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In a porous solid with open porosity e and large pore size compared to the mean free path of molecules, the diffusion coefficient D is inversely proportional to the porosity e.
True
The sinuosity coefficient of pores, s, is defined as the direct route traveled by a gas molecule in passing from one point to another inside the porous solid, distant one unit of length.
False
When the porous solid is a collection of spheres, the sinuosity coefficient is equal to r.
False
Diffusion coefficient D in a porous solid is always greater than the coefficient D1 outside it.
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In the transformation of a non-porous particle by a fluid, diffusion occurs through the boundary layer that surrounds the solid.
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A soluble or volatile product formed during a reaction allows diffusion through the solid itself.
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The phenomena of reaction and diffusion in porous solids can be easily observed due to the movement of the interface.
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The kinetic expression for reactions in dense solids is the same as that for reactions in porous solids.
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In gas-solid reactions with porous solids, the flux of reactant gas is given by Fick's first law.
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The change of flux in a gas-solid reaction results from the accumulation of gas in the pores of the solid.
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Assuming D is constant, the equation for the flow of gas in a gas-solid reaction is $-F rac{dc}{dx} = D rac{ ext{d}^2(C-C_0)}{ ext{d}z ext{d}y}$.
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The reaction velocity in gas-solid reactions is dependent on the volume of the porous solid.
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The transformation of a porous particle by a gas is a simple and well-defined process.
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In the case of scrap, there is no solution but only a question of heat absorption and diffusion.
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The solution of a piece of refractory metal in liquid steel is a second-order reaction.
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Reactions at the interface and diffusion through the boundary layer in metallurgical processes act as two resistances in parallel.
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When diffusion across the solid is very rapid, (4.26) and (4.44) describe the transformation of a particle in a chemical regime.
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In gas-solid reactions, chemical reactions and diffusion are separated in time.
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