Structural characterisation of the silica and alumina Zener pinning phases in nanocrystalline CeO2 by 29Si and 27Al nuclear magnetic resonance

Nanocrystalline CeO₂ samples have been manufactured using sol-gel techniques, containing either 15 % silica or 10 % alumina by weight to restrict growth of the ceria nanocrystals during annealing by Zener pinning. ²⁹Si and ²⁷Al MAS NMR have been used to investigate the structure of these pinning phases over a range of annealing temperatures up to 1000 °C, and their effect on the CeO₂ morphology has been studied using electron microscopy. The silica pinning phase resulted in CeO₂ nanocrystals of average diameter 19 nm after annealing at 1000 °C, whereas the alumina pinned nanocrystals grew to 88 nm at the same temperature. The silica pinning phase was found to contain a significant amount of inherent disorder indicated by the presence of lower n Qⁿ species even after annealing at 1000 °C. The alumina phase was less successful at restricting the growth of the ceria nanocrystals, and tended to separate into larger agglomerations of amorphous alumina, which crystallised to a transition alumina phase at higher temperatures.     

Thermostimulated luminescence characteristics of dolomitic rocks and their use as a gamma ray dosimeter

The thermostimulated luminescence (TSL) glow curve characteristics of ten dolomitic crystals of Salem and Namakkal districts of Tamilnadu are analysed. The natural thermoluminescence (NTL) measurements were carried out for all the samples and show two peaks at 270 °C and 335 °C. The sample irradiated with a gamma dose of 200 Gy shows an additional peak at 180 °C, when recorded with linear heating rate of 10 °Cs⁻¹. At the same time, the NTL peak at 270 °C is shifted to 260 °C while increasing in intensity and there is no change in the peak position of 335 °C. The annealed sample also shows the same trend. The sample was annealed in air at the temperatures ranging from 200 to 950 °C, at an interval of 50 °C, for 1 h duration. Annealing treatment above 250 °C increases the sensitivity of all three TSL peaks. On the other hand, annealing at 800 °C caused a collapse in the TSL sensitivity. The enhancement in TSL sensitivity was found to depend on the annealing temperature and time. Annealing treatment at 700 °C for 4 h followed by quenching in air is the optimum condition for TSL sensitization. The response to gamma irradiation is linear in the range from 0.5 to 10⁴ Gy. The number of glow peaks was identified through partial heating method. Using peak shape and initial rise method the kinetic parameters (activation energy (E), frequency factor (S) and order of kinetics (b)) were evaluated. The investigations show that the trapping centers are not affected by the annealing procedure. The emission spectra of all the samples show an emission at around 608 nm but with different intensities for each sample. With reference to earlier work, it may be assumed that the recombination site always involves Mn²⁺ ions.     

Comparative study on the effect of annealing treatments on RTL mechanism in natural quartz from different origins

The behaviour of trap centres and luminescence centres has been investigated for fired and unfired natural quartz from bricks and sediments irradiated at 100 Gy and annealed at different temperatures in the range 350-700 °C. The annealing treatment affects thermoluminescence (TL) glow curve as various changes were observed. The higher sensitization occurred for an annealing in the region 550-600 °C. At this annealing temperature, it has been observed the emergence of two peaks arising at 96 and 180 °C. At lower annealing temperatures, these peaks are overlapped by the peaks localized at 90 and 195 °C, respectively. Concerning the fired quartz, the higher sensitization occurred for an annealing in the region 500-550 °C for peak temperature around 200 °C and an unusual desensitization for the peak temperature around 100 °C. The behaviour of the two types of quartz is analyzed regarding to their kinetic parameters and luminescence emission and compared to literature data.     

