178 replies to this topic

[gruntguru]

It's not that I disagree so much as I don't even care. It's not relevant here. It's not a significant factor in a properly functioning O2 sensor and it doesn't support your argument anyway.

I'm sure you would like not to care, but unfortunately for you it confirms my original argument in post #2 and torpedoes your vehement statements that reducing agents have no effect on lambda sensor output.

Two problems with that:
1. The ECU does the "switching," not the O2 sensor. The sensor can only respond to O2 content, and its useful sensitivity range lies in a very narrow band around stoich. So the ECU must constantly retrim fuel delivery to keep the O2S value with the band -- otherwise the O2 value will quickly drift out of the sensor's range. Indeed, in the experiment you proposed earlier there is no O2S "switching" at all. The sensor maintains a constant ~450 mv because it has no "switching" function of its own.

I didn't say the lambda sensor did any switching. I called it an AFR "switch" because its output "switches" from low to high at stoich AFR. The absolute output "level" is not useful but the point where "switching" from low state to high state occurs is useful. The ECU considers the lambda sensor as a two state or binary device - a switch.

By the way the ECU doesn't "switch" anything. It considers the lambda sensor as a switch with 2 states - rich and lean. If it sees a "rich" signal, it leans out the mixture at a steady rate. If it sees "lean", it richens the mixture at a steady rate.

2. Lambda is a dimensionless equivalence value represented by unity.

I have heard this definition before and it is a very poor one. It suggests that lambda is a particular mixture value which it is not. Lambda is a dimensionless AFR scale which eliminates the need to know the stoichiometric AFR for the particular fuel being used. Thus an engine running at a dimensionless AFR (lambda) of 1.000 is at stoich regardless of the fuel. If the lambda reading is less than 1 the mixture is rich e.g. a reading of 0.90 indicates 10% excess fuel (about 13.2:1 for gasolene). Conversely for lean mixtures a value of 1.1 indicates 10% excess air (about 16.2:1 for gasolene). "Equivalence" ratio is another term often used in engine research. It is a dimensionless Fuel Air Ratio scale and is the inverse of the lambda ratio.

However, O2 content at lambda may represent an equivalent AFR of ~14.7:1 or it may not. That is entirely dependent on the stoichiometric value of the fuel.

Do you get that lambda is a dimensionless AFR scale and it doesn't matter what the fuel is? When I say the lambda sensor is responding to AFR - I mean the dimensionless AFR scale. Any AFR instrument based on exhaust analysis can only indicate the "Dimensionless AFR". To indicate a mass fraction AFR, it must be told what fuel is being used.

Here in the USA we have engine control systems that successfully accommodate fuels with stoich values from ~9.7:1 with E85 to ~15.7:1 with propane. (All with the same O2 sensor part number.) So obviously, the O2 sensor does not detect or determine AFR but only oxygen content. The ECU determines the AFR accordingly. More importantly, since the sensor operates in a narrow band around stoich, it cannot effectively measure exhaust content when the mixture is significantly above or below stoich.

I have never said otherwise.

If, as is often the case, an AFR of 12.5:1 for acceleration or 16:1 for economy are required, a narrow-band O2 sensor cannot measure an equivalent exhaust O2 content for them. In fact, the sensor cannot measure or determine AFR at any time or in any case, only exhaust O2 content.

Correct but irrelevant waffle. Except for the last sentence which is incorrect - the sensor output indicates precisely on which side of the chemically-correct AFR the engine is operating and in fact that is the ONLY thing the sensor can accurately do.

Edited by gruntguru, 02 May 2009 - 04:32.

[gruntguru]

I like ice cream.

Yes but with or without? (Waffle)

[gruntguru]

A quick note for anyone who would like to add their two bob's worth on this thread. Before you do so - check what the argument is actually all about and view post # 2 where I said ""Lambda sensor" is a more accurate name than "oxygen sensor" as its response is more closely related to AFR than exhaust oxygen content." which has been absolutely confirmed by the abstract posted above. Then read posts #3 and #5 where McGuire violently disagrees with my original (correct) statement.

