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Sintering and Microstructure Development
Published in Mohamed N. Rahaman, Ceramic Processing, 2017
The distribution of the liquid phase depends on the dihedral angle and the relative amount of liquid phase, as well as on the porosity. If sufficient liquid is present, initial rearrangement leads to a fully dense material. The relative amount of liquid and solid at this condition depends on the rearranged density of the particulate solid. For example, if the solid could rearrange to approach a dense random packing, then ~35 vol% of liquid would fill all the void space without further densification by other mechanisms. Such large volume fractions of liquid are often used in porcelains, and in cemented carbides. In the case of clayware and porcelains, the liquid phases are molten silicates which remain as glass after cooling [83]. This gives the ceramic ware a glassy appearance, and such ceramics are referred to as vitrified.
Infrastructure and the Need for Condition Assessment
Published in Justin Starr, Water and Wastewater Pipeline Assessment Technologies, 2021
While wooden sewers have been all but phased out of modern construction practices, vitrified clay is a material that has been used in sewers from ancient times to the modern era. Vitrified clay is formed by firing clay tubes in a furnace at temperatures exceeding 2000˚C, causing the outer layers to transform into an amorphous glassy material that is watertight. Sometimes further glaze is applied to increase the impermeability to water. The process of making vitrified clay dates back thousands of years, and examples of these types of pipes have been found in Roman and Greek sewer systems.
Liquid-Phase Sintering
Published in M. N. Rahaman, Ceramic Processing and Sintering, 2017
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.
Feasibility study on the use of thiosulfate to remediate mercury-contaminated soil
Published in Environmental Technology, 2019
Chao Han, Hui Wang, Feng Xie, Wei Wang, Ting’an Zhang, David Dreisinger
Various detoxification/remediation technologies for disposing of mercury-contaminated soils have therefore been developed. In the amalgamation process, Hg0 dissolves in other metallic ions, such as copper, to form solid solutions or semi-solid alloy ‘amalgam’. As this process is reversible, mercury can be released from these alloys by heating [16]. The elemental mercury can also react with elemental sulfur to form mercury sulfide (HgS), which is kinetically stable at room temperature [17]. The processes using HgS or HgSe for mercury stabilization are commonly used in HgO wastes and those solid wastes containing a large amount of mercury [18–19]. In adsorption treatments, adsorbents, mainly activated carbons, are used to stabilize Hg0 [20]. Thermal desorption, retorting and roasting, which all employ heating (at low or high temperatures), have been commonly used to treat mercury-contaminated soil, sediments and other solid wastes [21–24]. For the stabilization/solidification processes, the vitrification process is a high-temperature treatment technology designed to immobilize contaminants by incorporating them into vitrified end product. The research of Huang et al. showed that decontamination at higher temperature (>673 K) can lower Hg content to the regulation level [25]. Stabilization or immobilization can also be obtained through the formation of stable compounds or water non-soluble compounds which can be classified depending on the encasing materials, such as Portland cement, sulfur polymer cement, sulfide and phosphate binders, cement kiln dust, polyester resins and polysilioxane compounds [26–29]. Nowadays, it is difficult to judge which is the best technology to be applied, depending on the chemical and physical properties of the wastes to be treated.