Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/20—Silicates
  • C01B33/32—Alkali metal silicates
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P52/00—Grinding, lapping or polishing of wafers, substrates or parts of devices

Definitions

• the present invention relates to a novel method for producing a high-purity sodium silicate aqueous solution. More specifically, it provides a method for producing a high-purity sodium silicate aqueous solution, particularly one with a reduced nickel concentration, that is suitable as a raw material for silica sol for semiconductor polishing.
• Sodium silicate aqueous solution is widely used in a variety of fields, including civil engineering and construction, paper and pulp, detergents and soap, and ceramics, as a soil improvement agent, an additive for pulp bleaching agents, a binder for refractories and castings, and a flocculant for water purification.
• Sodium silicate aqueous solution is also used as a raw material to manufacture various silica products, such as precipitated silica, silica gel, and silica sol (colloidal silica dispersion), as well as detergent builders and silicate products such as zeolites.
• silica sol is used in a variety of applications, including as a coating agent that imparts hardness and scratch resistance to the surfaces of optical materials, as an anti-blocking agent for film materials, as an inorganic binder for ceramics, and for precision polishing of various substrate surfaces.
• a coating agent that imparts hardness and scratch resistance to the surfaces of optical materials
• an anti-blocking agent for film materials as an inorganic binder for ceramics
• silica sol is used in a variety of applications, including as a coating agent that imparts hardness and scratch resistance to the surfaces of optical materials, as an anti-blocking agent for film materials, as an inorganic binder for ceramics, and for precision polishing of various substrate surfaces.
• This demand for silica sol has also spilled over into the sodium silicate aqueous solution that is its raw material, and there is growing demand for high-purity sodium silicate aqueous solutions with reduced metal impurities.
• sodium silicate aqueous solution is produced by mixing silica sand with an alkali source such as soda ash or sodium hydroxide, melting the mixture at high temperature to produce anhydrous sodium silicate (also known as "cullet” because it is a glass-like solid), adding water, heating it in an autoclave to dissolve it, and then passing the dissolved solution through a filter press or similar to remove insoluble matter.
• an alkali source such as soda ash or sodium hydroxide
• Another method for producing sodium silicate aqueous solution is to heat and dissolve silica in an alkaline aqueous solution.
• Silica sol is generally produced by diluting the sodium silicate aqueous solution produced as described above as necessary, bringing it into contact with an H-type strongly acidic cation exchange resin, adjusting the pH of the resulting activated silica, removing impurities or foreign matter using methods such as ion exchange or ultrafiltration, heating to adjust the particle size of the silica particles, and stabilizing the pH by adding ammonia water or the like.
• a method for producing a sodium silicate aqueous solution with the aim of reducing metal impurities has been disclosed in which a high-purity silica source is dissolved in an alkaline aqueous solution such as sodium hydroxide.
• Examples include a method in which high-purity glass, a by-product of semiconductor and optical fiber manufacturing processes, is dissolved in an alkaline aqueous solution (see Patent Document 1), a method in which a commercially available sodium silicate aqueous solution is neutralized to produce high-purity hydrated silica, which is then dissolved in an alkaline aqueous solution (see Patent Document 2), and a method in which a sodium silicate aqueous solution is brought into contact with an ion exchange resin to produce high-purity silica sol or silica gel, which is then dissolved in an alkaline aqueous solution (see Patent Document 3).
• Another known method for producing a high-purity aqueous sodium silicate solution involves diluting a commercially available aqueous sodium silicate solution obtained by dissolving anhydrous sodium silicate in water, and then filtering the solution under pressure using a membrane filter with specific micropores (see Patent Document 4).
• the nickel concentration is not sufficiently reduced, and the resulting sodium silicate solution contains a large amount of nickel that has not been completely removed.
• the nickel captured by the chelating agent remains in the sodium silicate aqueous solution in the form of a metal chelate complex, and the method does not disclose an aqueous sodium silicate solution with reduced nickel. Furthermore, as a manufacturing method, there are concerns that the use of a chelating agent will increase manufacturing costs.
