Papers by Keyword: Color

Abstract: The thermochromic properties (color change with temperature) of n type doped SiC wafers of different polytypes (3C, 4H and 6H) have been investigated up to 500°C under air. It was found that 3C-SiC color passes from bright yellow at room temperature to deep orangeat 500°C leading to a color contrast (ΔE) as high as 64. The hexagonal polytypes undergo also a color change upon heating but far less pronounced, with ΔE values <20. All these semiconductors undergo band gap shrinkage upon heating which effect largely participated to the observed color change. This effect is very sensitive for 3C polytypesince its bandgap is already in the visible energy range at room temperature. The thermochromicity of 3C-SiC was found to be reversible thanks to its thermal stability and its resistance towards oxidation.

Abstract: In recent years, the use of hazardous heavy metals has been banned all over the world, and the development of alternative materials is required. As for inorganic pigments, heavy metals have been used so far, but there is an urgent need for development of inorganic pigments that do not use these. In this work, novel phosphate pigments imitated natural ore were prepared from copper, iron, aluminum nitrate solutions, ascorbic acid, and phosphoric acid at pH 5. The obtained precipitates were heated at 300 and 500oC for 1 hour. The precipitates and their thermal products were estimated with X-ray diffraction (XRD), Infrared (IR) spectra, ultraviolet–visible (UV–Vis.) reflectance spectra, and L*a*b* color space. By adjusting the Cu/Fe ratio and temperature, inorganic phosphate pigments of light blue, green, yellow, orange, brown and red could be obtained.

Abstract: There are shown studies on influence of film-forming components on the corrosion resistance of powder coating. Protective and decorative powder coatings - one of the most promising types of paints and varnishes for industrial use. Their main advantages are: absence of solvents, practically waste-free coating technology (the degree of powder utilization during application is close to 100 relative simplicity and cost-effectiveness of the production process of coating. The study of protective properties of powder coatings is associated with the detection of high performance properties and high corrosion resistance of the material. Although corrosion resistance of powder coating performance continues to improve via the design of more effective film-forming components the nomenclature of which is wide enough.

Abstract: Modern alternative to chemical methods of wood modification is heat treatment, which allows to increase biological stability, to reduce the hygroscopicity of the material and to improve the appearance of products. One of such technologies is heat treatment in liquids. However, this method is characterized by a considerable duration of the process because of cooling the material directly in the liquid. The aim of this work is to improve the technology of thermal modification of wood in liquids by reducing the duration of cooling phase without additional energy consumption. The results of experimental studies of the proposed technology of heat treatment of wood are presented. The obtained data on changes in wood density show that at increasing the average density of the material, there is a reduction in the density of its central layers that is explained by impregnation of the surface layers of wood with wood agent. It can be stated, basing on the analysis of the depth of impregnation of different wood species, that the rate of flow of impregnating liquid is directly proportional to the temperature of heat treatment, in the same time the depth of penetration of the treatment agent into the lumber depends not on treatability of natural wood but its basic density. Therefore, heat treatment of wood in hydrophobic liquids is more rational to use for hard species with greater density, and consequently, a smaller depth of penetration of the treatment agent, which will reduce the flow rate of hydrophobic liquid when carrying out the process and avoid large losses of material during subsequent mechanical processing.

Abstract: In dentistry, metal-free ceramic systems are used to improve optical properties in dental restorations. Ceramics based on tetragonal zirconia ZrO₂-Y₂O₃ are used in the manufacturing of dental prostheses for being biocompatible and for presenting proper mechanical and optical properties. Most of tetragonal zirconia blocks are commercialized in one only hue, which difficult the achievement of high aesthetic performance due to the tooth’s polychromatic characteristics. This work proposes to obtain tetragonal zirconia blocks fabricated by uniaxial cold pressing in different hues which could provide ceramic prostheses with better aesthetic results in less time. Zirconia blocks in two different colors were produced and characterized for their physical properties and mechanical resistance. The colors difference between the layers was obtained by using different amounts of Fe₂O₃. Ceramics with relative density superior to 99% were obtained by sintering the materials at 1530oC for 120 minutes. The mechanical properties evaluated indicated hardness close to 1270HV and fracture toughness of 7MPa.m^1/2. Blocks with different hues may be an alternative in order to favor the aesthetics in the cervical region and decrease the amount of ceramic veneering.

