GB2140458A - Tubular components of densely sintered ceramic materials - Google Patents

Abstract

Tubular components made from densely sintered aluminium nitride which has a satisfactory thermal conductivity, a high electrical resistance, satisfactory dielectric properties, as well as high strength. Advantageously one or more oxidic materials may be added to the aluminium nitride. Preferably yttrium oxide is used as an additive although the additives may consist generally of oxides of alkaline earth metals or of rare earth metals or of transition elements of the IVth, Vth or VIth groups of the periodic system or they may consist of aluminium oxide or silicon oxide. The invention is particularly useful for making laser tube components.

Description

SPECIFICATION Tubular components of densely sintered ceramic materials The present invention relates to tubular components of densely sintered ceramic materials.

Due to their satisfactory thermal conductivity and their high electrical resistance, use has hitherto been made for tubular components, or densely sintered aluminium oxide but if aluminium oxide ceramics do not fulfil the requirements, then densely sintered beryllium oxide is utilised (see Ullmanns Encyklopä- die der Technischen Chemie, 4th Edition, 1979, volume 17, pages 525-527).

Although densely sintered beryllium oxide has very satisfactory qualities, its high cost and the toxicity of the beryllium oxide dust militate against an extensive application of this material.

The invention consequently has as an object a tubular component made from a material that has satisfactory qualities analogous to those of densely sintered beryllium oxide, but which may be produced more economically and in a manner not injurious to health, and processed in like manner.

Accordingly the invention consists in a tubular component made of densely sintered aluminium nitride. This material meets the requirements hereinabove set forth.

Tube components of densely sintered aluminium nitride thus possess high strength, satisfactory resistance to sudden changes in temperature, high electrical resistance and satisfactory dielectric properties. Since, by contrast to those made of beryllium oxide, they retain their satisfactory thermal conductivity even at high temperatures, these components are particularly appropriate for laser tubes.

In view of the comparatively great coefficient of thermal expansion of the densely sintered aluminium nitride, the tube components in accordance with the invention may be joined satisfactorily to metals.

Pulverulent mixtures of aluminium nitride and 0.1 - 10% by weight of an oxidic additive, preferably form the initial material for the production of the tube components. These mixtures are processed by pressing in the cold state into green mouldings which are densely sintered in an inert atmosphere, preferably under nitrogen.

The coefficient of thermal expansion and the thermal conductivity of the densely sintered aluminium nitride may be affected in required manner by the nature and quantity of the oxidic additive.

One or more of the oxides of the alkaline earth metals, of the rare earth metals (scandium, yttrium and lanthanum up to lutetium), of the transition elements of the IVth, Vth and Vlth group of the periodic system, aluminium oxide and silicon oxide, may be utilised as oxidic additives.

Yttrium oxide proved to be particularly satisfactory.

Densely sintered aluminium nitride which contains yttrium oxide is unexpectedly extremely stable against humidity.

The production of tube components in accordance with the invention may advantageously be performed as described in the following example.

Example 5000 grammes of a mixture of 99% by weight of pulverulent aluminium nitride and 1% byweightof pulverulent yttrium oxide are ground for 40 hours in a ball mill containing ceramic grinding elements and under argon as a protective gas, and then passed through a screen having a mesh size of 100 micrometres.

A tubular pressing is produced by isostatic cold pressing (2500 bar pressure) from the powder having a grain size of less than 100 micrometres obtained by screening, and placed in an electrically heated sintering furnace. After evacuation down to 10-5 mbar, nitrogen is fed into the sintering furnace until the pressure amounts to 5 mbar. The sintering furnace is then heated whilst maintaining this pressure, until a temperature of 1200 C is reached within 3 hours. The nitrogen pressure is then raised to 140 mbar, and the temperature is raised to 1 850 C within an hour, when the nitrogen pressure amounts to 180 mbar.

This temperature and pressure are maintained for 2 hours, after which a cooling operation is performed.

The densely sintered tube components are extracted after venting the sintering furnace.

The tubular component produced in this manner has a coefficient of thermal expansion of 4 x 1 O-6K-', a thermal conductivity of 200 W/m K and a flexural strength of 320 N/mm2.

1. A tubular component of densely sintered aluminium nitride.

2. A component as claimed in claim 1, wherein one or more oxidic materials are added to the aluminium nitride.

3. A component as claimed in claim 2, wherein the additives are oxides of alkaline earth metals, of rare earth metals, of the transition elements of the IVth, Vth or Vlth group of the periodic system, or aluminium oxide or silicon oxide.

