Advanced Materials Research Vols. 941-944

Abstract: Study provides information about one type of bio-based composite – plastic with wood reinforcement in volume more than 50 % (advantage: renewable, inexpensive, can be used to isolate a sound and have got a low density) and about machining of this unique material. During the machining (turning process was use to produce a surfaces by removing material from a rotating workpiece) were changed two parameters – rotation speed and feed rate (depth of cut was constant). There were observed changes of parameter to surface roughness with change of conditions of machining process.

Abstract: SiC particle-reinforced Cu-Fe based braking materials were fabricated by the P/M hot pressing method. The phase composition, microstructure and the worn surface of the composite were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD).The tribological properties were evaluated using a disk-on-disk type laboratory scale dynamometer. Results indicate that the friction coefficient is 0.42 in 6800rpm, 0.7MPa. With the increase of rotation speeds the coefficient of friction and stable rate were decreased.

Abstract: A novel graphite/copper alloy-based self-lubricating composite materials were prepared using the powder metallurgy method by composing 663 bronze, Ni, W, nanoAl₂O₃, MoS₂, Ag, CaF₂, Sm₂O₃ as the basic alloy powder and adding 1wt.%, 1.5wt.%, 2wt.%, 2.5wt.%, 3wt.% graphite and nickel coated graphite powder respectively to the composite powder. The microstructure, mechanical properties and friction properties of the samples were studied. The results show that the samples with nickel coated graphite powder have their wettability and the composite structure between graphite and copper alloy matrix is improved. When the content of graphite is 3wt.%, the properties of samples prepared by Ni-coated graphite are improved compared with those prepared by uncoated graphite. The hardness is increased from 34HV to 38HV, the crushing strength is from 116MPa to 151MPa, the friction coefficient is reduced from 0.28 to 0.21, wear loss is reduced from 20mg to 12mg. The samples prepared by Ni-coated graphite have good self-lubricating performance.

Abstract: Silicon-aluminum composites with Si content of 42-70 wt. % were fabricated by an innovative method of liquid-solid separation. The microstructures and thermal conductivity analyzing and predicting by the Maxwell and Hasselman-Johnson models were executed. The results show that silicon particles in composites are near globular with dull angular and surrounded by the continuous Al matrix, and the interface among them is composed of element diffusion zone. The conductivities of four composites are beyond 120 W. m^-1 .K^-1 at 25°C but reduce with Si content adding. The coarse particle size is beneficial to the higher conductivity. The interface thermal resistance of composites obtained by theoretical calculation is 16.0×10⁷ W.m^-2.K^-1, and using it the H-J model can be employed to predict the conductivity.

Abstract: The porous starch was modified by xanthates, and the starch/natural rubber composite was prepared by blending the modified starch with natural rubber latex. The morphology, thermal stability, swelling behavior and mechanical properties of the composite were investigated. Morphology studies by SEM showed that the modified porous starch were homogeneously dispersed in NR matrix. The composite has higher solvent resistance and lower water resistance after adding modified porous starch. The mechanical properties of composite are improved significanly with the increase of modified porous starch.

Abstract: Cellulose hydrogel was prepared from cellulose/NaOH aqueous solutions. Silica was added into cellulose hydrogel by TEOS hydrolysis method. Finally aerogel was obtained by the freeze-drying technique. The influence of silica on the properties of cellulose aerogel was studied in detail. With cellulose content 3%, the water absorption of cellulose-SiO₂ composite aerogel was only about 50% of the water absorption of cellulose aerogel. The result showed that silica could effectively reduce the water absorption of cellulose aerogel significantly and reduce the extent of structural damage that resulted from highly water absorption of cellulose aerogel. At the same time, with the increase of cellulose content, density of cellulose aerogel increased, while porosity decreased. It led to the water absorption of aerogel decrease with the increasing of cellulose content.

Abstract: Laminated composites with a frequency selective surfaces (FSS) or more complex metamaterials are potential radome materials due to their unique characteristics of electromagnetic wave transmission. For making high-temperature resistant radomes, metamaterials or laminated composites with an FSS should be based on ceramic substrates. However, the processing methods for ceramic metamaterials are very limited and the conventionally used LTCC technique suffers from the shortcoming of large sintering shrinkage rates, which unfortunately impede the production of ceramic-based metamaterials. In this paper, a novel method of a low temperature co-fired ceramic (LTCC) technique combined with a technique of ceramic joining via green tapes was developed to fabricate the fused silica ceramic laminates sandwiched with the FSS. It was found that the newly developed composites with the FSS unit cells of the Ag-Pd strips exhibited near zero shrinkage of the unit cells, showed predictable transmission efficiencies of electromagnetic microwaves, and were able to overcome the poor transmission efficiencies below 11 GHz of the pure fused silica ceramic plates with an identical thickness.

Abstract: Nanometer Al₂O₃ particles reinforced Al-Zn-Mg-Cu composites were processed by cryogenic treatment with different cycle index of 1,2 and 3. Transmission Electronic Microscopy (TEM) was utilized to analyze the microstructural evolution of the treated samples. The results show that with the increase of cycle index the precipitate amount and dislocation density have been increased. The precipitates orientation exhibits some preferred orientation. The high amount of precipitates and dislocation density and preferred orientation of precipitates will benefit to increase the mechanical properties of composites.

Abstract: Al₃Ti and Al₃Zr particles reinforced 7055Al composites were processed by cryogenic treatment with different cooling speed at 1°C/min, 3°C/min and 5°C/min. Transmission Electronic Microscopy (TEM) was mainly used to analyze the microstructural evolution of the treated samples. The results show that with the increase of cooling speed the precipitate amount and dislocation density have been increased. The precipitates orientation exhibits some preferred orientation. The mechanical properties test demonstrates that for the samples treated at 5°C/min the tensile strength and elongation has arrived at the utmost.

Abstract: Resin-derived carbon foams with closed hollow spherical structure were prepared from mixtures of hollow phenolic microspheres and phenolic resin, followed by curing and carbonization. The resultant carbon foam had a bulk density of 0.45 g·cm^-3. Effects of hollow microsphere on the on the compressive property and thermal conductivity of carbon foams were investigated. The results revealed that the hollow microspheres played an important role in improving compressive fracture toughness and lowering the thermal conductivity of carbon foams. The compressive fracture characteristics of carbon foam exhibited gradient brittle fracture, and the compressive strength was 10.93 MPa. The thermal conductivity of the carbon foam was 0.907 W·m^-1·K^-1 at room temperature, which was lowered by 49.67 % in comparison with phenolic-based vitreous carbon.