JPS62245145A - Method for quantifying composition of electrolyte plate - Google Patents

Abstract

PURPOSE:To measure the composition of an electrolyte plate within a short time, by a method wherein lithium aluminate being the electrolyte holding material of a fuel battery, and lithium carbonate and potassium carbonate being electrolytes are melted under heating to be formed into a glass bead which is, in turn, subjected to fluorescent X-ray analysis. CONSTITUTION:The electrolyte plate of a molten carbonate type fuel cell is constituted of lithium aluminate being an electrolyte holding material, and lithium carbonate and potassium carbonate being electrolytes. Said electrolyte plate is heated and melted along with a flux agent at 650-1,000 deg.C to prepare a glass bead specimen. As the flux agent, a composition comprising a mixture consisting of anhydrous lithium borate being a main component, lithium carbonate and sodium iodide and having a compositional wt. ratio of 5:1:0.02-10:1:0.02 is used. The bead specimen is subjected to fluorescent X-ray analysis and lithium aluminate is quantified from AlKalpha fluorescent X-ray intensity while potassium carbonate is quantified from KKalpha fluorescent X-ray intensity and both values are subtracted from the whole to calculate lithium carbonate. Because the bead specimen is prepared and subjected to fluorescent X-ray analysis, the composition can be analyzed within a short time with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a method for analyzing the composition of an electrolyte plate, which is one of the main components of a molten carbonate fuel cell.

More specifically, the electrolyte plate contains a carbonate serving as an electrolyte (for example, Ls*COs I (acos)) and an electrolyte holding material (for example, LiALO) for holding the electrolyte in a molten state.
,) relates to a method for volumetric analysis of constituent material components of an electrolyte plate.

[Prior art and its problems]

The development of fuel cells has become active, and molten carbonate fuel cells use carbonates of various alkali metals as electrolytes, and generally lithium carbonate/potassium carbonate (L
It is often a binary system of t, co3/, Co, ).

For example, lithium aluminate (
Powder of LiAt (LiAt) and porous ceramic plate are used.

An example of the mixing ratio of such an electrolyte plate is 40% LiAt in terms of weight ratio of electrolyte holding material and electrolyte.

The level is 32 wt% *COs and 28 wt% Li1CO1. Known methods for manufacturing electrolyte plates include a method in which carbonate powder and lithium aluminate powder are mixed and pressure-molded using a hot press, and a method in which a sheet of electrolyte holding material is formed and impregnated with electrolyte.

The thickness of the electrolyte plate in this case varies depending on the design and manufacturing method, but it is a thin plate of about 1 m. The composition of this electrolyte plate greatly influences the mechanical strength of the electrolyte plate, battery characteristics, etc. In addition, the return rxffl may be lost during operation, shortening the service life. Therefore, quantitative evaluation of the electrolyte plate composition is necessary and important for battery research and development, and there is a need for a method for quickly and accurately quantifying the composition of the electrolyte plate.

In general, the composition of the electrolyte plate (LiAt0., Li,
Co.

It is desirable to be able to directly quantify K, Co1) in its compound form, and techniques such as X-ray diffraction can be considered as a method for this. However, since this method depends on the crystallinity of the sample to be measured, there is a problem in that accurate quantification cannot be achieved when the sample is amorphous or has an intermediate composition between the aforementioned compounds.

Therefore, a common method is to convert the quantitative analysis of the constituent elements into the composition of the compound.

Quantitative analysis methods for Li, At, and
It is thought that the following methods can be generally applied by combining the methods and pretreatments for each yuzu described in Revised Third Edition (1981) J. Li is determined by acid decomposition, lithium periodate precipitation, separation, iodine titration method, Yabo decomposition, and flame oxidation method.The red set meal is determined by acid decomposition, alkali fusion, and chelate titration method.The K set meal is determined by Lawrence Smith decomposition. (NH,Ct
and CaC0, mixed and heated and melted) and potassium chloroplatinate (
KIPt C4a) There are analytical methods such as gravimetric method and acid decomposition/atomic absorption method.

However, these methods require pretreatment suitable for the analysis method for each component, and have drawbacks such as complicated and time-consuming analysis operations and lack of speed. Furthermore, these methods are methods for separating and quantifying components in a sample, making simultaneous analysis and evaluation difficult.

