Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/12—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the method of spraying
  • C23C4/134—Plasma spraying
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  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
  • C04B35/48—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on zirconium or hafnium oxides, zirconates, zircon or hafnates
  • C04B35/486—Fine ceramics
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  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/62222—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products obtaining ceramic coatings
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  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/04—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the coating material
  • C23C4/10—Oxides, borides, carbides, nitrides or silicides; Mixtures thereof
  • C23C4/11—Oxides
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
  • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
  • C04B2235/3224—Rare earth oxide or oxide forming salts thereof, e.g. scandium oxide
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
  • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
  • C04B2235/3224—Rare earth oxide or oxide forming salts thereof, e.g. scandium oxide
  • C04B2235/3225—Yttrium oxide or oxide-forming salts thereof
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
  • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
  • C04B2235/3224—Rare earth oxide or oxide forming salts thereof, e.g. scandium oxide
  • C04B2235/3227—Lanthanum oxide or oxide-forming salts thereof
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
  • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
  • C04B2235/3224—Rare earth oxide or oxide forming salts thereof, e.g. scandium oxide
  • C04B2235/3229—Cerium oxides or oxide-forming salts thereof
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/50—Constituents or additives of the starting mixture chosen for their shape or used because of their shape or their physical appearance
  • C04B2235/54—Particle size related information
  • C04B2235/5418—Particle size related information expressed by the size of the particles or aggregates thereof
  • C04B2235/5436—Particle size related information expressed by the size of the particles or aggregates thereof micrometer sized, i.e. from 1 to 100 micron
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/50—Constituents or additives of the starting mixture chosen for their shape or used because of their shape or their physical appearance
  • C04B2235/54—Particle size related information
  • C04B2235/5418—Particle size related information expressed by the size of the particles or aggregates thereof
  • C04B2235/5445—Particle size related information expressed by the size of the particles or aggregates thereof submicron sized, i.e. from 0,1 to 1 micron
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/50—Constituents or additives of the starting mixture chosen for their shape or used because of their shape or their physical appearance
  • C04B2235/54—Particle size related information
  • C04B2235/5418—Particle size related information expressed by the size of the particles or aggregates thereof
  • C04B2235/5454—Particle size related information expressed by the size of the particles or aggregates thereof nanometer sized, i.e. below 100 nm
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
  • C04B2235/74—Physical characteristics
  • C04B2235/76—Crystal structural characteristics, e.g. symmetry

Definitions

• the invention relates to a suspension for the preparation of a feedstock for suspension thermal spraying.
• suspensions for thermal spray processing to generate coatings
• Suspension plasma spraying is described detailed further in patent application US2006/222777A1 , now abandoned.
• Suspension spraying was developed to allow nanometric, sub-micron or micrometric powder materials to be fed into a thermal spray torch that would not otherwise be possible using conventional dry powder feeding methods.
• the technique has shown to be capable of generating coating microstructures that are not possible to achieve using traditional dry powder spraying.
• a suspension is fed into a thermal spray torch either radially or axially.
• This is commonly a plasma torch but may also include combustion torch systems such as high velocity air or oxy-fuel systems.
• the suspension is atomized either by the interaction of the suspension stream with the plasma or combustion gas jet. Alternatively, it may be atomized prior to injection into the jet using the injector system itself.
• Within the hot jet further fragmentation and atomization of the suspension droplets occurs with the solvent being evaporated.
• Final droplets may contain individual solid particles or small clusters of agglomerates. These are subsequently melted or made semi-molten by the process heat within the jet. The droplets are meanwhile accelerated towards a target substrate to be coated. Coating microstructures produced depend greatly on the size of the particles, their momentum and temperature upon interacting with the substrate.
• Control of suspension parameters as well as thermal spray processing parameters can generate a large range of microstructures from practically completely dense to columnar and porous microstructures.
• Choice of coating structure is made dependent on the application and coating performance requirements.
• the critical step in the process is the injection of the suspension into the heat source and its fragmentation into its final droplet size.
• This final droplet size is influenced greatly by the behavior of the suspension in terms of its viscosity, surface tension and density. These parameters are dependent on the solvent, the particles, the particle size distribution and the solid content of the suspension. Heating and evaporation behavior of the solvent phase also has a bearing on energy input requirement for spraying appropriate microstructures.