Abstract: One of the most important urban areas is street s and intersections that play an important role in shaping the overall identity of a city. The city is defined by the presence of the humans at night and nightlife plus visual sense plays the most important role in the perception of urban space. In addition, most of the things that are received by the sense of sight are with the help of light. Therefore, light and lighting in urban spaces as a non-physical element will have a huge impact on the quality of urban space. The main question in this study is the effects of lighting on the pedestrians’ understanding of the sense of security in Valiasr Street .In this regard, two variables of light color and light intensity are evaluated and considered based on eight hypotheses. To test these hypotheses, the main variables were first investigated and scrutinized. Then, according to the survey conducted, indicators related to the variables were determined and the items were designed. The main data collection tool is the questionnaire and among the pedestrians of Valiasr Street in Tehran that were selected as statistical population, 228 persons were randomly questioned. Due to the discrete nature of variables, a nonparametric function was used for their analysis. Calculation method using Kendall’s correlation analysis was analyzed using SPSS software. The findings show that that the satisfaction rate of light intensity is low, but their satisfaction with the lighting, light color, sense of security, and the ability to recognize faces is assessed averagely. Regarding the light color, people preferred white color to yellow one. The findings in this study suggest that using the white light instead of yellow and increase of light intensity increase the sense of security in pedestrians.

Abstract: This study examined the chemical stability of malayaite pigments in ceramic glazes containing high amounts of zinc oxide (ZnO). The calcined pigments were embedded in a molten glaze which is basically corrosive glass. Within the glaze, ZnO has been known among potters to be undesirable as some pigments are not stable in glazes containing ZnO. The synthesized pigments’ particle size ranges from 4 to 18 μm without dominant preferential orientation. Their colors were in the red and yellow tones. Chemical stability between the pigments and glazes was tested using X-ray Diffraction (XRD). Slight changes were observed. Increasing amounts of ZnO resulted in an interfacial layer of approximately 50 μm between the crystalline pigment and surrounding amorphous glaze. The a color parameters gradually decreased while the b parameters switched to a negative value. The resulting glazes evolved from maroon to pale violet. The correlation between color and microstructural alterations was discussed.

Abstract: We report herein, the synthesis of colorful nanofibers by electrospinning and dyeing with various class of dyestuff. Results revealed that dyes impart better color yield with the acceptable colorimetric values, color yield and color fastness. Morphology of nanofibers showed smooth surface of the dyed nanofibers under SEM. Cellulose nanofibers in particular, were prepared using precursor cellulose acetate and then converted into cellulose under alkaline treatment. Results revealed that dyes impart better color yield with the adequate color yield (KS) and color fastness. Morphology of nanofibers showed smooth nanofibers after dyeing under SEM. Based results obtained, the colorful nanofiber can be a better choice for advance apparel applications.

Abstract: Content-based image retrieval (CBIR) system becomes a hot topic in recent years. CBIR system is the retrieval of images based on visual features. CBIR system based on a single feature has a low performance. Therefore, in this paper a new content based image retrieval method using color and texture features is proposed to improve performance. In this method color histogram and color moment are used for color feature extraction and grey level co-occurrence matrix (GLCM) is used for texture feature extraction. Then all extracted features are integrated for image retrieval. Finally, color histogram, color moment, GLCM and proposed methods are tested respectively. As a result, it is observed that proposed method which integrates color and texture features gave better results than the other methods used independently. To demonstrate the proposed system is successful, it was compared with existing CBIR systems. The proposed method showed superior performance than other comparative systems.

Abstract: The barium titanium based PTC ceramic with two kind of colors, light blue and yellow, were obtained by changing sintering processing. In order to reveal the relationship between color and electrical properties of the ceramics. The phase structure and microstructure of as synthesized samples were investigated by powder X-ray diffraction (XRD) and scanning electron microscopic (SEM) analysis. The micro area elements were characterized by electron probe micro-analyzer (EPMA) and x-ray photoelectron spectrometer (XPS). The thermo-sensitive properties were studied by resistance-temperature measurement system. The results reveal that two kinds of PTC ceramics have the same structure, similar elements, but different microstructure and valence concentration of titanium. It is suggested that difference of color of the PTC ceramics are originated from the defect concentration of titanium.