DE1261436C2 - Sintered body made of aluminum oxide - Google Patents

Description

i 261 436

3 4

Temperatures from 400 to 500 ° C, with quartz lamps those at high temperature are in connection with

not exceeding 600 to 900 ° C in the long run- the addition of in the vacuum does not volatilize-

be allowed to. the magnesium compounds an essential factor

The new material enables working temperatures to achieve a microcrystalline structure,

up to over 1200 ° C and thus a further considerable 5 at which the average grain size does not exceed

Increase in the light output and change of 10 μ lies. Appropriately, approximately 80 to 90%

Spectrum emission. It is because of its microcrystalline crystals have a grain size below 7 μ. the

linen structure and the resulting high strength- surprising technical effect that with so

also known materials from brief heating and despite the microcrystalline

superior to transparent aluminum oxide and al- ready enables a body with a very good structure

light results in lower wall thicknesses and thus greater transparency, is probably due to this.

Increase in the light transmission or at the same det that through the application of the low pressure

Wall thickness of the enveloping body higher internal pressures. while almost all pores are removed very quickly

The high density of the new material makes this one such pore elimination after the previous one

Body absolutely vacuum-tight. The bodies draw i ₅ procedures also in a hydrogen atmosphere or

This can also result from large electrical breakdowns if the pressure is insufficiently reduced

strength and low dielectric losses, even the long sintering times and the resulting

at high temperatures. large crystals was.

By adding coloring oxides, such as chromium oxide or cobalt oxide, for example, the use of short sintering times during sintering can be used to absorb certain spectral ranges, as has already been proposed in French patent specification 885 833, if necessary only light certain wavelengths, reasonable times isolators, for example for only ultrared, to pass. Cathode holders to manufacture. Such an essential insulation component of the invention is that the bodies only have to be mechanically just so strong, sintering by brief heating of approximately 25 that they can withstand low stresses, he-15 minutes at temperatures above 1800 ⁰ C but do not require a high density, but have taken place at a pressure of less than 10 torr. That insulators even have a certain porosity even after a heating period of a few sity. For this reason, the required sintering temperature of a very pure aluminum oxide is not assumed within minutes, nor is transparency comparable to that of coarsely crystalline magnesium oxide for preventing unrestrained sintered bodies, which was added surprisingly - crystal growth, and it is as if one worked on the basis of the previously known state of high proportion of plasticizers, the technique as it is in the Austrian patent that a dense sintering is impossible. Also, the documents 221007 and 212 280 are described, the sintering is not done in a vacuum.

Was of the opinion that the transparency is so much the better. the longer it is heated. For this reason, their technical objective is a developed process a heating time of 1000 minutes and more according to the French patent specification for the invention common, which inevitably could not give rise to coarse crystalline dung and therefore not Bodies leads The Austrian patent is suggested that by brief heating 212 280 mentions that instead of hydrogen as Sin 40 in a vacuum a sintered body with microcrystalline The atmosphere can also be used in a vacuum. Can achieve structure that is still high density and But it is also based on the assumption that transparency is present.

that long sintering times to achieve high As a starting material for the sintered body

Density and transparency are necessary. a pure, very fine-grained aluminum oxide

It has been shown that the quality of the sinter 45 turns, which advantageously contains a-aluminum

Body in the sense of the invention is all the better, has oxide of approximately 99.9%. This pure out

the lower the pressure under which sintering takes place. gang material are known to be conscious

In the high-temperature sintering technology, it is already added impurities up to 0.5 weight

knows, such sintering in hydrogen atmo- percent compounds of magnesium added,

Sphere. The invention proceeds from the 50 which prevent uncontrolled crystal growth

Finding out that to achieve a more transparent and uniform structure. The

Body made of aluminum oxide and magnesium oxide in powder mixture has an average grain size

Hydrogen atmosphere very long sintering times of less than 3 μ, the grain size of the is advantageous

Achieving a satisfactory level of transparency required - the majority even below 1 μ. For the manufacturing

are lich. This inevitably leads to a large grain process in which it has become possible to take along

growth and thus too low strength values, extremely short sintering times to an almost

especially since the magnesium pore-free, transparent sintered body, which inhibits grain growth, "

oxide as a result of reduction by the hydrogen, it is of considerable importance that the annealed

is volatilized. or fused alumina of one

However, the sintered body according to the invention has 60 mechanical pretreatment that is subjected

in the fully sintered state the added content of the individual grains a particularly high energy

of magnesium oxide unchanged. content, appropriately above 4 cal / g (measured as ad-

In the sintering carried out according to the invention, sorption energy compared to water vapor at 1.6 Torr

under a pressure of less than 10 Torr and at 30 ° C), by activating the surface

Surprisingly, it is issued after approximately 65. This is advantageous through a com

15-minute heating to temperatures above a combination of normal or tangential

1800 ° C, preferably to 1850 to 1900 ° C, the forces during mechanical processing

desired transparency. This short sintering times can be achieved, for example in a vibration mill,

5 6

in which a freely oscillating amplitude effect is achieved with the addition of 10 ml of ethylene glycol as an organic

give is. Shem binder pressed into a molded part. the

Molding is under a pressure of 10 ~ ⁴ Torr at

Example of a temperature of 1900 ° C sintered for 15 minutes.

