Materials

Using the seeding method, nickel-based single-crystal superalloy DD6 specimens with different growth orientations were prepared in a liquid metal cooling (LMC) directional solidification furnace. Subsequent standard heat treatment was carried out, and the influence of growth orientation on the microstructure of the (001) crystal plane of the alloy after heat treatment was investigated. Results show that with the increase in growth orientation deviation angle from the <001> orientation, the area fraction of residual eutectic content is reduced, the average size and volume of pore and γ′ strengthening phase increase, and the cubicity of the γ′ strengthening phase decreases. The growth orientation does not significantly affect the morphology of residual eutectic content or the morphology of the strengthening phase of the γ′ in the dendrite cores and interdendrite regions. However, the size uniformity of the γ′ strengthening phase in dendrite cores and the width of the γ matrix channels decrease as the growth orientation deviation angle increases.

The existing forms and evolution mechanisms of carbon impurities constitute the core scientific issue in the optimization of polysilicon purification processes. The depth of research on this issue directly determines the targeting and effectiveness of directional impurity removal strategies, and is even a key prerequisite for improving the quality and reducing the cost of polysilicon products. Based on HSC simulation calculations and using the Gibbs free energy of reactions as the judgment criterion, this paper investigated the existing forms and evolution mechanism of carbon impurities during the production of polysilicon via the modified Siemens process. The results show that the evolution mechanism of carbon impurities is as follows: the solute carbon in silicon powder reacts with hydrogen to generate CH₄. Subsequently, CH₄ synergistically undergoes radical rearrangement and the Rochow reaction with methylchlorosilanes in chlorosilane and CH₄ in recovered hydrogen. Meanwhile, CH₃· radicals combine with radicals generated from chlorosilanes to form a mixture of methylchlorosilanes dominated by SiH(CH₃)Cl₂ as well as CH₄. After distillation purification, SiH(CH₃)Cl₂ enters the SiHCl₃ stream, and then synergistically undergoes cracking and radical rearrangement with CH₄ in high-purity hydrogen, the solid-soluble elemental carbon forms and deposits in polysilicon. Simultaneously, a mixture of methylchlorosilanes dominated by SiH(CH₃)Cl₂ along with CH₄ is generated and then fed into the tail gas system. This will provide the necessary theoretical foundation for the development of efficient and low-cost impurity removal strategies.

Electrochemical water splitting requires electrocatalysts that operate efficiently and durably under disparate electrolyte environments. Herein, pristine CuCoO₂ particles were synthesized via a hydrothermal route as a single-phase rhombohedral (3R) delafossite structure composed of hexagonal, single-crystalline particles (~2.6 μm) with a uniform elemental distribution. The prepared CuCoO₂ was then evaluated as a bifunctional electrocatalyst for the alkaline oxygen evolution reaction (OER) and the acidic hydrogen evolution reaction (HER), with a deliberate separation of electrode-level performance and intrinsic per-site activity. X-ray photoelectron spectroscopy revealed mixed Cu⁺/Cu²⁺ and Co²⁺/Co³⁺ states, together with signatures of copper and oxygen vacancies, indicating a defect-rich surface chemistry. In 1 M KOH, the CuCoO₂ loaded on carbon fiber paper (CFP) delivered an OER overpotential of 404.38 mV at 10 mA/cm² in 1 M KOH (Tafel slope = 102.39 mV/dec; charge-transfer resistance (R_ct) decreased from 19.32 to 5.78 Ω with increasing potential) and an HER overpotential of 246.46 mV at −10 mA/cm² in 0.5 M H₂SO₄, with sluggish kinetics (Tafel slope = 429.17 mV/dec; high R_ct = ~1.0–1.1 kΩ). Despite this, CuCoO₂ exhibited markedly higher intrinsic activity in acidic HER (ECSA = 82.97 cm²; TOF = 0.1432 s⁻¹ at −0.2 V vs. RHE) than in alkaline OER (ECSA = 9.56 cm²; TOF = 0.079 s⁻¹ at 1.5 V vs. RHE), indicating that acidic HER performance is primarily limited by electrode-level microstructural factors. This work provides, to the best of our knowledge, the first evaluation of acidic HER activity of delafossite CuCoO₂ and underscores electrode-level microstructural engineering as a key route to better harness its intrinsic activity for practical water electrolysis.