4. A component as claimed in claim 2 or 3, wherein the proportion of oxidic additives amounts to 0.1 to 10% by weight.

5. A component as claimed in claim 2,3 or 4, wherein the oxidic additive is yttrium oxide.

6. A method of making a tubular component substantially as hereinbefore described with reference to the specific Example.

7. A lasertube component whenever made from a component as claimed in any of the preceding claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Tubular components of densely sintered ceramic materials The present invention relates to tubular components of densely sintered ceramic materials. Due to their satisfactory thermal conductivity and their high electrical resistance, use has hitherto been made for tubular components, or densely sintered aluminium oxide but if aluminium oxide ceramics do not fulfil the requirements, then densely sintered beryllium oxide is utilised (see Ullmanns Encyklopä- die der Technischen Chemie, 4th Edition, 1979, volume 17, pages 525-527). Although densely sintered beryllium oxide has very satisfactory qualities, its high cost and the toxicity of the beryllium oxide dust militate against an extensive application of this material. The invention consequently has as an object a tubular component made from a material that has satisfactory qualities analogous to those of densely sintered beryllium oxide, but which may be produced more economically and in a manner not injurious to health, and processed in like manner. Accordingly the invention consists in a tubular component made of densely sintered aluminium nitride. This material meets the requirements hereinabove set forth. Tube components of densely sintered aluminium nitride thus possess high strength, satisfactory resistance to sudden changes in temperature, high electrical resistance and satisfactory dielectric properties. Since, by contrast to those made of beryllium oxide, they retain their satisfactory thermal conductivity even at high temperatures, these components are particularly appropriate for laser tubes. In view of the comparatively great coefficient of thermal expansion of the densely sintered aluminium nitride, the tube components in accordance with the invention may be joined satisfactorily to metals. Pulverulent mixtures of aluminium nitride and 0.1 - 10% by weight of an oxidic additive, preferably form the initial material for the production of the tube components. These mixtures are processed by pressing in the cold state into green mouldings which are densely sintered in an inert atmosphere, preferably under nitrogen. The coefficient of thermal expansion and the thermal conductivity of the densely sintered aluminium nitride may be affected in required manner by the nature and quantity of the oxidic additive. One or more of the oxides of the alkaline earth metals, of the rare earth metals (scandium, yttrium and lanthanum up to lutetium), of the transition elements of the IVth, Vth and Vlth group of the periodic system, aluminium oxide and silicon oxide, may be utilised as oxidic additives. Yttrium oxide proved to be particularly satisfactory. Densely sintered aluminium nitride which contains yttrium oxide is unexpectedly extremely stable against humidity. The production of tube components in accordance with the invention may advantageously be performed as described in the following example. Example 5000 grammes of a mixture of 99% by weight of pulverulent aluminium nitride and 1% byweightof pulverulent yttrium oxide are ground for 40 hours in a ball mill containing ceramic grinding elements and under argon as a protective gas, and then passed through a screen having a mesh size of 100 micrometres. A tubular pressing is produced by isostatic cold pressing (2500 bar pressure) from the powder having a grain size of less than 100 micrometres obtained by screening, and placed in an electrically heated sintering furnace. After evacuation down to 10-5 mbar, nitrogen is fed into the sintering furnace until the pressure amounts to 5 mbar. The sintering furnace is then heated whilst maintaining this pressure, until a temperature of 1200 C is reached within 3 hours. The nitrogen pressure is then raised to 140 mbar, and the temperature is raised to 1 850 C within an hour, when the nitrogen pressure amounts to 180 mbar. This temperature and pressure are maintained for 2 hours, after which a cooling operation is performed. The densely sintered tube components are extracted after venting the sintering furnace. The tubular component produced in this manner has a coefficient of thermal expansion of 4 x 1 O-6K-', a thermal conductivity of 200 W/m K and a flexural strength of 320 N/mm2. CLAIMS

1. A tubular component of densely sintered aluminium nitride.

2. A component as claimed in claim 1, wherein one or more oxidic materials are added to the aluminium nitride.

3. A component as claimed in claim 2, wherein the additives are oxides of alkaline earth metals, of rare earth metals, of the transition elements of the IVth, Vth or Vlth group of the periodic system, or aluminium oxide or silicon oxide.

4. A component as claimed in claim 2 or 3, wherein the proportion of oxidic additives amounts to 0.1 to 10% by weight.

5. A component as claimed in claim 2,3 or 4, wherein the oxidic additive is yttrium oxide.

6. A method of making a tubular component substantially as hereinbefore described with reference to the specific Example.

7. A lasertube component whenever made from a component as claimed in any of the preceding claims.