Thermal expansion of lattice parameter of （powder） silicon up to 1473 K

The XRPD (X-ray powder diffxactometry) patterns of silicon powder with a unit cell structure of diamond were determined from 298 to 1473 K. Lattice parameters of Si linearly increase with temperature. The thermal shifts of the positions of all reflection peaks are linearly correlated with the temperature. The coefficients of the intrinsic linear thermal expansion and volumetric thermal expansion were determined as 3.87×10-6/K and 1.16×10-5/K respectively. It indicates that Si is still a suitable standard in the XRPD method at high temperatures.     

Relationship between the heat capacity, thermal expansion coefficient, and spontaneous magnetization in the invarlike compound YFe10Mo2

Heat capacity, thermal expansion coefficient (TEC), and spontaneous magnetization of the ferromagnetic compound YFe₁₀Mo₂ with a Curie temperature T _C = 390 K have been investigated in the temperature range from 2 to 400 K. Relationships between the temperature dependences of the magnetic part of heat capacity (C _m), the magnetic part of the thermal expansion coefficient (α_m), and the spontaneous magnetization (M _s) for the compound YFe₁₀Mo₂ have been considered. It has been found that the magnetic part of the heat capacity can be approximated well by a dependence C _m(T) = a × dM _s ² /dT ? b × dM _s ⁴ /dT with a > 0 and b s> 0, and the magnetic part of the TEC, by a dependence α_m = A × dM _s ² /dT + B × dM _s ⁴ /dT with A > 0 and B > 0 in the entire range of temperatures of magnetic ordering. It is assumed that the basic sources in the formation of the observed C _m(T) and α_m(T) dependences are the changes in the elastic, magnetoelastic, magnetovolume, and magnetostatic energies of the sample, which appear as a result of the spontaneous magnetostrictive deformation with a change in temperature. A comparison of the results obtained for YFe₁₀Mo₂ with the results of the approximation of the C _m(T) and α_m(T) dependences on dM _s ² /dT and dM _s ⁴ /dT and on the basis of data available for the Invar alloy Fe₆₅Ni₃₅.     

Effect of lattice defects on thermal conductivity of Ti-doped,Y2O3-stabilized ZrO2

The evolution of lattice structure and thermal conductivity has been studied systematically for a range of Ti-doped, Y₂O₃-stabilized ZrO₂ (YSZ) solid solutions. The mechanism of reducing the thermal conductivity by Ti doping has been determined. Ti⁴⁺ mainly substitutes for Zr⁴⁺ below a critical composition factor (x ? 0.08), above which the interstitial Ti⁴⁺ need to be considered separately. The effect of lattice defects caused by mass and radius differences between Ti⁴⁺ and Zr⁴⁺ ions on the phonon scattering coefficient was discussed quantitatively. And the reduction of oxygen vacancy by interstitial Ti⁴⁺ ions which increases the thermal conductivity at high Ti doping content was also determined. Concerning the integrated phase stability and thermo-mechanical properties, Ti-doped YSZ is believed to be a promising candidate for thermal barrier coatings at higher temperature.     

Characterization of the negative thermal expansion material Zr_(1-x)Hf_xW_2O_8

The oxide ZrW2O8 displays unusual property of isotropic negative thermal expansion in a large wide temperature range, which makes it have a number of important potential applications. The cubic Zr1-xHfxW2O8 (x = 0,0.3, 0.5, 0.7, and 1.0) were synthesized by standard solid state reaction technique. The high and low temperature X-ray diffraction analysis indicate that the substitution of the Hf4+ for Zr4+ only leads to reducing the lattice constants, and the changes of negative thermal expansion coefficients are not obvious. The linear expansion coefficients of Zr1-xHfxW2O8 (x = 0, 0.3, 0.5, 0.7, and 1.0) are about -6     

