不同粒度SiC颗粒低温制备SiC泡沫陶瓷的性能

以SiC陶瓷前驱体聚碳硅烷(polycarbosilane,PCS)为粘结剂、SiC微粉为填料、聚氨酯海绵为模板,低温制备出了SiC泡沫陶瓷.研究了SiC颗粒粒度和PCS含量对SiC泡沫陶瓷线收缩率、体积密度、微观结构与抗弯强度的影响.确定了不同粒度SiC颗粒制备泡沫陶瓷的最佳烧成温度.结果表明,随SiC颗粒粒度与PCS含量的增加泡沫陶瓷的线收缩率增大、体积密度降低;泡沫陶瓷的抗弯强度随SiC颗粒粒度的增大而降低;颗粒粒度小于1μm时,最佳烧成温度为1200℃,颗粒粒度大于1μm时,最佳烧成温度为1100℃;PCS在1100℃与1200℃热解可得到β-SiC晶粒,其晶粒尺寸为12.2 nm与19.6 nm.     

热处理对NiCuZn铁氧体磁性能的影响

利用化学共沉淀法制备了细小均匀的NiCuZn铁氧体前驱体粉体,通过XRD、TG-DSC、激光粒度仪(LPS)、精密阻抗分析仪、振动样品磁强计(VSM)等手段对粉体进行表征.研究前驱体的粒度分布及晶化过程,在不同的预烧温度下样品的磁性能,不同烧结温度的相结构、磁滞回线和磁性能.结果表明:前驱体粒度分布均匀,烧结后可以得到纯相的尖晶石型NiCuZn铁氧体.当预烧温度为500℃,烧结温度为900℃时,样品磁导率μi约为200,品质因数Q约为150,截止频率约为70 MHz.     

MPCVD法在基片边缘生长大颗粒金刚石的研究

本研究在自制的5 kW大功率MPCVD装置中,利用边缘效应成功的在基片边缘处以50μm/h的沉积速率沉积出品粒尺寸达500 μm左右的大颗粒金刚石并以70μm/h沉积速率同质外延修复长大了一颗天然的单晶金刚石.在实验中,利用SEM和Raman光谱对基片边缘区域和中央区域所沉积的金刚石颗粒进行了表征.结果表明,边缘处沉积的金刚石颗粒与中央区域沉积的金刚石颗粒相比,具有更大的晶粒尺寸和更好的质量.通过仔细观察实验条件,对边缘效应产生的原因进行了分析,发现由于基片边缘放电,使得基片表面的电场强度和温度分布发生变化,从而导致基片边缘区域的等离子体密度和温度高于中央区域,高等离子体密度和温度的综合作用是使得在基片边缘能以较高的沉积速率沉积出大尺寸金刚石颗粒的主要原因.     

不同粒度的Fe2O3对堇青石蜂窝陶瓷性能的影响

以高岭土、滑石粉、工业氧化铝和不同粒度的Fe2O3粉为原料,研究了Fe2 O3粉的粒度对堇青石蜂窝陶瓷相组成、微观形貌和孔径分布的影响.实验结果表明:随着外加Fe2O3粉粒度的减小,加快了离子扩散速率,固溶量增加,堇青石的固相反应速率增加.当Fe2O3粉粒度为5μm和50μm时试样的微观结构中有微裂纹产生,为降低材料的热膨胀系数打下了基础.随着加入Fe2O3粉粒度的逐渐增大,产生液相,填充了试样中微孔,使孔径尺寸减小,孔径数量减少.     

用碳化硅合成的金刚石微晶的抗氧化性

用碳化硅加Ni70Mn25Co5合金体系在高温高压下合成出具有完好晶形的金刚石微晶.通过粒度分析和热重量分析对这种晶体的热稳定性进行了评价.作为比较,对工业上用石墨合成的六种不同粒度的金刚石微粉和微晶也作了热重量分析.结果表明,用石墨合成的四种普通金刚石微粉的氧化温度随粒度的减小而明显降低,当粒度为80～100μm到1～2.5μm时,其起始氧化温度为770℃到627℃;两种未经破碎的金刚石微晶的抗氧化性能明显较高,其粒度为20～70μm,起始氧化温度为806℃和819℃.与它们相比,用碳化硅合成出的金刚石晶体的粒度分布在10～50μm范围,而起始氧化温度为838℃,完全氧化温度为1101℃,比用石墨合成的未经破碎的金刚石微晶具有更高的抗氧化性能.本文定性地讨论了用碳化硅合成的金刚石具有高耐热性的原因,认为完好的表面和硅杂质的存在可能对这种晶体热稳定性起了重要作用.     

