Papers by Keyword: Heat Treatment Temperature

Abstract: TiO₂ nanocrystalline powders were prepared by sol-gel method with different process parameters. The phase, morphology and the luminescent property of TiO₂ nanocrystalline powders were characterized by XRD, SEM and PL, respectively. The results indicated that the synthesized TiO₂ nanocrystalline powders were transformed from anatase into rutile with the increasing of heat treatment temperature, which begin at the temperature of 500 oC and was almost completed at the temperature of 700 oC. And with the increasing of pH value the rutile proportion become larger, the nanograins become fine and powders agglomeration was decreased. The good performance TiO₂ nanocrystalline powders were obtained when prepared temperature was 500°Cand pH value was 4. PL results show broad and strong luminescence band appeared near 470nm when TiO₂ nanocrystalline powders were excited at 325nm at room temperature.

Abstract: Previous fatigue tests show that the heat treatment temperature has a significant influence on high cycle fatigue behaviour of helical compression springs. In order to investigate the effect of the heat treatment temperature on the fracture behaviour and the cyclic life, fatigue tests in the very high cycle regime (VHCF) were conducted.The tested springs were manufactured from oil hardened and tempered SiCr-alloyed valve spring steel wire with a diameter of d = 1.6 mm. After winding and grinding of the spring endings, the springs were heat treated at either 360°C or 400°C for 30 minutes. In order to generate compressive residual stresses in the surface area, the springs were shot peened. After shot peening, the springs were again annealed at 240°C for 30 minutes.Fatigue tests were conducted at 40 Hz using a special spring fatigue device. Up to 900 springs were tested simultaneously at various stress levels to 5∙10⁸ or 10⁹ cycles. Fractured springs were investigated by means of a stereomicroscope as well as a scanning electron microscope to analyse the fracture behaviour and failure mechanisms. The vast majority of the springs show crack initiation at the surface at the inner side of the coil. Less frequently, crack initiation occurs at subsurface locations. Our results show that heat treatment at a temperature of 360°C leads to four times more subsurface cracks than at a temperature of 400°C and reduces the overall fatigue life time.

Abstract: MgO-Al₂O₃-ZrO₂ composite powders with 3 kinds of mass ratio were synthesized by sol–gel method using MgCl₂·6H₂O, AlCl₃·6H₂O and ZrOCl₂·8H₂O as starting materials, and NH₃·H₂O as a precipitant. The composite powders which match with zirconium oxide particle size and evenly distribute can are advantageous to the formation of metastable t-ZrO₂ and restrain the grain growth as the additive of modified sizing nozzle. Chemical composition, mineral phase, particle size distribution and micro-morphology of the composite powders were investigated by X-ray fluorescence instrument, X-ray diffractometer, laser particle size analyzer and scanning electron microscope. Research showed that under the process that the concentration of MgCl₂ solution 0.2 mol/L, AlCl₃ and ZrOCl₂ solution concentration 0.5 mol/L, the pH controlled between 10 ~ 11, PEG as the surfactant, drying at 70°C±5°C, heat treatment temperature at 800°C for 3h, particle size distribution of MgO-Al₂O₃-ZrO₂ composite powders were: d₁₀ = 1.28 μm, d₅₀ = 4.65μm, d₉₀ = 11.13μm (MgO 10%); d₁₀ = 1.15μm, d₅₀ = 5.80μm, d₉₀ = 15.13μm (MgO 15%);d₁₀ = 1.21μm, d₅₀ = 6.59μm, d₉₀ = 16.87μm (MgO 20%). With the rising of heat treatment temperature, the crystallization degree of composite powders increased, at 800 °C a small amount of t - ZrO₂ precipitated, meanwhile MgO and Al₂O₃ are still in the amorphous phase. The MgO-A1₂O₃-ZrO₂ composite powders under this condition have high reactivity and uniform distribution.

Abstract: ITO (Indium Tin Oxides) nanopowder was prepared by ammonium-calcining method. The chemical composition, morphology and crystal structure were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Base on the nucleation and growth mechanism of the powder, the temperature of heat treatment impacting on size and morphology was discussed briefly. The results showed that the nanoITO powder of particle size 20nm-40nm with well-pleasing particle shape and dispersion can be prepared at 800°C.

