Fluorescent ceramic, fluorescent ceramic inspection method, and fluorescent ceramic manufacturing method

Abstract

To provide ceramics having novel properties.SOLUTION: A fluorescent ceramic has: a first region comprising zirconium oxide as a main component, the zirconium oxide having a yttria concentration of C1[mol%]; and a second region comprising zirconium oxide as a main component, the zirconium oxide having a yttria concentration of C2[mol%](C1≠C2). A peak wavelength λp1 of a fluorescence spectrum in the first region is different from a peak wavelength λp2 of a fluorescence spectrum in the second region.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present disclosure relates to fluorescent ceramics.

Background Art

[0002] Generally, a sintered body of ceramics is produced by compacting and molding raw material powder and heat-treating the molded body at a high temperature. The heat treatment temperature (referred to as the sintering temperature) depends on the type of ceramics, but is 1200°C to 1500°C, and the sintering time is about several hours. In order to improve the density of the sintered body, in addition to the above-described general sintering method, various methods such as applying pressure from the outside (hot pressing method, HIP method, etc.) have been devised.

[0003] In recent years, a flash sintering method has been developed in which sintering can be completed at a lower temperature and in a shorter time than before by applying an electric field to ceramic green compacts (see Non-Patent Document 1). The feature of this sintering method is that when the temperature of the ceramic green compact is raised while applying an electric field, the sample current suddenly increases at a certain temperature (hereinafter, this phenomenon may be referred to as the "flash phenomenon"), and the sintering process ends instantaneously. It has also been clarified that when the electric field strength is increased, the temperature at which the shrinkage of the sintered body starts decreases, and the shrinkage behavior changes more steeply.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In such a situation, through intensive studies by the inventors of the present application, it was conceived that there is a possibility of obtaining a ceramic having new characteristics by manufacturing a ceramic by a method different from the conventional method of heat treatment at a high temperature.

[0006] The present disclosure has been made in view of such a situation, and one of its exemplary purposes is to provide a technique for obtaining a ceramic having new characteristics.

Means for Solving the Problems

[0007] In order to solve the above problems, a fluorescent ceramic according to an aspect of the present disclosure includes a first region mainly composed of zirconium oxide having a concentration of yttria of C1 [mol%], and a concentration of yttria contained in the first region. A second region mainly composed of zirconium oxide having a concentration of C2 [mol%] (C1≠C2). The peak wavelength λp1 of the fluorescence spectrum in the first region is different from the peak wavelength λp2 of the fluorescence spectrum in the second region.

Advantages of the Invention

[0008] According to the present disclosure, a ceramic having new characteristics can be realized.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0010] In order to solve the above problems, a fluorescent ceramic according to an aspect of the present disclosure includes a first region mainly composed of zirconium oxide having a yttria concentration of C1 [mol%], and a second region mainly composed of zirconium oxide having a yttria concentration of C2 [mol%] (C1≠C2). The peak wavelength λp1 of the fluorescence spectrum in the first region is different from the peak wavelength λp2 of the fluorescence spectrum in the second region.

[0011] According to this aspect, in a fluorescent ceramic mainly composed of zirconium oxide containing yttria, the fluorescence spectrum can be partially varied. In other words, the color tone of the fluorescent ceramic can be varied depending on the region.

[0012] When the concentration C1 of yttria in the first region is higher than the concentration C2 of yttria in the second region, the peak wavelength λp1 is shorter than the peak wavelength λp2. Thereby, the peak wavelength of the emission spectrum in the region with a high yttria concentration can be shortened.

[0013] The concentrations C1 and C2 (C2 < C1) are in the range of 2 to 12 [mol%], the excitation wavelength is 245 nm, or the peak wavelength λp1 of the fluorescence spectrum near 315 nm is in the range of 410 to 460 nm, and the excitation wavelength is 254 nm, or the peak wavelength λp2 (λp2 > λp1) of the fluorescence spectrum near 315 nm may be in the range of 410 to 460 nm. Thereby, by adjusting the concentration of yttria, members with partially different blueness can be obtained.

