What is this ceramic Rectifier from?

[60 oldjohn]

Originally Posted by Radio Wrangler

Watch out for high power semiconductors that the ceramic isn't Beryllia. Nasty stuff if damaged, possibly fatal.

David

So do Beryllia and ceramic look the same on the outside? Please explain a little.

John.

[Radio Wrangler]

Beryllia IS a ceramic. There are many ceramic materials. The most common one in electronics etc is Aluminium Oxide also known as Alumina. Alumina is bright white.

Beryllia is Beryllium Oxide, Chemical formula: BeO (nothing to do with danish record players). It is not quite as white as alumina having a slight creamy/orangey sort of cast. Some was deliberately tinted pink.

It's safe as long as dust isn't formed. It is highly carcinogenic, worse than asbestos. I remember reading that for inhaled dust and an average adult, 10 microgrammes had a 50% chance of fatality.

So if you suspect something is Beryllia, do not crack, drill, grind, sand, break or etch it.

Beryllia has a low dielectric constant and low dielectric loss, so it makes a great insulator at RF. It also is a particularly good thermal conductor as electrical insulators go. Again very desirable for insulation in power devices. There is one substance better in terms of ratio of electrical insulation to thermal conductivity: diamond.

RF power transistors in vhf-microwave transmitters often have the semiconductor mounted on a small chunk of BeO as an electrical insulator that conducts heat to their heatsink flange. Common in cellphones.

It's supposed to be perfectly safe unless dust is created.

Something to be aware of and to not take risks if you are unsure.

Also common in large amounts in big ceramic transmitting valves. 4CX250B, 8877 and larger ones!

David

[60 oldjohn]

Thank you David for explaining, the white surface is in perfect condition and possibly glazed. I was led to believe Beryllia was a powder Inside high power semiconductors, I did not realise it was a solid material on the outside of components.

John.

[G6Tanuki]

BeO is indeed nasty if ingested/inhaled; in times-past I needed some "thermal conduction modules" to sit between the anodes of a couple of Kilowatt-rated RF tetrodes and their 40-pounds-of-copper heatsinks [no fan-cooling allowed in this particular application!] and finding someone who could cast/machine the necessary was probably the greatest component of the project-cost.

You find BeO in even quite humble stuff like Pye Westminster 2-way-radios from the 1970s. Definitely not stuff to be trifled-with. [I gather it was also used in the brakes of early aircraft-carrier-carried jet aircraft, and that there were extensive decontamination procedures which needed to be followed after every landing!]

In the semiconductor-application though, provided the device is not broken-open or otherwise damaged, it's not likely to pose a significant hazard.

[Radio Wrangler]

Beryllia was included in the phosphor coating inside the tubes of early fluorescent lights. It is the reason behind the very serious warnings to not risk breaking one. Concerns of mercury came along later. It's a long time since they contained Beryllia. Mercury is still used in them.

David

[trobbins]

I'd suggest that the diode uses a benign oxide ceramic, and not berylia.

[Radio Wrangler]

Most probably, especially now it's said to be glazed. BeO is very rarely glazed. But it's worth knowing about and it's wise to be cautious unless certain. The consequences of getting it wrong sound horrible.

David

[factory]

Originally Posted by Radio Wrangler

To come round and close the circle; Westcode came out of Westinghouse, and George Westinghouse created the air brake for railways as a solution for America's runaway train problem (and resulting bad songs). Consequently his company was one of the early adopters of power electronics for controlling traction motors on, you guessed it, railways. Westinghouse also moved into nuclear power and a lot of other heavy industries. So they were one of the early big names in extra-high power semiconductors.

Their beefy rectifiers and SCRs also turned up in industrial DC welders and forklift battery chargers. There is very little intersection with domestic stuff.

David

Just had a look at Graces Guide and Westinghouse did have a range of metal rectifiers for radio & TV, EHT rectifiers and contact cooled Westalite rectifiers for radio & TV (could they be Selenium?), as well as the industrial grade stuff.
https://www.gracesguide.co.uk/Westin..._and_Signal_Co


I've also got a couple of consumer grade miniature generators (230V AC & DC and 12V for battery charging, max 250W total) from the early 1970s, with Westinghouse silicon bridge rectifiers for the 230V DC output, no pictures of the complete item as it's OT.


Very little on Graces Guide for Westcode, other than this advert from 1984 for power semiconductors, diodes, thyristors & transistors.
https://www.gracesguide.co.uk/Westcode_Semiconductors

David

[G6Tanuki]

Westinghouse are probably best known in radio circles for their "Westector" copper-oxide signal-rectifiers, which were a precursor of Germanium/Silicon diodes.

Used in the likes of the WWII 19/38-sets and the "Wartime Civilian Receiver".

https://www.radiomuseum.org/tubes/tu...westector.html

https://www.radiomuseum.co.uk/metalrec.html

[trobbins]

A work predecessor started as an apprentice at Westinghouse in the 1950's and remembered the Copper Oxide manufacturing area, and then went on to do a lot of Selenium work, and then into rectifier equipment. He came out to NZ and then Australia, and effectively spent his working life using Westinghouse/Westcode industrial power scr and diode devices, with larger current applications using hockey-puck style that needed to be clamped to water-cooled busbars using suitable torqued clamps, and lower current applications using large stud mounted devices or flat-face stud devices like the start of this thread. A wide variety of industrial and metal refining applications used either grunt rectified dc, or scr controlled regulated dc, and there are some interesting busbar books showing how massive some installations got decades ago.

[Keith956]

Originally Posted by Radio Wrangler

So if you suspect something is Beryllia, do not crack, drill, grind, sand, break or etch it.

As long as you don't go doing this it is reasonably safe.

Don't forget that emerald is a beryllium compound (Be3Al2(SiO3)6) !

[G6ONEDave]

Many years ago I was told that a lot of the RF output transistors contained Beryllium of some type or other and never to open the enclosing package material. I was also told that all military items containing it and needing to be disposed of had to be sent to a specialist company for safe disposal.

Dave

[The Philpott]

Thanks for the reminder. An LD50 of 10ug catches my attention.
This example is from Sharp, circa 1990's, at least it does have a pink tint.
Dave

[The Philpott]

I am now advised by Clive Mitchell ('Bigclive') that due to the expense of Beryllium Oxide, a domestic microwave magnetron of this type is much more likely to contain Aluminium Oxide, with a trace of Chromium Oxide (the latter causes the pink colour apparently)

Precautions are nevertheless recommended...just in case.

(It's almost as if he has visited this forum...in which case we should be honoured!)

Dave

[emeritus]

Many of the higher-power "turnstile" RF power transistors I was using in the early 1970's had BeO insulation. You could get BeO washers and rods for applications requiring good thermal conductivity and high electrical insulation, I should still have a catalogue with my old data sheets buried at the back of the shed.

Special arrangements were indeed made for disposing of scrap devices, but the devices were very expensive then and fortunately I never had to use the facility: the data sheets used to carry prominent warnings of the potential dangers in red ink.

[Radio Wrangler]

The device's maker has been identified, so a data sheet can be sought. Warnings about a possible hazard have been played out. So this thread has succeeded in its purpose and can be safely parked.

David