Porcelain thermally conductive insulators ?

N_Cook Inscribed thus:

I would check that ! Its more likely that they are Beryllium_oxide !

The dust from grinding or abrading Beryllium_oxide is highly toxic !

WARNING

WARNING

{snip}

Those ceramic insulators are made from beryllia (berylium oxide), a ceramic that has a higher heat conductivity than aluminum. You should be _extremely_ careful in handling them. Quoting from the Wikipedia article: "Like all berylium compounds, BeO is carcinogenic and may cause chronic beryllium disease. Once fired into solid form, it is safe to handle as long as it is not subjected to any machining that generates dust." Likewise the American Beryllia site says: "Exposure to fine, airborne beryllium oxide powder or dust in sufficiently large concentrations, may cause a lung disease in a small number of hypersensitive people."

Grinding a beryllia insulator is considered exceptionally dangerous. Please read the MSDS at

I once needed some microwave windows made of beryllia. I was going to order beryllia blanks, have the edges sputtered in gold, and braze them into 316 stainless waveguide sections. I called the engineers at National Beryllia (now American Beryllia) to discuss this application. In short order, they convinced me that they should manufacture the windows as there was a chance that the differential thermal expansion between the beryllia and the stainless steel waveguide could potentially shatter the ceramic and release beryllia powder. After learning the cost, I went with sapphire windows instead.

Some people are hypersensitive to beryllium compounds. If you are not in the hospital yet, consider yourself _very_ lucky. A small percentage of the population is so hypersensitive that the small amount of dust you created could be lethal.

Dr. Barry L. Ornitz WA4VZQ [my_ham_call at live.com]

N_Cook Inscribed thus:

Insulating ceramics are not porcelain (vitrified kaolin clay) but either alumina (white, very hard ceramic) or beryllia (usually tinted pink or purple, and toxic if it's made to dust).

In neither case is it advisable to remachine the hole...

"N_Cook" wrote in news:iohgfu$9e1$ snipped-for-privacy@dont-email.me:

they may be -alumina- slabs,not porcelain;TEK used to use ~5/8" sq. alumina slabs under the LVPS pass transistors on the 5000 series o'scope mainframes.

Unfortunately it would not grind. I assume it was not heating up because the grinding disc was just running over the surface without even rubbing , let alone grinding, so no dust, still the flat edge . Does BeO have that sort of translucent appearance of porcelain? I've managed to grind small sections of the ceramic used is high temperature "chock block" connectors, that has a normal solid white appearance. But given its use here then presumably BeO. It was the slightly milky/translucent porcelain-like appearance that convinced me.

Only BeO I've seen was pink, and I'd not try to grind it, toxic!

Safe if not shattered.

Grant.

the

let

of

of

BeO.

I've seen pink TO3, presumably BeO, insulators before but they did not have this transclucent like appearance.

N_Cook Inscribed thus:

The surface tends to have the appearance of good quality photocopy paper, very smooth with a barely visible grain. A bit like ferrite beads.

Both Aluminum oxide and Beryllium oxide are extremely hard materials. I belive that the pink dye was used later to specifically identify Beryllium. So its a good chance that the white insulators that you have are Aluminum oxide. Even so its not a good idea to try to grind them.

Ceramics are also used to machine metals, including some that are so tough that only ceramic cutters can be used on them.

Beryllia is white, the same as alumina. There is no standard on coloring beryllia insulators for use as heat transfer links. No dye is used as the beryllia is sintered (fired) at very high temperatures. Instead a colored inorganic metal oxide is added in small amounts. Beryllia has about seven to ten times the thermal conductivity of alumina, so if the links were used with high power parts, they are probably beryllia. Beryllia has about one third better thermal conductivity than aluminum nitride in the 25 to 300 C temperature range. Only diamond and cubic boron nitride are better thermal conductors (but at an exceptionally high cost).

Until you know for sure what these insulators are made of, treat them as beryllia. I.e., do not grind or crush them.

The 4CX250 transmitter tubes I used had white BeO ceramic insulators.

The next time I come across one I'll try passing a laser beam or bright light through it to see if any light passes through. It was that translucency appearance, like porcelain , that I noticed.

I had to get inside that amp again, yet another PbF problem from next to zero insertion force speaker connector at the PA 4 removal & inserts by me was enough , only 6 months old. The slabs pass red laser pointer light, but then on checking but so does the ceramic of high temp "choc block". These slabs are more trnasmissive and scatter the light throughout the slab not just the entry and exit area of the chock block.

N_Cook Inscribed thus:

Mmm ! Interesting. I have a small quantity of boxed TO3 BeO insulators. I'll have to get one out and see.

BeO is very expensive. I would be very surprised to find any in such application.

BeO is very expensive. I would be very surprised to find any in such application.

These were not made for the job. They have a hole for either TO220 or TOP66 maybe size transistors . So too wide for this use and the hole is not used . The layout does not mean they have to be 1.8mm thick , any thickness from mica up could have been accommodated. Normally you would go for the thinnest of insulators.

It maybe a function of thickness, these being 1.8mm thick slabs rather than wafers

josephkk Inscribed thus:

I wonder how much 12 dozen TO3 BeO insulators would be worth ?

N_Cook Inscribed thus:

I cracked open a box of TO3 BeO insulators this afternoon... I was very surprised ! I tried shining a red laser pointer through one. Its weird but they do seem to glow but no direct light through it.

Putting one against a small hole in a cardboard box and viewing the sun shows nothing, no light, nothing. Most odd !

Thast was the same here complete scarttering with no obvious bright spot directly opposite the entry point. Chock block ceramic was just the adjascent bright spot , much attenuated in comparison to the porcelain or vitrified BeO slab