Coarse‐Grained Refractory Composite Castables Based on Alumina and Niobium

Abstract

Niobium‐alumina composite aggregates with 60 vol% metal content and with particle sizes up to 3150 μm are produced using castable technology followed by sintering, and a crushing and sieving process. X‐Ray diffraction (XRD) analysis reveals phase separation during crushing as the niobium:corundum volume ratios is between 37:57 and 64:31 among the 4 produced aggregate classes 0–45, 45–500, 500–1000, and 1000–3150 μm. The synthesized aggregates are used to produce coarse‐grained refractory composites in a second casting and sintering step. The fine‐ and coarse‐grained material shows porosities between 32% and 36% with a determined cold modulus of rupture of 20 and 12 MPa, and E‐moduli of 37 and 46 GPa, respectively. The synthesized fine‐grained composites reached true strain values between 0.08 at 1100 °C and 0.18 at 1500 °C and the coarse‐grained ones values between 0.02 and 0.09. The electrical conductivity for the fine‐grained and the coarse‐grained material is 448±66 and 111±25 S cm−1, respectively.

Characterization of Sintered Niobium–Alumina Refractory Composite Granules Synthesized by Castable Technology

“…As shown by the results of XRD measurements, was present in all aggregates with ≈3–4.5 vol%. In our accompanying work, [ 15 ] the synthesized aggregates were used for producing coarse‐grained compounds. After the corresponding second sintering of the synthesized composite, the niobium carbide content increased to 5.5 vol% in the synthesized coarse‐grained material.…”

“…Heat treatment was done in a graphite tool‐based furnace under purified argon atmosphere at a temperature of 1600 °C for 2 h. The sintered material was then crushed and sieved into aggregate classes 0–45, 45–500, 500–1000, and 1000–3150 μm. Details of the synthesis and the properties of the raw materials are given in the study by Zienert et al [ 15 ]…”

“…Details of the synthesis and the properties of the raw materials are given in the study by Zienert et al [15] In the current work, three batches of aggregates were produced and studied, which are denoted here as batch 01, 02, and 03; the corresponding castable recipes are listed in Table 1. It should be mentioned that the batches 01 and 03 were denoted as 'fine-w43' and 'fine-w36' in the study by Zienert et al, [15] respectively. Batch 02 was synthesized with the same technological parameters as batch 01, and only the room temperature in our laboratory might be a few degrees higher than in case of mixing the castables of batch 01.…”

A New Approach for Sintering Simulation of Irregularly Shaped Powder Particles—Part II: Statistical Powder Modeling

“…The powders analyzed in this work were the same as in Zienert et al [41,42] The powders in question consist of presintered material that was crushed and sieved. Therefore, the regarded particles are aggregates and the different sieve classes are also called aggregate classes.…”

Nanoscale Oxide Formation at α‐Al2O3–Nb Interfaces

“…A novel approach in the field is the development of coarse-grained (particle sizes of up to a few mm) ceramic-metal composites [6,[11][12][13] to improve creep and thermal shock resistance compared to fine-grained composites. Heat treatments during manufacturing such as sintering can cause reactions of the involved phases with each other or with the environment, which will inevitably affect the properties of the composite.…”