• the process is so sensitive that deviations in suspension properties can adversely influence the coating produced and its performance.
• the suspension For spraying the suspension requires a viscosity in the range 1-100 mPa*s at high shear rates in the region of 100-1000 s -1 .
• the viscosity should be at the lower end of the range.
• Suspensions in this range have been demonstrated to function well in suspension plasma spraying (SPS) deposition.
• suspensions have been used in industry for decades as part of many industries.
• An example of suspensions used for slip or tape casting is disclosed in WO96/06811A2 , wherein a ceramic suspension is used to prepare a green body ceramic part for further processing.
• the suspension is designed to be a Bingham fluid, in that the slurry will not flow until a specific force is applied.
• Such slurries are used at solids loading of 30% for particles around 500 nm in diameter and a viscosity level around 3000 mPa ⁇ s.
• Suspensions with high content of solids are also known from the field of spray drying for production of granulated powders.
• Suspensions for spray drying and production of granulate powders are used at a solid loading level of 50-55%, though in some instances up to 80%. Examples for such suspensions are described in the article " Spray dried ceramic powders: A quantitative correlation between slurry characteristics and shapes of the granules" by G. Bertrand in the journal “Chemical Engineering Science” 60 (2005) 95 - 102 . There, flocculated slurries and dispersed slurries at 50 wt% solid content are disclosed.
• suspensions are not considered to be stable in terms of long term storage due to settling of the particles (in case of the dispersed slurry) or the flakes (in case of the flocculated slurry).
• a typical spray drying suspension may have a viscosity in the low shear range of 50-500 Pas, depending on its formulation.
• a suspension for the use in suspension plasma spraying is described in US 2020/0048752A1 .
• the disclosed suspension has a solid content of 10 to 45 wt %, a viscosity of less than 15 mPa*s and is reported to have a settling velocity of at least 50 ⁇ m/s (at least 1576.8 m/year).
• a suspension for suspension thermal spraying which is disclosed in WO2022/0214553A1 .
• a suspension comprising solid ceramic particles and a solvent is described, wherein the fine fraction ratio of said suspension is 0.5 or lower.
• the density of the ceramic particles is between 3.0 and 7.0 g/cm 3 and the particles are characterized by having a volume based d 50 value ranging from 2 ⁇ m to 10 ⁇ m.
• WO20222/14556A1 describing a suspension for suspension thermal spraying comprising solid ceramic particles having an average particle size of 2 ⁇ m or below and a liquid phase comprising an organic solvent.
• the organic solvent is characterized by having a flashpoint of at least 60 °C and at most 400 °C.
• the suspension has a viscosity of below 20 mPa*s, wherein the concentration of said solid ceramic particles in said suspension ranges from 5 wt% to 95 wt%.
• Viscosity As mentioned above, for being able to be sprayed in the suspension plasma spraying process, i.e., to be "ready to use", the viscosity of the suspension has to be in a range of 1 to 100 mPa*s in the range of a shear rate of 100 to 1000 s -1 . This shear rate range correlates with the shear rate of a pipe flow when a suspension is pumped from the feeder to the spray torch. If the viscosity is higher, the possibility of clogging increases. This problem is addressed in the prior art by using appropriate dispersants to lower the viscosity and/or by lowering the solid content to obtain a viscosity in the desired range.
• the suspension can be re-dispersed by using expensive high energy mixing equipment or by using low energy mixing equipment like low speed stirrers, roller mills or container shakers.
• the disadvantages of these mixing techniques are the high costs of the equipment, abrasion of the mixing tools, the long time of preparation to re-disperse the settled particles and the limitation of the slurry volumes that can be prepared with these techniques.
• a further existing problem is that a suspension container can leak during transport and storage. Leaking can be caused by damages to the container wall by high external forces, bursting of the container walls by internal forces due to over pressure caused by high temperatures or the unintentional formation of gases due to chemical reactions inside the container. Another common source of leaking is when the lid is not closed correctly. Leaking suspension exposes the environment to the possible harmful nature of suspensions that can cause a risk for health and safety, damage to the surroundings for e.g., by corrosion and/or at least pollution that causes costs for cleaning.