Edited by gruntguru, 02 May 2009 - 04:51.

[REN_AF1]

My "bob" as you say, would be to claim that "Lambda sensors" or O2 sensors, depending on temperament, does little more than act as the electrochemical cell it is, and provide a voltage output proportional to the difference between the oxygen partial pressure found in the exhaust gas (p.o.ex) and a reference pressure, namely that from the ambient atm. (p.o.atm)
Open circuit voltage can be calculated using Nernst equation:

V.0=(R*T)/(4*F) ln(p.o.atm/p.o.ex)

A/F ratio is something a piece of software deducts by comparing WHAT you actually put in the jar, to what came out.
O2 sensors is however a very useful tool, aiding in this process, NOT conduction it.

NB: "pollutants" (CO, HC, H, and C) doesn't enter the "equation" any more than a hammer would, had we used it to smash the flute of a sensor and tried to measure things.

R

[gruntguru]

A lot of posters are missing the point.

I have never said that a narrow band lambda sensor measures AFR. The only useful characteristic of a narrow-band lambda sensor is the point at which the voltage "steps" between "low" and "high". This point occurs at an AFR of 1.000. The exhaust gas oxygen level may actually vary at the "step" due to changes in engine combustion efficiency but this is corrected by reduction reactions (possibly catalytic) in the region of the sensor exhaust electrode. This is the basis for my original statement "its response is more closely related to AFR than exhaust oxygen content" (post #2).

The Abstract at the bottom of post 149 above confirms this.

Edited by gruntguru, 03 May 2009 - 23:41.

[McGuire]

That does not follow. The sensor is never exposed to air-fuel mixture, only exhaust gas; meanwhile, the zirconia can only conduct O2 ions.

[gruntguru]

That does not follow. The sensor is never exposed to air-fuel mixture, only exhaust gas; meanwhile, the zirconia can only conduct O2 ions.

Are you being intentionally obtuse? You know the lambda snsor output will respond to changes in AFR. It does not need to be exposed to air-fuel mixture to respond to AFR. Change the AFR -> the exhaust gas composition will change -> the lambda sensor output will change.

Yes the lambda sensor can only conduct O2 ions, but if reduction reactions occur in the region of the exhaust electrode, the oxygen concentration will be reduced and the sensor output will increase. So the sensor output has been altered by the presence of reducing agents in the exhaust.

[gruntguru]

I have read the full text of the previously mentioned research paper

("Operating characteristics of zirconia galvanic cells (lambda sensors) in automotive closed-loop emission control systems. Bozek, John W | Evans, Richard | Tyree, Clifford D | Zerafa, Kenneth L. SAE Special Publications , no. 910, pp. 1-17. 1992)

and found considerable support for my view of lambda sensor operating characteristics. Here are a few excerpts.

Page 5 Column 2 Paragraph 1.
"Catalyzed reactions also occur at the porous platinum electrode on the exhaust side of the thimble."

Page 12 Column 1 Paragraph 2 &3.
"This indicated that the wide variations in voltage that occur when a cell is operating in a closed-loop control system are not caused by the associated small changes in the concentration of oxygen in the exhaust gas mixture.” . . . . . . “showed that the presence or absence of oxygen on the sensing side of the cell thimble has little direct effect on cell voltage."

Page 16 Column 1 Paragraph 1 & 2.
"UPSTEAM OF THE CATALYST - RICH EXHAUST. A high voltage is generated because hydrogen and carbon monoxide in the exhaust are available for reaction with atmospheric oxygen that migrates through the thimble in ionic form. Such availability is possible because the concentration of oxygen in the exhaust is less than the stoichiometric concentrations of the reducing agents in the exhaust, such as hydrogen, carbon monoxide, hydrocarbons and oxygenated organic compounds.
"UPSTREAM OF THE CATALYST - LEAN EXHAUST. A low voltage is generated because the hydrogen and carbon monoxide in the exhaust react with the oxygen in the exhaust. As a result these reducing agents are not available for reaction with the atmospheric oxygen that would otherwise migrate through the thimble in ionic form."

