JP3131058B2 - Alumina sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alumina sintered body used as a dielectric ceramic for microwaves, for example.

[0002]

2. Description of the Related Art In recent years, for example, with the practical use of automobile telephones, cordless telephones, personal radios, and satellite broadcast receivers, dielectric ceramics have been widely used as circuit elements in the microwave region.

[0003] Such a dielectric ceramic for microwaves is mainly used for a resonator, and its required characteristics are that its relative permittivity is large for the demand for miniaturization and its dielectric loss (tan δ) at high frequencies. ) Is small, in other words, the Q value is large. However, when used in a higher frequency range (SHF band, frequency 3 GHz or more), since the wavelength of the radio wave used is a short wavelength (millimeter wave), the dielectric constant is rather 10 to 20 in terms of processing accuracy and the like.
It is known that a material with a low dielectric constant is required.

[0004] In recent years, among such low dielectric constant dielectric porcelains, alumina porcelain which operates at a high frequency as a waveguide of a high frequency electronic circuit has attracted attention.

[0005]

However, the conventional alumina porcelain is a sintered body having an alumina content of 99.9% or more and has an excellent characteristic of a dielectric constant (ε) of about 10. However, such alumina porcelain having an alumina content of 99.9% or more needs to be fired at 1800 ° C. or more, and has a problem of poor mass productivity.

From the viewpoint of mass productivity, the sintering temperature of the alumina-based sintered body increases as the amount of the alumina component increases, and it becomes difficult to manufacture the sintered body. Therefore, conventionally, various additives have been added to alumina in order to lower the firing temperature. However, in order to lower the firing temperature to a satisfactory level, the amount of addition is increased and the dielectric loss (tan δ) is increased. There was a problem that increases.

[0007]

The present inventors have [Problems To achieve the] a result of extensive investigations on the above problems, Sm ₂ O ₃ to Al ₂ O ₃
Is added in an amount of 0.5 to 40% by weight, the dielectric loss (tan δ) can be reduced to 1 × 10 ⁻⁴ or less in a high frequency range, and the firing temperature is set to 1500 to 1600.
° C, and it was found that it can be easily produced, leading to the present invention.

That is, the alumina-based sintered body of the present invention is made of Al
And the ₂ O ₃ 60 to 99.5 wt%, the Sm ₂ O ₃ 0.5 to 4
Alumina sintered body containing 0% by weight and Al ₂
O ₃ crystal phase exists, and SmAl is present in the Al ₂ O ₃ crystal phase grain boundary.
O ₃ is present.

The reason why Sm ₂ O ₃ is contained in an amount of 0.5% by weight or more is that the addition of Sm ₂ O ₃ causes solidification of unavoidable impurities, in particular, elements of Group 2a of the periodic rule such as MgO to alumina. This is for suppressing melting, preventing generation of lattice defects, reducing dielectric loss, and enabling firing at 1500 to 1600 ° C. In addition, Sm ₂ O ₃ is 0.1.
If the amount is less than 5% by weight, the dielectric loss increases. In particular, Al ₂ O ₃ 60-99% by weight, Sm ₂ O ₃ 1-4
It preferably comprises 0% by weight. This is because the dielectric constant within this range can be suppressed to 20 or less. In addition, SmAlO ₃ was present in the grain boundary phase.
This is to reduce the dielectric loss of the entire sintered body.

The alumina-based sintered body of the present invention contains unavoidable impurities.
There are O ₂ , MgO, FeO ₃ , and Na ₂ O. As for the abundance, 0.02% by weight or less of SiO _{2 and} 0.4% of MgO are present.
Wt% or less, Fe ₂ O ₃ is 0.03 wt% or less, Na ₂
O may be present in an amount of 0.08% by weight or less.

The alumina sintered body of the present invention has a purity of 99.
Al ₂ O ₃ powder having an average crystal grain size of 8% or more and an average crystal grain size of 2 μm or less;
0.5% by weight or more of Sm ₂ O ₃ powder of
For example, an organic solvent such as isopropyl alcohol is added,
Mix and crush with a ball mill or the like. After heating and drying the obtained slurry at a predetermined temperature, a binder such as paraffin wax is added and mixed by heating to obtain a mixed powder.

