Papers by Keyword: Microcell

Abstract: Formula for microcellular unsaturated polyester using chemical foaming method was studied. With the increase of NaHCO3 content, the cell size of microcellular unsaturated polyester slightly decreased with the increase of styrene content in the range of 1-2 %. The cell size increased in the range of 2-4 %. With the increase of curing agent content, the cell size increased in the range of 0.5-0.9 % and decreased in the range of 0.9-1.3 %. The cell size decreased with the increase of styrene content in the range of 30-40 %. The cell size had little variation when styrene content was in the range of 40-50 %. The average cell size and cell density of microcellular unsaturated polyester were strongly affected by accelerant content. The cell size decreased with the increase of accelerant content. The opposite was for the cell density. The microcellular unsaturated polyester prepared at 2% NaHCO3, 0.3% accelerantt, 0.9% curing agent, 40% styrene had the small cell size, high cell density, and strong compression strength.

Abstract: Microcellular unsaturated polyester was prepared by different foaming agents was studied. Compared with the cell size and density of microcellular unsaturated polyester prepared using azodicarbonamide (AC), the ones of microcellular unsaturated polyester prepared using NaHCO3 were small. For NaHCO3, the cell density of microcellular unsaturated polyester decreased with the increasing temperature. For microcellular unsaturated polyester prepared using NaHCO3 at 100 °C, the average cell size was about 18 μm and the cell density was 1.1×1010 cells/cm3. The compression strength at 100 °C is strongest among that of the materials at the other temperature. The average compression strength was 24.2 MPa. The compression strength-to-weight ratio of microcellular unsaturated polyester prepared at 90 °C and 100 °Cwas about twice that of unsaturated polyester.

Abstract: The corrosion characteristics of steel bar in concrete are decided by the corrosion current distribution along the circumference of the steel bar. It is a general assumption that carbonation lead to a general corrosion on the rebar. However, the destruction of a large number of specimens indicated that before corrosion cracking, the carbonation-induced corrosion mainly distributes on the surface of the steel bar facing the concrete cover. This paper examined the corrosion mechanism from fundamental electrochemical principles and experimental verification. It was illustrated that the macrocell corrosion must co-exist with microcell corrosion, both macrocell and microcell corrosion mechanisms could play significant roles, and the total corrosion could be underestimated if each of two is overlooked.

Abstract: Formula for glass fiber/microcellular unsaturated polyester composites (GF/MCUP) using supersaturated gas technology was studied by the way of orthogonal experiment. The results showed that these factors affecting average cell size from strongly to weakly were styrene content, accelerant content, glass fiber length, curing agent and glass fiber content, respectively. The factors affecting average cell density from strongly to weakly were accelerant content, styrene content, glass fiber content, curing agent content and glass fiber length, respectively. Curing agent content was the major factor affecting impact strength of GF/MCUP. The factors revealed no obvious difference in affecting tensile strength. Under the optimizing processing condition, the average cell size of GF/MCUP was about 8 μm and the cell density was 1.19×10⁹ cells/cm³. The 153.70 and 255.84 % increase in impact strength were gained over that of GF/UP and UP, respectively. The corresponding 20.24 and 82.51% increase in tensile strength-to-weight ratio were gained over that of GF/UP and UP, respectively.

Abstract: Glass fiber/microcellular unsaturated polyester composites (GF/MCUP) were prepared using the supersaturated gas technology. Technological process included three stages. The effect of processing parameters on average cell size, cell density, impact strength and tensile strength was investigaed by orthogonal experiment. The results indicated that the major factor affecting them was the temperature in stageⅡ(T2). Under the optimizing processing condition, the average cell size of GF/MCUP was about 8 μm and the cell density was 1.57×109 cells/cm3. It was found that impact strength of GF/MCUP increased 88.81 and 188.12 % than that of glass fiber/unsaturated polyester composites (GF/UP) and unsaturated polyester plastics (UP), respectively. The corresponding 16.56 and 69.25 % increase in tensile strength-to-weight ratio were gained over that of GF/UP and UP, respectively.

Abstract: The durability of metal structures depends most upon the corrosion behaviour of its materials as well as the on the electrochemical behaviour of joints and the technology employed to construct the joints itself. This work describes the effect of Laser Beam Welding (LBW) technology on the electrochemical and corrosion behaviour of parent materials and bead of several aluminium alloy joints. Investigation was carried out by using dc electrochemical techniques (open circuit potential monitoring, OCP, and anodic polarization) on selected micro areas of parent materials and bead by means of a suitable electrochemical microcell. With regards to the corrosion behaviour of heat affected zone (HAZ), no data has been presented due to the small area of HAZ when compared to the microcapillary area adopted in this study. Alloys investigated in this work are the AA 2139 and AA 6156 as skin in the form of rolled sheets, and AA 2139 and PA 765 as stringer, in form of extruded parts. In addition, the AA 4047 has been used as filler material in form of wire. Results obtained in this investigation indicated that no major corrosion concerns arise from the LBW of both laminated AA 2139 skin with extruded AA 2139 stringer and laminated AA 6156 skin with extruded AA 2139 stringer. In the former case, the bead exhibits corrosion potential nobler than that exhibited by the skin and stringer of circa 100 mV for the AA 6156 skin with extruded AA 2139 joint. This result is attributed to the presence of Si in the bead due to the process parameters adopted for such a weld. Quite similar corrosion behaviour was observed for the skin, stringer and bead in the latter case. Attention must be paid when laminated AA 2139 skin with extruded PA 765 stringer, and laminated AA 6156 skin with extruded PA 765 stringer are joined by LBW. In this case low potential and high surface activity were observed on the stringer and bead and attributed to the excess of Zn in the PA 765 alloy.