阅读说明：本技术 高温密封剂及其方法 (High temperature sealant and method ) 是由 M·A·德拉克 R·M·莫伦纳 于 2018-05-08 设计创作，主要内容包括：一种制备化学计量的独居石(LaPO<Sub>4</Sub>)组合物或者LaPO<Sub>4</Sub>和LaP<Sub>3</Sub>O<Sub>9</Sub>成分的混合物的方法,如本文所限定。还公开了用本文限定的组合物接合或密封材料的方法。(A method for preparing stoichiometric powderCurie stone (LaPO) 4 ) Composition or LaPO 4 And LaP 3 O 9 A method of mixing ingredients, as defined herein. Also disclosed are methods of joining or sealing materials with the compositions defined herein.)

1. Preparation of stoichiometric monazite (LaPO)₄) A method of composition comprising:

preparing La-phosphate glass frit particles comprising: at a suitable melting temperature (T)_Melting) Melting La at a molar ratio of 30:70₂O₃∶P₂O₅Then pouring, rolling and grinding the resulting molten mixture into frit particles of suitable particle size; and

mixing the resulting glass frit particles with a lanthanum source and heating to a reactive ceramming temperature (T)₁) And continued sufficiently to form stoichiometric LaPO₄A time of (a) wherein T_MeltingGreater than T₁。

2. The method of claim 1, wherein the glass frit has a suitable melting temperature (T ™)_Melting) 1400 ℃ and 1700 ℃ of reactive ceramic temperature (T)₁) At 1200 deg.c and 1500 deg.c for sufficient time.

3. The method of claim 1, wherein the suitable frit particle size is an average particle size of 10-15 microns.

4. Preparation of LaPO₄And LaP₃O₉The method of mixing of (a), comprising:

preparing La-phosphate glass frit particles comprising: at a suitable melting temperature (T)_Melting) Melting La at a molar ratio of 25:75 to 20:80₂O₃:P₂O₅Then pouring, rolling and grinding the resulting molten mixture into frit particles of suitable particle size; and

mixing the resulting glass frit particles with a lanthanum source and heating to a reactive ceramming temperature (T)₁) And continued sufficiently to form LaPO₄And LaP₃O₉Of a mixture of (1), wherein T_MeltingGreater than T₁。

5. The method of claim 4, wherein the glass frit has a suitable melting temperature (T ™)_Melting) 1400 ℃ and 1700 ℃ of reactive ceramic temperature (T)₁) 1200-.

6. A sealing composition comprising a mixture of a La-phosphate glass frit and a lanthanum source.

7. A method of joining and sealing two objects, comprising:

contacting the first and second objects with a sealing composition comprising a mixture of a La-phosphate glass frit and a lanthanum source;

heating the contacted first and second objects and sealing composition to 1200-; and

the first heated object and the sealing composition are heated a second time to 1500-.

8. The method of claim 7, wherein the first and second objects are the same or different materials.

9. The method of claim 7, wherein the first and second objects are selected from at least one of silicon carbide, alumina, zirconium, or combinations thereof.

10. The method of claim 7, wherein the first and second objects are respective ends of a furnace tube.

11. The method of claim 7, wherein the first and second objects are selected from sheets, tubes, rods, fibers, cylinders of the same or different materials.

Brief description of the drawings

In an embodiment of the present disclosure:

FIG. 1 shows La₂O₃-P₂O₅Binary system (% by weight).

FIG. 2 shows La₂O₃-P₂O₅The binary system (% by weight) shows a region of potential reactant frit (200).

FIG. 3 shows XRD of the monazite reaction couple (reaction couple) of the composition of example 4, which was fired at 1500 ℃ for 4 hours (hold at 1200 ℃ for 4 hours).

Figure 4 shows XRD of the monazite reaction couple for the sample of example 5, which was fired at 1500 ℃ for 4 hours (held at 1200 ℃ for 4 hours).

Figure 5 shows a partial overlay of the XRD patterns shown in figures 3 and 4, corresponding to the monazite reaction couples of example 4(500) and example 5 (510).

