The effect of SiC addition on the crystallization kinetics of atmospheric plasma–sprayed basalt-based coatings

The crystallisation kinetics of the conversion of a glass coating layer made from a mixture of natural basalt volcanic rock and SiC into glass-ceramic have been investigated. The process depends on the crystallisation temperature, time and amount of the SiC added. Coating powders were prepared from pure basalt and from basalt containing 10–50 wt% SiC. The powders were coated by an atmospheric plasma spray technique on the pre-coated AISI 1040 steel substrate with Ni–Al. The coating layer was vitrified by sudden cooling. The amorphous structure of the coatings was verified by X-ray diffraction (XRD) analysis. To obtain glass-ceramic, coatings were subjected to crystallisation heat treatment in an argon atmosphere. Crystallisation heat treatment temperatures of 800 °C, 900 °C and 1000 °C were chosen by using DTA. After the heat treatment process, augite, ferrian-diopsite, diopside, albite, andesine, and moissonite phases formed in the coating layer and were verified by XRD analysis. The crystallisation activation energies were determined to be between 323.4 kJ/mol and 253.2 kJ/mol, depending on SiC addition. The crystallisation activation energies decreased with increasing amounts of SiC addition. The Avrami parameters of the crystallisation process varied between 1.60 and 3.33, which indicates that internal crystallisation dominated for all of the compositions.     

Fading-ratio-based selection for massive MIMO systems under line-of-sight propagation

Wireless Networks - Massive multiple-input multiple-output (MIMO) enables increased throughput by using spatial multiplexing. However, the throughput may severely degrade when the number of users...     

Tribological Properties of SiC-Reinforced Basalt-Based Coatings

In the current study, the wear behaviour of basalt-based glass and glass–ceramic coatings was investigated. SiC-reinforced basalt-based powders were coated by an atmospheric plasma spray process and evaluated using the ball-on-disk wear test. X-ray diffraction analysis, scanning electron microscopy, and optical microscopy were employed for characterisation. The friction coefficients of the basalt-based glass and glass–ceramic coatings ranged from 0.38 to 0.55 and from 0.12 to 0.70, respectively, depending on the wear condition and SiC content. The wear test results show that SiC addition has a positive effect on the wear resistance of the glass and glass–ceramic coatings.     

Characterization of cordierite based h-BN doped ceramics as an electronic substrate/circuit board material

In this study, h-BN was added to the cordierite composition obtained from zeolite, which was prepared by the determined stoichiometry to facilitate machinability and increase thermal conductivity. Sintering behavior, hardness, machinability, and thermal/electrical properties of the samples obtained by sintering the compounds at different times were investigated. Thanks to these features, it is aimed to use cordierite as an alternative material to integrated circuit substrates and electronic packaging materials. The produced samples were analyzed by X-ray diffraction analysis, examined by scanning electron microscopy, and field emission scanning electron microscopy. Afterward, thermal properties such as thermal diffusivity, thermal conductivity, and electrical properties such as electrical conductivity and dielectric permittivity were measured. The hardness and machinability of samples were investigated. Cordierite, spinel, glassy phase, and h-BN phase were detected, and it was observed that the blocky cordierite grains turned into equiaxed grains with the increase of the h-BN. According to the results obtained from the thermal conductivity test, it was seen that the h-BN additive increased the thermal conductivity value in general. In addition, it was determined that with the increase of h-BN, the hardness decreased, and the machinability properties of the samples improved.     

Scenario-based query processing for video-surveillance archives

Automated video surveillance has emerged as a trendy application domain in recent years, and accessing the semantic content of surveillance video has become a challenging research area. The results of a considerable amount of research dealing with automated access to video surveillance have appeared in the literature; however, significant semantic gaps in event models and content-based access to surveillance video remain. In this paper, we propose a scenario-based query-processing system for video surveillance archives. In our system, a scenario is specified as a sequence of event predicates that can be enriched with object-based low-level features and directional predicates. We introduce an inverted tracking scheme, which effectively tracks the moving objects and enables view-based addressing of the scene. Our query-processing system also supports inverse querying and view-based querying, for after-the-fact activity analysis. We propose a specific surveillance query language to express the supported query types in a scenario-based manner. We also present a visual query-specification interface devised to facilitate the query-specification process. We have conducted performance experiments to show that our query-processing technique has a high expressive power and satisfactory retrieval accuracy in video surveillance.     

