The relationship between purity and mechanical (Knoop hardness) or electrical (room resistivity) properties of single and polycrystals of beta rhombohedral boron

Paper presented at the 6th International Symposium on Boron and Borides, Varna, Bulgaria, October 9 - 12, 1978International audienceDuring a wider study of the correlation between the purity and the physical properties of β rhombohedral boron, Knoop hardness and room resistivity measurements were performed on samples prepared by different methods (chemical vapour deposition (CVD) and fusion) and precisely analysed with a spark source mass spectrometer. We systematically measured the hardness (taking into account the surface state, the load, the anisotropy and the grain size) to determine small hardness variations within the range of 10%. Hardness HK200 (kg mm−2) increases regularly with the impurity content C (ppm) according to the equation HK200 = 0.015 λC + 2320 where λ = 1 for the molten samples and λ = 6.2 for the CVD samples; the different slopes are probably due to a different impurity distribution: the logarithm of the room resistivity ρ (MΩ cm) increases linearly with the purity according to the equation log10ρ = (0.6 −1.1) × 10−4C for samples of grain size 5-500μm; the Knoop hardness and resistivity are anisotropic in single crystals

Etude de la dureté du bore rhomboédrique b

International audienc

Towards life cycle sustainability assessent of cities. A review of background knowledge

This article analyses whether existing LCA and sustainability methods can be used in the assessment of a city or an urban region. The approach is performed through the review of current existing LCA-based and sustainability standards and guidelines. A focus is put into those LCA-based standards specially designed for the built environment. Moreover, a review of non-LCA based standards, indices and guides for the assessment of the sustainability of countries, cities or urban regions is done. The purpose is to check if these assessment tools can provide good results in the absence of LCA-based assessments for cities and urban regions. This review demonstrates the lack of consensus in the definition of both, the city and its boundaries, which hinders the development of useful sustainability standards. Furthermore, it is concluded that current sustainability assessment tools miss, at least, one of these aspects: (i) holistic point of view, (ii) focus on various environmental impacts, (iii) a Life Cycle (LC) perspective, and (iv) the possibility to compare the results among different cities or urban regions. From the LCA perspective, the deficiencies found also include the need for a definition of the function, functional unit (FU), and reference flow (RF) of neighbourhoods, cities, and urban regions. © 2017 Elsevier B.V

The evaluation of boron purity by means of electrical measurements

International audienceFrom measurements performed on boron samples thoroughly characterized with respect to their crystalline nature and impurity content, a correlation between electrical properties and purity is pointed out. In particular, the conditions under which room temperature resistivity measurements can be considered as a criterion of purity are discussed