Phases Of Reaction Products Research Articles

Effect of Secondary Oxidants (CO2 and/or H2O) on Oxidation of Fe-20Cr-(Mn, Si)

Ferritic heat resisting alloys are widely used in industry owing to their combination of economy, reasonable strength, and high temperature corrosion resistance. Alloy design centres on forming and maintaining an external, slow growing protective oxide scale by selective oxidation of the desired metal, commonly chromium. Design methods based on diffusion theory succeed when the service environment is oxygen or clean, dry air. However, they can fail badly when secondary oxidants (like CO2 and water vapour) are present, which is commonly the case in energy production etc. This work investigates the effect of CO2 and H2O on corrosion behaviour of Fe-20Cr, in comparison with that in pure O2. The alloying effect of Si and Mn on oxidation behaviour of Fe-20Cr in different gases is also investigated.Model alloys Fe-20Cr, Fe-20Cr-1Si, Fe-20Cr-2Mn (all in wt%) were arc melted and annealed. Sample coupons were cut, ground, mechanically polished to 3mm finish, and further electro-polished to remove subsurface deformation zones. They were then exposed to Ar-2O2, Ar-20H2O-2O2, Ar-20CO2-2O2, Ar-CO2-H2O and Ar-CO2-H2O-O2 (all vol%) gas mixtures, at 650°C for 150h. Corrosion products and cross-sections were examined using optical microscopy, X-ray diffraction, Raman Spectroscopy and scanning electron microscopy equipped with energy dispersive X-ray spectrometry.The alloy behaved protectively in Ar-2O2, forming a very thin Cr2O3 layer on its surface. However, when CO2 or/and H2O was added to oxygen, breakaway oxidation resulted, forming thick multi-layered oxide scales. Detailed analysis revealed that this multi-layered structure contains four layers, where the outer layer was Fe2O3, overlying an Fe3O4 layer and FeCr2O4 spinel innermost layer, and an internal oxidation zone was formed beneath the scale. In the low environment of Ar-20CO2-20H2O, Fe3O4 layer, FeCr2O4 spinel layer and internal oxidation zone formed a three-layered structure. No Fe2O3 was found, which is attributed to the decrease in oxygen partial pressure.Carburisation of Fe-20Cr also resulted from exposure to the three CO2-bearing gases. The deepest and densest internal carburisation zone formed in Ar-20CO2-2O2. In Ar-20CO2-20H2O-2O2 and Ar-20CO2-20H2O, internally precipitated carbides were sparser, but still obvious.Silicon addition dramatically improved the oxidation resistance of Fe-20Cr. Weight gains in all gases were sharply decreased compared with those of Fe-20Cr. As with Fe-20Cr, a very thin Cr2O3 layer on the Si-bearing alloy reacted in Ar-2O2,together with a thin underlying silica layer, indicating that the alloy was fully protected. Unlike Fe-20Cr, the Fe-20Cr-1Si alloy was also protected in Ar-20CO2-2O2. However, when water vapour was present, the alloy started to go into breakaway, forming local Fe-rich oxide nodules. In Ar-20H2O-2O2, some small nodules, consisting of external Fe2O3 and inner spinel were distributed on an otherwise thin, protective chromia scale. In Ar-20H2O-20CO2-2O2 and Ar-20H2O-20CO2, an additional Fe3O4 layer was observed in nodules, between Fe2O3 and inner spinel. Thus, for Fe-20Cr-1Si samples, Fe3O4 can only be observed if 20%CO2 and 20%H2O were both present. Additionally, some small internal oxide particles were observed at breakaway nodule areas in all these three gasses. Internal carbides were found only under the big iron oxides nodules grown in Ar-20CO2-20H2O-2O2.Manganese addition did not much influence the corrosion resistance of Fe-20Cr. In general, oxide morphologies were similar to those of Fe-20Cr. In Ar-2%O2 gas, a thin Mn rich chromium oxide layer was formed over the entire alloy surface, indicating that sample was fully protected. Multi-layered thick oxides developed when CO2 or/and H2O were added. For high gases with the addition of H2O or CO2 (Ar-20H2O-2O2, Ar-20CO2-2O2, and Ar-CO2-H2O-O2), three-layered oxide structures were found to be made up of Fe2O3, Fe3O4, and spinel layers, in sequence from the outer surface to the inner alloy. It is worth noting that the oxide layers were not completely continuous in Ar-20CO2-2O2. About 15% of the cross-section area was protected which indicated that Mn can slightly improve the corrosion resistance in dry CO2 and O2 environments. In lower oxygen partial pressure gas (Ar-CO2-H2O), no Fe2O3 was found, and only Fe3O4 and spinel constituted the oxide scale. The main difference was that the internal oxidation zone became tiny on Fe-20Cr-2Mn samples. Internal carbides were still found under inner oxide in all CO2 bearing gases, most obviously in Ar-20CO2-2O2. However, in all cases the carbide quantities were far less than those in Fe-20Cr, indicating that Mn addition partially inhibited carburisation.After the thermodynamics of the reaction product phase assemblages are considered, this complex pattern of reaction products is discussed in terms of the permeability of different oxides to carbon- and hydrogen-bearing species, along with interactions between secondary oxidants on oxide surfaces and grain boundaries.