5 The sintered body thus produced has a density

100 g of finely ground aluminum oxide with a thickness of 3.99 g / cm ³ , a flexural strength of 52 kg / mm ^2, average grain size of 1.5 μ and a transparency of 60% with a wall adsorption energy of 5.0 cal / g and a thickness of 0.5 mm. The grain size of Al ₂ O _{3 is} 99.9% and 0.50 g of MgCO ₃ is an average of 7 μ.

Claims (1)

such as cutting tools, drawing nozzles, turbine displays Patent applications ^ ^{em un <} ^ covers of metal vapor discharge lamps, which is characterized by a brief heating of approximately 15 minutes to the temperature From a pressed molding of pure 5 temperature of over 1800 ° C at a pressure of less aluminum oxide and up to 0.5 percent by weight than 10 Torr obtained microcrystalline structure of magnesium oxide by sintering at temperatures with average grain sizes not over 10 μ, over 1800 ⁰ C obtained Sintered bodies with a density above 3.96 and a transparency of improved mechanical and thermal properties of at least 40% in a wavelength range of shafts, in particular with an improved temperature of 0.4 to 2 μ with a wall thickness of 0.5 mm .
temperature change resistance, for the use The invention is based on the completely new as a high mechanical and / or thermal recognition that high mechanical strength objects such as cutting tools, quality properties on the one hand and good transparency of drawing nozzles, turbine blades and casings on the other hand can very well be present in a sintered body in a sintered body like metal vapor discharge lamps, labeled 15 if the body in its net by a short-term heating density exceeds the mentioned limit value and for approximately 15 minutes at the temperature the ^{grain remains below the specified average of over 1800 0} C at a pressure of less lent grain size. It has been shown that the microcrystalline structure obtained as 10 Torr is slightly exceeded for the density with average grain sizes not exceeding 20 - assuming the best previously achieved-10 μ, a density of 3.96 and a transparent degree of purity of the starting powder - limit of at least 40% in a given wavelength limit of 3.96, the transparency range from 0.4 to 2 μ rises steeply with a wall thickness curve. of 0.5 mm. This result is so surprising because 25 the previously known sintered bodies with a microcrystalline structure were always opaque and the prejudice was that because of the scattering of light only at the many inner interfaces of such an anisotropic product of a finely crystalline structure 30 opaque bodies were to be expected. In the case of the sintered bodies according to the invention, it is The invention relates to sintered bodies made of almost pure, thus succeeded by the microcrystalline structure Aluminum oxide and small amounts of magnesium result in maximum resistance properties oxide. combine with a very high density and with Such bodies find very good transparency under two 35 in technology. different viewpoints use. Particularly good sintered bodies in the sense of the invention On the one hand, because of their high mechanical strength, they are present at densities in the range of 3.96 niche strength for cutting tools, drawing nozzles, up to 3.98 g / cm ³ . In this density range, turbine blades or similar applications produce the best values for transparency and strength, used for purposes, whereby the high mechanical strength can even be reduced to 3.998 g / cm due to a particularly fine crystalline crystal ³ Increase, as a result of the high density build-up is achieved. On the other hand, these sintered bodies are characterized by a very good body, thermal conductivity and thus thermal shock resistance, which are characterized by good transparency, which they value in connection with good mechaparity, for example for the 45 niche strength, especially for use as the envelopes of metal vapor discharge lamps. In this cutting tools, tiarabine shovels and similar cases, the bodies have, for example, in the mechanically and thermally highly stressed parts of Austrian patents 221007 and 212 280 particularly valuable and, for example, as well as in the company publication Lucalox-Ceramic, the longer service life of cutting tools and higher company General Electric described syid, a roughly 50-temperature allow for turbine blades,
crystalline structure, which can be used to obtain the most surprising advantage of this body against- Transparency has to be accepted, although it is above the previously known but lies in the fact that it is in spite of Due to the mechanical properties, the microcrystalline structure impairs a very good transmission. . parence, for example in a body The aim of the present invention is a 55 of 0.5 mm thickness in a wavelength range of Sintered body which has the two valuable properties 0.4 to 2 μ 6O%. That is of particular concern high mechanical strength and good significance for moldings in which there is on Transparency, one of which has so far been highly transparent and the one at the same time always excluded the other, united in itself. thermally and mechanically highly stressed This aim will be achieved 60 according to the invention, such as for discharge lamps, by means of a molded part made from a molded part of Also in the ultra-red region of over 2 μ there is good through-purity Aluminum oxide and up to 0.5 weight percentage. cent magnesium oxide by sintering at temperatures for this purpose found so far high-melting Sintered body preserved above 1800 ° C with improved glasses and vessels made of pure silica mechanical and thermal properties, 65 manure. The amount of allowable temperatures of this especially with improved temperature change body is limited by the softening resistance, for the use as mechanical behavior or transformation processes of these substances, and / or objects subject to high thermal loads, so that in the case of glasses in the usual sense, wall temperature