Performance of digital patternless freeze-casting sand mould

Digital patternless freeze-casting technology is a new approach for obtaining frozen sand moulds using digital milling technology. The change law of tensile strength and air permeability of frozen sand moulds (100-mesh and 200-mesh silica sand, and zircon sand moulds) under different freezing temperatures and water contents was studied. Results show that with the decrease of freezing temperature and the increase of water contents, the tensile strength and air permeability of the sand moulds are gradually improved. Meanwhile, computed tomography technology was used to characterize the shape and size of the water film between the sand particles mixed with 4wt.% water. The results show that in silica sand moulds, the form of water film is lumpy, and 200-mesh silica sand moulds have more water films and higher proportion of small-sized water films than 100-mesh silica sand moulds, while in zircon sand moulds, the form of water film is membranous. At the same freezing temperature and water content, the tensile strength of zircon sand mould is the highest, and 100-mesh silica sand mould is the lowest. A comparative solidification experiment of A356 aluminum alloy was carried out in frozen sand mould and resin sand mould. The results show that the primary α-Al phase appears in the form of equiaxed and eutectic silicon phase is needle-like in freezing sand mould casting, but the primary α-Al phase grows in the form of dendrites, and the eutectic silicon phase is coarse needle-like in the resin sand mould casting. The difference of microstructure is caused by the different cooling rate. The cooling rate of A356 aluminum alloy in frozen sand mould is higher than that in resin sand mould.

Preparation of unidirectional porous AlN ceramics via the combination of freeze casting and combustion synthesis

Unidirectional porous AlN ceramics(UP-AlNs)have attracted great attention for their wide applications in catalyst supports,filters and composite reinforcements.However,traditional fabrication processes usually require high temperature and long production cycle.Herein,UP-AlNs were successfully fabricated via the combination of tertiary butyl alcohol(TBA)-based freeze casting and combustion synthesis route using Al and AlN powders as raw materials.The microstructure,open porosity,thermal conductivity and compressive strength of UP-AlNs can be manipulated by synergistically regulating the AlN diluent content and Al/AlN solid loading of the freezing slurries.The optimal UP-AlNs exhibited controllable structure wavelength(λ)and open porosity in a wide range of 21.1-47.1μm and 54.2%-86.0%,respectively.In addition,the corresponding products also possessed anisotropic thermal conductivity and compressive strength.This novel route for the fabrication of UP-AlNs has the advantages of low cost,energy-saving and high efficiency,which shows significant promise for industrial applications.

Processing micrometer-sized particles in crumpled graphene network for freestanding membrane enabled by freeze casting

Graphene oxide(GO)is widely used in the construction and application of various 2 D membrane-based materials due to its unique colloidal structure.Herein,we demonstrate that micrometer-sized particles can make up freestanding membranes enabled by the extraordinary amphiphilic and polymer-like properties of graphene oxide through freeze casting.The 2 D macromolecule,GO could well wrap the particles for better uniformity and stability in either dispersion or membrane.Importantly,freeze casting plays an important role in avoiding the severe aggregation of micrometer-sized particles in the solventremoving process.After reduction,the membrane exhibits good electrical conductivity while maintaining its integral structure,which can be directly used as a freestanding binder-free electrode.This work provides a universal approach to fabricate freestanding membranes with various micrometersized materials for energy storage.

Dual-aligned porous electrodes for enhanced hydrogen evolution in alkaline water electrolysis

The efficiency of water electrolysis is significantly affected by the bubbles on the surface and inside the electrode.To enhance the gas-liquid transfer within the porous electrodes,we developed an innovative design termed dual-aligned porous electrode(D-APE),achieved by integrating magnetic alignment with freeze casting techniques.This paper investigates the hydrogen evolution performance of porous electrodes prepared using four different methods:evaporation,magnetic-aligned evaporation,freeze casting,and dual-aligned methods.The findings demonstrate that the magnetic-aligned process effectively alters the electrode structure,resulting in improved hydrogen evolution performance.Notably,among all the examined electrodes,the D-APE exhibits the highest hydrogen evolution performance,with further enhancements observed with prolonged the time of magnetic alignment.Furthermore,a comparison is made between electrodes prepared using the freeze casting method and the dual-aligned method at various thickness.The results show that the thinner D-APE exhibits excellent hydrogen evolution performance at high current density.Moreover,the D-APE demonstrates significantly improved material utilization rates compared to the conventional freeze casting method,offering promising prospects for enhancing the efficiency of water electrolysis.

A Robust Wood-inspired Catalytic System for Highly Efficient Reduction of 4-Nitrophenol

Porous solid scaffolds play key roles in preventing nanocatalysts from agglomeration,greatly maintaining the catalytic efficiency and stability of nanocatalysts.However,facile preparation of robust scaffolds with high mass transfer efficiency for loading nanocatalysts remains a major challenge.Here,we fabricate a wood-inspired shape-memory chitosan scaffold for loading Au nanoparticles to reduce 4-nitrophenol via a simple“freeze-casting and dip-adsorption”approach.The obtained catalytic scaffold highly resembles the unidirectional microchannel structure of natural wood,resulting in robust mechanical properties and outstanding water absorption capacity.Additionally,Au nanoparticles can be firmly and uniformly anchored on the inner surface of these microchannels via electrostatic interaction,forming numerous microreactors.This catalytic system exhibits a high 4-nitrophenol conversion rate of 99%in 5 s and impressive catalytic stability even after continuously treating with more than 3 L of highly concentrated 4-nitrophenol solution(1 mmol/L).Therefore,the wood-like catalytic system presented here demonstrates the potential to be applied in the field of water treatment and environmental protection.

Porous Y_2SiO_5 Ceramic with Low Thermal Conductivity

Porous Y2Si05 ceramic was fabricated by freeze casting with tert-butyl alcohol as solvent. The porous Y2SiO5 ceramic possessed long straight pore structure. With decreasing solid loading from 20 to 10 vol.%, the porosity of the Y2SiO5 ceramic increased linearly from 45% to Y2%, while the compressive strength declined from 23.2 to 3.2 MPa. The thermal conductivity of Y2SiO5 decreased from 2.34 W/mK for the dense bulk to 0.05 W/mK for the porous body with a porosity of 57%.

Wet-resilient graphene aerogel for thermal conductivity enhancement in polymer nanocomposites

Three-dimensional(3 D)graphene-based aerogels have significant potential for adsorption,sensors,and thermal management applications.However,their practical applications are limited by their disorganized structure and ultra-low resilience after compression.Some methods can realize a well-aligned structure,however,they involve high costs and complex technology.Herein,a 3 D graphene hybrid aerogel with an anisotropic open-cell and well-oriented structure is realized by unidirectional freeze casting,which combines the‘soft’(e.g.graphene oxide,Tween-80)and‘hard’(e.g.graphene assembly)components to realize full recovery after flattening.A graphene aerogel annealed at a moderate temperature(200℃)can possess superhydrophilicity and outstanding wet-resilience properties,including after being pressed under40 MPa.Furthermore,the graphene aerogel annealed at a high temperature of 1500℃exhibits excellent thermal conductivity enhancement efficiency in polydimethylsiloxane(PDMS).The resultant nanocomposites clearly demonstrate anisotropic thermal conductivity and promising applications as thermal interface materials.This strategy offers new insights into the design and fabrication of 3 D multifunctional graphene aerogels.