (3) The material obtained in step (2) is crushed to below 4 mesh or crushed according to user requirements, and then sorted to remove loose material blocks and obtain dense material blocks.

[0066] (4) The dense block material obtained in step (3) is crushed, reprocessed and graded to the particle size required by the user, with a particle size of 45~125μm. After iron removal, it is tested and qualified to obtain the finished product yttrium silicate.

[0067] In Embodiment 2 of the present invention, the furnace charge is red when it is in a molten state. As the temperature decreases, its color becomes lighter, especially when it is naturally cooled to below 80°C, the color becomes grayish-white. When the temperature of the molten furnace charge is below 2200°C, it begins to solidify.

[0068] Example 3

[0069] An electrofusion manufacturing method for yttrium silicate comprises the following steps:

[0070] (1) By mass fraction, 24 parts of silica sand with SiO2 content > 99wt%, 8 parts of yttrium oxide with purity > 4N, and 68 parts of ytterbium oxide with purity > 4N are loaded into a mixer and mixed evenly to form furnace charge;

[0071] (2) The furnace charge obtained in step (1) is fed into the inclined three-phase electric arc furnace in batches for melting, and the electrodes in the electric arc furnace are gradually raised. The process is repeated 10 times until the requirements are met or the furnace is full.

[0072] The segmented melting-refining and heat-holding homogenization process is as follows: after the previous batch of furnace charge is put into the electric arc furnace, it is successively melted and refined and heat-holding homogenized, and then the next batch of furnace charge is put into the electric arc furnace, and then successively melted and refined and heat-holding homogenized.

[0073] During operation, the electric arc furnace contains a molten mixture in a liquid state.

[0074] After the last melting of each furnace, the furnace is held at the temperature for 1.5 hours. After the furnace is shut down for 12 hours, the furnace shell is removed and the melt is allowed to cool naturally. When the temperature drops below 80°C, the melt is first crushed and then sorted to remove the sludge, thus obtaining the material.

[0075] (3) The material obtained in step (2) is crushed to below 4 mesh or crushed according to user requirements, and then sorted to remove loose material blocks and obtain dense material blocks.

[0076] (4) The dense block material obtained in step (3) is crushed, reprocessed and graded to the particle size required by the user, with a particle size of 25~125μm. After iron removal, it is tested and qualified to obtain the finished product yttrium silicate.

[0077] In Embodiment 3 of the present invention, the furnace charge is red when it is in a molten state. As the temperature decreases, its color becomes lighter, especially when it is naturally cooled to below 80°C, the color becomes grayish-white. When the temperature of the molten material is below 2200°C, it begins to solidify.

[0078] Comparative Example 1

[0079] The yttrium silicate powder was prepared by solid-state sintering, and the steps are as follows:

[0080] (1) Raw material preparation: Take high-purity Y2O3, Yb2O3 and SiO2 powders, and prepare them according to the target yttrium silicate composition (e.g., Y). 2- x Yb x The stoichiometric ratio of Si2O7 is accurately measured and dried at 100~120℃ for 4~6h to remove adsorbed water from the powder surface.

[0081] (2) Ball milling: The weighed raw materials, anhydrous ethanol (dispersion medium), and zirconium oxide milling balls are mixed at a ball-to-material ratio of (5~10):1 and then ball milled in a planetary mill (200~300 r / min, 8~12 h) to ensure that the multi-component raw materials are mixed evenly.

[0082] (3) Drying and sieving: The slurry after ball milling is dried to constant weight in an oven at 80~100℃, and then ground and sieved through an 80~100 mesh sieve to remove large agglomerated particles;

[0083] (4) Pre-calcination: The sieved powder is placed into an alumina crucible and placed in a muffle furnace. It is pre-calcined at 700~900℃ for 2~4h to remove the organic medium and start the multi-component preliminary solid-phase reaction. The furnace is then cooled.

