热解过程中铁对神府褐煤焦结构的影响

酸洗褐煤负载不同含量的铁,研究热解过程中铁元素对褐煤焦结构的影响。XRD结果显示(002)峰和(100)峰的强度随着铁含量的增加不断降低,表明铁元素显著改变了煤焦微晶结构。Raman光谱分析显示I_G/I_(all)随着铁含量的增加不断减少,说明铁含量的增加导致煤焦的无序化程度也增加。气化实验表明煤焦气化反应性随着铁含量的增加而增加,超过2%的负载饱和度后气化反应性开始降低。     

Tb~(3+)掺杂含SrF_2纳米晶硅酸盐微晶玻璃的光谱性质

通过高温熔融法和后续热处理制得Tb~(3+)掺杂含SrF_2纳米晶的透明硅酸盐微晶玻璃。利用X射线衍射(XRD)、透射电子显微镜(TEM)、紫外可见透过光谱、荧光光谱、荧光寿命和X射线激发发光光谱(XEL)探讨了基础玻璃和微晶玻璃的结构和光谱特性。XRD结果表明,玻璃中析出晶体为SrF_2纳米晶,衍射峰随着热处理温度的升高和时间的延长而逐渐明显,晶粒也随热处理温度的升高和时间的延长越来越大。在376 nm紫外光和X射线激发下,与基础玻璃相比,微晶玻璃发光显著增强,且发光强度随热处理温度的升高和时间的延长而逐渐增强。     

脉冲激光沉积GaN薄膜的结构和光学特性研究

采用准分子脉冲激光,在Si(111)衬底上生长了带有AlN缓冲层的GaN薄膜, 利用X射线衍射(XRD)、原子力显微镜(AFM)和光致发光光谱(PL)等测试手段研究了不同沉积温度所生长的GaN薄膜结构特征和光学性能.研究表明:沉积温度影响GaN薄膜结构和光学性能,黄带发射峰主要与晶体缺陷有关.在400～700℃沉积范围内随着温度升高,GaN薄膜结构和光学性能提高.     

CVD法制备碳纳米管的TG-DTA研究--温度对CVD法制备碳纳米管的影响

基于碳纳米管粗产品中无定形碳和不同直径碳纳米管对氧的反应活性的差异 ,通过差热 -热重 (TG DTA)方法 ,结合透射电镜 (TEM)和X射线衍射 (XRD)的测试结果 ,研究了合成温度对以乙炔气体为碳源 ,用CVD法制备碳纳米管的石墨化程度、碳纳米管直径以及直径分布的影响 .结果表明 :反应中 ,由于催化剂Co/SiO2中活性组分 (Co)微晶随合成温度的升高而增大 ,导致所制备的碳纳米管的直径增大 ,从 2 0～ 30nm (6 5 0℃ )增加到 30～ 5 0nm (75 0℃ ) .碳纳米管的石墨化程度随着反应温度的升高而增加 .XRD实验结果还表明 ,当合成温度从 6 5 0℃增加到 85 0℃时 ,2θ值从 2 5 .8°增加到 2 6 .8°,(0 0 2 )晶面的层间距从 3.45 减小到 3.32 ,即随着合成温度的升高 ,碳纳米管 (0 0 2 )晶面的层间距减小 .通过DTA放热峰的峰温和半峰宽的分析得出 ,无定形碳的放热峰峰温Tp<380℃ ,其含量随着温度的升高而减小 .碳纳米管的DTA放热峰的峰温Tp 随着碳纳米管的直径和石墨化的程度的增加而升高 ,半峰宽随着碳纳米管的直径的分布范围增大而增宽 .低温 (6 5 0℃ )有利于生成直径小且均匀的多层碳纳米管 (2 0～ 30nm) ,而高温 (大于 75 0℃ )则有利于生成直径大的多层碳纳米管 (大于 30～5 0nm) .     

