Patent Application
20240369422
This invention relates generally to ceramic thermocouples designed for harsh environmental conditions. More specifically, this disclosure relates to ceramic composite thermocouples designed to provide reliable, accurate, long-term operation in environments greater than 1100° C.
An industrial challenge exists to accurately maintain and/or monitor the temperature of harsh environments that are greater than 1100° C. Typical industries in this application space include energy generation, metal/glass and alloy manufacturing, coal gasification, high-temperature turbines, engine health and operational monitoring, among others. Thermocouple devices can be an effective option for temperature sensing due to their ability to measure a wide spectrum of temperatures. However, most thermocouple devices applied to harsh environmental conditions have material and/or design deficiencies not well-suited to collectively achieve long-term durability and chemical stability, measurement accuracy, repeatability, and sensitivity, while also maintaining a low production cost. These inadequacies are often the result of one or more of the following issues: low material melting temperature, undesirable oxidation or chemical reactions, or thermomechanical material property incompatibilities or inconsistencies with substrate materials or environmental surroundings (e.g. gaseous atmospheres).
In accordance with the purpose(s) of the disclosure, as embodied and broadly described herein, the disclosure, in one aspect, relates to a thermocouple device fabricated from a composite mixture of undoped and/or doped lanthanum chromite (LaCrO3) (“thermoelectric”) materials and refractory oxide (“insulating”) materials, which are electrically-insulating, for high temperature applications. Each leg of the thermocouple can comprise a different composition with different intrinsic Seebeck coefficients in order generate a measurable thermoelectric voltage while in operation. The thermocouple can be fabricated as a monolithic structure or monolithic entity or as an embedded thermocouple such that a core thermoelectric material can be embedded within a partial to fully dense ceramic matrix with high chemical and thermomechanical stability with its surroundings. In another aspect, a plurality of discrete layers of the composite mixture can be applied to each leg of the thermocouple ranging from 100% to near 0% LaCrO3 (i.e., nearly 100% refractory oxide). In another aspect, the composite mixture can be continuously graded between 100% LaCrO3 to near 0% LaCrO3 (i.e., nearly 100% refractory oxide).
The disclosed thermocouple can be a relatively low-cost market replacement for solid-state thermocouples currently fabricated using precious metal compositions such as platinum (Pt), particularly as precious metal costs continue to rise over time. The disclosed thermocouple also enjoys extended longevity while operating in oxygen environments over 1100° C. compared to precious metal-based thermocouples.
In an additional aspect, the disclosure relates to methods of manufacturing a high-temperature composite ceramic oxide thermocouple using various processes. The composite mixture can be deposited by direct ink-writing, tape-casting, or similar methods on a sacrificial substrate wherein the substrate disintegrates and can be removed from the thermocouple during high-temperature treatment to densify the structure. Thermocouple sensor preforms can be manufactured to be easily incorporated into casts, molds, and other mechanisms used in the production of refractory articles to create temperature sensing articles.
Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with ordinary skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, and be protected by the accompanying claims. In addition, all optional and preferred features and modifications of the described embodiments are usable in all aspects of the disclosure taught herein. Furthermore, the individual features of the independent claims, as well as all optional and preferred features and modifications of the described embodiments are combined and interchangeable with one another.
Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
As used herein, “comprising” is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Moreover, each of the terms “by”, “comprising,” “comprises”, “comprised of,” “including,” “includes,” “included,” “involving,” “involves,” “involved,” and “such as” are used in their open, non-limiting sense and may be used interchangeably. Further, the term “comprising” is intended to include examples and aspects encompassed by the terms “consisting essentially of” and “consisting of.” Similarly, the term “consisting essentially of” is intended to include examples encompassed by the term “consisting of.
As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a metal,” “a metal oxide,” or “an oxidizing agent,” including, but not limited to, mixtures or combinations of two or more such metals, metal oxides, or oxidizing agents, and the like.
It should be noted that ratios, concentrations, amounts, and other numerical data can be expressed herein in a range format. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms a further aspect. For example, if the value “about 10” is disclosed, then “10” is also disclosed.
When a range is expressed, a further aspect includes from the one particular value and/or to the other particular value. For example, where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure, e.g. the phrase “x to y” includes the range from ‘x’ to ‘y’ as well as the range greater than ‘x’ and less than ‘y’. The range can also be expressed as an upper limit, e.g. ‘about x, y, z, or less’ and should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’ as well as the ranges of ‘less than x’, less than y’, and ‘less than z’. Likewise, the phrase ‘about x, y, z, or greater’ should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’ as well as the ranges of ‘greater than x’, greater than y’, and ‘greater than z’. In addition, the phrase “about ‘x’ to ‘y’”, where ‘x’ and ‘y’ are numerical values, includes “about ‘x’ to about ‘y’”.
It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a numerical range of “about 0.1% to 5%” should be interpreted to include not only the explicitly recited values of about 0.1% to about 5%, but also include individual values (e.g., about 1%, about 2%, about 3%, and about 4%) and the sub-ranges (e.g., about 0.5% to about 1.1%; about 5% to about 2.4%; about 0.5% to about 3.2%, and about 0.5% to about 4.4%, and other possible sub-ranges) within the indicated range.
