脱脂处理对樟子松单板苯醇抽提物含量的影响

采用正交实验,通过分析脱脂前后樟子松(Pinus sylvestris var.mongolica)单板的苯醇抽出物含量,研究了脱脂温度、NaOH浓度和时间对脱脂效果的影响.结果表明:随温度的升高、NaOH浓度的增加、时间的延长,脱脂后单板苯醇抽出物含量均有降低.方差分析表明:温度对脱脂后单板的苯醇抽出物含量没有显著影响,而NaOH的浓度和脱脂时间对脱脂后单板的苯醇抽出物含量均有显著影响.     

热致相分离法制备聚偏氟乙烯膜的研究

基于热致相分离基本原理,通过熔融共混聚偏氟乙烯/CaCO3/邻苯二甲酸二丁酯三元体系,制备了聚偏氟乙烯膜.考察了稀释剂和CaCO3含量对膜微观结构及拉伸强度的影响,以及CaCO3含量对聚偏氟乙烯结晶温度、结晶度的影响.结果显示,稀释剂和CaCO3含量对膜微观结构和拉伸强度影响显著;而CaCO3含量虽然对共混体系结晶度影响不太明显,但是对其结晶温度有较为显著的影响.     

刚玉莫来石复相陶瓷力学性能的影响因素分析

本文采用正交设计方法研究了硅微粉、氧化铝微粉及烧结温度对刚玉莫来石复相陶瓷常温强度和高温强度的影响机制.结果表明:氧化铝微粉对高温强度的影响较大,硅微粉次之,烧结温度最小.适当降低氧化铝微粉的含量,并提高硅微粉的含量和烧结温度,可以提高复相陶瓷的高温强度.通过调节硅微粉、氧化铝微粉及烧结温度可控制刚玉莫来石复相陶瓷的显微结构,改善刚玉莫来石复相陶瓷的高温强度.     

玄武岩增强硼酚醛树脂基复合材料工艺性能研究

利用正交试验方法,讨论冷却方式、成型压力、增强纤维百分含量、成型温度对玄武岩增强硼酚醛树脂基复合材料拉伸强度和弯曲强度的影响.结果表明:复合材料中增强纤维百分含量对其力学性能影响最大,成型压力增大有利于复合材料力学性能的改善,成型温度对基体材料的结构有较大影响,当成型温度较高时,复合材料具有较大的弯曲强度,延长冷却时间有利于复合材料力学性能的提高.     

工艺参数对铁尾矿合成Si_3N_4粉的影响

以铁尾矿和碳黑为原料,采用碳热还原氮化法合成Si3N4粉.利用X射线衍射法测定产物相组成及相对含量,研究了合成温度和恒温时间对反应过程的影响.结果表明,合成温度对碳热氮化合成Si3N4粉的影响显著,随合成温度的升高,产物中Si3N4相含量增加,1450℃时Si3N4相含量最高,是最佳的合成温度.恒温时间对产物相组成的影响不大,但适当延长恒温时间可使还原氮化反应进行得更充分,恒温8h时产物中Si3N4含量最高,是较理想的恒温时间.合成过程中SiO的挥发导致试样较大的质量损失,且随恒温时间的延长而增大.     

膨润土催化制备四脚状氧化锌晶须的研究

采用膨润土作为催化剂,通过高温气相氧化法制备了四脚状氧化锌(T-ZnO)晶须,并研究了实验条件对产物的影响.结果表明:实验温度、催化剂含量和空气流量对T-ZnO晶须的尺寸、规整性、产率等有显著的影响,实验温度为920～980 ℃,膨润土含量为33%左右以及适当的空气流量条件下,可以得到尺寸均一、结构规整、四脚状含量和晶须产率都较高的T-ZnO晶须.     

Sanicro25耐热钢中析出相的热力学计算与平衡相分析

利用热力学软件Thermal-Calc计算了Sanicro25耐热钢中的平衡态析出相,分析讨论了关键元素含量变化对析出相的影响规律.研究结果表明:增加钢中W、C含量可以升高M23C6的回溶温度以及增加M23C6的析出量,Cr、Co含量对M23C6的析出量没有明显影响;Cr含量越低,W含量越高,Laves相的回溶温度越高,析出量越大;Cr、N含量越低,Nb含量越高,MX相的析出量越高;Nb含量越高,N含量越少,Z相的析出量越大;W、Cr含量越高,σ相析出量越大,回溶温度越高.     

硅含量与氧化温度对含Nb高强钢氧化行为的影响

为了更真实地反映工业生产实际工况中硅含量与氧化温度对Nb高强钢氧化行为的影响,设计了4种不同的氧化温度,采用与工业现场类似的加热制度对不同Si含量的含Nb高强钢进行氧化.采用扫描电子显微镜及能谱仪分析了氧化铁皮形貌及确定氧化铁皮各层结构.研究了硅含量及氧化温度对含Nb高强钢氧化行为的综合影响.结果表明:在相同氧气含量及氧化时间下,含Nb高强钢的氧化增重取决于氧化温度及硅含量的综合作用;当加热温度低于1 173℃(硅酸亚铁熔点)时,硅含量增加,氧化铁皮总量减少;当加热温度高于1 173℃时,硅含量增加,氧化铁皮总量增加;当硅含量较高时(1.21％,质量分数),试样的氧化增重曲线主要遵循线性规律.     