• the object of the present invention is to provide a simple production method that can obtain a high-purity sodium silicate aqueous solution in which the nickel concentration has been reduced to an extremely low level from a nickel-containing sodium silicate aqueous solution (hereinafter also referred to as a crude sodium silicate aqueous solution).
• One aspect of the present invention is a method for producing a high-purity aqueous sodium silicate solution, comprising a capture step of capturing nickel from a nickel-containing aqueous sodium silicate solution using layered sodium silicate, and a separation step of removing the layered sodium silicate that has captured the nickel from the aqueous sodium silicate solution.
• Another aspect of the present invention is a high-purity aqueous sodium silicate solution having a nickel content of 100 ppb or less relative to the SiO2 component of sodium silicate .
• One aspect of the present invention provides a manufacturing method that can produce a highly pure aqueous sodium silicate solution in which nickel is reduced to an extremely low concentration.
• FIG. 2 is a diagram showing an X-ray diffraction chart of the residue separated in the separation step in Example 1.
• a method for producing a high-purity aqueous sodium silicate solution is characterized by comprising a capture step in which nickel is captured by layered sodium silicate from a nickel-containing aqueous sodium silicate solution, and a separation step in which the layered sodium silicate that has captured the nickel is removed from the aqueous sodium silicate solution.
• a high-purity aqueous sodium silicate solution having a nickel content of 100 ppb or less relative to the SiO2 component of sodium silicate can be produced with good reproducibility by simple means from a crude aqueous sodium silicate solution produced using a raw material contaminated with nickel.
• an aqueous sodium silicate solution having a nickel content of 100 ppb or less relative to the SiO2 component of sodium silicate which has not been achieved by conventional techniques, and such an aqueous sodium silicate solution can be suitably used as a silica sol raw material for semiconductor polishing.
• the crude sodium silicate aqueous solution that is the subject of one embodiment of the present invention is obtained by a known manufacturing method for producing a sodium silicate aqueous solution.
• manufacturing methods include a method of dissolving cullet in water, and a method of dissolving a silicon source such as silica or glass in a sodium hydroxide aqueous solution.
• dissolution is carried out at a temperature appropriate to the silicon source; for example, in the case of cullet, it is carried out in an autoclave at a temperature of approximately 140°C, and dissolution is generally completed in about one to two hours.
• partial dissolution of a portion of the cullet e.g., half of the cullet
• one embodiment of the present invention can be used to manufacture crude sodium silicate aqueous solutions obtained by either method.
• water glass commonly available as No. 1, No. 2, or No. 3 industrial standards established by the Sodium Silicate Committee of the Japan Inorganic Chemicals Association may also be used.
• the sodium silicate concentration of the crude sodium silicate aqueous solution is not particularly limited, but taking into consideration the ease of production of layered sodium silicate in the capture step and ease of handling in the separation step, it is preferably more than 10% by mass and not more than 35% by mass, particularly 12 to 30% by mass, calculated as SiO2.
• the molar ratio ( SiO2 / Na2O ) of the crude sodium silicate aqueous solution is also not particularly limited, but is generally 2.0 to 4.0.
• Nickel contamination into aqueous sodium silicate solutions is thought to occur mainly from the raw materials and manufacturing equipment for cullet when cullet is used, and mainly from the manufacturing equipment when sodium hydroxide solution is used.
• the amount of nickel contamination varies depending on the contamination source, but can reach 200 ppb or more, and in some cases, even 500 ppb or more, based on the SiO2 component of the aqueous sodium silicate solution.
• One embodiment of the present invention can be applied to aqueous crude sodium silicate solutions containing nickel at such concentrations.
• the most notable feature of the method for producing a high-purity sodium silicate aqueous solution according to one embodiment of the present invention is that it includes a capture step in which nickel in a nickel-containing sodium silicate aqueous solution is captured by layered sodium silicate.
• the nickel in the crude sodium silicate aqueous solution is captured by the layered sodium silicate, and by separating the layered sodium silicate that has captured the nickel from the crude sodium silicate aqueous solution, a high-purity sodium silicate aqueous solution with a significantly reduced nickel concentration can be obtained.
• the inventors have confirmed that, depending on the method for producing crude sodium silicate aqueous solution, particularly the method involving heating in an autoclave, extremely fine layered sodium silicate may be present, or trace amounts of layered sodium silicate particles may be present due to localized heating.
