Non-equilibrium synthesis of Fe-Cr-C-W alloy by laser cladding

Synthesis of Fe-Cr-C-W alloy using the laser cladding technique offered an opportunity to produce a novel wear-resistant material with fine and uniform microstructure. Use of preheating during laser cladding Fe-Cr-C-W provided crack-free clads. The preheating temperature was very critical to eliminate cracks in the clad. Different complex types of carbide were observed in this research. Overall laser process parameters such as power density or specific energy as well as preheating temperature affected the characteristics of the carbide precipitates in the matrix. The increase of solid solubility and high cooling rate resulted in good metallurgical characteristics. Mostly M₆C or M₂₃C₆ type carbides were observed. Usually diamond-shaped M₆C carbides showed good tribological characteristics. In general, increasing the power density brought an increase of average hardness, while decreasing the power density brought a decrease of wear scar width. The laser-clad Fe-Cr-C-W alloy showed better wear properties than laser-clad Fe-Cr-Mn-C and several times smaller scar width as compared to Stellite 6 hard-facing during line-contact wear testing.     

Novel synthesis methods for new materials in solid state chemistry

The most common method used for synthesizing inorganic solids is the so-called ‘ceramic method’ which involves synthesizing at elevated temperatures and leads to thermodynamically stable phases. This method has a serious limitation because many inorganic solids of current interest are rather metastable and consequently their preparation requires low temperature methods. In this article, we have reported some methods of synthesis which also include methods that belong to soft-chemistry routes. The selected examples presented in this paper are: (i) the intercalation and or deintercalation of oxygen in oxides by electrochemical oxidation or reduction in aqueous or nonaqueous solutions, (ii) the use of chemical agents such as NO₂ or borohydrides for obtaining oxides with tunneled and lamellar structures, (iii) a multistage synthesis processing for intercalating, in layered oxygenated materials, anionic species and acrylic monomers and polymers, (iv) the supercritical fluid processing for preparing nitrides, carbon-nitrides, lamellar oxides and oxy-(hydroxy-) fluorides, and (v) the mechanical alloying for synthesizing new Mg-based binary intermetallics.     

Opportunities for new materials synthesis by hot wire chemical vapor process

Over the last 20 years the hot wire chemical vapor deposition (HWCVD) technique is being explored as an effective alternative to the conventional plasma enhanced chemical vapor deposition (PECVD) for silicon based thin film devices and is claimed to have various advantages. An important point to be appreciated is the mixed nature of the HWCVD process. On one hand it offers all the benefits of being a chemical vapor process and on the other it has the flavor of physical vapor deposition due to the generation of precursors at a line/plane like source (wire array) far away from the substrate albeit with subsequent transport accompanied by secondary gas phase reactions. The possible control over the secondary gas phase reactions gives a unique feature to the HWCVD process. Apart from employing HWCVD for the preparation of a-Si:H and μc-Si:H with high deposition rates we have extended the applicability of the HWCVD to the synthesis of piezoresistive microcrystalline silicon, diffusion barriers of a-SiC:H, silicon nanowires, boron carbide for thermal neutron detectors, stress free a-SiN:H thin films for MEMS devices and metal nano-templates for semiconductor nanowire synthesis. We also established the applicability of HWCVD in surface nano-engineering to incorporate different functionalities (without actually depositing any film) i.e. nano-engineering or nano-modification of the surface to avoid electromigration on low-k dielectric layers and reduce surface defects in crystalline silicon and also bring about nano-crystallization of metallic thin films. Hence I would like to coin a more general nomenclature for this technique and refer to it as hot wire chemical vapor process (HWCVP). This paper discusses the results and outcomes of some of the case studies that we have carried out employing the HWCVP.     

Mechanochemical methods for the synthesis of new magnesium-based composite materials for hydrogen accumulation

We present a brief overview of works on the synthesis of magnesium hydrides and alloys by traditional methods and analyze mechanical methods for synthesis of these materials. Advantages of reactive milling for the preparation of new efficient hydrogen sorbents based on magnesium are discussed. It is shown that the reaction rate of the mechanochemical synthesis of MgH₂ increases four times as a result of the introduction of additives of intermetallic compounds based on Ti and Zr.     

Sol-gel synthesis of hybrid materials

Sol-gel chemistry allows the synthesis of hybrid organic-inorganic materials. Organic molecules can be used as complexing ligands to provide a chemical control over hydrolysis and condensation reactions, leading to the formation of stable suspensions of nanoparticles. They can also be trapped within the sol-gel matrix in order to provide some optical properties such as photochromism. When chemically bound to the oxide network via Si-C bonds they lead to hybrid nanocomposites that offer new possibilities in the field of materials science. Even biospecies, such as enzymes or antibodies, can be trapped within sol-gel matrices in order to make bio-sensors or bio-catalysts.     