Page 16 Column 2, 2nd last paragraph.
"2. In the temperature range that exists in a typical exhaust system, the operation of a zirconia cell involves oxidation/reduction reactions which are analogous to those that occur in an oxygen/hydrogen fuel cell
3. The oxidation/reduction reactions can take place in a cell only if reducing agents are present and available for reaction with the oxygen ions that migrate through the cell thimble."

In addition the graphs on page 6 are very telling. Reducing the oxygen concentration on the exhaust electrode to zero, using four different methods produced a maximum of 0.2 Volts sensor output. Normal sensor output voltages of 0.6 - 0.8 volts were only produced when hydrogen or carbon monoxide (at approximately 300 ppm) were introduced to the exhaust electrode side of the sensor.

Edited by gruntguru, 05 May 2009 - 07:02.

[McGuire]

Are you being intentionally obtuse? You know the lambda snsor output will respond to changes in AFR. It does not need to be exposed to air-fuel mixture to respond to AFR. Change the AFR -> the exhaust gas composition will change -> the lambda sensor output will change.

Nope, I am being intentionally accurate. The sensor does not respond directly to AFR but to exhaust oxygen content, which does not reflect any specific fuel-air ratio. The actual FAR represented by a given O2 value depends on the stoichiometric value of the fuel, among other things.

Lambda fuel metering requires a number of presumptions, not only in fuel value, but in the operating state of the engine, and it can only function to the extent these presumptions are warranted. For example, a cylinder misfire will produce an excessively rich mixture but with a surplus of exhaust O2, causing the ECU to deliver even more fuel. (Without sufficient fault intervention this will often produce a cascade effect, fouling the remaining plugs until the engine won't run at all.) Ignition timing, exhaust leaks, valve overlap, exhaust scavenging, etc will all affect the sensor's ouput independently of FAR. That's because the sensor does not measure FAR. It can only measure exhaust oxygen content.

[gruntguru]

Nope, I am being intentionally accurate. The sensor does not respond directly to AFR but to exhaust oxygen content, which does not reflect any specific fuel-air ratio. The actual FAR represented by a given O2 value depends on the stoichiometric value of the fuel, among other things.

In that case you are unintentionally demonstrating your ignorance because:
1. You can't have read the quotes I posted from the SAE paper since thaey confirm the sensor responds to AFR rather than exhaust gas oxygen.

2. For the third or fourth time I will state - "Stoichiometric value of the fuel is irrelevant to dimensionless AFR (lambda), which is the scale I refer to whenever I mention AFR in this thread."

Lambda fuel metering requires a number of presumptions, not only in fuel value, but in the operating state of the engine, and it can only function to the extent these presumptions are warranted. For example, a cylinder misfire will produce an excessively rich mixture but with a surplus of exhaust O2, causing the ECU to deliver even more fuel. (Without sufficient fault intervention this will often produce a cascade effect, fouling the remaining plugs until the engine won't run at all.) Ignition timing, exhaust leaks, valve overlap, exhaust scavenging, etc will all affect the sensor's ouput independently of FAR. That's because the sensor does not measure FAR. It can only measure exhaust oxygen content.

Read the paper (again?) - especially Page 12, Column 2, Point 2:
"2. In regard to the effects of changes in sample gas composition on voltage output, the three cells were similar in that they all exhibited
(a) essentially no response to changes in oxygen concentrations"

Edited by gruntguru, 06 May 2009 - 05:00.

[OfficeLinebacker]

LOL you guys are so silly. No a Lambda sensor does not measure AFR. One is able to infer AFR from the signal the lambda sensor sends, as in Joe Bosworth's post, given a set of assumptions.

