AU631700B2

AU631700B2 - Iib diamond sorting

Info

Publication number: AU631700B2
Application number: AU67806/90A
Authority: AU
Inventors: Edwin Harm Roos
Original assignee: De Beers Industrial Diamond Division Pty Ltd
Current assignee: De Beers Industrial Diamond Division Pty Ltd
Priority date: 1989-12-06
Filing date: 1990-12-06
Publication date: 1992-12-03
Anticipated expiration: 2010-12-06
Also published as: AU6780690A; BR9006198A; GB2239519B; GB2239519A; GB9026571D0

Description

631700 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION NAME ADDRESS OF APPLICANT: De Beers Industrial Diamond Division (Proprietary) Limited Main Street Johannesburg Transvaal Republic of South Africa NAME(S) OF INVENTOR(S): Edwin Harm ROOS ADDRESS FOR SERVICE: 444 44 @1 444 A 4 op 4.

4 0*4 .DAVES &-OGG4L-ISON- -P-a-t -t-A-t-t-eys- Philpes Orm esc .e 36-7 C--o 5 'r-s 'lrtU tf RA I F r c4k "a V/C 3 co aREG COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED: IIB diamond sorting Ii The following statement is a full description of this invention, including the best method of performing it known to me/us:- *t .444 4, 44 4

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4 t 2 0 a 0 on o neo BACKGROUND TO THE INVENTION I THIS invention relates to a sorting method E- F f..r.Tas and, more particularly, a method of sorting type IIB diamonds from other diamond types.

It is known that type IIB diamonds are semi-conductors while all other diamond types have a very low electrical conductivity. The present invention proposes to make use of this characteristic of type IIB diamonds to sort them from other diamond types.

SUMMARY OF THE INVENTION According to the invention, there is provided a method of S distinguishing type IIB diamonds from other diamonds, the method comprising the steps of subjecting diamonds to a varying magnetic field or to electromagnetic radiation chosen to induce eddy currents in the type IIB diamonds and i-Il- identifying type IIB diamonds as those diamonds which are heated up to a level greater than a predetermined level.

Further according to the invention, there is provided a method of sorting type IIB diamonds from other types of diamonds, the method comprising the steps of subjecting the diamonds to a varying magnetic field or to electromagnetic radiation, the field or radiation being chosen to generate eddy currents in type IIB diamonds, and sorting the diamonds on the basis of the level to which they are heated up.

SPECIFIC DESCRIPTION 15 The methods and apparatuses summarised above rely for their operation on the fact that type IIB diamonds are semi-conductors while other diamond types have a relatively low electrical conductivity, and upon the fact that it is possible to induce eddy currents in an electrically conductive body by subjecting the body to a S° varying magnetic field or to electromagnetic radiation.

According to the present invention, diamonds which are to be sorted into type IIB diamonds on the one hand and other diamond types on the other hand, are subjected to an alternating magnetic field or to electromagnetic radiation.

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I i LIT- ~lfL-u*- ru.n~-ll l.~~l".UYY pus;ruspslr~~ 4 In the latter case, the preferred radiation is high frequency radiation in the microwave or radio wave part of the electromagnetic spectrum.

The alternating magnetic field or radiation induces in the semi-conducting type IIB diamonds eddy currents which in turn heat up the type IIB diamonds by virtue of the electrical resistance of the diamonds. Diamond types other than type IIB are not heated up to the same degree because of their far lower electrical conductivity. Thus the type IIB diamonds can be distinguished from the other diamond types by the o o level to which they are heated up.

Q 00 The invention envisages that, having distinguished the type IIB diamonds from the other diamonds, it is possible to sort them automatically from the other diamonds by some or other sorting apparatus which is responsive to the detection of heat level in the various diamonds.

I4rIt~ For instance, the sorting apparatus which is used could employ infra-red detectors which would produce an appropriate signal when the eetected heat from a diamond is greater than a predetermined value. The diamonds could, for instance, be conveyed on conveyor belt and subjected to the relevant field A j or radiation while on the belt. The infra-red detectors could be aimed at the particles after they have passed through the field or radiation to detect the heated diamonds.

Thereafter the type IIB diamonds could be separated from the other diamonds, in response to signals from the detector, by microprocessor controlled fluid blast ejectors or the like.

Separation techniques of this kind are well known in the art.

As another alternative, the diamonds could, after passing through the relevant field, be dropped onto the surface of a body of ice. The various parameters, such as ice temperature and resistence time, would be chosen for the hot type IIB diamond to melt into the ice and thereafter be embedded in the ice when the ice refreezes. The cooler diamonds would have insufficient heat content to melt the ice and would therefore rest loosely on the ice surface. Physical separation could then be achieved merely by sweeping the surtace of the ice to remove the loose diamonds, leaving only the type IIB diamonds embedded in the surface of the ice.

EXAMPLE

A sample of diamonds consisting of two known type IIb diamonds, Stwo type Ia diamonds and one type Ib diamond was placed in an o open ended cavity which formed a microwave waveguide and o subjected to microwave radiation. The frequency of the radiation o was 2450 Hz delivered at 700W. While being irradiated, the diamonds were scanned using an infra-red scanner. It was noted that after a period of one minute the two type IIb diamonds had o reached a temperature of 83 degrees Celcius, while the other °0 diamonds had remained at the ambient temperature.

The microwave radiation was then switched off and the diamonds were immediately dropped on to a sheet of ice that had been formed on the surface of a water bath. The thickness of the ice was 2mm. The two type IIb diamonds quickly melted through the layer of ice and sank to the bottom of the bath, while the other diamonds remained on the ice surface.

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Claims

1. A method of distinguishing type IIB diamonds from other diamonds, the method comprising the steps of subjecting the diamonds to a varying magnetic field or to electromagnetic radiation, the field or radiation being chosen to generate eddy currents in type IIB diamonds, and identifying type IIB diamonds as those diamonds which are heated up to a level greater than a predetermined level.

2. A method according to claim 1 wherein the diamonds are subjected to high frequency electromagnetic radiation in the microwave or radio wave part of the electromagnetic spectrum.

3. A method of sorting type IIB diamonds from other 1 .*types of diamonds, the method comprising the steps of subjecting the diamonds to a varying magnetic field or to electromagnetic radiation, the field or radiation being I 0chosen to generate eddy currents in type IIB diamonds, and o sorting the diamonds on the basis of the level to which 00 o .they are heated up.

4. A method according to claim 3 wherein the level to which the diamonds are heated up is determined with the use of infra-red detectors.

5. A method according to claim 3 wherein the diamonds are sorted by placing them on a body of ice so that hotter diamonds lose heat to the ice, melt the ice and are subsequently captured by the ice when the ice refreezes while cooler diamonds are not able to melt the ice and therefore remain uncaptured by the ice.

6. A method of distinguishing type IIB diamonds substantially as herein described with reference to the Example. DATED: 28 September 1992 PHILLIPS ORMONDE FITZPATRICK L Attorneys for: DE BEERS INDUSTRIAL DIAMOND DIVISION (PROPRIETARY) LIMITED 4032Z 6