高岭石粒度对Pickering乳液稳定性的影响

固体乳化剂颗粒粒径是影响Pickering乳液稳定性的重要因素.本文以去离子水为水相,液体石蜡为油相,高岭石为乳化剂制备水包油型Pickering乳液,研究了高岭石粒度对乳液稳定性的影响.结果表明:高岭石颗粒与乳液液滴大小之间的匹配特征不仅影响乳化剂与乳液分散相表面之间的作用强度,而且影响其在连续相中形成网络结构的特征,进而影响乳液稳定性.高岭石粒度对乳液稳定的影响存在最佳值,当高岭石颗粒粒度D90值为1.42μm时,乳液粘度为378 mPa·s,乳液液滴粒径均匀,乳化剂颗粒在油水界面有序紧密分布,颗粒在连续相所形成三维网络结构趋于牢固,乳液稳定性好.当乳化剂颗粒粒度较小时,体系中的颗粒易受布朗运动因素影响,乳液液滴聚并速度快,乳液粘度低;而当乳化剂颗粒粒度较大时,油水界面上以及连续相中的颗粒易受自身重力的影响发生沉降,破坏三维网络结构,导致乳液粘度降低,乳液稳定性变差.     

热处理制度对透辉石微晶玻璃析晶与导热性能的影响

以SiO2、CaO和MgO为主要原料,采用传统高温熔融工艺制备了基础玻璃,并通过一步析晶热处理工艺制备了透辉石微晶玻璃.利用X射线衍射仪、电子扫描显微镜和激光导热仪分别研究了热处理温度和时间对透辉石微晶玻璃析晶和导热性能的影响.结果表明:随着热处理温度的升高,微晶玻璃的结晶度增加,晶粒尺寸增大,导热系数先增大后减小;随着热处理时间的延长,微晶玻璃的晶粒尺寸增大,导热系数先增大后减小.当热处理温度890℃,热处理时间120 min,升温速率为10℃/min,微晶玻璃晶粒尺寸为0.3～0.4μm,结晶度为79;,导热系数达到最大值2.59 W/(m·K).     

超声波对甲硝唑溶液结晶热力学性质的影响

本文采用降温结晶的方法,在搅拌和超声波作用下,分别测量了甲硝唑溶液结晶成核的介稳区和诱导期.通过分析超声波对甲硝唑溶液结晶的介稳区、诱导期产生的影响,从扩散系数、温度及能量角度分析了超声波促进晶体成核作用的机理.通过比较搅拌和超声波下得到的产品,从理论上对影响晶体粒度及结晶产率的因素进行了分析.     

静态溶液中KDP籽晶长大的浮力对流模拟研究

采用有限容积法,对KDP籽晶在静态溶液中的生长过程进行了数值模拟,研究了籽晶长大过程中的形状变化,考察了体过饱和度和籽晶特征尺寸对籽晶表面过饱和度及剪切力的影响,重点分析了籽晶长大过程中的尺寸效应.结果表明,当籽晶的特征长度小于临界尺寸时,籽晶的生长速率随着晶体尺寸的增大而加快;而当籽晶的特征长度大于临界尺寸时,籽晶的生长速率随着晶体尺寸的增大而减慢.     

Al粉粒度及其添加量对SiC陶瓷材料结构和性能的影响

以Al粉为烧结助剂,采用无压烧结工艺于1600℃下保温3 h烧制SiC陶瓷材料,研究了不同Al粉粒度及其添加量对SiC陶瓷材料结构和性能的影响.结果表明:Al粉可促进SiC陶瓷材料的烧结和力学性能的提高,同时起抗氧化的作用,且粒度较小的Al粉对其性能提升的幅度较大.当添加4wt;粒度为48μm的Al粉时,SiC陶瓷材料的性能较佳,体积密度和显气孔率分别为2.69 g/cm3和5.8;,显微硬度和抗折强度分别为2790 HV和189 MPa.SiC陶瓷材料烧结性能和力学性能的提高可归因于Al粉的促烧结作用,及其氧化产物Al2 O3和原位生成的少量莫来石分布在SiC颗粒间所起的强化作用.     

