共查询到20条相似文献,搜索用时 109 毫秒
1.
The type and the amount of silicate groupings existing in glassy and crystalline 2PbO·SiO 2 have been determined by direct chemical methods: paper chromatography, trimethylsilylation combined with gas-liquid partition chromatography and by the molybdate method. The results obtained by these three different methods are in good agreement and demonstrate, that glassy 2PbO·SiO 2 and each of the three main crystalline polymorphs are characterized by its own specific silicate anion distribution: the distribution in vitreous 2PbO·SiO 2 is of a polyanionic nature; in T---Pb 2SiO 4 dimetic groups [Si 2O 7] 6− prevail; M 1---Pb 2SiO 4 contains predominantly [Si 4O 12] 8− rings and H---Pb 2SiO 4 is a typical polysilicate with chain anions [SiO 32−] n. The results fit a structural model according to which glass is a random array of discrete polyatomic groupings; the gradual transition from the glassy state to the stablest crystalline structure is connected with degradation and polymerization of silicate anions. 相似文献
2.
In this study we report first measurements of wavelength-selective infrared-induced materials modification of bulk As 2S 3 and As 2Se 3. These materials are currently being considered as candidate materials for infrared optical fiber transmission in the range of 1–10 μm. Our study is aimed at modifying oxygen, hydrogen and carbon impurities bound to chalcogenide constituent elements in the materials to reduce absorption. Tunable infrared radiation from the W.M. Keck Free Electron Laser (FEL) at Vanderbilt was used to excite specific vibrational modes, S–O–H and CH x modes in bulk As 2S 3 and Se–H, CH x and S–H 2 modes in bulk As 2Se 3. Changes in vibrational mode amplitudes are monitored by measuring the intensity of the Fourier transform infrared (FTIR) spectra before and after irradiation at appropriate wavelengths. By tuning wavelengths to hydrogen vibrational modes, we find evidence that hydrogen is released and/or redistributed athermally. In particular, following irradiation at specific resonant wavelengths, vibrational mode amplitudes as monitored by FTIR associated with CH x are significantly reduced in bulk As 2S 3 and As 2Se 3 samples. In As 2S 3, the changes in CH x modes are reversed by heat treatment at 115°C for 35 min in nitrogen atmosphere. 相似文献
3.
A modified method to synthesize the new laser upconversion material Ba 2ErCl 7 using Er 2O 3, BaCl 2 2H 2O and NH 4CI is reported for the first time in this paper. Single crystals up to 5–8mm in diameter and 10–20 mm in length have been grown by Czochralski method. The transmittance spectra of Ba 2ErCl 7 single crystal has first been measured by using an HITACHI U-3500 spectrophotometer. There are three intense absorption peaks 4I9/24I11/2 and 4I 13/2 in the infrared range which can be excited by 803nm, 980nm and 1.5μm laser diodes (LDs), respectively. The cut-off wavelength of the crystal is 230mn. Intense green luminescence can be observed when the crystal is pumped by a ED at 803nm. The formation of the defects is also discussed. 相似文献
4.
The solubility of a series of hexaferrite derivatives of BaFe 12O 19 in solvents of the system Na 2O-B 2O 3 with oxide ratios of 7:3 and 3:2 has been investigated. The temperature dependences of the saturation concentration in these solvents are determined for ferrites with the nominal compositions Ba 0.8Pb 0.2Fe 12O 19, BaFe 10Ga 2O 19, BaFe 10Al 2O 19 and BaFe 8Mn 2 Ti 2O 19. Single crystals of BaFe 12O 19, in which part of the metal ions are replaced by various amounts of Pb 2+, Ga 3+, Al 3+ and Mn 2+ + Ti 4+ ions, are g rown from the solutions by the slow cooling technique. The distribution coefficients of the substituting ions and the compositions of the crystals obtained are established by microprobe analysis (EPMA). Information on the position of substitution is obtained from the Mössbauer spectra. 相似文献
5.