Figure 6 shows a SiC test coupon coated with the reaction blend of example 5b and held at 1500 ℃ for 120 hours.

Fig. 7 shows a schematic view of an assembly for testing high temperature hermeticity.

Fig. 8A to 8C show SEM images (fig. 8A and 8B) and EDAX scans (fig. 8C) of the stoichiometric reaction couple after failure of the hermeticity test.

FIG. 9 shows La of stoichiometric blend of pure monazite (900)₂O₃-P₂O₅The binary phase diagram and the phase composition of the non-stoichiometric monazite blend (910) of example 6.

FIG. 10 shows the reaction couple of example 6 after firing to 1500 ℃ for 4 hours. Monazite is the predominant crystalline phase with minor amounts of LaP₃O₉。

FIG. 11 shows the leakage rate versus cycle number test performance for the blends of example 6.

Fig. 12A to 12D show SEM and EDAX scans of the non-stoichiometric blend of example 6 after hermeticity testing.

Detailed Description

Various embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, if any. Reference to various embodiments does not limit the scope of the invention, which is limited only by the scope of the claims appended hereto. Additionally, any examples given in this specification are not limiting and merely set forth some of the many possible embodiments for the claimed invention.

Definition of

"stoichiometric blend" and like terms mean comprising, for example, a 30:70 weight ratio of La₂O₃:P₂O₅Pure monazite blends of (a).

"non-stoichiometric blend" and like terms refer to a compound or composition that is slightly different from the pure monazite blend described above, comprising, for example, 25:75 molar ratio or 35:65 weight ratio of La₂O₃:P₂O₅。

"glass frit," "frit," and similar terms refer to a ceramic composition that has been melted, quenched in a melting furnace to form glass and pelletized. The glass frits may form part of the batch used in compounding enamel and ceramic glazes or be used for frit bonding; the purpose of the pre-melting may be to render it insoluble, for example by combining any soluble or toxic components with the silica and other added oxides.

"ceramming," "vitrification," and similar terms refer to subjecting a glass substrate (having selected properties, such as crystal content) to additional thermal cycling at elevated temperatures. The crystals contained in the substrate grow and change the molecular structure of the substrate until the proper equilibrium (i.e., equilibrium) is formed between the crystalline phase and the residual glass in the substrate. Ceramization is also described in e.g. US 9,556,055. The glass sheet may be cerammed, i.e., heat treated, to produce the desired glass-ceramic product. The ceramic cycle may include the following steps: 1) heating the glass sheet from room temperature to a first temperature at a first heating rate; 2) maintaining the glass sheet at the first temperature for a predetermined time; 3) heating the glass sheet from the first temperature to a second temperature at a second heating rate; 4) maintaining the glass sheet at the second temperature for a predetermined time; 5) the glass sheet is cooled from the second temperature to room temperature at the first cooling rate.

"reactive ceramming" and like terms refer to the combination or reaction of a glass frit and at least one reactant to produce a final crystalline phase. Reactive ceramization is also described in, for example, commonly owned US 8,850,851.

"hermetic," "hermetic seal," "hermetic test," and similar terms refer to the hermetic quality of something (e.g., a container, structure, or similar vessel or structure). The hermetic seal or quality of a satisfactory seal made by the compositions and methods of the present disclosure can have, for example, less than or equal to 1 x10^-1atm-cm³Leakage rate in/s.

In embodiments, "consisting essentially of means, for example, of the disclosed ceramic composition, method of making or using the disclosed composition, or formulation of the present disclosure, and may include the components or steps listed in the claims, plus other components or steps that do not materially affect the basic novel properties of the compositions, articles, devices, or methods of the present disclosure, such as the particular reactants, particular additives or ingredients, particular reagents, particular surface modifiers or conditions, or similar structure, materials, or process variables selected. Items that may materially affect the basic properties of the components or steps of the disclosure, or that may impart undesirable characteristics to the disclosure, include, for example, excessive deviation from the disclosed batch proportions, particle sizes, heating profiles, firing profiles, reactive ceramic temperatures, melting temperatures, and the like.