The effects of thermal treatments on the thermoluminescence properties of biogenic minerals present in the seashells

In this study, thermoluminescence (TL) properties of the biogenic minerals present in the seashell samples at different temperatures and annealing times have been studied. Three explicit peaks are seen in the glow curves roughly at 100°C, 180°C, and 380°C. One of the prominent results is that annealing above 600°C affects enormously the TL intensity, whereas no remarkable TL intensity is observed for unannealed samples. The highest intensity and area under the curve were observed at 700°C annealing temperature, and 180 minutes annealing time and 1500 times bigger than the unannealed samples. A linear dose response is observed between 2.4 and 72?Gy and beyond this value, a sublinear relation is observed. Unfortunately, a huge decrease in TL intensity is observed about 51% of its initial value, after 5 hours of storage time.     

The effect of cerium oxide argon-annealed coatings on the high temperature oxidation of a FeCrAl alloy

Ceria coatings were applied in order to improve the adherence of alumina scales developed on a model Fe–20Cr–5Al alloy during oxidation at high temperature. These coatings were performed by argon annealing of a ceria sol–gel coating at temperatures ranging between 600 and 1000 °C. The influence of these coatings on the alloy oxidation behaviour was studied at 1100 °C. In situ X-ray diffraction (XRD) was performed to characterize the coating crystallographic nature after annealing and during the oxidation process. The alumina scale morphologies were studied by means of scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The present work shows that the alumina scale morphology observed on cerium sol–gel coated alloy was very convoluted. On the cerium sol–gel coated alloy, argon annealing results in an increase of the oxidation rate in air, at 1100 °C. The 600 °C argon annealing temperature results in a good alumina scale adherence under thermal cycling conditions at 1100 °C.     

Effect of annealing treatment on luminescence property of MgO nanowires

Magnesium oxide nanowires (NWs) were synthesized by a current heating process. The effect of annealing treatment in air on their structural and optical characteristics was investigated. As-grown NWs in diameter ranging from 30 to 70 nm and length up to several 10 μm were obtained. Carbon-coating layers were observed in the as-grown NWs which were oxidized during the annealing treatment at high temperature. Ionoluminescence spectra of the as-grown and annealed NWs have showed two emission peaks centered at 360 nm (UV emission) and 492 nm (green emission). The intensities of green emission were maximum at the annealing temperature of 650 °C for 2 h, whereas those of UV emission were decreased with increasing the annealing temperature. It is anticipated that maximum green emission correlates to the sufficient density of oxygen vacancies which was occurred by the optimum annealing parameters of both temperature and time.     

Fabrication and Characterization of CuO nanowires on V-shaped Microgroove surfaces

This study developed a facile and scalable thermal oxidation method to prepare CuO nanowires on the electro-discharge machining (EDM) processed V-shaped microgrooves. The formation feasibility, surface morphology, and wetting properties of nanowires on V-shaped microgrooves were explored by the variation of thermal oxidation temperatures from 300 to 600 °C, and oxidation times from 2 h to 8 h. Nanowires were found to successfully synthesized on the V-shaped microgrooves surfaces when annealing temperature was 400 °C or higher. The microvoids or microcavities on the EDM processed V-shaped microgrooves surfaces contributed to the stress grain boundary (GB) diffusion of copper atoms, and facilitated the growth of nanowires. The diameter of nanowires increased monotonically when the annealing temperatures increased, whereas it almost kept unchanged with increasing annealing times. The length of nanowires was influenced positively by both annealing temperature and annealing time. All the nanowire samples showed hydrophobic properties of water.     

Effect of annealing temperature on optical and magnetic properties of Cr doped ZnS nanoparticles

ZnS:Cr (3 at.%) nanoparticles were synthesized by chemical co-precipitation method using EDTA as capping agent. The samples were annealed in air for 3 h in steps of 100 °C in the temperature range of 200–700 °C. The effect of annealing temperatures on the structural and photoluminescence properties of Cr doped ZnS nanoparticles was investigated using X-ray Diffraction (XRD), a Scanning Electron Microscope (SEM), Energy Dispersive X-ray spectroscopy (EDS), Diffuse Reflectance Spectra (DRS), Vibrating Sample Magnetometer (VSM) and Photoluminescence (PL) techniques. EDS spectra confirmed the presence of Cr in the samples with expected stoichiometry. XRD studies confirmed the formation of ZnO above 500 °C. Photoluminescence studies on ZnS:Cr nanoparticles indicated that the emission wavelength is tunable in the range of 440–675 nm as a function of annealing temperature. VSM results indicated a decrease in ferromagnetism with increase in annealing temperature, perhaps due to appreciable variation in structural defects that are sensitive to annealing temperature.     