为将Ca(H 2PO 4) 2制备KH 2PO 4过程中的石膏资源化利用,以H 3PO 4与CaCO 3反应制备Ca(H 2PO 4) 2溶液,并与K 2SO 4溶液反应,进行Ca(H 2PO 4) 2-H 3PO 4-K 2SO 4体系中石膏晶型和形貌调控研究。结果表明:通过改变反应时间、反应温度、SO 2-4过量系数和CaO含量等参数可对Ca(H 2PO 4) 2-H 3PO 4-K 2SO 4体系中石膏晶型和形貌进行调控,制得短柱状α-CaSO 4·0.5H 2O。体系在温度高于95 ℃和CaO含量为3.0%~5.0%(质量分数,下同)时形成α-CaSO 4·0.5H 2O,在CaO含量为5.5%主要形成CaSO 4·2H 2O;反应时间长于20 min和SO 2-4过量系数大于1.4将形成K 2SO 4(CaSO 4) 5·H 2O,导致石膏晶体表面缺陷增加。本实验条件下,适宜反应条件为:反应时间10 min、反应温度95 ℃、SO 2-4过量系数1.2和CaO含量5.0%,此条件下可制得长度42~70 μm、直径13~24 μm的短柱状α-CaSO 4·0.5H 2O,其抗折和抗压强度分别可达5.61 MPa和33.74 MPa,滤液中钾收率和脱钙率分别可达94.23%和83.80%。 相似文献
6.
In order to investigate the mechanism of hydrogen-induced amorphization, the structure changes by hydrogen absorption in La 2Ni 7, LaNi 2, LaNi 1.5 and LaNi compounds are investigated by X-ray diffraction. Also thermal stabilities of the hydrogenated samples are examined by DSC and hydrogen desorption technique. In case of La 2Ni 7 compound, the severe lattice distortion is found as hydrogen is absorbed. However, as the hydrogen absorption-desorption cycle is repeated, the amorphization takes place. LaNi 2 and LaNi 1.5 compounds show the complete absence of diffraction lines when hydrogenated at room temperature, i.e. the hydrogen-induced amorphization has occurred. The DSC curve of the hydrogen-induced amorphous alloy shows a small exothermic peak related to the precipitation of LaH 2 and LaNi 5. LaNi compound may transform into another crystalline structure by hydrogenation at room temperature, which is different from that of original LaNi compound. It is suggested that the amorphization of a compound is dependent upon the stability of the compound and the decomposition rate to LaH 2 and LaNi 5. The mechanism of the amorphization is related to the lattice distortion caused by the motion of the metal atoms so that the surroundings of the hydrogen atoms in the amorphous state resemble those of hydrogen atoms in LaH 2. 相似文献
7.
为寻求新型热障涂层用陶瓷材料,本文采用高温固相烧结法制备了(Sm0.5 Gd0.2 Nd0.3)2(Hf0.3 Ce0.7)2 O7复合氧化物.利用XRD分析了其晶体结构,SEM分析其显微组织,膨胀仪测试其热膨胀性能,激光热导仪测试其热扩散系数.结果表明,成功制备了具有单一萤石晶体结构的(Sm0.5 Gd0.2 Nd0... 相似文献
8.
The 11B NMR spectra of xRb 2S+(1− x)B 2S 3 glasses in the range 0 x0.75 and of xCs 2S+(1− x)B 2S 3 glasses in the range 0 x0.60 are reported. The addition of Rb 2S to B 2S 3 creates on average approximately two and one-half tetrahedral borons for each added sulfur ion, whereas it is found that the addition of Cs 2S creates approximately 2 tetrahedral borons for each added sulfur ion. This behavior while more similar to that seen in the alkali borate glasses, contrasts that seen in the Na and K thioborate glasses, where six to eight and three, respectively, tetrahedral borons are formed for every sulfide anion added to the glass. These findings are supported by the IR and 11B NMR spectra of the di-thioborate polycrystals (c-Rb 2S:2B 2S 3 and c-Cs 2S:2B 2S 3) whose structures appear to be comprised of two BS 4 tetrahedrals and two BS 3 trigonals (N 40.5) like that in the alkali di-borate phases for both Rb and Cs. Unlike the 11B NMR resonances of the sodium thioborate glasses where a single sharp line is observed for the tetrahedral boron site and a single quadrupolar broadened line is observed for all the trigonal sites, a third resonance line is observed at high alkali fractions for the rubidium and cesium thioborate glasses. This new structural feature may arise from asymmetric MBS 2 (meta-thioborate groups) or tetrahedral boron groups possessing a non-bridging sulfur. 相似文献
9.
