JPH02307821A - Electrical insulating filler for high-temperature use and its production - Google Patents

Abstract

PURPOSE:To obtain a spherical filler having high electric resistance as well as specific lattice constant and lattice strain of MgO by precipitating CaO in a state of solid solution in grain boundaries by means of heat treatment and then removing, by dissolution, the above CaO in the filler composed princi pally of sintered MgO. CONSTITUTION:A powdered MgO consisting of, by weight, >=93% MgO, 0.3-1.5% CaO, <=4% SiO2, <=0.4% (Fe2O3+Al2O3), <=0.1% B2O3, and <=0.3% Igloss is heat-treated at >=1000 deg.C maximum temp. This powder is brought into contact with the acid solution of hydrochloric acid, etc., and then washed well with water, filtered, and dried, by which an electrical insulating filler in which the lattice constant of MgO and the lattice strain of MgO are regulated to <=4,2130A and <=7.0X10<-4>, respectively, is obtained. If the above lattice constant and lattice strain are beyond the above ranges, electric resistance is deteriorated and, as a result, this filler becomes unapplicable to the high temp. use.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an electrical insulating filler containing sintered magnesia (MgO) as a main component and having excellent electrical insulation resistance at high temperatures, and a method for producing the same. It is suitable as an insulating filler for heaters.

[Prior Art and Problems] MgO is characterized by extremely high electrical insulation resistance at high temperatures, and is used as an electrical insulating material, particularly as an insulating filler for sheath heaters.

The conventionally used electrofused magnesia is obtained in large lumps due to its manufacturing method, so in order to use it as an insulating filler for thin sheath heaters, it must be crushed and sized, and the crushed particles are angular. Because it has a shape,
Not only was it difficult to fill, but the heater was also damaged during the molding process after filling, causing a shortened lifespan.

Also, sintered magnesia is easy to manufacture and has attracted attention in recent years, but it has been published in Japanese Patent Application Laid-open Nos. 82-90807 and 62-288.
Even the sintered magnesia described in No. 002 did not satisfy the demand for high insulation resistance.

Further, the spherical sintered magnesia described by the present inventors in JP-A-62-90807 was suitable for making a thin heater, but had low insulation resistance.

[Problems to be Solved by the Invention] The present invention has a high electrical insulation resistance at high temperatures (and a spherical grain shape), and when used as an insulating material for a sheathed heater, it will not damage the heater during molding. The present invention aims to provide a spherical high-temperature electrical insulating filler and a method for manufacturing the same.

[Six means to solve the problem] It is known that sintered magnesia contains M g 01;: Ca O in solid solution, and this solid solution of CaO causes distortion of the MgO lattice. The lattice constant of MgO increases.

It is presumed that the reason why the insulation resistance of sintered magnesia is low is due to the solid solution of CaO and the resulting lattice strain of MgO.

The present invention aims to provide an electrical insulating filler having high electrical insulation resistance at high temperatures by precipitating the CaO in solid solution at grain boundaries through heat treatment and dissolving and removing this CaO with an acidic solution. It is.

[Means to solve the problem] Above:! The electrical insulating filler to solve jA21i is magnesia sintered powder with a) chemical composition of i) MgO≧93vt% ii) 0.3≦CaO≦1.5 vt%iii) S
i O2≦4 vt% iy) Fe20z+Al 20 co≦
0.4Wt%y) B20:+≦0.1wt% vi) 1gloss≦0.3wt%, b) MgO lattice constant is 4.2130 or less c) MgO
It is an electrically insulating filler having a lattice strain of 7.0×104 or less.

When the chemical composition of the magnesia sintered powder is within the above range, the electrical insulation resistance is sufficiently high, and when the chemical composition is outside the above range, the insulation resistance becomes low and it is no longer practical as a filler for high temperatures.

In the method for producing such an electrically insulating filler, magnesia powder is heat-treated at a maximum temperature of 1000° C. or higher, brought into contact with an acidic solution, and then thoroughly washed with water.

In producing the electrical insulating filler of the present invention, 42 out of spherical powders of a predetermined composition sintered in a rotary kiln etc.
It is appropriate to collect the part of the intestines that passes through a 0μ sieve and does not pass through a 25μ sieve. Further, the powder may contain an auxiliary agent such as ZnO2 within a range where other components do not affect the powder.

The manufacturing method is preferably such that the powder is adjusted to have a particle size of 420 to 25 μm at 95 wt% or more, and then heat treated at 1000°C or higher in a heating furnace such as a rotary kiln, and then brought into contact with an acidic solution. Wash thoroughly with water, filter, and dry.

