Selective preparation of furfural via the pyrolysis of cellulose catalyzed with nitrided HZSM-5

Furfural is a high-value compound that can be prepared by catalytic pyrolysis of biomass. In order to improve the selectivity of furfural in the process of cellulose catalytic pyrolysis, the ammonia-modified HZSM-5 (N-HZSM-5) was used as the catalyst for experimental research on a horizontal fixed bed. The effects of different nitriding temperatures and times on N-HZSM-5, and the effects of different catalyst to cellulose (CA to CL) ratios on furfural selectivity were evaluated. The results showed that N-HZSM-5 can effectively improve the selectivity for furfural. At the optimal conditions (nitriding temperature: 800 °C, nitriding time: 6 h, CA to CL ratio: 4), the selectivity of furfural was up to 24%, which was much higher than those of noncatalytic pyrolysis (1.2%) and HZSM-5 catalytic pyrolysis (3.6%). In order to better evaluate the performance of the catalyst, a series of characterizations were carried out on the N-HZSM-5. The results showed that compared with HZSM-5, N-HZSM-5 had an increased pore size, it was less acidic, and it had more uniform surface acidity. It was conducive to the selective formation of furfural. Therefore, the ammonia-modification can effectively control the structure and acidity of HZSM-5, and N-HZSM-5 exhibits a non-negligible potential in catalyzing the pyrolysis of cellulose for furfural.

Controlled thermogasocyclic nitriding processes

The existing basic nitriding methods do not exploit many of the potential opportunities. To intensify it and increase its efficiency, this paper considers and proposes a new method of low-temperature nitriding, which makes it possible to optimise the classical process and reduce the consumption of ammonia from 2 to 10 times, reduce the nitriding time by 4-6.5 times with an increase in the thickness of the diffusion layer by 2-6 times without reducing the physical and mechanical properties. During the experiment, gas-cyclic and thermogasocyclic nitriding of armco iron was carried out on an experimental setup, which included a system for monitoring and maintaining the temperature in the working volume, a gas supply system, monitoring the flow rate and degree of ammonia dissociation, cleaning and drying gas, as well as two electromagnetic gas valves controlled from the control panel, allowing the processes to be carried out automatically. As a result, a new method of low-temperature nitriding has been developed – under the conditions of a thermo-gas cycle. This method consists in periodic alternation of saturation cycles during flow nitriding and resorption of the nitrided layer with the maximum possible decrease in the saturating capacity of the atmosphere. The proposed new method of thermogasocyclic nitriding is a new, effective hardening technology that allows to reduce the consumption of saturating gas and emissions into the atmosphere by up to 10 times, the nitriding time by 4-6.5 times, and also to increase the thickness of the diffusion layer by 2-6 times without reducing the physical and mechanical properties. A new technological parameter has been established – the duration of half-cycles, which allows simply and effectively regulating the phase composition and structure of the layer in order to obtain the required physical and mechanical properties.

Application of Avinit vacuum plasma technologies Avinit to the manufacture of high-precision full-size gears

Avinit duplex technologies have been developed, combining Avinit N plasma nitriding of finished high-precision parts with subsequent application of Avinit superhard antifriction coatings in a single technological process Due to the absence of a brittle layer on the nitrided surface after precision nitriding, the preservation of the original geometric dimensions that do not require further mechanical refinement, and the compatibility of the processes of plasma precision nitriding of Avinit N and the vacuum plasma deposition of functional coatings Avinit C, duplex technologies allow the deposition of strong adhered, high-quality coatings. The effect of the duplex process on the dimensions of parts during plasma nitriding of high-precision gears and the application of Avinit C functional coatings was investigated, the properties of the nitrided layer and the parameters of Avinit coatings were studied. Plasma precision technology Avinit N allows nitriding of finished parts without changing dimensions, including gears of 4 degrees of accuracy. Avinit N nitriding time is 2 ... 4 times less than with gas nitriding. The coating of Avinit C310 parts increases the microhardness of the surfaces of the parts and reduces the coefficient of friction, while it has sufficient adhesion to the working surfaces of the gear teeth and bearing raceways. Manufacturing of high-precision gears with accuracy grade 4 using Avinit duplex technologies was carried out. Analysis of the results shows that, within the measurement accuracy, no changes in the profiles of the teeth, their location on the ring gear, as well as the location of the gear ring relative to the measuring bases are observed. Plasma nitriding makes it possible to reduce the nitriding time by more than two times compared to gas nitriding, while the thickness of the layer of the brittle phase with the maximum surface hardness is ensured within the specified values ​​to ensure the necessary indicators of contact and bending long-term strength in the manufacture of gears according to the degree of accuracy 4 without grinding after nitriding. Measurements of the ring gear after nitriding and coating showed that there were no changes in the geometry of the gear processed by duplex technology. Avinit C310 anti-friction coating 1.5 microns thick does not distort the geometry of the tooth profiles. All parameters of the ring gear manufactured using the Avinit duplex technology correspond to accuracy grade 4 in accordance with the requirements of technical documentation. The gears manufactured using the Avinit duplex technology were tested as part of the AI-450M engine reducer at the Ivchenko-Progress hydraulic brake stand according to the program of equivalent cyclic tests. A pair of experimental gears were installed in the engine reducer instead of the serial wheels of the second stage of the reducer. The total test time of the wheels was 26 hours. After testing, no damage to the gear, including the Avinit coating, was found. Antifriction coating Avinit C310 with a thickness of 1.5 microns does not distort the geometry of the tooth profiles during testing as part of the AI-450M engine reducer. Measurement of the parameters of the teeth showed a complete absence of wear.

