Temperature Effect on the Physical Properties of Enamel Paint Layer on Cement Plaster

The heating effect on the stability and visual colour of enamel paint on cement plaster is evaluated through light intensity ratio of three primary colours (RGB). The painted cement plaster is isochronally heated in an electric resistance furnace at different temperatures for one hour. The investigation of optical images reveals that the original colour of the paint layer on the plaster samples remains more or less unchanged up to heating at 100°C. However, thermal degradation of the samples becomes evident in colour when they are heated beyond 200°C and at 350°C the colour becomes already burned. The microstructural images of the samples at room temperature show fine and uniform grains. But at higher heating condition the microstructure of the colour sample is characterized by coarsening grain. The colour of the heated samples are then studied through tristimulus colour ‘L*’, ‘a*’ ‘b*’ and ‘E*’ values which were analyzed and evaluated in MATLAB software. The results show that after 200°C the hunter ‘L*’ value starts to decrease greatly up to 250°C. The hunter ‘a*’ value shows an increasing trend up to 100°C and then begins to decrease until 200°C. After 200°C the same increasing character is showed till 300°C. The change of hunter ‘b*’ value remains insignificant up to 100°C and shows decreasing trend between 100°C-250°C range and an increase after 250°C up to 300°C. It is graphically shown that the proportion of all three colours decreases with the increasing temparature. The overall change of colour ‘E*’ occurs with increasing heating temperature due to moisture releasing, chemical changes and thermal degradation simulteneously. The thickness of enamel paint layer comply the above degradation by showing the nature of decresing trend. Journal of Engineering Science 12(2), 2021, 103-108

Clinopyroxene Solid Solutions in the CaMgSi2O6 – Ca0,5AlSi2O6 Cross-Section at High P-T Parameters

Clinopyroxenes (Cpx) are one of the main rock-forming minerals, but stoichiometry of their compositions was called into question. In particular, an idea of hypothetical calcium molecule Eskola (CaEs, Ca0,5AlSi2O6) existence was expressed. This minal has structure vacancy and silica excess. Numerous experimental investigations in CMAS-system (CaO-MgO-Al2O3-SiO2) have showed that the question of non-stoichiometric Cpx existence remains open. This paper presents the results of an experimental study of the diopside Di (CaMgSi2O6) – calcium molecule Eskola CaEs (Ca0,5AlSi2O6) cross-section in the CMAS-system. The experiments were carried out in the following pressure and temperature range: P=10-4 – 3,0 GPa; T=966 – 15250C. Experiments at atmospheric pressure (10-4 GPa) were performed on a vertical shaft electric resistance furnace; high-pressure ones were performed on a "piston-cylinder" type apparatus. Samples obtained were analyzed using electron microprobe (EMP), scanning electron microscope (SEM) and Raman spectrometer. Depending on the P-T conditions, the samples contain the following phases: anorthite An, garnet Grt, diopside Di, clinopyroxene Cpx, quartz Qtz (tridymite Tr – for experiments at atmospheric pressure), and glass L. The data array on the composition of clinopyroxenes crystallized in this cross-section with diopside in various associations is generalized and supplemented. Clinopyroxenes were found to form quaternary solid solutions of diopside Di (CaMgSi2O6) – enstatite En (Mg2Si2O6) – calcium molecule Tschermak CaTs (CaAl2SiO6) – calcium molecule Eskola CaEs (Ca0,5AlSi2O6). The CaTs and CaEs minals contents are positively correlated with the amount of aluminum in clinopyroxene, and this relationship is particularly pronounced for CaTs. It is confirmed that clinopyroxenes in this cross-section can contain an excess of silica at both atmospheric and high pressures. Apparently, the cation vacancy that exists in pyroxene structure can participate in ordering processes. As a result the pyroxenes of another structure (not diopside – C2/c-symmetry) can be crystallized from total compositions in the Di-CaEs cross-section. Additional research is needed to support this hypothesis. Besides, at present investigation it was not possible to establish an unambiguous relationship between the Cpx composition and P-T-parameters, since it is also associated with both the mixture initial composition and the mineral association. Further experiments are required to justify any geothermobarometric dependence.

SINTERING OF MLCC’S BARIUM TITANATE WITH MICROWAVES

A comparison of microwave and conventional, in an electric resistance furnace, sintered layers of dielectric base barium titanate (BaTiO3) of the kind employed for multilayer ceramic capacitors (MLCC) was performed. Two kinds of samples were used for each processing method; the layers alone without electrodes, and the green MLCC with the layers and electrodes interdigitated. Samples were exposed to microwaves for 20 minutes and heated up to 1050°C and 1150°C for sintering in a crucible with graphite that acted as reduction agent and microwave susceptor. Conventional sintering was performed in the same arrangement but lasted 120 minutes since it was found that 20 minutes was not enough time to achieve sintering. Heating rate in both cases was 10 °C/min. It was observed that the layers without the electrodes achieve about the same densification for both processes, while in the case of the green MLCC’s the results were variable, ranging from sample that became dust, to cracked samples and some well sintered ones. At least in the microwave case, it is possible that the variability of the results is due to the importance of the location of the sample in the cavity that in turn affects the electric field pattern, especially because the presence of the electrodes that can cause overheating around them.