In embodiments, "consisting of … …" means, for example, a disclosed ceramic composition, a method of making or using a disclosed composition, or a formulation of the present disclosure, and includes only the components or steps recited in one or more claims.

"include," "include," or similar terms are intended to encompass, but not be limited to, both inclusive and non-exclusive.

The "about" used in describing embodiments of the present disclosure to modify values such as the amount, concentration, volume, process temperature, process time, yield, flow rate, pressure, viscosity, etc., of ingredients in a composition and ranges thereof, or part size and the like and ranges thereof, refers to the possible change in value, for example: typical measurement and processing procedures resulting from the formulations used to prepare the materials, compositions, composites, concentrates, assemblies, articles of manufacture, or use; due to inadvertent errors through these procedures; due to differences in the manufacture, source, or purity of the raw materials or ingredients used to carry out these methods; and the like. The term "about" also encompasses amounts that differ due to aging of a composition or formulation having a particular initial concentration or mixture composition, as well as amounts that differ due to mixing or processing of a composition or formulation having a particular initial concentration or mixture composition.

"optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

As used herein, the indefinite articles "a" or "an" and their corresponding definite articles "the" mean at least one or more unless otherwise indicated.

Abbreviations well known to those of ordinary skill in the art may be used (e.g., "h" or "hrs" for one or several hours, "g" or "gm" for grams, "mL" for milliliters, "rt" for room temperature, "nm" for nanometers, and the like).

Specific and preferred values for components, ingredients, additives, dimensions, conditions, time, and the like, and ranges thereof, disclosed herein are for illustrative purposes only and do not preclude other defined values or other values within the defined ranges. The compositions and methods of the present disclosure may include any value described herein or any combination of such values, specific values, more specific values and preferred values, including explicit or implicit intermediate values and ranges.

U.S. patent 6,716,407 entitled "monazite-based coating for thermal protection system" mentions monazite-based or xenotime-based cover coatings that stiffen ceramic fabrics but do not cause embrittlement at temperatures at least as high as 2400 ° F (i.e., 1315.5 ℃). This patent mentions a process for preparing coatings comprising synthesizing high purity monazite and xenotime powders wherein the stoichiometric ratio of metal to phosphorus is about 1: 1. Using a ceramic process, the product powder is considered porous. This reference is silent as to the method of making the article as provided in the present disclosure.

U.S. patent 7,871,716 entitled "damage tolerant gas turbine component" refers to damage tolerant components for use in high temperature combustion gas environments. The component includes a plurality of tiles (94) bonded to a substrate (92) for isolating any impact damage to the damaged tiles. Grout (98) may fill the gaps between adjacent bricks to passivate any crack tips extending from the damaged bricks. The tile barrier may be applied to two layers (56, 58) which differ in material properties, for example, the bottom layer being selected for thermal insulation properties and the top layer being selected for impact resistance properties. A layer of sealing material (100) may be applied over at least a portion of the tiles. This reference is silent as to the pure or 100% monazite or non-stoichiometric composition provided by the present disclosure.

Boakye et al, "monazite coating on SiC fiber I: fiber strength and thermal stability ", proceedings of the american society for ceramics (j.am.ceramic. soc.), 89: 3475 3480, 11.2006, mentions coating of monazite on SiC fibers; boakye et al, "monazite coating on fiber: II, no strength-reducing coating ", american ceramics institute bulletin, 84: 2793 2801, 12.12.2001, mention of coating phosphor-rare earth ore (LaPO)₄·xH₂O) sol to apply the monazite coating to selected fibers.

