共查询到20条相似文献,搜索用时 453 毫秒
1.
以焦宝石、活性炭和铝粉为原料,添加Na2CO3制备Al4SiC4/Al4O4C复合耐火材料.采用化学分析、XRD和SEM等测试技术,研究了Na+对材料物相组成和显微结构的影响.结果表明:添加Na2CO3加速了Al2O3和活性炭的反应,促进了Al4O4C的生成.未添加Na2CO3时生成的Al4SiC4晶粒表面光滑,添加Na2CO3后Al4SiC4晶粒粗糙、凹凸,缺陷明显增加.此外,未添加Na2CO3的试样中生成的Al4O4C呈短纤维状,添加Na2CO3后全部转变为细小颗粒. 相似文献
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We measured the order parameter near the interface between a liquid crystal and the solid substrate treated by several methods. The interfacial order parameter is different according to the surface treatment, and is larger than the bulk order parameter. Moreover, in the temperature above the clearing point, the interfacial order still has a finite value. 相似文献
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Giovanni Poeti Enzo Fanelli Mario Braghetti 《Molecular Crystals and Liquid Crystals》2013,570(1-2):145-160
Abstract The preparation and melting behaviour of the homologous series of 4-acetyl-4′-n-alkanoylox-azobenzenes, CH3-CO-C6H4-N?N-C6H4-O-CO-(CH2) n -CH3, (with n ranging from zero to 16) is reported. The melting behaviour has been investigated by means of thermal microscopy and differential scanning calorimetry. The experimental results indicate for almost all the compounds the presence of solid state polymorphism and a type A smectic; for one compound a type B smectic phase is also present. Some homologs present, in addition, a nematic phase. 相似文献
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Komornikov V. A. Timakov I. S. Zajnullin O. B. Grebenev V. V. Makarova I. P. Selezneva E. V. Ksenofontov D. A. 《Crystallography Reports》2019,64(6):984-990
Crystallography Reports - The phase equilibria in the CsHSO4–CsH2PO4–NH4H2PO4–H2O four-component aqueous salt system have been studied. The crystallization ranges and solubilities... 相似文献
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M. A. Gunina E. Kh. Lermontova S. M. Pestov L. G. Kuz’mina 《Crystallography Reports》2012,57(5):733-736
The molecular and crystal structure of 4??-hexyloxyphenyl 4-pentylbenzoate, C6H13O-C6H4-COO-C6H4-C5H11, which is a liquid-crystal compound, was determined by X-ray diffraction. This compound forms a nematic phase upon melting. The crystal contains three crystallographically independent molecules. In one of them, the alkyl chain is disordered. This is indicative of the looseness of the crystal packing in the aliphatic region. The crystal structure is stabilized by the following two types of weak directional interactions: hydrogen bonds with the participation of the terminal O atom of the ester group and the C-H group of one of the benzene rings and C-H????-system interactions. Only one of the three independent molecules is involved in the latter type of interactions. Hence, the structurization of the mesophase is most likely determined by hydrogen bonding. 相似文献
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The crystal structures of four liquid-crystal (LC) compounds belonging to 4-acylphenyl 4′-alkyloxybenzoates with the general formula C n H2n + 1-C(O)-C6H4-O-C(O)-C6H4-O-C m H2m + 1 numbered as 1/6, 1/7,2/7, and 3/7 (the numbers in the code indicate the ratios of the numbers of alkyl-chain units, n/m) are determined. Compounds 1/6 and 1/7 form smectic and nematic phases, but they are monotropic mesogens, whereas compounds 2/7 and 3/7 form only an