• the presence of this extremely fine layered sodium silicate has not previously been confirmed, and it cannot be separated even by filtration or other impurity removal methods commonly used in industry. It therefore remains present in the purified sodium silicate aqueous solution, and it is believed that the nickel concentration-reducing effect of layered sodium silicate has not been confirmed.
• the amount of layered sodium silicate produced by localized heating is extremely small, and even if it is removed as a foreign substance, the nickel concentration-reducing effect in the purified sodium silicate aqueous solution has not been confirmed.
• the capture step also involves capturing nickel by producing the layered sodium silicate particles described above, and furthermore, if necessary, nickel can be captured by adding additional layered sodium silicate to make up for any shortage.
• the layered sodium silicate that has captured nickel can then be removed in the separation step described below, thereby effectively reducing the nickel content in the crude sodium silicate aqueous solution.
• the capture process according to one embodiment of the present invention can be applied to both a crude aqueous sodium silicate solution containing layered sodium silicate produced in the sodium silicate aqueous solution manufacturing process as described above, and a crude aqueous sodium silicate solution not containing layered sodium silicate.
• the layered sodium silicate is not particularly limited as long as it is a layered crystal of SiO 2 —Na 2 O—H 2 O system. Specific examples include makatite, illaite, magadiite, Kenyaite, etc. depending on the SiO 2 content.
• the capture step is not particularly limited in its form, as long as it can produce a crude aqueous sodium silicate solution containing layered sodium silicate that has captured nickel in an amount and size that allows layered sodium silicate to be separated with a sufficient removal rate and amount in the separation step described below.
• Specific examples of the method include (1) producing layered sodium silicate from a portion of the sodium silicate in a crude sodium silicate aqueous solution, and (2) contacting layered sodium silicate with a sodium silicate aqueous solution.
• the above-mentioned embodiment (1) generates layered sodium silicate from a portion of the sodium silicate in a crude sodium silicate aqueous solution.
• a crude sodium silicate aqueous solution containing the fine layered sodium silicate this increases the amount of fine layered sodium silicate necessary for capturing nickel and grows the fine layered sodium silicate to a size that can be separated in the subsequent separation step.
• a crude sodium silicate aqueous solution containing a trace amount of layered sodium silicate this increases the amount of layered sodium silicate necessary for capturing nickel and grows the layered sodium silicate generated to a size that can be separated in the subsequent separation step.
• generating layered sodium silicate in the capture step refers to generating layered sodium silicate of a size that can be separated in the separation step.
• a suitable example of a method is to hold the crude sodium silicate aqueous solution under pressure at a temperature of 140 to 190°C.
• the holding time at this temperature should be a time that allows the layered sodium silicate to be produced with a sufficient removal rate and amount in the separation step described below.
• a method can be used in which the temperature (°C) x holding time (hr) is 500 to 5,000, particularly 1,000 to 4,000. Under these conditions, layered sodium silicate can be grown to an appropriate size that allows for easy removal in the separation step described below, and a sufficient amount of layered sodium silicate can be produced to capture nickel.
• the temperature is lower than 140°C, the production and growth of layered sodium silicate will be extremely slow even if the holding time is extended, making industrial implementation difficult.
• the lower limit of the temperature is preferably 145°C.
• some of the layered sodium silicate will further convert to cristobalite or quartz, reducing the amount of layered sodium silicate produced, raising concerns about a decrease in nickel capture ability.
• the upper limit of the temperature is preferably 180°C.
• the temperature (°C) x holding time (hr) is less than the above range, the amount of layered sodium silicate produced tends to be insufficient, resulting in an insufficient absolute amount of layered sodium silicate, or making it difficult to obtain layered sodium silicate particles of an appropriate size, i.e., a size that is easy to remove in the separation process.
• the suitable size of layered sodium silicate depends on the capacity of the separation process, but industrially, a particle diameter of 0.5 ⁇ m or more is preferred, and 1 ⁇ m or more is preferable.