Ca_(1-x)Al_2Si_2O_8∶Eu_x表面结构与荧光强度相互关系的研究

采用固相法分别在1 150,1 250,1 350,1 450℃下制备了Ca_(1-x)Al_2Si_2O_8∶Eu_x(x=0,0.01,0.05,0.15)系列微晶材料。通过X射线衍射仪(XRD)、拉曼光谱仪(Raman)、光致发光光谱仪(PL)和X射线荧光光谱仪(XRF)研究了CaAl_2Si_2O_8表面结构与荧光强度之间的相互关系。XRD和Raman结果表明:在制备CaAl_2Si_2O_8材料的过程中,随着温度不断升高,原材料逐渐结晶形成结构较为完整的CaAl_2Si_2O_8相;并且从拉曼光谱可以清晰看出,当Eu掺杂量相同时,随着烧结温度的升高,Si—O非晶相逐渐减少,硅氧四面体逐步形成,其振动峰位置逐渐向低波数移动,但当温度过高时硅氧四面体破坏形成宽化的的非晶峰;Eu的掺杂阻碍了Al取代Si位置的过程,因此在1 620波数处振动峰先增强后减弱。这种材料表面结构的变化与Eu的掺杂密切相关,影响着材料表面Eu原子数量分布。PL和XRF结果表明:相同Eu掺杂量时,温度越高越有利于Eu原子扩散到样品表面,从而使样品的荧光强度更强。因此样品的荧光强度和样品单位表面积Eu原子数量存在正比关系。     

退火温度对低温生长MgxZn1-xO薄膜光学性质的影响

用射频磁控溅射法在80℃衬底温度下制备出MgxZn1-xO(x=0.16)薄膜,用X射线衍射(XRD)、光致发光(PL)和透射谱研究了退火温度对MgxZn1-xO薄膜结构和光学性质的影响.测量结果显示,MgxZn1-xO薄膜为单相六角纤锌矿结构,并且具有沿c轴的择优取向;随着退火温度的升高,(002)XRD峰强度、平均晶粒尺寸和紫外PL峰强度增大,(002)XRD峰半高宽(FWHM)减小.结果证明,用射频磁控溅射法通过适当控制退火温度可得到高质量MgxZn1-xO薄膜.     

热解温度对溶胶-凝胶法制备B掺杂ZnO薄膜晶化行为及性能的影响

采用溶胶-凝胶方法制备了B掺杂ZnO(BZO)薄膜,系统研究了热解温度对薄膜的结晶行为和性能的影响. X射线衍射谱表明所有的BZO薄膜均具有六方纤锌矿结构,并沿c轴方向择优生长. 随着热解温度的升高,BZO薄膜的晶粒尺寸和RMS粗糙度增加. BZO薄膜的载流子浓度和载流子迁移率也随着热解温度的升高而增加,其可见光平均透过率均在90%以上.     

纳米磷化镓粉体中混杂石墨和金刚石微晶的拉曼光谱分析

利用Raman光谱并结合能量色散X射线显微分析(EDX)和X射线衍射图谱(XRD)对混杂于纳米磷化镓粉体内的石墨和金刚石纳米微晶进行了分析。结果表明,在纳米GaP粉体Raman光谱中,位于1324 cm-1和1572 cm-1的两个宽强散射谱带分别归属于金刚石的F2g模和石墨的E2g模振动。EDX结果证实纳米GaP粉体材料中含有碳元素。XRD图谱中出现了石墨和金刚石的低晶面指数衍射峰。     

退火对ZnO薄膜光学特性的影响

用射频磁控溅射法在蓝宝石衬底上制备出ZnO薄膜,通过X射线衍射(XRD)、扫描电镜(SEM)和光致发光(PL)谱等研究了退火温度对ZnO薄膜结构和光学性质的影响。测量结果显示,所制备的ZnO薄膜为六角纤锌矿结构,具有沿c轴的择优取向;随着退火温度的升高,(002)XRD峰强度和平均晶粒尺寸增大,(002)XRD峰半高宽(FWHM)减小,光致发光紫外峰强度增强。结果证明,用射频磁控溅射法通过适当控制退火温度可得到高质量ZnO薄膜。     

