3D freeze printing is a hybrid manufacturing method composed of freeze casting and inkjet-based printing. It is a facile method to fabricate lightweight, porous, and functional structures. Freeze casting is a well-known method for fabricating porous bodies and is capable of manipulating the micro-structure of the resulting product. Freeze casting simply involves solidification of a liquid suspension using low temperature and sublimation of the solvent using low temperature and pressure. After the sublimation of the solvent crystals, we obtain a porous structure where the pores are a replica of solvent crystal. Making use of the temperature gradient, as seen in unidirectional and bidirectional freeze casting, during the solidification with low temperature values, the solvent crystals grow along the temperature gradient. Furthermore, by manipulating the freezing kinetics during solidification, we can have a control on the average pore size distribution. For instance, when lower freezing temperatures result in finer pores with higher amount, higher freezing temperatures result in coarser pores with less amount. Also, the use of some additives inside the suspension leads to changes in the morphology of the solvent crystals as well as the resulting pores. However, the macro-structure of the fabricated body is highly dependent on the mold used during the process. In order to eliminate the dependency on the mold during the freeze casting process, our group recently combined this technique with inkjet-based 3D printing. With inkjet-based 3D printing, we fabricated uniform lines from single droplets, and complex 3D shapes from the lines. This provided us the ability of tailoring the macro structure of the final product without any dependency on a mold as seen in freeze casting. As a result of the 3D freeze printing process, we achieved fabricating lightweight, porous, and functional bodies with engineered micro and macro-structures. However, achieving fine droplets, and uniform lines by merging the droplets requires a good combination of fabrication parameters such as pressure adjustment inside the print head, print head speed, jetting frequency. Also, fabricating complex shapes from uniform lines requires well-adjusted parameters such as line thickness and layer height. In this study, we briefly explained the mechanics of the 3D freeze printing process. Following that we presented the development process of an open-source inkjet-based 3D printer. Finally, we explained the determination of inkjet dispensing and 3D printing parameters required for a high-quality 3D printing. During our experiments for the determination of fabrication parameters, we used a nanocellulose crystals-based ink due to its low cost and ease of preparation.

3D printing technology could be extremely beneficial for increasing the flexibly and reducing the cost of carbon fiber reinforced polymer composite (CFRP) production. However, this technology suffers from poor surface quality and uncertain engineering quality. Mechanical finishing processes could concurrently solve these surface issues with the 3D printed composites components. Herein, a mechanical finishing process for 3D printed CFRP composites via CNC milling is proposed to improve the surface quality of two 3D printing methods, namely fused deposition modeling (FDM) and laser assisted-laminated object manufacturing (LA-LOM). The 3D printed CFRP structures fabricated via both methods comprise of continuous carbon fiber reinforcement. The surface roughness and surface morphology of the original unfinished and finished surfaces with various cutting depths are extensively studied to investigate the feasibility of the proposed finishing technique. The surface morphology of the surfaces parallel and perpendicular to the 3D printed layers is the main focus of this work. After the CNC finishing process, the surface roughness of the 3D printed CFRP composites is improved by 70% and 60% for FDM and LA-LOM components, respectively. A smooth, consistent, and predictable surface morphology is achieved for various cutting depths demonstrating a substantial improvement over the original 3D printed surfaces.

Currently, SCR-DeNOx technology of flue gas has been widely applied in coal-fired power plants in China for its higher denitrification efficiency, lower ammonia escape and more stable operation performance. In order to overcome the shortages of the off-line method, an on-line method based activating was proposed. However, many key technologies also need to be researched that one of them is a cheap and efficient activating solution. First, activating solutions were prepared by means of single factor and experimental investigations of catalysts activation were conducted. Second, impacts of the catalysts, which were activated by the above mentioned solutions, NO removal and activity were tested and compared with that of the inactivated catalyst. The effect of active components (vanadium, tungsten, molybdenum, oxalic acid) and flue gas conditions on the activation of catalyst were investigated. Then, analysis of these catalysts by scanning electron microscopy (SEM), the specific surface area (BET), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were conducted. Finally, an ideal activating solution was found out through the analysis of the efficiency of denitrification and the macro and micro changes from catalysts. The following conclusions were obtained through the above mentioned activation experiments: 1) NO removal by activated catalysts is higher than that of inactivated catalyst; the De-NOx efficiency can be up to 99% in the following conditions: the reaction temperature (370 °C), the proportion of the active solution component (1.0%-V, 9%-W, 6%-Mo), the oxygen concentration (4%-O2) and the ratio of ammonia and nitrogen (NH3:N2 = 1:1); 2) the airspeed and the initial concentration of NO had little influence on catalyst activation; 3) the specific surface area and pore size of the activated catalyst were significantly increased that the active components of the catalyst surface were effectively added. Our investigation results to illustrate that the enhancement of active components, broadening of acid sites distribution, and including the surface labile oxygen and small pores opening to be the reason for high denitrification efficiency.

