Ultrahigh Temperature Flash Sintering of Binder-Less Tungsten Carbide within 6 s

We report on an ultrarapid (6 s) consolidation of binder-less WC using a novel Ultrahigh temperature Flash Sintering (UFS) approach. The UFS technique bridges the gap between electric resistance sintering (≪1 s) and flash spark plasma sintering (20–60 s). Compared to the well-established spark plasma sintering, the proposed approach results in improved energy efficiency with massive energy and time savings while maintaining a comparable relative density (94.6%) and Vickers hardness of 2124 HV. The novelty of this work relies on (i) multiple steps current discharge profile to suit the rapid change of electrical conductivity experienced by the sintering powder, (ii) upgraded low thermal inertia CFC dies and (iii) ultra-high consolidation temperature approaching 2750 °C. Compared to SPS process, the UFS process is highly energy efficient (≈200 times faster and it consumes ≈95% less energy) and it holds the promise of energy efficient and ultrafast consolidation of several conductive refractory compounds.

Supplemental Material: Ultrahigh-temperature granulite-facies metamorphism and exhumation of deep crust in a migmatite dome during late- to post-orogenic collapse and extension in the central Adirondack Highlands (New York, USA)

<div>Text S1: Supplemental text. Figure S1: Cathodoluminescence images for all analyzed zircon grains. Figure S2: REE spider plots for zircon. Figure S3: Tukey honestly significant difference (HSD) for the timing of anatexis. Table S1: Cathodoluminescence images for all analyzed zircon grains. Table S2. Grossular content of garnet used to calculate the 95% confidence intervals for isopleth modeling in Figure 13. <br></div>

Ultrahigh-temperature granulite-facies metamorphism and exhumation of deep crust in a migmatite dome during late- to post- orogenic collapse and extension in the central Adirondack Highlands (New York, USA)

This study combines field observations, mineral and whole-rock geochemistry, phase equilibrium modeling, and U-Pb sensitive high-resolution ion microprobe (SHRIMP) zircon geochronology to investigate sillimanite-bearing felsic migmatites exposed on Ledge Mountain in the central Adirondack Highlands (New York, USA), part of an extensive belt of mid-crustal rocks comprising the hinterland of the Mesoproterozoic Grenville orogen. Phase equilibrium modeling suggests minimum peak metamorphic conditions of 960–1025 °C and 11–12.5 kbar during the Ottawan orogeny—significantly higher pressure-temperature conditions than previously determined—followed by a period of near-isothermal decompression, then isobaric cooling. Petrography reveals abundant melt-related microstructures, and pseudosection models show the presence of at least ~15%–30% melt during buoyancy-driven exhumation and decompression. New zircon data document late Ottawan (re)crystallization at ca. 1047 ± 5 to 1035 ± 2 Ma following ultrahigh-temperature (UHT) metamorphism and anatexis on the retrograde cooling path. Inherited zircon cores give a mean date of 1136 ± 5 Ma, which suggests derivation of these felsic granulites by partial melting of older igneous rocks. The ferroan, anhydrous character of the granulites is similar to that of the ca. 1050 Ma Lyon Mountain Granite and consistent with origin in a late- to post-Ottawan extensional environment. We present a model for development of a late Ottawan migmatitic gneiss dome in the central Adirondacks that exhumed deep crustal rocks including the Snowy Mountain and Oregon anorthosite massifs with UHT Ledge Mountain migmatites. Recognition of deep crustal meta-plutonic rocks recording UHT metamorphism in a migmatite gneiss dome has significant implications for crustal behavior in this formerly thickened orogen.