• Non-dispersed slurries show a very high tendency to end up with agglomerated particles.
• Especially powders produced by the spray drying technique contain agglomerates in a large extent.
• Agglomerates increase the possibility to clog the pipes and spray torches and agglomerates influence the coating structure because of their larger particle size compared with the primary particles. So it becomes difficult to achieve the same coating quality from coating step to coating step.
• Agglomerates can be removed by mechanical dispersion, but it is a further step the skilled person wishes to avoid.
• a particular feedstock for suspension thermal spraying processes are ceramic particles comprising of or consisting of zirconia (ZrO 2 ), stabilized zirconia and mixed metal oxides containing zirconium as one of the metallic components.
• zirconia ceramic particles will be abbreviated as "zirconia ceramic particles”.
• the object of the present invention is solved by a suspension for the preparation of a feedstock for suspension thermal spraying comprising
• suspension containing zirconia ceramic particles that are storable for a longer period of time can be easily transported, and fulfill the above discussed requirements, can be obtained.
• the suspension of the present invention thus contains a continuous phase and homogeneous distributed particles.
• the separated particles form a homogeneous network in that they are "frozen" in the formed network.
• This suspension can then be shipped or stored without concerns for changes in suspension behavior.
• the suspension can easily be transformed to a ready-to-use (RTU) suspension with low viscosity and stabilized primary particles by merely adding a dispersant.
• RTU ready-to-use
• This separated particles network suspension can be shipped or stored at lower risks for health and safety in situations when a suspension container is accidentally damaged or not fully closed since leaking is prevented or at least reduced.
• suspension thermal spraying refers to the use of a suspension as a feedstock in a thermal spraying process, including plasma spraying (such as atmospheric plasma spraying and low pressure plasma spraying), high-velocity oxy-fuel spraying, high-velocity air-fuel spraying, flame spraying, cold spraying, laser spraying or laser cladding.
• plasma spraying such as atmospheric plasma spraying and low pressure plasma spraying
• high-velocity oxy-fuel spraying high-velocity air-fuel spraying
• flame spraying flame spraying
• cold spraying cold spraying
• laser spraying laser cladding
• the suspension according to the present invention is used in suspension plasma spraying and low pressure plasma spraying and high velocity oxy fuel spraying, most preferably in suspension plasma spraying, specifically in atmospheric suspension plasma spraying.
• rare earth metal refers to the group of 17 chemically similar metallic elements including the lanthanides, yttrium and scandium.
• the lanthanides are defined as the series of elements with atomic numbers 57 to 71, all of which, except promethium, occur in nature ( Gupta, C. K., & Krishnamurthy, N. (2005). Extractive metallurgy of rare earths. Boca Raton, Fla, CRC Press ).
• stabilized ZrO 2 refers to the stabilization of the tetragonal and/or cubic crystal structure of zirconium dioxide by the addition of at least one dopant, preferably a rare earth oxide. Stabilization of the cubic polymorph of zirconia over wider range of temperatures is accomplished by substitution of the Zr 4+ ions in the crystal lattice with larger ions of rare earth oxides, e.g., those of Y 3+ .
• the concentration of the solid ceramic particles in the suspension ranges from 55 wt% to 95 wt%.
• Concentration can be measured by a halogen moisture analyzer, such as Halogen Moisture Analyzer HR83 (Mettler-Toledo, USA) at a temperature of 110°C. Between 1 and 4 grams of the suspension are used for the measurement.
• the suspension of the present invention has a viscosity in the range of 50-10000 Pa*s at a shear rate of 0.1 s -1 .
• This is a much higher viscosity than the viscosity suitable for a ready-to-use suspension.
• Viscosity is measured for such suspension systems using a plate-plate Rheometer, Physica MCR 301 (Anton Paar, Graz, Austria), where the plate to plate gap is set at 0.5 mm and shear rate may be varied in a range 0.01 to 1000 s -1 .
• the shear rate is adjusted to 0.1 s -1 .
• the high viscosity generated by the networked structure provides high stability to the suspension reducing settling of the suspension to negligible levels.
