WO2021262351A1 - Methods and systems for synthesizing a geopolymer - Google Patents

Methods and systems for synthesizing a geopolymer Download PDF

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Publication number
WO2021262351A1
WO2021262351A1 PCT/US2021/033223 US2021033223W WO2021262351A1 WO 2021262351 A1 WO2021262351 A1 WO 2021262351A1 US 2021033223 W US2021033223 W US 2021033223W WO 2021262351 A1 WO2021262351 A1 WO 2021262351A1
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WO
WIPO (PCT)
Prior art keywords
slurry
support
geopolymer
range
dried material
Prior art date
Application number
PCT/US2021/033223
Other languages
French (fr)
Inventor
Agustin Sin Xicola
Alberto Conte
Valentina IODICE
Francesco VANNUCCI
Sandro DE DOMINICIS
Paolo Colombo
Original Assignee
Itt Italia S.R.L.
Itt Manufacturing Enterprises Llc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Itt Italia S.R.L., Itt Manufacturing Enterprises Llc filed Critical Itt Italia S.R.L.
Publication of WO2021262351A1 publication Critical patent/WO2021262351A1/en

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Classifications

    • CCHEMISTRY; METALLURGY
    • C04CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04BLIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B12/00Cements not provided for in groups C04B7/00 - C04B11/00
    • C04B12/005Geopolymer cements, e.g. reaction products of aluminosilicates with alkali metal hydroxides or silicates
    • CCHEMISTRY; METALLURGY
    • C04CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04BLIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B18/00Use of agglomerated or waste materials or refuse as fillers for mortars, concrete or artificial stone; Treatment of agglomerated or waste materials or refuse, specially adapted to enhance their filling properties in mortars, concrete or artificial stone
    • C04B18/02Agglomerated materials, e.g. artificial aggregates
    • C04B18/021Agglomerated materials, e.g. artificial aggregates agglomerated by a mineral binder, e.g. cement
    • CCHEMISTRY; METALLURGY
    • C04CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04BLIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/006Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing mineral polymers, e.g. geopolymers of the Davidovits type
    • CCHEMISTRY; METALLURGY
    • C04CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04BLIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/24Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing alkyl, ammonium or metal silicates; containing silica sols
    • C04B28/26Silicates of the alkali metals
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P40/00Technologies relating to the processing of minerals
    • Y02P40/10Production of cement, e.g. improving or optimising the production methods; Cement grinding

Definitions

  • Brake pads are part of a brake disc system used in vehicles.
  • a typical brake disc system may include a brake disc rotor for each wheel hub, where each brake disc rotor has an associated pair of brake pads.
  • the brake pads may be held in place and actuated by a caliper that is affixed to the wheel hub.
  • Brake pads often have steel back plates, where a surface of each steel back plate includes a friction material that faces the surface of the corresponding brake disc rotor.
  • the caliper squeezes the two brake pads together onto the brake disc rotor to slow and/or stop the vehicle.
  • Brake pads convert the kinetic energy of the vehicle to thermal energy through friction.
  • friction materials plays an important role in a brake system since brakes use friction to decelerate/stop the vehicle.
  • the friction materials typically include reinforcements, friction modifiers, and binders.
  • Asbestos widely used as a reinforcement for friction materials because of its thermal stability, is highly toxic to human health. Asbestos has been often replaced by a number of materials, including both inorganic and organic materials, as well as metal fibers.
  • Metal sulfides such as molybdenum disulfide, iron sulfides, copper, tin, graphite, and/or coke are example materials that may be used as friction modifiers.
  • the binders may be thermosetting polymers, such as phenolic resins. However, during repeated braking, organic binders may release volatile gaseous compounds or fine dust into the atmosphere, which may be harmful to human health.
  • geopolymers are a class of material that may be suitable as an alternative binder for a friction material of a brake pad.
  • Geopolymer materials can be synthesized from the reaction of an alumina-silicate powder with an alkaline siliceous solution under ambient temperature and pressure. The mechanical properties of geopolymer materials are reasonable, and they have good thermal stability at temperatures above 1000 °C. Thus, geopolymer materials may be suitable as an alternative binder in friction materials of brake pads.
  • a method for synthesizing a geopolymer may include mixing a silicate solution and metakaolin to form a slurry; spreading the slurry on a support to form a slurry film; subjecting the support and the slurry film to a thermal treatment, where the thermal treatment dries the slurry to form a dried material with a residual humidity in a range of about 0 wt% to about 20 wt%; detaching the dried material from the support; and milling the dried material to obtain a geopolymer with a particle size in a range of about 1 micron to about 300 microns.
  • mixing the silicate solution and metakaolin may include mixing in a weight ratio of about 3:1.
  • Mixing the silicate solution and metakaolin may include mixing at a speed from about 500 rom to about 1000 rpm and for an elapsed time in a range from about 1 minute to about 20 minutes.
  • Mixing the silicate solution and metakaolin may include mixing at a temperature in a range from about 20 °C to about 40°C.
  • Spreading the slurry on a support may include spreading the slurry on a paper, a plastic film or a steel sheet.
  • Spreading the slurry on a support may include spreading the slurry on the support to obtain a thickness of the slurry in a range of about 0.1mm to about 2 mm.
  • Spreading the slurry on a support may include spreading the slurry on the support at room temperature.
  • Subjecting the support and the slurry to a thermal treatment may include subjecting the support and the slurry to either a continuous or discontinuous thermal treatment.
  • Subjecting the support and the slurry to a thermal treatment may include heating the support and the slurry while monitoring humidity in-line with a near infrared light (NIR) sensor.
  • NIR near infrared light
  • subjecting the support and the slurry to a thermal treatment may include heating the support and the slurry while monitoring humidity in-line with a radio-isotope sensor.
  • Subjecting the support and the slurry to a thermal treatment may include weighing the support along with the slurry, drying the support and the slurry in a hot air furnace, and then weighing the support along with the slurry again.
  • Subjecting the support and the slurry to a thermal treatment may include heating the support and the slurry to a temperature in a range of about 80°C to about 200°C for an elapsed time in a range of about 5 min to about 30 min.
  • Detaching the dried material from the support may include detaching the dried material from the support having a thermal resistance of in a range of about 150°C to about 300°C.
  • Milling the dried material to obtain a geopolymer may include milling in a jar mill, a ball mill, or an impact mill.
  • a system for synthesizing a geopolymer may include a mixer machine configured to form a slurry from a mixture of an alkali silicate solution and metakaolin; a casting machine configured to cast the slurry on a support; a hot air furnace configured to thermally treat the slurry on the support to form a dried material, where the dried material has a humidity in a range of about 0 wt% to about 20 wt%; and a mill machine configured to mill the dried material to obtain a geopolymer with a particle size in a range of about 1 micron to about 300 microns.
  • the system may further include a jacket device configured to circulate water to control a temperature of the mixture of the mixture machine.
  • the mixer machine may have a mechanical stirrer with one or more dispersant tools.
  • the system may also include a controller device, where the controller device is configured to coordinate the operation of one or more of the mixer machine, the casting machine, the hot air furnace and the mill machine.
  • a system for synthesizing a geopolymer may include a means for forming a slurry from a mixture of an alkali silicate solution and metakaolin; a means for casting the slurry on a support; a means for thermally treating the slurry on the support to form a dried material with a residual humidity in a range from about 0 wt% and about 20 wt%; and a means for milling the dried material to obtain a geopolymer with a particles size with a diameter in a range of about 1 micron to about 300 microns.
  • the system may further include a means for controlling the operation of one or more of the means for forming the slurry, the means for casting the slurry, the means for thermally treating the slurry, and the means for milling the dried material.
