GB1561735A

GB1561735A - Infra-red energy source

Info

Publication number: GB1561735A
Application number: GB390976A
Authority: GB
Original assignee: English Electric Valve Co Ltd
Current assignee: Teledyne UK Ltd
Priority date: 1976-10-12
Filing date: 1976-10-12
Publication date: 1980-02-27

Description

(54) INFRA-RED ENERGY SOURCE (71) We, ENGLISH ELECTRIC VALVE COMPANY LIMITED, a British company, of 106 Waterhouse Lane, Chelmsford, Essex, CMI 2QU do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to infra-red energy sources of the kind which find application in spectrophotometry. Such energy sources are heated by passing an electric current through them, and some commonly used energy sources possess a resistance having a negative temperature coefficient which requires the use of special circuitry including stabilising resistors. Other energy sources which do not possess this problem suffer from operating difficulties which generally lead to early failure.The present invention seeks to provide an improved infra-red energy source.

According to this invention an infra-red energy source comrises a mantle of refractory material surrounding a filament containing a mixture of molybdenum disilicide and a metal salt.

The metal salt can be zirconium diboride or titanium diboride, either or both of which may be present in the filament.

Preferably the filament also includes alumina and a binder material.

Preferably the mantle of refractory material consists of alumina or quartz.

Conveniently the filament is in the form of an elongate solid rod. This is housed within a hollow cylindrical refractory mantle to form the inventive infra-red energy source.

The ends of the elongate rod are provided with electrical connections by means of which an electric current can be passed through the filament to heat it. A filament in accordance with this invention exhibits a positive temperature coefficient of resistance, and so requires no stabilising resistors.

Furthermore, the infra-red energy source is capable of operating at a temperature as high as 1470"K in air with a relatively long life.

The invention is further described by way of example with reference to the drawing accompanying the Provisional specification, which shows an infra-red source in accordance with the present invention.

Referring to the drawing, the infra-red energy source consists of a hollow cylindrical mantle 1, which contains an elongate solid filament 2, having electric connections 3, 4 at its ends joining it to gold electrical conductors 5, 6.

The filament may be made in accordance with the following method. Powdered molybdenum disilicide was mixed with powdered zirconium diboride, powdered alumina and a flour paste binder. The powders were fine enough to pass through a 300 mesh, and were combined in the following proportions, (by weight): molybdenum disilicide 100 parts, zirconium diboride 10 to 35 parts and alumina about 15 parts. Titanium diboride could be used in addition to, or instead of, the zirconium diboride.

The mixture was extruded into thin solid rods, about 2mm in diameter, and dried slowly under controlled conditions at room temperature over a period of about 2 days, during which the moisture content of the flour paste evaporated. The rods were then furnace fired at about 1400"C in air, for a period of up to 10 hours. During the furnace stage the extruded rods were supported in alumina boats, the rods having been dusted with yttria powder first. The furnace stage sinters the powders, and the mechanical strength of the rods is considerably increased. The rods were then allowed to cool slowly, and at this stage are suitable for use as filaments.

Each is inserted into a hollow mantle 1 which consists of alumina. Gold wires 5, 6 are fixed to the ends 3, 4 of the filament 2 by means of a jointing cement 7 which is stable at high temperatures. Alternatively, silver wires could be used. The method of fixing so as to ensure mechanical strength and good electrical properties can be as described in the Complete Specification of our copending Patent Application No. 3908/76 (Serial No. 15617345. The electrical joints 3, 4 are coated with a thin layer of alumina/ silica paste 8 (in the proportions of about 90% alumina, 10% silica) to protect the connection from the atmosphere.

The completed infra-red energy source can be operated at brightness temperatures up to 1470"K.

The molybdenum disilicide has very low electrical resistance, and the use of zirconium diboride or titanium diboride increases the resistance to a useful level, and also provides mechanical strength. The alumina is included in the filament since it sinters well and provides a further increase in strength and resistivity. Typically molybdenum disilicide has a resistivity of about 20 x 10-6 ohms cms, whereas a filament having a length of about 50mm passes a current of about 5 amps when a potential of about 20 volts is applied.

When such a current is passed through the filament it heats up and causes the surrounding mantle of alumina to glow brightly. The spectral emission can be modified, if desired, by coating the mantle with a material having selective spectral absorbtion.

WHAT WE CLAIM IS: 1. An infra-red energy source comprising a mantle of refractory material surrounding a filament contining a mixture of molybdenum disilicide and a metal salt.

2. An infra-red energy source as claimed in claim 1 and wherein the metal salt is zirconium diboride and/or titanium diboride.

3. An infra-red energy source as claimed in claim 1 or 2 and wherein the filament also includes alumina and a binder material.

4. An infra-red energy source as claimed in any of the preceding claims and wherein the mantle of refractory material consists of alumina or quartz.

5. An infra-red energy source as claimed in any of the preceding claims and wherein the filament is in the form of an elongate solid rod, and is housed within a hollow cylindrical refractory mantle.

6. An infra-red energy source as claimed in claim 5 and wherein the ends of the elongate rod are provided with electrical connections by means of which an electric current can be passed through the filament to heat it.

7. An infra-red energy source substantially as illustrated in and described with reference to the drawing accompanying the Provisional specification.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Each is inserted into a hollow mantle 1 which consists of alumina. Gold wires 5, 6 are fixed to the ends 3, 4 of the filament 2 by means of a jointing cement 7 which is stable at high temperatures. Alternatively, silver wires could be used. The method of fixing so as to ensure mechanical strength and good electrical properties can be as described in the Complete Specification of our copending Patent Application No. 3908/76 (Serial No. 15617345. The electrical joints 3, 4 are coated with a thin layer of alumina/ silica paste 8 (in the proportions of about 90% alumina, 10% silica) to protect the connection from the atmosphere. The completed infra-red energy source can be operated at brightness temperatures up to 1470"K. The molybdenum disilicide has very low electrical resistance, and the use of zirconium diboride or titanium diboride increases the resistance to a useful level, and also provides mechanical strength. The alumina is included in the filament since it sinters well and provides a further increase in strength and resistivity. Typically molybdenum disilicide has a resistivity of about 20 x 10-6 ohms cms, whereas a filament having a length of about 50mm passes a current of about 5 amps when a potential of about 20 volts is applied. When such a current is passed through the filament it heats up and causes the surrounding mantle of alumina to glow brightly. The spectral emission can be modified, if desired, by coating the mantle with a material having selective spectral absorbtion. WHAT WE CLAIM IS:

1. An infra-red energy source comprising a mantle of refractory material surrounding a filament contining a mixture of molybdenum disilicide and a metal salt.