In very much the same way, the speedometer doesn't REALLY measure the speed at which a car is traveling; rather, one infers the speed at which the car is traveling based on assumptions about tire size and traction, which are generally true. However, to argue about this is silly.

[gruntguru]

LOL you guys are so silly. No a Lambda sensor does not measure AFR. One is able to infer AFR from the signal the lambda sensor sends, as in Joe Bosworth's post, given a set of assumptions.

In very much the same way, the speedometer doesn't REALLY measure the speed at which a car is traveling; rather, one infers the speed at which the car is traveling based on assumptions about tire size and traction, which are generally true. However, to argue about this is silly.

Post #155 Replay.

"A lot of posters are missing the point.

I have never said that a narrow band lambda sensor measures AFR. The only useful characteristic of a narrow-band lambda sensor is the point at which the voltage "steps" between "low" and "high". This point occurs at an AFR of 1.000. The exhaust gas oxygen level may actually vary at the "step" due to changes in engine combustion efficiency but this is corrected by reduction reactions (possibly catalytic) in the region of the sensor exhaust electrode. This is the basis for my original statement "its response is more closely related to AFR than exhaust oxygen content" (post #2)."

The Abstract at the bottom of post 149 above confirms this. " As do the various excerpts from the same paper quoted in posts #158 and #160.

McGuire - the hilarious thing is that this research paper makes a more extreme case than I originally did. Did you know that the Nernst Effect is not the primary driver in a lambda sensor at temperatures below 850*C?

O.L.B. - your point is silly. We are not arguing about whether sensors measure properties or infer them. We are arguing about which property is more directly related to the lambda sensor voltage - EGO concentration or EG lambda value.

Edited by gruntguru, 06 May 2009 - 10:38.

[McGuire]

Post #155 Replay.
[i]
O.L.B. - your point is silly. We are not arguing about whether sensors measure properties or infer them.

No, OLB nailed it. That is exactly the issue.

H and CO are not AFR; they are products of combustion. Meanwhile, the zirconia can only conduct O2 ions, irrespective of any other effects as the paper makes clear.

So: O2 sensor is a perfectly fine name for the device; lambda sensor is suitable enough. However, it is flat wrong to claim that the sensor responds to AFR in any fashion, directly or indirectly. In any real and literal sense it can only respond to exhaust content as it is positioned in the exhaust stream. As we have seen, exhaust oxygen content does not correspond to any specific FAR. More than that, it may or may not even correspond to a rich or lean fuel-air mixture, as fuel-air mixture is by no means the sole factor in exhaust O2 content. FAR and exhaust oxygen content are at the opposite ends of a feedback loop. And as with any control loop, it is important to distinguish action from effect.

[McGuire]

LOL you guys are so silly. No a Lambda sensor does not measure AFR. One is able to infer AFR from the signal the lambda sensor sends, as in Joe Bosworth's post, given a set of assumptions.

Yes, I expect this must be like watching two people debate the spelling of Schenectady. For a proper description of sensor function one could simply look in the Bosch Handbook. Or if you want to read it here, REN_AF1 employed the same desciption almost word for word a bit earlier up the thread.

I had hoped to provide enough allied info along the way to make this otherwise useless thread worthwhile to anyone else who happens to look in. Joe made some interesting points I hope to explore further as time allows.

[OfficeLinebacker]

We are not arguing about whether sensors measure properties or infer them.

I know this is piling on, but sensors, lacking sentience, can infer nothing. So of course no one would argue that a sensor can infer something.

Thanks McGuire, I feel slightly less silly when I read your posts.

