Bijan Eftekhari Yekta

Bio: Bijan Eftekhari Yekta is an academic researcher from Iran University of Science and Technology. The author has contributed to research in topics: Crystallization & Fourier transform infrared spectroscopy. The author has an hindex of 12, co-authored 39 publications receiving 414 citations.

Floor tile glass-ceramic glaze for improvement of glaze surface properties

Abstract: Simultaneous improvement of surface hardness and glossiness of floor tile glaze, without changing its firing temperature, was the main purpose of the present paper. Thus, various glazes in the system of CaO–MgO–SiO2–Al2O3–ZrO2 were prepared and their crystallization behaviors within a fast firing cycle were investigated. With increasing amounts of calcium and magnesium oxides to base glass, the optimum glass-ceramic glaze was obtained. The results showed that with increasing of CaO and MgO part weights in frit, the crystallization peak temperature was gradually decreased and the intensities of diopside and zirconium silicate were increased. The comparison of micro hardness for the optimum glass ceramic glaze derived in this work with a traditional one used in floor tile industries indicates an improvement of 21%. It was found that the glaze hardness not only depend on the amount and type of crystalline phases, but also on the residual glass composition. Furthermore, it was observed that the glaze micro hardness is only slightly affected by thermal expansion mismatch of body and glaze.

Upconversion for Photovoltaics – A Review of Materials, Devices and Concepts for Performance Enhancement

Abstract: Upconversion of low-energy photons into high-energy photons increases the efficiency of photovoltaic devices by converting photons with energies below the absorption threshold of the solar cell into photons that can be utilized. In this review, an overview is provided of quantitative studies of the upconversion quantum yield of upconverter materials, and of the achieved efficiency enhancements in upconverting solar cell devices. Different materials and devices are compared based on well-defined figures-of-merit and the challenges to their accurate measurement are discussed. Internal upconversion quantum yields above 13% have been reported both for Er3+-based materials as well as for organic upconverters, using irradiance values below 0.4 W cm−2. On the upconverting solar cell device level, relative enhancements of the solar cells' short-circuit currents by up to 0.55% have been achieved. These values document progress by orders of magnitude achieved in the last years. However, they also show that the field of upconversion needs further development to become a relevant technology option in photovoltaics. Different options regarding how upconversion performance can be increased further in the future are outlined.

Is there a potential for durable adhesion to zirconia restorations? A systematic review

Abstract: Statement of problem With a number of zirconia ceramic materials currently available for clinical use, an overview of the scientific literature on the adhesion methods and their potential influence is indicated. Purpose The purpose of this systematic review was to classify and analyze the existing methods and materials proposed to improve adhesion to zirconia surfaces. Material and methods The current literature of in vitro studies examining the bond strength on zirconia ceramics, including clinical studies from 1998 until 2014, was analyzed. A search of the English language literature was undertaken using MEDLINE and PubMed, and a hand search was made for any relevant research paper from the library of a dental school. Papers evaluating only alumina restoration bond or ceramic-zirconia bond were excluded. Results A total of 134 publications were identified for analysis. Different adhesive techniques with different testing methods were reviewed. Results were difficult to compare in that the parameters varied in each research protocol. Conclusions Airborne-particle abrasion and tribochemical silica coating are reference pretreatment methods. Adhesive monomers are necessary for chemical bonding. Surface contamination and aging have negative effects on adhesion to zirconia. Many factors influence each combination of zirconia material, such as surface treatment, adhesive medium, and aging conditions. Laboratory studies should be confirmed by clinical trials.

Glass–ceramic glazes for ceramic tiles: a review

Abstract: Glass–ceramics are ceramic materials produced through controlled crystallisation (nucleation and crystal growth) of a parent glass. The great variety of compositions and the possibility of developing special microstructures with specific technological properties have allowed glass–ceramic materials to be used in a wide range of applications. One field for which glass–ceramics have been developed over the past two decades is that of glazes for ceramic tiles. Ceramic tiles are the most common building material for floor and wall coverings in Mediterranean countries. Glazed tiles are produced from frits (glasses quenched in water) applied on the surface of green tiles and subjected to a firing process. In the 1990s, there was growing interest in the development of frits that are able to crystallise on firing because of the need for improvement in the mechanical and chemical properties of glazed tiles. This review offers an extensive evaluation of the research carried out on glass–ceramic glazes used for covering and pavement ceramic tile is accomplished. The main crystalline phases (silicates and oxides) developed in glass–ceramic glazes have been considered. In addition, a section focused on glazes with specific functionality (photocatalytic, antibacterial and antifungal activity, or aesthetic superficial effects) is also included.

Vanadium Dioxide: The Multistimuli Responsive Material and Its Applications

Abstract: The reversible, ultrafast, and multistimuli responsive phase transition of vanadium dioxide (VO2 ) makes it an intriguing "smart" material. Its crystallographic transition from the monoclinic to tetragonal phases can be triggered by diverse stimuli including optical, thermal, electrical, electrochemical, mechanical, or magnetic perturbations. Consequently, the development of high-performance smart devices based on VO2 grows rapidly. This review systematically summarizes VO2 -based emerging technologies by classifying different stimuli (inputs) with their corresponding responses (outputs) including consideration of the mechanisms at play. The potential applications of such devices are vast and include switches, memories, photodetectors, actuators, smart windows, camouflages, passive radiators, resonators, sensors, field effect transistors, magnetic refrigeration, and oscillators. Finally, the challenges of integrating VO2 into smart devices are discussed and future developments in this area are considered.