JP3163704B2 - Partially stabilized zirconia sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a partially stabilized zirconia sintered body having excellent hydrothermal durability.

[0002]

_2. Description of the Related Art Zirconia (ZrO ₂ ) changes its crystal structure between a monoclinic system and a tetragonal system near a specific temperature, and its volume changes accordingly. Therefore, repeated use near the specific temperature results in fatigue and ultimately collapse. In order to suppress this, completely stabilized zirconia containing a large amount of yttria or the like in zirconia is known.
This fully stabilized zirconia is extremely stable in the range from room temperature to about 1500 ° C., but is inferior in mechanical strength.

[0003] Therefore, a partially stabilized zirconia in which the amount of yttria and the like is reduced from the above is known. This partially stabilized zirconia has excellent mechanical properties such as high bending strength and fracture toughness and low coefficient of thermal expansion. Therefore, instead of alumina, ferrules, sleeves, bonding capillaries, etc., which are recently incorporated into optical fiber connectors Is being used as a material.

[0004]

The partially stabilized zirconia described above undergoes aging at about 200 to 400 ° C. (particularly under steam), and the tetragonal phase which has been stable at room temperature gradually undergoes a phase transition to monoclinic phase. There is a disadvantage of causing deterioration with time due to the accompanying volume change. In order to solve this, conventionally, measures such as reducing the crystal particle diameter or preparing a composite with alumina have been tried, but satisfactory results have not been obtained.

[0005]

As described above, the reason why satisfactory characteristics cannot be obtained with the conventional means will be discussed below. First, Al ₂ O is contained in the raw material of the partially stabilized zirconia.
₃ , impurities such as SiO ₂ , Fe ₂ O ₃ , and Na ₂ O are inevitably mixed. FIG. 6 shows the relationship between the ionic strength of impurities in the sintered body produced using this raw material and the depth from the grain boundary interface.
Is shown in the graph.

From FIG. 6, it is considered that the strength of Fe and Al is not changed at the interface between the crystal grains and the inside thereof, so that Fe and Al are all segregated without segregation. Si exceeded the solid solution limit near the grain boundary (Na: ionic strength: 8 × 10 ² , Si: ionic strength: 2 × 10 ² ).
It is considered that they are segregated as shown in FIG.

When the partially stabilized zirconia in which Na segregates at the grain boundaries as described above is aged under hydrothermal conditions, Na and H ₂ O react with each other as shown in FIG. NaOH is generated at the same time, and the grain boundary is corroded by the high-concentration NaOH, thereby generating microcracks as shown in FIG. 7C. Further, it is presumed that when the internal stress due to the volume change accompanying the phase transition is applied to the microcracks, the microcracks further develop and lead to collapse.

Therefore, in the present invention, sodium segregated at the grain boundaries of the crystals constituting the partially stabilized zirconia sintered body is removed by an acid treatment.

[0009]

After sintering a molded article formed using a raw material for partially stabilized zirconia, the molded article is impregnated with nitric acid or the like to elute Na in the molded article.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a block diagram showing a manufacturing process of the partially stabilized zirconia sintered body according to the present invention,
In the present invention, 100 parts by weight of benzene as a solvent and 18 parts by weight of an organic binder are added to 82 parts by weight of the powder for partially stabilized zirconia as a raw material and mixed, and the mixture is mixed using a nylon mill and balls. After thorough mixing, heat distillation is performed to remove benzene. Then, the binder and the powder for partially stabilized zirconia are wetted by applying shear stress by kneading with a ceramic roll mill while heating until the binder and the powder for partially stabilized zirconia become uniform, and further pulverized by a ceramic stamp mill to obtain a ceramic compound.

The kneading is preferably performed by a mill or the like made of a non-metallic material such as a resin or a ceramic, because mixing of a metal and a metal oxide into the compound can be avoided. A metal kneader may be used to elute metals and metal oxides from the ceramic compound by the acid treatment described below.

The ceramic compound prepared as described above is injection molded at a temperature of 459 K and an injection pressure of 100 MPa into a molded body of 4 × 5 × 50 mm ³ , and the molded body is press-degreased (nitrogen gas atmosphere, 8 atm, 400
After raising the temperature to 72 ° C. for 72 hours, calcination is performed at 600 to 800 ° C. for about 1 hour in the air. Here, the calcination temperature is set to 60
The reason why the temperature is set to 0 to 800 ° C. is that if the temperature is lower than 600 ° C., the minimum strength required for setting in an acid treatment apparatus described later cannot be exerted. This is because it is difficult to be eluted.

After that, the calcined compact is brought into contact with nitric acid and subjected to an acid treatment for eluting Na mixed in the compact. Here, hydrochloric acid or aqua regia can be considered as the acid used in the acid treatment. However, since hydrochloric acid or aqua regia contains Cl, if Cr is mixed in the ceramic compound, it produces stable ClCl3 even at a high temperature. Is most preferred.