  • FIG. 1 is a flow chart illustrating a method for synthesizing a geopolymer material
  • FIG. 2 is a schematic representation of a system for synthesizing a geopolymer material
  • FIG. 3 is a graph illustrating variation of viscosity of a geopolymer material with shear rate
  • FIG. 4 is a graph illustrating geopolymer material content (wt%) as a function of particle size and residual humidity
  • FIG. 5 is a graph illustrating wear of a friction material with geopolymer material at different temperatures
  • FIG. 6 is a graph illustrating wear of a brake disc rotor with geopolymer material at different temperatures, all arranged in accordance with at least some embodiments described herein.
  • This disclosure is generally drawn, inter alia, to methods, system, and devices to synthesize geopolymer materials.
  • geopolymer materials can replace the conventional organic binders used for making the friction materials in brake pads. Some example benefits of the presently disclosed geopolymers materials are that they are safe for humans (e.g., they contain no harmful phenolic resins). The geopolymer materials of the present disclosure are comparatively less expensive than organic binders. Further, the presently disclosed geopolymer materials may facilitate the use of mild post curing conditions ((low pressures and ambient temperatures) for making the brake pads.
  • Some described methods may include mixing sodium silicate solution and metakaolin to form a slurry.
  • the slurry may be spread on a support.
  • the support and the slurry may be subjected to a thermal treatment to dry the slurry to form a dried material having a residual humidity in a range of about 0 wt% to about 20 wt%.
  • the dried material may be detached from the support and may be milled to obtain a geopolymer material with a particle size in a range of about 1 micron to about 300 microns.
  • FIG. 1 is a flow chart illustrating a method for synthesizing a geopolymer that is arranged according to aspects of the present disclosure.
  • the described method 100 may include block 102, “MIX SILICATE SOLUTION AND METAKAOLIN TO FORM A SLURRY”, block 104, “SPREAD THE SLURRY ON A SUPPORT”, block 106, “SUBJECT THE SLURRY AND THE SUPPORT TO A THERMAL TREATMENT”, block 108, “DETACH THE DRIED MATERIAL FROM THE SUPPORT”, and block 110, “MILL THE DRIED MATERIAL”.
  • An example process may begin at block 102, where materials are mixed to provide a slurry of silicate and metakaolin.
  • the slurry of geopolymer may be formed by using an alkali silicate solution such as a sodium silicate solution, a potassium silicate solution, a lithium silicate solution, or similar geopolymer family solutions.
  • Block 102 may be followed by block 104, where the slurry of sodium silicate solution and metakaolin may be spread on a support to provide a thickness adjusted slurry.
  • Block 104 may be followed by block 106, where the thickness adjusted slurry on the support may be subjected to a thermal treatment to provide a dried material.
  • Block 106 may be followed by block 108, where the dried material may be detached from the support.
  • Block 108 may be followed by block 110, where the detached dried material may be milled to form the geopolymer in a powder form.
  • sodium silicate solution and metakaolin may be mixed in a weight ratio (e.g., about 3:1) to form a slurry.
  • the metakaolin may correspond to Imerys ArgiealTM M1200s, in some examples.
  • sodium silicate may correspond to Ingessil® sodium silicate.
  • mixing may be done by a mixer device or mechanical stirrer using different types of dispersant tools as a function of the rheology and granulometry of the metakaolin powder. Due to the pseudoplastic behavior of geopolymers the rheology of the system may be optimized as much as is reasonably possible.
  • the system may include an impeller like sawtooth disc impeller or butterfly propellers.
  • temperature of the material in the mixer device may be controlled by a jacket water system.
  • the material may be in a container (e.g., a region of the mixer where the materials are mixed) where the jacket water system substantially surrounds the container.
  • a container e.g., a region of the mixer where the materials are mixed
  • either hot water or cold water may be circulated in the jacket to adapt the temperature of the container.
  • the monitoring of temperature and/or adjustment of the temperature of the mixing may be adapted responsive to a controller (not shown).
  • the mechanical stirrer device may operate at a speed of about 800 rpm. In other examples, the mechanical stirrer device (or mixer device) may be operated at a speed in a range of about 100 rpm to about 1500 rpm in function of the dispersant tool geometry. In various examples, the mixing time may be in a range of about 2 min to about 20 min.
  • the rotational speed and/or mix time of the stirring (or mixing) can be varied responsive to a controller (not shown), where the precise recipe of mixing time, temperature, and rotational speed may be varied based on the specific materials selected.
  • the weight ratios of sodium silicate solution and metakaolin may be varied from the above examples.
  • the weight ratio of 3: 1 may have a tolerance of about +1-1%, +1-5%, +/- 10% or even +/-15%.
  • the weight ratio may be in a range from about 2.5: 1 to about 3.5:1.
  • the weight ratio may be 2.8:1, 2.7:1, 3.1:1. 3.2:1, etc.
  • the ranges may depend on the alkali system, sodium or potassium, and on the type of the raw materials, in particular, metakaolin, because raw materials affect the viscosity and the water content of the solution necessary to have the optimal rheology.
  • a general range of 2 - 3.5 may be suitable.
  • the slurry may be cast on a sheet material.
  • the slurry may be cast on a plastic film.
  • the slurry may be cast on a steel sheet.
  • Sappi® paper may be used as a support.
  • Coveme® film may be used as a support. The choice of the support may depend on the tipology of the process. In some examples, the thickness of the deposited slurry may be in a range of about 0.1 mm to about 2 mm.
  • the thickness of the deposited slurry may be in a range of about 0.3 mm- 1.0 mm.
  • the spreading of the slurry on the support may be facilitated by a conveyor device.
  • a conveyor device may carry the support through a roller device that is adapted to spread the material to a substantially uniform thickness.
  • the motion of the conveyor device, including the speed thereof, as well as control of pressure exerted by the roller device may be adapted responsive to a controller (not shown) such that the thickness may be monitored and controlled to be within desired tolerances to provide a thickness adjusted slurry.
  • the thickness adjusted slurry and the support may be subjected to a thermal treatment.
  • the support with the thickness adjusted slurry may be subjected to the thermal treatment to cure and dry the slurry to provide a thin film or a sheet.
  • the thickness of the resulting thin film or sheet is a function of the materials used in the slurry, the thickness of the slurry cast on the support, as well as the reaction of those materials in the thermal treatment.
  • the thermal treatment may be done through a continuous process.
  • the thickness adjusted slurry may be moved by a conveyor device through a temperature-controlled oven (single stage or multi-staged oven), where the temperature-controlled oven may have a temperature profile that is adapted by a controller (not shown).
  • the temperature profile is a single temperature and elapsed time at that single temperature.
  • the temperature profile is multi-staged with different elapsed times at different temperature (e.g., a ramped heating up period, immersion at temperature, and ramped cool-down period).
  • An example continuous process may adjust various parameters in a heating system such as temperature, heating profile, speed, cooling profile, air flow volume and/or rate, and any other parameters that may control the humidity and/or heating to achieve a desired result of a cured material with a prescribed moisture content level (e.g., the residual humidity of the material).
  • the output of the thermal treatment may be improved by tight control of the humidity.
  • a microwave device may be used to control one or more of temperature and humidity. It may be desirable to continuously monitor the temperature and/or humidity levels to effect control of the residual humidity in the continuous thermal treatment process.
  • one or more sensors may be used to detect the humidity at appropriate points in the process.
  • a Near Infra-Red (NIR) sensor may be utilized to provide a non-contact measurement of humidity and/or temperature.
  • a radio-isotope sensor may be used to detect humidity and/or temperature. The NIR sensor or the radio-isotope sensor may be employed to facilitate control of the humidity and/or temperature through an in-line system that adaptively controls the process parameters.
  • the thermal treatment may be done by a discontinuous process.
  • the humidity may be controlled by a loss weight percentage with respect to a fully dried geopolymer. The humidity may be measured by weighing the support along with the slurry, drying the support and the slurry in an oven for several hours (in general, the time is a function of the final humidity) and then weighing again.
  • the immersion temperature for the thickness adjusted slurry material may be set in a range of about 80°C to about 250°C. In some other examples, the immersion temperature may be in any other appropriate range such as from about 100°C to about 150°C, about 100°C to about 200°C, about 130°C to about 190°C, etc.
