FX2 New Design + Material Tests
As with every new design, one does their best to select materials and designs that will withstand the theoretical test conditions. However, at some point you must test it and see what happens. This is just part of the scientific method; design, fabricate, test, observe results, re-design, modify, etc. until you achieve the desired design specifications. You then have to incorporate appropriate instrumentation so that all pertinent variables can be accurately measured and documented. Once all that is in place you might be ready to do a full controlled study. Even then, when you are exploring new areas of research that you know very little about, the unexpected often happens and you have to regroup, rethink and adapt.
Although the fixture used in Fossil Experiment #1, FX1, was very strong and would work as intended, it was very difficult to assemble and disassemble. The new design for FX2 would allow me to take it apart with only an Allen wrench. In order to measure the compressive force of the hydraulic sustem, I added a pressure gauge with a digital readout that I could calibrate to read in pounds force by multiplying hydraulic pressure by the piston surface area of the hydraulic cylinder. The compressive pressure within the sample chamber, or reaction vessel, would then be the ram force divided by the chamber piston area. The small tubing attached to the sample chamber allows me to externally measure the water or steam pressure within the chamber as it is being compressed and heated in the oven.
While testing the new fixture I decided to also test compatibility of lubricants with the O-rings I had planned to use. Many of the products that claim to be “High Temperature” do not actually specify at what temperature they fail or how long they will last under those conditions. Another problem I had to resolve was that even if a material like silicone rubber, would survive at 500F, would it remain unaffected by the lubricant in contact with it. I had already decided to try O-rings made of high temperature red silicone rubber thinking if they were rated at 400F or 450F in some books, maybe they would survive to 500F. So I ran a simple test with five O-rings and four different lubricants. Three of the O-rings I coated with three common types of grease and the fourth O-ring I coated with Fomblin RT15, a perfluoropolyether grease. The fifth O-ring was left clean.
As you can see from the below pictures, only the clean O-ring and the Fomblin coated O-ring survived. The Fomblin grease seemed completely untouched. The other greases hardened and dried up but also reacted chemically causing the O-rings to become very dry and brittle. Even though two of the O-rings survived, you can see from the other pictures what happens when they are under pressure. At 500F they extruded like children’s Playdough. Notice that where the steam broke through around the cylinder, it actually cut a groove in the edge of the stainless-steel cylinder. The only positive thing that came out of these material tests was the Fomblin grease. Unfortunately, Fomblin is very expensive at $180 / 100 grams.
Even though the O-rings failed, the mudstone fossils were very interesting. Two of the fish were fresh and the other two had started to decay after 3 days at room temperature before being compressed. It appears that the decayed fish had a tendency to rupture while the other two remained intact as the moisture was pressed out. This is the first time in several years of making fossils that a fish has ruptured like this. One thing that surprised me about the fern was the color or shade of the leaves. I had assumed that after heating to 500F the leaves would all be the same shade of black carbon film, making it very difficult to tell a dried leaf from a fresh one. But as you can see the dried leaf and dried tips are still very discernable from the fresh leaves. All the leaf and fern fossils that I found on the internet appeared to look fresh.
Experiment Details:
Matrix: Common all-natural potter’s clay pulled directly from the ground. Four layers. A geologist told me that various types of mudstone account for about 70-80% of the fossil record so this is a very appropriate matrix to experiment with.
Specimens: Fish and a fern leaf. Two of the fish were allowed to decay for 3 days in room temperature water.
The new tie rod fixture was assembled per standard procedure and mounted inside the oven.
Hydraulic compression was started at 3000 lbf, (~ 224 psi), and slowly raised in stages over four hours, to 20,000 lbf. (~ 1500psi).
Oven dial set to 500F. Actual oven air temperature operated between 470F and 490F.
As the water was being pressed out, the inlet pressure opposite the piston raised to over 1100 psig meaning that the clay under this much compression is almost watertight. I initially thought that as the water is pressed out, the clay would be porous enough to allow the water at the inlet to pass through the sample and the vented piston into the headspace above the piston. The water will eventually migrate through the clay sample but very slowly. During this time, the outlet pressure in the headspace above the piston remained at 0 psig.
As the sample and cylinder rose in temperature, the pressure at the outlet or headspace began to rise as expected according to the saturated steam tables to about 670 psig.
At some point during the night, all the O-rings failed and pressure went to zero.
Total compression time before heating was 4 hr. Total heating time 35 hr. Maximum temperature achieved 490F.
Total sample compression was 0.647 inches in height. Final sample thickness is 2.023 inches, therefore initial sample thickness was 2.670 inches. This means that the natural clay matrix used was compressed by 24% of its initial volume at 1500 psi compression. This reduction of volume was due to removal of water only.
A piece of the dry hardened matrix was placed in water. The sample dissolved back into a clay like consistency which means under these conditions, no cementation has occurred. It is also noted that since the O-rings blew out early in the test, all liquid water was boiled off. I have been told that without liquid water, cementation or permineralization cannot happen at these temperatures.
Conclusions and Observations:
If natural clay sediment layers formed at the bottom of a large body of water or river are ~24% water by volume and are later compressed to over 1500 psi by overburden, where did all that water go? For instance a layer of sediment 100 feet thick would have the equivalent of 24 feet of pure water pressed out of it as the overburden accumulated above it. Is it possible that this water source might support the theory that some caves are formed from the bottom up? The articles describing this method of cave formation simply refer to “ subterranean water sources” and do not suggest how the water got there in the first place.
As we can see from this experiment, and from the already established Saturated Steam Tables, that liquid water at 500 degrees F requires around 670 psig to remain liquid. Since the sedimentary overburden is porous, how did the water not boil off at these temperatures? And yet most of the fossils we find in nature are cemented and permineralized which I am told requires liquid water. So within a porous matrix, how was the pressure maintained to prevent the water from boiling? The vertical compressive “pressure” of the porous overburden by gravity is very different from the 3 dimensional hydraulic “pressure” created by the depth of water and gravity. Other than the affects of buoyancy, they are mutually exclusive of one another.
High temperature red silicone might survive 490F but is much too soft to withstand any significant pressure. Next attempt will be with AFLAS and PTFE O-rings.
Commonly use “High Temperature” greases dry up at 490F and react chemically with silicone rubber. Fomblin RT-15 Perfluoropolyether grease not only survived 490F but did not visibly react chemically with the silicone rubber O-rings.
Would like to understand how cementation and permineralization occurs in nature.