As used herein, the terms “about,” “approximate,” “at or about,” and “substantially” mean that the amount or value in question can be the exact value or a value that provides equivalent results or effects as recited in the claims or taught herein. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art such that equivalent results or effects are obtained. In some circumstances, the value that provides equivalent results or effects cannot be reasonably determined. In such cases, it is generally understood, as used herein, that “about” and “at or about” mean the nominal value indicated ±10% variation unless otherwise indicated or inferred. In general, an amount, size, formulation, parameter or other quantity or characteristic is “about,” “approximate,” or “at or about” whether or not expressly stated to be such. It is understood that where “about,” “approximate,” or “at or about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.
Unless otherwise specified, temperatures referred to herein are based on atmospheric pressure (i.e. one atmosphere).
As used herein, the term “high alumina cement” can be a mixture comprising multiple solid oxides, wherein aluminum oxide (Al2O3) makes up the majority solid constituent typically in a volumetric proportion greater than 90%. The following oxides typically comprise less than 10% of the solid oxide mixture: CaO2, SiO2, NaO2, and KO3. Other phases such as Al2CaO4 and H2CaO2 can be minorly present as well within a high alumina cement composition.
As used herein, the term “monolithic structure” or “monolithic entity” can be defined as a construction or component formed by a single, continuous material such that the structure is created as a single solid piece rather than being composed of separately assembled parts.
Disclosed herein are various embodiments of thermocouple devices developed for accurate temperature monitoring in harsh environments along with their respective methods of preparation, utilizing lanthanum chromite (LaCrO3)-based perovskite ceramics in combination with refractory oxides, for example aluminum oxide (Al2O3).
The two electrodes or legs of the thermocouple devices can comprise composite mixtures of undoped and/or doped LaCrO3 (“thermoelectric”) materials and refractory oxides (“insulating”) materials to form a ceramic composite. The thermoelectric and insulating materials can be dense or porous, single or multiphase solid material wherein porosity can be considered an additional phase. The constituents that make up the composite mixtures can comprise at least one inner layer or a plurality of inner layers to produce various configurations of electrical connectivity, restricting unwanted microstructural changes and instability during thermocouple operation. This is important for the interaction of the thermoelectric components within various gaseous environments and thermomechanical instability during thermal cycling.
For example,
The use of a LaCrO3 material in conjunction with a refractory oxide to form a composite mixture within a thermocouple can benefit from the existence of a microstructure with various layers of interconnectivity for reliable, long-term high temperature application.
Various configurations of multiple interconnected layers containing thermoelectric material can alter the overall thermoelectric properties in addition to the chemical and thermomechanical stability of the thermocouple. As defined by R. E. Newnham et al. [1, 2] for the connectivity of electrical ceramic composites, the dimensionality of connectivity, or contact of one phase to another for a multiphase composite, can be termed with the numbers 0 (no connectivity), 1 (linear connectivity), 2 (planar connectivity), or 3 (three-dimensional connectivity). For a two-phase composite material, a 2-2 composite indicates a laminar composite of the two phases. Another example of a two-phase composite material is a 3-3 composite, which designates a three-dimensional (3-D) interconnected mixture of the two phases. A 3-3 composite can appear similar to a sponge-like structure where the solid material is connected in 3-D space, as well as 3-D connectivity of the sponge porosity or void space.
For the following representation, the first number represents the connectivity of the thermoelectric material, and the second number represents the connectivity of the insulating material. Depending on the volumetric ratio of the thermoelectric to the insulating material and the particle size ratio of each respective material phase, a 3-0 composite (at typically less than 10% by volume insulating material) (see
An example thermocouple design to implement this framework is the use of multiple layers of 3-3 composites comprised of thermoelectric and insulating materials. A three-layer 3-3 composite can be used to construct each leg of the thermocouple. A large quantity of layers of smaller thicknesses can alternatively be used, and approach the point of a continuous functionally-graded composite material as the quantity of layers increase. As an illustration of a 3-3 composite,
Layer 1 can comprise a core or innermost thermoelectric layer, Layer 2 can comprise an intermediate functional gradient layer, and Layer 3 can comprise an outermost layer for protection and bonding and interaction with the exterior environment. Within each layer, a 3-3 composite is defined to control the electrical properties in addition to metering the degree of chemical and thermomechanical interaction. The 3-3 composite corresponds to an interconnected, multiphase granular structure of the thermoelectric and insulating materials at different respective volumetric ratios within each layer. Layer 1 can contain a high volumetric concentration of the thermoelectric material for the 3-3 composite (or even just a 3-0 composite) compared to Layer 3 which can contain a very low (to 0% volume concentration) of the thermoelectric material (see
In another aspect, multi-layer microstructural composites of a laminar composite with n additional composite 2-D laminar layers can be used. The illustration shown in
In one embodiment, a thermocouple device can comprise at least one inner layer embedded within an outer layer. The outer layer can comprise at least one phase of a first refractory oxide. At least one inner layer can comprise a first leg and a second leg. The first leg can comprise a first composite mixture of at least one phase of a first undoped or doped LaCrO3 in contact with at least one phase of a second refractory oxide. The second leg can comprise a second composite mixture of at least one phase of a second undoped or doped LaCrO3 in contact with at least one phase of a third refractory oxide. The first leg and the second leg can be in electrical contact with each other to form a junction. The first composite mixture and the second composite mixture can be different compositions such that a thermoelectric voltage can be generated between the first leg and the second leg.