  • the air flow rate and/or volume may be varied to adjust the drying speed of the thickness adjusted slurry and to acheive the desired amount of residual humidity.
  • the optimal humidity of the dried slurry may be in a range of about 8 wt% to about 11 wt%; or alternatively in a range of about 5 wt% to about 10 wt%, for example.
  • Block 106 may be followed by block 108, where the dried material may be detached from the support.
  • the support may be a Sappie® paper; a Coveme® film; or some other suitable sheeted material.
  • the Sappie® paper may have a better thermal resistance than the Coveme® film.
  • the Sappie® paper may be reused after the dried material is detached.
  • Block 108 may be followed by block 110, where the detached dried material may be milled to form the geopolymer powder.
  • the dried material may be milled by any appropriate mill device that provides a suitable particle size.
  • the dried material may be ground by ajar mill.
  • the dried material may be ground by a ball mill.
  • the geopolymer thus formed may have a particle size in a range of about 1 micron to about 300 microns; or another range from about 10 microns to about 100 microns, for example.
  • the detached material may be moved to the mill device by a conveyor device such as a belt conveyor, and/or a hopper- based conveyor, for example.
  • the particle size of the geopolymer may result in specific properties, such as porosity, finish, and mechanical strength of the geopolymer.
  • the final properties of the geopolymer may depend on the particle size and the residual humidity.
  • FIG. 2 is a schematic representation of a system 200 for synthesizing a geopolymer that is arranged in accordance with at least some embodiments described herein.
  • the described system 200 may include multiple devices such as a mixer 202, a tape casting machine 204, a hot air furnace 206, and a mill 208.
  • a controller may be utilized to coordinate the operation of system 200, such as via machine executable instructions that when executed by a processor (e.g., a micro process, micro-controller, DSP, or other processor) in the controller coordinate the operation of each of the devices for specified times, temperatures, and other process-based parameters for the devices.
  • a processor e.g., a micro process, micro-controller, DSP, or other processor
  • each of the described devices in system 200 may be configured and operated in response to signals (e.g., analog or digital signals) from the controller.
  • conveyance systems such as conveyor belts, hoppers, and other robot operated conveyors may be utilized, configured, operated or otherwise operated responsive to the controller, to transfer between the various devices.
  • Sensors may be arranged in communication with the controller, which can be utilized to monitor processing parameters such as mixing temperature, mixing speed, conveyor speed, heating, immersion and/or cooling temperature, air flow volume and/or rate, moisture or humidity levels, as well as other process parameters described herein.
  • the mixer 202 may be configured to mix materials 211 (sodium silicate solution and metakaolin) to form a slurry 212.
  • the choice of the mixer 202 may depend on the quantities and the metakaolin powder used to make the geopolymer slurry.
  • a mixer with a mechanical stirrer may be used.
  • a mixer having dispersant tools may be used.
  • sodium silicate solution and metakaolin may be mixed at a speed of about 800 rpm, but other mixing speeds may be suitable as previously described above.
  • sodium silicate solution and metakaolin may be mixed for about 10 min.
  • a pre- weighed slurry 212 along with a support may be placed in a tape casting machine 204 and may be cast to form a tape cast slurry on the support 213 (for example, paper).
  • the slurry 212 may be transported from the container of the mixer device to holding tanks and/or from holding tanks to the tape casting machine 204 via pipes, feed devices, and/or hopper devices.
  • the tape-casting machine is configured to cast the material at a temperature in a range of about 80°C to about 250°C, or any other appropriate casting temperature.
  • the slurry may be cast on a paper sheet material.
  • the slurry may be cast on a plastic film material.
  • the slurry may be cast on a steel sheet material.
  • the slurry may be transported from the container of the mixer device to holding tanks and/or from holding tanks to the tape casting machine 204 via pipes, feed devices, and/or hopper devices.
  • the tape-casting machine is configured to cast the material at a temperature in a range of about 80°C to about 250°C, or any other appropriate casting temperature.
  • the slurry may be cast on a paper sheet material.
  • the slurry may be cast on a plastic film material.
  • Sappi® paper may be used as a support.
  • Coveme® film may be used as a support.
  • the choice of the support 213 may depend on the tipology of the process parameters.
  • a blade 217 may be used to regulate the thickness of the slurry on the support 214 as the support 213 is rolled along the tape casting machine 204 In some examples, the thickness of the deposited slurry by the wheels 215.
  • the thickness of the slurry may be, for example, in a range of about 0.1 mm to about 2.0 mm; in a range of about 0.3 mm to about 1.0 mm; or in any other desired thickness level that may be reasonably appropriate.
  • the tape cast slurry along with the support 213 may be transferred, via a conveyor device (wheels 215), to an oven device such as a hot air furnace 206.
  • the tape cast slurry along with the support 213 may be subjected to a thermal treatment in the hot air furnace 206 to obtain a dried material 216.
  • the tape cast slurry along with the support may be subjected to the thermal treatment to cure and dry the slurry to obtain a thin film or a sheet of the dried material 216.
  • the thickness of the thin film or sheet of the dried material 216 may be a function of the thickness of the slurry cast on the support.
  • the thermal treatment may be done through a continuous process.
  • the slurry may be moved by a conveyor device through a temperature-controlled furnace (single stage or multi-staged oven), where the temperature-controlled furnace may have a temperature profile that is adapted by a controller (not shown).
  • the temperature profile is a single temperature and elapsed time at that single temperature.
  • the temperature profile is multi-staged with different elapsed times at different temperature (e.g., a ramped heating up period, immersion at temperature, and ramped cool-down period).
  • An example continuous process may adjust various furnace parameters such as temperature, heating profile, speed, cooling profile, air flow volume and/or rate, and any other parameters that may control the humidity and/or heating to achieve a desired result of a cured material with a prescribed moisture content level (e.g., the residual humidity of the material).
  • the output of the thermal treatment may be improved by tight control of the humidity.
  • a microwave device may be used to control one or more of temperature and humidity. It may be desirable to continuously monitor the temperature and/or humidity levels to effect control of the residual humidity in the continuous thermal treatment process.
  • one or more sensors may be used to detect the humidity at appropriate points in the process.
  • a Near Infra-Red (NIR) sensor may be utilized to provide a non-contact measurement of humidity and/or temperature.
  • a radio-isotope sensor may be used to detect humidity and/or temperature. The NIR sensor or the radio-isotope sensor may be employed to facilitate control of the humidity and/or temperature through an in-line system that adaptively controls the process parameters.
  • the thermal treatment may be done by a discontinuous process.
  • the humidity may be controlled by a loss weight percentage with respect to a fully dried geopolymer. The humidity may be measured by weighing the support along with the slurry, drying the support and the sample in an oven for several hours and then weighing it again.
  • the immersion temperature for the thickness adjusted slurry material may be set in a range of about 80°C to about 250°C. In some other examples, the immersion temperature may be in any other appropriate range such as from about 100°C to about 150°C, about 100°C to about 200°C, about 130°C to about 190°C, etc.
  • the air flow rate and/or volume may be varied to adjust the drying speed of the thickness adjusted slurry and to acheive the desired amount of residual humidity.
  • the optimal humidity of the dried slurry may be in a range of about 8 wt% to about 11 wt%; or alternatively in a range of about 5 wt% to about 10 wt%, for example.
  • the dried material 216 may be detached from the support 213.
  • the support 213 may be a Sappie® paper.
  • the support may be a Coveme® film.
  • the Sappie® paper may have a better thermal resistance than the Coveme® film.
  • the Sappie® paper may be reused as a support after the dried material is detached.
  • the dried material 216 may be milled in a mill 208 to form the geopolymer powder 218.
  • the mill 208 may be ajar mill.
  • the mill 208 may be a ball mill.
  • the geopolymer 218 thus formed may have a particle size in a range of about 1.0 micron to about 300 microns; or another range from about 10 microns to about 100 microns, for example.
  • the detached material may be moved to the mill device by a conveyor device such as a belt conveyor, and/or a hopper-based conveyor, for example.