[0014] Another aspect of the present disclosure is a method for inspecting a fluorescent ceramic. This method irradiates ultraviolet light on a fluorescent ceramic mainly composed of zirconium oxide, having an excitation wavelength of 254 nm, or a fluorescence spectrum having a peak wavelength in the range of 410 to 460 nm near 315 nm, to detect the deviation of the composition or density of the fluorescent ceramic.

[0015] According to this aspect, minute cracks, defects, and the presence or absence of compositional deviation that are difficult to detect visually can be easily inspected.

[0016] In addition, any combination of the above components, and those obtained by converting the expressions of the present disclosure among methods, apparatuses, systems, etc. are also effective as aspects of the present disclosure.

[0017] Hereinafter, embodiments for carrying out the present disclosure will be described in detail with reference to the drawings and the like. In the description of the drawings, the same elements are denoted by the same reference numerals, and duplicate descriptions will be omitted as appropriate. In addition, the configurations described below are examples and do not limit the scope of the present disclosure in any way.

[0018] (Method for manufacturing fluorescent ceramic) The fluorescent ceramic according to the present embodiment is a sample that is a green compact, a semi-sintered body, or a sintered body mainly composed of zirconium oxide, and is energized (a predetermined electric field is applied) in the process of heating in a predetermined temperature range, thereby imparting the property of emitting fluorescence under excitation light. Here, the sintered body is one that has been sintered in advance at a predetermined sintering temperature. The semi-sintered body is one in which impurities and the like contained in the raw material are removed in advance at a temperature lower than the sintering temperature to oxidize the raw material in order to sinter the raw material.

[0019] The inventors of the present application have intensively studied under what conditions a predetermined electric field should be applied when manufacturing ceramics in order to obtain a fluorescent ceramic having fluorescent properties. First, the method for manufacturing the sample will be described.

[0020] The raw material powder of the green compact is, for example, one in which Y2O3 (2 to 12 mol%) is dispersed and solid-solved in ZrO2. In addition, the raw material powder may contain a compound containing an element such as bismuth (Bi 3+ ), europium (E u 3+ ), praseodymium (Pr 3+ ), and thulium (Tm 3+ ) that serves as a dopant for the fluorescent center. Thereby, a fluorescent ceramic with improved durability in various applications such as high-hardness materials, use at high temperatures, conductive ceramics, solid electrolytes, and light-transmitting materials can be realized. For example, in the case of europium, the peak wavelength of the fluorescence spectrum is 547 nm to 549 nm. In the case of thulium, the peak wavelength of the fluorescence spectrum is 460 nm. The fluorescence measurement device used was the F-7100 manufactured by Hitachi High-Technologies Corporation. The excitation spectrum was measured by fixing the detection wavelength on the detection side of the fluorescence measurement device to the peak wavelength of the fluorescence spectrum and changing the excitation wavelength.

[0021] For example, in an example of the method for manufacturing a fluorescent ceramic according to the present embodiment, as a raw material powder of the ceramic, zirconia (ZrO2) powder (TZ-3Y: manufactured by Tosoh Corporation, hereinafter sometimes referred to as "3YSZ") in which 3 mol% of yttria (Y2O3) is uniformly dispersed and solid-solved was used. This raw material powder was compacted, and a rectangular parallelepiped sample (ceramic green compact) with a length of 15 mm and a cross-sectional shape of 3.5 mm × 3.5 mm was produced by uniaxial and isostatic pressing. After sample molding, platinum (Pt) foils were fixed as electrodes to both end faces in the longitudinal direction of the sample using Pt paste.