The preparation of glass-lined coating mould from gels in the ternary system of SiO 2–ZrO 2–B 2O 3 has been investigated. The crystallization characterization and high temperature structure stability of this coating mould are demonstrated. We can find that the crystallization of t-ZrO 2 as well as the tetragonal to monoclinic phase transformation are, respectively, retarded and impeded owing to the encasement of SiO 2 matrix. While the inhibitive effect of B 2O 3 on crystallization of the SiO 2–ZrO 2–B 2O 3 coating mould is explained. Finally, DD3 single crystal superalloy melt can realize highly undercooled rapid solidification by adopting this coating mould, which further evinces that SiO 2–ZrO 2–B 2O 3 coating mould has an ideal nucleation inhibition for superalloy. 相似文献
10.
Glass formation in the P 2O 5---WO 3---K 2O---Al 2O 3 system was investigated and the glass-forming regions are presented. the properties of the glasses in the P2O5---WO3---K2O---Al2O3 system (Al2O3 8 mol.%) are reported. The colouration of glass was studied. It was found that W5+ ions make glass blue. Infrared spectra were measured by means of making KBr pills. Results of the investigation suggest that P---O---P, P---O---W, and W---O---W bonds form a continuous network in the phosphate glasses. So we suggest that tungsten trioxide is a glass former. 相似文献
11.
Binary glasses containing no modifying oxides, such as SiO 2---GeO 2, SiO 2---B 2O 3, SiO 2---P 2O 5, GeO 2---B 2O 3, Al 2O 3---P 2O 5 and ternary glasses SiO 2---GeO 2---P 2O 5, Al 2O 3---B 2O 3---P 2O 5, B 2O 3---SiO 2---P 2O 5, Al 2O 3---ZrO 2---P 2O 5 have been prepared by melting and CVD methods. The Raman spectra have also been measured. Structural characteristics of SiO 2, GeO 2, B 2O 3, P 2O 5 in different glass systems are analysed. There exist coordination number changes in B 2O 3- and GeO 2-containing glasses and linkage changes between tetrahedra (SiO 4) and (PO 4) in SiO 2 and P 2O 5 containing glasses. The structure of Al 2O 3 containing glasses is homogeneous and the structure of B 2O 3 containing glasses is inhomogeneous. These experimental results are in coincidence with the X-ray small angle scattering analysis. 相似文献
12.
采用布里奇曼法成功制备出大尺寸( φ15 mm×50 mm)、高质量的全无机金属卤化物类钙钛矿Cs 3Bi 2I 9单晶。室温下,该晶体属于六方晶系,空间群为 P6 3/ mmc,密度为5.07 g/cm 3,晶胞参数为 a= b=0.840 nm, c=2.107 nm,熔点为632 ℃。采用粉末X射线衍射谱、紫外-可见-近红外漫反射光谱、 I-V测试等表征该晶体的性质。制备Au/Cs 3Bi 2I 9/Au三明治型器件结构,采用飞行时间技术测试Cs 3Bi 2I 9晶体的载流子迁移率,得到Cs 3Bi 2I 9晶体的电子迁移率为4.33 cm 2·V -1·s -1。根据Hecht单载流子方程拟合得到Cs 3Bi 2I 9晶体的载流子迁移率寿命积( μτ)为8.21×10 -5 cm 2·V -1,并且在500 V偏压下对α粒子的能量分辨率达到39%。 相似文献
13.
将有机物2,5-二溴对苯二甲酸(H 2L 1)和2,2′-联吡啶(L 2)作为双配体,使用溶剂热法和七水合硫酸锌(ZnSO 4·7H 2O)、六水合硝酸钴(Co(NO 3) 2·6H 2O)分别反应,得到配合物[Zn(L 1)(L 2)(H 2O)] n(1)和配合物[Co(L 1)(L 2)(H 2O)] n(2)。采用单晶X射线衍射、元素分析、红外光谱、紫外光谱、荧光光谱、热重分析等测试方法对这两种物质进行分析研究。单晶测试结果表明配合物1是单斜晶系,以Zn 2+配位连接L 2-1与L 2形成一维链状结构,各条链在分子间氢键和π…π共轭作用下有规律地堆叠形成三维网络结构。配合物2是三斜晶系,Co1离子和Co1 i离子由H 2L 1上的羧酸氧原子O4和O4 i连接,形成双齿螯合的配位结构单元,以Co 2+配位连接 L 2-1和L 2形成二维网格结构,各层在O—H…O分子间氢键和范德瓦耳斯力作用下有规律的堆叠形成三维网络结构。配合物1和2均含有芳香杂环、羧基杂环和氮杂环,具有良好的荧光性质和热稳定性,最大发射波长分别为345 nm和333 nm。 相似文献
14.