  • the particle size of the geopolymer may result in specific properties, such as porosity, finish, and mechanical strength of the geopolymer 218.
  • the final properties may depend on the particle size and the residual humidity of the geopolymer 218.
  • the small particle size of the geopolymer may have benefits in brake friction material applications.
  • the small particle size may reduce or eliminate cracks in the friction material that is made using the disclosed geopolymer.
  • the friction material including the disclosed geopolymer may also facilitate brake materials with a uniform surface profile.
  • the smaller geopolymer particles may improve the adhesion between the friction material and an under-layer that are used to make a brake pad.
  • the controller in the above illustrated systems, methods and devices may be of any variety of controller device that is adapted for use in the described embodiments.
  • the controller in one example can be a thermostat device.
  • the controller can be an analog electronic circuit, a digital electronic circuit, or a mixed analog/digital electronic circuit.
  • the controller can be a processor based device such as a micro-processor, micro controller, DSP controller, or some other variety of device that is configured by machine executable instructions to configure and operate the machines to follow the desired recipe for manufacturing geopolymer particles.
  • combinations of multiple controllers can also be utilized, where each manufacturing device has its own local controller, and a master controller collectively configures each of the local controllers to follow the desired recipe.
  • a mixer device could have a local controller that adapts the mixing speed of the mixer device; while the tape casting machine has its own local controller to adapt the casting thickness, furnace temperature profile, conveyance speed, etc.; and a master controller would instruct each of the local controllers to utilize the specified recipe for manufacturing a specific geopolymer.
  • FIG. 3 is a graph 300 illustrating a variation of viscosity of a geopolymer with shear rate.
  • vertical axis 302 represents viscosity (cP) and horizontal axis 304 represents shear rate (s 1 ).
  • s 1 shear rate
  • the viscosity of the geopolymer decreases from 100000 cP to 1000 cP as the shear rate increases from 0.1 to 1000 s 1 .
  • the graph shows typical pseudoplastic behavior required for a tape casting process in order to have a viscosity, which changes as a function of the stress and the shear rate, permitting to have a low viscosity and an easy mixing step for high shear rate, and at the same time a high viscosity for low shear rate when the slurry is cast and formed to a sheet on the support material, in order to maintain the shape.
  • FIG. 4 is a graph 400 illustrating geopolymer content (wt%) as a function of particle size (pm) and residual humidity (wt%).
  • the vertical axis 402 represents particle size (pm) and the right side horizontal axis 404 represents geopolymer content (wt%) and the left side horizontal axis 406 represents humidity (wt ).
  • the graphs 408, 410, and 412 show different residual humidity characteristics of varying version of the geopolymer materials. As shown, graph 408 has a residual humidity of about 10.5 wt%, while graph 410 has a residual humidity of about 9 wt% and graph 412 has a residual humidity of about 8 wt%.
  • the resulting particle sizes that can be achieved for these residual humidity’s varies based on the geopolymer content.
  • the binder properties of the geopolymer particles e.g., in a dried powder form
  • the granularity e.g., particle size
  • FIG. 5 is a graph 500 illustrating variation of wear of two friction materials as a function of temperature.
  • vertical axis 502 represents the wear of the friction materials and horizontal axis 504 represents the temperature in (°C).
  • the graph 506 represents variation of the wear of the friction material having a geopolymer of a particle size greater than 300 microns with temperature. In graph 506, the wear increases from 0.31 to 0.52 as the temperature increases from 50 °C to 200 °C and then decreases to 0.41 at 400 °C.
  • the graph 508 represents variation of the wear of the friction material having a geopolymer of a particle size lesser than 150 microns.
  • the wear increases from 0.21 to 0.31 as the temperature increases from 50 °C to 300 °C and then remains constant at 0.31. It is evident from these graphs that the wear of the friction material having a geopolymer of a particle size less than 150 microns is lesser than that of the friction material having a geopolymer of a particle size greater than 300 microns. This confirms that the smaller the particle size of the geopolymer, the greater the reduction in wear of the friction material.
  • FIG. 6 is a graph 600 illustrating variation of wear of two brake pads as a function of temperature.
  • vertical axis 602 represents the wear of the brake pads and horizontal axis 604 represents the temperature in (°C).
  • the graph 606 represents variation of the wear of the brake pad having a geopolymer of a particle size less than 150 microns with temperature.
  • the wear increases from 0.6 to 1 as the temperature increases from 50 °C to 200 °C and then increases to 8.3 at 400 °C.
  • the graph 608 represents variation of the wear of the brake pad having a geopolymer of a particle size greater than 300 microns with temperature.
  • the wear decreases from 5 to 1 as the temperature increases from 50 °C to 200 °C and then increases to 8.3 at 400 °C.
  • the following examples are intended as illustrative and non-limiting and represent specific embodiments of the present disclosure.
  • the examples show that the disclosed geopolymers are substantially free of phenolic resins.
  • the examples demonstrate that the friction materials are synthesized using the disclosed geopolymers.
  • the examples demonstrate that the brake pads including the disclosed friction materials have a high hardness, compressibility and detach.
  • Example 1 The slurry of Example 1 was transported in pipes from tanks on to the Sappie® paper in the tape casting machine and cast at a temperature in a range from about 15°C to about 40°C (room temperature). The thickness of the resulting slurry was about 0.3 mm.
  • the slurry spread on the Sappie® paper was heated in a hot air furnace at a temperature in a range from about 120°C to about 200°C under air flow.
  • the humidity of the slurry was continuously monitored using an NIR sensor and the slurry was heated until the humidity reached 6-10 wt% to form a dried material.
  • the dried material was then detached from the Sappie® paper.
  • the dried and detached slurry was milled in ajar mixer for about 10 hours or in a ball milling machine for about 30 min.
  • the particle size of the resulting powder had a diameter in a range from about 1 micron to about 300 microns.
  • any two components so associated may also be viewed as being “operably connected”, or “operably coupled”, to each other to achieve the desired functionality, and any two components capable of being so associated may also be viewed as being “operably couplable”, to each other to achieve the desired functionality.
  • operably couplable include but are not limited to physically connectable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.
  • ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non- limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, a range includes each individual member. Thus, for example, a group having 1 -3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth.

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Abstract

Technologies are generally described for a method and system for synthesizing a geopolymer. The method includes mixing an alkali silicate solution and metakaolin to form a slurry. The slurry is spread on a support. The support and the slurry are subjected to a thermal treatment to dry the slurry to form a dried material having a humidity in a range of 0-20 wt%. The dried material is detached from the support and milled to obtain a geopolymer with a particle size in a range of 1-300 microns.

Description

METHODS AND SYSTEMS FOR SYNTHESIZING A GEOPOLYMER
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to Italian Patent Application No. 102020000015202 filed on June 24, 2020 by the same inventors. The entirety of the disclosures of the priority application are incorporated by reference herein.
BACKGROUND
[0002] Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted as prior art by inclusion in this section.
[0003] Brake pads are part of a brake disc system used in vehicles. A typical brake disc system may include a brake disc rotor for each wheel hub, where each brake disc rotor has an associated pair of brake pads. The brake pads may be held in place and actuated by a caliper that is affixed to the wheel hub.
[0004] Brake pads often have steel back plates, where a surface of each steel back plate includes a friction material that faces the surface of the corresponding brake disc rotor. When braking is applied, the caliper squeezes the two brake pads together onto the brake disc rotor to slow and/or stop the vehicle. Brake pads convert the kinetic energy of the vehicle to thermal energy through friction. Thus, friction materials plays an important role in a brake system since brakes use friction to decelerate/stop the vehicle.
[0005] The friction materials typically include reinforcements, friction modifiers, and binders. Asbestos, widely used as a reinforcement for friction materials because of its thermal stability, is highly toxic to human health. Asbestos has been often replaced by a number of materials, including both inorganic and organic materials, as well as metal fibers. Metal sulfides such as molybdenum disulfide, iron sulfides, copper, tin, graphite, and/or coke are example materials that may be used as friction modifiers. The binders may be thermosetting polymers, such as phenolic resins. However, during repeated braking, organic binders may release volatile gaseous compounds or fine dust into the atmosphere, which may be harmful to human health.
