JPH0475187B2 - - Google Patents

Description

[Detailed description of the invention]

``Industrial Application Field'' The present invention relates to a method for manufacturing a new mica ceramic having excellent properties such as heat resistance and bending strength. ``Prior Art and its Problems'' Known manufacturing methods include (1) hot press method, (2) phosphoric acid bond method, (3) glass bond method, (4) crystallization method, and (5) fine particle embedding method. However, the above-mentioned hot pressing method (1) mainly involves the bonding of fluorine mica particles, and although the obtained mica has excellent insulating properties, it is unreasonable in terms of equipment and economics. The phosphoric acid bonding method (2) has the disadvantage of high costs, making it difficult to manufacture large products due to restrictions on firing time, and the glass bonding method (3) requires low melting point glass to be bonded. The crystallization method (4) randomly grows microcrystals of fluorine mica from glass with a suitable mica composition through heat treatment. It is commercially available from Corning Corporation under the trade name "Macol", and large products can be manufactured using dense glass-ceramics, but it has the disadvantage of high cost. The main component is fluorine mica with a size of 3 μ or less, and an appropriate sintering aid is added.
It is baked in a refractory powder containing fluorine.
Although it is possible to manufacture large products, the fluorine mica must be finely pulverized to a particle size of 3μ or less, and mica is difficult to pulverize due to its flat plate shape, resulting in high costs. In addition, in order to obtain a dense sintered body,
Since frits and fluorides are added as sintering aids, there is a drawback in that the heat resistance changes rapidly from around 500°C on the thermal expansion curve. "Summary of the Invention" The object of the present invention is to eliminate these drawbacks and provide mica ceramics that are inexpensive, have high bending strength, and can withstand a maximum operating temperature of 1000°C. Furthermore, the present invention is based on the previously filed "Method for producing cordierite-mica-based sintered bodies"
The purpose of the present invention is to provide mica ceramics that have dramatically improved machinability, which was a drawback of the previous method (No. 33253). Barium mica (BaMg ₃ Al ₂ Si ₂ O ₁₀ F ₂ ) produced by the production method of the present invention has a
It is known that it has high hardness and excellent heat-resistant insulation properties, and that sintered bodies produced by hot pressing have excellent machinability. The present inventors discovered that in the process of researching cordierite lilo-mica-based sintered bodies, cordierite (2MgO・2Al ₂ O ₃・5SiO ₂ ) decomposed and some Ba-
The present invention was achieved by discovering that it changes into mica and that the resulting sintered body has excellent properties. That is, the present invention provides a formulation containing 40 to 70% by weight of fluorine phlogopite and 30 to 60% by weight of synthetic cordierite.
To 100 parts by weight, add 10 to 30 parts by weight of barium fluoride, 2 to 10 parts by weight of aluminum oxide, and 0 to 10 parts by weight of magnesium fluoride, which react with cordierite and change mainly to barium mica and glass phase. It is characterized by being mixed, molded, buried in fluorine mica powder, and fired. The present invention will be explained in detail below. First, the ratio of fluorine phlogopite (KMg ₃ AlSi ₃ O ₁₀ F ₂ ) and synthetic cordierite is such that fluorine phlogopite is
If it is less than 40% by weight, the resulting sintered body will be hard and have poor machinability, and if it exceeds 70% by weight, the resulting sintered body will have a high water absorption rate and will be difficult to form a dense sintered body. Furthermore, considering machinability, water absorption rate, etc.
Fluorine phlogopite 50-60% by weight, cordierite 40
A range of ~50% by weight is optimal. BaF ₂
and Al ₂ O ₃ are required, and with the addition of BaF ₂ alone,
A dense sintered body cannot be obtained. The amount of each added is 50 to 60 parts by weight of fluorine phlogopite and 40 to 50 parts by weight of cordierite.
20 to 25 parts by weight of BaF ₂ and 5 to 6.5 parts by weight of Al ₂ O ₃ are optimal. If BaF ₂ is less than this, spinel is likely to be formed, especially if it is less than 10 parts by weight, only a slight peak of Ba-mica is observed in X-ray diffraction analysis, and the peak of spinel MgOAl ₂ O ₃ becomes large. , and since the glass phase is also thermally unstable, 500~
