Chromatography Forum

I was reading about pumps and there was mention of the damage done to plungers by crystals from dried up buffer that seeps through the plunger seal. I've seen this so no questions there.
My fascination is how come the plunger is scratched isn't it made from sapphire, supposed to be the hardest crystal (natural origin) after diamond and silicon carbide? or is it because artificial sapphire is weaker than natural sapphire?

I would guess its synthetic. And I wouldn't really worry about it. If its damaged just order another one and get back to your research/work.

In the past, synthetic sapphire was usually fused, not crystalline, and was not quite as hard. In the last few years, oriented crystalline synthetic sapphire has become available, and manufacturers are switching over to this harder material.

Usually dried buffers damage the soft polymer of the seals. If the damage is allowed to continue long enough, the steel spring starts to rub on the piston and eventually scratches it. This takes a lot of neglect.

Strong alkali mobile phases can chemically attack the pistons, but that is rather slow.

Friction is friction. Those of us who have played LPs on turntables
:: scans the room for old farts and audiophiles ::
can attest to the limited lifetime of a often used stylus, despite the business end having been carefully crafted from diamond. Even soft vinyl will wear them out, due to friction.