In a further aspect, at least one inner layer can have a porosity of about 0 to 80%.
In a further aspect, the first composite mixture can have a porosity of about 0 to 80%.
In a further aspect, the second composite mixture can have a porosity of about 0 to 80%.
In a further aspect, at least one phase of the first refractory oxide can comprise aluminum oxide or alumina (Al2O3), chromium (III) oxide or chromia (Cr2O3), zirconium dioxide or zirconia (ZrO2), silicon dioxide or silica (SiO2), magnesium oxide or magnesia (MgO), calcium oxide (CaO), ferric oxide (Fe2O3), phosphorous pentoxide (P2O5), or combinations thereof.
In a further aspect, at least one phase of the second refractory oxide can comprise Al2O3, Cr2O3, ZrO2, SiO2, MgO, CaO, Fe2O3, P2O5, or combinations thereof.
In a further aspect, at least one phase of the third refractory oxide can compromise Al2O3, Cr2O3, ZrO2, SiO2, MgO, CaO, Fe2O3, P2O5, or combinations thereof.
In a further aspect, at least one phase of the first refractory oxide, at least one phase of the second refractory oxide, and at least one phase of the third refractory oxide can comprise a similar refractory oxide.
In a further aspect, at least one phase of the first refractory oxide, at least one phase of the second refractory oxide, and at least one phase of the third refractory oxide can comprise Al2O3, Cr2O3, or combinations thereof.
In a further aspect, at least one phase of the first refractory oxide, at least one phase of the second refractory oxide, and at least one phase of the third refractory oxide can comprise Al2O3.
In a further aspect, at least one phase of the first refractory oxide, at least one phase of the second refractory oxide, and at least one phase of the third refractory oxide can comprise Cr2O3.
In a further aspect, at least one phase of the first refractory oxide can comprise a high alumina cement.
In a further aspect, at least one phase of the first undoped or doped LaCrO3 or at least one phase of the second undoped or doped LaCrO3 can comprise a composition represented by the formula (La1-xAx)(Cr1-yBy)O3, wherein A=calcium (Ca), strontium (Sr), barium (Ba), or yttrium (Y) and B=niobium (Nb), titanium (Ti), zirconium (Zr), manganese (Mn), iron (Fe), cobalt (Co), copper (Cu), nickel (Ni), zinc (Zn), aluminum (Al), gadolinium (Gd), neodymium (Nd), or samarium (Sm), 0≤x≤0.5 and 0≤y≤0.5.
In a further aspect, at least one phase of the first undoped or doped LaCrO3 or at least one phase of the second undoped or doped LaCrO3 can comprise a composition represented by the formula (La1-xAx)CrO3, wherein A=Ca or Sr, 0<x≤0.3.
In a further aspect, at least one phase of the first undoped or doped LaCrO3 or at least one phase of the second undoped or doped LaCrO3 can comprise a composition represented by the formula (La1-xAx)CrO3, wherein A=Ca, 0.2≤x≤0.3.
In a further aspect, at least one phase of the first undoped or doped LaCrO3 or at least one phase of the second undoped or doped LaCrO3 cam comprise a composition represented by the formula (La1-xAx)CrO3, wherein A=Ca, x=0.3.
In a further aspect, at least one phase of the first undoped or doped LaCrO3 and at least one phase of the second refractory oxide can be present in the first composite mixture in a volumetric ratio ranging from about 70:30 to 99:1, respectively. At least one phase of the second undoped or doped LaCrO3 and at least one phase of the third refractory oxide can be present in the second composite mixture in a volumetric ratio ranging from about 70:30 to 99:1, respectively.
In a further aspect, at least one phase of the first undoped or doped LaCrO3 and at least one phase of the second refractory oxide can be present in the first composite mixture in a volumetric ratio ranging from about 90:10 to 99:1, respectively. At least one phase of the second undoped or doped LaCrO3 and at least one phase of the third refractory oxide can be present in the second composite mixture in a volumetric ratio ranging from about 90:10 to 99:1, respectively.
In a further aspect, at least one phase of the first undoped or doped LaCrO3 and at least one phase of the second refractory oxide can be present in the first composite mixture in a volumetric ratio ranging from about 90:10 to 95:5, respectively. At least one phase of the second undoped or doped LaCrO3 and at least one phase of the third refractory oxide can be present in the second composite mixture in a volumetric ratio ranging from about 90:10 to 95:5, respectively.