Plasma sprayed TiC–Ti5Si3–Ti3SiC2 composite coatings from Ti–SiC-graphite powders with different SiC particle size

The TiC–Ti5Si3–Ti3SiC2 coating was successfully prepared by reactive plasma spraying with agglomerated Ti–SiC-graphite powders as raw material. The effect of SiC particle size on the microstructure and properties of plasma sprayed TiC–Ti5Si3–Ti3SiC2 coating was studied. The results were that, as the size of SiC particles decreased, the TiC content of the reaction product phase increased, while the content of Ti5Si3 and Ti3SiC2 decreased. Compared to coarse SiC, the coating prepared with fine SiC as the raw material had a reduced surface roughness, the highest density, (porosity:11.76%), and highest hardness, (1132 HV0.2). In addition, the coating prepared with small size SiC exhibited more uniform elemental distribution. Moreover, it had the best wear resistance with a weight loss of 0.4 mg, which was ∼1/40 of 45 steel substrate.

Modeling the phase evolution in alkali-activated slag cements upon interaction with seawater

The stability of different phases in a binder exposed to seawater is essential when assessing the performance of structures in a marine environment. The understanding of stability of alkali-activated slag upon interaction with seawater is insufficient. In this study, phase changes in alkali-activated slag systems upon interaction with seawater were investigated by employing thermodynamic calculations. The results show that C-N-A-S-H and Mg-Al LDH, the main reaction product phases in alkali-activated slag systems, are stable at lower seawater quantities and destabilize to ettringite and M-S-H with an increase in the seawater content. M-S-H, Al(OH)3 and calcite are observed to be the stable phases within the interaction mass of seawater considered here. The Ca/Si ratio of C-N-A-S-H reached a value of ∼1 at a higher seawater content regardless of the activator used. A significant increase in the volume of the system is observed during the destabilization of C-N-A-S-H. The current study improves our understanding of the spurious volume changes of different phases in alkali-activated slag systems upon interaction with seawater.

Effect of Y content on interface reaction and wettability between a nickel-base single crystal superalloy melt and ceramic mould

In this paper, the effect of Y content on interface reaction and wettability between a nickel-base single crystal supperalloy melt and ceramic mould were studied by means of sessile drop tests. The microstructural characterization of the alloy-ceramic interface and the elemental compositions of reaction products were performed by scanning electron microscope (SEM) and electron probe micro-analyzer (EPMA), the phases of reaction products were identified by X-ray diffraction (XRD), and the surface analysis of reaction products was carried out by X-ray photoelectron spectroscopy (XPS). The results showed that Al and Hf in the alloy reacted with SiO2 in the ceramic mould when Y content was lower than 0.011 wt%, and the reaction products were Al2O3 and HfO2, with little change in the wetting angle. However, when Y content was higher than 0.017 wt%, Y and Al in the alloy reacted with SiO2 in the ceramic mould, and the wetting angle decreased significantly. 0.017 wt% was the critical concentration of Y content that would cause interface reactions. The reaction products of 0.017 and 0.025 wt% Y alloys were Y3Al2(AlO4)3, the reaction products of 0.1 wt% Y alloy were Y3Al5O12 and Y4Al2O9, and the reaction products of 0.5 and 1.0 wt% Y alloys were double reaction layer composed of Y2O3 and Y3Al5O12. Si generated by the interface reactions could react with O2 in the atmosphere to form SiOx during the cooling of the alloy-ceramic couples.

