MoSi2 and MoSi2 - Based Materials as Structural Ceramics

MoSi2, because of its mixed covalent-metallic atomic bonding, is a borderline intermetallic compound which has many attractive properties that can be exploited in high temperature structural applications . Foremost amongst these is its stability in corrosive atmospheres up to about 1600 C . However, there are a few undesirable prooperties that need to be addressed before it can become a viable material in high temperature applications . Since MoSi2 forms thermodynamically stable composites with both metals and ceramics, many reinforcing materials are incorporated into the matrix to improve the fracture toughness and creep properties . The low temperature oxidation can be controlled by compaction to high density . Mo(Al, Si)2, a related ceramic, which also has good high temperature properties besides having better low temperature toughness . However, presence of Mo5Si3 phase, which has low oxidation resistance, needs to be controlled . This is being achieved by synthesizing Mo(Al, Si)2 at as low a temperature as 1300 C. This article summarizes important attempts that are made in improving the properties of MoSi2 by reinforcement with other materials

Effect of Double Reinforcements on Elevated-Temperature Strength and Toughness of Molybdenum Disilicide

Flexural strength and fracture toughness of molybdenum disilicide and its composites with 10 wt% TiB2 and 10 wt% TiB2 � 10 wt% SiC, synthesized by the hot-pressing technique, were evaluated as a function of temperature, ranging from ambient temperature to 1600°C. Results show that the composites have higher strength and slightly lower toughness as compared with monolithic MoSi2 at room temperature. At high temperatures, the composites exhibit higher strength as well as higher toughness vis-a`-vis monolithic MoSi2. Among the composites, the double reinforcement of SiC and TiB2 was found to be more effective in improving the mechanical properties. A transition from brittle to ductile behavior was observed at temperatures greater than 1300°C for all materials tested. The high-temperature mechanical behavior was found to be significantly influenced by the flow of an intergranular glassy phase and the attendant cavity nucleation and growth along the grain boundaries. Micromechanisms responsible for the ambient as well as the elevated-temperature property improvement in composites are discussed with the aid of fractography

Sodium Zirconium Phosphate Based low Tiermal Expansion Materials : A Review

The new family of low thermal expansion materials based zirconium phosphate - NaZr P 0 (NZP) have wide applica- tions in various fields of science 2 snd12 technology. In addition to having the low thermal expansion behaviour they possess good thermal shock and corrosion resistance. R e structural formula for the NZP materials is [M 1 ' ][M quot; ][A2 ][B]01 where M' and M ' are interstitial sites occupied 'by Na or sulstitJtion ions of alkali or alkaline earths or rare earth ions, A and B are lattice sites occupied by Zr and P or other substitution ions like Si, Ti etc. They have a skeletal frameko-rk structure of [Zr P 0 } with rhombo- hedral symmetry of RR space group. The Na+ idns occupy the octa- hedral site of large interstitial space formed by the Zr 2P 0 2 network. This crystal structure gives the flexibility of the substit ution of various ions in the lattice sites. It is possible to get near zero thermal expansion materials and zero thermal expansion anisotropy for wide range of temperatures by tailoring the compo- sitign5, Some13; the NZP materials have good thermal and chemical stability upto 1500 C.13

Synthesis and Properties of Molybdenum Disilicide Based Composites

Molybdenum Disilicide (MoSi } and its composites have attracted considerable interest because of their unique combination of properties. The processing of MoSi 2 composites by the reinforcement of different elements such as Al, Ta, Nb, W. Mo, A1 2 0 , SiC, Si N , ZrO2 and mullite has been reviewed. The addition of c mpounds have been achieved by different methods such as powder metallurgy, soW state displacement, plasma spraying, exothermal dispersion (XD ) and self propagating high temperature synthesis (SIBS). The influence of these additions on the microstructural and mechanical properties have been discussed. The fracture toughness of MoSi 2 i s considerably improved by the ductile and brittle phase reinforcements. An improvement in the creep resistance is achieved by the addition of SiC

Thermal expansion behaviour of barium and strontium zirconium phosphates

Ba1.5-xSrxZr4P5SiO24 compounds with x = 0, 0.25, 0.5, 0.75, 1.0, 1.25 and 1.5, belonging to the low thermal expansion NZP family were synthesized by the solid state reaction method. The XRD pattern could be completely indexed with respect to R (3) over bar space group indicating the ordering of vacancy at the divalent cation octahedral sites. The microstructure and bulk thermal expansion coefficient from room temperature to 800 degreesC of the sintered samples have been studied. All the samples show very low coefficient of thermal expansion (CTE), with x = 0 samples showing negative expansion. A small substitution of strontium in the pure barium compound changes the sign of CTE, Similarly, x = 1.5 sample (pure strontium) shows a positive CTE and a small substitution of barium changes its sign, X = 1.0 and 1.25 samples have almost constant CTE over the entire temperature range. The low thermal expansion of these samples can be attributed to the ordering of the ions in the crystal structure of these materials

Strengthening Tribal and University Relations on Sugar Island and Beyond

This project was an extension of efforts initiated by the Sault Ste Marie Tribe of Chippewa Indians(Sault Tribe) and in collaboration with the University of Michigan (University) with beginning discussions provided in a historical document published in 2019 by Knute Nadelhoffer (University of Michigan), Christine McPherson (Executive Director, Sault Tribe), Eric Clark (Sault Tribe Wildlife Program), Nicholas Reo (Sault Tribe Member), and Dr. Robin Michigiizhigookwe Clark (Sault Tribe Natural Resources Department and Sault Tribe Member). In 2022, the project was proposed as a master’s capstone project for the University of Michigan School for Environment and Sustainability (SEAS) and upon request from the Sault Tribe, the historical document was updated in June of 2023 (Nadelhoffer et al, 2019). For the revised historical document see (Appendix B). This chapter outlines the historical and current ecological conditions of the Chase Osborn Preserve and emphasizes the relationship and inseparable ties of the Sault Tribe and Sugar Island. Components of this report and its contents were conducted upon request by the Tribe in an attempt to expand capacity and efforts towards tribal self-determination, reciprocity, and continued relationship building with the University.Master of Science (MS)School for Environment and SustainabilityUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/193030/1/Sugar Island Project.pd

Role of in situ generated tribofilm on the tribological characteristics of monolith and TiB2 reinforced MoSi2 intermetallic

Wear experiments performed on steel disc with increasing load for monolithic MoSi2 of different densities and its composite with TiB2 showed three distinct wear regimes. The specimens exhibited severe wear rate below the lower and above the upper critical loads and mild wear in between the two critical loads. The increase in density of the monolith and the reinforcement of TiB2 were effective in reducing the coefficient of friction and the specific wear rate. The wear experiments have been performed in these three regimes (15, 50 and 75 N). The tribofilm formed on the pin surface was found to contain both pin and disc materials. The temperature of the pins during the sliding against EN-24 disc was calculated using one dimensional heat transfer equation at different loads for each composition. The composite experiences lower temperatures compared to the monoliths. (C) 2002 Elsevier Science B.V. All rights reserved

Performance of monolithic and TiB2 reinforced MoSi2 in dry sliding contact with steel

MoSi2 and its composite with TiB2 (10 and 20 wt.%) particulates were synthesized by the hot pressing technique. Dry sliding wear experiments were done on these samples by pin-on-disc method on an EN-24 steel disc. It was observed that the densification and the reinforcement of the matrix are beneficial in reducing the friction and wear Of MoSi2. The tribofilm that was formed during sliding contained both the disc and the pin material. (C) 2002 Elsevier Science B.V. All rights reserved