In a further aspect, at least one phase of the first undoped or doped LaCrO3 and at least one phase of the second refractory oxide can be present in the first composite mixture in a volumetric ratio of about 70:30, respectively. At least one phase of the second undoped or doped LaCrO3 and at least one phase of the third refractory oxide can be present in the second composite mixture in a volumetric ratio of about 70:30, respectively.
In a further aspect, at least one phase of the first undoped or doped LaCrO3 and at least one phase of the second refractory oxide can be present in the first composite mixture in a volumetric ratio of about 80:20, respectively. At least one phase of the second undoped or doped LaCrO3 and at least one phase of the third refractory oxide can be present in the second composite mixture in a volumetric ratio of about 80:20, respectively.
In a further aspect, at least one phase of the first undoped or doped LaCrO3 and at least one phase of the second refractory oxide can be present in the first composite mixture in a volumetric ratio of about 90:10, respectively. At least one phase of the second undoped or doped LaCrO3 and at least one phase of the third refractory oxide can be present in the second composite mixture in a volumetric ratio of about 90:10, respectively.
In a further aspect, at least one phase of the first undoped or doped LaCrO3 and at least one phase of the second refractory oxide can be present in the first composite mixture in a volumetric ratio of about 95:5, respectively. At least one phase of the second undoped or doped LaCrO3 and at least one phase of the third refractory oxide can be present in the second composite mixture in a volumetric ratio of about 95:5, respectively.
In a further aspect, three-dimensional microstructure connectivity can be present in the first composite mixture, the second composite mixture, or combination thereof.
In a further aspect, three-dimensional microstructure connectivity can be present in the at least one phase of a first undoped or doped LaCrO3, the at least one phase of a second undoped or doped LaCrO3, or combination thereof.
In a further aspect, at least one phase of the first refractory oxide or at least one phase of the second refractory oxide can have no microstructure connectivity, or combination thereof.
In a further aspect, at least one phase of a first undoped LaCrO3 and at least one phase of a second refractory oxide can be present in the first composite mixture in a volumetric ratio ranging from about 70:30 to 99:1, respectively. At least one phase of a second doped LaCrO3 represented by the formula La0.7Ca0.3CrO3 and at least one phase of a third refractory oxide can be present in the second composite mixture in a volumetric ratio ranging from about 70:30 to 99:1, respectively. At least one phase of a first refractory oxide, at least one phase of a second refractory oxide, and at least one phase of a third refractory oxide can comprises Al2O3, Cr2O3, or combination thereof.
In a further aspect, at least one phase of a first undoped LaCrO3 and at least one phase of a second refractory oxide can be present in the first composite mixture in a volumetric ratio ranging from about 70:30 to 95:5, respectively. At least one phase of a second doped LaCrO3 represented by the formula La0.7Ca0.3CrO3 and at least one phase of a third refractory oxide can be present in the second composite mixture in a volumetric ratio ranging from about 70:30 to 95:5, respectively. At least one phase of a first refractory oxide, at least one phase of a second refractory oxide, and at least one phase of a third refractory oxide can comprises Al2O3, Cr2O3, or combination thereof.
In a further aspect, at least one phase of a first undoped LaCrO3 and at least one phase of a second refractory oxide can be present in the first composite mixture in a volumetric ratio ranging from about 90:10 to 95:5, respectively. At least one phase of a second doped LaCrO3 represented by the formula La0.7Ca0.3CrO3 and at least one phase of a third refractory oxide can be present in the second composite mixture in a volumetric ratio ranging from about 90:10 to 95:5, respectively. At least one phase of a first refractory oxide, at least one phase of a second refractory oxide, and at least one phase of a third refractory oxide can comprise Al2O3, Cr2O3, or combination thereof.
In a further aspect, at least one inner layer and the outer layer can form a monolithic structure.
In a further aspect, the thermocouple device can be a monolithic structure.
In a further aspect, at least one inner layer can comprise a plurality of inner layers. The plurality of inner layers has a functionally graded microstructure such that the volumetric ratio of refractory oxide within each layer increases from an inner most layer to the outer layer.
In a further aspect, the thermocouple device can have a stable temperature sensing range from about 100 to about 1500° C.
In a further aspect, the thermocouple device can have a stable temperature sensing range from about 20 to about 1500° C.
In a further aspect, the thermocouple device can have an effective Seebeck coefficient of about 230 to about 250 μV/K.
In another embodiment, a temperature sensing article can comprise at least one inner layer embedded within an outer layer. At least one inner layer can comprise a first leg and a second leg. The first leg can comprise a first composite mixture of an undoped or doped LaCrO3 in contact with a refractory oxide in a volumetric ratio ranging from about 70:30 to 95:5, respectively. The second leg can comprise of a second composite mixture of an undoped of doped LaCrO3 in contact with a refractory oxide in a volumetric ratio ranging from about 70:30 to 95:5, respectively. The first leg and the second leg can be in electrical contact with each other to form a junction. The first composite mixture and the second composite can be different compositions such that a thermoelectric voltage is generated between the first leg and the second leg. The doped LaCrO3 can be represented by the formula La0.7Ca0.3CrO3. The outer layer can comprise a refractory oxide. The refractory oxide can comprise Al2O3, Cr2O3, ZrO2, SiO2, MgO, CaO, Fe2O3, P2O5, or combinations thereof. The temperature sensing article can be a monolithic structure.