In some embodiments, the present disclosure provides a method of making stoichiometric monazite (LaPO)₄) A method of composition comprising:

preparing La-phosphate glass frit particles comprising: at a suitable melting temperature (T)_Melting) For example, melting La at 1400 to 1700 ℃ (e.g., 1600 ℃) in a molar ratio of 30:70₂O₃:P₂O₅A mixture of (a); the resulting molten mixture is then poured, rolled and ground into frit particles of suitable size, for example, an average particle size of 10 to 15 microns; and

mixing the resulting glass frit particles with a lanthanum source (e.g., La)₂O₃) Mixing and heating to a reactive ceramming temperature (T)₁) For a time sufficient to form stoichiometric LaPO₄I.e. pure LaPO₄Or monazite, or LaPO₄Of non-stoichiometric mixtures, e.g. 2/3LaPO₄(monazite) and 1/3LaP₃O₉(by weight) of which T_MeltingGreater than T₁。

Suitable melting temperature (T)_Melting) 1400 to 1700 ℃ and a reactive ceramization temperature (T)₁) May be, for example, 1200 to 1500 c and for a sufficient time.

Suitable particle sizes are average particle sizes of 10 to 15 microns, for example 6 to 20 microns.

In some embodiments, the present disclosure provides for the preparation of LaPO₄Glass and La₂O₃The method of mixing of (a), comprising:

preparing La-phosphate glass frit particles comprising: at a suitable melting temperature (T)_Melting) For example 1400 ℃ 1700 ℃, for example 1600 ℃, melting La in a molar ratio of 25:75 to 20:80₂O₃:P₂O₅A mixture of (a); the resulting molten mixture is then poured, rolled and ground into frit particles of suitable size, for example, an average particle size of 10 to 15 microns; and

mixing the resulting glass frit particles with a lanthanum source (e.g., La)₂O₃) Mixing and heating to a reactive ceramming temperature (T)₁) Maintaining for a sufficient time to form LaPO₄Mixtures of (A) such as 2/3LaPO₄(monazite) and 1/3LaP₃O₉(by weight) of which T_MeltingGreater than T₁。

Suitable melting temperature (T)_Melting) May be, for example, 1400 to 1700 ℃, reactive ceramization temperature (T)₁) 1200 to 1500 ℃ and for a sufficient time.

Suitable particle sizes may be 1 to 25 microns, e.g., 10 to 15 microns, an average particle size of 6 to 20 microns, and similar sizes, including intermediate values and ranges.

In some implementationsIn one aspect, the present disclosure provides a sealing composition comprising stoichiometric LaPO₄Or lanthanum phosphate glass frit and lanthanum source such as La₂O₃Of non-stoichiometric LaPO₄And (3) mixing.

In some embodiments, the present disclosure provides a method of joining and sealing two objects, comprising:

contacting the first and second objects with a sealing composition comprising a lanthanum phosphate frit (see, e.g., frits of examples 1 and 2) and a lanthanum source (e.g., La₂O₃Or LaCO₃(see, e.g., the glass frits of examples 1 and 2, and the glass frit and La source mixtures of examples 4 and 5));

heating the contacted first and second objects and sealing composition to 1200-; and

the first heated object and the sealing composition are heated a second time to 1500-.

In some embodiments, the first object and the second object are the same or different materials.

In some embodiments, the first and second objects are selected from at least one of silicon carbide, alumina, zirconium, or combinations thereof.

In some embodiments, the first and second objects may be, for example, respective ends of a furnace tube.

In some embodiments, the first and second objects may be selected, for example, from sheets, tubes, fibers, cylinders, and similar geometric objects or devices of the same or different materials.

In some embodiments, the present disclosure is advantageous in several respects, including, for example:

providing a high temperature sealant that is hermetic at 1500 ℃ and has a melting temperature greater than 2000 ℃;

the sealant is based on monazite (LaPO)₄) Using a low temperature frit as one of the reactants;

the sealant composition can be used, for example, to seal SiC furnace tubes end-to-end in joints; and

the sealant composition can be used in many different high temperature sealing applications, such as high temperature mortars, refractory bricks in high temperature furnaces, or similar structures and conditions.

In some embodiments, the present disclosure provides a method of making a sealant that is stable (as defined herein) and hermetic at high temperatures.

In some embodiments, the present disclosure provides a reactive ceramization process for making a sealant.