退火温度对低温生长MgxZn1－xO薄膜光学性质的影响

用射频磁控溅射法在80℃衬底温度下制备出Mg_xZn_1-xO(x=0.16)薄膜，用X射线衍射(XRD)、光致发光(PL)和透射谱研究了退火温度对Mg_xZn_1-xO薄膜结构和光学性质的影响.测量结果显示，Mg_xZn_1-xO薄膜为单相六角纤锌矿结构，并且具有沿c轴的择优取向；随着退火温度的升高，(002)XRD峰强度、平均晶粒尺寸和紫外PL峰强度增大，(002)XRD峰半高宽(F 关键词： xZn_1-xO薄膜')" href="#">Mg_xZn_1-xO薄膜 射频磁控溅射 退火     

High-temperature pyrolysis of petroleum coke and its correlation to in-situ char-CO2 gasification reactivity

The understanding of the pyrolysis behavior of petroleum coke (PC), a by-product of oil refining, is very critical to its energy utilization. Different from most previous work, this investigation particularly focused on PC pyrolysis at high temperatures > 1273 K. The CO₂ gasification reactivity of in-situ char, rather than quenched char, was evaluated and correlated to PC pyrolysis behavior at different temperatures. A Chinese PC with sizes below 100 μm was tested on a high-temperature thermogravimetric analyser (TGA). Three sets of tests were carried out for different purposes. The first set was to simultaneously obtain sample mass loss and gas evolution data during pyrolysis through thermogravimetry-mass spectrometry (TG-MS). The second set aimed to collect char samples for subsequent analyses by scanning electron microscopy (SEM) and Raman spectrometry. The third set was to evaluate in-situ char-CO₂ gasification reactivity through the TGA. The results showed that, in addition to the commonly-observed primary pyrolysis stage at low temperatures, there was a secondary PC pyrolysis stage at high temperatures > 1300 K. In this process, the gases such as HCN, CO₂ and SO₂ were significantly released. The observed changes of char morphology suggested a four-staged thermoplastic transformation of the PC during pyrolysis, which has little been discussed previously. At different stages, i.e. softening, plasticizing, resolidification and graphitization, the rate of carbon ordering was different. The in-situ char-CO₂ gasification reactivity was found to first increase, then decrease and finally increase again with increasing temperature. Such changes coincided with the thermoplastic state of the pyrolyzed char, but not with the changes of char surface area or carbon ordering. The obtained knowledge is new and highlights the potentially important roles of char thermoplastic state in determining its reactivity towards CO₂.     

Effect of pyrolysis conditions on gasification reactivity of woody biomass-derived char

The effect of pyrolysis conditions on char reactivity has been studied using Raman spectroscopy. This paper reports on the relationship between the properties of biomass char and the gasification rate. The gasification kinetics of biomass char have been revealed by measuring the rate of weight loss during its reaction with CO₂ as a function of temperature. First-order kinetic rate constants are determined by fitting the weight loss data using a random pore model. The relationship between the char structure and CO₂ gasification reactivity was investigated in the range of 15–600 °C/min at a constant pyrolysis pressure (0.1 MPa), and 0.1–3.0 MPa at a constant heating rate (15 °C/min). The experimental results reveal that the reactivity of biomass char is determined by the pyrolysis condition. The CO₂ gasification rates in char generated at 0.1 MPa exhibited approximately twice the values as compared to those obtained at 3 MPa. This is because the uniformity of the carbonaceous structure increases with the pyrolysis pressure. The uniformity of carbonaceous structures would affect the CO₂ gasification reactivity, and the decreasing uniformity would lead to the progression of cavities on the char surface during the CO₂ gasification process. The gasification rate of biomass char increases with the heating rate at pyrolysis. This is due to the coarseness (surface morphology) of biomass char and rough texture, which increases with the heating rate.     

Further development of Raman Microprobe spectroscopy for characterization of char reactivity

