Advanced Materials Research Vols. 881-883

Abstract: Positive temperature coefficient of resistivity (PTCR) effect and electrical properties of (Ba_n-xSm_x)TiO₃ (BSMT ) samples with different Ba-site/Ti-site ratio (n) and various concentration of the donor-doped Sm³⁺ (x) sintered in a reducing atmosphere and reoxidized in air are investigated. The results show that the room temperature resistivity (ρ_RT) of the semiconducting BSMT ceramics first decreases and then increases with increasing of concentration of the donor-doped Sm³⁺, especially when x is 0.005 mol, the ρ_RT of the BSMT ceramics is the lowest. Moreover, the ρ_RT of the Ba-excess BSMT (n = 1.01) specimens reoxidized at 800 oC for 1 h after sintering at 1270 °C for 30 min in a reducing atmosphere is lower than the Ti-excess ones (n = 0.99), in addition, the ρ_RT of the BSMT specimens increases with an increase of both sintering temperature and reoxidized time.

Abstract: Porous silica ceramics were prepared from rice husk ash with a small amount of soft clay as workability agent by the in situ combustion pore-forming technique. Then, the effects of the forming pressures on the linear shrinkage, density, porosity, absorption of water and mechanical strength were investigated. The results showed that the pores in the samples consisted of two groups. One was original porous texture from rice husk silica, which ranged from 1-10 μm. The other was formed by burning of carbon and grain packing. Obviously, the greater the forming pressure, the denser the sample. Especially, the amounts of the pores with bigger diameter dropped significantly when the forming pressure was greater than 25KN. Porous ceramics with density 1.07g/cm³ have high porosity and excellent comprehensive properties up to 10MPa.The preparation of porous ceramics utilizing high content rice husk would provide advantages of economical and ecological aspect.

Abstract: With Al₂O₃ micro-powder as main raw material, a kind of microporous corundum aggregate was prepared by adding nanoAl₂O₃ powder. Effect of nanoAl₂O₃ powder on the properties of microporous corundum aggregates and its sintering mechanism were studied. The results show that, the closed porosity of sinter is too low when adding too less nanoAl₂O₃ powder; however, excessive nanoAl₂O₃ powder would lead to the separation of grain boundary and pores during the sintering process, partial crystal grow up abnormally, the relative density of sinter reduces. Microporous corundum aggregate with 5.2% apparent porosity and 9.2% closed porosity can be obtained with 3wt% nanoAl₂O₃ powder in this study.

Abstract: Using the natural forsterite and Na2CO3 as a raw material, the forsterite lightweight material was prepared in Na2CO3 molten salt. The reaction between forsterite and Na2CO3 and sintering mechanism of forsterite were studied in the paper. The sintering temperature was 1000 °C, 1100 °C, and the holding time was 1 h, 3 h, 5 h, 7 h, 10 h, respectively. The sintered samples were characterized by XRD and SEM for their microstructure and phase composition analysis which determined the mechanism of the chemical reaction and sintering in the sintering process. The product of Na2MgSiO4 phase in In earlier period of the reactions promoted the rearrangement of particles of forsterite in the initial stage of sintering process. The sintering mechanism was mainly controlled by the diffusion mechanism.

Abstract: In this paper, the effects of briquetting pressure on the performance of in-situ formed Sialon in Al₂O₃-C refractory bricks are investigated. The phase compositions and microstructure of the Al₂O₃-C refractory were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM).The results show the briquetting pressure hardly has effect on the phase of the sintered specimens, two new phases of Sialon with a Z value of 2 and SiC formed. The micrographs of Sialon crystals have the shape of both column and tabular column, but with a cone tip in the specimens sintered at 200MPa and 300MPa and smooth tip in specimens sintered at 400MPa and 500MPa.

Abstract: Abstract. SiCp/Cu composites because of their excellent performance in the aerospace, carrying tools in the field with a wide range of applications, but the poor interfacial bonding limits its application. To improve the interfacial bonding between SiCp and copper, we use Copper Plating on SiCp particles coated handle. The results show that the optimal process parameters for electroless plating copper on SiC particle is followed as:CuSO4•5H2O concentration of 30g/L, EDTA•2Na concentration of 1g/L, potassium ferrocyanide concentration of 2g/L, potassium sodium tartrate concentration 105g/L, plating temperature is 50°C, plating time was 40 minutes.With the increase of the pH from 10 to 13, the uniform dense electroless plating copper exists on SiC particle. With increase of temperature of electroless plating bath, the smooth copper coating on SiC particle can be obtained at 50°C.

Abstract: Beginning from the manufacture process of metal rubber material, the structure and electromagnetic shielding mechanic were studied. Based on the flange coaxial test, the shielding efficiency of metal rubber samples was measured and the mathematic model of electromagnetic shielding efficiency was deduced. Using Schelkunoff formula the number and fitting curve of shielding efficiency were got. It can be concluded as a new kind of functional material, the metal rubber material would be widely used in the field of electromagnetic shielding and packing.

Abstract: According to the principle of electromagnetic wave absorption, functionally reforming thermal insulating materials for building, through designing and theoretically simulating of the λ/4 model, using carbon fiber film, the article has successfully prepared insulation coatings for X-band electromagnetic wave absorption. Result shows, with the thickness of 3.0 mm in 8 ~ 12 GHz band, 100% of bandwidth below-10 dB can be reached. New materials can be used such as the surface of the thermal insulation of buildings and X-band electromagnetic interference protection.

Abstract: In order to improve acoustic stealth performances at high-frequency of underwater objects, macroporous resin beads–elastomer coatings with 2 mm of thickness were introduced for high-frequency acoustic-absorption. Meanwhile, an acoustic model was theoretically built on the transfer matrix method to calculate and analyze the influences of the coating loss factor, density, Young's modulus and the frequency on underwater acoustic absorption properties. Simulation results showed that the acoustic absorption coefficient curves had a periodic change own to the steel plate resonance effect, meanwhile, the greater coating loss factor, the better acoustic absortpion properties; the greater coating density, the better effect of acoustic absorption at low frequencies, but at middle and high frequency. the larger Young's modulus of coating, the smaller the acoustic reflection coefficient and then the better the acoustic absorption performance.

Abstract: Amorphous hydrogenated Ge1-xCx films are prepared by radio frequency (RF) magnetron cosputtering using Ge/graphite composite target and their composition, optical and chemical bonding properties as a function of bias have been investigated. The results show a decrease in the deposition rate with increasing bias, and the optical gap nearly keep constant due to effects of both composition and chemical bonding. Through the analysis of X-ray photoelectron spectroscopy, we find that the content of Ge-C bonds first increases and then decreases as increasing bias while the Ge-O bond decreases monotonically.