Influence on the long afterglow properties by the environmental temperature

Sr₂MgSi₂O₇:Eu²⁺, Dy³⁺ (SMED) and Ba₂MgSi₂O₇:Eu²⁺, Dy³⁺ (BMED) were synthesized with the solid-state reaction. The SMED shows long afterglow while the afterglow of BMED is not visible at room temperature. When the environmental temperature is 150 °C, the afterglow of SMED is not obvious while the BMED shows the long afterglow. The decay curves measured at different temperatures conform to this phenomenon. It ascribes to the different trap depths of different samples. The thermoluminescence (TL) curves of SMED peaks at 80 °C. BMED has two TL peaks peaking at about 80 and 175 °C respectively. The low temperature peak is weak and its density is small. The high-temperature peak reveals that one trap of BMED is deeper than the one of SMED. The afterglows of the phosphors strongly depend on the environmental temperature since the lifetime of the trapping carriers is temperature-dependence. BMED is a potential optimum long afterglow phosphor for the purpose of high-temperature application.     

Effect of annealing temperature on determining trap depths of quartz by various heating rates method

The aim of this study is to determine the trap parameters (trap depth E, frequency factor s) of quartz using various heating rates method and also to investigate the effect of annealing temperature on determining trap depths. The method is based on the positions of the thermoluminescence peaks, obtained from the change in temperature of the peak at maximum caused by changing the heating rate at which the sample is measured. In the present work, powder quartz samples were annealed first at different temperatures before irradiation. Then samples irradiated to different doses were measured with a TL reader at different heating rates and the glow curves were recorded. In order to calculate the trap depth E and the frequency factor s, the glow parameter T_m was determined experimentally from the glow curve by measuring the shift of the maximum peak temperature depending on heating rate β. The calculation of trap parameters was repeated for each annealing temperature. Then the effect of annealing temperature on trap depths calculated by the various heating rates method was evaluated.     

Influence of annealing temperature on structural, optical and magnetic properties of Zn0.95Cu0.02Cr0.03O powders

Zn_0.95Cu_0.02Cr_0.03O powders have been synthesized by the sol-gel method and sintered in argon atmosphere under different temperatures. The structural, optical and magnetic properties of the powders were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and vibrating sample magnetometer (VSM). The XRD results demonstrated that Cr and Cu ions are incorporated into ZnO successfully when annealing temperatures were 600 and 700 °C. But when the samples were annealed at 500 °C, the crystallinity of the samples was not very good. However, when the annealing temperature was increased to 800 °C, the secondary phase of Cu and ZnCr₂O₄ appeared in the samples. The PL spectra revealed that the position of the ultraviolet (UV) emission peak of the samples showed a blue shift and the green emission peak enhanced significantly with the annealing temperature increasing from 600 to 700 °C. Magnetic measurements indicated that the room temperature ferromagnetism of Zn_0.95Cu_0.02Cr_0.03O was intrinsic in nature. In addition, the saturation magnetization (Ms) increased from 0.0078 to 0.0088 emu/g with the annealing temperature increased from 600 to 700 °C.     