The obtained powder is formed by a known molding method, for example,
It is formed by press molding, for example, at a firing temperature in the range of 1500 to 1600 ° C.
Baking for up to 5 hours to obtain an alumina sintered body. The obtained alumina-based sintered body has an Al ₂ O ₃ crystal phase or an Al ₂ O ₃ crystal phase and an Sm ₂ O ₃ crystal phase, and SmA is included in the grain boundary phase.
The 10 ₃ crystal phase is present.

[0013]

According to the present invention, the Al ₂ O ₃ and Sm ₂ O ₃ 0.5
By containing -40% by weight, it is possible to suppress solid solution of unavoidable impurities, in particular, elements of Group 2a of periodic rule such as MgO into alumina, prevent generation of lattice defects, and reduce dielectric loss. , 1500-1600 ° C.

The presence of SmAlO ₃ in the grain boundary phase makes it possible to reduce the dielectric loss of the sintered body.

[0015]

The present invention will be described below with reference to the following examples. Purity 9
9.8%, Al ₂ O ₃ powder having an average crystal grain size of 0.5 μm, and Sm ₂ O ₃ powder having a purity of 99.9%, and an average crystal grain size of 1 μm.
Powder was added at the ratio shown in Table 1, and an organic solvent composed of isopropyl alcohol and alumina balls 100 were added thereto.
g and put in a polyethylene pot and mixed and pulverized for 48 hours. The resulting slurry was heated and dried at 80 ° C., passed through an 80-mesh sieve, a binder made of paraffin wax was added, mixed by heating, and then passed through a 40-mesh sieve to obtain a raw material powder.

The obtained powder is subjected to a pressure of 1000 kg / cm ^2.
, And molded to a diameter of 60 mm and a thickness of 2 mm, and fired at a temperature as shown in Table 1. The sintered body thus obtained was subjected to ultrasonic cleaning with acetone for 10 minutes and then naturally dried to obtain a sample.

The obtained sample was subjected to a dielectric constant and a dielectric loss (tan) at a measurement frequency of 8 to 9 GHz using a network analyzer (HP-8775C) and a synthesized sweeper (HP-8747C) by a cavity resonator method.
δ) was measured. Table 1 shows the results.

[0018]

[Table 1]

In Table 1, it is found that when Sm ₂ O ₃ is less than 0.5% by weight, the dielectric loss becomes very high. On the other hand, in the case of the alumina-based sintered body of the present invention to which 0.5 to 40% by weight of Sm ₂ O ₃ is added, the firing temperature is 1550 to 1600 ° C., the dielectric constant is 10 to 22,
It can be seen that the dielectric loss in the GHz band is as low as 1 × 10 ⁻⁴ or less.

The crystal phase of the alumina-based sintered body of the present invention was confirmed by X-ray diffraction, and the sintered body chemically etched with hot phosphoric acid was subjected to local analysis using a wavelength-dispersive microanalyzer. al ₂ O ₃ crystal phase is present, it was confirmed that SmAlO ₃ crystal phase is present in the grain boundary phase.

[0021]

As described above, in the alumina-based sintered body of the present invention, the content of Al ₂ O ₃ is 60 to 99.5% by weight,
Since m ₂ O ₃ is contained in an amount of 0.5 to 40% by weight, unavoidable impurities, particularly elements of the periodic group 2a such as MgO, are suppressed from being dissolved in alumina, lattice defects are prevented from being generated, and dielectric loss is reduced. It can be fired in the range of 1500 to 1600 ° C. This makes it possible to provide an optimal dielectric porcelain for use in the high frequency SHF band (frequency of 3 GHz or more) and to provide a dielectric porcelain suitable for mass production.

The presence of SmAlO ₃ in the grain boundary phase can reduce the dielectric loss of the sintered body.

Claims (1)

(57) [Claims] (1) 60 to 99.5% by weight of Al ₂ O ₃ ,
Containing ₂ O ₃ in a ratio of 0.5 to 40% by weight;
_{While a 2} O ₃ crystal phase exists, SmA
An alumina-based sintered body characterized in that IO ₃ is present.