The effect of heat treatment on reactivity of cellulose char was investigated, using two methods: (1) Raman Microprobe spectroscopy analysis (RMA) and (2) thermogravimetric analysis (TGA). The heat-treatment was in the temperature range of 600–2600 °C, temperature prevailing in combustion of coal-chars. In the RMA, first- and second-order Raman spectra in the range of 800–2000 and 2000–3600 cm⁻¹, respectively, were measured for all samples. In the first-order Raman spectra, the following bands have been observed: D band and G (at 1350 and 1590 cm⁻¹ respectively), 1150 and 1450 cm⁻¹. In the second-order Raman spectra, four bands have been observed at 2450, 2700, 2940 and 3250 cm⁻¹. Both first- and second-order Raman spectra were fitted by Lorentzian functions. The Lorentzian parameters (bandwidth and intensity ratio) showed significant changes with heat treatment, which is consistent with structural modification. Also, from TGA experiments we observed the expected significant influence of heat treatment on char reactivity. Attempts were made to correlate the Lorentzian parameters with char reactivity. A good correlation was found between the 2940 cm⁻¹ bandwidth in the second-order Raman spectrum and char reactivity, confirming the strong connection between char structure and its reactivity, and illustrating the usefulness of RMA in such studies.     

Heterogeneous fixation of N2: Investigation of a novel mechanism for formation of NO

Formation of NO initiated by heterogeneous fixation of N₂ during pyrolysis is investigated experimentally and theoretically. The experiments were conducted with beech wood as well as with the pure biomass components cellulose, xylan, and lignin. The NO formation during char oxidation was recorded as function of pyrolysis atmosphere (N₂ or Ar), pyrolysis temperature (700–1050 °C), and oxidizing atmosphere (O₂ in N₂ or Ar). The results confirm earlier reports that biomass char may be enriched in N during pyrolysis at 900 °C and above. The N-uptake involves re-capture of N-volatiles as well as uptake of N₂. During char oxidation, the captured N is partly oxidized to NO, resulting in increased NO formation. The NO yield from oxidation of beech wood char made in N₂ increases with pyrolysis temperature, and is about a factor of two higher at 1050 °C than the corresponding yield from chars made in Ar. The experiments with pure materials show that the lignin char has the strongest ability to form NO from uptake of N₂, while xylan char forms only small amounts of NO from N₂. Density Functional Theory (DFT) calculations on model chars have revealed a number of chemisorption sites for N₂, many of which are weakly bound and therefore expected to have a short half-life at the higher pyrolysis temperatures. However, the chemisorption of N₂ across a single ring of the armchair surface was found to have an activation energy of 344 ± 30 kJ mol⁻¹ and form a stable, exothermic product with cyano groups. This demonstrates that at least one channel exists for the high-temperature incorporation of N₂ into a char which could give rise to the observed increase in NO release in subsequent char oxidation.     

压汞法分析生物质焦孔隙结构

对于稻壳、树叶、棉花杆、玉米杆四种生物质焦,通过压汞法测量了其在大孔和部分中孔范围内的孔隙结构,发现热解温度、热解保持时间、热解快／慢速都会影响着焦样的比表面积和平均孔径。四种生物质中,树叶焦样的比表面积最大,玉米杆的比表面积最小;稻壳焦样的平均孔径最小,玉米杆的平均孔径最大。不同生物质焦样的孔径分布规律有很大不同。热解温度、热解速度和热解保持时间对孔径分布规律的影响不大,决定孔径分布规律的是生物质本身。在中孔和大孔的范围内,四种生物质焦样的孔径分布曲线都呈现出双峰结构。     

Effect of phosphorus (P) on the structure and reactivity of biochars produced from the pyrolysis of acid-washed biomass loaded with P of various forms

This paper investigates the effect of phosphorus (P) on char structure and reactivity of char prepared from the fast pyrolysis of purposely-prepared P-loaded biomass samples at 1000 °C in absence of other inorganic species. Biomass was first acid-washed then loaded with P of three different occurrence forms (one organic P i.e. phytic acid, and two inorganic P i.e. orthophosphoric acid and polyphosphoric acid) at the same P content of 0.8 wt%. Experimental results show that both organic and inorganic P substantially increase char yields during pyrolysis from 6.2% for the biomass sample without P to 23.0–26.0% for P-loaded samples due to the enhanced crosslinking by P-containing structures in char, leading to increases in the char C and H contents and decrease in O content. The presence of P in biochars from fast pyrolysis of various P-loaded biomass samples plays important role in the evolution of char structure and intrinsic reactivity measured during low-temperature oxidation at 500 °C in air under chemical-reaction-controlled regime. After pyrolysis and subsequent char oxidation, all P in biomass either as organic or inorganic P are found to be present in forms of acid-insoluble organic structures. For char prepared from acid-washed wood, char reactivity increases with char conversion due to the increasing pore surface area at higher conversion. Comparatively, for char prepared from acid-washed wood loaded with various P at char conversion below 60%, the presence of P increases char intrinsic reactivity due to the enhanced crosslinking of reactive carbon structures and reduced condensation of char structures. However, at conversions above 60%, P-containing species in char lead to a significant decrease in char reactivity, due to the formation of abundant CO-P bonds, that is highly resistant to the oxidation in air, in the reacting chars.     