At 600℃, the sintered body undergoes a graying phenomenon. Moreover, if it exceeds 30 parts by weight, it is difficult to obtain a dense sintered body. It is presumed that the addition of Al ₂ O ₃ affects the formation of Ba-mica and thermally stable glass.
Products without Al ₂ O ₃ additives can only achieve a water absorption rate of about 0.5%. Al ₂ O ₃ is effective when added in small amounts;
In particular, addition of 5 to 6.5 parts by weight is optimal. If it exceeds 10 parts by weight, spinel and celsian (BaO.Al ₂ O ₃ .2SiO ₂ ) will increase as crystal phases, resulting in hardness and impaired machinability. It is estimated that the addition of MgF ₂ increases the amount of Ba-mica produced. Although the properties of the sintered body can be maintained at a certain level even without additives, the insulation properties of the system with MgF ₂ added are even better. However, if it exceeds 10 parts by weight, Mg becomes excessive compared to the amount necessary for Ba-mica production, which is not preferable. The fluorine phlogopite used in the present invention is preferably ball-milled and 44 μm or less; if particles coarser than this are included, densification is difficult and problems tend to occur in terms of strength. It is also advantageous in that particles of 44μ or less can be easily obtained by sieving with a 350-mesh sieve. The synthetic cordierite used is 13.8% by weight of MgO of the theoretical composition of cordierite,
Optimal is Al ₂ O ₃ 34.9% by weight and SiO ₂ 51.3% by weight, but commercially available MgO 5-17% by weight, Al ₂ O ₃ 30-53% by weight, SiO 43-60% by weight can also be used. I can do it. The calcination is preferably carried out in fluorine mica powder, particularly fluorine phlogopite, which has a melting point above the calcination temperature. This is because fluorophlogopite rapidly decomposes from around 1300°C and mainly generates SiF ₄ as a decomposition gas. On the other hand, since the firing temperature of the refractory powder containing fluorine is as high as 1,320 to 1,360°C, the refractory powder itself also sintered, and good results were not obtained. Furthermore, firing in a fluorine gas atmosphere was unsuitable because the sintered body warped. In the fluorine phlogopite powder used in the present invention, the occurrence of warpage in the obtained sintered body is small, and the reaction between the fluorine phlogopite and the sintered body causes a slight amount of fluorine phlogopite to stick to the surface. This can be easily removed with a file, sandpaper, etc. Although the firing temperature varies depending on the blending ratio of raw materials, the desired sintered body can be obtained at a temperature of 1320 to 1360°C. The firing temperature range on the furnace is 10~
Since the temperature is 20℃, there is no problem in practical use. The sintered body obtained in this way is mainly
Fluorine phlogopite and Ba-mica are bonded through a glass phase that can withstand temperatures up to 1000°C. Mica ceramics are dense, have strong bending strength, and have excellent heat resistance, machinability, and insulation properties. It is. That is,
The sintered body according to the present invention is produced by sintering fluorine phlogopite, cordierite, BaF ₂ , Al ₂ O ₃ and even MgF ₂ in fluorine phlogopite powder at a temperature of 1320 to 1360°C. The decomposition of elementary phlogopite is slight, if at all, and produces cordierite, BaF ₂ , Al ₂ O ₃ , and even
MgF mainly changes into a glass phase and Ba-mica, and this glass phase becomes a binding phase for fluorine phlogopite. Although it is not clear in electron microscopy, there is also Ba-mica in the glass phase, which is the binding phase. It is estimated that it has a composite structure in which fine particles are precipitated. Furthermore, low-cost synthetic cordierite can be used to a large extent, and the particle size of fluorine phlogopite is sufficient to be less than 44 μm, so the raw material cost is low, and the manufacturing process can be done using conventional ceramic methods. Since this is sufficiently possible, mica ceramics can be provided at low cost. "Example" Next, the present invention will be further explained with reference to Examples.
The invention is not limited to these examples. Example 1 Fluorine phlogopite of 44μ or less, commercially available cordierite powder (composition approximately 2MgO・2Al ₂ O ₃・5SiO ₂ ), and BaF ₂ , Al ₂ O ₃ , or MgF ₂ as shown in Table 1 They were prepared in the proportions shown (parts by weight), mixed and ground together with water in a pot mill for 24 hours, and then dried.