[gruntguru]

However, it is flat wrong to claim that the sensor responds to AFR in any fashion, directly or indirectly. In any real and literal sense it can only respond to exhaust content as it is positioned in the exhaust stream. As we have seen, exhaust oxygen content does not correspond to any specific FAR. More than that, it may or may not even correspond to a rich or lean fuel-air mixture, as fuel-air mixture is by no means the sole factor in exhaust O2 content. FAR and exhaust oxygen content are at the opposite ends of a feedback loop. And as with any control loop, it is important to distinguish action from effect.

Are you an idiot?
Read the paper!
It repeatedly refers to lambda sensors responding to AFR.
Exhaust analysis will define a unique AFR (dimensionless) regardless of fuel type.
The "step" in sensor output correlates best to AFR - not oxygen concentration. This is the simple fact behind my argument. It has nothing to do with control loops, fuel types or whether AFR correlates strongly to oxygen content - which it doesn't - you are correct there and that is my point. The sensor output correlates to AFR and not oxygen content.

Edited by gruntguru, 07 May 2009 - 05:23.

[McGuire]

However, let me paint a word picture. When very rich, (fuel surplus). CO2 in the combustion products are close to nil, CO is very high and O2 is zero. As the air:fuel ratio becomes less rich and moves to stoichemetric the CO2 in exhaust gasses rise, CO percent falls and O2 percent stays at zero. At the point of stoichemetric ratio we have the theoretical situation in the exhaust products of:
CO is zero
O2 is zero
CO2 is at a max with the percentage depending on the number of C molecules in the fuel. This varies from about 13% to about 18%.
Then as the air:fuel ratio goes leaner, (air/O2 surplus) the CO2 starts to fall, CO stays at zero and the percentage of O2 in the exhaust starts rising.
There are a lot of very sophisticated pieces of equipment available that allows one to read the percentages of O2, CO and CO2 in exhaust gasses. A Lambda sensor is one of the less sophisticated in some respects, it just happens to be cheap, accurate and long lived, though does not provide the whole picture directly or indirectly. But perfect for automotive use!
All of these pieces of equipment do not measure A/F ratios. They provide information relative to percentages of constituents in the exhaust gasses.

I am going to both agree and disagree with the above, not to pick an argument, but because you are knowledgeable and in the furtherance of discussion, etc. Below I have posted some art which is sorta accurate, though the crayon is a bit wide as the stoichiometric value of automotive gasoline is somewhat variable, due to oxygen content for example. Fuel also contains above-trace ingredients including detergents, anti-olefins, etc.

With stoichiometric combustion the exhaust fraction will contain maximum CO2, and minimum O2 and CO, but not necessarily zero O2 and CO. In practice they can be very low, in the range of .4 or .5 percent or less by mass, and near/at stoich O2 and CO will be very similar. This is some very fine whittling but we don't get true zero HC or CO because we never quite get true stoichiometric combustion. We have finite burn time; fuel particles are trapped in the ring crevices etc. HC is simply associated and dissassociated fuel molecules, while CO is simply CO2 that couldn't find its second O. Atmospheric CO2 is .05 percent, in traffic more than that as the cars are all outputting 10 to 15 percent CO2. And with so little O2 content we can see that the O2 sensor actually handles a tiny fraction of the exhaust content irrespective of recent arguments either way. At leaner than stoich O2 spikes up, the limitation of narrow-band O2 but a good thing if we have a cat to operate. And again, CO2 is always max at stoich, an unfortunate fact if we are concerned about greenhouse gases. But in practice, current model cars will produce even less CO and HC than at quasi-stoichiometric. That's because they don't really run in stoichiometry, but in a narrow band through both sides of it via FAR perturbation, discussed earlier. Among other things this allows the cat to work with maximum efficiency via O2 reserve.

So just as you say, with traditional two and four gas analyzers, at idle (or any no-load rpm for that matter) you will have trouble getting any HC or CO reading at all with a current-model automobile. You might see a little spike at throttle snap. You will have to disable the secondary air injection (if equipped) and/or sample pre-cat, and run on a real chassis dyno (one more purpose for which inertia dynos are useless) or with some other stable form of engine loading to see any consistent HC or CO numbers. This is not so surprising, really, in that most current emissions standards worldwide are well under 10 grams/mile. So to get meaningful values inside the building we are going to need an IM-240 compliant four or five-gas analyzer and a chassis dyno. If anyone was wondering what is IM-240, it's a shortened, 240 second version of the full-length EPA drive cycle, adapted for field emissions validation.