[0006] The present disclosure appreciates that geopolymers are a class of material that may be suitable as an alternative binder for a friction material of a brake pad. Geopolymer materials can be synthesized from the reaction of an alumina-silicate powder with an alkaline siliceous solution under ambient temperature and pressure. The mechanical properties of geopolymer materials are reasonable, and they have good thermal stability at temperatures above 1000 °C. Thus, geopolymer materials may be suitable as an alternative binder in friction materials of brake pads.
SUMMARY
[0007] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings, the detailed description, and the claims.
[0008] According to some examples, a method for synthesizing a geopolymer may include mixing a silicate solution and metakaolin to form a slurry; spreading the slurry on a support to form a slurry film; subjecting the support and the slurry film to a thermal treatment, where the thermal treatment dries the slurry to form a dried material with a residual humidity in a range of about 0 wt% to about 20 wt%; detaching the dried material from the support; and milling the dried material to obtain a geopolymer with a particle size in a range of about 1 micron to about 300 microns.
[0009] According to other examples, mixing the silicate solution and metakaolin may include mixing in a weight ratio of about 3:1. Mixing the silicate solution and metakaolin may include mixing at a speed from about 500 rom to about 1000 rpm and for an elapsed time in a range from about 1 minute to about 20 minutes. Mixing the silicate solution and metakaolin may include mixing at a temperature in a range from about 20 °C to about 40°C. Spreading the slurry on a support may include spreading the slurry on a paper, a plastic film or a steel sheet. Spreading the slurry on a support may include spreading the slurry on the support to obtain a thickness of the slurry in a range of about 0.1mm to about 2 mm. Spreading the slurry on a support may include spreading the slurry on the support at room temperature. Subjecting the support and the slurry to a thermal treatment may include subjecting the support and the slurry to either a continuous or discontinuous thermal treatment. Subjecting the support and the slurry to a thermal treatment may include heating the support and the slurry while monitoring humidity in-line with a near infrared light (NIR) sensor.
[0010] According to further examples, subjecting the support and the slurry to a thermal treatment may include heating the support and the slurry while monitoring humidity in-line with a radio-isotope sensor. Subjecting the support and the slurry to a thermal treatment may include weighing the support along with the slurry, drying the support and the slurry in a hot air furnace, and then weighing the support along with the slurry again. Subjecting the support and the slurry to a thermal treatment may include heating the support and the slurry to a temperature in a range of about 80°C to about 200°C for an elapsed time in a range of about 5 min to about 30 min.
Detaching the dried material from the support may include detaching the dried material from the support having a thermal resistance of in a range of about 150°C to about 300°C. Milling the dried material to obtain a geopolymer may include milling in a jar mill, a ball mill, or an impact mill.
[0011] According to some examples, a system for synthesizing a geopolymer may include a mixer machine configured to form a slurry from a mixture of an alkali silicate solution and metakaolin; a casting machine configured to cast the slurry on a support; a hot air furnace configured to thermally treat the slurry on the support to form a dried material, where the dried material has a humidity in a range of about 0 wt% to about 20 wt%; and a mill machine configured to mill the dried material to obtain a geopolymer with a particle size in a range of about 1 micron to about 300 microns.
[0012] According to other examples, the system may further include a jacket device configured to circulate water to control a temperature of the mixture of the mixture machine. The mixer machine may have a mechanical stirrer with one or more dispersant tools. The system may also include a controller device, where the controller device is configured to coordinate the operation of one or more of the mixer machine, the casting machine, the hot air furnace and the mill machine.
[0013] According to other examples, a system for synthesizing a geopolymer may include a means for forming a slurry from a mixture of an alkali silicate solution and metakaolin; a means for casting the slurry on a support; a means for thermally treating the slurry on the support to form a dried material with a residual humidity in a range from about 0 wt% and about 20 wt%; and a means for milling the dried material to obtain a geopolymer with a particles size with a diameter in a range of about 1 micron to about 300 microns.
[0014] According to further examples, the system may further include a means for controlling the operation of one or more of the means for forming the slurry, the means for casting the slurry, the means for thermally treating the slurry, and the means for milling the dried material. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The foregoing and other features of this disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings, in which:
FIG. 1 is a flow chart illustrating a method for synthesizing a geopolymer material;
FIG. 2 is a schematic representation of a system for synthesizing a geopolymer material;
FIG. 3 is a graph illustrating variation of viscosity of a geopolymer material with shear rate;
FIG. 4 is a graph illustrating geopolymer material content (wt%) as a function of particle size and residual humidity;
FIG. 5 is a graph illustrating wear of a friction material with geopolymer material at different temperatures;
FIG. 6 is a graph illustrating wear of a brake disc rotor with geopolymer material at different temperatures, all arranged in accordance with at least some embodiments described herein.
DETAIFED DESCRIPTION
[0016] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. The aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein.
[0017] This disclosure is generally drawn, inter alia, to methods, system, and devices to synthesize geopolymer materials. [0018] The present disclosure recognizes that geopolymer materials can replace the conventional organic binders used for making the friction materials in brake pads. Some example benefits of the presently disclosed geopolymers materials are that they are safe for humans (e.g., they contain no harmful phenolic resins). The geopolymer materials of the present disclosure are comparatively less expensive than organic binders. Further, the presently disclosed geopolymer materials may facilitate the use of mild post curing conditions ((low pressures and ambient temperatures) for making the brake pads.
[0019] Briefly stated, technologies are generally described for methods, systems, and devices to synthesize geopolymer materials. Some described methods may include mixing sodium silicate solution and metakaolin to form a slurry. The slurry may be spread on a support. The support and the slurry may be subjected to a thermal treatment to dry the slurry to form a dried material having a residual humidity in a range of about 0 wt% to about 20 wt%. The dried material may be detached from the support and may be milled to obtain a geopolymer material with a particle size in a range of about 1 micron to about 300 microns.
[0020] Because of the presence of the disclosed geopolymer materials in the friction materials, no substantial amount of harmful gaseous compounds or fine dust will be released into the atmosphere during repeated braking of a vehicle.
[0021] FIG. 1 is a flow chart illustrating a method for synthesizing a geopolymer that is arranged according to aspects of the present disclosure. The described method 100, may include block 102, “MIX SILICATE SOLUTION AND METAKAOLIN TO FORM A SLURRY”, block 104, “SPREAD THE SLURRY ON A SUPPORT”, block 106, “SUBJECT THE SLURRY AND THE SUPPORT TO A THERMAL TREATMENT”, block 108, “DETACH THE DRIED MATERIAL FROM THE SUPPORT”, and block 110, “MILL THE DRIED MATERIAL”.
[0022] An example process may begin at block 102, where materials are mixed to provide a slurry of silicate and metakaolin. The slurry of geopolymer may be formed by using an alkali silicate solution such as a sodium silicate solution, a potassium silicate solution, a lithium silicate solution, or similar geopolymer family solutions. Block 102 may be followed by block 104, where the slurry of sodium silicate solution and metakaolin may be spread on a support to provide a thickness adjusted slurry. Block 104 may be followed by block 106, where the thickness adjusted slurry on the support may be subjected to a thermal treatment to provide a dried material. Block 106 may be followed by block 108, where the dried material may be detached from the support. Block 108 may be followed by block 110, where the detached dried material may be milled to form the geopolymer in a powder form.
[0023] At block 102, sodium silicate solution and metakaolin may be mixed in a weight ratio (e.g., about 3:1) to form a slurry. The metakaolin may correspond to Imerys Argieal™ M1200s, in some examples. In various examples, sodium silicate may correspond to Ingessil® sodium silicate. In some additional examples, mixing may be done by a mixer device or mechanical stirrer using different types of dispersant tools as a function of the rheology and granulometry of the metakaolin powder. Due to the pseudoplastic behavior of geopolymers the rheology of the system may be optimized as much as is reasonably possible. The system may include an impeller like sawtooth disc impeller or butterfly propellers.