Plasma nitriding of AISI 431 steel: surface hardness - hardness profile [Nitruración por plasma del acero AISI 431: dureza superficial – perfil de durezas]

The present research evaluated the effect of the nitriding time in plasma in the range of 5 to 15 hours, on the hardness profile of the cross section of stainless steel samples AISI 431; in addition to taking and differentiating the data on surface hardness, effective layer depth and nitride layer thickness. The nitriding process was by plasma, the process temperature was kept constant at 400 °C. The evaluated samples were machined (rolled and countersigned), and were left in one inch diameter and one inch in length. The times of 10 and 15 hours of nitriding time were obtained by accumulating time of 05 hours of nitriding per week; the hardness profiles were obtained by using the LECO model LMV-50V micro durometer; The ASTM E3-91 standard was used to collect the aforementioned hardness data, from these it was possible to determine that the maximum surface hardnesses are (1053, 1252 and 1327) HV-0.01, for nitriding times of (5,10 and 15) hours respectively, the average effective layer thicknesses were (37.75, 33 and 28.75) μm; while the nitride layer thicknesses were (4.9, 7.03 and 10.7) μm corresponding to times of (5, 10 and 15) hours respectively. The hardness in the core after the nitriding treatment was kept in the range of (275-277) HV-0.01. These values were determined by microscopic evaluation of the tested samples, the metallography reagent used was 3% Nital by electrolytic attack for 3 minutes in each case. The statistical analysis corresponded to Student's “t” tests, in the form of pairwise comparison, from which the non-significant difference between repetitions and the significant difference between the different levels of study were determined.

The Anisotropic Stress-Induced Diffusion and Trapping of Nitrogen in Austenitic Stainless Steel during Nitriding

Plasma nitriding of austenitic stainless steels at moderate temperatures is considered in the presented work. The anisotropic aspects of stress-induced diffusion and influence of nitrogen traps are investigated by kinetic modeling based on rate equations. The model involves diffusion of nitrogen in the presence of internal stress gradients induced by penetrating nitrogen as the next driving force of diffusion after the concentration gradient. The diffusion equation takes into account the fact that nitrogen atoms reside in interstitial sites and in trapping sites. Stress-induced diffusion has an anisotropic nature and depends on the crystalline orientation while trapping–detrapping is isotropic. The simulations are done considering the synergetic effects of both mechanisms and analyzing the properties of both processes separately. Theoretical curves are compared with experimental results taken from the literature. Good agreement between simulated and experimental results is observed, and gives the possibility to find real values of parameters needed for calculations. The nitrogen depth profile shapes, the dependences of nitrogen penetration on nitriding time and on diffusivity, are analyzed considering crystalline orientation of steel single crystal.

EFFECT OF SALT BATH NITRIDING TIME ON THE PERFORMANCES OF 304 STAINLESS STEEL

In this study, salt bath nitriding was carried out at 565℃ for various times for 304 stainless steel (304SS). The effect of salt bath nitriding time on the microstructure, micro-hardness and wear resistance was investigated systematically. The results showed a nitriding layer was formed during salt bath nitriding, and the thickness of effective hardening layer is duration dependant. The maximum microhardness value of 1200HV0.01 was obtained at optimal duration of 150min, which was five times higher than that of the untreated sample. And the wear resistance could be significantly improved by salt bath nitriding, the lowest weight loss after wear resistance was obtained while nitriding for 150min, which was one tenth of that of untreated sample.