enantiotropic smectic phase. Compound 3/7 crystallizes in two crystal modifications—triclinic with Z′ = 2 (3/7 tr ) and monoclinic with Z′ = 4 (sp. gr. P2, 3/7 mon ). All crystals consist of alternating aromatic and aliphatic regions and are characterized by the presence of weak directional interactions, such as C-H...O hydrogen bonds and π-stacking interactions. This provides the necessary conditions for the formation of a mesophase, and the existence of two types of structure-forming units is in line with the formation of a smectic phase. An explanation is proposed for the monotropic properties of 1/6 and 1/7. 相似文献
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L. G. Kuz'mina I. I. Konstantinov A. V. Churakov 《Molecular Crystals and Liquid Crystals》2018,664(1):95-100
4-methoxyphenyl-4′-n-nonyloxybenzoate have been investigated by single crystal X-ray structural analysis. Crystal packing of the compounds does not represent a precursor of the mesophse although the typical for liquid crystal compounds separation of crystal packing on aromatic and aliphatic areas is observed here. Possible reason for monotropic properties are discussed. 相似文献
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M. Akkurt S. Ö. Yıldırım A. Kerbal B. Bennani M. Daoudi Z. H. Chohan V. McKee T. Ben Hadda 《Journal of chemical crystallography》2010,40(3):231-234
The title compound, 3′-(4-methoxyphenyl)-2-phenyl-4′-(4-ethoxyphenyl)-1,2-dihydro-4H,4′H-spiro[isoquinoline-3,5′-isoxazol]-4-one was synthesized from the reaction of dipolarophile with p-methoxybenzadoxime in the presence of sodium hypochlorite in chloroform solution. The structure of the synthesized compound was determined by IR, 1H NMR, mass spectroscopic data, 13C NMR spectroscopy, elemental analysis and X-ray crystallography. The structure was solved in monoclinic, space group C2/c with a = 21.941 (4), b = 17.233 (3), c = 15.404 (3) Å, β = 122.193 (2), V = 4928.9 (16) Å3, Z = 8 and with Rint = 0.154. The geometry of the title compound showed that the piperidine ring adopts a half-chair conformation. In the crystal structure, molecules are linked by C–H···O and C–H···N contacts. Weak C–H···π interactions plays an important role in stabilizing the supramolecular structure. 相似文献
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The bend elastic constants (k 33) and order parameters (S) derived from optical measurements in the nematic phase of pentlyl, hexyl, heptyl and octyl cyanobiphenyls (5CB, 6CB, 7CB and 8CB respectively) are reported. The odd-even effect is clearly seen in the K 33 values of all four compounds and in the S values of the first three. 5CB, 6CB and 7CB show only the nematic mesophase but their elastic constants indicate the existence of smectic-like short range order. For example, even the lowest homologue, 5CB, does not obey the law k 33 ∞ S 2 given by the mean field throry. 7CB, has about the same order parameter as 5CB but a much higher elastic constant. 8CB, which shows a smectic A phase as well, exhibits a lower k 33 than 7CB near the nematic-isotropic transition point but a pronounced pretransitional increase near the A-N transition. 相似文献
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Rajnikant V. K. Gupta R. Gupta A. Kumar R. K. Bamezai N. K. Sharma B. Varghese 《Crystallography Reports》2000,45(1):98-102