Phase stability, hardness and oxidation behaviour of spark plasma sintered ZrB2-SiC-Si3N4 composites

Despite significant efforts to develop ultra-high temperature ceramics, the phase stability together with high hardness and oxidation resistance remains to be addressed in ZrB2-SiC based ceramics. ZrB2-20 vol% SiC (ZS20) ceramics with varying amounts of Si3N4 (2.5, 5 and 10 vol%) were processed by multi stage Spark Plasma Sintering (SPS) over a range of temperature (1800–1900 °C) for 3 min under 50 MPa. All the ZS20-Si3N4 composites could be densified to more than 98% theoretical density (ρth) after SPS at 1900 °C. The XRD, SEM-EDS analysis of the ZS20-Si3N4 composites revealed the presence of reaction product phases (ZrO2, BN, ZrN) along with SiC and ZrB2 major phases. Sintering reactions were proposed to explain the existence of such new phases and extinction of Si3N4. Thermo-Calc software was also used to further confirm the formation of these new phases in the ZS20-Si3N4 samples. The hardness of ZS20-Si3N4 composites varied between 25.50 and 30.56 GPa, in particular, ZrB2-20 vol% SiC-5vol% Si3N4 measured with the maximum hardness. In fact, it is the highest ever reported hardness for the ZrB2 composites. Considering oxidation resistance, the weight gain of ZrB2-20 vol%SiC composites decreased (from 13.84 to 9.84 mg/cm2) and oxide layer thickness increased (64–128 μm) after oxidation at 1500 °C for 10 h in air. The cross sectional microstructure of oxidized ZS20-Si3N4 composites consists of thick dense outer layer of SiO2, intermediate (ZrO2-SiO2) layer and unreacted bulk. The formation of dense SiO2 layer and absence of SiC depleted layer from the oxidized samples are signatures of improved oxidation resistance of Si3N4 reinforced ZrB2-20 vol% SiC.

Role of operating conditions on cross contamination of products of the Bunsen reaction in iodine-sulfur process for production of hydrogen

In iodine-sulfur (I-S) thermo-chemical process for hydrogen production, Bunsen reaction is studied to identify the role of different operating conditions on purity of Bunsen reaction product phases. The focus of this work is to find out the level of contamination in each of the Bunsen reaction product phases. Hydroiodic acid and iodine are contaminants in sulfuric acid phase and sulfuric acid is contaminant in hydroiodic acid phase. Enhancing the level of purity in two product phases will reduce the burden on purification steps in downstream of I-S process. Bunsen reaction has been studied in continuous co-current reactor made of tantalum in the range of 50–75 °C, 2–6 bar (g) with HIx (mixture of hydroiodic acid, water and iodine) flow rate of 0.8 l/h - 3.3 l/h, sulfur dioxide 0.06 g/s – 0.24 g/s & oxygen 0.008 g/s −0.016 g/s. At 4 bar (g), 70 °C with HIx and SO2 flow rates of 1.8 l/h and 0.24 g/s respectively, purity of sulfuric acid phase is maximum i.e. 99.85 mol percent. At 4 bar (g), 60 °C with HIx and SO2 flow rates of 1.5 l/h and 0.12 g/s respectively, purity in HIx phase is maximum i.e. 99.66 mol percent.

Friction and Wear Properties of αAlB<sub>12</sub>-NiAl Cermet Prepared by Spark Plasma Sintering

In this study, αAlB12-20vol% NiAl cermet disk specimens were prepared by spark plasma sintering, and their microstructure, Knoop hardness, fracture toughness, and friction and wear properties were investigated. The αAlB12-20vol% NiAl disk specimens were obtained by spark plasma sintering blended αAlB12 and NiAl powder at 1573 K for 600 seconds. No reaction product phases were observed between the αAlB12 and NiAl phases. The αAlB12-20vol% NiAl disk specimens exhibited friction coefficients lower than 0.2 and specific wear rates as low as 1.3 × 10-6 mm3/Nm when sliding against Si3N4 ball specimens in water. O-rich phases were observed on the worn surfaces of the NiAl and αAlB12-20vol% NiAl disk specimens after sliding against Si3N4 ball specimens in water. The Knoop hardness of the disk specimens was as high as 10 GPa and the fracture toughness was as high as 7 MPa m1/2.