[Purpose of the invention]

The present invention has been made in view of the above points, and its purpose is to provide an analysis method that can obtain accurate quantitative analysis results for the composition of an electrolyte plate containing LiAt02-Li2C01-K1CO3 in a short time. .

[Key points of the invention]

In the present invention, an electrolyte plate of a molten carbonate fuel cell is composed of LiAtO as an electrolyte holding material and Co as an electrolyte.
We have found optimal sample preparation conditions that can quickly produce homogeneous glass beads by simply heating and melting them together with a flux.

Furthermore, the prepared glass beads were measured using fluorescent X-rays, and the fluorescent X-ray intensities of ktKα, KKα and LiAt0, -
It was found that there is an open correlation with Co3, and by applying this method, the electrolyte plate 1, i
Atom and ICo can be quantified simultaneously and accurately. Regarding the amount of L 1 t COn in the electrolyte component, after determining the quantitative value of Co in addition to LiAt0*, it is determined as the remainder of the constituent components of the electrolyte plate. It was made so that it could be done.

[Embodiments of the invention]

The present invention will be explained below based on examples. In the present invention, after glass-melting an electrolyte plate, the components of the electrolyte plate contained in glass beads are determined by fluorescent X-ray analysis. First, a method for preparing an analysis sample will be described.

- The electrolyte plate of a mosquito-molten carbonate fuel cell is made of an inert inorganic material (e.g. L 1 AtO or A) as an electrolyte holding material.
T! O, etc.) and electrolyte carbonate (e.g. Li, co3°K, Co3), so when evaluating the composition of the electrolyte plate,
There are cases where the amounts of the above-mentioned constituent components are determined simultaneously or only one of them, and it is important to apply a method for preparing an analytical sample and a method for measuring the same in order to satisfy this requirement.

Therefore, we used an alkaline melting method to prepare the analytical samples, which allows the holding material and electrolyte to be processed simultaneously without having to be separated. More specifically, an electrolyte plate sample is heated and melted together with a flux to obtain a glass bead-shaped analysis sample.

According to this method, in the fluorescence Xg analysis method, it is possible to prevent various influences on quantitative analysis due to the particle size of the sample and minerals such as IJ socks. Furthermore, there is an advantage that the above-mentioned components can be quantified simultaneously from one glass bead.

The glass bead here refers to a sample and a flux in a suitable melting container (for example, approximately 5Qc made of 95% Pt-5% Au).
c crucible), heated and melted, then cooled and solidified into a button shape (e.g. 35 to 40 wφ).

Thickness: 2-3 van). The method of this virtue is, for example, "Iron and Steel Institute of Japan Standard 18IJ 201 (1977)"
"Fluorescence Xfs analysis method for iron ores using glass beads"
However, this method targets minerals such as ore, sintered ore, and placer, and the flux used is limited and the heating temperature is set at 1100℃ or higher. There is. Furthermore, there is no provision for application to things such as electrolyte plates made of inorganic materials and carbonates.

Therefore, in the present invention, it is possible to prepare glass beads using the electrolyte plate as a sample, and experiments were conducted on the type of flux, its composition, and the setting conditions of the melting temperature so that the composition can be determined.

In the experiment, various conditions were examined in advance to satisfy the following requirements.

■Glass beads must be homogeneous and have sufficient mechanical strength to avoid breakage during cooling at room temperature or during handling such as measurement.

■Easy melting operation for glass bead production. In other words, the type and amount of flux (including stripping agent), heating temperature, etc. must be practical.

■Glass beads have low absorption of Xa in terms of fluorescence X-ray chord density, and should not undergo long-term deterioration. In other words, these must be taken into consideration when selecting a flux.

From the above, assuming that the above required conditions are satisfied,
As a fluxing agent, we investigated the application of reagents (e.g. diborates, carbonates, etc.) in preliminary experiments, and found that lithium borate (Li) was used as the fluxing agent.
Lithium carbonate (Li, co
A mixture of l) has been found to be suitable. This is L
The aim is to increase alkalinity and lower the melting point by adding i1CO1.

Furthermore, in order to facilitate the peeling of the glass beads from the melting container (platinum crucible) after melting, it is essential to add a small amount of halide, and after various studies, we found that sodium iodide was suitable, and in this experiment Added milligrams. Next, the composition of the flux, the flux and the amount of sample were examined under the following conditions.

