OT - ceramic knife blades

[David.WE.Roberts]

We needed some new small knives for the kitchen, so I bought some ceramic paring knives from Lidl.

O.K. - ceramic suggests some kind of fused glass/clay material instead of metal.

Paring knife suggests a small knife used in food preparation - used to be used for peeling stuff (hence the name) but these days usually just reflects the size.

There are some interesting warnings in the leaflet.

Don't try and sharpen it yourself because it is likely to splinter and can leave shards in the food. Hmm.... O.K. seems reasonable as most sharpening tools are designed for metal.

Don't use on a ceramic chopping board, use on plastic or wood. Reasonable

- ceramic on ceramic could chip or shatter.

Do not use for chopping or scraping?

So what can you use the damn thing for? Peel a potato but don't scrape anything and don't cut it?

Don't scrape a carrot or chop a carrot?

Is this over the top safety warning crap or should I return the unopened ones?

Anyone used ceramic kitchen knives long term?

Cheers

Dave R

P.S. only upside of ceramic blades seems to be that they probably won't set off a metal detector.

[Andrew Gabriel]

Dad eagerly bought one a few years ago when they first came out, and were much more expensive than they are now.

First thing he used it for - an avocado pear. Cut very nicely around the outside so he could separate the two halfs. Then stabbed the stone with it to flip it out as he normamlly would, and the end snapped off inside the stone. I think the knife lasted less than 10 seconds...

[fred]

In article , Andrew Gabriel writes

LMFAO

In the short time that I used one I found it excellent for cutting raw chicken breast but of course useless for boning or jointing a chicken and no better than my other excellent steel/stainless knives for anything else. It (they) went back after one blade chipped when it was in the washing up bowl with (heaven forbid) some other knives.

Knowing they had a reputation for being brittle I had bought 2 of each size, large & small, from Lidl/Aldi but chipping on the second wash was just too much and the lot went back straight away.

I can't see the need for them unless it's for someone who doesn't know how to keep a good knife sharp.

Beat me to it but don't expect it to be much use as an offensive weapon, it's probably break before doing too much damage.

[David.WE.Roberts]

O.K. - will return the unopened 3 and keep 1 as an experiment, to be used with care.

[harryagain]

Retrograde step. May as well go back to flint! :-)

[Chris Hogg]

They are made of Zirconia (zirconium oxide). This is an 'advanced ceramic', aka 'engineering ceramic', and is much stronger than your average teacup or wash basin, although like more common ceramics, they are not very tough and are brittle, although zirconia is generally better than some other advanced ceramics such as silicon carbide of silicon nitride, due to an internal toughening mechanism (note that in the advanced ceramic terminology, words such as 'strong' and 'tough' have specific and rather different meanings to when they are used colloquially). The blades have to be sharpened by a diamond wheel, as any other type of sharpener gets abraded by the zirconia blade, not the other way round which is what you want. Ceramic knives can be _extremely_ sharp. They are used by top Japanese chefs for slicing raw fish very thinly when preparing Sushi. Mere steel no longer cuts it (IYSWIM)! Kyocera in Japan are the world's leading manufacturer.

I'm surprised by the 'do not use for chopping or scraping'. Provided you don't hit something that might chip the blade, I would have thought they would be perfectly OK. The biggest hazard with them is cutting yourself and not realising it until everything turns red, because they can be _so_ sharp that you don't feel it!

See

and scroll down to 'Transformation Toughening' and similar in the thumbnails at the side.

[David.WE.Roberts]

Thanks - all interesting stuff.

I assume the 'not for scraping' is probably because the blades have limited flexibility before shattering whereas steel is extremely flexible.

'Not for chopping' may just be arse covering in case the knives are used with more force than they can cope with.

Whatever, they seem to be specialised rather than general purpose.

If I ever decide to become a sushi chef I may reconsider them.

Cheers

Dave R

P.S. I though Zirconia was mainly used for fake diamonds as sold on shopping channels.

[Nightjar]

On 18/10/2013 15:55, David.WE.Roberts wrote: ...

They are also exceptionally sharp, hence the popularity of ceramic blades in some types of scalpel.

Colin Bignell

[Chris Hogg]

The fake diamonds are zircons, zirconium silicate, ZrSiO4 sometimes written ZrO2.SiO2, whereas the knives and other advanced ceramic items are the oxide, ZrO2. See

Finely ground Zircon is also the opacifier used in almost all the white-glazed washbasins and toilets made these days.

[alan]

They are also pretty useless for peeling. Mine snapped in two the first time I dropped it. This was after losing the tip in the washing when I put a glass bowl on top of it.

It a fashion accessory not a kitchen accessory

[alan]

Sharp when first used but they don't stay that way.

[polygonum]

I found some very cheap ceramic peelers were quite good - especially on fruit. Unfortunately the plastic handles/blade carriers were poor and they tend not to last very long. Also a bit on the less-than-delicate side because the blade is thicker than a metal blade, plus the plastic mount. Have reverted to a halfway decent metal bladed one.

[Andrew Gabriel]

So was mum. She phoned me to tell me, but she was laughing so much she couldn't actually get the words out, and I spent a minute on the phone wondering what on earth had happened.

[Chris Hogg]

Addendum! Yes, you're quite right, zirconia in its single crystal cubic form is used in jewellery, as well as zircon (bit of brain fade there! Been twenty years since I was involved in any of this). The stuff used in advanced ceramics is polycrystalline. There are also differences in the additives used to stabilise the cubic form for jewellery, otherwise the phase changes that occur in the crystal structure during cooling from the high-temperature melt, set up such big stresses that the single crystals disintegrate to powder. See

[dennis]

I have some about 5 years old.

They are still sharp.

They don't have much bending strength so they don't want you to scrape them across an unknown surface as they could snap.

They don't like shocks much either so don't chop bones, etc.

I haven't broken one yet or smuggled one through an airline check. I have been stopped for trying to smuggle a rocket launcher through an airline check!

[Nightjar]

Scalpels are single use.

Colin Bignell

[John Rumm]

Sounds more like an instruction not to use it in an impact style of chopping like a cleaver, rather than the colloquial use of chopping for cutting.

[fred]

In article , Andrew Gabriel writes

Tee hee, bet your dad loved that! Still, at least he was unarmed ;-)

[Bob Eager]

I don't think the knife was quite that sharp...

[SteveW]

Very odd. I can't see any problem with either, as long as chopping is done on a softish surface.

Go on, take a risk, just go ahead and ignore these OTT warnings ;)

They should. According to a programme I saw a year or so ago on the making of these knives, there is an internationally agreed minimum metal content specifically to ensure that they cannot be smuggled through airport security.

SteveW