[0022] Next, the sample with the electrodes fixed was placed in a differential thermal dilatometer (Thermo plus EVO2 TMA8301: manufactured by Rigaku Corporation) that was modified so that a DC and AC power supply could be connected. Then, after heating this sample to 1200°C, a predetermined electric field (an alternating electric field of 100 V / cm and 100 Hz) was applied to the sample. When sintering, 300 ppm of Bi2O3 was placed in the same atmosphere as the sample. Thereafter, when the limiting current value was reached, the temperature increase of the electric furnace was stopped, and then the sample was held at that temperature for a predetermined time (5 minutes), after which the voltage application was stopped and natural cooling (furnace cooling) was performed. As a result, Bi in Bi2O3 was solid-solved on the sample surface and functioned as a fluorescence center, so that the sample became a fluorescent ceramic. Note that the electric field applied to the sample is not limited to the above, and for example, in the case of an alternating electric field in the range of 30 to 200 V / cm and 1 to 1000 Hz, the sample can also become a fluorescent ceramic.

[0023] Fig. 1 shows the excitation spectra (X1’~X2’) and fluorescence spectra (X1~X2) of each sample of 3YSZ. The excitation spectrum X1’ and fluorescence spectrum X1 shown in Fig. 1 are those of the sintered body obtained by applying an electric field to the 3YSZ sample after heating and sintering. The excitation spectrum X2’ and fluorescence spectrum X2 are those of the sintered body obtained by sintering the 3YSZ sample without applying an electric field. As shown in Fig. 1, the sintered body with an applied electric field shows a fluorescence (PL) spectrum with a peak wavelength of about 440 nm, and it can be seen that the intensity of the PL is significantly increased compared to the fluorescence spectrum X2 of the sintered body sintered without applying an electric field. That is, it can be seen that the PL intensity of the fluorescent ceramic doped with the dopant serving as the fluorescence center increases when an electric field is applied after heating during manufacturing and sintering.

[0024] Similar investigations were also carried out on zirconia (ZrO2) powder in which 8 mol% of Y2O3 was dispersed and solid-solved in ZrO2 (hereinafter sometimes referred to as "8YSZ"). Fig. 2 shows the excitation spectra (X3’~X4’) and fluorescence spectra (X3~X4) of each sample of 8YSZ. The excitation spectrum X3’ and fluorescence spectrum X3 shown in Fig. 2 are those of the sintered body obtained by applying an electric field to the 8YSZ sample after heating and sintering. The excitation spectrum X4’ and fluorescence spectrum X4 are those of the sintered body obtained by sintering the 8YSZ sample without applying an electric field. As shown in Fig. 2, the sintered body with an applied electric field shows a fluorescence (PL) spectrum with a peak wavelength of about 420 nm, and it can be seen that the intensity of the PL is significantly increased compared to the fluorescence spectrum X4 of the sintered body sintered without applying an electric field. Also, it can be seen that the 8YSZ sample has a larger amount of Y2O3 solid-solved in ZrO2 compared to the 3YSZ sample, and the peak wavelength of the fluorescence spectrum shifts to the short-wavelength side.

[0025] Fig. 3 shows the differences in the intensities of the fluorescence spectrum and excitation spectrum due to the differences in the current values when sintering the 3YSZ sample by applying an electric field after heating. As shown in Fig. 3, the greater the current value when sintering by applying an electric field, the greater the intensity of the peak wavelength of the fluorescence spectrum. Note that when the current value changes, the density of the sample also changes.

[0026] Next, another manufacturing method of the fluorescent ceramic according to this embodiment will be described. Also in this method, zirconia (ZrO2) powder (3YSZ) in which 3 mol% of yttria (Y2O3) is uniformly dispersed and solid-dissolved as a raw material powder of ceramic was used in the same manner as described above. This raw material powder was compacted, and a rectangular parallelepiped sample (ceramic green compact) with a length of 15 mm and a cross-sectional shape of 3.5 mm × 3.5 mm was produced by uniaxial and isostatic pressing. After sample molding, platinum (Pt) foils were fixed as electrodes to both end faces in the longitudinal direction of the sample with Pt paste. Note that the green compact sample may contain a dopant (for example, bismuth) serving as a fluorescence center that is extremely minute (extremely low concentration or extremely small amount) and cannot be detected by a general measuring device. Alternatively, there may be another member containing an extremely minute (extremely low concentration or extremely small amount) dopant in the same atmosphere as the green compact during sintering. In this case, the dopant volatilized from the member is solid-dissolved as an impurity on the surface of the green compact and functions as a fluorescence center of the fluorescent ceramic.

