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= Acoustic attenuation in nepers/cm. To convert units to dB/cm, multiply by 8.686 ¥ f2 where f is the frequency of interest in Hz. This conversion assumes that the attenuation increases with the square of frequency and is only valid for low loss materials such as glass.
ZS = Shear wave impedance ( ¥ VS) ¥ 10-6 in kg/m2s
MPDA = Meta-phenaline-diamine, a good epoxy hardner. Use vendors D, handle, or rather don’t handle with care. This product can be difficult to obtain fresh, should arrive in the form of whiteish flakes. When handling, take care to use gloves and apron, do not breath the powder. It is best stored in jars filled with dry nitrogen at 0C. When opening a new jar, allow it to equilibrate to RT first.
R1 = Recipe 1: Heat the resin to 70C, add the MPDA and keep the mixture in the oven until the MPDA melts. Sift the W through a 100 mesh screen and add to the epoxy. Stir thoroughly, and outgas the mixture to a 100 micron vacuum. Cure at 40°C for 1 hour, then leave in oven over night at 70°C.
R2 = Recipe 2: Mix alumina to resin. Alumina is very light and fluffy and does not need to be sifted first. It is so light in fact, that any mixture having more than about 100PHR of it will be fixatropic and hard to pour. Next add the hardner, then stir thoroughly and outgas to 200 microns. Use an engraving tool on the beaker to facilitate pouring. Cure at RT for 48 hours.
R3 = Recipe 3: Sift the W through a 100 mesh screen before adding to the resin at RT. Stir and outgas the mixture to 150 microns vacuum. Add the hardner, stir and outgas again. We have noted that epoxy hardened by DEH20, if exposed to the atmospheric moisture, will still be sticky after curing. This is called blushing and usually does not effect the experiment.
R5 = Recipe 5: Vacuum impregnation. To make these materials a vessel is required which is vacuum tight at the bottom and open at the top, i.e. a test tube or jig. The jig is mold released and the filler material is poured into it, usually no more than a third of the way to the top. Next the jig is warmed in an oven to the specified temperature to preheat it and bake on the mold release. The resin is melted, usually in the same oven at this time, and then the MPDA is added and allowed to melt into the resin. Thiokol may also be added at this time if specified. The mixture is stirred, then poured over the filler material, usually no more than two thirds of the way to the top. This assembly is outgassed till a vacuum of 100 microns is reached, usually in about 10 minutes depending on the size of the jig etc. When the vacuum is broken, the epoxy is forced into the filler material by atmospheric pressure. Bake at 70°C overnight.
R11 = Recipe 11: Stir W into RTV 560 and outgas Then add the DBT, stir and outgas again. Pour or scrape into jig mold released with “Heavy Duty Silicon Mold Release” from Sprayon Products, Anaheim, CA. Let stand at room temperature for 4 hours to let cure, then bake at 40°C overnight. Immediate baking will cause material to stick through the mold release.