In an alternate embodiment, a thermocouple sensor preform can comprise a first leg, a second leg, and a sacrificial substrate. The first leg can comprise a first composite mixture of an undoped or doped LaCrO3 in contact with a refractory oxide in a volumetric ratio ranging from about 70:30 to 95:5, respectively. The second leg can comprise a second composite mixture of an undoped or doped LaCrO3 in contact with a refractory oxide in a volumetric ratio ranging from about 70:30 to 95:5, respectively. The first leg and the second leg can be disposed on the sacrificial substrate and can be in electrical contact with each other to form a junction. The first composite mixture and the second composite mixture can be different compositions such that a thermoelectric voltage is generated between the first leg and the second leg. The doped LaCrO3 can be represented by the formula La0.7Ca0.3CrO3. The sacrificial substrate can disintegrate at a temperature lower than the sintering temperature of the first composite mixture and the second composite mixture.
In an alternate embodiment, there can be a method of making a thermocouple device, comprising the steps of:
In a further aspect, the heat-treating process can be a sintering process.
In a further aspect, the plurality of layers is sintered to about 1500° C. for at least 2 hrs.
In a further aspect, the first outer layer and the second outer layer can be formed by casting at least one phase of a first refractory oxide material and at least one phase of a second refractory oxide material, respectively, into the cavity of a mold.
In a further aspect, at least one inner layer can comprise the first leg and the second leg can be produced via tape casting.
In a further aspect, at least one inner layer can comprise the first leg and the second leg is produced via direct ink writing onto the sacrificial substrate.
In a further aspect, the sacrificial substrate can be a coarse filter paper or a dissolvable filter paper.
In a further aspect, the sacrificial substrate can be a filter paper with about 2.5 μm
In a further aspect, the sacrificial substrate can be a filter paper with about 30 to 50-μm pore size.
In a further aspect, the sacrificial substrate can be a solid film such that it disintegrates or volatizes at temperatures greater than 800° C.
Many modifications and other embodiments disclosed herein will come to mind to one skilled in the art to which the disclosed compositions and methods pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the disclosures are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. The skilled artisan will recognize many variants and adaptations of the aspects described herein. These variants and adaptations are intended to be included in the teachings of this disclosure and to be encompassed by the claims herein.
Chemical composition formulas are referred to using acronyms followed by a number to indicate, if applicable, the doping level. For example, LCC10 refers to La0.9Ca0.1CrO3, or lanthanum chromite doped with 10% calcium (calcium 0.1 mol content on the La-site of the composition). Table 1 lists example chemical composition formulas and their respective acronyms that will be referred to herein.
For simplicity, the composition designation of [thermoelectric percent volume−insulator percent volume] is used to identify the volumetric percentage of the composites. For example, LCC20-Al2O3 [90-10 or 90-10] indicates a 90% volume of LCC20 and 10% volume of Al2O3.
Ref. 1: Tresslera, J. F.; Alkoya, S.; Doganb, A.; Newnham, R. E. Functional composites for sensors, actuators, and transducers. Composites: Part A 30 477-482 (1999).
Ref. 2: Pilgrim S. M.; Newnham, R. E. New Composites Connectivity. Mat. Res. Bull. 21, 1447-1454 (1986).
Ref. 3: J. A. Mena, V. Mendoza-Estrada, E. M. Sabolsky, K. Sierros, K. Sabolsky, R. González-Hernández, K. S. Varadharajan Idhaiam, “Exploring the Impact of Multivalent Substitution on High-Temperature Electrical Conductivity in Doped Lanthanum Chromite Perovskites: An Experimental and Ab-initio Study,” Journal of the European Ceramic Society, 2024, ISSN 0955-2219 (DOI: 10.1016/j.jeurceramsoc.2024.04.062).
The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices and/or methods claimed herein are made and evaluated, and are intended to be purely exemplary of the disclosure and are not intended to limit the scope of what the inventors regard as their disclosure. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ° C. or is at ambient temperature, and pressure is at or near atmospheric.
A six-layer thermocouple can be fabricated using LCC20-Al2O3 [80-20] and LC-Al2O3 [80-20] compositions as the core or inner most thermoelectric materials for Leg 1 and Leg 2, respectively. The six-layer thermocouple utilizes three layers of differing composition mirrored about the inner most layers to fabricate six total layers. The six layers from this example are listed from bottom to top in Table 2.