• the above-mentioned means for producing layered sodium silicate may be carried out during or subsequent to the production process of the crude sodium silicate aqueous solution, or may be carried out on a separately produced crude sodium silicate aqueous solution.
• the temperature at which the cullet, etc. is dissolved is within the temperature range suitable for embodiment (1) in the capture step, and the time after the silica concentration of the crude sodium silicate aqueous solution reaches 10% by mass is included in the retention time for producing layered sodium silicate.
• a method is preferred in which the step of contacting the crude sodium silicate aqueous solution with the layered sodium silicate includes an addition step of adding the layered sodium silicate to the crude sodium silicate aqueous solution.
• the layered sodium silicate may be any commercially available product without any particular restrictions, but may also be produced by a known production method.
• the size of the layered sodium silicate to be added should preferably have a particle diameter of 0.5 ⁇ m or more, preferably 1 ⁇ m or more, in consideration of ease of removal in the separation process. There is no particular upper limit to the average particle size, but it may be approximately 10 ⁇ m.
• the appropriate amount of layered sodium silicate to be added should be an amount that achieves the removal rate and amount of layered sodium silicate that has captured nickel and is removed in the separation process described below.
• the addition step it is preferable to thoroughly stir the layered sodium silicate after adding it to the aqueous solution of crude sodium silicate.
• the contact time after addition There are no particular restrictions on the contact time after addition, but ensuring 30 seconds or more is sufficient.
• the added layered sodium silicate is brought into contact with an aqueous solution of crude sodium silicate to capture nickel, which is then removed in the separation process described below.
• the above-mentioned embodiment (2) is particularly effective for crude sodium silicate aqueous solutions that do not contain layered sodium silicate or that contain only trace amounts of layered sodium silicate particles.
• a trace amount of layered sodium silicate particles refers to the amount of layered sodium silicate particles that is present when, for example, dissolution in the production process of the crude sodium silicate aqueous solution is carried out outside the range of temperature (°C) x retention time (hr) that is preferred in the embodiment (1) above.
• the separation step is a step in which the layered sodium silicate that has captured nickel in the capture step is removed from the aqueous solution of crude sodium silicate, and any means capable of performing this operation may be used without particular limitation.
• removal by filtration is preferred for industrial implementation.
• the filter medium used for the above filtration is preferably determined taking into consideration the removal rate and filtration speed of the layered sodium silicate present in the crude sodium silicate aqueous solution. Furthermore, taking into consideration the prevention of secondary contamination due to filtration, filter medium materials made of polymeric materials such as polypropylene, fluororesin, nylon, polysulfonic acid, polyethersulfone, and cellulose are preferably used. Furthermore, it is desirable to set the pore size of the filter medium to a size that enables as much of the layered sodium silicate that has captured nickel to be removed as possible in the separation process.
• the pore size of the filter medium may be appropriately determined based on the particle size of the layered sodium silicate, and be an industrially advantageous size that achieves the removal rate described below. For example, it may be 1.0 ⁇ m or less, or 0.5 ⁇ m or less. Furthermore, the pore size may be 0.05 ⁇ m or more, 0.1 ⁇ m or more, or 0.25 ⁇ m or more.
• a filter cloth with an air permeability of approximately 10 ((cm 3 /(cm 2 ⁇ s)), JIS L 1096) "Testing Methods for Woven and Knitted Fabrics"
• a filter aid such as diatomaceous earth or perlite.
• the use of a filter aid allows the produced layered sodium silicate to be efficiently removed by the voids in the filter aid, which are smaller than the pore size of the filter medium.
• methods such as a filtration method using the filter medium, methods such as atmospheric filtration, pressure filtration, reduced pressure filtration, and centrifugation can be used without any particular limitation.
• the nickel removal effect is determined by the removal rate and amount of layered sodium silicate that captures nickel and is removed from the crude sodium silicate aqueous solution through a combination of the capture step and separation step.
• the amount of layered sodium silicate removed from the crude sodium silicate aqueous solution is at least 100 times, preferably at least 1,000 times, the nickel content in the crude sodium silicate aqueous solution, by mass.
• the upper limit of the amount of layered sodium silicate removed be 50,000 times, by mass, the nickel content in the crude sodium silicate aqueous solution.
