WO2018112296A1 - Creuset revêtu de céramique d'oxyde d'yttrium - Google Patents

Creuset revêtu de céramique d'oxyde d'yttrium Download PDF

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WO2018112296A1
WO2018112296A1 PCT/US2017/066583 US2017066583W WO2018112296A1 WO 2018112296 A1 WO2018112296 A1 WO 2018112296A1 US 2017066583 W US2017066583 W US 2017066583W WO 2018112296 A1 WO2018112296 A1 WO 2018112296A1
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crucible
yttrium oxide
oxide based
based ceramic
coating
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PCT/US2017/066583
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English (en)
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Eric FEINER
Rudolph A. Olson, Iii
Kurt SCHIEFELBEIN
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Porvair Plc
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Definitions

  • the present invention is related to an improved crucible which is
  • the present invention is related to a yttrium oxide coating on, particularly, a high alumina crucible.
  • a large number of crucibles used in molten metal processing are a mixture of alumina, silica and aluminosilicate based materials, which are often referred to as "high-alumina" crucibles. These materials are relatively inexpensive and do a fair job in limiting the reaction between molten metal and the crucible in most applications.
  • Alumina based materials tend to be more inert and therefore more resistant to chemical reaction with more aggressive metals at higher temperatures.
  • Silica and aluminosilicate based materials also have relatively low coefficients of thermal expansion and therefore tend to be more resistant to thermal shock than alumina. Therefore, silica and aluminosilicates are often included when thermal gradients within a crucible are large or the crucible is intended to experience a high number of thermal cycles.
  • alumina based materials such as aluminosilicates like mullite and clay
  • silica bearing materials such as aluminosilicates like mullite and clay
  • alumina In certain aggressive applications, no ratio of alumina to silica is adequate to provide acceptable levels of both inertness and thermal shock resistance at low cost.
  • One example of such an application is the melting and processing of molten titanium. Titanium is easily oxidized at high temperature and rapidly reacts with silica bearing based materials. Pure alumina based materials can survive for a short time in contact with very aggressive metals, but will eventually succumb to reaction. In addition, the thermal shock resistance of pure alumina crucibles is generally undesirable.
  • a coating of inert material is preferably only on the inside of the crucible.
  • the difficulty in employing such a coating is applying it thick enough such that reaction between the metal and crucible is sufficiently inhibited, but not too thick such that the coating cracks or delaminates from the surface, thereby allowing pieces of coating to end up in the molten metal.
  • the present invention is related to an improved crucible comprising a stable coating thereon and a method of manufacturing the improved crucible.
  • the present invention is related to a high alumina crucible comprising a yttrium oxide based ceramic coating thereon and a method of manufacturing the improved crucible.
  • the present invention is related to a method of manufacturing a crucible comprising forming a yttrium oxide based ceramic on the interior surface of a high alumina crucible.
  • a ceramic core precursor comprising a solids component comprising 40-60 wt% alumina and 40-60 wt% aluminosilicate;
  • a ceramic coating precursor slurry comprising yttrium oxide, and a solvent; placing the ceramic coating precursor slurry on at least a portion of the green-state crucible wherein the green-state crucible depletes the ceramic coating precursor slurry of the solvent, thereby forming a coated green-state crucible;
  • a yttrium oxide based ceramic coated crucible comprising a crucible comprising a sintered ceramic of 40-60 wt% alumina and 40-60 wt% aluminosilicate.
  • a yttrium oxide based ceramic coating is on at least a portion of a surface of the crucible wherein the yttrium oxide based ceramic coating comprises a first zone closest to the crucible and a second zone with the first zone between the second zone and the crucible.
  • the first zone is relatively alumina rich, and preferably comprises YAG, and the second zone is relatively alumina depleted.
  • Fig. 1 is a graphical representation of an embodiment of the invention.
  • Fig. 2 is a graphical representation of an embodiment of the invention.
  • Fig. 3 is a graphical representatioin of an embodiment of the invention.
  • an improved process for coating the inside of an inexpensive, thermal shock resistant, refractory, strong high-alumina crucible with a relatively thick coating of yttrium oxide to inhibit reaction between molten metal is also provided herein.
  • the present invention provides a tenaciously adhered, relatively thick, thermally stable, and inert coating of a yttrium oxide onto at least a portion of the surface of a crucible and preferably just an inner portion of the crucible.
  • a particular advantage of the instant invention is that the crucible with coating can be prepared in a cost-effective manner.
  • a yttrium oxide based coating precursor is applied to a green state ceramic crucible followed by co-firing to form a crucible with ceramic coating adhered thereto.
  • the present invention provides a novel structure achieved by a co-firing step wherein the crucible and coating are sintered simultaneously, which is referred to herein as being co-sintered or co-sintering.
  • the co-sintering provides a coating with zones, with the first zone being relatively alumina rich, wherein a primary function of the first zone is to provide adhesion of the yttrium oxide coating to the ceramic of the crucible, as illustrated schematically in Fig. 3.