[0024] In some examples, temperature of the material in the mixer device may be controlled by a jacket water system. For example, the material may be in a container (e.g., a region of the mixer where the materials are mixed) where the jacket water system substantially surrounds the container. Depending on the desired temperature for mixing, either hot water or cold water may be circulated in the jacket to adapt the temperature of the container. The monitoring of temperature and/or adjustment of the temperature of the mixing may be adapted responsive to a controller (not shown).
[0025] The mechanical stirrer device may operate at a speed of about 800 rpm. In other examples, the mechanical stirrer device (or mixer device) may be operated at a speed in a range of about 100 rpm to about 1500 rpm in function of the dispersant tool geometry. In various examples, the mixing time may be in a range of about 2 min to about 20 min. The rotational speed and/or mix time of the stirring (or mixing) can be varied responsive to a controller (not shown), where the precise recipe of mixing time, temperature, and rotational speed may be varied based on the specific materials selected.
[0026] The weight ratios of sodium silicate solution and metakaolin may be varied from the above examples. In other examples, the weight ratio of 3: 1 may have a tolerance of about +1-1%, +1-5%, +/- 10% or even +/-15%. Thus, the weight ratio may be in a range from about 2.5: 1 to about 3.5:1. In still further examples, the weight ratio may be 2.8:1, 2.7:1, 3.1:1. 3.2:1, etc. The ranges may depend on the alkali system, sodium or potassium, and on the type of the raw materials, in particular, metakaolin, because raw materials affect the viscosity and the water content of the solution necessary to have the optimal rheology. A general range of 2 - 3.5 may be suitable. [0027] At block 104, the slurry may be cast on a sheet material. In various examples, the slurry may be cast on a plastic film. In some examples, the slurry may be cast on a steel sheet. In one example, Sappi® paper may be used as a support. In another example, Coveme® film may be used as a support. The choice of the support may depend on the tipology of the process. In some examples, the thickness of the deposited slurry may be in a range of about 0.1 mm to about 2 mm.
In some examples, the thickness of the deposited slurry may be in a range of about 0.3 mm- 1.0 mm.
[0028] The spreading of the slurry on the support may be facilitated by a conveyor device.
For example, after the slurry material is deposited on the support, a conveyor device may carry the support through a roller device that is adapted to spread the material to a substantially uniform thickness. The motion of the conveyor device, including the speed thereof, as well as control of pressure exerted by the roller device may be adapted responsive to a controller (not shown) such that the thickness may be monitored and controlled to be within desired tolerances to provide a thickness adjusted slurry.
[0029] At block 106, the thickness adjusted slurry and the support may be subjected to a thermal treatment. The support with the thickness adjusted slurry may be subjected to the thermal treatment to cure and dry the slurry to provide a thin film or a sheet. The thickness of the resulting thin film or sheet is a function of the materials used in the slurry, the thickness of the slurry cast on the support, as well as the reaction of those materials in the thermal treatment.
[0030] In some examples, the thermal treatment may be done through a continuous process. For example, the thickness adjusted slurry may be moved by a conveyor device through a temperature-controlled oven (single stage or multi-staged oven), where the temperature-controlled oven may have a temperature profile that is adapted by a controller (not shown). In some examples the temperature profile is a single temperature and elapsed time at that single temperature. In other examples, the temperature profile is multi-staged with different elapsed times at different temperature (e.g., a ramped heating up period, immersion at temperature, and ramped cool-down period).
[0031] An example continuous process may adjust various parameters in a heating system such as temperature, heating profile, speed, cooling profile, air flow volume and/or rate, and any other parameters that may control the humidity and/or heating to achieve a desired result of a cured material with a prescribed moisture content level (e.g., the residual humidity of the material). The output of the thermal treatment may be improved by tight control of the humidity. In various examples, a microwave device may be used to control one or more of temperature and humidity. It may be desirable to continuously monitor the temperature and/or humidity levels to effect control of the residual humidity in the continuous thermal treatment process. In some examples, one or more sensors may be used to detect the humidity at appropriate points in the process. In some examples, a Near Infra-Red (NIR) sensor may be utilized to provide a non-contact measurement of humidity and/or temperature. In some other examples, a radio-isotope sensor may be used to detect humidity and/or temperature. The NIR sensor or the radio-isotope sensor may be employed to facilitate control of the humidity and/or temperature through an in-line system that adaptively controls the process parameters.
[0032] In some examples, the thermal treatment may be done by a discontinuous process. In a discontinuous process, the humidity may be controlled by a loss weight percentage with respect to a fully dried geopolymer. The humidity may be measured by weighing the support along with the slurry, drying the support and the slurry in an oven for several hours (in general, the time is a function of the final humidity) and then weighing again.
[0033] In an example thermal treatment, the immersion temperature for the thickness adjusted slurry material may be set in a range of about 80°C to about 250°C. In some other examples, the immersion temperature may be in any other appropriate range such as from about 100°C to about 150°C, about 100°C to about 200°C, about 130°C to about 190°C, etc. In some examples, the air flow rate and/or volume may be varied to adjust the drying speed of the thickness adjusted slurry and to acheive the desired amount of residual humidity. In some examples, the optimal humidity of the dried slurry may be in a range of about 8 wt% to about 11 wt%; or alternatively in a range of about 5 wt% to about 10 wt%, for example.
[0034] Block 106 may be followed by block 108, where the dried material may be detached from the support. In some examples, the support may be a Sappie® paper; a Coveme® film; or some other suitable sheeted material. The Sappie® paper may have a better thermal resistance than the Coveme® film. In various examples, the Sappie® paper may be reused after the dried material is detached.
[0035] Block 108 may be followed by block 110, where the detached dried material may be milled to form the geopolymer powder. The dried material may be milled by any appropriate mill device that provides a suitable particle size. In some examples, the dried material may be ground by ajar mill. In various examples, the dried material may be ground by a ball mill. In some examples, the geopolymer thus formed may have a particle size in a range of about 1 micron to about 300 microns; or another range from about 10 microns to about 100 microns, for example. The detached material may be moved to the mill device by a conveyor device such as a belt conveyor, and/or a hopper- based conveyor, for example. In various examples, the particle size of the geopolymer may result in specific properties, such as porosity, finish, and mechanical strength of the geopolymer. Thus, the final properties of the geopolymer may depend on the particle size and the residual humidity.
[0036] FIG. 2 is a schematic representation of a system 200 for synthesizing a geopolymer that is arranged in accordance with at least some embodiments described herein. The described system 200 may include multiple devices such as a mixer 202, a tape casting machine 204, a hot air furnace 206, and a mill 208.
[0037] A controller (not shown), may be utilized to coordinate the operation of system 200, such as via machine executable instructions that when executed by a processor (e.g., a micro process, micro-controller, DSP, or other processor) in the controller coordinate the operation of each of the devices for specified times, temperatures, and other process-based parameters for the devices. Thus, each of the described devices in system 200 may be configured and operated in response to signals (e.g., analog or digital signals) from the controller. Additionally, conveyance systems (not shown) such as conveyor belts, hoppers, and other robot operated conveyors may be utilized, configured, operated or otherwise operated responsive to the controller, to transfer between the various devices. Sensors (not shown) may be arranged in communication with the controller, which can be utilized to monitor processing parameters such as mixing temperature, mixing speed, conveyor speed, heating, immersion and/or cooling temperature, air flow volume and/or rate, moisture or humidity levels, as well as other process parameters described herein.
