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1

Gaseous Nitriding of Binary Ni-Cr Alloys - Observation and Interpretation of Microstructural Features

Kodentsov A., Cserháti C.

Archives of Metallurgy and Materials

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2022

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Vol. 67, iss. 3

1007--1020

EN

Gaseous nitriding of binary Ni-Cr solid-solution alloys was studied at 1125ºC over the range 1 to 6000 bar of N2-pressure. At the specified temperature the nitriding response of the Ni-Cr alloys depends on the Cr-content in the initial alloy and activity (fugacity) of nitrogen at the gas/metal interface. Transition from cubic δ-CrN to hexagonal β-Cr2N precipitation occurs within the reaction zone after nitrogenization at 1125ºC under nitrogen pressure 100-6000 bar when chromium content in the initial alloy is 28 at. % or higher. It was found that a ternary phase, π (Cr12.8Ni7.2N4.0) is formed inside the Ni32Cr alloy upon cooling in nitrogen after nitriding at 1125ºC and 1 bar of N2. Experimental evidence is presented that π-phase is involved in peritectoid relations with β-Cr2N and γ-(Ni-Cr) solid solution. It was also demonstrated that nitriding behaviour of the Ni-Cr alloy can be rationalized using pertinent phase diagram information, but, in some cases, effect of mechanical stresses induced upon the internal precipitation can vitiate this prediction.

2

Aluminum Nitride Formation From Aluminum Oxide/Phenol Resin Solid-Gel Mixture By Carbothermal Reduction Nitridation Method

Mylinh D. T., Yoon D. H., Kim C.-Y.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1551--1555

EN

Hexagonal and cubic crystalline aluminum nitride (AlN) particles were successfully synthesized using phenol resin and alpha aluminum oxide (α-Al2O3) as precursors through new solid-gel mixture and carbothermal reduction nitridaton (CRN) process with molar ratio of C/Al2O3 = 3. The effect of reaction temperature on the decomposition of phenol resin and synthesis of hexagonal and cubic AlN were investigated and the reaction mechanism was also discussed. The results showed that α-Al2O3 powder in homogeneous solid-gel precursor was easily nitrided to yield AlN powder during the carbothermal reduction nitridation process. The reaction temperature needed for a complete conversion for the precursor was about 1700°C, which much lower than that when using α-Al2O3 and carbon black as starting materials. To our knowledge, phenol resin is the first time to be used for synthesizing AlN powder via carbothermal reduction and nitridation method, which would be an efficient, economical, cheap assistant reagent for large scale synthesis of AlN powder.

3

Electrical and mechanical properties of nitrided sol-gel derived TiO2 and SiO2-TiO2 films

Kościelska B., Murawski L., Wicikowski L.

Materials Science Poland

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2005

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Vol. 23, No. 1

93--100

EN

The results of measurements of electrical conductivity for titanium-nitride films prepared by the ammonolysis of sol-gel derived TiO2 and SiO2-TiO2 coatings are presented. Sol-gel derived films on silicon and quartz substrates were nitrided by ammonia treatment in the temperature range from 500 to 1200 C. The dc conductivity of nitrided films has been measured from 10 K to 900 K. It was found that conductivity is related to the amount of TiO2, which is converted to TiN during ammonolysis. In this way it is possible to change the electrical conductivity of samples by many orders of magnitude. The observed activation energy of the samples containing large amounts of TiN is below 0.1 eV. This indicates that the conductivity mechanism may be interpreted as electrons tunnelling between metallic TiN granules. The mechanical properties were evaluated by a nanoidentometric technique. The results of nanoidentometric measurements confirm an increase in microhardness and Young's modulus for nitrided SiO2-TiO2 films containing large amounts of TiN.

4

Gel–glass transition in silica and nitrided silica aerogels – experiment and computer modelling

Szaniawska K., Murawski L., Rybicki J., Witkowska A., Walewski M.

Optica Applicata

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2003

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Vol. 33, nr 1

75-81

EN

Nitrided silica aerogel was sintered at 1600 °C in vacuum or nitrogen atmosphere and the effect of densification was compared with that observed in silica aerogel. It has been shown that homogeneous oxynitride glasses containing 8.4–13 wt% can be obtained by densification of nitrided aerogels. The densification process of nitrided aerogels was simulated by computer modeling using classical molecular dynamics (MD) simulations. MD simulations have shown that densification process proceeds in a similar way as in the experiment. In addition, the simulations indicate that oxynitride glasses can be obtained by densification of Si–O–N system.