氧化铝原料对合成SrAl2O4(Eu,Dy)材料余辉发光性能的影响

通研究不同氧化铝原材料的组成和形貌,分析它们对合成稀土铝酸盐长余辉发光材料性能的影响,发现原晶结构和晶粒类型是影响合成产物长余辉发光性能的重要因素;而通常氧化铝原料的纯度基本上可以满足合成原料的纯度要求。     

Solid solution extent of WC and TaC in Ti(C,N) as revealed by lattice parameter increase

Materials development of cermets for cutting tools has come to a new stage where molybdenum is no longer indispensable. The key is the addition of a solid-solution treatment of hard phase powder mixtures before sintering with metallic binders. In this paper, ceramic powders of Ti(CN), TaC and WC are mixed, compacted and heat treated to form (Ti, W, Ta)(C,N) solid solutions at elevated temperatures. The influence of temperature and duration of the treatment on the solid solution extent is examined through measurement of the X-ray diffraction (XRD) spectra and the lattice constant. After treating at 1700°C for 1 h, the XRD spectra revealed the disappearance of the WC peaks. The lattice parameter of titanium carbonitride increased with increasing reaction time and temperature and stabilized after treating at 1700°C for 1·5 h. Cold isostatic pressing (CIP) at 350 MPa following uniaxial pressing at 180 MPa did not seem to have too much added influence on the solid solution extent, but CIP ed samples did give less scattered data.     

Crystal structures and thermal expansion properties of Y2-xErxMo4O15 （x=0.0-2.0） solid solutions

A new series of rare earth compounds,Y2-xErxMo4O15 （x=0.0-2.0）,were synthesized and their structures were determined by powder X-ray diffraction （XRD）. Rietveld analysis of XRD patterns reveals that the compounds of this series crystallize in monoclinic system with space group P21/c. The lattice parameters a,b,c,β and the unit cell volume V de-crease linearly with increasing Er content. The thermal expansion properties of these compounds were studied under high-temperature XRD. Positive thermal expansions of compounds Y2-xErxMo4O15 are found to be anisotropic along the three crystallographic directions where a and c axes expand while b axis contracts in the whole temperature range. By analysis of data,the expansion of weak band Mo2-O14 with rising temperature should be responsible for positive thermal expansion.     

Energetics of stepwise disordering transformation in pyrochlores,RE2Ti2O7 (RE = Y,Gd and Dy)

The capacity to incorporate actinide cations makes pyrochlore titanates first-choice phases in titanate-based waste form ceramics. Despite broad interest in the pyrochlore order–disorder transformation due to the cumulative effects of ²³⁸U, ²³⁵U and ²³²Th radioactive decay and their daughter products, only limited thermodynamic data, mainly based on simulations of ion-beam irradiation experiments, have been reported. In this work, for the first time, heavily disordered pyrochlores, RE₂Ti₂O₇ (RE = Y, Gd and Dy), from mechanical milling of their constituent oxides, were thermochemically investigated. Two types of thermal events were identified using high-temperature differential scanning calorimetry and correlated to the structural disorder in the cation and anion sublattices. Moreover, the excess formation energy measured by oxide melt solution calorimetry shows that the smaller the ionic radius of the RE, the easier it is to remove damage domains.     

CeO2,Dy2O3,Yb2O3及Y2O3烧结助剂对氮化硅陶瓷热导率的影响

研究了CeO2-MgO(CeM),Dy2O3-MgO(DyM),Yb2O3-MgO(YbM)及Y2O3-MgO(YM)体系烧结助剂对氮化硅陶瓷的热导率及电学性能的影响.结果表明与YM烧结助剂相比,添加DyM烧结助剂的氮化硅陶瓷热导率较低;添加CeM烧结助剂的氮化硅陶瓷的热导率最高,为85.4W/m·K;添加YbM烧结助剂的氮化硅陶瓷也有较高的热导率,但体电阻率较低.组织分析表明,添加不同稀土元素的烧结体组织形貌基本相同,晶界相不同,添加DyM,YbM和YM烧结助剂的氮化硅陶瓷在烧结过程中分别形成了含氧晶界相Dy2Si3N4O3,Yb2Si3N2O5和Y2Si3N3O4.     