Solid-Free Flexible Colloidal Completion Fluid with Variable Density for Gas Well Completion in High-Temperatureand High-Pressure Reservoirs: Experimental Study and Pilot Test

Summary Despite the increasing contribution of renewables to global energy, fossil fuels such as oil and gas still play an important role in energy supply. The development of deep and ultradeep oil and gas reservoirs has become more urgent. Typically, the ultrahigh-temperature and high-pressure (HTHP) environment is a big challenge. Solid-free brine is often used as a weighting component of high-density well completion fluid in the process of well operation, but the large amount of free water can easily cause water blocking damage to the reservoir. Therefore, there is an urgent need to develop a high-density completion fluid system that can be used in HTHP reservoir environments with little free water. In this paper, based on the theory of dispersion, degradation, viscosity extraction, and viscosity stabilization of polymer flexible colloidal particles in brines, an ultrahigh-temperature (180°C)-resistant, solid-free flexible colloidal completion fluid (SFCCF) with variable density and low corrosion was prepared. It breaks through the classical Flory’s water absorption theory. The phosphate brine was selected as the weighting base fluid of SFCCF, and the flexible colloidal particles were saturated with the phosphate brine to improve the density of SFCCF, as well as to reduce free water to lower the potential of water blocking damage. The results show that the dynamic viscosity of SFCCF is adjustable and ranges from 27 to 690 mPa·s, and the density is adjustable in the range of 1 to 1.8 g/cm3. SFCCF is a typical pseudoplastic fluid with shear dilution property, which is the result of the network destruction and the shear deformation of the flexible colloidal particles. The pump rate vs. dynamic viscosity curve is drawn. Under the pump rate of 50 to 800 L/min, the dynamic viscosity of SFCCF (1.2 to 1.7 g/cm3) is less than 40 mPa·s. In addition, SFCCF is viscosity stable for at least 4 days at 180°C and has excellent clay swelling resistance and reservoir fluid compatibility. Finally, SFCCF provides good reservoir protection and rock carrying capabilities and has the advantage of low cost. The successful application of SFCCF in a high-pressure gas well in the East China Sea is summarized, and some recommendations are proposed. The developed SFCCF can significantly reduce water blocking damage in HTHP well operations, providing a new avenue for HTHP well completions.

Synthesis of Fullerenes from a Nonaromatic Chloroform through a Newly Developed Ultrahigh-Temperature Flash Vacuum Pyrolysis Apparatus

The flash vacuum pyrolysis (FVP) technique is useful for preparing curved polycyclic aromatic compounds (PAHs) and caged nanocarbon molecules, such as the well-known corannulene and fullerene C60. However, the operating temperature of the traditional FVP apparatus is limited to ~1250 °C, which is not sufficient to overcome the high energy barriers of some reactions. Herein, we report an ultrahigh-temperature FVP (UT-FVP) apparatus with a controllable operating temperature of up to 2500 °C to synthesize fullerene C60 from a nonaromatic single carbon reactant, i.e., chloroform, at 1350 °C or above. Fullerene C60 cannot be obtained from CHCl3 using the traditional FVP apparatus because of the limitation of the reaction temperature. The significant improvements in the UT-FVP apparatus, compared to the traditional FVP apparatus, were the replacement of the quartz tube with a graphite tube and the direct heating of the graphite tube by impedance heating instead of indirect heating of the quartz tube using an electric furnace. Because of the higher temperature range, UT-FVP can not only synthesize fullerene C60 from single carbon nonaromatic reactants but sublimate some high-molecular-weight compounds to synthesize larger curved PAHs in the future.

Microstructure and Oxidation Behavior of Nb-Si-Based Alloys for Ultrahigh Temperature Applications: A Comprehensive Review

Nb-Si-based superalloys are considered as the most promising high-temperature structural material to replace the Ni-based superalloys. Unfortunately, the poor oxidation resistance is still a major obstacle to the application of Nb-Si-based alloys. Alloying is a promising method to overcome this problem. In this work, the effects of Hf, Cr, Zr, B, and V on the oxidation resistance of Nb-Si-based superalloys were discussed. Furthermore, the microstructure, phase composition, and oxidation characteristics of Nb-Si series alloys were analyzed. The oxidation reaction and failure mechanism of Nb-Si-based alloys were summarized. The significance of this work is to provide some references for further research on high-temperature niobium alloys.