• the defined particle radius may refer to the average particle size for the suspension product as identified via particle size distribution.
• Particle size distribution may be determined using a variety of techniques; however for the purpose of this invention the particle size is determined for the suspension using a laser diffraction system Microtrac X100 or more recent S3500 system (Microtrac GmbH, Krefeld, Germany).
• the beam of the laser is scattered by the particles of the sample, and the angle of light scattering is inversely proportional to particle size.
• the particle size distribution is typically determined in intervals ("boxes").
• the suspension is prepared by the following procedure: 5 ml of the suspension was mixed with 5 ml of pure solvent (water deionized in the case of water based suspensions and ethanol in the case of ethanol based suspensions) by hand. 1-2 droplets of the so prepared suspension were taken into the measurement chamber. The following parameters are used: analysis mode: Fraunhofer, refractive index of 1.33, flow rate of 70% and without ultrasonic power.
• the d 50 value is to be understood as the "average particle size” and is determined from the particle size distribution.
• the d 50 value is known as median diameter or medium value of the particle size distribution, being determined from a volume-based representation or from a number based representation.
• all "d x " values refer to the volume-based representation, i.e. the particle diameter at "x" vol% in the cumulative distribution (e.g. a d 50 of 5.0 nm means that 50 vol% of the particles have a smaller diameter than 5.0 nm).
• the suspension of the present invention contains solid phase particles with a d 50 value in the range from 5 nm to 20 ⁇ m, preferably between from 30 nm to 15 ⁇ m, more preferably between from 45 nm to 12 ⁇ m.
• the density of the particles and of the solvent in the suspension are important properties for achieving the preferred settling velocity.
• the density of the ceramic particles in said suspension may be determined by a gas pycnometer (Ultrapyc 1200e) after drying the suspension.
• the following parameters for measurement are used: Cell size "medium”, measurement is performed at room temperature.
• the density of the solvent in said suspension may be determined gravimetrically using a graduated measurement cylinder and a laboratory balance. To perform the measurement, particles and solvent of said suspension can be separated before determining the density of the solvent.
• the used volume of the solvent is approximately 100 ml.
• Solids loading may be considered a critical factor for a separated particles network non-settling suspension. Solids loading is commonly expressed as weight percent of solids in the liquid phase. This may be measured using a Halogen Moisture Analyzer such as the HR83 (Mettler-Toledo, USA) at a temperature of 110°C.
• the suspension of the present invention has a zeta potential of between +15 mV and -15 mV, more preferred between +10 mV and -10 mV.
• the zeta potential of the suspension depends on the nature of the solvent and the solid particles.
• the zeta potential is an expression for the potential difference present between the liquid medium and the stationary double layer of fluid attached to the particle surface.
• Zeta potential is a measure of the degree of electrostatic repulsion available between particles in the suspension and therefore a measure of stability. High charge (either positive or negative) will result in repulsion of particles and stability to coagulation or flocculation.
• Zeta potential may be measured by electroacoustic equipment such as the DT310, by covering the sensor with approx. 5 mm suspension for the measurement.
• the electroacoustic sensor which is built as probe measures the zeta potential upon contact with the sample. Electroacoustic techniques have the advantage of being able to perform measurements in intact samples, without dilution.
• streaming potential measurement and electrophoresis may require dilution of the sample. Dilution might affect the properties of the sample and change the zeta potential.
• Streaming potential is typically used for the determination of the zeta potential of larger particles (diameter >25 ⁇ m) and electrophoretic methods like electrophoretic light scattering are often applied for measuring the zeta potential of particles with a diameter of up to 100 ⁇ m.
• the suspension is substantially free of agglomerates.
• Agglomerates are loosely bound grains that can be separated by medium sheer forces (stirring, ultrasonic). They are bound together by intermolecular forces such as van der Waals or dipole-dipole forces (Ho, C.A. (2004). Modelltechnisch der Prismagglomeration imargues des Euler-Lagrange-Verfahrens und für für Betician der Staubabscheidung im Zyklon).
• the suspension By virtue of the suspension essentially being free of agglomerates, the suspension can be converted into a ready-to-use suspension also containing no agglomerates and, thus, being perfectly suitable to be employed in a suspension thermal spraying process. Especially no high energy mixing equipment or long time mixing to prepare the ready-to-use suspension for thermal spraying is needed.