5

Preparation of silicon oxynitrides by the reaction of ammonia with high disperse silica

Truckenbrodt B., Breitbarth F. W., Vogelsberger W.

Bulletin of the Polish Academy of Sciences. Chemistry

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2002

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Vol. 50, No. 1

77-92

EN

Nanosized silica is nitrided at different temperatures up to 1200° C by the reaction with gaseous ammonia. The nitridation degree of silica is determined as a function of time. After a nitridation time of 119 h and a temperature of 1200° C the mass fraction of nitrogen in the nitrided sample was found to be 35.4%. This corresponds to the stoi-chiometric formula SiO(18)Ni (1.21). It could be shown that the progressive nitridation of the samples is accompanied by a decrease of the specific surface area. The different degree of nitridation can be followed by IR spectroscopical investigations. Several absorption bands of silica and the nitrided species can be detected in dependence of nitridation time. EPR spectroscopical investigation of irradiated samples provide information about the bonding in the samples. Furthermore, a relation between the concentration of defect centers and the degree of nitridation is found. The process of nitridation is also determined by X-ray diffraction measurements. It was shown to be possible to separate the diffraction patterns of SiO(2)2, Si(2)ON(2) and Si(3)N(4). This separation could be established by NMR spectroscopy. Thus it was possible to follow the development of the mentioned three species in dependence of nitridation time. A phenomenological consecutive reaction scheme describes the time dependent appearance of the three species well.

6

Reaction bonded X-sialon-mullite ceramics - the influence of attrition milling on nitridation.

Sopicka-Lizer M., Winiarska-Uhlig K., Włodek T., Bracisewicz M., Bourdin E., Duhoux B.

Inżynieria Materiałowa

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2001

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R. XXII, nr 5

861-864

EN

A mixture of kaolin, corundum and silicon has been chosen in order to produce X-sialon-mullite ceramics. Similarity of the both physical and chemical properties, abundance of raw materials and simplicity of the reaction bonding process are attractive features of that material. The oxide-nitride ceramic was produced by simultaneous nitridation and sintering at 1400 degrees centigrade of the mixture prepared by concurrent milling in an attritor. The influence of the time of milling on nitridation and phase composition has been tested. It has been found that specimens were not fully reacted and some amount of elemental silicon was present in the center of the specimens if the shorter time of milling or/and nitridation was applied. The time of milling changed significantly the rate of nitridation and phase composition of the resulted product. The higher X-phase yield was observed if the longer time of milling was applied. In contrary, the longer time of nitridation of the shorter milled batches favored O'-sialon formation.

PL

Przedmiotem badań było otrzymywanie ceramiki sialonowo-mulitowej z mieszaniny kaolinu, elektrokorundu i krzemu. Atrakcyjność takiego materiału wynika z podobieństwa własności mulitu i sialonu X, prostoty reakcyjnego spiekania i powszechnej dostępności wyjściowych materiałów. Ceramika tlenkowo-azotkowa była otrzymywana drogą równoczesnego azotowania i spiekania w temperaturze 1400 stopni Celsjusza masy przygotowanej w atrytorze. Badano wpływ czasu mielenia na efekty azotowania i skład fazowy. W wyniku badań stwierdzono, że krótszy czas mielenia lub azotowania prowadził do niepełnego przereagowania próbek, w których stwierdzono obecność Si. Czas mielenia masy wpływał na szybkość późniejszego azotowania jak i ostateczny skład fazowy. Wydłużanie czasu mielenia prowadziło do powstania większej ilości fazy X, podczas gdy przedłużanie czasu azotowania krócej przemielanych próbek powodowało powstawanie większej ilości sialonu O'.

7

Carbothermal Reduction and Nitridation as a Production Method of Beta-sialon

Sopicka-Lizer M., Serkowski S.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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1999

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Vol. 47, nr 4

423-439

EN

Sialon ceramics appear to be an attractive engineering material because of their excellent mechanical and thermal properties. Carbothermal production can be the most economical route for the production of the relevant sialon powders if some problems of multiphase composition are overcome. Thermodynamic calculations of the equilibrium composition in the Si-O-N-C and Al-O-N-C systems have been performed in order to predict the most suitable parameters for carbothermal reduction and nitridation. The kinetic parameters influencing the process are reviewed. Special attention is paid to the type of phases occuerring during several stages of the reduction. A new model of chemical reactions in the SiO2-Al2O3-C-N2 system has been proposed.