This is a far cry from the old days of the '70s when the specs actually called for and mechanics would adjust the CO to 2.0 percent and beyond (Bosch K-Jetronic for example, also idle circuits on carbureted cars) for smooth idle and best driveability. Top efficiency and minimum emissions might be at stoichiometry, but who cared. They ran considerably fatter than stoich. Best power and transient response are closer to 13:1, and a little on the rich side never hurt anything except fuel economy and the air we need to breathe. This is why as emissions standards started to become more stringent, key to the mission was making the systems tamper-proof. Otherwise those dumb mechanics out in the field would adjust the cars to run right.

But all that said, the standard four-gas exhaust analyzer was a powerful field tool back in the day. So was the ignition oscilloscope. A sharp engine guy could diagnose a fuel metering problem with the scope or an ignition problem with the gas analyzer. These kids today with their scanners and CAN bus etc., spoiled and lazy.

[Joe Bosworth]

McG

No disagreement at all between us.

You quoted that part of my post addressing the theoretical.

I later went on to, "Now let me go from the theoretical to the practical. When you have large combustion spaces and long burn times the theoretical picture of products in exhaust gasses is accurate. But automotive applications have very restrictive combustion spaces and very short combustion times. Theory flies out the window and practice strolls in the door. Rather than very clear percentage delineations at the stoichemetric point we find very small amounts of O2 present while still a little bit on the rich side. (We also find very small amounts of CO present while a little bit on the lean side. But the relationships remain constant. Lower O2 equals higher CO and v-v.)

I also have to admit that my readings include both many many (1000s) of industrial applications where there is sufficient combustion space and constant temperatures where the chemicaal reactions can go to completion. I started many years ago and used my industrial gear for my dyno work and road testiing but have to admit that I never ever tested anything other than engines that were 100% mechanically perfect, with state of art fuel metering and ignition systems and with minimum transient operations. I was always only interested in developing for race type applications.

One can always find the exception when you are testing **** condition engines and/or compromised designs. The reality is that today our everyday road car (as long as it is relatively low mileage) comes quite close to emulating race engine technology but scaled down to lower rev needs.

I did get a big wake up call recently when I did a real life g-force test to prove a point over on the v8-v10 engine thread. I took my daily driver which is a nicely modified 5L Ford V8 with only 72000 Km (45000 miles) on it. Despite having 100,000 mile rated plugs and ignition system as is standard these days I found it running like a pig once I put my instruments on it and gave it a bit of stick. This despite running the cleanest burning 98 octane exclusively.

I bet it would have been belching HC like crazy. Took a new set of plugs to restore its HP and T as I had it originally. Have also run a couple of full tanks through it since and found about an additional 60 km per tank that I had lost.

So much for going to sleep thinking modern technology was a panacea to good maintenance!!

I also know you are correct relative to doing the vehicle tests on a rolling road standard where the exhaust gasses get bagged and tested via gas chromatograph. But some of these tests often include a start up cycle during which 90 to 95% of all HC occurs due to the time it takes to come up to temperature. The GC readings get down to accurately reading PPM and PPB numbers that are below the detection limits of even the best continuous fast acting instruments such as those I have used.

But I am sorry to see you even posting again. What are you trying to do? Stir somebody up??

[phantom II]

Only when the trees start replacing their leaves and the agricultural growth is in full swing in the summer in the northern hemisphere will the CO2 % be that high. So you still think that there is global warming and we are the cause of it? I'm moving to China where there are far fewer Bolsheviks than in the USSA.

