Abstract:

The observation and analysis have been operated about the structural features of Betula schmidtii by those instruments biomicroscope and ESEM. Result showed that iron birch belonged to diffuse-porous wood, structure was even and smooth, the zone of demarcation of growth increments were visible, the color was greatly different during heartwood and sapwood, and pores were visible by naked eye. Pore arrangement involved solitary one and multiple one, pore cluster was slim, multiple pore were usually ribbon-like aggregations of 2, 3 or 4 cells extending in the radial direction, intervessel pit was the type of alternate, perforation plates was that of scalariform, rays amount was from 1 to 5, and longitudinal parenchyma was thin. The physical nature and mechanical properties of Betula schmidtii have been testde, analysed and studyed contrastively with other kinds of wood. The results showed that the basic density of iron birch was 0.747 g·cm^-3, air-dry density was 0.904 g·cm^-3, and oven dry density was 0.875 g·cm^-3. The shrinkage coefficient of radial direction in the state of air-dry was 0.12%, the tangential one was 0.20%, and the volume one was 0.38%. The coefficient of radial shrinkage in the state of oven dry was 0.23%, the tangential one was 0.28%, and the volume one was 0.53%. The bending strength of tangential direction was 233.32 MPa, the modulus of elasticity of bending strength was 17.87GPa, the shear stresses at right parallel to the grain in the radial surfaces was 16.32 MPa, the tangential one was 16.40 MPa. The crushing strength at right parallel to the grain was 89.88 MPa. the strength of toughness was 153.71 kJ·mm^-2. The strength of rigidity in the radial section was 8 042.22 N, the tangential was 7 794.17 N, and the cross one was 8 778.85 N.

Key words: Betula schmidtii, iron birch, structural features of wood, properties of wood