Influence of sintering temperatures on LiF:Mg,Cu,P with various magnesium concentrations

The dependence of LiF:Mg,Cu,P samples with various concentrations of Mg on sintering temperatures was investigated to find a new dosimeter. The influence of high sintering temperatures on LiF:Mg,Cu,P chips depends strongly on Mg concentrations. The height of the main peak versus the sintering temperatures exhibits a maximum, the position of which varies between 690 °C and 750 °C, depending on the Mg concentration in the range studied. The high temperature peaks of LiF:Mg,Cu,P for various Mg concentrations reduce basically when the sintering temperature is increased. LiF:Mg,Cu,P is much less sensitive than LiF:Mg,Cu,Si to sintering temperature. LiF:Mg,Cu,P with 0.6 mol% of Mg can be re-used at annealing temperature of 260 °C, regardless of the sintering temperature. It was found that the optimum concentration is Mg: 0.6 mol%, the optimum sintering temperature is 750 °C, considering that LiF:Mg,Cu,P with a low residual signal and good sensitivity can be re-used at annealing temperature of 260 °C and produced in a large scale. The new optimum LiF:Mg,Cu,P formation has 52 times higher than that of the TLD-100, and an extremely low residual signal of 0.07% without an initialization readout procedure.     

低温燃烧合成法制备的氧化铝陶瓷粉体的发光特性

α-Al₂O₃∶C单晶具有优良的热释光特性,被用做热释光剂量计,但α-Al₂O₃∶C晶体剂量计的形状不易加工,生产成本高且碳在晶体中难以掺杂均匀。采用低温燃烧合成法以无水乙醇为溶剂,尿素为染料,硝酸铝为反应物制备少团簇、分散均匀的片状α-Al₂O₃∶C陶瓷粉体。探讨不同点火温度和不同退火温度对其光致发光特性的影响,不同退火温度对热释光特性的影响以及热释光与辐射剂量(90Sr β)的关系。通过分析α-Al₂O₃∶C陶瓷粉体的光致发光光谱得出：α-Al₂O₃∶C陶瓷粉体的发射波长在395 nm附近,点火温度T≤800℃时,点火温度为500 ℃制备的α-Al₂O₃∶C陶瓷粉体的光致发光强度最强;在相同点火温度T=500 ℃下,经不同温度退火制备α-Al₂O₃∶C陶瓷粉体,点火温度为500 ℃制备的α-Al₂O₃∶C陶瓷粉体经1 000 ℃退火后光致发光强度最强。通过分析α-Al₂O₃∶C陶瓷粉体的热释光曲线得出：退火后的α-Al₂O₃∶C陶瓷粉体在200 ℃左右的热释光峰值占主导,900 ℃退火的α-Al₂O₃∶C陶瓷粉体在200 ℃附近的热释光峰值最强;通过峰高法对900 ℃高温退火处理后的α-Al₂O₃∶C陶瓷粉体位于200 ℃左右的热释光峰做剂量响应曲线,可以看出,在1～50 Gy剂量范围内具有良好的热释光剂量线性响应关系,在50～200 Gy剂量范围内出现超线性响应关系。与α-Al₂O₃∶C晶体(1～10 Gy)和多孔Al₂O₃∶C薄膜(1～10 Gy)相比,α-Al₂O₃∶C陶瓷粉体的线性剂量响应范围明显扩大。此研究可为提高氧化铝陶瓷粉体的热释光性能提供思路。     

TL and PTTL in natural fluorite previously irradiated with gamma rays and heavy ions

The effect of annealing temperature on the phototransfer thermoluminescence (PTTL) signal was studied to determine the appropriate annealing temperature for treating the natural powder before irradiation. The temperatures used to anneal virgin natural fluorite samples (only natural dose without giving the samples any artificial doses) were 150, 250, 350, 450, 550, 650 and 750°C for a duration of 1 h in each case. The results show that the PTTL response did not change for anneal temperatures up to 450°C, but at higher temperatures the signal decreased rapidly. The height of the 90°C peak decreased by two orders of magnitude as the anneal temperature increased from 450 to 750°C, whilst the height of the 180°C peak decreased by three orders of magnitude between the same two annealing temperatures. In order to investigate the effect of previous gamma rays and heavy ion irradiation on thermoluminescence (TL) and PTTL signals, powdered samples of natural fluorite from Cornwall, England, were annealed at 500°C and then irradiated (at GSI, Darmstadt, Germany) with ¹⁶¹Dy ions of energy 13 Mev/n; the range of fluences used was from 10⁴ to 10¹² ion cm⁻². Identical samples were given gamma doses in the range 1 Gy to 2.6 × 10⁴ Gy in order to compare the effects of gamma rays and heavy ions. The sensitivities of TL and PTTL were studied by giving the samples a gamma test dose of 1 Gy after annealing the samples at 500°C for 30 min in order to eliminate the TL resulting from previous gamma or heavy ion irradiation.     