The structure of a liquid crystal of 4-cyano-4′-n-octyloxybiphenyl (C21H25NO) is determined by X-ray diffraction analysis. The compound crystallizes in the triclinic crystal system with unit cell parameters a = 7.322(1) Å, b = 12.693(3) Å, c = 20.393(2) Å, α = 92.45(1)°, β = 99.96(1)°, γ = 99.35(2)°, and space group $P\bar 1$ . The structure is solved by the direct method and refined to R = 0.057. Two independent molecules are located in the asymmetric unit. No short intermolecular contacts are observed in the crystal packing. 相似文献
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采用固相反应制备了不同浓度Mn4+掺杂的硅酸锆粉末,研究了Mn4+对硅酸锆光致发光性能的影响。采用XRD表征 ZrSiO4∶Mn4+的结构,结果显示在1 400 ℃粉末已被完全合成。研究了不同掺杂浓度下ZrSiO4∶Mn4+粉末的光谱性能,在0.3%Mn4+掺杂浓度(摩尔分数)下,其发光性能最好。在激发谱中,位于363 nm的峰是由O2--Mn4+的电荷迁移带和自旋允许的Mn4+的4A2-4T1的能级跃迁叠加产生的,而450 nm的激发峰则是因为Mn4+的4A2-4T2能级跃迁导致的。发射谱中的最强峰位于667 nm,这是由Mn4+的2E-4A2的能级跃迁产生的,还有一个位于698 nm的峰则是由于反斯托克斯声子边带发射造成的。测试了ZrSiO4∶Mn4+粉末的荧光衰减曲线,Mn4+离子浓度为0.1%时寿命为0.204 1 ms。结果表明,ZrSiO4∶Mn4+粉末拥有良好的发光性能,是一种有望应用于白光LED的荧光粉。 相似文献
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4H-SiC同质外延生长及Ti/4H-SiC肖特基二极管 总被引:2,自引:0,他引:2
利用台阶控制外延生长技术在偏晶向Si-面衬底上进行了4H-SiC的同质外延生长研究,衬底温度为1500℃,在厚度为32μm、载流子浓度为2~5×1015cm-3的外延材料上制备出了反向阻塞电压大于1kV的Ti/4H-SiC肖特基二极管,二极管的正向与反向电流的整流比(定义偏压为±1V时的电流比值)在室温下超过107,在265℃的温度下超过102,在20~265℃的温度范围内,利用电流电压测量研究了二极管的电学特性,室温下二极管的理想因子和势垒高度分别为1.33和0.905eV,开态电流密度在2.0V的偏压下达到150A/cm2,比开态电阻(Ron)为7.9mΩ·cm2,与温度的关系遵守Ron~T2.0规律. 相似文献
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M. Sasaki K. Takeuchi H. Satobar H. Takatsu 《Molecular Crystals and Liquid Crystals》2013,570(2-4):169-178
A series of 3-fluoro-4-cyanophenyl 4′-n-alkylbenzoates, which show monotropic nematic phases, was prepared and their transition temperatures and melting enthalpies were measured. The 3-fluoro-4-cyanophenyl 4′-n-propylbenzoate, 3-chloro-4-cyanophenyl 4′-n-propylbenzoate and 4-cyanophenyl 4′-n-propylbenzoate were mixed with a nematic mixture (A) of 4-n-alkoxyphenyl 4′-n-alkylcyclohexane-1′-carboxylates. 3-Fluoro-4-cyanophenyl 4′-n-propylbenzoate decreases the N-1 transition temperature less, increases the birefringence more, and increases the bulk viscosity less than 3-chloro-4-cyanophenyl 4′-n-propylbenzoate, and reduces the threshold voltage to the greatest extent. The dielectric anisotropies of 3-fluoro-4-cyanophenyl 4′-n-propylbenzoate and 4-cyanophenyl 4′-n-propylbenzoate determined from a series of solutions of the compounds in nematic mixture (A) are 35.9 and 29.6, respectively. 相似文献
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J. M. Buisine 《Molecular Crystals and Liquid Crystals》2013,570(2-4):143-157
By using a metabolemeter, the phase transitions of bis-[4, 4′-n-heptyloxybenzylidene]-1, 4 phenylenediamine (HBPD) and terephthalylidene-bis-[4-n-decylaniline] (TBDA) have been studied. The weakly first order phase transitions (SG-SF and SF-SI) and the narrowly separated phase transitions (SC-SA and SA-I) of TBDA are detectable. For HBPD, both transitions SG-SI and SI-SC are individually observed and the enthalpy changes are deduced from pressure increments at the tranformations: two triple points are detected, one directly by a change of slope in the drawing of the equilibrium curves. The pressure-temperature phase diagrams are given; for each transiton, the volume increases on increasing the temperture. 相似文献