Sintering vitrification

In general, the presence of a hquid phase facilitates sintering. Vitrification is the rale for silicate ceramics where the reactions between the starting components form compounds melting at a rather low temperature, with the development of an abundant quantity of viscous liquid. Various technical ceramics, most metals and cermets are all sintered in the presence of a liquid phase. It is rate that sintering with liquid phase does not imply any chemical reactions, but in the simple case where these reactions do not have a marked influence, surface effects ate predominant. The main parameters are therefore i) quantity of liquid phase, ii) its viscosity, iii) its... 

T0088 Battelle Pacific Northwest National Laboratory, Terra-VIT Vitrification Technology T0151 Ceramic Immobilization of Radioactive Wastes—General T0169 Clemson University, Sintered Ceramic Stabilization T0178 Constructed Wetlands—General... 

The use of inorganic ion exchangers to solidify liquid radioactive waste followed by pressure sintering to produce a ceramic waste form appears to be a viable alternative to calcina-tion/vitrification processes. Both the process and waste form are relatively insensitive to changes in the composition of the waste feed. The stability of the ceramic waste form has been shown to be superior to vitrified wastes in leaching studies at elevated temperatures. Further studies on the effects of radiation and associated transmutation and the influence of temperature regimes associated with potential geologic repositories are needed for a more definitive comparison of crystalline and amorphous waste forms. 

Description of the process. The simplified process flow diagram is shown in Figure 16.12. The shredder waste (ASR, plastic and electronic waste as well as MSW) is fed in an IRFB, which operates in a reducing atmosphere and at temperatures as low as 500-600°C, allowing easy control of the process. The IRFB reactor separates the combustible portion and the dust from the inert and metallic particles of the fed waste the obtained mixture of metallic and inert particles is sent to a mechanical metal separation while fuel gas and carbonaceous particles are burnt in a cyclonic combustion chamber for energy production and fine ash vitrification. Metals such as aluminium, copper and iron can be recycled as valuable products from the bottom off-stream of the IRFB as they are neither oxidized nor sintered with... 

In this work the mode of occurrence of coal silicate minerals, and the flame induced vitrification and sodium initiated sintering mechanisms have been studied. The pulverized coal flame temperature is sufficiently high to vitrify the quartz particles. 

In viscous-flow sintering, some 20% of the initial solid melts at the sintering temperature and the densification of the material occurs by crystallisation of this phase (or vitrification if it becomes a glass) during cooling. Porcelains are prepared by this method. 

If the densification of liquid-phase sintering is achieved due to the viscous flow of a liquid that is able to fill up the pore spaces between the solid grains, it is called vitrification [112-114]. The driving force for vitrification is the reduction of solid-vapor interfacial energy, because the flow of the liquid covers the surfaces of the solid. Traditional clay-based ceramics are usually densified through vitrification. However, it is very unlikely to be observed in the processing of transparent ceramics, because the content of liquid phase must be controlled to a limited level. 

Yang HT, Yang GT, Yuan RZ (1998) Vitrification and devitrification of MgO during sintering of Si3N4-Mg0-Ce02 ceramics. Mater Chem Phys 57 178-181... 

If sufficient liquid is present (on the order of 25-30 vol%), rearrangement of the solid phase coupled with liquid flow can lead to a fully dense material. Such large volume fractions of liquid are commonly used in traditional, clay-based ceramics such as porcelains and in cemented carbides. In the traditional ceramics, the liquid phases are molten silicates that remain as a glassy phase after cooling, giving the fabricated materials a glassy appearance. The ceramics are referred to as vitrified, and the sintering process is referred to as vitrification. 

Ramming Material. Graded refractory aggregate, or a mixture of aggregates, with or without the addition of a plasticizer ramming materials are usually supplied at a consistency that requires a mechanical method of application chemical bond(s) may be incorporated. The rammed mass becomes strong and monolithic by vitrification or sintering in situ. 

Adachi T., Sakka S. Preparation of monolithic silica gel and glass by the sol-gel method using N,N -dimethylformamide. J. Mater. Sci. 1987a 22 4407-410 Adachi T., Sakka S., Okada M. Preparation of the silica gel monolith by the sol-gel method using N,N -dimethylformamide and the vitrification ofthe gel. J. Ceram. Soc. Jpn. 1987b 95 970-975 Adachi T., Sakka S. Sintering of silica gel derived from the alkoxysilane solution containing N,N -dimethylformamide. 1988 100 250-253... 

Figure 3.2. Top, vitrification the liquid phase is abundant enougfi to fill the interstices between the particles in the middle, liquid phase sintering the liquid is not suffieient to fill the interstiees bottom, solid phase sintering organization and shape of the partieles are extremely modified. This diagram does not show the grain coarsening in fact, the grains of the sintered material are appreeiably coarser than the starting particles [BRO 91 If...

The liquid dissolves the surface asperities and also dissolves the small particles. The granular rearrangement is limited to the hquid phase sintering itself, but it can be enough to allow complete densification if the hquid phase is in sufficient quantity, as is the case in the vitrification of sihcate ceramics ... 

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