Crystal structure analyses of bis(triphenyl- phosphoranyliden)ammonium bis(pentafluoroethyl) argentate, [Ph3P=N=PPh3][Ag(C2F5)2] and bis[bis(triphenylphosphoranyliden)ammonium] tetrachloro-diargentate, [Ph3P=N=PPh3]2[ClAg(μ-Cl)2AgCl]

Bis(triphenylphosphoranyliden)ammonium bis(pentafluoroethyl)argentate, [Ph₃P=N= PPh₃][Ag(C₂F₅)₂] (1) and bis[bis(triphenylphosphoranyliden)ammonium]tetrachloro-diargentate, [Ph₃P=N=PPh₃]₂[ClAg(μ-Cl)₂AgCl] (2) were crystallized from the reaction mixture of pentafluoroethylsilver(I) and bis(triphenylphosphoranyliden)ammonium chlo-ride. Crystallization of 1 occurs in the centrosymmetric monoclinic space group P2₁/c (No. 14) with a = 17.083(2) Å, b = 11.600(2) Å, c = 19.833(2) Å, β = 109.66(1)°, V = 3700.8(7) ų, Z = 4. 2 crystallizes in the centrosymmetric orthorhombic space group Pbca (No. 61) with a = 19.540(1) Å, b = 15.926(1) Å, c = 20.160(1) Å, V = 6273.6(3) ų, Z = 8.     

Selective area laser deposition of FCC beta silicon carbide

Silicon Carbide (SiC) has been deposited onto an alumina substrate by the thermal decomposition of the gaseous precursor tetramethylsilane (TMS). A 500 W ytterbium fibre laser was used to heat the surface of an alumina substrate locally, resulting in deposition of SiC at the sample surface. The SiC deposit was analysed using energy dispersive X‐ray spectroscopy and X‐ray diffraction (XRD). The deposit was confirmed to be silicon carbide and found to be face centre cubic (FCC) crystal structure. Raman spectroscopy was used to measure the stoichiometry of the deposit which initially was found to be carbon rich. Further analysis by Raman spectroscopy suggests the deposit may be more stoichiometric following a two hour thermal treatment of the sample at 600 degrees celcius in an atmosphere of air.     

Structural characterization of a zinc(II) complex of a tris(oxime)amine ligand

The ligand tris(1-propan-2-onyl oxime)amine (TRISOXH₃) binds to zinc(II) acetate as a tridentate N₃ donor, with a third oxime group remaining unbound and extending into the crystal lattice. The crystal structure shows a distorted trigonal bipyramidal geometry around the zinc center. An intramolecular hydrogen bonding interaction between a coordinated oxime donor and an oxygen of a bound acetate is observed. This structure is similar to that of a previously reported zinc(II) complex of a related bis(oxime)amine ligand. However, the structure of Zn(TRISOXH₃)(OAc)₂ is different in ligand coordination mode and metal coordination number from those of the previously reported complexes Ni(TRISOXH₃)Cl₂ or [Ni(TRISOXH₃)(NO₃)(H₂O)]NO₃.     

Synthesis and characterization of ternary L-histidine complexes. Crystal structure of (2,2′-dipyridyl)-(L-histidinato-N,N′,O)copper(II) perchlorate 1.5 hydrate

