Activation Energy (delta G)

Activation Energy (delta G)

  2:33 PM    yallascience

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The diagram shows a system with a metastable state (a), an unstable state (b), and a stable state (c). Energy is required to cause the system to go between these states. The activation energy (DG), for the a-> c process, is (Gb - Ga), that for the c -> a process is (Gb - Gc).

if the system is in contact with a thermal reservoir at a temperature T K, the probability of state (a) acquiring the required activation energy from thermal fluctuations in the system is given by: 
P = exp(- DG/kT) , where k is Boltzmann's constant


Source:
1-Freefullpdf for Scientific Publications
2-Barrett, Nix, and Tetelman,"The Principles of Engineering Materials," Prentice Hall (1973)

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Acousto-Optical

Acousto-Optical

  2:21 PM    yallascience

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Acousto-Optical

An acousto-optical material is one for which the refractive index can be changed by the density fluctuations (strain) produced by an acoustic wave. 

The change in the dielectric constant, e_l, is related to the mechanical strain, e, through the photoelastic coefficient, p, such that: 

D(1/e_l ) = pe.

If a longitudinal acoustic wave is sent through an acousto-optically active solid, it establishes a density grating in the material that will diffract a light beam in the manner shown below. The diffracted beam will not be present if there is no acoustic signal (only the transmitted beam will remain) and the device can, therefore, act as an optical switch. 

the table shows some parameters of optoacoustic substances.

Source:
1-Freefullpdf for Scientific Publications
2-Solymar and Walsh, "Lectures on the Electrical Properties of Materials," Oxford Science Publications (1988)

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Alloy Steels | 4340 Steel

Alloy Steels | 4340 Steel

  11:53 AM    yallascience

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Alloy Steels 

43xx sheets of steel are low alloy steels containing Fe, Ni, Cr, and Mo. 

Alloy Steels | 4340 Steel composition

Fe - 0.4 %C, 0.7 %Mn, 0.2% Si, 1.8%Ni, 0.8% Cr, 0.25% Mo. The alloy may not contain more than 0.04% of either 

S or P. The material has a tensile strength between 980 and 1960 MPa, the yield stress of 895 to 1570 MPa, and an elongation to fracture between 21 and 11%.

More scientific publications about Alloy Steels | 4340 Steel

Source:
1-Freefullpdf for Scientific Publications
2-princeton.edu

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Aluminum Alloys, 2017-T3, 2024-T2, -T3, -T4

Aluminum Alloys, 2017-T3, 2024-T2, -T3, -T4

  11:31 AM    yallascience

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Aluminum Alloy, 2017-T3

Aluminum alloy has copper as its major alloying element and is one of the wrought alloys. 

Aluminum Alloy 2017-T3 contains 

4.0% Cu, 0.7% Mn, 0.6% Mg, 0.5% Si, with the balance being aluminum. 

The T3 heat treatment requires furnace solution heat treatment followed by a quench to room temperature and cold work.

The Aluminum Alloy has an ultimate tensile strength of about 300 MPa, yield stress in the tension of 165 MPa, and elongation in 50 mm of 27%.

 Aluminum Alloys, 2024-T2, -T3, -T4 

The 2000 series of aluminum alloys have copper as the major alloying element, and the Tn designation is associated with the heat treatment. 

Aluminum Alloy 2024 contains 

The nominal composition is 4.4%Cu, 0.6% Mn, 1.5% Mg, in an aluminum matrix. T2 signifies an alloy that has been cooled from the single-phase condition to room temperature, cold worked, and naturally aged; T3 is an alloy of the same composition that has been furnace solution heat-treated, quenched to room temperature, and cold-worked; for the T4 alloy furnace solution heat treatment is followed by quenching and natural aging.

For 2024-T3: UTS = 485 MPa, Tensile yield stress = 345MPa, 

Elongation in 50 mm = 18%

For 2024-T4: UTS = 470 MPa, Tensile yield stress = 325 MPa, 

Elongation in 50 mm = 20%

More scientific publications about Aluminum Alloy

Source:
1-Freefullpdf for Scientific Publications
2-princeton.edu

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