11-16-2018, 11:53 PM
Please understand that, not being a chemist or metallurgist, I’m speaking out of my expertise and this is just my attempt to explain what is happening here. I would more than welcome and hopefully someone here can offer edification, clarification or refutation.
In this post, http://bessex.com/forum/showthread.php?t...03#pid4203 Mr. Mark spoke of creating a lot of sparks when grinding hard carbon steel. I responded in a following post by stating that I have never encountered sparking during basic sharpening with a Kally. Mr. Mark then suggested that I try the tip of a file. I did, and indeed, even the lightest grinding produced glowing sparks much like burning a sparkler. Even just barely touching the file to the 150 grit Cubitron belt created sparks. It’s rather remarkable. So much so that it seemed that if only one abrasive particle on the belt touched the file a corresponding spark was produced. Try it. You’ll like it!
So, what’s gong on here? It would be logical to assume that there must be something about the steel that increases friction so dramatically as to generate enough heat to melt steel to the point of glowing red hot with even the most minor and ephemeral contact with abrasives. That makes sense, but I think that explanation is erroneous and there is another cause of the sparking.
Oddly, very fine particles of iron are pyrophoric. Pyrophoric materials spontaneously ignite when exposed to oxygen rich environments such as air, due to heat generation caused by extremely rapid exothermic oxidation.
I’m sure many of us have witnessed flash rusting of freshly ground iron. They don’t call it flash rusting for nothing! Rust starts to form almost instantly if the material is not protected. In this case, as soon as flash rusting starts it slows dramatically because the instantaneous coating of rust (oxidation) isolates the surface from exposure to oxygen in the surrounding environment.
Grinding during sharpening produces extremely small iron particles. When grinding, not only is the protective layer of oxidation stripped from the outer surface of the blade by the abrasive, but when particles are torn from the edge the freshly exposed “underside” of these particles, also not protected by a layer of oxidation, is exposed. This creates the maximum surface area relative to the particle size possible that is available for oxidation. Even the small additional heat generated by grinding facilitates the oxidation process and the particles burn in the air.
So, I did some searching around and found a pretty good explanation of what I think is going on:
https://www.amazingrust.com/Experiments/...ic_Fe.html
I always found it odd that iron and steel can actually burn. My first exposure to this was when I was a kid with a chemistry set. I remember being surprised to see iron filings burn when sprinkled into the flame of an alcohol burner, and equally fascinated to find out how easily steel wool can be ignited with a lighter. I guess I shouldn’t have been considering I loved setting strips of magnesium on fire. I highly recommend igniting magnesium as entertainment for kids. Hours of fun there! Oddly I still have all my fingers and vision in both eyes.
In this post, http://bessex.com/forum/showthread.php?t...03#pid4203 Mr. Mark spoke of creating a lot of sparks when grinding hard carbon steel. I responded in a following post by stating that I have never encountered sparking during basic sharpening with a Kally. Mr. Mark then suggested that I try the tip of a file. I did, and indeed, even the lightest grinding produced glowing sparks much like burning a sparkler. Even just barely touching the file to the 150 grit Cubitron belt created sparks. It’s rather remarkable. So much so that it seemed that if only one abrasive particle on the belt touched the file a corresponding spark was produced. Try it. You’ll like it!
So, what’s gong on here? It would be logical to assume that there must be something about the steel that increases friction so dramatically as to generate enough heat to melt steel to the point of glowing red hot with even the most minor and ephemeral contact with abrasives. That makes sense, but I think that explanation is erroneous and there is another cause of the sparking.
Oddly, very fine particles of iron are pyrophoric. Pyrophoric materials spontaneously ignite when exposed to oxygen rich environments such as air, due to heat generation caused by extremely rapid exothermic oxidation.
I’m sure many of us have witnessed flash rusting of freshly ground iron. They don’t call it flash rusting for nothing! Rust starts to form almost instantly if the material is not protected. In this case, as soon as flash rusting starts it slows dramatically because the instantaneous coating of rust (oxidation) isolates the surface from exposure to oxygen in the surrounding environment.
Grinding during sharpening produces extremely small iron particles. When grinding, not only is the protective layer of oxidation stripped from the outer surface of the blade by the abrasive, but when particles are torn from the edge the freshly exposed “underside” of these particles, also not protected by a layer of oxidation, is exposed. This creates the maximum surface area relative to the particle size possible that is available for oxidation. Even the small additional heat generated by grinding facilitates the oxidation process and the particles burn in the air.
So, I did some searching around and found a pretty good explanation of what I think is going on:
https://www.amazingrust.com/Experiments/...ic_Fe.html
I always found it odd that iron and steel can actually burn. My first exposure to this was when I was a kid with a chemistry set. I remember being surprised to see iron filings burn when sprinkled into the flame of an alcohol burner, and equally fascinated to find out how easily steel wool can be ignited with a lighter. I guess I shouldn’t have been considering I loved setting strips of magnesium on fire. I highly recommend igniting magnesium as entertainment for kids. Hours of fun there! Oddly I still have all my fingers and vision in both eyes.