[0084] (5) Secondary ball milling and drying: The pre-calcined powder is repeatedly ball-milled, dried and sieved to further refine the particles and ensure that the distribution of Y, Yb and Si elements is uniform;

[0085] (6) Sintering: After the powder is placed in the crucible, it is placed in the muffle furnace and heated to 1300-1500℃ at a heating rate of 5-10℃ / min. The temperature is held for 4-6 hours (in air atmosphere) and then naturally cooled to room temperature after the solid-phase reaction is completed.

[0086] (7) Post-processing: The sintered block is crushed and ground, and passed through a 200-300 mesh sieve to obtain yttrium silicate powder;

[0087] The density and porosity of yttrium silicate powders prepared in Examples 1-3 and Comparative Example 1 were tested using electrofusion and solid-state sintering methods, respectively. The results are shown in Table 1.

[0088] Table 1. Statistical analysis of density and porosity of yttrium silicate powders prepared in Examples 1-3 and Comparative Example 1

[0089]

[0090] As shown in Table 1, the present invention uses an electric arc furnace melting process, and the powder produced by the high-temperature chemical reaction in the electric arc furnace has a higher density and lower porosity than that produced by the solid-state sintering method.

[0091] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for electro-melting yttrium silicate, characterized in that, The process includes the following steps: mixing 22-35 parts of silica sand, 1-66 parts of yttrium oxide and 1-77 parts of ytterbium oxide by mass to obtain furnace charge, and then feeding it into an electric arc furnace in batches for smelting to obtain ytterbium yttrium silicate. The smelting process involves segmented melting, refining, heat preservation, and homogenization.

2. The method for electro-melting yttrium silicate according to claim 1, characterized in that, The silica sand contains >99% SiO2; the yttrium oxide has a purity >4N; and the ytterbium oxide has a purity >4N.

3. The method for electro-melting yttrium silicate according to claim 1 or 2, characterized in that, Includes the following steps: (1) Silica sand, yttrium oxide and ytterbium oxide are mixed in a mixer to obtain furnace charge; (2) The furnace charge obtained in step (1) is fed into the electric arc furnace in batches for smelting, and the electrodes in the electric arc furnace are gradually raised. The above operation is repeated until the requirements are met or the furnace is full. The smelting process is segmented melting, refining, heat preservation, and homogenization. After the last smelting of each furnace, the furnace is held for 1-2 hours and then shut down for 12 hours. The furnace shell is removed, and the melt is allowed to cool naturally to below 80°C. The melt is then subjected to a first crushing and a first sorting process to remove the shavings, thus obtaining the material. (3) The material obtained in step (2) is subjected to a second crushing and a second sorting to obtain dense block material; (4) The dense block material obtained in step (3) is crushed and reprocessed, iron is removed, and the material is tested to obtain yttrium silicate.

4. The method for electro-melting yttrium silicate according to claim 3, characterized in that, When the electric arc furnace in step (2) is a fixed three-phase electric arc furnace, the molten state of the mixture inside the electric arc furnace during operation is a melt of solid outside and liquid inside.

5. The method for electro-melting yttrium silicate according to claim 3, characterized in that, When the electric arc furnace in step (2) is an inclined three-phase electric arc furnace, the mixture inside the electric arc furnace is in a molten state during the working process, and the molten liquid is cast into the desired product.

6. The method for electro-melting yttrium silicate according to claim 3, characterized in that, The melting voltage in step (2) is 180~320V and the current is 3000~10000A.

7. The method for electro-melting yttrium silicate according to claim 6, characterized in that, The melting voltage in step (2) is 220V and the current is 5000~8000A.

8. The method for electro-melting yttrium silicate according to claim 6, characterized in that, In step (2), the ratio of melting time to refining time in the smelting process is 1:

1.

9. The method for electro-melting yttrium silicate according to claim 6, characterized in that, In step (3), the second crushing is to crush the material to a particle size ≤ 4 mesh, or to the particle size required for use; the second sorting is to remove loose material blocks.

10. The method for electro-melting yttrium silicate according to claim 6, characterized in that, In step (4), the material is crushed and reprocessed to the particle size required for use.

Images