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Hello. I have a question about the sol-gel process and nanoparticles.
I dont know if its a silly question what would happen if you took rubber cement like a neoprene glue that uses a solvent to dry with and used the process to make an aerogel on it? would love to know.
Well give it a shot and keep us posted with the results! At this stage it’s cooking, not baking–go by feel for now, look for signs the gel has been penetrated by cross-sectioning after infiltrating with your polystyrene solution, after replacing the pore fluid with hexane, and after evaporative drying, and adjust your solutions accordingly to make the process go smoothly. Start with concentrations of polystyrene on the order of 5-10% and then around 50% and compare the results. Move accordingly from there.
Four approaches to the sol−gel synthesis of ..
A: More than enough. Most gelation procedures use a concentration of about 4%, not more than 10%. Remember, this concentration will be comparable to the % solid the aerogel will be, so if you want an aerogel that’s 95% air, a concentration of 5% would be around what you want.
To add to Szymon’s response below, the classic way of preparing aerogels through subcritical drying is to treat the silica gel precursor with a hydrophobic agent such as trimethylchlorosilane (TMCS) or hexamethyldisilazane (HMDS) prior to evaporative drying. The trick here is to a) eliminate hydroxyl groups that will stick to each other when the gel shrinks a little bit and b) to balance the modulus of the gel matrix against the capillary stress induced by evaporation. The way this is done is by preparing a silica gel through any suitable method, exchanging the pore fluid into, say, acetone and then into hexane, then exchanging the gel into a solution of ~6 wt% TMCS in hexane one to three times, preferably at elevated temperature (say 60 deg C). After that you would purify the gel with additional hexane and then slowly evaporate the hexane. Gentle ambient heating sometimes is applied. This is basically the method described first by Smith, Desphande, and Brinker in Ceramic Transactions v31 1993. We will post the long-overdue procedure for subcritical drying of aerogels under the Make section later this week. Check out the response to MOHIT’s quiestion below as well.
Sol−Gel Synthesis of Organized Matter
I see a tremendous potential for the marketing of aerogels & aerogel-based products, but after browsing through articles from this site and other resources on the internet, the downside of this is that the manufacture of aerogels does not look too cost-effective. Ageing, soaking & supercritical drying would take long periods of time and consume lots of solvent like ethanol and also liquid CO2. This dilemma is comparable to that faced by those engaged in the biochem industry (e.g: Manufacture of penicillin, Synthesis of drugs, etc.). The big question I would like to ask now is… Will the cost of selling aerogel & aerogel-based products outweigh the cost of manufacturing it?
I dont know if its a silly question what would happen if you took rubber cement like a neoprene glue that uses a solvent to dry with and used the process to make an aerogel on it? would love to know. thanks Storm
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Sol–gel synthesis and characterization of α-Fe ..
You can use less than 200-proof ethanol in the synthesis of the gels but not in the solvent exchanges to prepare the gels for supercritical drying unless it is anhydrous ethanol and does not contain ketones or aromatics. You can use acetone for the gel purification steps instead if that’s easier.
Sol-gel synthesis of solids by J
4) You should place the gel under ethanol in the reactor but you should remove all of it before trying to do supercritical drying! Remember, there are two processes going on in the reactor–first, a solvent exchange of ethanol with liquid CO2 and second supercritical extraction. You need to drain/vent the ethanol from the vessel, refill with liquid CO2, let the gel soak in CO2 for a day or so, repeat 2-3 more times, then if you aren’t smelling ethanol in the exhaust and seeing ethanol leftover after the dry ice sublimes, then you are go for supercritical drying.
Sol-gel auto-combustion synthesis of spinel-type …
A: Most of these numbers are arbitrary anyways so it really just depends on your system. Don’t worry about the 7 bar h-1. Just do it slowish. You’ll get the feel for how fast you can go with practice. I generally depressurize slow between 600 and 1200 psi and a little faster below 600, and much faster below 200 psi. For your manuclave, you can pressurize slowly by just cracking the ball valve (that’s what I do). At this stage in the processing, as long as it’s slow enough, there should be no effect. The risk here is if the materials cool too fast and crack or rapidly depressurize and get blown apart. Remember after partially depressurizing the vessel at supercritical conditions, when you drop below the critical point the fluid in the pores of the gels has reverted to a gas phase, not a liquid phase, and can exert no capillary stress on the gels. It’s just high pressure gas at that point. Cracking and colllapse at this stage in the supercritical drying process is really due to unseen residual solvent in the aerogel.
(575v) Analysis of the Sol-Gel Synthesis of Tungsten …
I am drying isopropanol (IPA) alcogels (rinsed 4 times after synthesis with reagent grade isopropanol – but not necessarily dry because the bottle is open to humid air when pouring, etc.). I am pressurizing to roughly 1500 psi and heating to roughly 300 deg C (beyond the critical point of IPA). However, I am getting cracked, somewhat-shriveled pieces, and not un-shrunkened monoliths after sc-drying. I heat the sample in about 1 hour, hold beyond the critical point with periodic venting to prevent excess pressure for about 1 hour, hold isobarically and isothermally at about 300 deg C and 1500 psi for about 1 hour, and finally depressurize over 1 hour. I also pull a vacuum on the autoclave once it is fully depressurized until it cools to below the normal boiling point of IPA. Could the problem be residual water in the IPA (up to 12% by mass, unlike EtOH which picks up only ~5% water)? Is water soluble in scIPA? Am I depressurizing too fast? Any suggestions? Should I just do scCO2? If so, do I have to re-exchange the IPA away with acetone?
The sol-gel synthesis of cotton/TiO2 composites and …
Carbon monoxide is a poisonous and hazardous gas and sensitive sensor devices are needed to prevent humans from being poisoned by this gas. A CO gas sensor has been prepared from WO3 synthesized by a sol-gel method. The sensor chip was prepared by a spin-coating technique which deposited a thin film of WO3 on an alumina substrate. The chip samples were then calcined at 300, 400, 500 or 600 °C for 1 h. The sensitivities of the different sensor chips for CO gas were determined by comparing the changes in electrical resistance in the absence and presence of 50 ppm of CO gas at 200 °C. The WO3 calcined at 500 °C had the highest sensitivity. The sensitivity of this sensor was also measured at CO concentrations of 100 ppm and 200 ppm and at operating temperatures of 30 and 100 °C. Thermogravimetric analysis of the WO3 calcined at 500 °C indicated that this sample had the highest gas adsorption capacity. This preliminary research has shown that WO3 can serve as a CO gas sensor and that is should be further explored and developed.
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