• the agglomerates in the suspension are analyzed by measuring the particle size with a laser diffraction system Microtrac S3500 system (Microtrac GmbH, Krefeld, Germany). The measurement is done as described above but without using ultrasonic or a dispersant or any other method/addition that could influence the measurement of the agglomerates.
• analysis mode Fraunhofer
• particle transparency transparent
• refractive index for water of 1.33 flow rate of 70%.
• the volume-based size distribution of the particles in suspension is ideally unimodal (i.e. no agglomerates at all are present). Realistically, a fully unimodal size distribution is difficult to achieve.
• the term "essentially free” as used herein also encompasses bimodal volume-based size distributions with one main peak around the d 50 value, wherein one further peak at sizes larger than the d 50 value may be present but represents not more than 10 vol.% of all the particles.
• Unimodal refers to a single clearly discernable peak on a particle size distribution curve (e.g., weight percent, volume percent or intensity on the ordinate or Y-axis, and particle size on the abscissa or X-axis).
• An unimodal particle size distribution is distinct from a bimodal particle size distribution which refers to two clearly discernable peaks on a particle size distribution curve.
• a bimodal particle size distribution curve exhibits two peaks wherein one peaks may even exist as a hump, shoulder or tail relative to the other peak.
• the suspension according to the present invention is essentially free of an additive capable of creating steric, electrostatic or electro-steric stabilization of the particles, such as an additive selected from the group consisting of a dispersant, an acid, a base, a deflocculant and a polyelectrolyte.
• an additive capable of creating steric, electrostatic or electro-steric stabilization of the particles, such as an additive selected from the group consisting of a dispersant, an acid, a base, a deflocculant and a polyelectrolyte.
• the particles comprise or consist of ZrO 2 , preferably stabilized by at least one rare earth oxide selected from the group consisting of Y 2 O 3 , Yb 2 O 3 , Gd 2 O 3 , Dy 2 O 3 , Er 2 O 3 , Eu 2 O 3 , CeO 2 , Pr 2 O 3 , Nd 2 O 3 , La 2 O 3 , Lu 2 O 3 , Hf 2 O 3 , Sm 2 O 3 , Tb 2 O 3 , Tm 2 O 3 , Ho 2 O 3 , Sc 2 O 3 and SrO, preferably said particles comprise ZrO 2 stabilized by Y 2 O 3 .
• rare earth oxide selected from the group consisting of Y 2 O 3 , Yb 2 O 3 , Gd 2 O 3 , Dy 2 O 3 , Er 2 O 3 , Eu 2 O 3 , CeO 2 , Pr 2 O 3 , Nd 2 O 3 , La 2 O 3 , Lu 2 O 3 , Hf 2 O 3 , Sm 2
• the zirconia may be present in the cubic or in the tetragonal phase, optionally stabilized by a primary stabilizing oxide as listed above.
• HfO 2 is often found as an additional, non-problematic impurity oxide.
• Examples of such oxides may be yttria-stabilized zirconia and dysprosia stabilized zirconia.
• the primary stabilizing oxide may be partially substituted by one or several secondary oxides selected (again) from the group consisting of Al 2 O 3 , TiO 2 , CaO, Y 2 O 3 , Yb 2 O 3 , Gd 2 O 3 , Dy 2 O 3 , Er 2 O 3 , Eu 2 O 3 , CeO 2 , Pr 2 O 3 , Nd 2 O 3 , La 2 O 3 , Lu 2 O 3 , Hf 2 O 3 , Sm 2 O 3 , Tb 2 O 3 , Tm 2 O 3 , Ho 2 O 3 , Sc 2 O 3 , and SrO.
• secondary oxides selected (again) from the group consisting of Al 2 O 3 , TiO 2 , CaO, Y 2 O 3 , Yb 2 O 3 , Gd 2 O 3 , Dy 2 O 3 , Er 2 O 3 , Eu 2 O 3 , CeO 2 , Pr 2 O 3 , Nd 2 O 3 , La 2 O 3 , Lu 2 O
• said solid ceramic particles comprises or consists of oxides with the pyrochlore or defect fluorite structure A 2 B 2 O 6 or A 2 B 2 O 7
• a site ions can consist of the ions Y, Yb, Gd, Dy, Er, Eu, Ce, Pr, Nd, La, Lu, Hf, Sm, Tb, Tm, Ho, Sc, or Sr.