1) Examination of composition of flux ■Fluxing agent; Li, B, O: LiICO3 is 4=1 (total i
5g) to 15:1 (total amount 16g) 0.02g of release agent was added to all.

■ Melting container; 95% Pt-5% Au / L / pot (J
& surface 40■φ, height 30m) ■Heating device; Electric furnace type glass melting device (set temperature 950℃, heating time 8 minutes) ■Recovery of glass beads; Cooling at room temperature ■Quality judgment; Appearance observation From this, The composition of the flux is L 12B40 in weight ratio.
;Li, Co3: NaI 5:1:0.02-10
:1:0.02 revealed that good glass beads could be prepared. Furthermore, if the amount of flux is less than 5 g in the above composition ratio, the amount is small relative to the container, and the required glass beads cannot be prepared. On the other hand, if it exceeds 10 g, the glass bead becomes thick and cracks may occur during cooling, which may be due to the difference in cooling rate, which is not appropriate.

More preferably, the composition ratio of the flux is Li, B4o, :Lil
Co, :N310 weight ratio 7:1:0.02 total amount &
02g is optimal.

2) Examining the mixing ratio of flux and sample amount ■ Flux: L”xB+Ot * L t2cO3: N
aI (total ji8.02g at 7e 1e O,02) ■ Mixing ratio of sample and flux; electrolyte plate powder: flux (1:4~
Total at 1:800: jft 10 g or less) ■ Melting container; 95% PT-5% Au crucible (bottom 40-
(φ, height 30 dew) ■Heating device; Electric furnace type glass melting device (set temperature 950℃, heating time 8 minutes) ■Recovery of glass beads; Cooling at room temperature ■Quality judgment: Visual inspection and fluorescent X-ray analysis device Measurement of AAKα, KWα X-ray intensity.

From this, glass beads can be produced within the studied mixing ratio range. However, if the amount of sample is large, the amount of alkali increases too much during melting, which tends to cause discoloration and corrosion of the crucible. If the amount is too low, the X-ray intensity will decrease due to dilution with the flux. As a result of the study, the mixing ratio of the sample and flux was 1:8 to 1:8 by weight.
00 is good, and more preferably 1:16 to 1:160 (for example, sample amount 0.5 to 0, 05g:I!it agent aozg).

Next, it is important to clarify the heating behavior of the flux and the sample electrolyte plate, and to set the glass bead production conditions, such as the heating temperature during glass melting. Therefore, the flux was measured using a differential thermal balance, and the flux and the sample electrolyte plate were subjected to heating loss measurements. The amount of sample measured in the former case was 30 milligrams, and the amount in the latter case was 0.5 g.

FIG. 1 shows a fluxing agent (for example;
This is a thermogravimetric/differential thermal analysis curve of Lt2B,O,: hi-co, weight ratio of 7:1). In Figure 1, DT
A (differential thermal analysis) 1 and TG (thermogravimetry) 2 are shown. 1
a is L 1. co, has a melting point of 633°C, and 1b has a melting point of 8
32℃, IC has a melting point of 893℃, which is Li, B2O-r
This is thought to be due to. From this, Li, Co,
Due to the coexistence of Li, B, 0. The original melting point of (915℃
), and most of it melts at 832°C. Therefore, it can be seen that the fluxing agent completely melts at 893°C or higher. Next, from the thermogravimetric measurement curve, it can be seen that the weight loss progresses by about 9% up to 633°C, and then remains almost constant until 1000°C. This weight loss is excluded from the weight loss due to the release of carbon dioxide gas (Co) by the decomposition reaction of the following formula above the melting point of charcoal [IJ thium.Li1CO1-+ Li, 0 +CO.

Also, calculated from the Li and Co3 contents in the mixed flux, the amount other than the above reduction is CO! This value corresponded to the amount released.

Therefore, it can be said that the heat treatment for forming glass beads can be applied since it is clear that the loss is not due to the loss of other coexisting components.

