Design thinking on using quartz glass in high temperature environment - Page 1
Forum section: electronics / projects

author: xufei
author_rank: Newbie
timestamp: June 23, 2025, 02:08:35 pm
content: Hi everyone, I'm working on a small project recently, which involves some electronic equipment that needs to be resistant to high temperature and high precision. In this process, I began to pay attention to some material selection, especially relatively unpopular materials like quartz glass. Its characteristics gave me a new understanding of the thermal management and stability of the equipment, especially in some high temperature environments.In my project, I mainly considered the following aspects:High temperature tolerance: The high temperature resistance of quartz glass made me interested in its potential in some high-power devices. For example, in some heating equipment and lithography machines, its heat resistance seems to bring stable performance.Transparency and optical applications: In some application scenarios where light needs to be transmitted, the transparency and UV transmission ability of quartz glass are particularly important. Although this feature is not the main focus of my project, it still makes me realize its important role in optical equipment.Low thermal expansion coefficient: The stability of quartz glass when the temperature changes also makes me think about its application in some designs that are sensitive to temperature changes. Its low thermal expansion coefficient seems to be able to effectively reduce the deformation problem caused by thermal expansion, especially in high-frequency devices.My current project is still in the design stage, mainly focusing on material selection and thermal management. For a small project like mine, whether these characteristics of quartz glass can bring actual performance improvement needs further verification.I would like to ask if you have similar experience, or friends who have used this material in design, can you share some application cases or design ideas? Especially in the fields of semiconductors, sensors or optics, what is the application of quartz glass?

author: LaserSteve
author_rank: Super Contributor
timestamp: June 23, 2025, 03:30:49 pm
content: I assume you are referring to synthetic quartz, known as fused silica, which is amorphous. "Quartz" in English generally refers to the natural, or sometimes hydrothermal grown crystalline form with a tetrahedral molecular form and a hexagonal crystal structure with a well defined axis and crystallographic optical, mechanical, and piezo-electric properties.Calling it a glass is sort of a misnomer, the amorphous form is glass like.The crystalline form is not very glass like, even though it melts like somewhat like glass in a torch flame.So, you mean "Synthetic Fused Silica" Here in Ohio, we have the largest concentration of facilities for making Fused Silica in the United States, and the electrical forms are not made from molten quartz sand but are formed by flame hydrolysis from gaseous precursors.Shaping and polishing quartz /fused silica is very much like shaping and polishing glass. The difference comes when you try to flame work or melt the material. Glasses generally are very viscous and flow/bend, fused silica, not so much. In its molten state, quartz / fused silica requires a much higher level of skill to handle, it does not melt smoothly, and unlike glasses that readily join when molten, and has a wide melting range, quartz is very close to devitrification when flame worked. You have to "push" it into a junction when molten, whereas glass will readily fuse.Fabricating glass is generally easy, fused silica requires much greater skill.I do laboratory glassblowing as part of my skill set and optical work. Fused silica is best left to professionals who know its properties and have the proper tools.You want fused silica for most things related to fabrication of electronic devices, and this is a well-known art worldwide.If working with hot or molten fused silica wear safety glasses to protect your eyes (cornea) from the immense far infrared emissions it gives off. If your working with molten fused silica, there are immense white visible light and ultraviolet emissions that are extremely dangerous to your eyes. People who lampwork or handle molten fused silica for decades are often easily recognizable by their rough white corneas, at least when I was young. Take precautions.Unlike most glasses, even borosilicate materials, fused silica is well suited for extreme stress at high temperatures.You need to make sure you know your material's origin, manufacturing process, purity grade, and optical properties.Semiconductor grade fused silica is selected for its purity and lack of additives or natural inclusions.For certain electronics work, ie fused silica substrates, or optical windows for laser / spectroscopy work, you may need Oriented Quartz with a known crystallographic orientation or Swept Quartz, which has impurities drawn out of it by setting in a high electrical field while nearly molten for months.Without knowing exactly what you are trying to accomplish, it will be difficult to help you further, this post is an overview.Steve

author: GlassMaster
author_rank: Newbie
timestamp: September 25, 2025, 10:48:00 am
content: I’ve worked a bit with quartz glass in high-temperature applications and found it performs very differently depending on the grade and how it’s mounted. For example, we’ve been using quartz discs in setups up to around 1100 °C where thermal shock and contamination are big concerns.One option people might find useful isthese quartz discs— they’re made specifically for high-temp environments and come in several grades. In our experience, the transparency and purity at high temperatures can be quite a bit better than standard fused quartz, especially if you’re working with UV or IR applications.I’m curious how others here are handling:Sealing and differential expansion between quartz and metal partsLong-term exposure to reactive gases or fluxes at high tempAlways interested in hearing other engineers’ experiences with these materials.

author: calzap
author_rank: Frequent Contributor
timestamp: September 25, 2025, 01:36:34 pm
content: Check the Hellma and Corning websites. There is a lot of information there. If you have questions, they should be able to give you additional information. Mike

author: RJSV
author_rank: Super Contributor
timestamp: September 25, 2025, 07:30:54 pm
content: Friend worked as a glass cutter. They made glass 'BOATS' which mainly needed purity so to not contaminate the 3 inch round IC wafers of silicon that they carried, into oven and out.About size of your forearm and 2 cm thick, maybe those BOATS were a little cloudy. Now I wonder about the distinctions you've mentioned, but I always assumed it was mined in a big block, to start...then cut in a band saw like machine that ran for hours and hours, to cut and separate slabs.Rick B.