• the removal rate (%) of layered sodium silicate is the value calculated by ((W1 - W2)/W1) x 100, where W1 is the amount of layered sodium silicate in the crude sodium silicate aqueous solution containing layered sodium silicate obtained in the capture step, and W2 is the amount of layered sodium silicate in the high-purity sodium silicate aqueous solution obtained in the separation step.
• the amount of layered sodium silicate in each sodium silicate aqueous solution was determined by filtering a sample of the sodium silicate aqueous solution through a filter with a pore size of 0.1 ⁇ m, measuring the weight of the layered sodium silicate remaining on the filter, and converting it into the weight in the sodium silicate aqueous solution.
• the amount removed is expressed as the mass ratio (W S /W N ) calculated from the mass (W S ) of the layered sodium silicate removed in the separation step, calculated by subtracting W2 from the mass (W S ) of nickel in the aqueous solution of crude sodium silicate, calculated from the nickel concentration in the aqueous solution of crude sodium silicate .
• the capture step and separation step can be carried out simultaneously. That is, in the above-mentioned embodiment (2), an example is a method in which the crude sodium silicate aqueous solution is passed through a packed bed containing layered sodium silicate.
• a preferred embodiment of this method involves placing a packed bed containing layered sodium silicate midway through the flow path of the crude sodium silicate aqueous solution, and passing the crude sodium silicate aqueous solution through the packed bed to bring it into contact with the layered sodium silicate.
• Another example is a method in which a basket filled with layered sodium silicate is immersed in the crude sodium silicate aqueous solution contained in a container, and the crude sodium silicate aqueous solution is circulated or stirred as necessary.
• the layered sodium silicate packed into the packed bed is preferably either of a size that prevents the layered sodium silicate from leaking out, or in the form of a packing that supports the layered sodium silicate.
• the inner surfaces of containers, piping, etc. used in the process, including the capture process and separation process be made of materials that minimize the elution of nickel.
• the high-purity sodium silicate aqueous solution obtained through the separation step has an extremely low nickel content, which has been a particular problem due to contamination from raw materials and equipment, and can achieve a nickel content of 100 ppb or less relative to the SiO2 component of sodium silicate.
• the high-purity sodium silicate aqueous solution obtained by the production method according to one embodiment of the present invention has a nickel content of 100 ppb or less relative to the SiO2 component of sodium silicate.
• the contents of other metal impurities are not particularly limited, but it is preferable that the concentrations of metal impurities such as Cr, Cu, and Zn are 1 ppm or less. Such concentrations can be achieved by known methods.
• the high-purity sodium silicate aqueous solution according to one embodiment of the present invention has an extremely low nickel content, making it useful in applications requiring a high-purity sodium silicate aqueous solution, such as as a raw material for silica sol for semiconductor abrasives.
• layered sodium silicate has an excellent ability to capture nickel present in the aqueous solution of sodium silicate. They have also found that by trapping nickel in the layered sodium silicate and then removing the layered sodium silicate that has trapped nickel from the aqueous solution by a method such as filtration, an extremely high-purity aqueous solution of sodium silicate having a nickel concentration of 100 ppb or less can be obtained, and have completed the present invention.
• the method for producing a high-purity sodium silicate aqueous solution according to aspect 1 of the present invention is characterized by comprising a capture step of capturing nickel from a nickel-containing sodium silicate aqueous solution using layered sodium silicate, and a separation step of removing the layered sodium silicate that has captured the nickel from the sodium silicate aqueous solution.
• the removal rate of the layered sodium silicate in the separation step is 90% or more, and the amount of layered sodium silicate removed in the capture step is 100 times or more by mass relative to the nickel content in the aqueous sodium silicate solution, which is preferable, as this enables a high degree of nickel removal.
• the method for producing a high-purity aqueous sodium silicate solution according to aspect 3 of the present invention is preferably the same as that according to aspect 1 or 2, in which the capture step is carried out by producing the layered sodium silicate from a portion of the sodium silicate in the aqueous sodium silicate solution.
• the layered sodium silicate is preferably produced by holding the aqueous sodium silicate solution at a temperature of 140 to 190°C so that the temperature (°C) x holding time (hr) is in the range of 500 to 5,000.