Refractory compounds, such as pollucite (Cs), have previously been synthesized using reactive ceramming methods₂O·Al₂O₃·4SiO₂，T_mAbout 2800 ℃ C.) and xenotime (YPO)₄Sister compounds of monazite, T_m2150 ℃ (see, for example, U.S. patent No. 5,094,677, commonly owned and assigned by Morena, "preparation of pollucite ceramics"; commonly owned and assigned U.S. patent No. 6,770,111, "pollucite-based ceramics with low CTE"; U.S. patent No. 8,850,851, commonly owned and assigned to Lamberson et al, "ceramic manufacture by reactive ceramization of frits".

In some embodiments, the seal preferably can withstand temperatures up to 1500 ℃ or more and is gas tight.

Rare earth phosphate monazite (LaPO)₄) Is a very refractory and stable compound, the melting temperature (T)_m) At 2250 ℃. Due to its extremely high refractoriness, the synthesis of this compound by the traditional ceramic powder route requires high temperatures to obtain phase pure amounts from the starting reactants. Similarly, synthesis of the material via a glass-ceramic route would also require higher process temperatures to melt the precursor glass. The glass-ceramic route is also less likely to produce phase purity.

Monazite is a highly refractory material that is difficult to synthesize in reasonable purity by the glass-ceramic route. Having 50 mol% La₂O₃Even glass formation is not possible with stoichiometric monazite. If so, any glass must be melted to at least 2300 ℃ due to the liquidus of 2300 ℃, which proves that the glass-ceramic route is impractical to obtain monazite. Similar difficulties exist in obtaining sintered monazite products via the ceramic route. The reactive ceramming approach disclosed herein provides a route to the synthesis of high temperature compounds (monazite) that cannot be conveniently and easily prepared by alternative methods.

The following scheme summarizes three possible synthetic routes:

ceramic: reactant 1+ reactant 2 → ceramic product

Glass-ceramic: precursor glass → glass-ceramic product + residual glass

Reactive ceramics: reactant 1+ frit → reactive ceramming product

The advantage of the reactive ceramization route over the other two routes is that the synthesis can be done at much lower temperatures. This indicates that the diffusion process of the frit occurs at a higher rate than other techniques due to viscous flow. This is particularly important when the reactant glass is a relatively low temperature glass.

In some embodiments, monazite has been selected as a possible candidate sealant material for joining SiC pipe segments because of its high temperature compatibility with SiC, and because monazite has been used as an oxidation resistant coating for SiC fibers in high temperature fiber reinforced composites, such as in sol-gel processes. Although monazite itself has a specific SiC ratio (35X 10)^-7CTE/c) relatively high coefficient of thermal expansion (e.g., CTE 90x10^-7/° c), but this CTE difference is not expected to be problematic for high temperature sealing applications (e.g., the sealed component is not cooled, e.g., below 600 to 800 ℃) (see, e.g., Boakye et al, "monazite coating on SiC fibers I,same as above(ii) a And Boakye et al, "monazite coating on fiber: II, performing a chemical reaction on the mixture of the two components,same as above”。

In other words, the disclosed sealing or bonding compositions have high temperature CTE compatibility due to the presence of a liquid phase and low temperature CTE incompatibility due to the absence of a liquid phase.

General procedure

A. Synthesis of monazite or monazite mixtures

FIG. 1 shows La₂O₃-P₂O₅Binary system (in% by weight), stoichiometric monazite (LaPO)₄) Occurs at about 30% P₂O₅To (3). Note monazite (LaPO)₄) At 30% by weight P₂O₅The melting temperature was 2250 ℃.

FIG. 2 shows the same binary system diagram as FIG. 1, and also shows the region (200) representing a binary system having 50-70 wt% P₂O₅The reactant glass frit composition of (1), which may be mixed with 30 to 50 wt% of La₂O₃The reaction forms monazite. These reactant frit compositions are selected because they are pourable melts at less than or equal to 1650 ℃ and P₂O₅Is not so high as to cause problems of hygroscopicity or durability.