author: TimFox
author_rank: Super Contributor
timestamp: September 25, 2025, 08:52:49 pm
content: Glasses are rarely mined (obsidian is one): SiO2in nature is usually crystalline.Silica glass (or fused quartz) was made originally by melting quartz crystals, hence the name "fused quartz". There are now other methods to synthesize it as well.

author: LaserSteve
author_rank: Super Contributor
timestamp: September 26, 2025, 02:54:55 pm
content: Quartz windows are fused into or onto stainless steel discs in an induction heated vacuum or hydrogen filled furnace. Either a low melting point frit with a correct coefficient of expansion and a known level of stress is used, or the alternative is a titanium cored ring of a special brazing wire. The ~3% titanium core forms a titanium hydride that acts a flux and bonding layer. What no one talks about is how the stainless is brightened and passivated prior to fusing.It is nowhere as easy as it sounds. Believe me, as I use the frit method. I have a lifetime supply of the frit salvaged from a closed plant. Even then there is not much there, a few kilograms. The frit means I don't have to have an induction furnace, and can fire in air, but my windows are tiny. Had I not received the CNCed precision tooling and tiny furnace for the process at the auction, chances of pulling it off in a home lab would be nil. The rod goes to a friend's house prior to sealing to be lapped "VERY" flat on a lapidary setup.Quartz to metal seals start with a molybdenum foil. It must be very thin, and the commercial seals start with a foil electrochemically etched to an elliptical profile with very, very, thin edges. The real material used for bulk production of halogen lamps is Molybdenum 0.05% Lanthanum alloy or Platinum Coated Molybdenum.Special techniques have to be developed to make the Moly rod or tube seals, and other then a few publications, no one is talking. Some of them are a Moly Housekeeper seal, others like arc lamp makers don't talk.For low temperature window seals to thick tubing, evaporated nickel for adhesion, followed with evaporated gold on both sides of the seal, and sealed with 99 In, 1% PB thin foil as a "One Shot" solder. The tubing end has to be polished flat and ground to 1/8th wave. For various reasons you need a vacuum evap coater, as sputter coaters do not work well for this.Laser grade windows get sealed on to quartz stems with optical contacting, and some heat and high voltage applied to speed the fusion. How that is done is not something I can further discuss.Obtaining 0.002 / 0.05 mm foil is not fun. Putting the correct profile on the end of a Moly tube tends to take it out of the range of those without a very good machine shop. Whatever your sealing needs welded to the foil. Take a look at a halogen lamp or two and you get the idea.Very fine moly wire will seal to quartz directly, but the surface prep is either etching the wire or firing in a hydrogen furnace. Hobbyists just take their chances and make the seal after mechanical scrubbing. Little tiny surface cracks in the wire from the manufacturing process can come back and hurt you, just like tungsten rod seals in hard glass. Thus the surface prep is critical.Steve

author: RJSV
author_rank: Super Contributor
timestamp: September 26, 2025, 08:11:51 pm
content: Hey, Good Day to You:Systron-Donner might have some legacy developers that could talk of the Moly-wound wire, infused with gaseous hydrogen, although I don't know how much is proprietary.Moly wire, vacume pumps, and hydrogen to produce an outgas in times of aircraft (accidental) fires. That wire got placed inside the fire/overheat detector that snapped a diaphragm switch. The detection tubing could be 20 ft. long, around an engines cowling, or, in land, around a diesel back-up generator in a hospital or other critical places.Overheat detection was done just by the gas pressure going up, but a third function was a diaphragm switch to detect pressure leak faults, in the detector tube itself.The whole factory wasn't super clean-room, or with as much chemical complexities, as you've mentioned, they did a lot of bake-outs and leak detection. HP supplied the mass-spec hydrogen leak detector, for production line use. I think it was owned by 'Charles Lindberg Co.' before Concord,CA Systron Donner.Considered the Cadillac of fire detection.Flight deck captains hated, when having to shut down an engine in flight, so no tolerance for any false alarms! (Makes sense).

author: coppercone2
author_rank: Super Contributor
timestamp: September 26, 2025, 08:29:55 pm
content: my quartz lab ware is pretty cloudy and actually often has a non round shape (many facets) (old)The cheaper quartz things I have like a crucible look like glass. (china, new)the main problem with hydrogen is that it will react with heating elements (reduction)I suggest that looking into induction heater based systems probobly makes sense because the cost/knowhow about induction heaters is way better then ages ago. Kilns are very messy/fragile/annoying to use, and I would rather have to deal with the complex electronics then the 'mechanical' parts of kilns. Every time I have to do something with it, its a affair. While water cooled capacitors might seem intimidating, its probobly alot better then dealing with fragile fiber bricks, high temp seals and other kiln shitI found that the typically 'affordable' limit on kilns, which is around 1100c, is very limiting, alot of cool stuff happens at higher temperatures. Induction can do it. Things like vacuum kilns get mechanically complicated and the heating system is no longer trivial IMO (MoSi), when you want to go higher then 1100c. And the wiring gets bizzare, at least induction is just like thick cables, but with kilns you have odd braids and odd ceramic-metal contacts and its not cheap/easy/fun. Even going to the kanthal wire instead of nichrome sucks, its like fragile. IMO nichrome heater elements are like the limit of what 'easy' or 'hobby' is...