Materials Science Forum Vols. 663-665

Abstract: With the development of GPRS technology in the field of mobile communication, GPRS has been used in the system of radio data transmission at present. This paper explores the applications of GPRS in the mine monitoring and control system. In this paper we have done three things. we talk about the core cutting and moving and the system structure. we give a plan to realize the GPRS communication.

Abstract: The effects of Li2CO3-V2O5 (LV) co-doped on the sinterability, phase compositions and microwave dielectric properties of Mg4Nb2O9-CaTiO3 composite ceramics have been investigated. The phase compositions and microstructure were analyzed using X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy techniques. The densification sintering temperature is lowed from 1275oC to 1200oC with an amount LV addition. For the specimen with 1.5 wt% LV addition sintered at 1200oC for 5 h exhibited dielectric properties: εr=23, Q·f=24 000 GHz (at 7.7GHz ), τf =1.0 ppm/oC. These properties were correlated with the formation of non-stoichiometric compound Mg4(Nb1-xTix)2O9-δ.

Abstract: According to the definition, the calculation for the velocity resolution of a signal composed of several rectangular pulses is always complex, especially when it is a multiple-period signal. Apart from the definition formula of the resolution, the paper proposes a new fast algorithm for calculating velocity resolution by searching for the rows where the ‘half power value’ exists in ambiguity function matrix and then finding ‘half power point’ wide, avoiding the complicate and duplicated calculation and raising the efficiency.

Abstract: Nano-granular ZnO thin films were deposited on Si (100) by molecular beam epitaxy (MBE) by varying growth time. The atomic force microscopy (AFM) and Raman scattering experiments were performed to study the surface morphology and vibrational properties of ZnO layer. The results show that the ZnO thin film grows in the Stranski-Kranstanow (SK) mode, and the critical thickness in our experimental condition is between 5.5 and 8.2 nm.

Abstract: High quality boron-doped p-type freestanding diamond (FSD) films with smooth nucleation surface were prepared by hot filament chemical vapor deposition (HFCVD) method. The effects of B/C ratios on the electrical properties of FSD films were investigated by Hall effect measurement system. N-type Al-doped ZnO films were prepared on p-type FSD films by radio-frequency (RF) magnetron sputtering method to fabricate heterojunction. The I-V characteristic of the heterojunction was examined. The results showed a rectifying behavior of this structure.

Abstract: Undoped GaAs single crystal has been grown in PBN crucibles by the pulling-down method. The temperature profile of the furnace was optimized with a narrow melting zone and a small temperature gradient at the solid-liquid interface. Quartz ampoules were used to protect the evaporation of As during the growth and the deformation of the ampoule was discussed as a function of temperature, time and pressure differential. A Ø56 mm×70 mm GaAs crystal with nearly 100 % single crystalline yield was obtained. X-ray rocking curve analysis revealed the excellent crystalline quality. The average EPD and electrical properties of the crystal were tested comparable to those of the crystal produced by the VGF method. Therefore, the pulling down method was a feasible approach for GaAs crystal production.

Abstract: Amorphous nickel hydroxide powders doped with rare earth La3+ and Al3+ were synthesized by the combined chemical precipitation and rapid freezing method. The microstructure of the samples was characterized by XRD and Raman spectra. The electrochemical performance of the prepared samples was analyzed by electrochemical impedance spectroscopy and charge-discharge tests. The results showed that this amorphous nickel hydroxide codoped with La3+ and Al3+ had more structural defects than those of the undoped amorphous nickel hydroxide and La3+ singly doped amorphous nickel hydroxide. These abundant structural defects with La3+ and Al3+ codoped amorphous nickel hydroxide decreased the electrochemical impedance spectroscopy and improved the electrochemical reversibility of the amorphous nickel hydroxide electrode.

Abstract: The transmitted intensity and the modulation depth of plane polarized light are implemented to investigate influences of the low frequency external magnetic field on the ferrofluid film. The frequency of AC magnetic field is modulated from 5Hz to 400Hz, and the thickness of ferrofluid films are changed as 12 μm, 25 μm, 140 μm and 520 μm, and the mass concentration of magnetic nanoparticles is 5 %, 10 %, 20 % and 33.6 %, respectively. The experimental results show that (1) the mean value of the optical transmittance of ferrofluid film is decided by the thickness of ferrofluid film and the mass concentration of nanoparticles, but the frequency of magnetic field has no direct relation with it; (2) under a given magnetic field intensity, the optical modulation depth of ferrofluid film is determined by the film thickness, the nanoparticle concentration and the magnetic field frequency. It is further found that the single relaxation characteristics of magnetic nanoparticle, whose size is smaller than the critical value of the single magnetic domain, is the important factor of the frequency properties of nanoparticle in ferrofluid. These results may be beneficial to applications of ferrofluid in magneto-optic sensors.

Abstract: A thermal curable silver conducting paste used for preparation of the tag antenna coils of the radio frequency identification (RFID) tag was presented. The typical composition of the paste was determined as (wt%): flake silver powder, 59.80, spherical silver powder, 5.20, organic vehicle solution, 35.00. The paste was screen printed on the substrates of papers, and then thermal cured at the peak temperature of 130~150 Celsius degrees for 60-120 seconds. The SEM image indicated that the cured film was perfectly flat and compact. The sheet resistance of the cured film was about 2 milli-ohms per millimeter square at the thickness of 25 micros determined by a four-point probe technique. The pencil hardness (H) of the cured film was more than 2H. In addition, the rheological behavior of the typical paste demonstrated shear thinning property. The thixotropy behavior shown that the silver particles in the paste have flocculated weakly at rest.

Abstract: The glasses (80-x)TeO2·xV2O5·20MO (M=Sn, Bi, Ca, Na and K) had been examined as potential replacements for PbO-based glass frits with low firing temperature. The glasses with TeO2 0-44 mol%, and V2O5 39-82 mol% are not suitable for glass frit since they are easy to crystallize. The glasses with the content of the TeO2 54-74 mol%, and the V2O5 9-29 mol% were investigated by differential scanning calorimetry, X-ray diffraction, infrared spectra and fluidity evaluation experiments. The glasses possess appropriate fluidity and do not crystallize in the re-melting process at 723-753 K. The glass transition temperature of the glasses is at 544-578 K. The structure of the glasses is layer upon layer mainly connected by the structure units of [VO4] and [TeO3]. Other modifier ions locate mainly between the layers. The isolated V=O band from the VO5 bipyramids is not occurred in the vitreous structure of the glasses.