IMPROVEMENT OF WEAR RESISTANCE OF SHREDDER BLADES USED IN A REFUSE-DERIVED FUEL (RDF) FACILITY BY PLASMA NITRIDING

Refuse-derived fuel (RDF) is a kind of renewable energy source to produce energy for replacement of fossil fuels. Aggressive working conditions in RDF facilities cause the shredder blades to wear out quickly. So, the purpose of this paper was to study the effect of plasma-nitriding process on wear resistance of shredder blades made of AISI D2 tool steel in the service condition of RDF facility. Shredder blades were commercially available from two different suppliers (A and B suppliers). These hardened shredder blades were plasma-nitrided in the mixed nitrogen and hydrogen atmosphere at a volume ratio of 3:1 at 450∘C for 12, 18 and 24[Formula: see text]h at a total pressure of 250 Pa. Characterisation of plasma-nitrided layers on the shredder blades was carried out by means of microstructure and microhardness measurements. Wear tests of plasma-nitrided shredder blades were performed under actual working conditions in the RDF facility. Wear analysis of these shredder blades was conducted using three-dimensional (3D) optical measuring instrument GOM ATOS II. The compositional difference of the shredder blades provided by A and B suppliers played an important role on the nitrided layer. The case depth of A-blades significantly increased with increasing plasma-nitriding time. However, the case depth of B-blades was fairly lower at the same nitriding time and only slightly increased with increasing plasma-nitriding time. Plasma-nitriding process significantly improved the surface hardness of the shredder blades. Maximum surface hardness values were achieved at nitriding time of 18 h for both blades. In this case, this increase in surface hardness values was above 100%. At nitriding time of 24[Formula: see text]h, the maximum surface hardness of A-blades significantly decreased, whereas this decrease in surface hardness of B-blades was the negligible value. The wear test results showed that plasma-nitriding process significatly decreased the wear of shredder blades; 18 h nitriding for A-blades and 24[Formula: see text]h nitriding for B-blades had better wear-reducing ability in the service condition of RDF facility. In these cases, the decreases in the total volume wear loss for A- and B-blades were 53% and 60%, respectively.

Hardness Optimization Based on Nitriding Time and Gas Pressure in the Plasma Nitriding of Aluminium Alloys

Plasma nitriding has attracted much interest to improve the hardness of aluminium alloys. However, the contradictive properties can be produced on the metal surface due to the saturated condition of the diffused nitrogen atom in the metal surface layer. The objective of this work was to investigate the effect of nitriding time and gas pressure to improve the hardness of aluminium using plasma nitriding. The nitriding processes were conducted in a DC glow discharge with nitrogen gas flowing inside the vacuum chamber. Firstly, the sample was nitrided using a fixed gas pressure of 1.2 mbar with the varied nitriding times of 3, 4, 5 and 6 hours. The optimum time producing the highest hardness of the surface was then used in the next nitriding process with varied gas pressure of 1.2, 1.4, 1.6 and 1.8 mbar (1 bar = 105 Pa). The optimum gas pressure producing the highest hardness was then used again in the last nitriding process using varied nitriding time of 3, 4, 5 and 6 hours. The result showed that the highest hardness was achieved using the gas pressure and nitriding time of 1.6 mbar and 4 hours, respectively. The formed AlN phase on the aluminium surface was identified by XRD, whereas the surface morphology was observed by SEM image. Compared to the untreated sample, the hardness of the treated samples was significantly high.

Coating of 1.4404 stainless steel by a combination of brazing and nitriding

In the current research, surface hardening of 1.4404 stainless steel was investigated. A hard Ni-containing coating was prepared by brazing at 1150 °C using a Ni foil with Si powder. The hardness behavior was increased by nitriding as well. The nitriding experiments were performed at low and high temperatures (460 and 640 °C) for a different period (3 and 6 h). The microstructure and material properties were characterized using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and Micro Vickers hardness testing. Results show that the hard phase and the binding Ni foil were well distributed into the hard layer. The hard coating material was composed of a Si-phases and Ni-containing compound dispersion.After the nitriding, the hardness of the samples was increased with increasing the nitriding time and temperature and increasing the brazing time. The 10 min brazing and 6h nitriding at 640°C resulted in 32% higher hardness than the non-nitride sample.Strong metallurgical bonding is formed between the stainless steel substrate and the coating layer, as well as between the binding Ni foil and the hard phase; because of the mutual diffusion of alloying elements, the hardness of this hard coating was 2 to 3 times higher than the initial hardness of steel substrate.