Sizing Soak time

Another way to examine the effeet of earbon partiele size on kineties is to look at the bleed emissions from a earbon eanister [20,35]. Bleed emissions are those emissions that oecur prior to break through. They are the result of the diffusion of gasoline vapor components that ean develop during extended soak times between purge and adsorption events. 

Heat Treatment Temperature and Soak Time. A study of Mochida and Marsh (53) indicates, unlike classical kinetics, that time and temperature for mesophase formation are not interdependent. The reason for this is the controlling influence of viscosity (not found for reactions in the gas or solution phase). Maximum size of optical texture and coalescence results if the mesophase is formed under conditions which provide a minimum viscosity as quickly as possible. Probably, rate controlling processes for mesophase growth are not the dehydrogenated polymerization reactions. Therefore, the attainment, relatively quickly, of temperature of 400°C has provided the necessary size of molecule and consequently the resultant mesophase sbbws minimum viscosity because it is at a high temperature ( 400°C). Mesophase formed at lower (relative) temperatures can have a higher viscosity and coalescence behaviour can be restricted. 

The dependence of the amount of H2SO4 that has reacted with 10 g of 3BS or 4BS paste as a function of soaking time is shown in Fig. 3.10. 4BS pastes react with H2SO4 much more slowly than do 3BS pastes. The smaller surface area and the greater thickness of the crystals in 4BS pastes cause the rate of the reaction of sulfation to slow down within the first 30 min of soaking [11-16]. The structure of the lead sulfate layer that covers the 4BS crystals has been examined [11-14]. First, polyhedral particles with an average size of up to 2 pm are formed on the surface of... 

This characteristic pattern is termed the optical texture of the coke Optical texture increases in size with increasing fluidity (decreasing plasticity) of the mesophase Mesophase viscosity can be affected by parameters of carbonization such as heating rate, HTT and soak time but the single most important factor is chemical reactivity (13) If reactivities are too high, early polymerisation leads to the formation of isotropic carbon because of randomly aligned interactions Low reactivities give rise to a low viscosity mesophase which flows and coalesces easily Hence the size and type of optical texture is predominantly a function of the parent material carbonized and may be used to characterise the coke It is therefore necessary to define precisely the different types of optical texture seen in cokes A standard... 

The five resultant pitch cokes and the coals listed above (numbers 5, 6 and 7) were ground to sieve sizes 600 ym - 1 17 mm Blends of coal and pitch coke (9 1 by weight) and the single coals were carbonized in a horizontal electrical tube furnace under N2 to 1250 K (977°C) at 3 K min" with 0 5 h soak time ... 

The 4BS paste reacts with H2SO4 much more slowly than its 3BS counterpart, because of the smaller surface area and the bigger size of the crystals in the 4BS paste. Therefore, the industrial approach to soaking 3BS and 4BS pastes should be different. 4BS pastes require sufficient soaking time and temperature to reach adequate growth of the PbS04 content. In contrast, 3BS pastes should be soaked at lower temperature and for shorter period of time. 

A perfect heating situation would have each load piece completely surrounded (360 degrees in all planes) by equally high heat transfer rates to all its surfaces. That is often impossible or impractical because of (a) load shape and size, (b) handling and support problems, and (c) lack of appropriate piers, posts, or kiln furniture. The resultant uneven heating necessitates a long soak time to let the temperatures even out within the load, with possible increased fuel costs. Long soak times may cause excessive surface oxidation, and they surely cause lowered furnace productivity. 

It is established that the rank and chemistry of the parent coal strongly influence the optical textures of cokes. Several studies show that the development of anisotropy (size, shape, and intensity) during carbonization varies mainly with (1) coal rank (2) petrographic composition of the coals (3) plasticity of the parent coal (4) carbonization conditions such as rate of heating, soak time, and gas overpressure as well as (5) the nature of additives used in the coal blends. 

Powders Aluminum nitride is customarily synthesized by the carbothermal reduction of a mixture of aluminum oxide and carbon black, under a nitrogen pressure of 0.2-0.3MPa at 1800-1900 °G, and with a variable isothermal soaking time. The best results are obtained at 1800 °G and with a nitrogen pressure of 0.3 MPa, from a charge of stoichiometric composition. The resultant powders, with an AIN content up to 99 mass%, consist of isometric grains with a narrow size range of between 2 and 6(xm (Makarenko and Mahajan, 2002). 

Gonzdlez et al. (1997) prepared three different chars from olive stones, 1-1.5 mm particle size, carbonized in three ways. (I) slow carbonization in a vertical furnace, heating rate 5 °C min , nitrogen flow rate of 1275 cm min , HTT of 850°C, soak time of 1 h, giving a char yield of 26.9 wt%. (II) flash carbonization in a vertical furnace preheated to 850 °C, nitrogen flow rate of 1275 cm min", HTT of 850 °C, soak time of 1 h, giving a char yield of... 

BiFeOs (BFO) Hydrothermal (HTMW) Microwave furnace with frequency of 2.45 GHz and variable power up to 300 W Different soaking times 5 min, 30 min. and 1 h at the temperature of180°C Uniform nanoparticles with very few structural defects, homogenous size distribution, and orthorhombic structure were observed... 

Figure 4.13a shows the effect of the soaking time on the O2 permeance. A soak time as short as 10 min gives the permeance smaller than PAN membrane of zero soak time since the carbonization is not completed. Partially carbonized membranes possess impermeable bulk stmcture and the formation of the porous stracture is yet incomplete. The gas transport is difficult to occur either by solution diffusion or by sieving mechanism. The maximum permeance is achieved at 120 min. A maximum in the selectivity is also achieved at this soak time. At a longer soak time, the pore size is reduced and the permeance starts to decrease. 

The thermal soak time can be different depending on the final pyrolysis temperature [24]. This parameter may be used to fine-tune the transport properties of a ear-bon membrane using a particular final pyrolysis temperature [91], Previous studies showed [41,87, 89, 91,92] that increments in thermal soak time would inerease the selectivity of carbon membranes. It is beheved that only mierostmctural rearrangement occurs during the thermal soak time, thus affeeting the pore size distribution and average porosity of carbon membranes [34]. 

W. Khongwong, M. hnai, K. Yoshida, T. Yano, Influence of raw powder size, reaction temperature, and soaking time on synthesis of SiC/Si02 coaxial nanowires via thermal evaporation, J. Ceram. Soc. Jpn. 117 (2009) 439-444. 

Within the scope of the various test methods available, the change in dimensions is reported with corresponding test duration. Firing temperature and soak times at temperature may vary depending on the material and its operating conditions. Across the various methods available, the test piece size can be of a standard brick or rectangular prisms or cylinders. 

---