A series of ternary complexes of copper(II), cobalt(II) and zinc(II) with L-histidine, 1,10-phenanthroline, 2,2-dipyridyl or imidazole having perchlorate or acetate as counterions were synthesized and characterized by conventional methods and for [Cu(bipy)(L-hist)]ClO₄·1.5H₂O and X-ray crystal structure was determined. The crystals belong to the monoclinic space groupC2 witha=18.843(3),b=10.582(2),c=11.020(2), =115.20(10)°,Z=4,R=0.0535. The structure is consistent of [Cu(bipy)(L-hist)]⁺ cations, perchlorate ions and water molecules. The geometry around copper is trigonal bipyramidal with one N,N,O tridentate L-histidine molecule and one 2,2-dipyridyl ligand, the apical sites are occupied by the -amino nitrogen [Cu–N(71) 1.995(8)] and by N(11) of 2,2-dipyridyl [Cu–N(11) 1.983(7)], the equatorial plane is formed by the N(3) imidazole -nitrogen [Cu–N(3) 2.140(6)], O(82) carboxylic oxygen [Cu–O(82) 2.009(5)] and N(22) [Cu–N(22) 2.010(7)].     

Palladium(II) and platinum(II) tetrakisthiourea dichloride bis(7-hydroxy-5-methyl[1,2,4]triazolo[1,5a]pyrimidine) dihydrate solvates

The title compounds palladium(II) and platinum(II) tetrakisthiourea dichloride bis(7-hydroxy-5-methyl[1,2,4]triazolo[1,5a]pyrimidine (Hmtpo)) dihydrate solvates, have been synthesized by reacting thecis-[MCl₂(Hmtpo)₂] (where M=Pt(II), Pd(II)) complexes with an excess of thiourea (tu) and the structure of the palladium compound was solved by X-ray diffraction. Crystals of [Pd(tu)₄]Cl₂·2Hmtpo·2H₂O are triclinic with space groupP and unit cell dimensionsa=7.972(1),b=9.049(1),c=11.808(2)Å, =88.20(1), =75.15(1), =76.54(1)^o. The cation [Pd(tu)₄]²⁺ is centrosymmetric involving four sulfur thiourea atoms in a near square planar environment. The triazolopyrimidine molecules, chloride anions and water molecules do not take part in the metal center coordination but interact by hydrogen bonding between them and the thiourea moieties. A comparison between powder diffraction data of palladium(II) and platinum(II) compounds clearly indicates that both compounds are isomorphous.     

Crystal structures of the cobalt(III), nickel(II), copper(II), and zinc(II) complexes of 2-thio-6-picoline N-oxide

Structures of the following compounds have been solved: tris(2-thio-6-picoline N-oxide)cobalt(III), [Co(6MOS)₃], orthorhombic, Pca2₁, a = 17.871(3), b = 14.061(2), c = 15.964(2) Å, V = 4011(1) ų, Z = 8, and = 1.193 mm^–1; bis (2-thio-6-picoline N-oxide)nickel(II), [Ni(6MOS)₂], orthorhombic, Pbca, a = 15.602(8), b = 13.606(4), c = 13.348(8) Å, V = 2833(4) ų, Z = 8, and = 1.655 mm^–1; bis(2-thio-6-picoline N-oxide)copper(II), [Cu(6MOS)₂], orthorhombic, Pbca, a = 13.914(5), b = 12.984(5), c = 15.663(6) Å, V = 2830(2) ų, Z = 8, and = 1.836 mm^–1; and bis(2-thio-6-picoline N-oxide)zinc(II), [Zn(6MOS)₂], triclinic, P – 1, a = 7.9737(8), b = 11.7786(9), c = 7.9206(8) Å, = 104.502(7), = 104.495(8), = 93.445(8)°, V = 691.3(1) ų, Z = 2, and = 2.106 mm^–1. The steric effect of the methyl group in the six-position of the N-oxide ring is considered in comparing these structures to complexes of 2-thiopyridine N-oxide.     

Structures of Bis(1-ethylbenzimidazol-2-yl)alkyl Copper(II) Dichlorides: An Unusual Cocrystallization

