EFFECTS OF OV-POSS NANOPARTICLES ON THE VULCANIZATION KINETICS OF NATURAL RUBBER COMPOUNDS

Polyhedral oligomeric silsesquioxanes (POSSs) are new-generation additives, which can provide improved properties in polymer matrices by physical and/or chemical interactions between the polymer molecules and their reactive sites. In the case of rubber-based polymeric systems, POSSs are also able to accompany with the vulcanization reaction. In this study, it was aimed to investigate the effect of octavinyl functionalized POSS (OV-POSS) on sulphur vulcanization of a model natural rubber (NR) based compound. The reaction kinetics was studied by using various kinetic approaches based on Moving Die Rheometry and Differential Scanning Calorimetry. Rheometric data was evaluated by using a common non-linear cure kinetic model, which is called Isayev and Deng Model. Kissinger, Flynn-Wall-Ozawa, and Crane Models were used to process thermal data for curing reactions. All the models were found to be able to analyze vulcanization kinetics of OV-POSS containing NR-based rubber compounds as well as the effect of OV-POSS incorporation.

A NOVEL DESIGN OF PERISTALTIC CARBON NANO PUMP AND AN ANALYSIS OF HELIUM FLOW

A novel nano-scale pump that can transport atoms or small molecules with a peristaltic motion is designed. It is proven by molecular-dynamics simulations that the introduced nano-pump design works properly. The designed nano-pump consists of one main carbon nanotube named the flow tube and two rotors where multi-walled carbon nanotubes are attached. The pumping of helium atoms by the designed peristaltic carbon nano-pump is investigated by molecular-dynamics simulations. For varying rotor speeds and blade counts, time-averaged velocity, temperature, and pressure results of pumped helium atoms are calculated, and relationships between them are modeled as polynomial surfaces. The results showed that rotor frequency increases the velocity of helium linearly and the temperature and pressure of helium non-linearly. Furthermore, the blade count of the proposed mechanism does not substantially affect the velocity as per the previous studies in the literature.

OPTIMIZATION OF TRIBOLOGICAL PROPERTIES OF AN EPOXY HYBRID POLYMER COMPOSITE REINFORCED WITH ZrB2 AND PTFE PARTICLES USING RESPONSE SURFACE METHODOLOGY FOR HIGH-TEMPERATURE TRIBOLOGICAL APPLICATIONS

Hybrid PTFE/epoxy composites are widely used as materials for self-lubricating spherical bearing which are used in a high-temperature environment. In the present work, zirconium diboride (ZrB2) particles are incorporated to enhance high-temperature tribological properties of PTFE/epoxy composites. Pin on disc experiment is conducted with the aid of design of experiments (DOE) using central composite-response surface methodology (RSM). Under a load of 40 N and 1.25 m/s sliding speed, the optimum content 5.95 vol% of PTFE and 5.05 vol% of ZrB2, yields an ultralow coefficient of friction (COF) in conjunction with a low wear rate of the composite. The addition of ultra-high-temperature ceramic ZrB2 particles and solid lubricant PTFE is found to enhance the thermal conductivity and improve the heat transfer thereby reducing contact temperature. The use of optimum composition of the composite is capable of reducing the wear rate and high local temperature due to friction, implying its potential use as a self-lubricating spherical bearing liner material.

CHARACTERISTIC OF XONOTLITE SYNTHESIZED BY HYDROTHERMAL REACTION USING RICE HUSK ASH AND ITS APPLICATION TO ABSORB CHROME (III) SOLUTION

In this paper, we report on synthesizing xonotlite, calcium silicate hydrate (CSH), via a hydrothermal reaction using rice husk from the Mekong Delta, Vietnam. The rice husks were burnt at 1000 °C for 3 h. Grey rice husk ash was collected, then mixed with Ca(OH)2 at a Ca/Si molar ratio of 1 : 1. This was followed by a hydrothermal reaction at 180 °C for 24 h and 48 h to obtain the xonotlite mineral. Before and after adsorption, 3-mm xonotlite pellets were thoroughly characterized using X-ray diffractometry (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and ultraviolet-visible (UV-VIS) spectroscopy. This material has potential application in chromium(III) removal during a chrome-plating process. The adsorption efficiency of the 3-mm pellet samples reached more than 76 % after 12 h.

EFFECT OF DIFFRENT LOADS ON THE WEAR BEHAVIORS OF 5Cr5Mo2V STEEL AT 700 °C

The effect of different loads on the high-temperature wear behavior of 5Cr5Mo2V steel at 700 °C was investigated. Wear morphologies, oxide compositions and matrix evolution were studied. The results showed that the wear rate increased with an increased test load, and the wear mechanism transformed from abrasive-oxidative wear to adhesive-oxidative wear. The relation between a delaminated oxide layer and cracks in the matrix were investigated. The exfoliation of carbides and displacement difference between the matrix and carbides caused a crack initiation. The wear rate strongly related to carbides, and coarse M6C carbides with poor holding power led to a high wear rate. Besides, a diagram of wear characteristics under different loads was suggested in this work.