Undoped and Ca-doped LaCrO3-based powders were prepared via a Pechini sol-gel method by employing citric acid (HO2CCH2—C(OH)(CO2H)CH2CO2H) (99.9% purity) and La(NO3)3.6H2O (99.9% purity), Cr(NO3)3.9H2O (99.9% purity), Sr(NO3)2 (99.5% purity), Ca(NO3)2.4H2O (99.5% purity) and Mn(NO3)2.4H2O (99.0% purity) as metals sources from Sigma Aldrich, USA. The accuracy of the final metal solution concentrations were established by ICP-MS measurements. The solution amounts of metallic species for each composition (See Table 2) were weighted and mixed with citric acid in deionized water at an equivalent molar ratio of about 1:2 metal cations to citric acid. The solutions were heated to about 80° C. using a hotplate for about 16 hours to form a viscous gel that yielded a purple solid precursor. The gel can then be heat treated at about 400° C. using a furnace with a heating rate of about 1° C. per minute and then held at about 400° C. for about 1 hour to remove any remaining organic materials. Samples were pulverized manually in a mortar and calcined in a furnace at 900° C. for about 5 hours. The resulting powders were milled with isopropyl alcohol (99.5% purity) in 3-mm ZrO3-milling media for about two hours. The milled powders were then characterized by X-ray diffraction (XRD, PANalytical X'pert PRO, Cu Kα radiation, model number PW 3040 Pro, West Virginia University). Power requirements during the operation were 45 kV and 40 mA. The divergence slit angle for the incident X-ray beam can be set to 0.5°. Scans were performed with a 0.033°/s scan rate and a 40 second step time. More detailed scans were performed using a 0.016°/s scan rate and a 400 second step time. Jade v9.6 Materials Data Inc. can be used for phase identification and pattern analysis.
The 3-3 LaCrO3-based composite powders were then prepared. The composite consisted of 80% by volume LCC20 with 20% by volume Al2O3 (Al2O3; 99.8%, SSA: 8.6 m2/g) (volume ratio). The composite powder can be generally prepared by mixing both powders in the required volumetric ratio, alumina, zirconia milling media and isopropyl alcohol. The mixture can be left for about 2 hours on a US Stoneware 755RMV ball rolling system. After milling, the zirconia media can be strained out and the powder-alcohol mixture can be dried on a hot plate at about 90° C. for about 8 hours.
0-3 Al2O3 inks were prepared by mixing 66 grams of powder with about 38.7 g of an ethanol-xylene mixture (50-50% by weight) and 1.4 grams of a fish oil solution in xylene for about 4 hours on a US Stoneware 755RMV ball rolling system. Finally, 3.0 g of Plasticizer UCON50HB2000 (Polyalkylene Glycol), 3.0 g of Plasticizer S-160 (butyl benzyl phthalate) and 6.0 g of Polyvinyl butyral (PVB) were added to the previous mixture and mixed for about 8 hours on a US Stoneware 755RMV ball rolling system. The method to form the ink is shown in
A three-part mold for the desired specification can be fabricated from polylactic acid (PLA) with dimensions 2.5×18×2-cm. An oil release agent can be applied to the inside of the mold pieces, and the base and middle frame were assembled for casting. The high alumina cement can be fabricated using the manufacturer's instructions (280 grams of high alumina cement mixed with 12% by weight of water). The high alumina cement can be poured into the mold to form Layer 1. While the refractory can be wet and setting, the mold can be moved to a Nordson Direct Ink Jet Printer (3-Axis EV Series Automated Fluid Dispensing Robot) to print Layer 2 and then Layer 3. The previously prepared inks were placed into printing syringes, capped, and then set aside for use. The Al2O3 ink (Layer 2) can be printed over Layer 1, whereby Layer 2 covered a slightly wider area than Layer 1 to be printed. The 3-3 Layer 3 composite inks (the two inks for each leg of the thermocouple to form the U-shaped thermocouple design) can be printed over Layer 2. This method can then be performed for Layer 1 through Layer 3, but in reverse for symmetry to form six total layers. Table 3 describes the printing setting for each of the direct-written layers (i.e., Layers 2 through 5).
A 6-layer thermocouple can be fabricated using LCC20-Al2O3 [80-20] and LC-Al2O3 [80-20] and LCC20-Al2O3 [50-50] and LC-Al2O3 [50-50] compositions as the primary and secondary core or inner most thermoelectric materials for Leg 1 and Leg 2, respectively. The six-layer thermocouple utilized three layers of differing composition mirrored about the inner most layers to fabricate six total layers. The six layers from this example are listed from bottom to top in Table 4.
The preparation methods to produce the thermocouple in Example 2 were the same as those performed in Example 1, but with the altered compositions identified in Table 4 and
Doped LCC30-Al2O3 and undoped LC-Al2O3 composites were used to fabricate thick-film thermocouples by stencil printing methods. The effects of dopant concentration (within the LC composition) and the Al2O3 composite content on the chemical stability, microstructure, and thermoelectrical properties were examined. Chemical phase development can be characterized by utilizing X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The microstructure evolution can also be characterized by scanning electron microscopy (SEM).