In amorphous (a-) GeS 2 there is only one medium-range order (MRO) dependent X-ray scattering feature, i.e., the ‘first sharp diffraction peak’ (FSDP), whereas in a-Sb 2S 3 all scattering features in the interval 1–2.4 Å −1 are in fact MRO-dependent. The basic element of MRO in a-GeS 2 is a part of a chain of corner bound tetrahedra extracted from the high temperature form of c-GeS 2; in a-Sb 2S 3 it is a part of a crystalline-like (Sb 2S 3) n band. Ordering of parts of these bands is characterized by a greater interband separation than in the crystal. By contrast with a-GeS 2, the MRO-dependent medium-angle scattering features in a-Sb 2S 3 are less sensitive to fluctuations of the interband (intercluster) ordering distance. 相似文献
15.
The electrical and dielectric properties for three series of MoO 3–Fe 2O 3–P 2O 5 and one series of SrO–Fe 2O 3–P 2O 5 glasses were measured by impedance spectroscopy in the frequency range from 0.01 Hz to 3 MHz and over the temperature range from 303 to 473 K. It was shown in Part I that the MoO 3 is incorporated into phosphate network and the structure/properties are strongly influenced by the overall O/P ratio. The Fe 2O 3 content and Fe(II)/Fe tot ratio in these glasses have significant effects on the electrical conductivity and dielectric permittivity. With decreasing Fe 2O 3 content in MoO 3–Fe 2O 3–P 2O 5 glasses with O/P at 3.5 the dc conductivity, σ dc(ω) decreases for two orders of magnitude, which indicates that the conductivity for these glasses depends on Fe 2O 3 and is independent of the MoO 3 content. Also, the dielectric properties such as ′(ω), ″(ω) and σ ac(ω) and their variation with frequency and temperature indicates a decrease in relaxation intensity with increase in the concentration of MoO 3. On the other hand, the dc conductivity for MoO 3–Fe 2O 3–P 2O 5 glasses with O/P > 3.5 increases with the substitution of MoO 3 which has been explained by an increase in the number of non-bridging oxygens and formation of Fe–O–P bonds that are responsible for formation of small polarons. The increase in the dielectric permittivity, ′(ω) with increasing MoO 3 content is attributed to the increase in the deformation of glass network with increasing bonding defects. For SrO–Fe 2O 3–P 2O 5 glasses the conductivity and dielectric permittivity remained constant with increasing SrO. 相似文献
16.
Fresnoite type compound Sr 2TiSi 2O 8 was found as a new nonlinear optical material. This compound was synthesized by substituting Sr 2+ for Ba 2+ in fresnoite Ba 2TiSi 2O 8. X- ray diffraction data showed Sr 2TiSi 2O 8 and fresnoite are isostructural. The second harmonic generation (SHG) effect of Sr 2TiSi 2O 8 is about 8 times larger than that of KH 2PO 4 (KDP). The ultraviolet absorption edge of Sr 2TiSi 2O 8 is around 270nm. 相似文献
17.
采用湿化学法合成了Eu原子掺量5%的Lu 2O 3陶瓷前驱体,通过SEM、XRD研究了煅烧前后前驱体和1 100 ℃煅烧4 h后粉体的形貌、结构以及物相。结果表明煅烧后的粉体为纳米类球形、高分散且结晶性良好的颗粒。颗粒尺寸为68.5 nm。使用煅烧后的粉体为原料,在1 650 ℃真空烧结30 h制备了高透过率的Eu:Lu 2O 3陶瓷,晶粒尺寸为46 μm,在611 nm处的直线透过率可以达到66.3%。此外对陶瓷的吸收曲线、光致激发和发射光谱特性以及X射线激发发射光谱进行研究。可观察到,Eu:Lu 2O 3陶瓷存在基质和激活离子两类吸收,光致发光光谱和X射线激发发射光谱均可以看出Eu:Lu 2O 3陶瓷存在极强的 5D 0→ 7F 2跃迁发光,位于611 nm处。对比商业的BGO单晶的X射线发射光谱,可得本实验中制备的陶瓷的光输出为85 000 ph/MeV。Eu:Lu 2O 3陶瓷本身有着高X射线以及高能粒子的阻止能力,结合高光输出特性,表明Eu:Lu 2O 3陶瓷在X射线成像等领域具有巨大的潜在应用价值。 相似文献
18.
