عباس هنربخش رئوف

In this study a nontoxic aldehyde with high boiling point entitled glyoxal was used for reaction with urea and Kraft lignin to prepare green adhesive entitled urea- lignin- glyoxal (LUG). The prepared LUG resin had used in particleboard manufacturing. Then the influence of nanoclay addition on various properties of particleboard made from LUG resin was investigated. For this reason, the kraft lignin (10 wt%) was used instead of second urea in urea- glyoxal resin synthesis. After LUG resin synthesis in acidic condition and measuring physicochemical properties of the prepared resins, the prepared LUG resin was mixed with the 0.5, 1 and 1.5% nanoclay by mechanically stirring for 5 min at room temperature. Then the prepared resin was used in particleboard manufacturing. The physical properties of the prepared resins such as viscosity, gelation time, solid content and density as well as physical (water absorption) and mechanical (internal bond strength and flexural properties) properties of manufactured panels were measured according to standard methods. Also X-ray Diffractometry (XRD) was used to investigate the distribution of nanoclay on LUG resin. The physical test results indicated that gelation time of the LUG resin is slower than that of UF resin. Addition of nanocaly from 0.5 to 1.5% accelerates the gelation time of the prepared resins whereas the fastest gelation time related to the LUG resin containing 1.5% nanocaly. Also XRD analysis indicated that nanoclay could good separate when was mixed with LUG resin. Based on obtained result, the addition of nanoclay decreased the water absorption content of the manufactured panels, significantly. The internal bond strength and flexural strength of the panels was increased by addition the amount of nanoclay. Finally it must be noted that the addition of nanoclay had no significant effect on flexural modulus of the manufactured panels.

In this study, some of the physical and mechanical properties of polypropylene fiber/ wood fiber/ cement composites were investigated. For this aim, three levels of polypropylene fiber, namely 2 wt.%, 3 wt.% and 4 wt.% were mixed with 15 wt.% of wood fiber mixed with cement in a rotary type mixer. The samples were formed by cold press method. Then water absorption, thickness swelling, flexural modulus, flexural strength, and impact strength of the manufactured composites were evaluated according to ASTM standard methods. The results showed that polypropylene fiber exhibited a positive effect on physical and mechanical properties of the wood- cement composites. The physical test results indicated that the hybrid composites containing 4% PP fiber/11% wood fiber exhibited the lowest water absorption and thickness swelling values. The mechanical test results also indicated that greater flexural strength and impact strength can be achieved by addition of 4% polypropylene fiber to wood- cement composites. Also the three point bending test results showed that addition of PP fiber from 2 to 4% decreased flexural modulus of the wood- cement composites, continuously.

Certain amount of retained austenite can increase ductility of steels because of the TRIP phenomenon during plastic deformation. One method for achieving this is partitioning of carbon into austenite to stabilize it at room temperature. The quenching and partitioning (Q&P) heat treatment leads to a microstructure consisting of martensite and stabilized retained austenite between martensite plates، which provides a better combination of strength and ductility. In this study، the effect of parameters of Q&P process (quenching temperature، partitioning temperature and partitioning time) on the microstructure and retained austenite volume fraction of a low alloy medium carbon steel was investigated. The results showed that the high increase in partitioning time causes the disappearance of martensite blades and reduction of austenite volume fraction. However، increasing of partitioning temperature made the retained austenite films become thicker and its volume fraction increase. On the other hand، by increasing the quenching temperature، carbon content of retained austenite increased sharply.

The quenching and partitioning (Q&P) process is a new heat treatment cycle to produce the third generation of advanced high strength steels based on diffusion of carbon from martensite to retained austenite phase. The application of this process for various steels leads to a remarkable combination of mechanical properties including high strength and good ductility. Using this process in automotive industry causes better mechanical performance, greater car safety, weight saving and cost reduction. In this study, a low alloy high carbon steel has been subjected to Q&P process and its microstructure and mechanical properties have been investigated. The results showed that the microstructure of the quenched and partitioned steel contains carbon-enriched stabilized austenite and carbon-depleted martensite resulting in increasing the strength of steel with an acceptable ductility. Conducting Q&P heat treatment caused the retained austenite content and the hardness of steel to increase. Fracture in specimens treated by Q&P process was of brittle type and their fracture surface was considered to be quasi-cleavage.

Safety، economical and environmental problemsin automotive industry are leading to the development of advanced high strength steels (AHSS) with improved mechanical properties. One of the newest and most promising heat treatments for the production of AHSS is quenching and partitioning (Q&P) process. The application of this new process in various times and temperatures leads to interesting combinations of mechanical properties including high strength and good ductility. In this study،variations of mechanical properties influenced by variation of partitioning time and temperature on 1. 5142 steel was investigated. The results showed that application of Q&P process on the steel causes severe increasing of hardness. Increasing of partitioning time and also temperature leads to decreasing of hardness and increasing of elongation. With increasing of partitioning time، tensile strength initially increases and then decreases،However، increasing of partitioning temperature leads to decreasing of strength and increasing of elongation and ductility.

Effect of cryogenic treatment on microstructure, hardness, and wear resistance of high Cr-C tool (D6) steel has been studied, in comparison with effect of conventional quench-temper treatments on those properties. Cryotreatment includes austenitizing, quenching in hot oil, immediate cooling of steel down to -78 or -180˚C, and keeping the samples at one of those temperatures for 6 or 24 hours. The results show that retained austenite decreases in microstructure and submicron carbides precipitate in matrix of steel after cryotreated samples, in relative to those after conventional quench-temper treatment. Wear resistance in cryotreated samples significantly increases in comparison of conventialy treated samples, however, hardness variation is moderate. Hardness and wear resistance increases as time and/or cooling increases during cryotreatment. It is revealed that increasing holding time in cryogenic environment from 6 to 24 hours improves wear resistance by 23%, however decreasing temperature of cryogenic environment from -78 to -180˚C provides only 4% improvement in wear resistance. Increasing velocity of wear disk increases wear resistance, whereas, increasing applied load decreases wear resistance of steel. In general, wear resistance of D6 steel after cryotreatment is significantly superior to those properties in D6 steel after conventional quench-temper treatment.