Dy含量对(Nd,Dy)2(Fe,Co,Nb,Ga)14B/α-Fe纳米复合材料微结构和磁性能的影响

用熔体快淬 晶化处理的方法制备了不同Dy含量的Nd8-xDyxFe83 5Co2 Nb1Ga1B4 5(x =0 ,0 2 ,0 5 ,0 8,1 0 )纳米复合材料 ,用差动 (扫描 )分析 (DSC)、X 射线衍射 (XRD)、透射电镜 (TEM )等研究了样品的晶化过程及微结构 ,用振动样品磁强计 (VSM)测量了磁性能。实验结果表明 :硬磁性相的晶化温度随Dy含量的增加逐渐升高 ,在最佳热处理条件下 ,矫顽力随Dy含量的增加首先有较大的提高 ,在Dy含量x >0 8以后增加较缓慢。剩磁随Dy含量的增加逐渐下降 ,在Dy含量x >0 8以后下降更加显著 ,磁能积在x =0 5～ 0 8附近出现峰值。剩磁和矫顽力与Dy含量的非线性关系是由于软、硬磁性晶粒之间交换耦合作用的强弱导致的。     

Synthesis,crystal structure and thermal behavior of Na4[B10O16(OH)2]·4H2O

New hydrated sodium borate Na₄[B₁₀O₁₆(OH)₂]·4H₂O has been synthesized under mild hydrothermal conditions at 170 °C. The structure was determined by single-crystal X-ray diffraction and further characterized by FT-IR, Raman spectra and DTA-TG. It crystallizes in the monoclinic space group Pc with a unit cell of dimension a = 11.323(2) Å, b = 6.5621(14) Å, c = 12.244(3) Å, α = 90°, β = 91.050(3)°, γ = 90°, V = 909.7(3) Å³, Z = 2. The crystal structure of Na₄[B₁₀O₁₆(OH)₂]·4H₂O consists of Na–O polyhedra and [B₁₀O₁₆(OH)₂]⁴⁻ polyborate anions. Dehydration of this compound occurs in three steps and leads to an amorphous phase which undergoes crystallization.     

Kinetics of Therm al Decom position of[ Eu_2( p- M O B A)_6(phen)_2]( H_2 O)_2 in Static Air Atmospher

１ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｃｏｍｐｌｅｘｅｓｆｏｒｍｅｄｂｙｒａｒｅｅａｒｔｈａｎｄａｒｏｍａｔｉｃｃａｒｂｏｘｙｌｉｃａｃｉｄｈａｖｅｍａｎｙｓｐｅｃｉａｌｓｔｒｕｃｔｕｒｅｓａｎｄｉｎｔｅｒｅｓｔｉｎｇｌｕｍｉｎｏｕｓｐｒｏｐｅｒｔｉｅｓ,ｔｈｕｓａｒｏｕｓｅｐｅｏｐｌｅ′ｓｉｎｔｅｒｅｓｔｔｏｓｔｕｄｙｔｈｅｍ．Ｂａｓｅｄｏｎｔｈｅｐｒｅｐａｒａｔｉｏｎａｎｄｄｅｔｅｒｍｉｎａｔｉｏｎｏｆｔｈｅｃｒｙｓｔａｌｓｔｒｕｃｔｕｒｅａｎｄｌｕｍｉｎｅｓｃｅｎｃｅｓｐｅｃｔｒｕｍｏｆ１,１…     

Effects of thermal stress induced by cyclic heat treatment on sintered (Nd,Dy)-Fe-B magnets