Strontium (Sr), calcium (Ca) and strontium/manganese (Sr/Mn) substituted or doped lanthanum chromite (La1-xSrxCrO3, La1-xCaxCrO3 and La0.8Sr0.2Cr1-xMnxO3 (0.1≤x≤0.3)) compositions were synthesized by a Pechini sol-gel method, employing citric acid (HO2CCH2—C(OH)(CO2H)CH2CO2H) (99.9% purity) as a complexing agent and La(NO3)3.6H2O (99.9% purity), Cr(NO3)3.9H2O (99.0% purity), Sr(NO3)2 (99.5% purity), Ca(NO3)2 (99.5% purity) and Mn(NO3)2.xH2O (99.0% purity) as the metal salt sources (all from Sigma Aldrich, USA). To simplify nomenclature, compositions are labeled as follows: LCCx, LSCx, and LSCMx for Ca, Sr and Sr/Mn substitution, respectively, where x indicates the percentage of molar substitution level (i.e., 0 to 30%). All metal nitrates were dissolved in deionized water, and the accuracy of the final metal concentrations can be established by an inductively coupled plasma-mass spectrometer (ICP-MSPerkin Elmer NexION 2000, USA) following the EPA Method 200.8.
The necessary solution concentration of metal species for each desired composition cam be weighed and mixed with citric acid at an equivalent molar ratio of 1:2 (metal cations: citric acid). Solutions were heated to about 80° C. until a viscous gel formed which finally yielded a purple solid precursor while slow drying. The dried gel can then then thermally treated at about 400° C. for 1 hr to remove the organic material. Samples were pulverized manually in a mortar and calcined at about 1200° C. for 3 hrs. Before the ceramic composite thick-film thermocouples were fabricated, doped LaCrO3—Al2O3 composite powder mixtures were prepared. Table 6 lists the compositions. As a reminder, the following designation of [X-Y] can be used to identify the composition and volume percentage of the prepared composites. For example, LCC20-Al2O3 [90-10] indicates 90% by volume of LCC20 and 10% by volume of Al2O3. The symbol “//” represents the thermocouple junction, wherein the compositions to the left and right of “//” represent the composition of a first leg and second leg of the thermocouple, respectively. The appropriate amounts of doped LaCrO3 powders were mixed with alumina (Al2O3) powder (99.8%, SSA: 8.6 m2/g, Almatis, Leetsdale, PA) and posteriorly ball-milled in a high-density polyethylene (HDPE) jar, using isopropyl alcohol and 5-mm diameter zirconia milling media (Tosoh Corporation, Japan) for 2 hrs. The final uniform powders mixtures were dried at 80° C. in a vacuum oven.
The doped LaCrO3—Al2O3 composite ink used in the stencil printing of the thick-film thermocouples can be prepared by mixing an organic vehicle (63-2 vehicle, Johnson Matthey, USA) and the previously prepared composite powders using an ultra-sonication probe. The composite powder to organic vehicle ratio can be 70:30 by percent weight for all ink formulations. The high-density alumina substrates were acquired from MTI Corporation (USA, CA). The stencil to pattern the thermocouple legs (L-shaped form pattern) can be cut from normal 3M masking tape (Backing: Crepe paper; Adhesive: Synthetic rubber solventless; width: 24 mm; length: 50 m; thickness: 0.10 mm) using a CO2 laser cutter (BossLaser BOSS-LS 1416). The cutting power can be 60 W with a cutting speed of 60 mm/s. To fabricate the thermocouple pattern, two layers of 3M masking tape were stacked onto each other and pushed together to make a thickness of 0.2 mm. The L-shaped pieces of masking tape were cut by a laser cutter to dimensions of 100 mm and 6 mm. The L-shaped pieces were then placed and pushed down to stick to the electronic grade alumina substrate (120×30 mm) using a rubber blade pushed over the surface to adhere in all locations. Approximately 2 g of undoped LaCrO3—Al2O3 composite ink can be pipetted at the long end of the channel and pushed down the L-shaped channel mold parallel to the channel length using a rubber edge. At the 90° location, the ink can be pushed parallel to the direction of the smaller channel design to fill the whole channel evenly using a rubber blade. Excess material can be pushed up onto the masking tape. The printed electrode or leg can be dried at 70° C. in an oven for 20 min. Two separate layers of tape were stacked and pressed onto one another to make a 0.2-mm thickness. A new L-shaped piece of masking tape can be cut by the laser cutter. The second two-layer stack of tape can be aligned to the other pre-printed L-shapes on the alumina substrate to make a channel between the two L-shaped pieces. Again, about 2 g of undoped LaCrO3 ink can be pipetted at the long end of the channel, spread and dried in a similar method as the first leg. Finally, a third L-shaped piece of masking tape can be again cut, and the layers were placed onto the previous two layers on the alumina substrate to build a total stack of 3 tapes that were 0.6-mm thick. The same methods were repeated to stencil and dry a third layer.