• the B site ion comprises or preferably is Zr.
• Especially preferred oxides of this type are Gd 2 Zr 2 O 7 or La 2 Zr 2 O 7 .
• Compositions may include additional substitution of ions on the A and or B site with minor additions of ions from the rare earth group.
• said solid ceramic particles comprise or consist of oxides with perovskite structure ABO 3 where A site ions may be selected from the rare earth elements Y, Yb, Gd, Dy, Er, Eu, Ce, Pr, Nd, La, Lu, Hf, Sm, Tb, Tm, Ho, or Sc in addition to Sr.
• the B site ion comprises or preferably is Zr.
• a preferred oxide of this type is SrZrO 3 .
• doped compositions examples of which may be strontium zirconate co-doped with yttrium and ytterbium.
• said solid ceramic particles comprise or consist of ceramics with the rhombohedral structure A 4 B 3 O 12 , where A site ions may be one or a mixture of ions selected from the group consisting of Y, Yb, Dy, Er, Ce, Lu, Hf, Tb, Tm, Ho, Sc, and Sr.
• B site ions may be consisting of Zr, preferably Yb 4 Zr 3 O 12 .
• said solid ceramic particles comprise or consist of ceramics having a hexagonal structure A 3 B 4 O 12 , where A site ions may be one or a mixture of ions selected from the group consisting of Y, Yb, Gd, Dy, Er, Eu, Ce, Pr, Nd, La, Lu, Hf, Sm, Tb, Tm, Ho, Sc, and Sr.
• the B site ion comprises or preferably is Zr, A preferred oxide of this type is Zr 3 Sc 4 O 12 .
• suspensions may be manufactured with mixtures of oxide and non-oxide ceramics.
• the ceramic particles for the production of the suspension in accordance with the present invention can be produced by different routes such as precipitation and calcining, fusion and crushing, wet milling, sol gel processes, hydrothermal processes, emulsion detonation synthesis, solid state synthesis, synthesis from a gaseous phase or any other for an expert in the field of powder production.
• the preferred particle size can be adjusted with known methods in the art, for instance, by wet milling wherein particles in a suspension are dispersed in a liquid by shearing or crushing.
• wet milling is performed without dispersing agent.
• the ceramic particles of the present invention can be dried by spray drying. During spray drying, the suspension can be atomized and fluidized as known in the art.
• the suspension according to the present invention further comprises a liquid phase essentially consisting of a solvent.
• the difference in density between solid particle and solvent can be considered to have an influence on settling behavior. As the difference in density between the solid and liquid component is increased, the sedimentation rate will increase proportionally. Such situations would occur where higher density solids are utilized or lower density solvents are required.
• the density of the solvent in said suspension can be determined as described above.
• said solvent is selected from the group consisting of water, a monoalcohol, a ketone, a glycol, glycerol and any combination thereof.
• Solvents that may be a single compound of mixture of compounds commonly used as industrial solvents.
• said monoalcohol is selected from the group consisting of ethanol, methanol, iso-propanol propan-1-ol, butanol and any combination thereof.
• said solvent comprises a ketone, wherein said ketone is selected from the group consisting of methyl-ethyl ketone and methyl-isobutyl ketone and any combination thereof.
• said solvent comprises a glycol, wherein said glycol is selected from the group consisting of ethylene glycol, propylene glycol and diethylene glycol and any combination thereof.
• Solvents are selected according to the viscosity required in the transportation and spraying stages. The solvent is also determined by the need for low reactivity with the solid phase. In addition, further compounds may be added to the solvent for purpose of modifying fluid viscosity and or surface tension. These may be glycerol, polyethylene glycol or other long chain organic molecules known to the field.
• the particles and the solvent can be mixed together.
• agglomerates in the suspension can be destroyed by dispersion. It has been found that the presence of agglomerates can be further avoided by pumping the suspension formed through a wet mill at least once.