[0027] Note that as the raw material powder of the ceramic, those in which 2 to 12 mol% (preferably 3 to 10 mol%) of Y2O3 is dispersed and solid-dissolved in ZrO are preferable. In this embodiment, in addition to the aforementioned 3YSZ and 8YSZ samples, samples made of ZrO2 powder in which 4 mol% (4YSZ), 6 mol% (6YSZ), and 10 mol% (10YSZ) of Y2O3 are uniformly dispersed and solid-dissolved were also produced.

[0028] Next, the sample with the electrodes fixed was installed in a differential thermal dilatometer modified so that a DC and an AC power supply could be connected. Then, after heating this sample to 1200°C, an alternating electric field of 100 V / cm and 100 Hz was applied to the sample. Thereafter, when the limiting current value was reached, the temperature increase of the electric furnace was stopped, and thereafter the sample was held at that temperature for 5 minutes, and then the voltage application was stopped and natural cooling (furnace cooling) was performed. Note that the sample may be sintered by heating while applying an electric field.

[0029] Figure 4 shows the change in the linear shrinkage rate of a sample when a constant electric field is applied after heating up to 1200 °C using a green compact of zirconium oxide as the starting sample. In Figure 4, samples of 3YSZ (line L1), 6YSZ (line L2), and 8YSZ (line L3) are illustrated. However, since all of them are heated up to 1200 °C, the lines would overlap as they are. Therefore, line L1 is shifted to a position -40 °C (to the left of line L3) with respect to line L3, and line L2 is shifted to a position -20 °C with respect to line L3 for illustration. Note that similar results have been obtained for samples of 4YSZ and 10YSZ which are not shown in Figure 4. Also, the sintered body density of all sintered body samples is 95% or more.

[0030] Next, the characteristics of the fabricated sintered body samples will be described. Figure 5 shows a photograph of the appearance of each sintered body sample under indoor lighting. Figure 6 shows a photograph of the fluorescence state of each sintered body sample irradiated with black light (peak wavelength 365 nm). Each sample in the photographs shown in Figures 5 and 6 is a sample of 3YSZ, 4YSZ, 6YSZ, 8YSZ, and 10YSZ from left to right. As shown in Figure 6, all samples exhibit fluorescence characteristics. It has also become clear that when the addition amount of yttria changes, the color (blueness) of the fluorescence changes.

[0031] Figure 7 shows the excitation spectra (L1”~L5”) and fluorescence spectra (L1’~L5’) of each sample. As shown in Figure 7, it can be seen that the peak wavelength of the fluorescence spectrum of each sample shifts to the short wavelength side as the addition amount of yttria increases. Figure 8 shows a diagram of the relationship between the concentration of yttria and the peak wavelength of each sample. As shown in Figure 8, in each sample according to this embodiment, the peak wavelength of the fluorescence spectrum when the concentration of yttria is 3 mol% is about 440 nm, and the peak wavelength of the fluorescence spectrum when the concentration of yttria is 10 mol% is about 422 nm.

[0032] As described above, the inventors of the present application have found that by adjusting the addition amount of yttria, the peak wavelength of the fluorescence spectrum can be adjusted. In other words, they have found a method for manufacturing a fluorescent ceramic in which the peak wavelength of the fluorescence spectrum is adjusted by adjusting the addition amount of yttria. Therefore, the inventors of the present application have made further inventions using these phenomena. Fig. 9(a) is a diagram showing a photograph of the appearance of a single sintered body sample in which the addition amount of yttria varies depending on the location, and Fig. 9(b) is a diagram showing a photograph of the fluorescence state when the sintered body sample shown in Fig. 9(a) is irradiated with a black light. Each sintered body sample shown in Figs. 9(a) and 9(b) was prepared by compacting a powder molding so that the left part had a composition of 3YSZ and the right part had a composition of 8YSZ, and sintered under the same conditions as described above.