We investigated the mechanisms of coercive force enhancement on Nd₁₁Dy₄Fe_76.5TM_2.5B₆ (TM = Co, Cu, Al) induced by a number of cyclic heat treatments (CHT) at temperatures from 350°C to 450°C. The difference in thermal expansion coefficients between Nd-rich and Nd₂Fe₁₄B phases induced penetration of the Nd-rich phase into the Nd₂Fe₁₄B grain boundary through capillary force and compress pressure by CHT. Also, dislocations in the Nd₂Fe₁₄B grain were formed by thermal stresses from thermal expansion and contraction, which caused the domain wall pinning effect. Consequently, coercivity was enhanced from 2,303 kA/m before CHT to 2,480 kA/m after CHT, and a remanence of 1.18 T was maintained after two cycles.     

VO2(B)热转化为VO2(R)和V2O3的高温XRD原位表征

以草酸和V2O5为原料,采用水热法制备VO2(B)。通过高温原位X射线衍射技术研究VO2(B)在氮气保护下升高温度过程中的相变特性,采用X射线衍射仪(XRD)和场发射扫描电子显微镜(FE-SEM)分析所制备样品及其在不同温度热相变产物的微观形貌和物相组成。结果表明：以草酸和V2O5为原料,用水热法可制得单斜晶系VO2(B),颗粒呈纳米片状;升温至430~700℃,VO2(B)不可逆转化为四方晶系VO2(R),形貌由纳米片状变为亚微米及微米近球形;升温至1000℃左右,VO2(R)开始分解形成Magn閘i相系列化合物（VnO2n?1）;升温至大约1200℃完全转变为具有刚玉结构的V2O3烧结块。     

纳米SrAl2O4:Eu,Dy发光特性及浓度猝灭

用溶胶-凝胶法合成了不同Eu2+掺杂浓度的SrAl2O4Eu2+,Dy3+纳米晶体,探讨了纳米晶体的发光性能及浓度猝灭.结果发现纳米晶体与相应的常规尺寸的发光粉末材料相比,发射光谱和激发光谱的主峰位置均出现了明显的蓝移,发光强度和猝灭浓度有明显的提高,余辉衰减速度加快.认为蓝移现象以及余辉衰减变快,主要归因于发光粉体纳米粒子的量子尺寸效应.     

NaOH-NaAl(OH)4-Na2CO3-H2O体系活度因子的计算模型

应用Bromley模型,通过对氢氧化钠、铝酸钠和碳酸钠等溶液体系活度因子的实验数据进行校验与回归分析,获得了各电解质合理的Bromley参数,建立基于Bromley模型的NaOH-NaAl(OH)4-Na2CO3-H2O体系活度因子的计算模型,其适用范围为:质量摩尔浓度分别为m(NaOH)≤8 mol/kg,m(NaAl(OH)4)≤3 mol/kg,m(Na2CO3)≤3 mol/kg且离子强度I≤9 mol/kg.使用该模型和Rard方法计算所得水的活度比较结果表明:该模型正确有效,计算精度较高,各电解质的Bromley参数取值合理;该模型也可用于NaOH-NaAl(OH)4-H2O体系活度因子的计算.     

High-temperature thermoelectric properties of Ln(Co,Ni)O3 (Ln = La,Pr, Nd,Sm, Gd and Dy) compounds

The high-temperature thermoelectric properties of polycrystalline LnCo_0.95Ni_0.05O_3±δ (Ln = La, Pr, Nd, Sm, Gd and Dy) compounds have been investigated. The substitution of the lanthanide element produces changes in the crystal structure and in the unit cell lattice parameters. A semiconductor to metal transition takes place for all the compounds at 500 K < T < 800 K. The transition temperature, also monitored by differential scanning calorimetry, shifts to higher temperature with the decrease in the size of the lanthanide element. The Seebeck coefficient has positive values up to T = 1240 K. The thermal conductivity is mainly dominated by the lattice contribution. The dimensionless figure of merit ZT can be enhanced at different temperatures depending on which lanthanide element occupies the A-site in the ABO₃ perovskite-type phases.