Small-angle X-ray scattering (SAXS) measurements on V 2O 5· nH 2O sols and gels, prepared by dissolving V 2O 5 glass into water at room temperature, show that there are V 2O 5 polymeric fibers entangled like random coils in the sol of n 5000, while the deviation from the random coil behavior occurs in the dilute sol of n 6000. A Bragg peak appears at the scattering vector h 0.02 Å−1 to be superimposed on an asymptotic h−2-course in the SAXS curve of the concentrated sol of n 680. This means that the spatial correlation between V2O5 polymeric fibers takes place even in the fluid state. V2O5·nH2O sols completely lose fluidity at n 250 to transfer to the gel state, where V2O5 polymeric fibers begin to pile up in the parallel with a substrate surface. Such a layer structure is preserved up to the gel of n 4. However, V2O5 polymeric fibers are randomly oriented within each layer. 相似文献
19.
The high viscosity in melts of the Li 2O---B 2O 3 system makes it very difficult to grow large crystals of lithium triborate. The viscosity and IR characteristics of molten li 2O---B 2O 3 system are reported in this paper. When the temperature increases the viscosity of li 2O---B 2O 3 system decreases and follows an Arrhenius-type relationship. With an increasing 13203 ratio in Li 2O---B 2O 3 melts, the viscosity rises gradually to a maximum with a composition Li 2O: 3.513203 then it falls rapidly. In order to find active agents to reduce the viscosity, Na 2O, NaCl, LiF, P205, M003, W03 etc oxides were added to Li 2O---B 2O 3 samples respectively and investigated using the orthogonal method. The experimental results show that the addition of acidic oxides can significantly decrease the viscosity in the Li 2O---B 2O 3 system. For Li 2O: 4.513203, an ideal additive agent is 20wt% Li 2O:: 2MoO 3. Near the composition for crystal growth, the percentage reduction of viscosity is 62.2%. The IR spectra of Li 2O---B 2O 3 system revealed that the BO 4−/NO 3− ratio is reduced in the melt using Li 2O: 2MoO 3 as an additive. It is proposed that the M003 reduced the concentration of bridging oxygen atoms of BO 4−. The change of structure explains the decline in the viscosity. In the crystal structures of lithium triborate, the matrix spaces are so small that larger other cations than Li+ are very difficult to enter the crystal matrix. So the use of additive agents to reduce the viscosity is a possible method if no new phase appears. 相似文献
20.
氟化钡(BaF 2)晶体是已知响应最快的闪烁晶体,在高能物理、核物理及核医学等领域有着广泛的应用前景。抑制BaF 2晶体的慢发光成分对其工程应用至关重要。本文利用坩埚下降法制备了高Y 3+掺杂浓度5%、8%、10%(摩尔分数)的BaF 2晶体,并采用Y 3+与碱金属离子(Li +、Na +)共掺杂的方法形成电荷补偿阻止间隙F -的产生,制备了双掺杂型BaF 2快响应闪烁晶体,进而基于优化的5 ns和2 500 ns时间门宽测试方法,研究了Y 3+掺杂浓度以及Y 3+与碱金属离子(Li +、Na +)共掺杂浓度对BaF 2闪烁晶体快/慢成分比的影响规律。结果表明,生长的高浓度Y 3+掺杂BaF 2晶体的光学质量优异,在220 nm和300 nm处透过率分别高于90%和92%;随着Y 3+掺杂浓度由0提高至10%,BaF 2晶体的慢发光成分显著降低,快/慢成分比由0.15提高至1.21;生长的Y 3+/Li +及Y 3+/Na +共掺杂BaF 2晶体的慢发光成分较Y 3+掺杂BaF 2晶体进一步降低,快/慢成分比最高分别可达1.63和1.61。研制的双掺杂BaF 2快响应闪烁晶体有望应用于高能物理、核物理前沿实验等重要领域。 相似文献
|