Abstract  Two structures containing pseudo-tetrahedral Cu(II)N₂Cl₂ coordination complexes are reported. The first molecular structure (A) of the compound, 1,1′bis(1-ethylbenzimidazol-2-yl)propane copper(II) dichloride (triEtBBIM)Cu(II)Cl₂, 1, is reported. The complex crystallized in the triclinic space group P-1 with a = 8.616(3) ?, b = 9.302(3) ?, c = 14.314(4) ?, α = 85.613(6)°, β = 85.170(6)°, γ = 66.117(6)° and V = 1044.1(5) ?³ with Z = 2. The second structure (B) contains 1 and (3,3′bis(1-ethylbenzimidazol-2-yl)pentane) copper(II) dichloride (tetEtBBIM)Cu(II)Cl₂, 2, both of which, cocrystallize in an equal molar ratio with a nitromethane solvate molecule. The complex crystallized in the monoclinic space group P2₁/c with a = 18.876(4) ?, b = 14.975(3) ?, c = 18.344(4) ?, β = 116.75(3)°, and V = 4630.3(16) ?³ with Z = 4. The cocrystallization of such discrete complexes has been coined a chemical Janus. Graphical Abstract  The title complexes contain pseudo-tetrahedral Cu(II)N₂Cl₂ coordination. One of the structures is the result of an unusual cocrystallization, in which two different discrete Cu(II) molecules cocrystallize in an equimolar ratio with a nitromethane solvate molecule.      

稀土焦硅酸盐Re2Si2O7闪烁晶体的研究进展

铈掺杂稀土焦硅酸盐系列晶体Re2Si2O7(其中Re=Lu3+、Y3+、Gd3+等)作为新型无机闪烁晶体材料,近来引起科研人员的关注.本文阐述了稀土焦硅酸盐系列晶体Re2Si2O7的结构、晶体生长方法、闪烁性能和有待进一步研究的问题.     

凝胶浇注法制备中温固体氧化物燃料电池Sm_(0.5)Sr_(0.5)Co_(1-x)Fe_xO_(3-δ)多孔阴极材料的研究

以碳酸盐和氧化物为原料,通过凝胶浇注法制得了Sm_(0.5)Sr_(0.5)Co_(1-x)Fe_xO_(3-δ)(SSCF, x=0～1.0)粉体,对不同温度煅烧所得粉体的相组成和微观形貌进行了测定.制备的Sm_(0.5)Sr_(0.5)Co_(1-x)Fe_xO_(3-δ)粉体模压成形后烧结得到SSCF烧结体.测定了烧结体的密度和孔隙率并对烧结体的微观结构进行了观测,用直流四端子法测定了烧结样品的电导率并对其热膨胀系数及电化学性能等进行了测定.结果表明:干凝胶在1000 ℃煅烧可以得到粒度均匀细小的SSCF粉体,其晶体结构随Fe含量发生变化;一定温度烧结的Sm_(0.5)Sr_(0.5)Co_(1-x)Fe_xO_(3-δ)材料具有多孔结构,随烧结温度的增加,烧结体的密度增大,孔隙率减小;Fe的掺杂降低了Sm_(0.5)Sr_(0.5)CoO_(3-δ)材料的热膨胀系数,Sm_(0.5)Sr_(0.5)Co_(0.2)Fe_(0.8)O_(3-δ)材料在800 ℃时的热膨胀系数为16.4×10~(-6) K~(-1);SSCF材料的电导率随Fe含量的增加而减小,但在500～800 ℃,其电导率均大于100 S·cm~(-1).此外,Sm_(0.5)Sr_(0.5)Co_(1-x)Fe_xO_(3-δ)材料均表现出良好的催化活性.     

Er~(3+)/Yb~(3+): KY(WO_4)_2晶体光谱的各向异性分析

在室温下测量和分析Er~(3+)/Yb~(3+): KY(WO_4)_2晶体三个折射率主轴方向上的吸收光谱和荧光光谱,其吸收光谱和荧光光谱谱带强度明显呈现各向异性;用修正的Judd-Ofelt理论计算Er~(3+)/Yb~(3+): KY(WO_4)_2晶体中Er~(3+)在三个折射率主轴方向上的强度参量Ω_t (t=2,4,6)和各吸收谱带的电偶极跃迁振子强度,同时计算了Yb~(3+)在三个轴向上980 nm波长处的积分吸收截面.结果表明:Er~(3+)/Yb~(3+): KY(WO_4)_2晶体吸收光谱和荧光光谱存在各向异性,N_p轴为Er~(3+)/Yb~(3+): KY(WO_4)_2激光晶体的最佳泵浦轴向.