AlexKelamis

I've posted this before. I'll post it again. Fumed silica + water DOES NOT equal colloidal silica. Doesn't matter if it is hydrophilic or hydrophobic. Fumed silica is basically a silicon atom connected to four oxygen atoms, and this pattern repeats to molecules of various sizes. If you add this to water, you simply have fumed silica in an aqueous solution. Yes, if will bind to the surface of your ceramic fiber. But not very strongly--its hydrogen bonds. It can easily be rubbed off. It may seem harder. The hardness you feel is simply a dried caked layer of fumed silica powder. Now, at room temperature fumed silica powder is not as dangerous to inhale as ceramic fiber dust. However, if either are heated, they both become extremely dangerous. Water glass is made by adding sodium hydroxide to an aqueous solution of fumed silica. If you take this, heat it and use catalysts and chromatography or some other purification method, you end up with colloidal silica. It is not easy, and you aren't going to do it in your kitchen or workshop. Colloidal silica is a repeating structure of silicon atoms, each one bound to three oxygen atoms. They form an amorphous structure, meaning there is no definite pattern. It's random. Along the periphery of all these bound silicon atoms and oxygen atoms you will have tons of hydroxyl molecules. These are very water soluble. This is why the colloidal silica dissolves in water. Hydroxyl molecules react readily and easily with the oxygen atoms present in the ceramic fiber structure. This quickly forms a covalent bond between the two. It isn't going to mechanically be removed. Once dehydrated, it is going to be rigid because the colloidal silica penetrates into many of the "air pockets" to fill those without changing the thermodynamic properties (much). When you heat this, and drive off the last bit of free water, the colloidal silica becomes even more bound to the ceramic fiber and therefore even more rigid. Therefore, no dust particles fly off. You don't get this with fumed silica. Period. Maybe fumed silica is "good enough". Or maybe not. I can't say with 100% certainty. But I can say this, it's one or the other. It's either safe enough, or it isn't. Restrictive lung disease, like progressive massive fibrosis from breathing in silica particles, is really not cool. By the time you know something is wrong, it's too late. Oh yeah, it will also damage your kidneys, and ultimately your heart. It can also cause severe damage to joints and skin, but who cares at this point. You just want to be able to breath. Most of us will probably be fine. But, about 15% of the people reading this will have a genetic mutation that makes them extremely susceptible to developing the deadly lung disease (and kidney, heart, etc.) associated with ceramic fibers. For that 15%, it takes very low levels of exposure, and it will cause terminal (ie: you are going to die) disease in as little as 3 years. So, this means roughly 1 in every 7 people reading this are high risk for developing deadly disease, and quickly. What group do you think you fall into? Are you willing to bet your life on fumed silica working? I don't claim to be in expert in everything. But I do know what I am an expert in. I'm not talking out my backside with this. We need experienced blacksmiths with the chemical knowledge background to chime in on this. We need to make sure the advice being dessiminated on these forums is safe and sound. There are always exceptions, but we need to make sure we are setting other up for success in their future, not deadly medical problems. I am all open for comments. What are your thoughts?

Also, there are different types of fumed silica. The type most people use is "M5", or the hydrophilic type. There are fumed silicas that are hydrophobic (typically, long or large organic chains are attached to them). Regardless of the type of fumed silica you use, the results are the same--it isn't a rigidizer, it isn't colloidal silica, and it isnt protecting you from ceramic fiber.