[0033] The fluorescent ceramic shown in Fig. 9(b) has a right region mainly composed of zirconium oxide with a yttria concentration of 8 [mol%] and a left region mainly composed of zirconium oxide with a yttria concentration of 3 [mol%]. The peak wavelength λp1 of the fluorescence spectrum in the right region is different from the peak wavelength λp2 of the fluorescence spectrum in the left region. Thus, in a fluorescent ceramic mainly composed of zirconium oxide containing yttria, the fluorescence spectrum can be made partially different. In other words, the color tone of the fluorescent ceramic can be made different depending on the region.

[0034] Also, when the yttria concentration in the right region is higher than the yttria concentration in the left region as in the fluorescent ceramic shown in Fig. 9(b), the peak wavelength λp1 (about 423 nm) of the fluorescence spectrum in the right region is shorter than the peak wavelength λp2 (about 440 nm) of the fluorescence spectrum in the left region. Thus, the peak wavelength of the emission spectrum in the region with a high yttria concentration can be made shorter.

[0035] Note that the concentration of yttria in the fluorescent ceramic according to the present embodiment is preferably in the range of 2 to 12 [mol%], but it may exceed that range. FIG. 10 is a diagram showing the relationship between the concentration of yttria in each sample and the peak wavelengths (the peak wavelength PL1 of the fluorescence spectrum, and the peak wavelengths PLE1 and PLE2 of the excitation spectrum). The peak wavelengths PL1, PLE1, and PLE2 are the peak wavelengths of the spectra typified by the 3YSZ sample shown in FIG. 1, and in FIG. 10, the values of the peak wavelengths in samples of 4YSZ, 6YSZ, 8YSZ, and 10YSZ other than 3YSZ are also plotted. As shown in FIG. 10, in the fluorescent ceramic according to the present embodiment, the peak wavelength of the fluorescence spectrum with an excitation wavelength of 254 ±10 nm, or around 315 ± 10 nm, is in the range of 410 to 460 nm. Thus, by adjusting the concentration of yttria, ceramic phosphors with partially different blueness can be obtained.

[0036] (Inspection method for fluorescent ceramic) Next, a method for inspecting a fluorescent ceramic by utilizing the fact that the peak wavelengths of the emission spectra in regions where the composition and density of yttria (for example, differences in crystal systems and the amount of voids) are different will be described. FIG. 11(a) is a diagram showing a photograph of a sintered body sample made of ZrO2 powder in which Y2O3 is uniformly dispersed and solid-solved, in a broken state. FIG. 11(b) is a diagram showing a photograph of the sintered body sample shown in FIG. 11(a) being irradiated with a black light. FIG. 11(c) is a diagram showing a photograph of the sintered body sample shown in FIG. 11(a) being irradiated with a black light from a direction different from that in FIG. 11(b).

[0037] As shown in FIG. 11(b), it can be seen that the color development at the crack part is different from that at other places. Also, as shown in FIG. 11(c), parts with different color developments are also scattered outside the crack part. Therefore, the inventors of the present application made zirconium oxide the main component, and the excitation wavelength is 254A method was devised to irradiate a fluorescent ceramic with a peak wavelength of the fluorescence spectrum in the range of 410 to 460 nm at 315 nm or near 315 nm to detect the deviation of the composition or density of the fluorescent ceramic. As a result, it is possible to easily inspect minute cracks, defects, and the presence or absence of compositional deviation that are difficult to see visually (for example, in the state of Fig. 11(a)).

[0038] The present disclosure has been described based on the embodiments. It should be understood by those skilled in the art that these embodiments are illustrative, and various modifications are possible for each combination of these constituent elements and each processing process, and such modifications are also within the scope of the present disclosure.