• the particle size distribution of the suspension prior dispersion can show a bimodal distribution due to the presence of agglomerates.
• the obtained suspension after wet milling is characterized by a monomodal particle size distribution and is essentially free of agglomerates.
• the particle size distribution of the primary particles remains constant before and after milling.
• the present invention is particularly useful for preparing a suspension for thermal spraying.
• the present invention is directed to the use of the suspension according to the present invention for preparing a ready-to-use suspension for thermal spraying.
• the use of the separated particles network suspension in a direct to spray processing enables higher solid contents and therefore higher throughputs in the thermal spray process.
• Higher solid content in the suspension is possible when the dispersant is added, viscosity of the suspension is reduced to the suitable range for spraying of coatings without the need of diluting.
• the use of this kind of suspension will allow higher productivity of the spraying process.
• the network of separated particles in the suspension of the present invention can be destroyed very easily by adding a dispersant, acid, alkaline solution or any other additive that creates steric, electrostatic or electro-steric stabilization of the particles and destroys the network structure.
• a further aspect of the present invention relates to method for preparing a suspension for thermal spraying comprising
• RTU ready to use
• said acid is selected from the group consisting of mono-and polycarboxylic acids, such as acrylic acid, methacrylic acid, acetic acid, citric acid, oxalic acid and their derivates.
• said ready-to-use suspension has a viscosity of 100 mPa*s or below at a shear rate of 100 s -1 .
• the ready-to-use suspension may have a zeta potential of below -15 mV or above + 15 mV.
• the network of separate particles in the suspension can be destroyed very easily by adding a dispersant, acid, alkaline solution or any other additive that creates steric, electrostatic or electro-steric stabilization of the particles.
• This chemical additive creates a low viscosity suspension.
• This suspension may contain a high solids loading of particles.
• additives are mono-and polycarboxylic acids (such as acrylic acid, methacrylic acid, acetic acid, citric acid, oxalic acid) and their derivates or common available dispersants, defloculants or plyelectrolytes, for example from Zschimmer and Schwarz (such as Dolapix CE 64, Dolapix CA).
• Example 1a The raw material was mixed at 75 wt% concentration of solids in 1.00 kg ethanol (Donau Chemie, Austria). Approx.1000 g of the suspension was separated for Example 1. The remainder of the suspension was dispersed by using a wet ball mill (Dyno Mill Multi Lab from Willy A. Bachofen, Swiss). The so produced YSZ suspension contained 75.3 wt% of solids (Example 1a ).
• Example 2 59.8 g of the suspension of Example 1 was mixed with 0.38 g [2-(2-methoxyethoxy) ethoxy] acetic acid (from Euticals, Germany, in the following referred to as "MEEA") by shaking by hand for 10 to 15 seconds.
• MEEA [2-(2-methoxyethoxy) ethoxy] acetic acid
• Example 1a 59.9 g of the suspension of Example 1a was mixed with 0.39 g MEEA by shaking by hand for 10 to 15 seconds.
• the so produced RTU suspension was analyzed and the particle size in the RTU suspension, viscosity of the RTU suspension, density of particles, density of solvent, zeta potential of the RTU suspension and solid loading of the RTU suspension are summarized in Table 2.
• the raw material was mixed at 77.8 wt% concentration of solids in 1.00 kg ethanol (Donau Chemie, Austria). Approx. 1000 g of the suspension was separated for Example 2.
• the remainder of the mixture was dispersed by using a wet ball mill (Dyno Mill Multi Lab from Willy A. Bachofen, Swiss).
• the so produced GdZr suspension contained 77.6 wt% of solids (Example 2a).
• the raw material was mixed at 69.6 wt% concentration of solids in 1.0 kg deionized water. Approx. 700 g of the suspension was separated for Comparative Example 1. The rest of the mixture was dispersed by using a wet ball mill (Dyno Mill Multi Lab from Willy A. Bachofen, Swiss) (Comparative Example 1a). The so produced Al 2 O 3 suspension contained 69.2 wt% of solids.

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• 2022
  • 2022-12-14 EP EP22213566.7A patent/EP4385966A1/de active Pending

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