JPS6362468B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to low expansion zirconium phosphate porcelain with improved mechanical strength and thermal shock resistance. Zirconium phosphate porcelain has a thermal expansion coefficient of RT~
At 1000°C, it has a low expansion of 2.5×10 ^-6 /°C, making it a promising material for thermal shock resistance. However, since this material is difficult to sinter, it is difficult to obtain a dense sintered body with high mechanical strength. Recently, in order to solve this problem, there are examples of research into adding manganese dioxide, niobium pentoxide, etc. as sintering aids, but these have either low mechanical strength or low thermal shock resistance. Shortcomings remained. Furthermore, when the amount of the sintering aid added exceeds a certain level, ZrO ₂ becomes liberated. The present invention solves the problems in view of these circumstances and provides a zirconium phosphate resistive expansion porcelain with improved mechanical strength and thermal shock resistance. That is, the gist of the present invention is characterized by containing 0.5 to 6% by weight of magnesium phosphate [Mg ₃ (PO ₄ ) ₂ ]. Hereinafter, the elucidation of the present invention and conventional sintering aids will be described in detail. Manganese dioxide MnO ₂ and niobium pentoxide Nb ₂ O ₅
have melting points of 847℃ and 1460℃, respectively.
Under firing conditions of 1400°C to 1500°C, it plays the role of a liquid phase sintering aid. Furthermore, these materials tend to cause abnormal grain growth of zirconium phosphate and generate microcracks at grain boundaries. These _MnO2
Although the causes of abnormal grain growth of Nb ₂ O 5 and Nb 2 O ₅ have not been fully elucidated, they act as a fluxing agent with great dissolving power for zirconium phosphate, causing rapid grain growth during the dissolution precipitation process. It is thought to have been caused by ivy. On the other hand, magnesium phosphate as a sintering aid has a melting point of about 1360℃,
At a firing temperature of 1500°C, densification is achieved by liquid phase sintering. Since the main raw material for the magnesium phosphate of the present invention is also a phosphorus compound, it is considered that it does not have a very large dissolving power, and therefore it is considered that grain growth proceeds slowly and densification occurs smoothly. Ta. Zirconium phosphate porcelain containing less than 0.5% magnesium phosphate by weight has a transverse rupture strength of 1000
If it is less than Kg/ ^cm2 , it becomes weak, and if it is more than 6%, the quenching resistance temperature difference decreases to 350℃ or less. The zirconium phosphate porcelain of the present invention has a transverse rupture strength.
1100 to 1900 Kg/cm ² and a quenching resistance temperature difference of 480 to 660°C. In contrast, conventional porcelain containing 2% MnO ₂ has an excellent transverse rupture strength of 2000 Kg/cm ² but The rapid cooling temperature difference is as low as 400℃, and
Porcelain containing 2% Nb ₂ O ₅ has a weak transverse rupture strength of 100 Kg/cm ² and a low quenching temperature difference of 550° C., which shows that the present invention has succeeded in improving both mechanical strength and thermal shock resistance. Example: Zirconium oxide with a fineness of 85% or less of 1.5 μm or less
535.6 g of ZrO ₂ , 582.6 g of reagent first grade ammonium phosphate (NH ₄ ) ₂ HPO ₄ and 900 g of water with an internal volume of 6.5
Melt and mix for 24 hours in an alumina ball mill. This slurry was atomized using a nozzle and blown into n-hexane cooled to below -30°C with dry ice to form frozen granules. Next, the granules are dried in a vacuum freeze dryer (Tokyo Rika FD).
-5 type) for 24 hours to obtain dry granular powder with a particle size of about 500 μm. This powder was calcined in an electric furnace at 1600°C in the atmosphere for 2 hours to produce zirconium oxypyrophosphate (ZrO) ₂ P ₂ O ₇ powder. To 320 g of the powder obtained in this way, magnesium phosphate Mg ₃ (PO ₄ ) _{2.8H 2} O was added as Mg ₃ (PO ₄ ) ₂ in a range of 0.5 to 8% by weight as shown in Table 1 below. 210 g of water was added to each of the mixed powders in different amounts, and the mixture was mixed and ground for 24 hours in an alumina ball mill with an internal volume of 2. After passing this slurry through a 100 mesh sieve,
It was dried in a dryer at 150°C for 3 hours. This powder
Passed through a 60 mesh sieve. A test piece with dimensions of 10 x 30 x 6 tmm was made from this powder using a mold press at a molding pressure of 300 kg/cm ² . Furthermore, this was placed in a vinyl chloride bag and sealed, and was molded using a hydrostatic press machine at a pressure of 1500 kg/cm ² .This was then fired in an oxidizing atmosphere at the respective predetermined temperatures shown in Table 1 below. Various properties of each sintered product were measured and shown in the same table.

【table】

[Table] Shows the degree difference.
As is clear from Table 1, 0.5 to 6% by weight of magnesium phosphate is added to the main component zirconium phosphate.
% of the low expansion porcelain of the present invention has the effect of increasing transverse rupture strength and rapid cooling temperature difference, especially sample No. 4.
-6 with a magnesium phosphate content of 2.0 to 5.0% had the greatest effect. The present invention improves both the mechanical strength and thermal shock resistance of zirconium phosphate low-expansion porcelain compared to conventional products.
Welding nozzles and ceramic heaters exposed to thermal shock,
It is an excellent product that can be used for precision mechanical parts such as thermocouple protection tubes, heat exchangers, and high-temperature microscope parts used at high temperatures.

Claims (1)

[Claims] 1. Zirconium phosphate [(ZrO) ₂ P ₂ O ₇ ] low expansion porcelain characterized by containing 0.5 to 6% by weight of magnesium phosphate [Mg ₃ (PO ₄ ) ₂ ].