Abstract: Abstract. This paper investigated the Cf/SiC ceramic matrix composites. By utilizing different interfacial treatment processes to prepare carbon-fiber preform, the preform was then densified by infiltration and pyrolysis(PIP) with polycarbosilan/xylene solution as precursor, and the Cf/SiC ceramic matrix composite specimens were fabricated. Mechanical tests such as bending test and fracture toughness were performed for Cf/SiC samples. The results show that the interfacial bonding strength in the sample with high-temperature treatment process was improved due to removing surface sizing. The samples which were treated up to 1400°C exhibited the highest three-point flexural strength, up to 595MPa; The samples which were treated up to 1400°C and deposited by pyrolytic carbon(PyC) coating shows the highest fracture toughness value which was 20.70MPa•m1/2.

Abstract: ITO (Indium Tin Oxides) nano-powder was prepared by the method of ammonia complexation. The chemical composition, morphology and crystal structure were characterized by X-ray diffraction (XRD) ,transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy analysis(XPS). Base on the nucleation and growth mechanism of the powder, the temperature of heat treatment impacting on size and morphology was discussed briefly. The results showed that the nano-ITO powder of particle size 20nm-40nm with well-pleasing particle shape and dispersion can be prepared at 800°C.

Abstract: The SiO2-ZrO2-Al2O3-Cr2O3 film is coated on the surface of stainless steel using analytical reagent TEOS, ZrOCl2·8H2O, Al(NO3)3·9H2O and Cr(NO3)3·9H2O as precursor and basing on mole ratio to calculate through Sol-gel method. The phase transformation behavior，erosion resistance，thermal shock resistance and abrasion resistance of ceramic coating by different heat treatment are studied. The results show that: 1)The SiO2-ZrO2-Al2O3-Cr2O3 gel coatings has non-crystalline structure after the treatment at 700°C and 800°C. New substance is not created below 700°C 2) The stainless steel substrate with ceramic coating has a higher erosion resistance at high temperature (700°Cand 800°C)than that without coating.3) Thermal shock resistance of the samples treated in 700°C is the best which has reached within 17-21cycles (900°C, air cooling). 4) The stainless steel substrate with ceramic coating has a higher abrasion resistance than that without coating. The samples treated at 700°Cand 800°C have the best abrasion resistance.

Abstract: ITO (Indium Tin Oxides) nano-powder was prepared by the method of ammonia complexation. The chemical composition, morphology and crystal structure were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Base on the nucleation and growth mechanism of the powder, the temperature of heat treatment impacting on size and morphology was discussed briefly. The results showed that the nano-ITO powder of particle size 20nm-40nm with well-pleasing particle shape and dispersion can be prepared at 800°C.

Abstract: To prepare the amorphous SiO₂ optical fiber preform which has lower attenuation, we selected TEOS as raw material, H₂O as menstruum, HCl as catalyst, CH3NO as anti-cracking agent, prepared the mandrel material of SiO₂ optical fiber preform by sol-gel method. The XRD, SEM, FT-IR and TG were used to study the characteristic of the samples. The results show that the TEOS and H2O can be uniformly mixed with vigorous stirring and water increasing. The hydrolysis rate of TEOS will increase with the increasing HCl volume. The transparency will decrease when the HCl reaches a fixed value. The CH₃NO can play a role of anti-cracking agent, it also can affect the transparency if it is more. The optimal capability parameter TEOS: H₂O: HCl: CH₃NO = 1: 25: 0.5: 0.1. The optimal heat treatment process was determined by TG and FT-IR as follows: the temperature was risen slowly to 170°C and 300 °C for 1h, and then reluxed at 900°C for 2h.

Abstract: Unburned Al₂O₃ - C slide plate specimens were prepared at different temperatures, using tabular corundum, graphite, Al, Si powder as starting materials and silicone resin as binder. The results reveal that heat treatment temperatures have a significant impact on the performance of unburned Al₂O₃ - C slide plate. Between 200°C and 600 °C, the internal structure of the specimens is loose, and the apparent porosity increases significantly, meanwhile the cold crushing strength is very low. Between 800 oC and 1000 °C, the bulk density increases significantly, the apparent porosity have a sharp decline, and the cold crushing strength value increases. Over 1000 °C, there are many holes in the specimens, specimen mass and thermal expansion significantly increases, the bulk density decreases, and the apparent porosity increases, in the same time, the cold crushing strength has a downward trend.