• the capture step is preferably carried out by contacting the layered sodium silicate with the aqueous sodium silicate solution.
• any one of aspects 1 to 5 it is preferable that the operation of removing the layered sodium silicate in the separation step is filtration.
• the sodium silicate concentration of the sodium silicate aqueous solution is more than 10% by mass and not more than 35% by mass, calculated as SiO2 .
• Aspect 8 of the present invention also provides a high-purity aqueous sodium silicate solution, which can be obtained by the production method of any one of Aspects 1 to 7, and which is characterized in that the nickel content is 100 ppb or less relative to the SiO2 component of sodium silicate.
• the high-purity sodium silicate aqueous solution according to Aspect 8 is useful as a raw material for silica sol for semiconductor abrasives.
• Removal rate and removal amount of layered sodium silicate in separation step The removal rate is measured by taking 100ml of the crude sodium silicate aqueous solution that has been through the capture step, filtering through a filter with a pore size of 0.1 ⁇ m, washing the residue on the filter material, drying, then measuring the weight of the layered sodium silicate, and converting this into the layered sodium silicate amount (W1) of the total amount of crude sodium silicate aqueous solution.
• W1 the layered sodium silicate amount of the total amount of crude sodium silicate aqueous solution.
• the amount removed was expressed as the mass ratio (W S /W N ) calculated from the mass (W S ) of the layered sodium silicate removed in the separation step, calculated by subtracting W2 from the mass (W S ) of nickel in the aqueous solution of crude sodium silicate, calculated from the nickel concentration in the aqueous solution of crude sodium silicate .
• the collected sodium silicate aqueous solution had a high viscosity, it was diluted to an appropriate concentration that allowed filtration, and then the above method was carried out. Specifically, when filtering the sodium silicate aqueous solution, if the viscosity did not meet the condition of 50 mPa ⁇ s or less, the solution was diluted to meet this condition.
• Table 1 also shows the removal rate and amount of layered sodium silicate removed in the separation process, the particle size of the removed layered sodium silicate, and the nickel concentration of the resulting high-purity sodium silicate aqueous solution.
• Example 6 In Example 2, 0.7 g of separately prepared layered sodium silicate (Kenyaite) powder was added to 1 kg of the crude sodium silicate aqueous solution, and the mixture was thoroughly stirred at 40°C to carry out a capture step, thereby obtaining a high-purity sodium silicate aqueous solution.
• Kenyaite layered sodium silicate
• the removal rate of layered sodium silicate in the separation process was 100%, the removal amount was 26,000, and the nickel concentration of the resulting high-purity sodium silicate aqueous solution was 30 ppb or less.
• Example 7 A capturing step was carried out immediately after the step of dissolving the cullet in water to produce a crude sodium silicate aqueous solution. Specifically, 15 g of cullet ( SiO2 : 75.5%, Na2O : 24.5%) and 60 g of ultrapure water were placed in a PTFE crucible, which was then inserted into a stainless steel jacket and heated in an electric furnace set at 160°C for 12 hours, after which the crucible was removed from the electric furnace and cooled.
• the time until the SiO2 concentration of the crude sodium silicate aqueous solution reached 10 mass% was checked using the same feed, and it was found to be 2 hours. Therefore, the time (10 hours) obtained by subtracting 2 hours from the 12 hours was determined to be the heating time for the capture step.
• the crude sodium silicate aqueous solution had a concentration of 14.99% by mass in terms of SiO 2 , a concentration of 4.91% by mass in terms of Na 2 O, and a nickel content of 360 ppb, and contained layered sodium silicate.
• the crude aqueous sodium silicate solution obtained through the capture step was used to carry out a separation step in the same manner as in Example 1.
• the removal rate of layered sodium silicate in the separation step was 100%, the removal amount was 1,800, and the nickel concentration of the obtained high-purity aqueous sodium silicate solution was 80 ppb.

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• 2025
  • 2025-01-15 JP JP2025573531A patent/JPWO2025164297A1/ja active Pending
  • 2025-01-15 WO PCT/JP2025/000933 patent/WO2025164297A1/ja active Pending
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