Industrial Applicability

[0039] The fluorescent ceramic of the present disclosure can be used in the production of industrial polishing and grinding materials, dental ceramic materials, solid electrolyte membrane materials using electrical conductivity, and ceramic materials for sensors.

Claims

1. A layered first region mainly composed of zirconium oxide with the concentration of yttria being C1 [mol%] and containing a dopant, and a layered second region in contact with the first region, mainly composed of zirconium oxide with the concentration of yttria being C2 [mol%] (C1≠C2) and containing a dopant, wherein the dopant functions as a fluorescence center, the concentration C1 is higher than the concentration C2, the peak wavelength λp1 of the fluorescence spectrum in the first region is shorter than the peak wavelength λp2 of the fluorescence spectrum in the second region, and the concentration of the dopant in the first region and the second region is the same, or the dopant is uniformly dissolved in the entire surfaces of the first region and the second region. A fluorescent ceramic characterized by this.

2. The dopant is selected from the group consisting of bismuth (Bi ３＋ ), europium (Eu ３＋ ), praseodymium (Pr ３＋ ), and thulium (Tm ３＋ ), and the fluorescent ceramic according to claim 1 is characterized in that.

3. The concentrations C1 and C2 (C2 < C1) are in the range of 2 to 12 [mol%], the peak wavelength λp1 of the fluorescence spectrum with an excitation wavelength of 254 nm is in the range of 410 to 460 nm, The fluorescent ceramic according to claim 2, wherein the peak wavelength λp2 (λp2 > λp1) of the fluorescence spectrum with an excitation wavelength of 254 nm is in the range of 410 to 460 nm.

4. A method for inspecting a fluorescent ceramic, which mainly contains zirconium oxide containing yttria and contains a dopant that functions as a fluorescence center. By irradiating ultraviolet rays on the fluorescent ceramic and observing the color development of the fluorescent ceramic, the deviation of the composition or density of the fluorescent ceramic is detected. The color development of the part with the deviation of the composition or density is different from the color development of other places.

5. A method for manufacturing a fluorescent ceramic mainly containing zirconium oxide containing yttria and containing a dopant that functions as a fluorescence center, including a step of applying a predetermined alternating electric field to a sample that is a green compact, a pre-sintered body, or a sintered body mainly composed of zirconium oxide during the process of heating the sample in a predetermined temperature range, wherein the sample contains a dopant, or in the step, a member containing a dopant is placed in the same atmosphere as the sample. The peak wavelength of the fluorescence spectrum of the fluorescent ceramic is adjusted by adjusting the addition amount of yttria instead of the addition amount of the dopant, and the peak wavelength of the fluorescence spectrum shifts to the short wavelength side by increasing the addition amount of yttria. A method for manufacturing a fluorescent ceramic, characterized by this.

6. A step of preparing a sample having a first region mainly composed of zirconium oxide having a yttria concentration of C1 [mol%] and a second region mainly composed of zirconium oxide having a yttria concentration of C2 [mol%] (C1 ≠ C2) is included. The method for manufacturing a fluorescent ceramic according to claim 5, characterized in that the peak wavelength λp1 of the fluorescence spectrum in the first region is different from the peak wavelength λp2 of the fluorescence spectrum in the second region.

7. The method for manufacturing a fluorescent ceramic according to claim 6, characterized in that when the yttria concentration C1 in the first region is higher than the yttria concentration C2 in the second region, the peak wavelength λp1 is shorter than the peak wavelength λp2.

8. The concentrations C1 and C2 (C2 < C1) are in the range of 2 to 12 [mol%]. The peak wavelength λp1 of the fluorescence spectrum with an excitation wavelength of 254 nm is in the range of 410 to 460 nm. The method for manufacturing a fluorescent ceramic according to claim 7, wherein the peak wavelength λp2 (λp2 > λp1) of the fluorescence spectrum with an excitation wavelength of 254 nm is in the range of 410 to 460 nm.

Images