[0038] In some example configurations, the mixer 202 may be configured to mix materials 211 (sodium silicate solution and metakaolin) to form a slurry 212. The choice of the mixer 202 may depend on the quantities and the metakaolin powder used to make the geopolymer slurry. In some examples a mixer with a mechanical stirrer may be used. In some examples, a mixer having dispersant tools may be used. In various examples, sodium silicate solution and metakaolin may be mixed at a speed of about 800 rpm, but other mixing speeds may be suitable as previously described above. In some examples, sodium silicate solution and metakaolin may be mixed for about 10 min. [0039] A pre- weighed slurry 212 along with a support may be placed in a tape casting machine 204 and may be cast to form a tape cast slurry on the support 213 (for example, paper).
The slurry 212 may be transported from the container of the mixer device to holding tanks and/or from holding tanks to the tape casting machine 204 via pipes, feed devices, and/or hopper devices. The tape-casting machine is configured to cast the material at a temperature in a range of about 80°C to about 250°C, or any other appropriate casting temperature. In one example, the slurry may be cast on a paper sheet material. In another example, the slurry may be cast on a plastic film material. In some examples, the slurry may be cast on a steel sheet material. In one example,
Sappi® paper may be used as a support. In another example, Coveme® film may be used as a support. The choice of the support 213 may depend on the tipology of the process parameters. A blade 217 may be used to regulate the thickness of the slurry on the support 214 as the support 213 is rolled along the tape casting machine 204 In some examples, the thickness of the deposited slurry by the wheels 215. The thickness of the slurry may be, for example, in a range of about 0.1 mm to about 2.0 mm; in a range of about 0.3 mm to about 1.0 mm; or in any other desired thickness level that may be reasonably appropriate.
[0040] The tape cast slurry along with the support 213 may be transferred, via a conveyor device (wheels 215), to an oven device such as a hot air furnace 206. The tape cast slurry along with the support 213 may be subjected to a thermal treatment in the hot air furnace 206 to obtain a dried material 216. The tape cast slurry along with the support may be subjected to the thermal treatment to cure and dry the slurry to obtain a thin film or a sheet of the dried material 216. The thickness of the thin film or sheet of the dried material 216 may be a function of the thickness of the slurry cast on the support.
[0041] In some examples, the thermal treatment may be done through a continuous process. For example, the slurry may be moved by a conveyor device through a temperature-controlled furnace (single stage or multi-staged oven), where the temperature-controlled furnace may have a temperature profile that is adapted by a controller (not shown). In some examples the temperature profile is a single temperature and elapsed time at that single temperature. In other examples, the temperature profile is multi-staged with different elapsed times at different temperature (e.g., a ramped heating up period, immersion at temperature, and ramped cool-down period).
[0042] An example continuous process may adjust various furnace parameters such as temperature, heating profile, speed, cooling profile, air flow volume and/or rate, and any other parameters that may control the humidity and/or heating to achieve a desired result of a cured material with a prescribed moisture content level (e.g., the residual humidity of the material). The output of the thermal treatment may be improved by tight control of the humidity. In various examples, a microwave device may be used to control one or more of temperature and humidity. It may be desirable to continuously monitor the temperature and/or humidity levels to effect control of the residual humidity in the continuous thermal treatment process. In some examples, one or more sensors may be used to detect the humidity at appropriate points in the process. In some examples, a Near Infra-Red (NIR) sensor may be utilized to provide a non-contact measurement of humidity and/or temperature. In some other examples, a radio-isotope sensor may be used to detect humidity and/or temperature. The NIR sensor or the radio-isotope sensor may be employed to facilitate control of the humidity and/or temperature through an in-line system that adaptively controls the process parameters.
[0043] In some examples, the thermal treatment may be done by a discontinuous process. In a discontinuous process, the humidity may be controlled by a loss weight percentage with respect to a fully dried geopolymer. The humidity may be measured by weighing the support along with the slurry, drying the support and the sample in an oven for several hours and then weighing it again.
[0044] In an example thermal treatment, the immersion temperature for the thickness adjusted slurry material may be set in a range of about 80°C to about 250°C. In some other examples, the immersion temperature may be in any other appropriate range such as from about 100°C to about 150°C, about 100°C to about 200°C, about 130°C to about 190°C, etc. In some examples, the air flow rate and/or volume may be varied to adjust the drying speed of the thickness adjusted slurry and to acheive the desired amount of residual humidity. In some examples, the optimal humidity of the dried slurry may be in a range of about 8 wt% to about 11 wt%; or alternatively in a range of about 5 wt% to about 10 wt%, for example.
[0045] The dried material 216 may be detached from the support 213. In some examples, the support 213 may be a Sappie® paper. In various examples, the support may be a Coveme® film. The Sappie® paper may have a better thermal resistance than the Coveme® film. In some examples, the Sappie® paper may be reused as a support after the dried material is detached.
[0046] The dried material 216 may be milled in a mill 208 to form the geopolymer powder 218. In some examples, the mill 208 may be ajar mill. In various examples, the mill 208 may be a ball mill. In some examples, the geopolymer 218 thus formed may have a particle size in a range of about 1.0 micron to about 300 microns; or another range from about 10 microns to about 100 microns, for example. The detached material may be moved to the mill device by a conveyor device such as a belt conveyor, and/or a hopper-based conveyor, for example. In various examples, the particle size of the geopolymer may result in specific properties, such as porosity, finish, and mechanical strength of the geopolymer 218. Thus, the final properties may depend on the particle size and the residual humidity of the geopolymer 218.
[0047] The small particle size of the geopolymer may have benefits in brake friction material applications. For example, the small particle size may reduce or eliminate cracks in the friction material that is made using the disclosed geopolymer. The friction material including the disclosed geopolymer may also facilitate brake materials with a uniform surface profile. Further, the smaller geopolymer particles may improve the adhesion between the friction material and an under-layer that are used to make a brake pad.
[0048] The controller in the above illustrated systems, methods and devices may be of any variety of controller device that is adapted for use in the described embodiments. The controller in one example can be a thermostat device. In another example the controller can be an analog electronic circuit, a digital electronic circuit, or a mixed analog/digital electronic circuit. In still other examples, the controller can be a processor based device such as a micro-processor, micro controller, DSP controller, or some other variety of device that is configured by machine executable instructions to configure and operate the machines to follow the desired recipe for manufacturing geopolymer particles.
[0049] In some examples, combinations of multiple controllers can also be utilized, where each manufacturing device has its own local controller, and a master controller collectively configures each of the local controllers to follow the desired recipe. For example, a mixer device could have a local controller that adapts the mixing speed of the mixer device; while the tape casting machine has its own local controller to adapt the casting thickness, furnace temperature profile, conveyance speed, etc.; and a master controller would instruct each of the local controllers to utilize the specified recipe for manufacturing a specific geopolymer.
[0050] FIG. 3 is a graph 300 illustrating a variation of viscosity of a geopolymer with shear rate. In graph 300, vertical axis 302 represents viscosity (cP) and horizontal axis 304 represents shear rate (s 1). In graph 306, the viscosity of the geopolymer decreases from 100000 cP to 1000 cP as the shear rate increases from 0.1 to 1000 s 1. The graph shows typical pseudoplastic behavior required for a tape casting process in order to have a viscosity, which changes as a function of the stress and the shear rate, permitting to have a low viscosity and an easy mixing step for high shear rate, and at the same time a high viscosity for low shear rate when the slurry is cast and formed to a sheet on the support material, in order to maintain the shape.
[0051] FIG. 4 is a graph 400 illustrating geopolymer content (wt%) as a function of particle size (pm) and residual humidity (wt%). The vertical axis 402 represents particle size (pm) and the right side horizontal axis 404 represents geopolymer content (wt%) and the left side horizontal axis 406 represents humidity (wt ). The graphs 408, 410, and 412 show different residual humidity characteristics of varying version of the geopolymer materials. As shown, graph 408 has a residual humidity of about 10.5 wt%, while graph 410 has a residual humidity of about 9 wt% and graph 412 has a residual humidity of about 8 wt%. As shown, the resulting particle sizes that can be achieved for these residual humidity’s varies based on the geopolymer content. As demonstrated by this graph, the binder properties of the geopolymer particles (e.g., in a dried powder form) can be tuned by varying the granularity (e.g., particle size) and the residual humidity of the powder.
