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Author: Subject: Nitrides
Eddygp
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[*] posted on 30-4-2012 at 23:50
Nitrides


Some nitrides are quite easily synthesized, such as Mg3N2, by heating magnesium metal in a nitrogen athmosphere.
Can aluminium nitride be made in the same way? Is there any other way of making this nitride using ammonia, like zinc nitride is made?
And, in general, any information on nitrides or similar ions :D .




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AJKOER
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[*] posted on 1-5-2012 at 00:43


Here is an online Google book "High-Temperature Corrosion and Materials Applications" by G. Y. Lai. Per page 85: apparently, high temperature exposure to NH3 results in the formation of 'internal nitrides' including AlN.

Link:
http://books.google.com/books?id=tfDwOe7xWeQC&pg=PA85&am...


Also, "Carbides and Nitrides". Most of the material is, unfortunately, unavailable.
Link:
http://books.google.com/books?id=0N-3d-LfiWEC&pg=PA330&a...

Finally, some sample articles:

"Deposition of silicon nitride from SiCl4 and NH3 in a low pressure r.f. plasma", by Y. Ron,..., 1983.
Abstract
Silicon nitride coatings were deposited in a low pressure (1–10 Torr) r.f. plasma from SiCl4 and NH3 in the presence of argon onto stainless martensitic steel grounded and floating substrates at 300 °C and 440 °C respectively. The heating of the substrates depends mainly on the position and the induced r.f. power. The coatings were identified as silicon nitride by X-ray investigation and were found to contain chlorine by energy-dispersive analysis of X-rays. The growth rate, the microhardness and the chlorine concentration of the coatings were determined as a function of the total gas pressure, the r.f. power input and the NH3-to-SiCl4 ratio. It was observed that the coatings on the floating substrates have higher deposition rates and are of superior quality.

"Microstructural investigation of iron nitride layers formed by low-temperature gaseous nitriding", by
D. K. Iniaa1, A. M. Vredenberga1 c1, D. O. Boermaa2, F. D. Tichelaara3, H. Schuta4 and A. van Veen
Abstract
Iron nitride layers were formed by a novel low-temperature gaseous nitriding process. Nitriding occurs at a temperature of 325 °C through NH3 decomposition at the surface of Ni (25 nm) coated Fe, followed by N transport through the Ni film into the underlying Fe, where nitride precipitation takes place. The role of Ni is to protect Fe from oxidation by gas impurities and to serve as a catalyst for NH3 decomposition. The precipitation behavior and the development of microstructure were studied by means of elastic recoil detection, cross-sectional transmission electron diffraction (XTEM), and positron annihilation (PA). From PA and XTEM no evidence was found for the occurrence of porosity during nitriding (an effect found at higher temperatures due to the decomposition of the nitrides into Fe and N2). XTEM showed that the original columnar α–Fe grains transform into smaller ′–Fe4N grains which subsequently transform into larger ε–Fe3−xN grains. This microstructural evolution of smaller ′ grains forming in the original columnar α–Fe structure occurs in one of two growth modes of the nitride in the Fe layer, i.e., throughout the entire depth range of the Fe layer, or preferentially at the Ni/Fe interface when an iron oxide layer is present at this interface.
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Eddygp
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[*] posted on 1-5-2012 at 11:31


OK, thank you. Does that then mean nitrides can't be made in STP?



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[*] posted on 1-5-2012 at 16:28


Lithium nitride can be.



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AJKOER
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[*] posted on 2-5-2012 at 09:15


Per Wiki, "Calcium nitride is formed along with the oxide, CaO, when calcium burns in air. It can be produced by direct reaction of the elements:

3 Ca + N2 → Ca3N2 "

Interestingly, Calcium nitride absorbs hydrogen above 350 °C:

Ca3N2 + 2 H2 → 2 CaNH + CaH2

Perhaps,

Ca3N3 + 3 Al --> 3 AlN + 3 Ca

in a reaction that parallels Calcium carbide reaction with Aluminum (no guarantee of success or commercially viability), I once saw in a patent. The goal here being a possibly higher cost, but much lower temperature synthesis.
-------------------------------------------------
I found in Brauer’s ‘Preparative Inorganic Chemistry’ three methods for AlN preparation (see p.827, available in ScienceMadness’s library):

Aluminum
AlN
Nitride
= AlN
41.0
A nickel boat is filled with very pure aluminum powder which
has been degreased and dried either by extraction with ether or
by heating to 150°C in a stream of nitrogen. The boat is placed
in a quartz or porcelain tube and heated in an electric furnace
while purified nitrogen is passed over it. Even though the nitride
starts to form on the surface below 650°C, the reaction proper
begins only at 820°C, when the entire mass begins to glow. At
this point the flow of nitrogen should be increased to prevent the
Ns pressure from decreasing owing to the rapid reaction. When
the reaction is essentially complete, the mass is allowed to cool
in a stream of nitrogen. Since the product still contains some
unreacted metal, it is pulverized and reheated under nitrogen for
1-2 hours at 1100-1200°C. The product obtained is nearly white
and has a nitrogen content not far below theoretical.
II. Al + NH3 = AlN + 3/2H2
27.0 17.0 41.0
To obtain silicon-free AlN, aluminum powder pretreated as
above is placed in a trough of molybdenum sheet inside a nickel
reaction tube, and NH3 is led through while the tube is heated to
1300°C in an electric furnace.
III. AlCl3 • NH3 = AlN + 3 HCl
150.4 41.0 109.4
The reaction is performed in the apparatus shown in Fig. 246,
which consists essentially of a thick-wall Pyrex tube with an
enlargement in the middle and four necks at the top. A thin
glass tube (nitrogen inlet) passes through the middle neck and
reaches nearly to the bottom. The two side necks contain silver
wire leads to a tungsten heating coil w suspended in the reaction
tube at the level of the bulb. The fourth neck is an outlet for the
gas. The reaction tube is thoroughly dried and AlCl3- NH3, prepared

These preparations were brought to my attention by Blogfast25.


[Edited on 2-5-2012 by AJKOER]
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AndersHoveland
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[*] posted on 2-5-2012 at 22:54


Unlike magnesium, aluminum cannot burn in nitrogen. It is not because the Al-N bonds are not very strong, but just because not enough energy is released to vaporise the AlN on the surface.

Lithium, magnesium, and calcium will burn in nitrogen. But not sodium or potassium, because the alkali metal nitrides are not very stable.

I would think refluxing molten anhydrous AlBr3 with NH3 gas would work.

[Edited on 3-5-2012 by AndersHoveland]
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