Advanced Powder Technology最新文献

In the wood processing industry, wood dust commonly mixes with other processing by-products to form piles, which generally have large voidage due to differences in component sizes. It is essential to understand the effect of voidage on the true ignition and smoldering behavior of wood dust layer on hot plates. In this study, wood dust and shavings were selected as experimental materials. The effects of voidage on the minimum ignition temperature of the dust layer (MITL), ignition delay time, and smoldering behaviors were investigated by means of a hot plate test. The results showed that the addition of large-sized shaving particles significantly enhanced the overall voidage of the dust layer. With the increased deposit voidage, the ignition delay time decreased, and smoldering propagation accelerated. When the shavings content was less than 50%, the MITL decreased; however, further addition of shavings significantly increased the MITL. The analysis shows that voidage affects the ignition and smoldering behavior of the dust layer mainly by influencing oxygen transport and heat transfer processes. These findings offer a new insight for the prevention and control of dust fires under real working conditions.

Flotation separation of copper-sulfur at low alkalinity has attracted soaring interest in the beneficiation of copper sulfide ore. In this work, application of calcium hypochlorite (Ca(ClO)₂) and carboxymethyl chitosan (OCMC) as combined depressants for selective flotation separation of chalcopyrite from pyrite was investigated. A maximum recovery difference of 71.35 % between both minerals is observed under the recommended conditions ([Ca(ClO)₂] = 60 mg/L, [OCMC] = 400 mg/L and 40 mg/L SBX at pH=8). Besides, the copper-sulfur flotation separation indexes were assessed by the artificial mixed-mineral tests. Results of contact angle measurement, zeta potential and adsorption amount analysis reveal that the combined depressants severely impede the collector adsorption onto pyrite surfaces, and has a light effect on the chalcopyrite. OCMC exhibits a stronger complexing ability on Ca²⁺ and Fe²⁺ ions than Cu²⁺ ions. XPS results confirm that the combined depressant interact with pyrite surfaces intensively, and prompt a deep conversion of S₂^2- and S_n^2-/S⁰ into S^2- and SO₄^2- species, as well as a deep transformation of Fe(II)-S into Fe(III)-O/OH on the pyrite surface. ToF-SIMS and thermodynamic calculation results afford the favorable evidence for the selective suppression of the pyrite with added the combined depressant. Thereby the selective oxidation and intense complexation on the pyrite stemming from the combined depressant synergy are responsible for the selective separation of chalcopyrite from pyrite.

This study proposed a novel method for acquiring inexpensive and efficient seeds of calcium alumina silicate hydrate (C-A-S-H). Specifically, C-A-S-H seeds (CASH) (i.e., around 373 nm) with two morphologies (i.e., foil-like and fiber-like) were observed by using fly ash and carbide slag after 4 h nano-milling and 3 days wet grinding. Moreover, the utilization of sulfate-rich lithium slag (LS) in cementitious materials was rarely reported until now. In this study, the combination effect of nano-sized LS and CASH on cement hydration was investigated systematically. It was discovered that the compressive strength of cement mortar with the combined use of very low dosage (i.e., 0.1 %) CASH and 2.0 % nano-sized LS shows around 20 MPa at the age of 18 h, which exceeds two times that of plain cement mortar and still increased by 16 % at the age of 28 days. The superior combined accelerating effect on cement hydration using the above CASH and nano-sized LS provides a choice for the requirement of high early-strength concrete and the highly-added value utilization of fly ash and lithium slag.

Dense medium has a certain impact on the separation efficiency of gas–solid fluidized bed separation. Geldart A^- particle, a new type of dense medium, can effectively improve the expansion of the emulsion phase and the separation efficiency in the fluidized bed. This work is aimed to investigate the differences of bubble dynamics for Geldart A, B, D and A^- particle fluidized beds with digital image analysis technology in a two-dimensional gas–solid fluidized bed. The bubble number and size distributions are consistent with those in literature for Geldart A, B and D particle fluidized beds. The bubble size is smaller for Geldart A^- particle fluidized beds. Due to the bubble rupture neglected in the Darton bubble growth model, a new correlation based Darton bubble growth model has been extended, which has approximately 15% accuracy region. Additionally, the bubble rising velocity was studied. The extended Davidson correlation, which has approximately 15% accuracy region, is a good method to predict the bubble rising velocity. Thus, the separation efficiency of gas–solid fluidized bed separation could be improved for Geldart A^- particle.