  • the second zone is separated from the surface of the crucible by the first zone and is relatively alumina depleted and said second zone, preferably comprises displaced silica that migrates from the crucible.
  • the reaction between yttrium oxide and aluminum oxide in the first zone produces a ceramic phase known as yttrium aluminium garnet, also referred to as YAG, having a chemical formula of Y3AI5O12. While not being limited by theory, it is hyposthesized that the crystallization of the YAG phase refines the first interfacial zone, thereby excluding silica, which is present on either side of the first zone, but not in the first zone.
  • a ceramic precursor slurry is cast into the desired shape and size, preferably in a mold. While not limited thereto, a gypsum mold is particularly suitable for demonstration of the invention. After removal of the water from the slurry by the gypsum mold, the cast ceramic core precursor is self- supporting and can be removed from the mold and dried further, preferably air-dried, to form a green state crucible. Heat can be applied to form the green state crucible as long as the temperature is below that necessary to sinter the ceramic core precursor.
  • a yttrium oxide based ceramic coating precursor slurry is applied to those surfaces of the green state crucible to be coated.
  • the ceramic coating precursor slurry is dried to form a dried coating on the green state crucible.
  • the dried coating and green state crucible are co-fired to a temperature sufficient to sinter the ceramic in both the crucible and the coating and the temperature is held at the sintering temperature for a sufficient time to allow the yttrium oxide coating and the crucible to bond via reaction of yttria and alumina to form an intermediate YAG layer with migrated silica from the crucible into the yttria coating. Maintaining the sintering temperature for 30 minutes to 8 hours is sufficient to demonstrate the invention. While not limited thereto, a temperature of about 1482-1593°C (2700-2900°F) for a period of at least four hours is exemplary for demonstration of the invention.
  • the crucible preferably has a high alumina content with 40-60 wt% alumina and 40-60 wt% aluminosilicate which comprises about about 14-21 wt% silica and 65-98 wt% alumina. More preferably the crucible has a high alumina content with 45-55 wt% alumina and 45-55 wt% aluminosilicate which comprises about about 16-19 wt% silica and 73-89 wt% alumina. Optimum is high alumina content with about 49 wt% alumina and 51 wt% aluminosilicate which comprises about 17 wt% silica and 83 wt% alumina.
  • alumina is the sintered product of reactive alumina and tabular alumina to increase strength and refractoriness.
  • the binder is chosen to be compatible with the firing conditions with clay or other silica-bearing phases being exemplary for demonstration of the invention.
  • the ceramic core precursor is prepared preferably as a slurry in a solvent with water being particularly preferred as the solvent.
  • the yttrium oxide based ceramic coating precursor comprises materials that are difficult to reduce after sintering.
  • the ceramic coating precursor can comprise additional components with alumina being particularly preferred due to the enhanced adhesion achieved by the inclusion.
  • Binders are preferred to improve the rheology of the slurry as well as give the coating green strength when dried, wherein the binder is typically volatilized during sintering.
  • Exemplary binders include materials such as xantham gum, polyvinyl alcohol, or acrylic latex.
  • the ceramic coating precursor slurry is typically in a solvent with water being particularly preferred.
  • colloidal alumina it is preferable to add 6 to 24 wt% colloidal alumina, based on the weight of the slurry, to the ceramic coating precursor slurry to enhance green strength and to improve sintering between the yttrium oxide coating and the crucible. More preferably about 10-14 wt% colloidal alumina is added to the slurry with about 12 wt% colloidal alumina being optimum Below about 6 wt%, the advantage is not sufficiently realized. Above about 24 wt%, the colloidal alumina is detrimental to the inertness of the coating.
  • the alumina phase in the yttrium oxide coating precursor be colloidal in nature, as this lets the colloidal alumina particles transport to the interface between the high-alumina crucible and yttria based coating during the coating casting step.
  • This concentration of colloidal alumina then promotes the bonding between the high-alumina crucible and yttria coating, wherein the YAG phase is formed, forcing silica to migrate into zone two, as illustrated in Fig. 3.
  • a particular feature of the crucible as designed is a similar coefficient of thermal expansion to yttrium oxide, which minimizes the stresses that can occur as the composite is heated or cooled.
  • a gypsum mold containing a desired crucible shape was generated.
  • An aqueous ceramic core precursor slurry with conventional appropriate rheological properties was prepared comprising a solids fraction comprising 10 wt% reactive alumina (Almatis A1000SGD), 10 wt% reactive alumina (Almatis CTC-40), 21 wt% tabular alumina (Almatis/-325 LI), 30 wt% coarse mullite (Washington Mills/-40 Duramul), 8 wt% reactive alumina (Almatis A-10) and 21 wt% clay (Imerys/Kingsley).
  • the ceramic coating precursor slurry was cast into the gypsum mold. After the gypsum mold had sufficiently dewatered the slurry, the green state crucible was extracted from the mold and air-dried.
  • a yttrium oxide based ceramic coating precursor slurry was prepared wherein the ceramic coating precursor slurry comprised about 29.33 wt% coarse yttria powder (American Elements), about 14.45 wt% fine yttria powder (Treibacher), about 12.26 wt% colloidal alumina (Evonik/W450X), and about 0.18 wt% xanthan gum (TIC), with the balance being water.