The molded body from which Na has been removed by acid treatment is heated to 1420 ° C. in the air for 12 hours and fired, and the sintered body is 3 × 4 × 4 with a diamond grinding and polishing machine.
A sample of 0 mm ³ was obtained.

FIG. 2 is a graph showing the relationship between the depth from the grain boundary interface and the ionic strength of the impurity element of the sintered body obtained by firing the above-mentioned acid-treated compact under the conditions described below. Thus, it was found that Na segregated at the interface of the crystal grains was removed by the acid treatment, and a trace amount of Na was uniformly dissolved in the sintered body. Here, the segregation state of the impurity element at the grain boundary is determined by a secondary ion mass spectrometer (SIMS:
It was measured in the depth direction from the sample fracture surface (grain boundary) using Thomson Japan PF6300).

[0016]

The bending strength and Weibull coefficient of the above sample (partially stabilized zirconia sintered body according to the present invention) and a conventional partially stabilized zirconia sintered body before and after hydrothermal treatment are shown below. It is shown in Table 1). Here, regarding the bending strength, a three-point bending tester (Shimadzu Corporation: OSS-5)
00) according to JISR1601 under the conditions of a span of 30 mm and a crosshead speed of 0.5 mm / min.

[0017]

[Table 1]

As is apparent from Table 1, the partially stabilized zirconia sintered body according to the present invention has a significantly higher bending strength and Weibull coefficient after hydrothermal treatment than the conventional partially stabilized zirconia sintered body. You can see that it has improved.

FIGS. 3 to 5 show micrographs of the surface and fracture surface of the sample and the conventional partially stabilized zirconia sintered body before and after the hydrothermal treatment. Here, the observation of the surface and the fracture surface of the sample is performed by a scanning electron microscope (SEM: Hitachi, Ltd.
-800), and the hydrothermal treatment was performed for 9 hours under a steam of 573 K and 8 MPa using an autoclave (manufactured by Pressure Glass).

Before the hydrothermal treatment, both the partially stabilized zirconia sintered body according to the present invention and the conventional partially stabilized zirconia sintered body are mirror-finished, and the fracture surfaces are all shown in FIG. As shown in the figure, pores are observed inside, but no microcracks are observed. On the other hand, after the hydrothermal treatment, the partially stabilized zirconia sintered body according to the present invention, which was subjected to the acid treatment, showed a line showing a grain boundary on the surface as shown in FIG. No micro-cracks were observed on the surface of the conventional partially stabilized zirconia sintered body not subjected to the acid treatment, as shown in FIG. 4 (b). Similarly, in the partially stabilized zirconia sintered body according to the present invention, as shown in FIG. 5 (a), no microcrack is observed on the fracture surface, and the conventional partially stabilized zirconia sintered body without acid treatment is shown in FIG.
Microcracks are clearly observed on the fracture surface as shown in (b).

As apparent from the above test results, according to the present invention, sodium segregated at the grain boundaries of the partially stabilized zirconia sintered body was removed by an acid treatment before firing, so that the growth of microcracks was suppressed. Thus, a material having excellent durability even under hydrothermal conditions can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a manufacturing procedure of a partially stabilized zirconia sintered body according to the present invention.

FIG. 2 is a graph showing the relationship between the depth from the grain boundary interface of the partially stabilized zirconia sintered body according to the present invention and the ionic strength of impurity elements.

FIG. 3 is a micrograph showing a grain structure of a fracture surface of a partially stabilized zirconia sintered body according to the present invention before hydrothermal treatment and a conventional partially stabilized zirconia sintered body.

FIG. 4A is a micrograph showing the particle structure of the surface of a partially stabilized zirconia sintered body according to the present invention after hydrothermal treatment,
(B) is a micrograph showing the particle structure of the surface of the conventional partially stabilized zirconia sintered body after the hydrothermal treatment.

FIG. 5 (a) is a micrograph showing a grain structure of a fracture surface of a partially stabilized zirconia sintered body according to the present invention after hydrothermal treatment,
(B) is a micrograph showing a grain structure of a fracture surface of a conventional partially stabilized zirconia sintered body after hydrothermal treatment.

FIG. 6 is a graph showing the relationship between the depth from the grain boundary interface of a partially stabilized zirconia sintered body and the ionic strength of an impurity element.

FIG. 7 is an enlarged view showing the erosion process of a grain boundary by NaOH.

────────────────────────────────────────────────── ─── Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C04B 35/48 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A partially stabilized zirconia sintered body containing magnesia, yttria or calcia in zirconia, wherein sodium segregated at grain boundaries is removed by acid treatment. Partially stabilized zirconia sintered body.