Herein, a novel flame retardant and smoke suppression auxiliaries was synthesized with the motivation of sustainability strategy. Porous diatomite (p-DIA) as a purely natural raw material and melamine formaldehyde-phytic acid (MFPA) as a synergist to produce DMFPA, which acts as the novel auxiliaries to endow epoxy resin (EP) with excellent fire safety. The thermal stability of EP composites with 15 wt% DMFPA was improved, as evidenced by a 31.0% reduction in its maximum thermal decomposition rate and an enhancement of residual char to 22.7 wt%. Moreover, EP composites also exhibited superior flame retardant and smoke reduction properties, as reflected by its peak heat release rate (PHRR), peak smoke release rate (PSPR), peak CO release rate and smoke factor (SF) that were 56.5%, 56.3%, 58.7% and 77.7% less than those of unmodified EP, respectively. These results correlated strongly with the powerful adsorption of smoke and flammable debris by porous diatomite, the physical barrier effect of the highly stable expanded char layer facilitated by DMFPA, the dilution effect of non-flammable gases resulted from pyrolysis by melamine and the free radicals quenching effect produced by phytic acid.

Cassiterite, a vital source of tin, is commonly separated via flotation. This study presented a mixed collector comprising sodium oleate (NaOL) and salicylaldoxime (SAOX) for cassiterite flotation. Micro-flotation experiments showed that the recovery of cassiterite increased to above 90 % upon adding mixed NaOL/SAOX collectors under the concentration of 0.6*10⁻⁴ mol L⁻¹ with a molar ratio of 1:3 at pH 7. The classical first-order model offered the most suitable fit for the experimental data. It exhibited fast-floating behavior as the k value of cassiterite increases to 1.77 under the mixed collector system. Zeta potential measurements revealed that both NaOL and SAOX could adsorb onto the cassiterite surface. The mixed collector NaOL/SAOX leads to a significant change in the zeta potential of cassiterite, indicating that this mixed collector may interact with the surface of cassiterite. Contact angle measurements indicated that the mixed collector increased the contact angle of cassiterite, thereby enhancing its hydrophobicity. FTIR analysis revealed the chemical adsorption and synergistic effect of the mixed collectors on the cassiterite surface. XPS analysis further confirmed this synergism on the cassiterite surface. Overall, this paper introduces a mixed collector for cassiterite flotation, elucidates the synergistic adsorption mechanism of NaOL and SAOX on the cassiterite surface, and provides a new approach for improving the flotation efficiency of cassiterite.

Ultrafine Ni particles are important materials for the fabrication of electrodes for multilayer ceramic capacitors (MLCCs). However, the problems of particle oxidation and thermal shrinkage mismatch still need to be resolved. Herein, Ni@MgO core–shell ultrafine particles are prepared by a method in which Mg(OH)₂ shells are coated on pre-synthesized Ni ultrafine particles by a chemical solution method. After heat treatment, the Mg(OH)₂ shells decompose into MgO shells, and Ni@MgO core–shell structure is therefore formed. The as-prepared Ni and Ni@MgO core–shell ultrafine particles are further made into pastes, printed on ceramic substrate and sintered into conductive films. In comparison with pure Ni particles, enhanced performances of anti-oxidation and thermal shrinkage resistance are achieved for Ni@MgO core–shell particles. The sintered films made by pure Ni particles exhibits a severe shrinkage with a large area of disconnected regions whereas the Ni@MgO core–shell films show much better film integrality. The results suggest that coating MgO shells on Ni ultrafine particles to form a core–shell structure can be an effective way to reduce the thermal shrinkage and improve the integrity of Ni electrode for the potential applications of MLCCs.

Aiming at the problems of reservoir collapse and pipeline blockage caused by serious sand production in the exploitation of natural gas hydrate, the downhole spiral-cyclone coupled in-situ separator is used for sand removal. The separator structure is determined by the physical parameters and empirical formulas. The structure is analyzed and optimized by CFD numerical simulation. The optimal structural parameters of the separator are obtained: the position of the vortex guide plate is 28 mm, the number of inlets is 6, the spiral flow channel structure is a circular section, the number of spiral lines is 2, and the depth of the overflow pipe is 100 mm. At this time, the sand removal efficiency of the separator is 89.55 %. The experimental verification was carried out. The maximum sand removal efficiency of the indoor test was 84.46 %, and the relative error with the simulation was 5.51 %. Through the comparison between experimental phenomena and numerical simulation, it is clear that the spiral-cyclone coupling separator has good performance in the separation and sand removal of natural gas hydrate underground mining. The research in this paper can provide some reference for the design and optimization of natural gas hydrate downhole in-situ separators.