  • Two additional slurries were prepared wherein one slurry comprised an additional 2 wt% titania, based on the solids composition, and a second slurry comprised an additional 5 wt% titania, based on the solids
  • the ceramic coating precursor slurry was poured into the crucible.
  • the colloidal alumina added to the slurry was done at a high enough level to enhance green strength and sintering between yttrium oxide particles, but a low enough concentration to not detract from the inertness of the coating.
  • Examples with titania added to the coating in 2 and 5 wt% loadings to the main composition, relative to the solids, were prepared in an effort to improve sintering between the yttrium oxide coating and the crucible.
  • the dried green state crucible effectively dewatered the yttrium oxide precursor slurry, thereby slowly building a coating on the inside wall of the green state crucible. After several minutes, the slurry was poured from the crucible and a relatively thick coating of about 1 mm in thickness remained. The green state crucible with the dried ceramic coating precursor was then dried further and subsequently fired to approximately 1565°C (2850°F) for 5 hours, resulting in a yttrium oxide based ceramic coated ceramic crucible.
  • a precursor thickness of at least 0.5 mm can be achieved, and more preferably 1 mm, with a deviation in thickness of less than 10% over a 10 mm length of coating.
  • the precursor thickness represents the approximate thickness of the sintered ceramic coating, which is otherwise difficult to measure precisely.
  • the ceramic formulations for both the crucible and the coating were designed to have very similar shrinkage during firing, which is typically controlled through manipulation of the ceramic formulation, starting particle size, and particle packing. When the difference between shrinkage values was too great, the resultant bonding between the coating and crucible was poor and the coating could be separated relatively easily from the crucible with a sharp instrument. Table 1 provides separately determined shrinkage values for the coating and the crucible, wherein PLC is percent linear change.
  • a separately determined shrinkage difference of no more than 1 .5% between the crucible and coating, preferably no more than 1 % and even more preferably no more than 0.5% allows for the formation of an adherent coating on the ceramic with minimal adhesion failures and minimal thermal stress failures.
  • the ceramic formulation for the crucible and coating were prepared to provide thermal expansion values that were very similar as a function of temperature and preferably within a difference of no more than about 2.0 x 10 "6 in/in/°C. Significant phase transformations are also undesirable, as phase transformations can create significant stresses due to thermal expansion mismatch.
  • the separately determined change in length per unit length as a function of temperature for the crucible and yttrium oxide coating material is provided in Figs. 1 and 2, respectively.
  • the coefficient of thermal expansion for the crucible between room temperature and 1200°C is approximately 6.9 x 10 "6 in/in/°C on heating, and that on cooling is 7.8 x 10 "6 in/in/°C.
  • Values for the yttrium oxide coating material without titania are approximately 8.0 x 10 "6 in/in/°C on heating and 9.6 x 10 "6 in/in/°C on cooling.
  • Colloidal alumina was introduced to the yttrium oxide slurry to enhance green strength, improve sintering between yttrium oxide particles, and improve sintering bonding between the crucible and the yttrium oxide coating.
  • a reddish layer of reacted ceramic material was observed at the interface between the crucible and coating.
  • the crucible is acting to form the coating by dewatering the yttrium oxide bearing ceramic coating precursor slurry, thereby effectively drawing the colloidal alumina through the water towards the crucible and concentrating the colloid at the interface of the crucible and coating.
  • the relatively increased concentration of colloidal alumina at the interface is hypothesized to promote the formation of yttrium aluminum garnet (YAG) phase.
  • YAG yttrium aluminum garnet
  • the formation of this YAG phase at the interface displaced the silica residing in this zone, pushing it to either side of the first zone, or zone 1.
  • the crucibles having a yttria coating comprising titania at 2 and 5 wt% concentrations exhibited a slightly yellowish phase at the interface, indicating it may have formed a slightly different phase than YAG.
  • the interface was examined using scanning electron microscopy and energy dispersive spectroscopy.
  • a high magnification image of the interface between crucible and coating, without titania, showed colloidal alumina and fine yttria concentrated at the interface with the crucible in a first zone, with the appearance of the coating being well-bonded to the crucible.
  • the silica had migrated into the coating, forming deposits at about 10-15 microns away from the crucible in the second zone, or zone 2.
  • the first zone, or zone 1 is preferably at least 5 microns thick to no more than 20 microns thick and preferably at least 10 microns thick to no more than 15 microns thick as illustrated schematically in Fig. 3.
  • the high-silica bearing microstructure in the second zone preferably comprises displaced silica, which is indicative of silica being forced from the first zone due to the precipitation of YAG phase.
  • the microstructural features demonstrated in the first zone and second zone indicate the region is well-sintered, thereby improving the strength and adherence of the coating at the interface.
  • a similar microstructure is obtained at the interface in samples containing 2 and 5 wt% titania.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Inorganic Chemistry (AREA)
  • Composite Materials (AREA)
  • Dispersion Chemistry (AREA)
  • Compositions Of Oxide Ceramics (AREA)