The reaction of the present preparation method can be represented as:

La₂O₃+ La-phosphate frit → LaPO₄

Precursor glass frits (such as those mentioned in examples 1, 2 and 3) were melted in batches of, for example, 800g each. The raw materials used to prepare the precursor frit were phosphorus pentoxide and technical grade (98.6% purity) lanthanum oxide in the indicated weight percentages. Melting of the feedstock is accomplished, for example, at 1600 c for 12-16 hours in a covered Pt crucible, and the melt is then poured to form a tape and ball milled, for example, for about 8 hours or until an average particle size of 10-15 microns or-325 mesh (i.e., 44 microns) is achieved. Two specific precursor frits were selected, the compositions of which are listed in table 1, along with the desired La₂O₃To obtain stoichiometric LaPO₄。

In some embodiments, the composition of example 1 (base glass composition) (La)₂O₃:P₂O₅Mole percent 20:80) is less desirable due to hygroscopicity.

In some embodimentsComposition of example 2 (another base glass composition) (La₂O₃:P₂O₅Mole% ═ 30:70) is excellent because it does not absorb moisture.

In some embodiments, the composition of example 3 is a repeat of example 2 and is also excellent because it does not absorb moisture.

TABLE 1 precursor glass frits and reaction couples

TABLE 2 reactive ceramicizing blends and preliminary results

TABLE 3 reaction sequence and XRD results for the reaction couple of example 5b

Figures 3 and 4 show XRD of the two blends fired to 1200 ℃ for 4 hours, then to 1500 ℃ for 4 hours. All peaks in both samples were identified as monazite. However, in the samples of example 4(500), there is a very small unidentified peak (520) at about 22 ° 2 θ, which is not present in the samples of example 5(510) (see superimposed graph in fig. 5). After firing, there appeared to be no residual glass in both samples.

Based on the very small unidentified peak in the sample of example 4, and the precursor of the glass of example 1 due to P₂O₅High levels with slight hygroscopicity focused further evaluation on the reaction couple involving example 2. To investigate the reaction sequence and temperature range for monazite formation, the starting batch of example 2 was remelted as example 3 and a 59 frit to 41La was prepared₂O₃A stoichiometric mixture of monazite reaction couples was used as a sample of the blend in example 5b (a repeat of example 5). The samples were then fired at a range of temperatures and then analyzed by XRD. The results are shown in Table 3.

Note that in Table 3, monazite (LaPO)₄) At a temperature as low as 600 ℃ and a large amount of unreacted La₂O₃And unreacted glass. Despite the unreacted glass together with a large amount of two binary phases (La)₃PO₇And LaP₃O₉And LaPO₄) Still present, but La₂O₃Disappeared above 600 ℃. From 800 to 1000 ℃, the XRD intensity of monazite increases rapidly, while in the same temperature range the intensities of the two binary phases decrease rapidly. Monazite is the only crystalline phase at temperatures greater than or equal to 1000 ℃, and as the reaction temperature increases, the XRD intensity increases. Rapid increase in monazite peak height and La₃PO₇And LaP₃O₉The rapid decrease in peak height indicates, although not limited by theory, that monazite formation occurs through the following reaction:

La₃PO₇+LaP₃O₉→4LaPO₄

B. high temperature adhesive

1. Compatibility with SiC

Compatibility of the monazite reactive ceramicized blend with SiC was first evaluated before any sealing experiments with SiC were performed. Initial evaluations involved coating a SiC coupon with the unreacted blend paste, firing it to 1500 ℃, and then holding it at this temperature for 120 hours. Figure 6 shows the test specimen of example 5b after testing. The coating appears to be unaffected by prolonged periods of time, high temperatures or contact with SiC. This confirms the compatibility of the disclosed monazite system with high temperature and SiC.

2. High temperature adhesion and air tightness evaluation

A suitable sealant for joining the SiC tube segments together is preferably capable of forming a hermetic seal both after high temperature exposure and high temperature thermal cycling. The test assembly consists of two SiC tubes (one with a closed end)) The SiC tubes are bonded together by a reactive ceramicized blend. After bonding at 1500 ℃, the individual assemblies were placed in a circulating oven, pressurized with He, and then subjected to 150 thermal cycles between 1200 ℃ and 1500 ℃ (fig. 7). Less than 1.00x10^-1atm.cm³The leakage rate in/s is considered acceptable.