[Table]
The powder mixture thus obtained was molded into disks with a thickness of 3 mm and diameters of 60 mm and 28 mm at a molding pressure of 750 kg/cm ² . This material was buried in fluorine phlogopite powder with a particle size of 80 mesh or more and fired at a temperature of 1320 to 1360°C. The holding time was 1 hour, and a sintered body was obtained by cooling. Temperature rise above 1000℃ is 70~100℃/
hr. Table 2 shows the water absorption rate of the obtained sintered body,
Qualitative superiority and inferiority of machinability by iron saw cutting and
Crystal phase determined by line diffraction analysis (〇 indicates high peak intensity, △
indicates low peak intensity).

[Table] Table 3 shows the properties of typical materials with water absorption close to zero and good machinability.

[Table] As is clear from the above results, the coefficient of thermal expansion is
The coefficient of thermal expansion is 8.8×10 ^-6 or higher, which is close to the coefficient of thermal expansion of metals, so it is convenient as a bonding member with metals. Further, the thermal expansion curve changes slightly between 700 and 800°C, but it shows an almost gentle linear change up to 1000°C, and no sudden changes are observed. The bending strength shows a value of 1190 Kg/cm ² or more, which is enough to withstand machining. Also, 6.0mm
When holes were drilled using a φ HSS drill, there was no damage to the edges and the finish was good. The electrical properties also showed excellent values, with a Te value of 750°C or higher, tan δ of 31×10 ^-4 or lower, and a withstand voltage of 16 KV/mm or higher. According to the measurement results of Vickers hardness (HV) and Shore hardness (HS), Hv = 170 to 250 and Hs = 63 to 79, and the two hardnesses did not correspond. It is presumed that this is because the fracture stress generated is different between the indentation hardness measurement method and the rebound hardness measurement method. Although the Vickers hardness was measured under a load of 1 kg, the indentation did not show a clear rhombus shape and the measured values varied widely. Furthermore, no crack propagation was observed on the sample surface, and it is assumed that the crack stopped at the mica crystal. The sintered body of the present invention is pulverized, and the heating rate is 10℃/
As a result of DTA-TG analysis at 1000°C to 1100°C, there was a weight loss of about 1%, but no change was observed up to 1000°C, indicating good heat resistance. The apparent specific gravity of the sintered body was as high as 2.71 to 2.80, and when the fracture surface was observed using a scanning electron microscope, it was found that there were almost no pinholes and that it had a dense structure in which mica crystals were randomly interlocked. "Effects of the Invention" As stated above, the mica ceramic sintered body of the present invention exhibits superior properties than conventional ones, and therefore can be used as an easily machined ceramic for insulating materials, heat-resistant parts, high-temperature mechanical parts, etc. It is expected that it will be used widely.

Claims (1)

[Claims] 1. 10 to 30 parts by weight of barium fluoride and 2 to 30 parts by weight of aluminum oxide to 100 parts by weight of a preparation containing 40 to 70% by weight of fluorine phlogopite and 30 to 60% by weight of synthetic cordierite. 10 parts by weight, magnesium fluoride 0-10
1. A method for producing mica ceramics, which comprises adding parts by weight, mixing, shaping, embedding in fluorine mica powder, and firing. 2 50 to 60 parts by weight of fluorine phlogopite, 40 to 50 parts by weight of synthetic cordierite, 20 to 20 parts by weight of barium fluoride
25 parts by weight of aluminum oxide and 5 to 6.5 parts by weight of aluminum oxide. 3. The method for producing mica ceramics according to claim 1, wherein the fluorine phlogopite has a particle size of 44 μm or less. 4. The method for producing mica ceramics according to claim 1, wherein the fluorine mica powder is fluorine phlogopite powder. 5. Production of mica ceramics according to claim 1, wherein the synthetic cordierite has a composition ranging from 5 to 17% by weight of MgO, 30 to 53% by weight _{of Al2O3} , and 43 to 60% by weight of _SiO2 . Law.