Obtaining soft magnetic powder composites of the system ferromagnetic – diamagnetic

A method has been developed for producing a powder material of the ferromagnetic – diamagnetic system, intended for the manufacture of composite radar absorbing materials and coatings in the ultra-high frequency range. Composite powder material with a polymer diamagnetic matrix reinforced with a ferromagnetic nanocrystalline hardener is obtained by the method of ultrafast mechanosynthesis. The proposed technology of superfast mechanosynthesis allows to obtain a powder composition where each particle is a single mechanically connected system, while reducing the degree of amorphousness (no more than 80%) by maintaining the proportion of nanocrystalline precipitates in the amorphous matrix and, accordingly, increasing the magnetic permeability (up to 90 or more). The composite powder of the ferromagnetic – diamagnetic system thus obtained can be used to obtain radar absorbing materials with high shielding efficiency and a large absorption coefficient (at least 25 dB) in the frequency range from 1 MHz to 40 GHz.

Development of SiC/PVB Composite Powders for Selective Laser Sintering Additive Manufacturing of SiC

Subsphaeroidal SiC/polymer composite granules with good flowability for additive manufacturing/3D printing of SiC were prepared by ball milling with surface modification using polyvinyl butyral (PVB). PVB adheres to the particle surface of SiC to form a crosslinked network structure and keeps them combined with each other into light aggregates. The effects of PVB on the shape, size, phase composition, distribution and flowability of the polymer-ceramic composite powder were investigated in detail. Results show that the composite powder material has good laser absorptivity at wavelengths of lower than 500 nm.

Utilization of Construction Waste Composite Powder Materials as Cementitious Materials in Small-Scale Prefabricated Concrete

The construction and demolition wastes have increased rapidly due to the prosperity of infrastructure construction. For the sake of effectively reusing construction wastes, this paper studied the potential use of construction waste composite powder material (CWCPM) as cementitious materials in small-scale prefabricated concretes. Three types of such concretes, namely, C20, C25, and C30, were selected to investigate the influences of CWCPM on their working performances, mechanical properties, and antipermeability and antifrost performances. Also the effects of CWCPM on the morphology, hydration products, and pore structure characteristics of the cement-based materials were analyzed. The results are encouraging. Although CWCPM slightly decreases the mechanical properties of the C20 concrete and the 7 d compressive strengths of the C25 and C30 concretes, the 28 d compressive strength and the 90 d flexural strength of the C25 and C30 concretes are improved when CWCPM has a dosage less than 30%; CWCPM improves the antipermeability and antifrost performances of the concretes due to its filling and pozzolanic effects; the best improvement is obtained at CWCPM dosage of 30%; CWCPM optimizes cement hydration products, refines concrete pore structure, and gives rise to reasonable pore size distribution, therefore significantly improving the durability of the concretes.

Temperature Field Simulation of Wood Powder/PES Composite Powder Material

In view of the physical process of the wood powder/PES composite powder material selective laser sintering forming ,this article establishes the plane moving Gaussian heat source as the input laser heat source model .Based on selective laser sintering wood powder/PES composite powder sintering theory and combined with thermal conductivity of composite powder, specific heat, density and other related theoretical analytical models .It establishes three dimensional finite element model of selective laser sintering process of wood powder/PES composite powder transient temperature field .The laser sintering simulation experiment of wood powder/PES composite powder under different laser power obtains temperature field distribution law of the wood powder/PES composite powder forming under different laser power distribution, and the influence of the forming parts forming quality of wood powder/PES composite powder materials caused by the temperature field. The simulation results also provide certain theoretical basis for the choice of laser power in the subsequent laser sintering experiment.

Study on Preparation and Photocatalytic Activity of Nano-TiO2/Precipitated Silica Composite Material

Using precipitated silica as the carrier, a kind of composite photocatalyst was prepared through hydrolysisde positing method. The obtained composite material was characterized by XRD, SEM, TEM, FT-IR. Based on the experimental results and analysis of characterization, the preparation mechanism of composite powder material was studied. The photocatalytic degration experiment of Rhodamine-B indicates that the precipitated silica is an ideal carrier of the TiO2,and the photocatalyst can combine with the silica tightly. The photocatalytic activity of the obtained composite material is stabilize and constant.