Heating-rate-controlled sintering

For any real system where the dihedral angle 0 is smaller than 180°, there exists a critical size of isolated pores relative to grain size that cannot shrink by pressureless sintering (atmospheric pressure sintering). This result can be explained in terms of either the curvature of the isolated pore or the total interfacial energy. Is there a fimdamental difference between the two explanations Discuss. 

What does a high dihedral angle mean in the initial and final stage of sintering of real powder compacts  

Derive equations of pore migration by (a) gas diffusion and (b) evaporation/condensation. 

For pore migration (movement) by gas diffusion, what is the effect of pore size on pore migration velocity The gas pressure in the pore is assumed to be in equilibrium with the pore capillary pressure. 

When a pore at a grain boundary moves by the evaporation/condensation mechanism, the pore mobility is inversely proportional to the square of the pore radius. What is the velocity ratio of pores with a radius of r and a radius of r2 in two different samples with the same porosity Assume that the driving force of grain growth is the same for the two samples. 

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Modification of the thermal cycle provides opportunities to improve the sinterability of powder compacts. Typical examples are fast firing and heating-rate-controlled sintering. 

Figure 21 Rate controlled sintering of a ceramic under air. The rate of temperature rise is controlled by the rate of change in length over pre-set temperature ranges with a limiting maximum heating rate 2°C min ...

Ovens. PTFE is an excellent thermal insulator. Its thermal conductivity (0.25 W/m K), roughly 2,000 times less than copper, impacts the rate of sintering of a preform. The most common way of delivering heat to a preform is by circulation of hot air. Ideally, the sintering oven is electrically heated for use up to 425 °C and should be equipped with override controllers to prevent overheating. 

The size of sinter, pellet, coke, lump coal was 10-12.5mm for simplifying the process of the experiments. The weights of sinter, pellet and coke or lump coal were 188.5g, 101.5g, lOg, respectively. AH the materials were manually mixed. The heating rate and gas composition were selected by simulating the actual conditions in the blast furnace as given in Table IV. The gas flow was precisely controlled by volume flow controllers with a total gas flow rate of 10.0 NL-min. The load on the burden in the experimental process was Ikg-cm. ... 

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