不同退火温度的Al_2O_3:C薄膜热释光和光释光性能

α-Al_2O_3:C晶体的热释光和光释光性能优越,但其制备要求高,需高温和高还原气氛.与α-Al_2O_3:C晶体性能接近的α-Al_2O_3:C陶瓷,热释光峰不单一.本文采用两次阳极氧化法在0.5 mol/L的草酸溶液中5℃恒温制备高度均匀有序的多孔Al_2O_3:C薄膜,主要研究不同退火温度对其热释光和光释光特性的影响.结果表明,经不同温度退火后的Al_2O_3:C薄膜均为非晶结构;不同退火温度的Al_2O_3:C薄膜热释光的主发光峰约在310℃左右,符合通用级动力学模型.600℃退火后的Al_2O_3:C薄膜热释光灵敏度最强,其热释光剂量曲线在1-10 Gy范围内具有很好的线性响应,在剂量10-120 Gy范围内出现超线性响应;在相同的辐照剂量下,随着退火温度的升高(≤600℃)光释光的初始发光强度逐渐增强.不同退火温度的Al_2O_3:C薄膜光释光衰减曲线都呈典型的指数衰减且快衰减速率相比α-Al_2O_3:C晶体显著加快.600℃退火后的Al_2O_3:C薄膜光释光灵敏度最强,其光释光剂量响应曲线在1-200 Gy整体上都具有很好的剂量线性关系.与热释光相比,Al_2O_3:C薄膜的光释光具有更宽的线性剂量响应范围.此研究为Al_2O_3:C薄膜作为光释光辐射剂量材料做出了有益的探索.     

Effect of annealing temperature on the optical properties of nanosilicon produced from silicon monoxide

Silicon nanoparticles (Si-NPs) capable of photoluminescence (PL) over the energy range from 790 nm to 900 nm were synthesized from silicon monoxide by increasing annealing temperatures from 25 °C to 950 °C. The PL of nanoparticles has remained stable for more than ten months from the date of the hydrosilylation of their surface by 1-octadecene. Solid samples of Si-NPs grafted with 1-octadecene are stable in the air up to 220 °C. The mean sizes of particles and their size distribution density function were derived from SAXS and XRD experiments and compared with TEM and HRTEM images and values calculated by the quantum limit model in accordance with the experimental optical absorption gap values. The absorption spectra of Si-NPs synthesized at 25 °C, 200 °C and 300 °C exhibited a blue shift of the fundamental absorption edge with respect to silicon single crystals; the absorption of Si600 and Si950 at the same incident photon shows energies increase. The PL peak of Si-NPs shifted toward longer waves as the synthesis temperature increased and exhibited a stronger red shift with respect to the photoexcitation wavelength. An analysis of the red shift led us to conclude that the surface states related to (Si-O) bonds influenced the effectiveness of PL. The Si-NPs PL quantum yield increased as the annealing temperature grew and reached a maximum of ∼12% for Si-NPs at 950 °C.     