FIG. 2 is a curve showing the heating loss of the electrolyte plate and flux of a sample for explaining the present invention in detail, where 11 is the electrolyte plate and 12 is the flux (e.g. Li!B, O, :L). The weight ratio of imported Co is 7:1). This is done by placing the sample in a platinum crucible at 0%.
The reduction in t was calculated by weighing 5g and heating time at each specified temperature in an electric furnace (Matsuful furnace) for 30 minutes.Compared to the thermogravimetric analysis of the above method, the amount of sample is larger, and accuracy is reduced by maintaining the heating temperature. This is a measurement method that takes into account improvement. 2 in Figure 2
The sample electrolyte plate has a 0.5% drop at 600°C, which is almost constant up to 1000°C, and z3 at 1100°C.
You will start to see a decrease in weight. Furthermore, the flux is 700℃
It can be seen that the weight loss is approximately 9 inches at 100°C, and remains almost constant up to 1000°C. In other words, when producing glass beads, the heating temperature should be set in the range of 650 to 1000 degrees Celsius based on previous measurement results, and good results can be obtained if the temperature is as high as possible considering the melting operation. Therefore, a temperature of 900-1000°C is recommended, where the flux is completely melted. 1000 here
It is known that the weight loss below ℃ is due to the release of carbon dioxide gas such as charcoal, thium, etc. in the flux, and there is no loss on heating of other components during glass bead treatment. The absence of loss indicates that the glass bead preparation method is suitable. Therefore, based on the results of this experiment, it is considered that it is practical to set the heating temperature to 950°C in general.

Based on the above experimental results, the glass bead manufacturing conditions are summarized in Table 1. The sample preparation time under these conditions is:
It takes about 30 minutes from weighing to preparing glass beads and cooling them to a state where they can be measured.

Table 1 Next, regarding the composition determination of the jlt solution board of the present invention, Li
A method for measuring the concentration of kLOx and Co will be described.

Glass beads were produced according to the Cubspeed production conditions 1 described above. In this case, measurement using atomic X-rays of Li generally cannot detect it because the wavelength involved is long.

Furthermore, since a Li-based material is used for the electrolyte holding material and the electrolyte, the experiment was conducted using a method in which lCo3 was determined from LiAAO, which is a constituent element of the electrolyte plate, and Li1C03 was determined as the remainder. The detection method is L 1 by fluorescence X-ray analysis method.
kLOx is AtKα, and Co3 is X-ray intensity ratio of elbow α and LiAt0. , Convert the relationship between the concentrations of K2CO2 into a calibration curve.

FIG. 3 shows the L i kLOx and C
o.

This is to explain the concentration measurement method of L i kLO
This is a calibration curve of x and co. FIG. 3 shows glass beads prepared under the above-mentioned glass bead preparation conditions, and AtKα
, KKα fluorescence X-ray intensity ratio and Likl O! pK
Goose CO! The calibration curve 21 is for ICo, and the calibration curve 22 is for LiAt0*. In both cases, the linearity of the calibration curve was good, and the L in the crow beads was
It can be seen that the correlation coefficient between iAt0, ICo, AtKα, and KKα is 0.999, which is good. moreover,
The equations for determining the calibration edge constants of the test 1i21 and the test *22 can be expressed by the following equations.

Calibration curve 21 formula 2 to Goose C (wt%) = 28.64 X
−3,32 (x: KKα X-ray intensity ratio) Calibration curve formula 22: LiAt0* (wt%) =45.
76X 0.22 (x: "AlKα X-ray intensity ratio)
This method can be applied to glass bead samples prepared under the above-mentioned predetermined conditions. In addition, the accuracy of repeated analysis at this time was good with a coefficient of variation of 1% or less, and it was further confirmed that quantification could be performed with the same analytical accuracy even when glass beads were prepared with the amount of electrolyte plate o or o s g. ing.

Next, specific analysis results using the present invention will be described. The sample is an electrolyte plate of a molten carbonate fuel cell before operation. Analytical samples were prepared under the glass bead preparation conditions shown in Table 1 above, and Table 2 shows an example of the results of illegal quantitative analysis. For the compositional analysis of the electrolyte plate, ten glass bead samples were prepared and repeated analyzes were conducted to examine the accuracy of the analysis. Furthermore, Table 3 shows the results of a study in which quantitative values were determined using conventional chemical analysis methods, and relative errors with the illegal quantitative values were determined.