Temperature dependence of the lowest frequency <Emphasis Type="BoldItalic">E</Emphasis><Subscript><Emphasis Type="Bold">g</Emphasis></Subscript> Raman mode in laser-synthesized anatase TiO<Subscript>2</Subscript> nanopowder

Nanosized titanium dioxide (TiO₂) powder was prepared by a laser-induced pyrolysis. Specific surface area of the as-grown powder measured by BET method was 109 m²/g. The grain size (14.5 nm) estimated from these data coincides well with the crystallite size (12.3 nm) determined by XRD measurements. The average grain size (∼35 nm) obtained from the subsequent SEM measurements refers to considerable agglomeration of nanoparticles. Raman spectroscopy has been used to investigate the structural properties of TiO₂ nanopowder and its anatase structure is confirmed. The blueshift and broadening of the lowest frequency E_g Raman mode at temperature range ∼25–550 K have been analyzed using a phonon-confinement model. Dominant influence of the strong anharmonic effect at higher temperatures was demonstrated. PACS 81.07.Wx; 78.30.-j; 63.22.+m     

Mn doped ZnO nanostructured thin films prepared by ultrasonic spray pyrolysis method

Mn-doped ZnO thin films with different percentage of Mn content (0, 1, 3 and 5 at.%) and substrate temperature of 350 °C, were deposited by a simple ultrasonic spray pyrolysis method under atmospheric pressure. We have studied the structural and optical properties by using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and ultra-violet visible near infrared (UV–Vis-NIR) spectroscopy. The lattice parameters calculated for the Mn-doped ZnO from XRD pattern were found to be slightly larger than those of the undoped ZnO, which indicate substitution of Mn in ZnO lattice. Compared with the Raman spectra for ZnO pure films, the Mn-doping effect on the spectra is revealed by the presence of additional peak around 524 cm⁻¹ due to Mn incorporation. With increasing Mn doping the optical band gap increases indicating the Burstein–Moss effect.     

Structural and optical characterization of wurtzite type ZnS

ZnS films were grown on (001) GaAs substrates at different temperatures by RF magnetron sputtering. The ZnS chemical stoichiometry was determined by Energy-dispersive X-ray spectroscopy (EDS), besides it allowed to find the residual impurities, mainly oxygen. The X-ray diffraction (XRD) analysis and Raman scattering reveal that ZnS deposited thin films showed hexagonal wurtzite crystalline phase. The films average crystallite size range was from 8.15 to 31.95 nm, which was determined using the Debye–Scherrer equation for the peak W(101). Besides an experimental study of first- and second-order Raman scattering of ZnS films is made. An energy level diagram involving oxygen traps and interstitial sulphur ions is used to explain the origin of the radiative transitions observed in the room temperature photoluminescence (PL) spectra.     

Nanostructure of thin silicon films by combining HRTEM, XRD and Raman spectroscopy measurements and the implication to the optical properties

A series of thin silicon films with different degrees of crystallinity were prepared by decomposition of silane gas highly diluted with hydrogen, in radiofrequency glow discharge. The crystallite size, shape, and the portion of crystalline phase were investigated by high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), Raman spectroscopy (RS), and X-ray powder diffraction (XRD). The absorption coefficient (α) was calculated from the measurement of UV-vis-transmittance. By using RS, the volume fractions of the crystalline phase were estimated from the ratio of the integrated intensities of transversal optical (TO)-related crystalline and amorphous bands. These results were in excellent agreement with the mean crystallite sizes measured in HRTEM images and crystallite sizes refined from XRD measurements. The red shift of absorption, appearing as a result of the increase of the crystal fraction, depends on the size and distribution of nanocrystals.