In this test, a preliminary evaluation of the blend of example 5b showed an initial low leak rate, then increased to greater than 1.00x10 after several tens of cycles^-1atm.cm³And s. The reason for the poor sealing performance can be seen from the SEM microstructure of the frit-sealed area of the actual test sample shown in fig. 8A (500 microns) and fig. 8B (50 microns). The SEM (fig. 8A to 8B) shows a highly crystalline single phase but porous microstructure. As shown in fig. 8C, position in the SEM image of fig. 8B "⁺1 "and"⁺EDAX (energy dispersive X-ray analysis) of 2 "(circled) indicates a La/P ratio of about 1, further indicating that the single phase is LaPO₄Or monazite.

FIG. 9 shows La₂O₃–P₂O₅A binary phase diagram showing: from 30 wt% of La₂O₃And 70 wt% of P₂O₅A stoichiometric or equilibrium blend of pure monazite of composition (900); and phase composition of the non-stoichiometric blend of example 6 (910): liquid and monazite at a temperature above 1050 deg.C, and monazite and LaP at a temperature below 1050 deg.C₃O₉。

By breaking the idea of a pure monazite phase, a microstructure is designed comprising monazite and a second phase, wherein the second phase is liquid at the test temperature, whereby poor high temperature sealability is improved. This is accomplished by reactive ceramicizing blend example 6, designed to form a reactive ceramicizing blend consisting of approximately 2/3LaPO at a temperature of less than 1050 ℃₄(monazite) and 1/3LaP₃O₉A two-phase mixture of compositions. At temperatures above 1050 ℃, the phase composition consists of monazite and liquid.

Table 4 non-stoichiometric blend of example 6

The XRD of the reactive ceramic couple of example 6 after firing to 1500 ℃ is shown in figure 10. Monazite was observed as the major phase with a small amount of LaP₃O₉Consistent with the phase diagram.

Fig. 11 shows the results of a hermeticity test of a reactive ceramic couple using the test apparatus shown in fig. 7. Fig. 7 shows a schematic view of an assembly for testing high temperature hermeticity. The test assembly includes an oven (700) that is thermally cycled, for example, between 1200 ℃ and 1500 ℃; a silicon carbide sample (710); two silicon carbide tubes (720a, 720b) bonded to a silicon carbide sample (710), one of the silicon carbide tubes (720a) having a closed end (750) and the other of the silicon carbide tubes (720b) having an open end (730); a helium source (740); and a reactive ceramicized blend composition (740) for joining (760) the ends of the tubes or sealing (760) the tubes together. The seal satisfied 1.00x10 in 150 cycles from 1200 ℃ to 1500 ℃^-1atm-cm³Leakage requirement of leakage rate per s.

While not being bound by theory, a possible explanation as to why the non-stoichiometric blend of example 6 meets the hermeticity/cycle requirement and the phase-pure monazite blend does not, can be seen in fig. 12A to 12D, which show SEM and EDAX scans of the test seals after the leak test was completed. Fig. 12A and 12B show SEM images of two-phase microstructures at 500X and 5,000X magnification, respectively. Fig. 12C and 12D show EDAX scans of the light phase region (12C, from position "+ 1" in 12B) and the dark matrix region (12D, from position "+ 2" in 12B), respectively. Fig. 12A and 12B show the microstructure of the seal after testing. A two-phase microstructure can be observed, the main phase consisting of large and bright angular crystals (angular crystals) in a matrix of the second dark phase. Fig. 12C shows EDAX for one of the bright corner crystals. The La/P ratio of this phase was about 1, indicating that these crystals were monazite. EDAX results for the dark phase are shown in fig. 12D. The La/P ratio of this phase is much less than 1, indicating that the darkness corresponds to LaP₃O₉. As previously described, LaP₃O₉Melting at 1050 ℃ is inconsistent and forms monazite and liquid. The liquid forms a continuous matrix phase, resulting in improved gas tightness of non-stoichiometric monazite compared to pure monazite.

Examples

The following examples illustrate the preparation, use and analysis of the disclosed compositions and methods according to the general procedures described above.