Molten silicate reactions with plasma sprayed ytterbium silicate coatings

Abstract The reactions between molten calcium aluminum magnesium silicates (CMAS) at 1300 °C and atmospheric plasma spray (APS) deposited environmental barrier coatings on SiC substrates have been investigated. The tri-layer coatings comprised a silicon bond coat protected by a layer of mullite and either Yb 2 SiO 5 (ytterbium monosilicate, YbMS) or Yb 2 Si 2 O 7 (ytterbium disilicate, YbDS) as the topcoat. The APS deposition process resulted in two-phase top coats; the YbMS coating contained Yb 2 O 3 regions in a matrix of Yb 2 SiO 5 while the YbDS coating contained Yb 2 SiO 5 in a matrix of Yb 2 Si 2 O 7 . Exposure of both coatings to a model CMAS resulted in dissolution of the topcoat accompanied by a rapid rise in the concentration of Yb in the melt, and formation of the same Ca 2 Yb 8 (SiO 4 ) 6 O 2 apatite reaction product phase. The thickness of the apatite layer initially varied with (time) 1/4 , but transitioned to approximately parabolic kinetics after 5–10 h of CMAS exposure. The reaction mechanism on the YbMS layer was consistent with recent observations on Y 2 SiO 5 , wherein molten CMAS transport to the undissolved silicate was controlled by diffusion through thin amorphous films at the apatite grain boundaries. The reaction mechanism for the YbDS layer was more complex, and involved preferential reaction with the YbSiO 5 rich regions, resulting in a reaction zone that contained CMAS, the apatite reaction compound and undissolved Yb 2 Si 2 O 7 . The coating composition and microstructure significantly influenced the mechanism and rate at which the YbDS top coat was consumed by the reaction.

Mechanical and micromechanical properties of alkali activated fly-ash cement based on nano-indentation

This paper presents mechanical and micromechanical properties of alkali activated fly-ash cement (AAFA) based on statistical analysis with nano-indentation test. Mix proportions of AAFA are designed using Taguchi’s approach. Four variables viz, silica fume (SF), sand to cementitious material ratio (s/c), liquid to solid ratio (l/s) and superplasticiser (SP) content were the parameters tested. Indentation elastic modulus, hardness and packing density are studied. The results show that the increase in sand has the greatest contribution to the increase in density. For compressive strength, normal paste without SF, sand and SP with l/s of 0.6 gives the highest strength and the increase in SF significantly contributes to the adverse effect on compressive strength. For the indentation data, the analysis using deconvolution technique confirms the four phases of reaction products of AAFA. The main phase is sodium aluminosilicate hydrate (N-A-S-H), which is over 40% of the volume fraction. The microporomechanics of AAFA paste and mortar also demonstrate the relationships between the N-A-S-H volume fraction and strength; and activation degree and strength.

WC-Co Particles Reinforced Aluminum Matrix by Conventional and Microwave Sintering

Metal matrix composites of Al-WC (10, 15 and 20 wt%) were prepared by microwave (without holding) and conventional sintering (held for 1 hour) processes at various temperatures between 650-950 °C. The results indicated that the highest density of conventional and microwave sintering corresponds to 97.4 ± 1.2% and 98.6 ± 0.8 of theoretical density, respectively; The highest bending strength of conventional and microwave sintered samples were 223 ± 12 and 256 ± 12 MPa, respectively. XRD patterns showed the decomposition of WC particles and formation of Al5W and Al12W interfacial reaction product phases in both processes. SEM studies showed that WC reinforcement particles were more likely to be agglomerated in microwave compared to conventional sintering process.

Nanoindentation characteristics of calcium hydroxide-metakaolin blended with sodium hydroxide solutions

In order to determine the active mechanism of metakaolin (MK) as partial replacement of cement in concrete from the nanoscale structure perspective, nanoindentation characteristics of calcium hydroxide (CH)-MK blended with 5 M sodium hydroxide (NaOH) solutions simulating the condition of MK in concrete has been studied. The results indicate that three distinct phases are found by the nanoindentation and BSE tests, such as HD C-S-H gel, LD C-S-H gel and the reaction products with the network structure, the residual unreacted MK and CH, respectively. The volume fraction of HD C-S-H gel is about 96% of all reaction product phases. This means that the use of MK in concrete can increase the volume fraction of HD C-S-H gel and thus will improve the properties of concrete.

Influences of Progressing Parameters on Flake BaBi<sub>4</sub>Ti<sub>4</sub>O<sub>15</sub> Powder Synthesized by Molten Salt Synthesis Method

Abstract. BaBi4Ti4O15 powder was synthesized by molten salt synthesis (MSS) method in NaCl-KCl and Na2SO4-K2SO4 fluxes. The phases of reaction products and the microstructures at different calcined temperatures were detected by X-ray diffraction (XRD) and scanning electron microscope (SEM). As a result, the flaky BaBi4Ti4O15 powder with anisotropy was synthesized by molten salt synthesis method in NaCl-KCl and Na2SO4-K2SO4 fluxes in the range of 850～1050°C. Compared with BaBi4Ti4O15 powder synthesized in the sulfate flux, the anisotropy level of BaBi4Ti4O15 powder which was synthesized in chloride flux increased, the average particle size(APS) of BaBi4Ti4O15 powder synthesized in the chloride flux is slight larger than in the sulfate flux. The thickness of BaBi4Ti4O15 powder was synthesized by molten salt synthesis method in the chloride flux decreased than in the sulfate.