Atmospheric CO2 is .05 percent,

[cheapracer]

But I am sorry to see you even posting again. What are you trying to do? Stir somebody up??

But I am sorry to see you even posting again. What are you trying to do? Stir somebody up??

[cheapracer]

I'm moving to China where there are far fewer Bolsheviks than in the USSA.

Got a spare room Mate. (They used to say Comrade but its all changed now).

[Bill Sherwood]

From the Motec forum ...

I am not aware of anybody here testing this but... Lambda does not change during the combustion process but the oxygen content of the exhaust does and this can have an effect on the lambda readings when using a lambda sensor(PLM or otherwise). This is because the Lambda sensor is using oxygen to measure the difference between Lambda 1 and the gas being sampled. For example we would see a small difference between the PLM reading from a sensor mounted close to the engine (where mixture is still burning in the exhaust) compared to one mounted say a meter further down the pipe where the oxygen content is lower. When a catalyst is functioning there is a differeence between pre and post cat of about 0.5% oxygen so I would expect to see a difference even though the actual Lambda value hasn't changed.
The PLM (and Mx00) lambda tables can be adjusted to give different lambda values as a function of pump current so that if the sensor location is not ideal you can still have the correct values. I would use a 5 gas analyser to do this.

HTH. (Though this has already pretty much been mentioned)

[gruntguru]

When a catalyst is functioning there is a differeence between pre and post cat of about 0.5% oxygen so I would expect to see a difference even though the actual Lambda value hasn't changed.

Note he says "I would expect to see".

The fact is the research paper mentioned earlier in this thread contradicts this expectation since the Lambda value (dimensionless AFR) and not oxygen content is the primary determinant of lambda sensor output.

[cheapracer]

Bill's thing with McGuire is Bill's thing with McGuire so it would be nice please if some of you others would take the time to edit that part out of the quote.

[gruntguru]

Bill's thing with McGuire is Bill's thing with McGuire so it would be nice please if some of you others would take the time to edit that part out of the quote.

Thanks Cheapy. Don't think I'll bother.

[Wolfie242]

I know that Zirconia is used as a thermal protector in racing, supplied by www.zircotec.com for example. But is it also used in wear parts to protect the bulk material from getting too hot? If so, does zirconia have good tribological properties? I am not that interested in coefficient of friction, more in its abrasive wear properties for example. It should have pretty good abrasive wear properties as I suppose it is fairly hard. The crystal form of zirconium dioxide is at least quite hard.

Does anyone know of other coatings that could be used as thermal insulators?

Thanks in advance

[OfficeLinebacker]

Wolfie is what you're talking about also called DLC (Diamond Like Coating)?

[Wolfie242]

DLC (Diamond Like Carbon) is another type of coating applied to components. Depending on how much sp3-bindings (diamond) there are compared to sp2-bindings (graphite) it can be made very hard. DLC-coatings are usually only a couple of micrometers thick but still improves the wear properties of the material significantly while at the same time ofter decreases the friction. Diamand, though, is a very good heat conductor so it doesn't work as a thermal insulator.

Zirconia coatings are 200-300 micrometers thick if I am not mistaken.

Edited by Wolfie242, 01 March 2011 - 19:13.

[Kelpiecross]

I know that Zirconia is used as a thermal protector in racing, supplied by www.zircotec.com for example. But is it also used in wear parts to protect the bulk material from getting too hot? If so, does zirconia have good tribological properties? I am not that interested in coefficient of friction, more in its abrasive wear properties for example. It should have pretty good abrasive wear properties as I suppose it is fairly hard. The crystal form of zirconium dioxide is at least quite hard.

Does anyone know of other coatings that could be used as thermal insulators?

Thanks in advance

What are the space shuttle tiles made of? This remarkable stuff - I have seen demonstrations of people using bare hands to hold tiles that are still hot enough to glow. Apparently the conductivity is so low that the inner heat is not conducted to the surface of the tile.