Which of the following most closely typifies the sintering temperatures in PM? (a) 0.5 Tm, (b) 0.8 Tm, (c) Tm, where Tm = melting temperature of the metal?

The correct option is;

(b) 0.8 Tm

Explanation:

Sintering is a form of heat treatment given to introduce a material in powdery form in order to introduce the properties of integrity and strength

by the application of heat to the powder at a temperature below its melting point.

With regards to imparting favorable metal properties in the metal to undergo sintering such as ductility, toughness, porosity, hardness, strength it is required to select a sintering temperature higher than 0.6 - 0.8 Tm.

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.