Low-temperature sintering and microwave dielectric properties of 3Z2B glass–Al 2O 3 composites

A potential low temperature co-fired ceramics system based on zinc borate 3ZnO–2B 2O 3 (3Z2B) glass matrix and Al 2O 3 filler was investigated with regard to phase development and microwave dielectric properties as functions of the glass content and sintering temperature. The densification mechanism for 3Z2B–Al 2O 3 composites was reported. The linear shrinkage of 3Z2B glass–Al 2O 3 composites exhibited a typical one-stage densification behavior. XRD patterns showed that a new crystalline phase, ZnAl 2O 4 spinel, formed during densification, indicating that certain chemical reaction took place between the 3Z2B glass matrix and the alumina filler. Meanwhile, several zinc borate phases, including 4ZnO·3B 2O 3, crystallized from the glass matrix. Both of the reaction product phase and crystallization phases played an important role in improving the microwave dielectric properties of composites. The optimal composition sintered at 850–950 °C showed excellent microwave dielectric properties: ɛ r = ∼5.0, Q· f 0 = ∼8000 GHz, and τ f = ∼−32 ppm/°C at ∼7.0 GHz.

Geometric, electronic and elastic properties of dental silver amalgam γ-(Ag 3Sn), γ 1-(Ag 2Hg 3), γ 2-(Sn 8Hg) phases, comparison of experiment and theory

Geometric, electronic and elastic properties of three intermetallic systems, including starting alloy (Ag 3Sn) and two reaction product phases (Ag 2Hg 3 and Sn 8Hg), are characterized by state-of-the-art density functional theory (DFT) experiments. The traditional mean-field approach failed for Sn 8Hg (γ 2-phase) due to inaccurate description of site occupancy, remedied through the use of supercells. Results were in quantitative agreement with experiment for all phases, within 3.2% and 2.7% for unit cell parameters and Young modulus (of elasticity), respectively. An efficient procedure is presented which may lead to the rational design of novel filling materials for such service, prior to physical trials being initiated.

Quantitative Electron Microprobe Characterizations of Oxidized ZrB2 Containing MoSi2 Additives

This study reports the oxidation behavior of hot-pressed ZrB2 ceramics, with 10, 20 and 40 vol.% MoSi2 additives, exposed to dry air at 1500 °C for up to 10 h. The effect of the amount added MoSi2 on oxidation resistance was assessed. Quantitative electron microprobe characterizations of the oxidized ZrB2 with MoSi2 additives were carried out with electron probe micro analysis. Parabolic oxidation behavior was observed for the three compositions. The oxidation resistance was significantly improved with MoSi2 additives. Reaction-product phase compositions and phase distribution were thoroughly characterized from the oxidized surface through to the unreactive bulk material. It was found that the oxidation products consisted of nonstoichiometric amorphous SiO2, stoichiometric crystalline ZrO2, and MoB. The amounts of these phases in the oxidized reactive region were qualitatively determined.

Vapor Generation of Inorganic Anionic Species After Aqueous phase Alkylation with Trialkyloxonium Tetrafluoroborates

Aqueous phase reaction of trialkyloxonium tetrafluoroborates, R3O+BF4− (R═Me, Et) has been tested in the alkylation of simple inorganic anionic substrates such as halogen ions, cyanide, thiocyanate, sulphide and several oxoanions or their corresponding oxoacids. Gaseous products were separated and identified by gas chromatography mass spectrometry (GC-MS). Alkylated derivatives RI, RBr, RCl were obtained for iodide, bromide, and chloride, respectively, while for fluoride its conversion efficiency to RF is very poor. RCN and R2S were obtained for cyanide and sulphide, while thiocyanate gives RSCN as a main reaction product with a minor amount of alkylisothiocyanate, RNCS (<7%). Among tested oxoanions only nitrites and nitrates give volatile derivatives under the form of R—O—NO and R—O—NO2, respectively. Reaction performed by adding Et3O+BF4− in CH2Cl2 to aqueous sample with extraction in the organic phase of reaction products, failed to identify other less volatile reaction products. Using 2 mL sample in 4 mL reaction vial (T = 25 °C), 100 μL of 2 M Et3O+ BF4− and injecting 250 μL of headspace into GC-MS, detection limits (3 s) are in the range of 1−280 ng mL−1. Application to determination of bromide in groundwater certified reference material (BCR-612, 252 ± 10 μg kg−1 of bromide) gave results in excellent agreement with certified values. The method, being not responsive to iodate, allows the selective determination of iodide in the presence of iodate. Total iodine can be determined after reduction of iodate to iodide by NaBH4. Application of the method to iodide-iodate speciation in table salt gave results in excellent agreement with parallel analysis performed by ion chromatography as a reference method.