The magnesia powder of the present invention preferably has an insulation resistance of 1.8×10 9 Ω·am or more after being maintained at 800° C. for 24 II r. More preferably 2.5X 10'Ω
・The number of layers is 0 or more.

Furthermore, it is well known that the flow time of the filling is an important factor in manufacturing, especially in terms of work efficiency, when filling sheath heater powder.
It is industrially significant that it is 100gr or less, especially 180scc/100gr or less.

Furthermore, in the present invention, the lattice constant of MgO is 4.2130A.
Hereinafter, it is necessary that the lattice strain of MgO be 7XIO-' or less, and if it is outside this range, the insulation resistance will deteriorate and the material will not be practical for high-temperature use. More preferably, the lattice strain of MgO is 5×10' or less.

In the manufacturing method of the present invention, if the maximum temperature is less than 1000'C, the effect of heat treatment will be small, so it is desirable that the maximum temperature is 1000C or higher, preferably 1200 to 1400C.

Next, it is brought into contact with an acidic solution for 1 minute or more, separated from this solution, thoroughly washed with water, filtered, and dried.

That is, the magnesia sintered powder, which has few impurities on its surface, has excellent insulation resistance at high temperatures without impairing the above-mentioned fluidity.

[Examples] Hereinafter, the present invention will be specifically explained using Examples and Comparative Examples.

Among the chemical compositions of Examples in the present invention, Mg0SCab
SS i02, Fe2O3, Al2O3, and B2O3 are prepared by hot dissolving magnesia powder in aqueous hydrochloric acid solution, and then Z
roz is NazCO3, Na2B2Qr 1OHzo
After melting with an alkali and then hotly dissolving in an aqueous nitric acid solution, measurements were taken using an ICAP manufactured by Jarel Ash 575-■.

1 gloss is the weight loss expressed in weight percent after accurately weighing the log of the sample, placing it in a platinum crucible, and placing it in an electric furnace for 1000°C x 1hr.

The high-temperature insulation resistance of magnesia in the example of the present invention was obtained by compressing and filling the gap between the metal pipe with an inner diameter of Loam and the center rod of an outer diameter of 5 with an insulating filler to a length of about 25cm at a pressure of 1.5Teem'. A platinum wire was attached to the material and placed in an electric furnace, and the insulation resistance at each temperature was measured (Fuettary method). The material of the metal pipe and center rod used was SUS 304.

The 11PI constant of lattice strain is determined by X-ray diffraction (IR-I manufactured by Rigaku Denki).
Type A) 40kL 20111^, l/4deg/
■, M under the condition of time constant 5sec
go's (1,1,1), (2,0,0), (2,2,
0), (3,1,1), (2,2,2), (4,0
, 0), (4, 2, 0), and
Separate correction (Reference 1) and standard correction (Reference 1) of kαI and kα2 are performed to determine the true half-width. A 1llall plot (Reference 2) was performed from the obtained half-width, and the slope was determined by linear regression using the least squares method, and the value of 1/2 of the slope was taken as the lattice distortion.

The marker sample is magnesia r1 with MgO purity of 99.9%.
After crushing 1 crystal, 44~20μ Akebono is 130μ
The sample was heat-treated at 0°C for 5 hours. The measurement sample was also adjusted to have a particle size in the range of 44 to 20 μm.

(Reference 1 above) r The leasuremen
tol'particle 5ize by the
X-ray 1methodJ by P.

W,Jones,,Prpc,Roy,Soc,,^1
86.16 (1938).

(Above document 2) Ilal, W, Il, Pr
oc, Phys, Soc, .

A62. ．． 741 (1949).

Also, all of the lattice constants! The value was determined from Bragg's equation using silicon as an internal standard. M g O (3,1
,l), (2,2,0), (3,1,l), (2,2,
2), the diffraction angle was read from the peak of (4, 2, 0) using the half-width midpoint method, the separation correction of kαI and kα2 was performed, and the lattice constant was determined using the least squares method.

In addition, 8 metal pipes (cells) filled with the above insulating filler were used.
The sample was placed in an air furnace at 00°C for 7 days, and changes in insulation resistance over time were measured.

Figures 1 and 2 show the results after firing at 800°C for 24 hours.
Alternatively, the resistance value after firing for 72 hours is shown.

In addition, the powder tap density and flow time are A S T
The American Boeh Tool and
Δp1 was determined using a device manufactured by DleCoIIpan>'.

The particle size distribution was determined by sieving using a JIS sieve.

Note that the amount (%) of each component shown in the examples is ff1m%.

