Fluorine nitrides

Nitrogen and sodium do not react at any temperature under ordinary circumstances, but are reported to form the nitride or azide under the influence of an electric discharge (14,35). Sodium siHcide, NaSi, has been synthesized from the elements (36,37). When heated together, sodium and phosphoms form sodium phosphide, but in the presence of air with ignition sodium phosphate is formed. Sulfur, selenium, and tellurium form the sulfide, selenide, and teUuride, respectively. In vapor phase, sodium forms haHdes with all halogens (14). At room temperature, chlorine and bromine react rapidly with thin films of sodium (38), whereas fluorine and sodium ignite. Molten sodium ignites in chlorine and bums to sodium chloride (see Sodium COMPOUNDS, SODIUM HALIDES). 

The methods of choice for beryUium oxide in beryUium metal are inert gas fusion and fast neutron activation. In the inert gas fusion technique, the sample is fused with nickel metal in a graphite cmcible under a stream of helium or argon. BeryUium oxide is reduced, and the evolved carbon monoxide is measured by infrared absorption spectrometry. BeryUium nitride decomposes under the same fusion conditions and may be determined by measurement of the evolved nitrogen. Oxygen may also be determined by activation with 14 MeV neutrons (20). The only significant interferents in the neutron activation technique are fluorine and boron, which are seldom encountered in beryUium metal samples. 

With boron there is immediate ignition with fluorine sometimes followed by an explosion. Boron oxide becomes incandescent and so does boron nitride. 

Although most of the fluorine calorimetry has been done with the elements, it has been used to burn oxides, carbides, nitrides, and chal-cogenides and hence determine their heats of formation. In some instances it has proved superior to oxygen bomb calorimetry. Thus the oxidation of boron tends to be incomplete because of oxide coating, whereas fluorination produces gaseous boron trifluoride without surface inhibition. A summary of modem fluorine calorimetry results is assembled in Table III. 

Oxygen becomes oxide Nitrogen becomes nitride Fluorine becomes fluoride Chlorine becomes chloride Sulfur becomes sulfide Carbon becomes carbide... 

If a single metal film is deposited on an oxide, the sheet resistance measurement results can by easily interpreted and converted to the thickness. In practice, however, this is not usually the case. For example, in W CVD, the tungsten is not directly deposited on oxide due to high residual stress and unreliable adhesion. A titanium (Ti) layer must be first deposited as a glue layer. In addition, to prevent the fluorine in the CVD-precursor WFg from directly reacting with Ti (a strong catalytic reaction will occur), a barrier layer of titanium nitride (TiN) must be deposited on top of the Ti. As a result, we have a trilayer film of W on TiN on Ti on oxide, as shown schematically in Fig. 21. This poses some problems in accuracy in the four-point probe measurements. Based on the resistivities in Table VI, the... 

Fire or explosion hazard may arise from the foUowing ammonia reactions Reaction with halogens produces nitrogen trihahdes which explode on heating its mixture with fluorine bursts into flame reacts with gold, silver, or mercury to form unstable fulminate-type shock-sensitive compounds similarly, shock-sensitive nitrides are formed when ammonia reacts with sulfur or certain metal chlorides, such as mercuric, or silver chloride liquid ammonia reacts violently with alkah metal chlorates and ferricyanides. 

The chlorides, bromides, iodides, and cyanides are generally vigorously attacked by fluorine in the cold sulphides, nitrides, and phosphides are attacked in the cold or may be when warmed a little the oxides of the alkalies and alkaline earths are vigorously attacked with incandescence the other oxides usually require to be warmed. The sulphates usually require warming the nitrates generally resist attack even when warmed. The phosphates are more easily attacked than the sulphates. The carbonates of sodium, lithium, calcium, and lead are decomposed at ordinary temp, with incandescence, but potassium carbonate is not decomposed even at a dull red heat. Fluorine does not act on sodium bofate. Most of these reactions have been qualitatively studied by H. Moissan,15 and described in his monograph, Lefluor et ses composes (Paris, 1900). 

Since nitrides have lower heats of formation than oxides, the reaction between chlorine and nitrides will be more complete than between chlorine and oxides. Nitrides react with chlorine to give chlorides and nitrogen. Chlorine, in fact, can displace all negative elements from their compounds, with the exceptions of oxygen and fluorine only. 

Although the literature often indicates catastrophic reactions of fluorine with oxides, nitrides, carbides, silicides, borides and the like, many such species may be reacted under controlled conditions to produce oxyfluorides, nitro-fluorides such as TINF, ZrNF, HFNF, ThNF, and UNF, and other interesting ternary systems. 

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