After drying, masking tapes can be removed and sintered in a tube furnace (Nabertherm RHTH 120/150/18/ furnace, Germany) within a dry air atmosphere using the following heating procedure: 30° C. to 600° C. at 2° C./min, then heated up to 1500° C. at 3° C./min and held for 60 min, then cooled down to 30° C. at 2° C./min. This procedure can be used to print and bond one side (or first leg) of the thermocouple (in this case, the LaCrO3 (LC) side of the thermocouple). To produce the entire thermocouple, the second leg (the doped LaCrO3 compositional side) can be replicated as a mirror image of the first leg, with a slight overlap to create a junction between the two legs. The same stencil printing method can be used to produce the second leg, with the only difference being the doped LaCrO3 ink composition. After stenciling the second leg, overlapping the first LC leg by about 1 to 3 mm, the thermocouple can be sintered in a tube furnace (Nabertherm RHTH 120/150/18/ furnace, Germany) under a dry air atmosphere, using the following heating program: 30° C. to 600° C. at 2° C./min, then heat up to 1500° C. at 3° C./min and hold for 60 min, then cooling down to 30° C. at 2° C./min.
To complement the understanding of the thermoelectrical properties of LCC3-Al2O3 composites, electrical conductivity measurements as a function of temperature up to 1500° C. were performed.
SEM and EDS chemical analysis were completed to illustrate the effect of Al2O3 content on the microstructure and phase distribution in sintered thermocouple legs based on LCC30-Al2O3 composites.
The level of connectivity of the conductive phase in the ceramic composite (LCC30) altered its thermoelectric properties as well as its chemical and thermoelectrical stability. For a two-phase material such as LCC30-Al2O3, a 3-3 composite, which designates an interconnected mixture of the two phases, appears like a sponge-like structure where the solid material is connected in three dimensions, as well as the 3-D connectivity of the porosity or void space of the sponge-like structure. Depending on the volumetric ratio of LCC30 and Al2O3 (and the particle size ratio of each of these constituents), a 3-0 composite (at typically ≤10 vol % Al2O3 content) or a 3-3 composite (at typically >10 vol % Al2O3 content) formed. No connectivity can be observed between Al2O3/aluminates grains at 10 vol % of Al2O3, indicating a 3-0 composite formation as shown in
Table 7 lists experimental Seebeck coefficients for three LCC30-Al2O3//LC-Al2O3 ceramic composites thermocouples, which shows the Seebeck coefficient increasing depending on the amount of Al2O3 content. The formation and distribution of Al2O3 grains throughout the composite microstructure increased electrical resistivity.
Undoped and doped LaCrO3—Al2O3 composite inks for stencil printing were prepared by mixing 66 g of composite powder with about 38.7 g of an ethanol-xylene mixture (50-50% by weight) and 1.4 grams of a fish oil solution in xylene for about 4 hrs on a US Stoneware 755RMV ball rolling system. Finally, 3 g of Plasticizer UCON50HB2000 (Polyalkylene Glycol), 3 g of Plasticizer S-160 (butyl benzyl phthalate), and 6 g of Polyvinyl butyral (PVB) were added to the previous mixture and mixed for about 8 hrs on a US Stoneware 755RMV ball rolling system. The stencil to pattern the thermocouple legs (L-shaped pattern) can be cut from high density, 0.35-mm thick plastic sheets using a CO2 laser cutter (BossLaser BOSS-LS 1416). The cutting power can be 60 W with a cutting speed of 60 mm/s. Four double L-shaped pieces of plastic were cut by a laser cutter to 228.6 mm (length) and 6 mm (width) dimensions (see
Additional performance results on thermocouple devices embedded within refractory cement can be obtained. Thermocouples were fabricated by a stencil printing method and embedded into 1.0×0.5×6.0-in refractory brick. These bricks were cast, sintered, and tested in a gas-fired kiln. The stencil thickness evaluated can be 350 μm. The stencils were adhered onto filter paper and the filter paper with dried, green sensing material can be embedded into the brick during casting process. The bricks were sintered at 1500° C. With the 350-μm thick stencil, only one layer of sensing materials can be applied for each leg of the thermocouple.
Additional tests were performed with an alternative stenciling ink formulation used to deposit sensor materials. Thermocouple legs can be deposited onto Waltman filter paper number 42 using a stencil acting as the sacrificial substrate, for example. The deposited paper can then placed in a brick during casting of the refractory. While the brick is sintered, the paper disintegrates or dissolves, leaving behind a sensor embedded within the fired brick. Two additional sacrificial substrates were evaluated: coarse filter paper (30-50 mm pore size) and dissolvable paper alongside the Waltman 42 filter paper (2.5 mm pore size). Six sensors were fabricated and tested for each substrate.
All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided herein can be different from the actual publication dates, which can require independent confirmation.
This application claims the benefit of U.S. provisional application entitled “Ceramic Composite High Temperature Thermocouples and Methods Thereof” having Ser. No. 63/500,261, filed May 4, 2023, which is hereby incorporated by reference in its entirety.
This invention was made with government support under contract no. DE-FE0031825 awarded by the U.S. Department of Energy. The Government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63500261 | May 2023 | US |