As an emerging and effective nano-manufacturing technology, the directional freezing based 3D printing can form 3-Dimensional (3D) nano-structures with complex shapes and superior functionalities, and thus has received ever increasing publicity in the past years. One of the key challenges in this process is the proper heat management, since the heat induced melting and solidification process significantly affects the functional integrity and structural integrity of the 3D printed nano-structures. To address this challenge, this paper proposes a novel path planning modeling and optimization framework to intelligently control the internal and external heat transfer process and ultimately optimize both the macro- and micro-structure of the printed part. Specifically, a heuristic tool path planning model was formulated and optimized based on thermal analysis process. The simulation results demonstrate that the tool path planning highly affects the spatial and temporal temperature distribution of the being printed part and the optimized tool path planning can effectively improve the uniformity of the temperature distribution which will consequently enhance the performance of the fabricated nano-structures.

Bioceramics with porous microstructure has attracted intense attention in tissue engineering due to tissue growth facilitation in the human body. In the present work, a novel manufacturing process for producing hydroxyapatite (HA) aerogels with a high density shell inspired by human bone microstructure is proposed for bone tissue engineering applications. This method combines laser processing and traditional freeze casting in which HA aerogel is prepared by freeze casting and aqueous suspension prior to laser processing of the aerogel surface with a focused CO 2 laser beam that forms a dense layer on top of the porous microstructure. Using the proposed method, HA aerogel with dense shell was successfully prepared with a microstructure similar to human bone. The effect of laser process parameters on surface and cross-sectional morphology and microstructure was investigated in order to obtain optimum parameters and have a better understanding of the process. Low laser energy resulted in fragile surface with defects and cracks due to low temperature and inability of laser to fully melt the surface while high laser energy caused thermal damage both to surface and microstructure. The range of 40–45 W laser power, 5 mm/s scanning speed, spot size of 1 mmm and 50 % overlap in laser scanning the surface yielded the best surface morphology and micro structure in our experiments.

This paper presented a novel 3D printing technique to fabricate graphene aerogel based on directional freezing. Thermal property of the graphene ink is one of key factors in this process which affects the material integrity and morphology as well as process efficiency and reliability. The major objective of this paper is to develop a heat transfer model to efficiently and reliably predict the temperature evolution of the printed materials and the waiting time between the layers for any input geometry. The simulation results show that the input geometry significantly affects the temperature evolution and waiting time. The proposed technique can not only improve the process efficiency and reliability, it can also serve as a flexible tool to predict and control the microstructure of the printed graphene aerogels.

Graphene is one of the most promising carbon nanomaterial due to its excellent electrical, thermal, optical and mechanical properties. However, it is still very challenging to unlock its exotic properties and widely adopt it in real-world applications. In this paper, we introduces a new 3D graphene structure printing approach with pure graphene oxide material, better inter-layer bonding, and complex architecture printing capability. Various parameters related to this novel process are discussed in detail in order to improve the printability, reliability and accuracy. We have shown that the print quality largely depends on the duty cycle of print head, applied pressure and travel velocity during printing. A palette of printed samples are presented to demonstrate the effectiveness of the proposed technique along with the optimal parameter settings. The proposed process proves to be a promising 3D printing technique for fabricating multi-scale nanomaterial structures. The theory revealed and parameters investigated herein are expected to significantly advance the knowledge and understanding of the fundamental mechanism of the proposed directional freezing based 3D nano printing process. Furthermore the outcome of this research has the potential to open up a new avenue for fabricating multi-functional nanomaterial objects.

This paper describes an approach combining thermal stress and magnetic force in order to generate α-Fe 2 O 3 nanosheets on the surface of various iron substrates that include plate and powder and their application of nanosheets on water treatment. A typical procedure involved the thermal oxidation of these substrates on the hot plate with magnetic field in air and with fixed temperature of 500°C for different times. A possible mechanism — magnetic force adding on iron ions — was proposed to explain the growth of nanosheet at the width direction. Electron microscopic studies indicate that these nanosheets show a parabolic relation with time of thermal oxidation for the growth at width direction. A comparison of heavy metal (As, Cr) ion adsorption effect of nanosheets and nanowires was also investiged, which show that nanosheets have a much better adsorption ratio than nanowires.

A hybrid manufacturing process, which contains Laser Sintering (LS) and Laser shock peening (LSP), is introduced to generate iron-TiN nanoparticle nanocomposites. It is a two-step process including LS followed with LSP. Before LS, TiN nanoparticles mixed with iron powders are coated on samples surface. After LS, TiN nanoparticles are embedded into iron matrix to strengthen materials. Then LSP is performed to introduce work hardening and compressive residual stress. The existed nanoparticles increase the dislocation density and also help to pin the dislocation movement. Better residual stress stability under thermal annealing can be obtained by better dislocation movement stabilization, which is beneficial for fatigue performance.

In this study, aluminum alloy 7075 (AA 7075) is processed by WLSP and compared with LSP at room temperature (RT-LSP). The microstructure of AA 7075 after processing is characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Tensile test and hardness test were carried out to investigate the effect of WLSP to material strength and ductility. It has been found that highly dense nanoscale precipitate particles are generated after WLSP. These nanoscale precipitate particles effectively block dislocations and thus increase the material strength.

We report a method to half-embed nanoparticles into metallic materials. Transparent and opaque nanoparticle (laser wavelength 1064 nm) were both successfully half-embedded (partial part of nanoparticles embedded into matrix while other parts still stay above the matrix) into metallic materials. Nanoparticles were coated on sample surface by dip coating before laser irradiation. After laser irradiation of different pulses and laser fluencies, nanoparticles were embedded into metal. The mechanism and process of embedding were investigated.