Example 1 and Comparative Example 1 lnm fired at a temperature of 2000°C in an 0-tally kiln
The following high-purity magnesia powder was sieved from 420 μm to 25 μm using a stainless steel wire mesh. This was fired using a rotary kiln at a maximum temperature of 1200°C.

2.5 kg of the above magnesia powder was added to 0.2 N hydrochloric acid solution I (19) and stirred for 5 minutes, the supernatant liquid was discarded, water 101 was added, stirred and washed twice, and the mixture was vacuum filtered. This filter residue was further sprinkled with water 551, washed with water, and dried in hot air at 120°C. (Hereinafter, this treatment method will be referred to as acid washing.) Chemical composition, particle size distribution, flow time, and initial insulation of this magnesia powder. Table 1 and FIG. 1 show the resistance and the change in resistance over time at 800°C.

In addition, the above measured values of magnesia powder used as a raw material as Comparative Example 1 are also shown.

Table 1 Table 1 Continued Example 2 The magnesia powder used in Example 1, which had been sieved to 420-25 μm, was placed in a box-shaped electric furnace. The pieces were fired at a temperature of 400°C, left in a furnace until the temperature reached room temperature, and then washed with acid water. The change in resistance of this magnesia powder at 800° C. over time was investigated, and the values after 24 hours and 72 hours were plotted against the heat treatment temperature in FIG. 2.

It has been shown that the resistance value is more than twice as high as that of the commercially available mug (for high temperature use) shown in the comparative example.

[Effects of the Invention] As explained above, the electrical insulating filler of the present invention has 800
It has high insulation resistance at high temperatures of ℃ or higher and excellent flow characteristics, making it an excellent insulating filler for sheath heaters. Furthermore, as shown in FIGS. 1 and 2, the deterioration of insulation resistance is small and the life of the heater is long.

[Brief explanation of drawings]

FIG. 1 shows changes in insulation resistance over time at 800° C. of Example 1 and Comparative Example 1. Figure 2 shows the heat treatment temperature and the temperature of magnesia powder after washing with acid water.
The resistance value at 0°C is shown. White circles indicate 24 It r values, and black circles indicate 72 Hr values. □ 1 Procedural amendment (spontaneous) 1. Indication of the case Patent Application No. 1983-83029 2. Title of invention: High-temperature electrical insulating filler and method for manufacturing the same] Name: Shin Nippon Chemical Co., Ltd. 4. Agent: 5 6. Subject of amendment (1) The following matters are inserted between lines 9 and 10 on page 6 of the specification. ' In addition, in the present invention, the packing density of the filling is 2.
．． 10 to 2J5 (g/cc) is preferable, and 2.10 (
g/ee), the life of insulation resistance decreases significantly, and
．． If it exceeds 35 (g/cc), the insulation resistance will be low from the beginning, and any of them will not be practical for high temperature applications. (2) The following matters should be inserted between lines 5 and 6 of page 13. Example 3 Samples 1 to 5 with different packing densities were prepared in the same manner as in Example 2 by adjusting the particle size distribution from the sample used in Example 1. The insulation resistance was investigated and the results are shown in Table 2 and Figure 3.Table 2'' (3) Insert the following information next to the last line of page 13. "Figure 3 shows the insulation resistance after 24 hours and 240 hours at 800°C. The symbols in the figure are as follows. White circles are after 24 hours and black circles are after 240 hours." (4) Drawing (attached sheet) Figure 3) is added. Procedural amendments dismissed July 12, 1990 Toshi Uematsu, Commissioner of the Japan Patent Office1, Indication of the case Japanese Patent Application No. 83-830292, Name of the invention High-temperature electrical insulating filler and method for manufacturing the same3, Amendment. Relationship with the case of the person who filed the patent application Patent applicant: 107 (telephone: 58B-8854) Address: 4-13-5-5 Akasaka, Minato-ku, Tokyo Date of amendment order: Sent on June 22, 1990 82 Heisei July 3, 2017

Claims (2)

[Claims] (1) Magnesia sintered powder has a) chemical composition: i) MgO≧93wt% ii) 0.3≦CaO≦1.5wt% iii) SiO_2≦4wt% iv) Fe_2O_3+Al_2O_3≦0.4wt%
v) B_2O_3≦0.1wt% vi) 1gloss≦0.3wt%, b) MgO lattice constant is 4.2130A or less c) MgO
An electrically insulating filler characterized by having a lattice strain of 7.0×10^-^4 or less. (2) A method for producing an electrically insulating filler, which comprises heat-treating magnesia powder at a maximum temperature of 1000° C. or higher, bringing it into contact with an acidic solution, and then washing thoroughly with water.