Grain growth kinetic in xTiO2–6 wt.% Bi2O3–(94 − x) ZnO (x=0, 2, 4) ceramic system

The grain growth kinetics in the 0, 2 and 4 wt.% TiO₂ added ZnO–6 wt.% Bi₂O₃ system was studied using the simplified phenomenological grain growth kinetics equation together with the physical properties of the sintered samples. The grain growth exponent value (n) and the apparent activation energy for the ZnO–6 wt.% Bi₂O₃ system was 5 and 218 kJ/ mol, respectively. The addition of the TiO₂ to the ZnO–6 wt.% Bi₂O₃ system inhibited the ZnO grain growth. At 2 and 4 wt.% TiO₂ additions, the apparent activation energies were calculated as 467 and 346 kJ/ mol, respectively. The addition of TiO₂ to the system inhibited the grain growth of ZnO ceramics.     

Square-Wave Operation of a Thermal Conductivity Detectort†

SUMMARY

Equipment is described for the operation of thermal conductivity detectors with square-wave bridge current. The resulting ac output signal allows amplification without the need for low-level choppers. With phase-locked demodulation of the amplified signal, bridge unbalance signals of the order of 10 nV can be detected. This performance exceeds the requirements of presently available detector cells, which produce noise levels of the order of 100 nV.

The instrument is compatible with most existing hot wire detectors and may be used with economical recorders. Air and other permanent gases can be reliably analyzed at levels of 0.02 μl, with detection limits of the order of 0.002 μl. This performance makes the instrument attractive in the field of air pollution and opens the way to further research in the design of low-noise detector cells.     

Chain extension reactions of unsaturated polyesters with bis(2‐oxazoline)s

Two different bisoxazolines, 2,2′‐(1,3‐phenylene) bis(2‐oxazoline) (1,3‐PBO) and 2,2′‐bis(2‐oxazoline) (BO) were investigated as chain extenders for short chain unsaturated polyesters (UPEs). These extenders reacted readily with carboxyl ends of unsaturated polyesters, leading to rapid molecular weight increase through coupling of oligomeric chains. Commercially available unsaturated polyesters commonly have molecular weights around 1500, usually reached after a 20‐h polyesterification reaction. When bisoxazolines were reacted with short UPE chains obtained at the 6th hour of a commercial polyesterification reaction, the molecular weight of UPE reached 1500 within 5–30 min, which provides economies and prevents the glycol loss and yellowing which are associated with extended reaction times. Styrene solubility, gel time, and thermal and mechanical properties of the chain extended polyesters remained comparable to the commercial UPE, with 8–10 min of gel time and a storage modulus about 3000 MPa. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The effect of chromite ore addition on crystallization kinetics of basalt based machinable glass-ceramics

In this study, the properties of machinable glass-ceramic materials produced from basalt and chromite ore were investigated. Three different compositions by adding chromite ore in different ratios to the main composition produced from basalt and MgF₂ were prepared. In this way, the effects on the machinable glass-ceramic of chromium and iron oxides in the chromite ore were investigated. Thermal degradation of chromite ore and the effect of its compounds on the crystallization of machinable glass-ceramics were investigated. The samples were subjected to machinability testing. Scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) were used for characterization. The results show that chromite addition has positive effects on crystallization and machinability. Also, crystallization kinetic studies were realized. It was seen that the effect of iron oxide in chromite ore on crystallization is higher than that of chromium oxide for the crystallization conditions that used chromite ore as a nucleating agent.