Abstract

L'invention concerne un creuset en céramique amélioré. Le creuset est un creuset revêtu de céramique à base d'oxyde d'yttrium comprenant un creuset comprenant une céramique frittée de 40 à 60 % en poids d'alumine et de 40 à 60 % en poids d'aluminosilicate. Un revêtement céramique à base d'oxyde d'yttrium se trouve sur au moins une partie d'une surface du creuset, le revêtement céramique à base d'oxyde d'yttrium comprenant une première zone la plus proche du creuset et une deuxième zone, la première zone se situant entre la deuxième zone et le creuset. La première zone est relativement riche en alumine et comprend de préférence du YAG et la deuxième zone porte de la silice.
PCT/US2017/066583 2016-12-15 2017-12-15 Creuset revêtu de céramique d'oxyde d'yttrium WO2018112296A1 (fr)

Applications Claiming Priority (2)

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US201662434784P 2016-12-15 2016-12-15
US62/434,784 2016-12-15

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WO2018112296A1 true WO2018112296A1 (fr) 2018-06-21

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CN110256077A (zh) * 2019-07-09 2019-09-20 中国航发北京航空材料研究院 一种精密铸造用氧化钇基陶瓷型芯及其制备方法
CN112430092A (zh) * 2020-12-16 2021-03-02 湖南仁海科技材料发展有限公司 一种钛合金mim制品烧结用氧化钇涂料及其在刚玉-莫来石承烧板上的应用
US10974078B2 (en) 2012-12-27 2021-04-13 Brainsonix Corporation Treating degenerative dementia with low intensity focused ultrasound pulsation (LIFUP) device

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10974078B2 (en) 2012-12-27 2021-04-13 Brainsonix Corporation Treating degenerative dementia with low intensity focused ultrasound pulsation (LIFUP) device
CN110256077A (zh) * 2019-07-09 2019-09-20 中国航发北京航空材料研究院 一种精密铸造用氧化钇基陶瓷型芯及其制备方法
CN112430092A (zh) * 2020-12-16 2021-03-02 湖南仁海科技材料发展有限公司 一种钛合金mim制品烧结用氧化钇涂料及其在刚玉-莫来石承烧板上的应用

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