Mechanochemical synthesis of Co-C materials

Using mechanochemical processing, we prepared nonequilibrium Co-C solid solutions supersaturated with carbon to above 7 at %. X-ray diffraction characterization showed that the formation of fcc Co_{1 ? x} C _x solid solutions was accompanied by an increase in the probability of deformation stacking faults. In Co + C mixtures containing more than 10 at % carbon, the fcc solid solution converted to the metastable cobalt carbide Co₃C with an orthorhombic structure. We assessed the thermal stability of the nonequilibrium Co_{1 ? x} C _x solid solutions and the heat effect of the decomposition of the cobalt carbide Co₃C: ?ΔH = 23 kJ/mol.     

Non-equilibrium grain-boundary segregation kinetics

A new model is proposed in this article concerning non-equilibrium grain-boundary segregation kinetics. The model not only includes the isothermal non-equilibrium grain-boundary segregation kinetics but also provides a formula for calculating the non-equilibrium segregation level under continuous cooling. Results calculated from the non-equilibrium grain-boundary segregation model for boron in steel grade Type 316 and chromium in steel grade % Cr-1 % Mo are in satisfactory agreement with the observed data for experimental measurements.     

Some aspects of synthesis of nanocrystalline materials

Abstract

This paper reviews research work at the Institute for Materials and Advanced Processes, University of Idaho, on the synthesis of nanocrystalline materials and their consolidation. Nanocrystalline materials have been synthesised by a number of ‘far from equilibrium’ processes including mechanical alloying (MA), mechanochemical processing (MCP), supercritical fluid processing (SCFP), and severe plastic deformation (SPD). Examples of the materials include the TiAl based intermetallic compounds and composites produced by MA and SPD, Ti base alloys and metal carbides synthesised by MCP, thin film Cu produced by SCFP, and Al–Fe alloys produced by SPD. Details of the processes used and the enhancement of properties owing to the nanoscale structures in consolidated material will be presented. The potential of these processes to substitute for conventional methods of production will also be discussed.     

Machine learning-guided synthesis of advanced inorganic materials

Synthesis of materials with minimum number of trials is of paramount importance towards the acceleration of advanced materials development. The enormous complexity involved in existing multi-variable synthesis methods leads to high uncertainty, numerous trials and exorbitant cost. Recently, machine learning (ML) has demonstrated tremendous potential for material discovery and property enhancement. Here, we extend the application of ML to guide material synthesis process through the establishment of the methodology including model construction, optimization, and progressive adaptive model (PAM). Two representative multi-variable systems are studied. A classification ML model on chemical vapor grown MoS₂ is developed, capable of optimizing the synthesis conditions to achieve a higher success rate. And a regression model is constructed on the hydrothermal-grown carbon quantum dots, to enhance the process-related properties such as the photoluminescence quantum yield. The importance of synthesis parameters on experimental outcomes is particularly extracted from the constructed ML models. Furthermore, off-line analysis shows that enhancement of the experimental outcome with minimized number of trials can be achieved with the effective feedback loops in PAM, suggesting the great potential of involving ML to guide new material synthesis at the beginning stage. This work serves as a proof of concept for using ML in facilitating the synthesis of inorganic materials, thereby revealing the feasibility and remarkable capability of ML in opening up a new promising window for accelerating material development.     

Purification of fluorides for optical materials synthesis

This paper considers processes for the ultrapurification of starting materials for the preparation of heavy metal fluoride glasses with the lowest possible impurity content. Based on the results of physicochemical studies of reactions between fluorination agents and components of fluoride glasses, we have proposed novel techniques for the preparation of fluorides and glasses free of oxygen-containing impurities.     

新型炭吸油材料的表征

为了解决环境污染中油污染的问题,世界各国相继投入大量的财力开发新型高效吸油材料.本研究针对多孔炭材料中膨胀石墨(EG)和植物炭疏水亲油的特点,分别以重油和20号柴油为吸附质,对膨胀石墨和炭化玉米秸秆、炭化油菜秸杆和炭化竹子3种植物炭的吸油特性和影响因素进行了详细的表征和研究.实验结果表明(1)蠕虫状膨胀石墨样品具有最大的吸油率,理想状态下可以达到80 kg/kg EG;(2)油类的粘度在很大程度上影响吸附速率,从而在很大程度上影响等温吸附曲线的形状;(3)膨胀石墨的循环再利用性能比较差;(4)3种代表性植物炭材料中,炭化玉米秸杆对20#柴油的吸附率最高,其次为炭化油菜秸秆,最小的是炭化竹子;(5)比表面积的改变,对液态吸附过程影响不大.