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.

Application of technical nitrogen during gas nitriding austenitic steels

The possibility of using technical nitrogen including 0,2% O2 for activation austenitic steels surfaces during gas nitriding were investigated. By changing mole fraction of technical nitrogen i NH3 /N2t mixture one can regulate oxygen potential of gas atmosphere during heating the steel to nitriding temperature and sometimes during nitriding process. Four representative austenitic steels were nitrided with good results at 570°C and under 450°C. New method can be alternative to regulating oxygen potential by air and allows avoiding installing of firing mechanism and safety control.

Influence of Nitriding Temperature on Mechanical and Tribological Properties of Titanium

One of the commonly used methods for the surface hardening treatment of pure titanium was nitriding. Based on the study of nitriding temperatures on the properties of the pure titanium, some conclusions can be drawn in this paper. The surface hardness of samples after nitriding was gradually increased firstly and then decreased with the processing temperature increasing. And the hardness of the diffusion layer reached the maximum value of 1792 HV when the processing temperature at 1050°C. At the same temperature, the indentation modulus also reached the maximum value of 270 GPa. The wear depth reached the minimum value at 1050°C. At different nitriding temperatures, the minimum of wear depth was 14.8 μm. In summary, when the processing temperature at 1050°C, the nitriding of pure titanium can improve the comprehensive properties.

Preparation of Iron Nitride Material from Natural Iron Sand

Iron nitride is a promising material for soft magnetic composite. In the current research, iron nitride compound was produced from natural iron sand, involving coprecipitation and gas nitriding. Prior to coprecipitation, natural iron sands were separated magnetically to obtain pure Fe3O4. Afterward, the coprecipitation was carried out to obtain nanosized Fe3O4. Gas nitriding of Fe3O4 powders was performed at different temperatures i.e. 500 °C, 600 °C and 700 °C, under flowing NH3 gas. Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) are used to investigate the phases obtained after the nitriding process. XRD patterns of the resulted powder indicate that nitriding temperature at 600 °C and 700 °C can produce iron nitride material, i.e. ε-Fe3N. While nitriding temperature of 500 °C is not able to yield iron nitrides. SEM examination reveals that the ε-Fe3N has irregular lamellar morphology. Some impurities are still detected, in the form of Fe3O4, Fe2O3, Ti2O3 and TiO2. Further works regarding the examination of the magnetic properties of the powders will be carried out.

Application of Active-Screen Plasma Nitriding to an Austenitic Stainless Steel Small-Diameter Thin Pipe

Low-temperature active-screen plasma nitriding (ASPN) was applied in this study to improve the bending rigidity and corrosion resistance of a small-diameter thin pipe composed of austenitic stainless steel (SUS 304). The inner and outer diameters of the pipe were ϕ0.3 and ϕ0.4 mm, respectively, and the pipe length was 50 mm. The jig temperature was measured using a thermocouple and was adopted as the nitriding temperature because measuring the temperature of a small-diameter pipe is difficult. The nitriding temperature was varied from 578 to 638 K to investigate the effect of temperature on the nitriding layer and mechanical property. The nitriding layer thickness increased with an increase in nitriding temperature, reaching 15 μm at 638 K. The existence of expanded austenite (S phase) in this nitriding layer was revealed using the X-ray diffraction pattern. Moreover, the surface hardness increased with the nitriding temperature and took a maximum value of 1100 HV above 598 K. The bending load increased with an increase in the nitriding temperature in relation to the thicker nitriding layer and increased surface hardness. The nitrided samples did not corrode near the center, and corrosion was noted only near the tip at high nitriding temperatures of 618 and 638 K in a salt spray test. These results indicated that the bending rigidity of the small-diameter thin pipe composed of austenitic stainless steel was successfully improved using low-temperature ASPN while ensuring corrosion resistance.

Primary Recrystallization Behaviors of Hi-B Steel with Lower Initial Nitrogen Produced by the Thin Slab Casting and Rolling Process

Based on low-temperature high-permeability grain-oriented silicon steel designed with an initial nitrogen content of 0.0055% and produced by the thin slab casting and rolling process, the effect of total nitrogen content and nitriding temperature on primary recrystallization microstructure and texture were studied by optical microscope, scanning electron microscope, transmission electron microscope, and electron backscatter diffraction. The nitriding temperature affects the primary recrystallization behaviors significantly, while the total nitrogen content has a small effect. As the nitriding temperature is 750–850 °C, the average primary grain size and its inhomogeneity factor are about 26.58–26.67 μm and 0.568–0.572, respectively. Moreover, the texture factor is mostly between 0.15 and 0.40. Because of the relatively sufficient inhibition ability of inherent inhibitors in a decarburized sheet, the nitriding temperature (750–850 °C) affects the primary recrystallization microstructure and texture slightly. However, as the nitriding temperature rises to 900–950 °C, the average primary grain size and its inhomogeneity factor increase to 27.75–28.26 μm and 0.575–0.578, respectively. Furthermore, because of the great increase on the area fraction of {112} <110> grains, part of texture factor is increased sharply. Therefore, in order to obtain better primary grain size and homogeneity, better texture composition, and stability of the decarburized sheet, the optimal nitriding temperature is 750–850 °C.

Investigation of the Surface Properties and Wear Properties of AISI H11 Steel Treated by Auxiliary Heating Plasma Nitriding

This paper presents an auxiliary heating method to maintain a uniform specimen temperature and precisely control nitriding temperature during plasma nitriding. The surface properties and wear properties of AISI H11 steel treated by auxiliary heating plasma nitriding are investigated. Firstly, the specimens with different diffusion layers and different hardness levels are fabricated through changing the plasma nitriding temperature. Secondly, the surface properties of the plasma-nitrided H11 steel specimens are characterized by a scanning electron microscope (SEM), X-ray diffractometer, metallographic microscope and microhardness tester. The results show that the surface hardness of the plasma-nitrided specimen is almost twice as high as that of the untreated specimen. The thickness of diffusion layer increases with the increase of nitriding temperature. However, the surface hardness firstly increases and then decreases with the increase of the nitriding temperature. Finally, the wear properties of untreated and plasma-nitrided H11 steel specimens are investigated under different friction conditions. The results show that the plasma-nitriding method can significantly improve the wear resistance of AISI H11 steel. The friction coefficient fluctuations of the plasma-nitrided specimens are all lower than those of the untreated specimens. In addition, the wear rates of the plasma-nitrided specimens rise along with load, and reduce along with the sliding speed and friction temperature.