Free sintering

For many applications it is found that the technique of free sintering is quite satisfactory. This simply involves heating the preform in an oven at about 380°C for a time of 90 minutes plus a further 60 minutes for every 0.25 in (0.65 cm) thickness. For example a sample 0.5 in (1.25 cm) thick will require sintering for 3.5 hours. The ovens should be ventilated to the open air to prevent toxic decomposition products accumulating in the working area. 

Free shear flows, 77 757-760 Free sintering, 73 300 Free spectral range (FSR), 74 671-672 Free surface vaporization, 24 724-725 Free-vibration instruments, 27 745 Free-volume coefficient of self-diffusion, 23 102... 

For free sintering, the diffusion potential is proportional to curvature A s/A s will scale as 1/A. The ratio A/s/A/s also scales as 1/A. 

Free-sintering of the perform in an oven at about 380°C is also satisfactory. The sintering period depends on the thickness of the sample. For example, a 0.5-in. (1.25-cm)-thick sample will need sintering for 3.5 h. Granular polymers may also be extruded, though at very low rates (2.5-16 cm/min), by screw and ram extruders. The extrudates are reasonably free of voids. 

Hu CL, Rahaman MN (1994) Dense AI2O3/Z1O2 particulate composites by free sintering of coated powders. J Am Ceram Soc 77 815-819... 

PABM free-sintering is achieved at 15,000 psi in a 15 sec. cold-mold cycle time. 

KINEL 5505 KINEL 5508 KINEL KINEL 5511 5517 free sintered KINEL 5518 ... 

Figures 12 and 13 show the percent retention of flexural strengths and moduli for KINELs 5505, 5508, and 5517 (ccmipression molded and free-sintered).

This equation correlates the densification rate of a constrained film, Sz, with the densification rate of a free sintered body, e/, via the viscous Poisson s ratio, Vp. As the grain size is comparable to the thickness of a thin film, however,... 

Se atmosphere at 550 °C in a quartz box for 1 hour. Crack and defect free sintered films formed from surfactant free CZTS can be promising option for low cost solar cells. 

In Eqn. 3 the first term represents the shear deformation, the second term represents the volume change due to the mean stress and the third term represents the volume change due to the sintering potential. A uniform compact of any shape shrinks according to the third term if it is unconstrained and not subject to any external force. Therefore this term as a whole can be determined from free sintering experiment using uniform samples according to that... 

Next we show the sintering of a more bulky object of non-uniform density considered by Kiani et al. [17] which is shown in Fig. 5. The dumb-bell shaped powder is free sintered. To create an extreme case of non-uniform sintering, an initial relative density of D=0.4 is assigned to the top and the bottom parts of the compact and D=0.7 to the middle part. Perfect bounding is assumed for the interfaces throughout the sintering process. 

It is useful to show a case in which the reduced method does not work at all. Such cases have been hard to find for free sintering. Huang and Pan [18] devised a heavily constrained case which is shown in Fig. 11. A rectangular powder compact is placed between two rigid bodies with perfectly bounded interfaces. The plane strain condition is assumed (i.e. no shrinkage is allowed in the direction normal to the paper). The material is so heavily constrained that only the middle parts of its left and right surfaces can shrink towards each other. 

Free-sintered articles do not have the same dimensions as the mold cavity because they shrink at right angles to the direction of the preform pressure and grow in the direction of the applied pressure. 

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