Transformation of Oxide Inclusions in Stainless Steel Containing Yttrium during Isothermal Heating at 1473 K

To provide fundamental information on the control of rare earth inclusions in solid steel, two 18 mass% Cr-8 mass% Ni stainless steels with different yttrium additions were prepared using an electric resistance furnace and the evolution of yttrium-based oxide inclusions during heat treatment of the steels at 1473 K was investigated. In both as-cast steels, homogeneous spherical Al-Y-Si(-Mn-Cr) oxide inclusions were observed; however, the steel with larger yttrium additions also had some heterogeneous oxide inclusions with double phases. After heating, a new oxide phase with higher yttrium content precipitated from the original inclusions and resulted in partitioning to Y-rich and Al-rich parts in both steels. The average size and number density of inclusions slightly increased, and the morphology of inclusions changed from spherical to irregular. The transformation mechanism during isothermal heating was proposed to be the mutual effects of (i) internal transformation of the yttrium-based inclusions owing to crystallization of glassy oxide and (ii) interfacial reaction between inclusions and the steel matrix.

Study on Sulfur Transfer Behavior during Refining of Rejected Electrolytic Manganese Metal

A slag treatment method was proposed to recycle rejected electrolytic manganese metal. To improve the sulfur removal ratio, computational fluid dynamics and experimental studies of the sulfur transfer behavior during the refining process were carried out. Experiments of slag-metal reaction for desulfurization were carried out using an electric resistance furnace at temperatures ranging from 1773 K to 1923 K. A transient three-dimensional coupled numerical model was established to represent the three-phase flow, heat and mass transfer in the experiment. The desulfurization rate was described by a metallurgical kinetics module, which was related to the slag composition, the interfacial tension coefficient, the flow and the temperature of the melt. The predicted sulfur content agreed reasonably well with the measured data. The temperature of the fluids at the outer side of the crucible was higher than that at the center, resulting in a larger sulfur partition ratio and a more vigorous flow. The sulfur transfer rate was higher at the outer edge of the molten slag–molten manganese interface. The sulfur removal ratio increased from 51.4% to 85.1% with a change in heating temperature from 1773 K to 1873 K, and slightly dropped to 83.3% when the heating temperature increased to 1923 K. The heating temperature of 1873 K is the optimal choice for recycling in the present work.

Pack-Boriding of Pure Iron with Powder Mixtures Containing ZrB2

Boriding of pure iron was investigated using the powder pack method with boriding powder mixtures containing different weight fractions of ZrB2 (5 %, 10 %, 15 % and 20 %). The samples were borided in an electric resistance furnace for an exposure time of 4 h at 1,173 K temperature under atmospheric pressure. Borided samples were characterized by optical microscopy, X-ray diffraction analyses and microhardness tests. Results showed that the boride layers consisted mainly of FeB and Fe2B phases. No significant difference in boride layer thicknesses (average 140 μm) could be observed as a function of ZrB2 content. The needle-like morphology of the boride layer became more prominent with increasing weight fraction of ZrB2 in the boriding powders. The average microhardness of the boride layer decreased with increasing ZrB2 content due to changes in the morphology of the boride layer.

Sericitic Phyllite as Addition in Portland Cement

Pozzolans are materials that when milled are able to react with the cement, forming compounds with binder properties. Seeking to reduce costs and improve Portland cement performance, the cement industry has used mineral additions such as pozzolans, partially replacing clinker in Portland cement. Sericitic Phyllite is a metamorphic rock, considered sterile by iron mining. It is extracted from the pit to enable the extraction of iron ore and is disposed in sterile piles, representing an environmental liability. The present work evaluated the possibility of the Sericitic Phyllite acquires pozzolanic properties from thermal treatment, to be used as mineral addition in the partial substitution of Portland cement in mortars. The material was processed by milling in its natural moisture of 8% using a high performance planetary mill, and calcination in an electric resistance furnace at different temperatures (350, 550 and 850oC) for thirty minutes each. It was characterized by laser granulometry, X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal and thermogravimetric analysis (DTA/TGA). After characterization, specimens were prepared with 25% substitution by weight of the Portland cement by the Sericitic Phyllite. The calcined material in 350, 550 and 850oC reached, respectively, 70%, 76% and 82% of the resistance of the control mortar. The results indicate the feasibility of using the Sericitic Phyllite as mineral addition in Portland cements as the mortars with the calcined material in all temperatures reached 32MPa.