Potassium nitrate melting point

Salt baths that are used for certain thermal treatments of aluminium alloys such as homogenisation and solution heat treatment are mixtures of sodium nitrate (melting point, 307 °C) and potassium nitrate (melting point, 334 °C)." The mass loss of aluminium in a nitrate bath is 20 mg-m -h of immersion, which corresponds to a decrease in thickness of less than 0.01 p,m h. This is very acceptable for thermal treatments that do not exceed a few hours. 

Primary aromatic amides are crystaUine sohds with definite melting points. Upon boiling with 10-20 per cent, sodium or potassium hydroxide solution, they are hydrolysed with the evolution of ammonia (vapour turns red htmus paper blue and mercurous nitrate paper black) and the formation of the alkah metal salt of the acid ... 

For purification the crude product is boiled with glacial acetic acid (preferably in the extraction apparatus shown in Fig. 27). Fine red needles melting point 289°. Sublimation in a vacuum from a sausage flask is also to be recommended the sausage should be fixed low down and the bulb completely immersed in a nitrate bath (equal parts of potassium and sodium nitrates). Much poorer yields of alizarin are obtained by using an open round-bottomed flask at 189°-190°. 

Table 6.13 Melting points and decomposition temperatures of potassium nitrate and potassium sulfate.

At a temperature of 338 °C, the vibrational and translational motion overcomes the electrostatic forces holding the lattice together and the KNO3 melts. The relatively low melting points of substances such as potassium nitrate are normally directly related to ease of ignition a very important feature of gunpowder type products. 

Because of its higher melting point and less-exothermic decomposition, potassium perchlorate produces mixtures that are less sensitive to heat, friction, and impact than those made withKClO] [2]. Potassium perchlorate can be used to produce colored flames (such as red when combined with strontium nitrate), noise (with aluminum, in "flash and sound" mixtures), and light (in photoflash mixtures with magnesium). 

Barium nitrate is a white, crystalline, non-hygroscopic material with a melting point of approximately 592°C. It is commonly used as the principal oxidizer in green flame compositions, gold sparklers, and in photoflash mixtures in combination with potassium pert hlorate. ... 

Mixtures containing barium nitrate as the sole oxidizer are typically characterized by high ignition temperatures, relative to potassium nitrate and potassium chlorate compositions. The higher melting point of barium nitrate is responsible for these higher ignition values. 

Table 5. 3 shows that several potassium nitrate mixtures with low-melting fuels have ignition temperatures near the 334°C melting point of the oxidizer. Mixtures of KNO 3 with higher-melting metal fuels show substantially higher ignition temperatures. 

FIG. 5.2 Thermogram of pure potassium nitrate. Endotherms are observed near 130° and 334°C. These peaks correspond to a rhombic-to-trigonal crystalline phase transition and melting. Note the sharpness of the melting point endotherm near 334°C. Pure compounds will normally melt over a very narrow range. Impure compounds will have a broad melting point endotherm. 

FIG. 5.4 The potassium nitrate /sulfur /aluminum system. Endo-therms for sulfur can be seen near 105° and 119 c, followed by the potassium nitrate phase transition near 130 C. As the melting point of potassium nitrate is approached (334 C), an exotherm is observed. A reaction has occurred between the oxidizer and fuel, and ignition of the mixture evolves a substantial amount of heat. 

Preparation of Potassium Nitrite. Melt 1-2 g of potassium nitrate in a test tube and heat it above its melting point until oxygen bubbles stop evolving. Dissolve the cooled substance in water and add 1-2 ml of a dilute sulphuric acid solution. What happens ... 

A fused salt bath consisting of 8.5 parts (by weight) of sodium nitrite and 10 parts of potassium nitrate has a melting point of about 140° and may replace the metal bath. 

According to the views of Weyl and Marboe on the kinetics of melting (42), potassium nitrate expands at its melting point because of the formation of ionic clusters separated by the fluctuating fissures. The large internal surface of such a melt, which is responsible for its fluidity, makes it also susceptible to the ambient atmosphere. 

Alkali nitrates, when healed above their melting-points, yield the corresponding nitrite and oxygen but the gas is contaminated with nitrogen resulting from partial decomposition of the nit rite. In the ease of potassium nitrate the reaction may be represented by the equation ... 

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