Contact angle a contact angle of 0°. This is often the case for water on bare metallic or ceramic surfaces, although the presence of an oxide layer or contaminants on the solid surface can significantly increase the contact angle. Generally, if the water contact angle is smaller than 90°, the solid surface is considered hydrophilic and if the water contact angle is larger than 90°, the solid surface is considered hydrophobic. Many polymers exhibit hydrophobic surfaces. Highly hydrophobic surfaces made of low surface energy (e.g. fluorinated) materials may have water contact angles as high as ~120°. Some materials with highly rough surfaces
Type 97 90 mm Infantry Mortar Type 97 90 mm Infantry Mortar The Type 97 90 mm Infantry Mortar was a simplified version of the Japanese Type 94 90 mm Infantry Mortar. The Type 97 designation was given to this gun as it was accepted in the year 2597 of the Japanese calendar (1937). The Type 90-mm mortar is a Stokes-Brandt type mortar similar in appearance to the US 81-mm mortar, M1 and the Japanese Type 97 81 mm piece. It is believed that the 90 mm weapon has been introduced later than its model number would imply, as a captured specimen was marked "Model 97