COMPARISON OF THE CORROSION PROPERTIES OF CoCrMo DENTAL ALLOYS IN ARTIFICIAL SALIVA

CoCrMo alloys are known for their biocompatible properties, which, together with their favorable mechanical properties, mean they can be efficiently used in dentistry. With the development of selective laser melting for the fabrication of 3D printed objects, interest in the corrosion properties of this alloy has risen in the field of prosthodontics. In the study, CoCrMoW dental alloys were studied in artificial saliva at body temperature i.e. 37 °C. Different forms of CoCrMoW alloy were selected: a reference sample, i.e. original material as-received from the supplier, a casted sample acquired from an ordinary procedure in a dental laboratory, and two 3D printed samples made from CoCrMoW powder using the selective laser melting method (SLM). Electrochemical, spectroscopic and hardness measurements were conducted. It was shown that the reference and cast samples have similar microstructural and electrochemical properties, while the electrochemical properties of the 3D printed samples differ, most probably due to the effect of the higher micro porosity and chemical composition of the alloys.

EFFECT OF SALT-WATER AGING ON THE MECHANICAL PROPERTIES OF FLAX-WOVEN FABRIC-REINFORCED EPOXY COMPOSITES

In this investigation four varieties of plain derived-irregular basket-woven-flax fabric-reinforced epoxy (F-E) composites pre-treated with alkali and trimethoxymethylsilane (ATS) were prepared with a hand lay-up process by varying their weight fraction of fiber loadings (0; 25; 35; 45) w/%. A water-absorption test (salt water) as per ASTM D 570-98 was performed over the fabricated composites and studied its consequences on their static mechanical properties (such as tensile, flexural, impact and interlaminar shear strength) in accordance with the ASTM standards. The results revealed that salt-water-soaked ATS-treated F-E composites exhibited poorer mechanical properties than unsoaked ones. Moreover, this study elaborated the kinetics of water absorption and showed that the moisture-absorption rate depends on the weight fraction of fibre content. Furthermore, scanning electron microscopy (SEM) disclosed fiber splittings and severe damage at the fiber-matrix interface as experienced by soaked F-E composites.

RESEARCH ON MATERIAL FLOW-STRESS BEHAVIOR AND THE DIE-FORGING PROCESS FOR FORGED-STEEL BRAKE DISCS FOR HIGH-SPEED TRAINS

Due to the large size and complicated features, the brake discs of high-speed trains are difficult to forge, so a reasonable design of the process and the die parameter are prerequisites for successful forming. The flow stress of 23CrNiMoV, a forged-steel brake disc material for high-speed trains, was investigated by a uniaxial compression experiment on a Gleeble 1500 test machine. Based on the obtained flow-stress data, a series of numerical simulation analyses of the die forging of high-speed-train brake discs were carried out by using finite-element software. The effects of forging temperature, flash groove parameters and forming speed on the flow filling, forming load and temperature change of metal during die forging were studied. The simulation results were optimized and better process parameters were obtained. Based on the obtained process parameters, the simulation of the forming process was completed and a better forming quality was obtained.

HIGH-TEMPERATURE DEFORMATION BEHAVIOR AND HOT-PROCESSING MAP OF 25CrMo4 AXLE STEEL BASED ON FRICTION CORRECTION

The deformation behavior and microstructure of 25CrMo4 axle steel was systematically investigated by thermal compression deformation. The hot-compression test of a 25CrMo4 axle steel sample was carried out on a Gleeble-3800 thermal mechanical simulation tester. The flow behavior of the alloy was studied at the deformation temperature (900–1200 °C), strain rates (0.01; 0.1; 1.0) s–1 and the maximum deformation of 60 %. The flow curves under different deformation conditions were obtained, and the effects of the deformation temperature and strain rate on the appearance of the flow curves are discussed. The true stress-strain curve obtained by experiment is modified by friction. Based on the corrected experimental data, the activation energy determined by the regression analysis was Q = 311 kJ/mol, and the constitutive model was constructed. The high-temperature flow behavior of the 25CrMo4 axle steel was described by the Zener-Hollomon parameter. The optimum hot-deformation process parameters were determined based on the hot processing maps, followed by the analysis of the microstructure characteristics of the alloys under optimum hot working. The results show that the suitable hot-deformation process parameters of the alloy are as follows: deformation temperature is 1050–1200 °C, and strain rate is 0.01 s–1 to 0.14 s–1.

SUPERVISED TUNING OF A CHILLER WITH A COLD PHASE-CHANGE MATERIAL USING AN RSM-SMITH PREDICTOR

The proposed work is focused on the tuning of the latent-heat storage of a PCM with MWCNT encapsulation for a chiller system in the milk-pasteurization process using an RSM-based predictive Smith controller. The PCM was synthesized using sodium polyacrylate and MWCNT particles, encapsulated in spherical balls stored in the IBT (ice bank tank of the chiller unit). Experimental work is conducted on the heat-transfer characteristics of the chiller unit with servo-operated flow-control valves based on the central composite design of experiments. The system is cascaded using a PID controller with a Smith predictor to stabilize the latent temperature of milk cooling in the chiller system. The system is considered to be a first-order transformation with the rise and settling time. The plant model is obtained, using the response-surface method based on the transfer function to minimize the error derivatives of the chiller system. Results of the proposed method show a robust performance in keeping the PCM temperatures and bacterial-growth value stabilized, allowing a less drastic control compared to the cascade-model predictive control.