[0052] FIG. 5 is a graph 500 illustrating variation of wear of two friction materials as a function of temperature. In graph 500, vertical axis 502 represents the wear of the friction materials and horizontal axis 504 represents the temperature in (°C). The graph 506 represents variation of the wear of the friction material having a geopolymer of a particle size greater than 300 microns with temperature. In graph 506, the wear increases from 0.31 to 0.52 as the temperature increases from 50 °C to 200 °C and then decreases to 0.41 at 400 °C. The graph 508 represents variation of the wear of the friction material having a geopolymer of a particle size lesser than 150 microns. In graph 508, the wear increases from 0.21 to 0.31 as the temperature increases from 50 °C to 300 °C and then remains constant at 0.31. It is evident from these graphs that the wear of the friction material having a geopolymer of a particle size less than 150 microns is lesser than that of the friction material having a geopolymer of a particle size greater than 300 microns. This confirms that the smaller the particle size of the geopolymer, the greater the reduction in wear of the friction material.
[0053] FIG. 6 is a graph 600 illustrating variation of wear of two brake pads as a function of temperature. In graph 600, vertical axis 602 represents the wear of the brake pads and horizontal axis 604 represents the temperature in (°C). The graph 606 represents variation of the wear of the brake pad having a geopolymer of a particle size less than 150 microns with temperature. In graph 606, the wear increases from 0.6 to 1 as the temperature increases from 50 °C to 200 °C and then increases to 8.3 at 400 °C. The graph 608 represents variation of the wear of the brake pad having a geopolymer of a particle size greater than 300 microns with temperature. In graph 608, the wear decreases from 5 to 1 as the temperature increases from 50 °C to 200 °C and then increases to 8.3 at 400 °C.
EXAMPLES
[0054] The following examples are intended as illustrative and non-limiting and represent specific embodiments of the present disclosure. The examples show that the disclosed geopolymers are substantially free of phenolic resins. In addition, the examples demonstrate that the friction materials are synthesized using the disclosed geopolymers. Further, the examples demonstrate that the brake pads including the disclosed friction materials have a high hardness, compressibility and detach.
Example 1 Mixing
[0055] 1 OOOg of metakaolin Imerys Argical™ Ml 200s was mixed with 2731 g of Ingessil® sodium silicate solution. The mixture was stirred in a lab mixer at about 800 RPM for about 10 min. to form a slurry.
Example 2 Tape casting
[0056] The slurry of Example 1 was transported in pipes from tanks on to the Sappie® paper in the tape casting machine and cast at a temperature in a range from about 15°C to about 40°C (room temperature). The thickness of the resulting slurry was about 0.3 mm.
Example 3
Drying and detaching
[0057] The slurry spread on the Sappie® paper was heated in a hot air furnace at a temperature in a range from about 120°C to about 200°C under air flow. The humidity of the slurry was continuously monitored using an NIR sensor and the slurry was heated until the humidity reached 6-10 wt% to form a dried material. The dried material was then detached from the Sappie® paper.
Example 4 Milling
[0058] The dried and detached slurry was milled in ajar mixer for about 10 hours or in a ball milling machine for about 30 min. The particle size of the resulting powder had a diameter in a range from about 1 micron to about 300 microns.
[0059] The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, are possible from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.
[0060] The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. Such depicted architectures are merely examples, and in fact, many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality may be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermediate components. Likewise, any two components so associated may also be viewed as being "operably connected", or "operably coupled", to each other to achieve the desired functionality, and any two components capable of being so associated may also be viewed as being "operably couplable", to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically connectable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components. [0061] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
[0062] In general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation, no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, means at least two recitations, or two or more recitations).
[0063] Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general, such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
[0064] For any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non- limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, a range includes each individual member. Thus, for example, a group having 1 -3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth.
[0065] While various aspects and embodiments have been disclosed herein, other aspects and embodiments are possible. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

CLAIMS WHAT IS CLAIMED IS:
1. A method for synthesizing a geopolymer, the method comprising: mixing a silicate solution and metakaolin to form a slurry; spreading the slurry on a support to form a slurry film; subjecting the support and the slurry film to a thermal treatment, wherein the thermal treatment dries the slurry to form a dried material with a residual humidity in a range of about 0 wt% to about 20 wt%; detaching the dried material from the support; and milling the dried material to obtain a geopolymer with a particle size in a range of about 1 micron to about 300 microns.
2. The method of claim 1 , wherein mixing the silicate solution and metakaolin comprises mixing in a weight ratio of about 3:1.
3. The method of claim 1, wherein mixing the silicate solution and metakaolin comprises mixing at a speed from about 500 rom to about 1000 rpm and for an elapsed time in a range from about 1 minute to about 20 minutes.
4. The method of claim 1 , mixing the silicate solution and metakaolin comprises mixing at a temperature in a range from about 20 °C to about 40°C.
5. The method of claim 1, wherein spreading the slurry on a support comprises spreading the slurry on a paper, a plastic film or a steel sheet.
6. The method of claim 1, wherein spreading the slurry on a support comprises spreading the slurry on the support to obtain a thickness of the slurry in a range of about 0.1mm to about 2 mm.
7. The method of claim 6, wherein spreading the slurry on a support comprises spreading the slurry on the support at room temperature.
8. The method of claim 1, wherein subjecting the support and the slurry to a thermal treatment comprises subjecting the support and the slurry to either a continuous or discontinuous thermal treatment.
9. The method of claim 1, wherein subjecting the support and the slurry to a thermal treatment comprises heating the support and the slurry while monitoring humidity in-line with a near infrared light (NIR) sensor.
10. The method of claim 1, wherein subjecting the support and the slurry to a thermal treatment comprises heating the support and the slurry while monitoring humidity in-line with a radio isotope sensor.
11. The method of claim 1, wherein subjecting the support and the slurry to a thermal treatment comprises weighing the support along with the slurry, drying the support and the slurry in a hot air furnace, and then weighing the support along with the slurry again.
12. The method of claim 1, wherein subjecting the support and the slurry to a thermal treatment comprises heating the support and the slurry to a temperature in a range of about 80°C to about 200°C for an elapsed time in a range of about 5 min to about 30 min.
13. The method of claim 1, wherein detaching the dried material from the support comprises detaching the dried material from the support having a thermal resistance of in a range of about 150°C to about 300°C.
14. The method of claim 1, wherein milling the dried material to obtain a geopolymer comprises milling in ajar mill, a ball mill, or an impact mill.
15. A system for synthesizing a geopolymer, the system comprising: a mixer machine configured to form a slurry from a mixture of an alkali silicate solution and metakaolin; a casting machine configured to cast the slurry on a support; a hot air furnace configured to thermally treat the slurry on the support to form a dried material, wherein the dried material has a humidity in a range of about 0 wt% to about 20 wt%; and a mill machine configured to mill the dried material to obtain a geopolymer with a particle size in a range of about 1 micron to about 300 microns.
16. The system of claim 15, further comprising a jacket device configured to circulate water to control a temperature of the mixture of the mixture machine.
17. The system of claim 15, wherein the mixer machine has a mechanical stirrer with one or more dispersant tools.
18. The system of claim 15 further comprising a controller device, wherein the controller device is configured to coordinate the operation of one or more of the mixer machine, the casting machine, the hot air furnace and the mill machine.
19. A system for synthesizing a geopolymer, the system comprising: a means for forming a slurry from a mixture of an alkali silicate solution and metakaolin; a means for casting the slurry on a support; a means for thermally treating the slurry on the support to form a dried material with a residual humidity in a range from about 0 wt% and about 20 wt%; and a means for milling the dried material to obtain a geopolymer with a particles size with a diameter in a range of about 1 micron to about 300 microns.
20. The system of claim 19, further comprising a means for controlling the operation of one or more of the means for forming the slurry, the means for casting the slurry, the means for thermally treating the slurry, and the means for milling the dried material.
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