Study of the Preparation Technology and Properties of BaBi&lt;sub&gt;4&lt;/sub&gt;Ti&lt;sub&gt;4&lt;/sub&gt;O&lt;sub&gt;15&lt;/sub&gt; Ceramics

BaBi4Ti4O15 ceramics was prepared by molten salt synthesis method (MSS) and conventional solid phase process (CS). The phase of reaction products and the microstructure were detected by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that the evident anisotropic flake structure of BaBi4Ti4O15 powder prepared by MSS was obtained at 850°C and the level of anisotropy of BaBi4Ti4O15 powder decreased with increasing temperature. After calcined at 950°C, sintering in the range of 1100~1170°C, the sintering temperature and the maximum permittivity of BaBi4Ti4O15 ceramics prepared by MSS at same frequency was lower than those prepared by CS. Additionally, the apparent degree of orientation was obtained and the lotgering factor (f) calculated according to the XRD results showed a value of 0.63.

Biomorphous Metal-Ceramic-Composites with High Coefficient of Friction

Metal ceramic composites were fabricated by Si-Cu-alloy infiltration into porous biocarbon preforms derived from medium density fiber board. β-SiC and Si-Cu3Si were found as the major reaction product phases with minor amounts of residual C. Increasing Cu content in the Si-Cu infiltration melt was found to result in decreasing thickness of β-SiC reaction layers both on the outer as well as inner (e.g. lumae) surfaces of the hollow biocarbon fibres. A high coefficient of friction of μ = 0.6 and a good wear resistance were obtained with an optimised compromise of infiltration behaviour and mechanical properties e.g. strength and toughness at a Si/Cu ratio of 75/25.

Isothermal corrosion Fe 3Si alloy in liquid zinc

The isothermal corrosion testing, microscopic examination and the performance of Fe 3Si alloy as materials of construction for bath hardware in continuous hot-dipping lines were studied. The corrosion of Fe 3Si alloy in molten zinc was controlled by attacking the grain boundaries preferentially. Aluminum reacted with iron of Fe 3Si alloy firstly while the samples were immersed in molten zinc, although aluminum contents in the molten zinc were very low. The phase of reaction product was thought to be Fe 2Al 5. The corrosion rate of the Fe 3Si alloy in molten zinc was determined to be approximately 2.9×10 −3 mm/h, therefore the liquid zinc corrosion resistance of Fe 3Si alloy was very weak.

Aluminothermic Reduction of Niobium Pentoxide in a Hydrogen Plasma Furnace

The aluminothermic reduction is a highly exothermal reaction between a metal oxide and aluminium. Conventionally this reaction is ignited by an electric resistance and the reaction products after cooling are in the form of a rigid block of mixed metal and aluminium oxide. In this work a new process of aluminothermic reduction is presented, in which the reaction is ignited by a hydrogen plasma. The niobium oxide and aluminium powders are high energy milled for six hours to form particles constituted of oxide and aluminum. Stoichiometric, substoichiometric and superstoichiometric mixtures were prepared. The mixture was placed in a stainless steel tube (the hollow cathode) inside the reactor chamber. The chamber was firstly evacuated. Then hydrogen at low pressure was introduced. In the following an electric discharge between the cathode and the anode localized just above the cathode ignites the plasma. The plasma heats the particles on the surface of the powder layer and starts the reaction that proceeds in each particle since the reactants are intimately mixed. The heat generated by the reaction propagates deeper in the layer until the whole mixture reacts. Substoichiometric mixtures can be used because hydrogen takes part of the reduction. The Nb2O5 – Al starting powder mixture and the products of the reaction are characterized by laser grain size measurement and X-Ray diffraction (XRD). The products are in form of powder or agglomerates of particles. Phases of reaction products was determined by XRD analysis and the particle size trough SEM.