"Is there a temporary adhesive to bond glass and withstand 1400°F?"

Before this question can be answered, we need to ask for the definition of temporary. Only some materials will withstand up to 1400°F. Companies like Cotronics Corp and Aremco (to name a few) offer high-temperature adhesives. These adhesives are often modified with fillers like Alumina, Zircon, mica, ceramics, etc. that allow the adhesive to withstand higher-temperature environments. Some materials, including liquid materials or tape-type products, have a continuous service temperature of 1500°F, and a melting point of 2800°F. So in one sense, it is permanent at 1500°F, but temporary as you raise the temperature. Some epoxy systems can withstand up to 400°F and 500°F, so the question becomes - how long does it need to survive at 1400°F? If the answer is minutes, then finding a material that can survive short bursts of high temperature for only a little while may be sufficient. There are a number of different chemistries available such as silicone or epoxy. Typically, unfilled organic adhesives like acrylics and urethanes will break down long before 1400°F.

Other questions to ask are about which properties are required, such as: Does it (the adhesive) need to be clear or is opaque okay, or how do you want to remove the material? Unfortunately there isn’t a simple answer to this question. Some of the technical support groups at these companies may be able to help further, or recommend other options for you to consider.

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"Our research lab is looking for a medical-grade adhesive to bond:
1.) Dacron cloth to silver plate and
2.) Glass and PMMA optical cylinder in a silver tube.
It needs to be moisture resistant and should last for a long time (20 years).
Please suggest a product."

Dacron is a commercial name for PET, or polyethylene terephthalate. Bonding cloth to a rigid substrate like a silver plate can be done in a few different ways. Bonding to cloth is mostly a mechanical lock that forms by encapsulating strands of the cloth and then locking them to the rigid substrate. The viscosity of the adhesive will play a role, as the thinner the viscosity, the more it will wick into the cloth. A very high viscosity will not wick very far into a cloth. A 2-part epoxy, such as found from Loctite or 3M, or a 2-part urethane, such as found from Lord Corporation, are just two products that you might want to explore. A silicone adhesive may also do the trick, and would suggest contacting representatives of Dow Corning, Momentive Performance Materials, NuSil Technology, or any of the other silicone manufacturers.

To bond glass and PMMA you may be able to use the same adhesive, but the application might require a lower-viscosity material, depending on the gap between the parts and method of assembly. The epoxy and silicone systems will be moisture resistant and have good usage life, but most manufacturers will not warrantee a 20-year usage lifetime. A 1-part, light-curable urethane acrylate, like 203A-CTH or 209-CTH from DYMAX, are options if you can get light to the adhesive.

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