Novel synergy of Si-rich minerals and reactive MgO for stabilisation/solidification of contaminated sediment

Mechanical and fracture properties of concrete reinforced with recycled and industrial steel fibers using Digital Image Correlation technique and X-ray micro computed tomography

Preparation and properties of porous mullite ceramics with high-closed porosity and high strength from fly ash via reaction synthesis process

Accelerating advancements in technological systems have demonstrated a need for alloys with drastically improved thermomechanical and chemical properties, called superalloys. Ceramic molds are typically used in near-net shape investment casting processes of superalloy components due to their chemical inertness and high-temperature capabilities. Ceramic molds, however, often suffer from shortcomings in vital properties including flexural strength, thermal shock resistance, permeability, dimensional stability, corrosion resistance, and leachability, which have restricted their ability to adequately process modern alloy castings. This study analyses these limitations and illustrates how to address them, particularly regarding ceramic mold and slurry design, processing of shells and cores, material selection, and testing and characterization. By utilizing advanced processing methods including additive manufacturing and gel-casting, more dimensionally accurate and preferentially built molds can be formed. Additionally, by varying the mold composition to achieve more chemically inert structures, reactions with the mold can be mitigated to reduce chemically induced defects.

An overview of ceramic molds for investment casting of nickel superalloys

Mechanism of microbial dissolution and oxidation of antimony in stibnite under ambient conditions.

This study presents a new lightweight periclase-magnesium alumina spinel castable (LPSC) for the working lining of steel ladles using porous periclase-spinel aggregates to replace conventional dense magnesia aggregates. The porous periclase-spinel aggregates were produced by an in-situ decomposition technique resulting in an apparent porosity of 23.3% and a median pore size of 5.66 μm. Scanning electron microscopy revealed a better porous aggregate/matrix interface bonding in the LPSC, which significantly improved its strength and thermal shock resistance. Additionally, the higher amount of micropores of the porous aggregates in the LPSC absorbed more penetrated slag from the matrix, which enhanced the slag resistance. Thus, compared with conventional castables, the LPSC had a lower bulk density of 9.2–10.8% and a lower thermal conductivity of 18.8% (1000 °C) while at the same time a higher strength, thermal shock resistance and slag resistance was achieved.

Energy efficient lightweight periclase-magnesium alumina spinel castables containing porous aggregates for the working lining of steel ladles

Fabrication of mullite-corundum foamed ceramics for thermal insulation and effect of micro-pore-foaming agent on their properties

A comparative study on the microstructures and mechanical properties of a dense and a lightweight magnesia refractories

In this paper, the formation of the fracture process zone (FPZ) of industrially produced magnesia spinel and magnesia refractories was analysed using digital image correlation (DIC). Compared to pure magnesia materials, the magnesia spinel materials exhibited a higher amount of microcracks, causing a larger FPZ. A critical displacement, where the cohesive stress between the crack faces decreases to zero, is determined by analysing the development of the localized zone. Critical displacement determined from the changes of the FPZ width and length is used to determine the onset of macro-cracking and locate the crack tip. The development of the fracture process zone for a magnesia spinel initiates before reaching the maximum load, and the onset of the macro-crack is in the post-peak region. The FPZ size increases until the formation of a macro-crack takes place, but decreases afterwards. For the magnesia refractory, no pronounced FPZ could be detected.

Observation and quantification of the fracture process zone for two magnesia refractories with different brittleness

Refractories with reduced brittleness show a pronounced deviation from linear elastic behaviour and an enhanced thermal shock resistance. This paper aims to study the influence of microstructure on the fracture behaviour of magnesia refractories. The wedge splitting test(WST), which enables stable crack propagation for quasi-brittle materials, was used to identify the fracture behaviour and evaluate the energy dissipation. The evaluation of the crack lengths of the magnesia and magnesia spinel materials during the entire cyclic WST is based on the localized strain evaluated using the digital image correlation (DIC). A significant fracture process zone develops in the magnesia spinel material. The relationship between the dissipated energy and the actual crack length, which was used to characterize the crack growth resistance, was determined. The refractory materials that showed reduced brittleness consume a small amount of energy for fracture initiation but a large amount of energy for further crack propagation.

Yajie Dai

Papers

Energy efficient lightweight periclase-magnesium alumina spinel castables containing porous aggregates for the working lining of steel ladles

Fabrication of mullite-corundum foamed ceramics for thermal insulation and effect of micro-pore-foaming agent on their properties

A comparative study on the microstructures and mechanical properties of a dense and a lightweight magnesia refractories

Observation and quantification of the fracture process zone for two magnesia refractories with different brittleness

Determination of the fracture behaviour of MgO-refractories using multi-cycle wedge splitting test and digital image correlation