The effect of pre-irradiation annealing on the thermoluminescence of LiF:Mg,Cu, P phosphor grown by EFG technique

LiF crystal doped with magnesium (Mg), copper (Cu) and phosphorous (P) was grown in the form of multicrystalline sheet using Edge-defined film-fed growth (EFG) technique for dosimetry application. These crystals were grown in argon gas atmosphere using graphite crucible and stainless steel die. Dosimetry peak was observed at 210 °C for as-grown crystal. As reported earlier LiF:Mg, Cu, P is a highly sensitive material but losses its sensitivity if annealed at temperature above 240 °C. In this paper, the effect of annealing temperature on thermoluminescence glow-curve structure, maximum peak temperature, peak height and integrated area of the glow peak of EFG grown samples was investigated in detail. Annealing temperature range from 220 °C to 500 °C was considered for the study. Experimental results of the obtained glow curve show that with increase in annealing temperature, glow peak shift towards higher temperature region with substantial increase in TL intensity. Annealing at 500 °C for 10 min gave maximum TL intensity with main dosimetry peak positioned at 233 °C. Change in the defect structure with different pre-annealing temperature was analysed using trapping parameters.     

Influence of electrolyte temperature on properties and infrared emissivity of MAO ceramic coating on 6061 aluminum alloy

6061 aluminum alloy was treated by MAO at various temperatures of the alkali silicate electrolyte using pulsed bipolar current mode for ten minutes. The surface microstructures and properties were studied using SEM, EDX, and XRD. The infrared emissivities of the MAO ceramic coatings were measured at the 70 °C using FTIR spectrometer. The electrolyte temperature strongly affected all the surface properties. The MAO alumina ceramics prepared in cold electrolytes have volcano-like and accumulated particles microstructures, while those prepared in hot electrolytes were: rougher, thinner and contained grainy spherical hollow bulgy microstructures with more pore density and more sillimanite and cristobalite phases which enhanced the IR emissivity. Also, the increment of sillimanite and cristobalite phases moved the apparent peaks toward longer wavelengths, and broadened the opaque region of the IR spectra. As a result, the increment of electrolyte temperature from 12.3 °C to 90.5 °C increased the average of LWIR emissivity from 80.4% to 94.4%, respectively, for the MAO ceramic coatings.     

Heat treatment effects on the structural and electrical properties of thermally deposited AgIn5S8 thin films

The heat treatment effects on structural and electrical properties of thermally deposited AgIn₅S₈ thin films have been investigated. By increasing the annealing temperature of the sample from 450 to 500 K, we observed a change in the crystallization direction from (420) to (311). Further annealing of the AgIn₅S₈ films at 550, 600 and 650 K resulted in larger grain size in the (311) preferred direction. The room temperature electrical resistivity, Hall coefficient and Hall mobility were significantly influenced by higher annealing temperatures. Three impurity levels at 230, 150, and 78 meV were detected for samples annealed at 350 K. The electrical resistivity decreased by four orders of magnitude when the sample annealing temperature was raised from 350 to 450 K. The temperature dependent electrical resistivity and carrier concentration of the thin film samples were studied in the temperature ranges of 25-300 K and 140-300 K, respectively. A degenerate-nondegenerate semiconductor transition at approximately 180 was observed for samples annealed at 450 and 500 K. Similar type of transition was observed at 240 K for samples annealed at 600 and 650 K.     

Research on double resonance peaks and abnormal frequency shift in permeability spectra of annealed FeCoB films

A FeCoB magnetic film was prepared by a magnetron sputtering method and then was divided into several small pieces for vacuum annealing at different temperatures. The dependence of the coercivity along the hard axis on the annealing temperature reveals a degeneration of softness with the growth of grain size when the annealing temperature is above 350 °C. In permeability spectra measurements, double resonance peaks and an abnormal positive shift in the resonance peak at higher frequency with the increase in annealing temperature are observed. The existence of two peaks is attributed to the double magnetic phases (Fe and FeCo) in the films. The positive shift in the resonance peak at higher frequency has been analyzed and ascribed to the enhanced internal stray fields with the annealing temperature. This phenomenon of positive frequency-shift is very fascinating and novel, which makes the ferromagnetic films more efficient for the applications in the noise absorbing area.