No abstract

No abstract

Nanocellular foam has raised much interest because its physical and mechanical properties are superior to those of microcellular foams. The hot-bath foaming method has been common on a laboratory scale due to its faster heat transfer rate. However, because of the nature of the free foaming process, the hot-bath foaming method may not be capable of making large, flat samples. This study uses the hot-press process to produce nanocellular foam. The results of hot-bath and hot-press foaming methods were compared with theoretical simulations. Both processes were able to produce cell sizes lower than 40 nm. The hot-press foamed samples exhibited larger cell size, higher expansion ratio, and higher aspect ratio (AR) than the hot-bath foamed samples. The hot-press foaming process demonstrated that it has the potential to create sizable and flat nanocellular samples. The AR of cells foamed in the hot-press method was as high as 1.93, creating a new manufacturing method for anisotropic nanocellular foam with a cell size of less than 100 nm.

The inhalation of radon decay products is the second most leading reasons for lung cancer after smoking. Building materials are an important source of indoor radon. This article describes the determination of the exhalation rate of radon from construction materials by the use of commercially available digital radon measuring device. Six types of construction materials were collected from the study area; these are cement, metal, sand, rock, clay brisk and gypsum. The measurements of effective radium content and radon concentration in those materials were investigated. The concentration was measured by alpha spectroscopy detection technique with Corentium digital radon detector. It was found that the overall average radon concentration in the construction materials varied from 58.46 Bq/m 3 to 307.84 Bq/m 3 , which is above the recommended action level. The average effective radium content varies from 69.85 Bq/kg to 367.79 Bq/kg which is below the maximum permissible value of 370 Bq/kg as recommended by Organization for Economic Corporation and Development (OECD) but it is near to maximum, so it can pose significant threat to the population. The average annual effective inhalation dose varied from 0.53 mSv/yto 2.77 mSv/y. The mean excess lung cancer risk estimated by this work was found to range from 1.17% to 6.16% within average value of 2.92%. The average of Excess Lifetime Cancer Risk (ELCR) is greater than with the estimated risk of 1.3% due to a radon exposure of 148 Bqm -3 which is the action level of Environmental protection agency (EPA). The mass exhalation rates of radon vary from 14.98 × 10 −6 to 97.91 × 10 −6 Bq.kg −1 .d −1 with a mean value of 57.91×10 −6 Bq.kg −1 .d −1 . The surface exhalation rates of radon have been found to vary from 23.85 × 10 −5 to 155.91 ×10 −5 Bq.kg −1 .d −1 with a mean value of 91.46 × 10 −5 Bq.kg −1 .d −1 . This indicates the contributions of construction materials in the indoor radon are very high.