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If atoms have well defined energy levels and those differences correspond to the frequencies of light that can be absorbed, how is it that opaque objects absorb all or most visible light frequencies get absorbed Photons in almost all frequencies hitting an object are absorbed in different ways (absorbed, reflected, refracted, scattered, ...


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If atoms have well define energy levels and the differences correspond to the frequencies of light that can be absorbed, This is correct how is it that opaque objects absorb all or most visible light frequencies get absorbed and you basically don't have any visible light coming out on the other end? The crux of the matter is the word "objects". ...


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If you draw the phase diagram of water, the phase boundaries will be the points at which the free energy change for phase change is zero, that is the two phases are in thermodynamic equilibrium. However thermodynamic equilibrium is the infinite time limit of the system so at the phase boundary the phase change will only take place if you wait long enough. ...


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The caption in your image is "strength after abrasion damage test". Typically, the strength of a material under stress strongly depends on surface defects. A defect (crack, groove) leads to a stress concentration at the tip: this stress concentration allows a material to break (a crack to propagate) with a relatively low applied force. You experience this ...


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The fact that the picture is describing "Strength after abrasion damage" would seem to imply that the discussion falls under the rubric of fracture mechanics. "Abrasion damage" would imply that small cracks already exist IMO. In that case, the major influences would be the characteristics of the material and the geometry of the crack, and only then would ...


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The way to distinguish intermetallics (or any other phases) is to used the commonly accepted phase description, such as Mg$_{2}$Pb as you did above. This phase descriptor than points people to information on the crystal structure, thermodynamics of the phase, etc. The point is that these are thermodynamically distinct phases - a first order phase transition ...


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Yes, you're right that sample sizes need to be standardized in strength tests. In the picture you included, we see a ring-on-ring strength test. A small ring on top presses against a sample of uniform thickness resting on a larger ring. The loading is (up to second order effects) localized within the disc-shaped area of the sample located above the lower ...


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You don't appear to be asking for strength here, but rather asking for hardness - a wholly different concept. Resistance to penetration or distortion by a small focused force? Neither strength (which is an inherent property of the material) nor hardness (also an inherent property) can be changed by altering dimensions. RESISTANCE TO BREAKAGE may be, if ...


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Things like flower and lamb leg become brittle because of large portion of water contained in them. Water gets frozen into ice upon cooling, which is brittle. Basically, brittleness is related to the directionality of chemical bonds. Materials form by more directional bonds tend to be more brittle. Meanwhile, they tend to be harder.


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The creep mechanism of grain boundary sliding is also sometimes referred to as superplastic or granular flow. The macroscopic deformation of the sample is caused by the rearrangement of grains as they slide past one another along grain boundaries. The microscopic displacements along grain boundaries is caused by the glide and climb motion of grain boundary ...


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Many organic substances will become brittle at the temperature of liquid nitrogen, but there are plenty of material choices left for e.g. vacuum seals, pipes, containers, etc., which are not. Indeed, we have constructed entire rocket fuel systems at the temperature of liquid hydrogen, which retain most of their mechanical properties. If you go down further, ...


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As far as I remember, yes, everything becomes brittle at low enough temperatures. This is due to the brittle-to-ductile transition (BDT - or sometimes referred to in reverse as DBT, ductile-to...). This transition is temperature dependent (amongst others (strain-rate ...)). Can every composition actually reach low enough temperatures, or do some have a ...


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Tungsten has been known to bait gold bars (historically). There are a few methods we use to determine if something in front of use is gold or if it is alloyed, or if its plate, fill or scrap. You can cut the bar in half...You will then know immediately of you got bunk gold. You can do a specific gravity check of your gold. There are scales designed for ...


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Well, the wiki page pointed to in your question states early on that, indeed, tensile stresses exist in the material as well as compressive stresses. The plastic deformation induced by shot peening results in compression at the surface (where it dramatically extends fatigue life) at the cost of tensile stresses below the surface. Since cracks are most ...


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Well I think you may be more interested in the permeability, and not just the diffusion. (here's a link, http://users.encs.concordia.ca/~woodadam/GCH6101/Diffusion%20and%20permeability%20in%20polymers.pdf) I find it very interesting that CO2 goes through a rubber ballon faster than Helium. The reason is that CO2 is more permeable in rubber, not the ...


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Depending on the experimental setup, using metal flex lines might be an option. One example would be Swagelok, say the FJ series metal hose. The 1/4" tubing has a dynamic bend radius of 11cm. Some of the bending issues can be alleviated with longer hoses to yield less bend per unit length, depending on the design of the system. For example, for two boxes ...


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The $E$ he is refering to is the Young's Modulus, which is the elastic modulus that tells you how the tensile stress for a wire relates to its extensional strain, i.e. $$ \text{stress} = E \text{ strain} $$ in a thin wire. In the experiment he is summarizing in the graph, you pull a thin wire until it breaks, while measuring the stress on each end. The ...


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Wikipedia takes a swing at explaining this phenomenon. There it says that the velocity saturation is caused by scattering from optical phonons, with $$ \frac{1}{2}m*v_s^2 \approx \hbar \omega_o $$ where $m*$ is the effective mass of the carrier (depends on conduction band), $v_s$ is the drift velocity in saturation and $\omega_o$ is the angular frequency of ...



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