Fumed silica added to water is not colloidal silica. Period. It is NOT a rigidizer, either. And no, you cannot make colloidal silica from fumed silica, unless you have an extensive chemistry laboratory. I am not trying to start an argument with anyone. I am trying to clear up a safety issue. People using ceramic fiber blankets rely on accurate advice in order to protect themselves from the heated silicates (there are many types of silicates). I will be the first to admit that the resources available on the internet are horrible when it comes to fumed silica vs colloidal silica. I do not claim to be an expert in many things, and I am not a blacksmith expert. But I do take issue with experts giving advice that is not accurate. This needs to be cleared up, and the expert members of this forum need to make efforts to consolidate this information so others do not practice unsafe rigidizing. Fumed silica is Silicon dioxide (one silicon atom with two oxygen atoms covalently bonded). In fumed silica, the SiO2 molecules connect randomly in an amorphous arrangement (ie: there is no repeating crystalline structure--its totally random within 3D space). The size of the overall aggregate SiO2 molecules varies. This is fumed silica. Powder form. It is hydrophilic (loves water). If you add it to water, you simply get an aqueous solution of fumed silica, also known as "fumed colloidal silica"--this is NOT the same as colloidal silica (without the "fumed"). Fumed silica added to water is not a rigidizer. And yes, I have tried it just to prove the point. One reason it isnt a rigidizer is because it is hydrophilic, versus ceramic fiber (the type we use) which is, overall, hydrophobic. If you add fumed silica to water and apply it in any manner, let it dry and heat cure it, you will end up with very little silica being bonded to the ceramic fibers. Instead, you end up with fumed silica powder on the surface of the fiber blanket. This makes the ceramic fiber blanket, if anything, even more dangerous, because now it is littered with fumed silica powder on the surface. This accomplishes us harming ourselves even more. Colloidal silica is made up of silicon atoms connected to two hydroxyl groups (hydroxyl is O-H, as opposed to -O, or oxygen) usually with a hydrogen atom/proton (H+) next to each -OH group connected by hydrogen bonding, suspended in water. Sometimes, instead of H+ ions, it may be sodium (Na+) ions, or even aluminum (Al+) ions, depending on the type of colloidal silica (this is irrelevant for the purpose of the discussion). These molecules of Si(OH)2 polymerize, or combine together, to form chains, in a water solution (no this is not being mistaken for water glass, or sodium silica--keep reading). This solution is unique, in that the silica (Si(OH)2) chains themselves exhibit hydrophobic properties, as well as hydrophilic properties; water surrounds the hydrophilic portions, leaving only the hydrophobic portions exposed to bond with the ceramic fiber. So, it is very good at penetrating, and binding to, ceramic fibers. When you use true colloidal silica, regardless of application method, you will have zero dust/powder on the surface of the blanket. Colloidal silica is one effective rigidizer; there are others. To clarify, fumed silica is not a rigidizer. Fumed silica added to water is not a rigidizer (I don't care what else you add with it--soap, jet dry, detergent--it isn't a rigidizer). Fumed silica added to water is never, ever, ever colloidal silica. You cannot make colloidal silica from fumed silica (unless you have extensive chemistry laboratory access). Again, I am not trying to argue, and I am not trying to embarrass anyone. This is a safety issue. Experts need to be absolutely certain of the advice they give, because when an expert speaks/writes, most people take it for face value without fact checking. It is going to be interesting how people respond to this. If you are really serious about spreading blacksmithing knowledge safely, then please help in clearing up the facts about rigidizing. If, instead, you chose to attack me over this, just know that you'll be showing others that you care more about attacking people behind a computer screen than you do helping to spread sound safe knowledge to others. I'll share one experience I had about 6 months ago. My "day job" is being a physician. July 2021, a 24 year old man came to see me. He had developed chest pain, recurrent infections/pneumonia, and shortness of breath that was now constant. A chest x-ray showed his lungs looking like a "white blizzard" (lungs should look dark on x-ray). He has terminal silicosis. At 24 years of age. He is now on a lung transplant waiting list. He must have lung transplant surgery to live, or he will be dead by 30 years of age. His chances of getting a lung transplant is about 20%. He started working as a blacksmith in 2017, using a gas forge/being close to a hot gas forge (with ceramic blanket) on average of about 6 hours daily, five days a week. In 4 years, he went from perfectly healthy to terminal. To be fair, he has a genetic mutation that makes him very, very susceptible to lung damage from many things, like silicates. About 12% of the population has this same mutation. Which means about 12% of the people on this forum who read this have the same mutation, and are at extremely high risk of developing a lung disease that can kill them, especially if they dont properly rigidizer ceramic fiber. Happy new year. Stay alive.

Well, reading the end of this thread made me feel like I was, oh, about 10 years old again, with my father slamming his closed fist onto the dinner table while yelling at me to "shut the xxxx up!". Takes you back. Good times.

If you want equations to understand the flow, resistance, and overall fluid Dynamics of a ribbon burner, just look at the fluid Dynamics equations: v=Q/A, where v is velocity (cm/sec), Q is flow (mL/sec), A is area (cm²). Q=∆P/R, where ∆P is pressure difference (pressure beginning minus pressure at end), and R is resistance (see below next). R=8nL/πr⁴, n is viscosity of fluid (negligible, or 1, for gas), L is length of tube (cm), r is radius of tube. For ribbon burners, it is a parallel series of tubes, nozzels, etc. Point is, it's parallel. Now, the total resistance of a parallel system is: 1/R[total]= 1/R[1] + 1/R[2] + 1/R[3] .... This means the total resistance of the entire parallel system will be LESS than any single individual "nozzel" resistance (calculate it if you dont believe me). Put another way, as the number of nozzels/outlet ports increases, the total resistance of the system (burner) will decrease. As the resistance decreases, the flow through the system will increase (ie: you will be using more gas overall--thats not a brain-buster). As the number of nozzels increases, you can push higher volumes of gas through. But, if you keep your PSI at the regulator the same, you'll obviously have less flow, and less velocity and pressure difference, coming out each nozzel. So, again none of this should be surprising. I'm just explaining it so people will realize the equations are correct. Further, if you are designing something involving explosive gas, it doesn't hurt to "check" your plans with the equation. Hopefully the equations will be useful. Without having more info myself I can't provide much more. But, if you want my input feel free to ask. I'll tell you what I know. If I don't know the answer to something, I'll be the first person to say "I don't know". Best of luck.