Table 3 In Table 2, the values of Li and CO are determined in advance by LiAt0. At the same time, C03 was quantified and obtained as a residue.

According to the method for quantifying the composition of an electrolyte plate of the present invention, the coefficient of variation is 1
% or less, it can be seen that analysis can be performed with high accuracy.

The measurement time for one sample at this time is within 1 minute.

In Table 3, the chemical analysis values are based on the conventional method, and LiAA
O! was determined by the chelate titration method for At, and Kco3 and LiICOI were determined by the flame method for K and Li. The time required for analyzing the three components at this time is about 20 hours or more because each pretreatment is complicated. In addition, the relative error was calculated using the following formula.

From this, it can be seen that the present method is a good method that allows quantitative determination with a relative error of 2.1% or less compared to conventional chemical analysis methods.

By applying the method for quantifying the composition of an electrolyte plate of the present invention, quantitative analysis can be performed quickly and with high accuracy, making it easier to manage the composition of the electrolyte plate. Furthermore, by applying this method to quantifying the composition of electrolyte plates before and after operation, it is possible to quickly evaluate the electrolyte holding material and the amount of electrolyte as a whole or individually, which can be said to be an extremely practical method.

〔Effect of the invention〕

The electrolyte plate of a molten carbon salt fuel cell consists of an electrolyte holding material and an electrolyte, and in order to evaluate the composition, it is necessary to simultaneously determine the amount of one of the constituent materials. was manufactured by simultaneously melting and solidifying the holding material and the electrolyte to form glass beads, so that the composition of the constituent materials can be determined with high accuracy (coefficient of variation of 1% or less) from a single glass bead using fluorescent X-ray analysis. , it became possible to perform simultaneous quantification in a short time (within about 30 minutes from sample preparation to measurement).

In addition, during sample preparation, we find the optimal processing conditions by clarifying the flux, the heating behavior of the sample, etc.
It is now possible to quantify the composition of an electrolyte plate even with a small amount of sample at the milligram level.

Further, after operation, the electrolyte plate contains metals or metal oxides of the electrodes constituting the battery due to adhesion or the like. According to the present invention, it is possible to apply it to the simultaneous determination of such mixed metal components, and its effects are significant.

[Brief explanation of drawings]

Figure 1 is an approved balance measurement curve diagram to explain the four heating movements of the flux used to prepare glass bead samples.
The figure is a heating loss measurement curve diagram to explain the heating behavior of the sample electrolyte plate and flux, and the M3 diagram is LiAt0! and to,
FIG. 2 is a diagram for explaining a method for quantifying the composition of CO. 1...DTA (differential thermal analysis curve), 1a...melting point (
633°C), lb...Melting point (832°C), IC...
Melting point (893°C), 2...TG (thermogravimetry curve),
11... Electrolyte plate, 12... Fluxing agent, 21... K,
Co3 calibration curve, 22...L 1ALOx weight line.・Ij\illness, i′,: enemy 7 no ro and Ka08
5KN ('C) v7 z ■

Claims (1)

[Claims] 1) In compositional analysis of an electrolyte plate of a molten carbonate fuel cell consisting of lithium aluminate as an electrolyte holding material and lithium carbonate and potassium carbonate as electrolytes, by heating and melting the electrolyte plate together with a flux. 1. A method for determining the composition of an electrolyte plate, comprising preparing a glass bead-shaped sample, and simultaneously adding an electrolyte holding material and electrolytes such as lithium aluminate, lithium carbonate, and potassium carbonate in the sample. 2) In the method described in claim 1, the flux is mainly composed of anhydrous lithium borate and a mixture of lithium carbonate and sodium iodide, and the composition ratio is 5:1 by weight.
:0.02 to 10:1:0.02, and the mixing ratio of the sample to the flux is 1:8 to 1:800 by weight. 3) A method for determining the composition of an electrolyte plate according to claim 1, wherein the heating melting temperature is 650 to 1000°C. 4) In the method according to claim 1, the analyzer is a fluorescence X-ray analyzer,
The method is characterized by determining the amounts of lithium aluminate and potassium carbonate by applying a calibration curve prepared in advance from the relationship between the radiation intensity and lithium aluminate, the fluorescent X-ray intensity of KKα, and the concentration of potassium carbonate. A method for quantifying the composition of electrolyte plates.