微乳化乙醇柴油热物性计算与分析

车用清洁型微乳化油是内燃机的理想代用燃料之一.微乳化油热物性参数难以计算,从而影响在内燃机上对它的定量计算研究.以微乳化乙醇柴油为例,用经验公式计算其蒸发焓、生成焓、液体比热容、导热率和微乳化油蒸气的扩散系数,分析了温度和压力以及不同溶醇量对热物性参数的影响规律,为微乳化油热物性参数的计算提供一种工程方法.结果表明:随着温度的增加,微乳化乙醇柴油蒸发焓、导热率降低,定压比热容和微乳化油蒸气扩散系数增加;随着压力增加,微乳化油蒸气扩散系数降低;随着混合燃料中乙醇含量的增加,定压比热容和混合气扩散系数均增大,蒸发焓减小;乙醇含量对混合燃料导热率的影响与燃料温度有关,在一定温度下乙醇含量效应发生逆转;微乳化乙醇柴油中乙醇含量增加有利于燃料蒸发.     

反应温度对苯热合成氮化硼纳米晶的影响

研究了不同反应温度对苯热合成立方氮化硼的影响,研究结果表明以Li3N和BBr3为原料制备立方氮化硼时,温度对产物中立方相含量有很大影响,在200～400℃,产物主要为六方相氮化硼,随温度升高,立方氮化硼的含量随之增加;继续升高温度立方相含量在480℃达到极大值,这时样品中仍然是六方相氮化硼与立方氮化硼共存,但立方氮化硼占优势;继续升高温度,立方氮化硼迅速减少,六方氮化硼含量增加.     

The effects of solid-state phase transformation upon stress evolution in laser metal powder deposition

To investigate the influences of solid-state phase transformation on stress evolution during multi-pass laser metal powder deposition (LMPD) process, a 3D finite-element (FE) thermo-mechanical model considering phase transformation has been established. The influences of phase transformation such as mechanical properties changes, volume change and transformation induced plasticity (TRIP) are taken into account. Furthermore, the influences of high magnitude stress upon martensitic transformation characteristic temperature and TRIP are considered. The temperature and history (microstructure) dependent material properties used in the present research are obtained by experiments. The stress field during LMPD process is analyzed with and without solid-state phase transformation, respectively. Stress measurement of X-ray diffraction (XRD) method is applied to deposited samples, and the measuring data are compared with the computational predictions. The results show that phase transformation has a dominant effect on the stress evolution, longitudinal residual stresses significantly reduced as a result of solid-state phase transformation. In addition, the effect of stresses on martensitic transformation temperature is important for accurate prediction of residual stresses (stress state after cooling of the clad to ambient temperature). Residual stresses are lower when the phase transformation temperature is reduced.     

NiTi形状记忆合金相变过程中的超声波声速特性

用超声脉冲反射法测试了NiTi形状记忆合金（SMA）在相变过程中的纵波声速,研究了合金声速随温度变化的规律。结果表明：在非相变温度范围内,NiTi合金声速随温度缓慢变化,但在发生相变的温度范围内,声速的变化趋势发生明显改变;测得NiTi合金的各相变温度与常规电阻法基本一致,与电阻法等其他测量相变温度的方法相比,纵波声速法具有简单易行、测量方便以及对工件无损伤等优点。     

Effects of composition on the phase transformation behavior of anatase TiO2 in photocatalytic ceramics

The present work focuses on the phase transformation mechanism of TiO₂ nanoparticles in photocatalytic ceramics. TiO₂ nanoparticles were mixed with fused quartz, glaze No.1, and glaze No.2 respectively and heat-treated. The phase transformation behavior of anatase TiO₂ was analyzed by XRD. The results show that the phase transformation behavior of anatase TiO₂ in photocatalytic ceramics is highly dependent on the glaze compositions rather than the crystal size effect, which is significantly different with TiO₂ alone. The phase transformation from anatase to rutile always starts near the softening temperature and finishes below the sphere temperature of the glaze. The higher flux contents in glaze the lower phase transformation temperature. The significant retarding effects of silica and phosphate on the anatase-to-rutile phase transformation appear negligible when modified TiO₂ are applied in glaze. The eutectic liquid is essential for the phase transformation behavior of anatase TiO₂ in photocatalytic ceramics.     

Influence of Heat Transfer on Determination of Transient Temperatures for Ni<Subscript>53.6</Subscript>Mn<Subscript>27.1</Subscript>Ga<Subscript>19.3</Subscript> Shape Memory Alloy from Dilatometric Data

The martensitic phase transformation in a Ni_53.6Mn_27.1Ga_19.3 shape memory alloy is an athermal phase transformation that starts practically, immediately after reaching a certain transient temperature. The final temperature is given at each point of the sample by two processes: heat conduction and phase transformation. Both processes take place in tandem. The thermal expansion and calculation of the temperature fields in a dilatometer are used to determine the transient temperatures and to study the transient temperature ranges.     

Effects of Ni-Ti-Cu alloy composition and heat treatment temperature after cold working on phase transformation characteristics

With regard to Ni-50Ti-Cu (at%) shape memory alloys, phase transformation characteristics under no stress were studied at the copper content of 6–9 at% using differential scanning calorimetry and X-ray diffraction analysis. In solution-treated materials, B2-orthorhombic transformation occurs at the copper content of 7.6 at% or more. With the increase in copper content, the temperature for B2-orthorhombic transformation gradually increases, whereas the temperature for the orthorhombic-monoclinic phase transformation resulting from decreasing temperature rapidly falls. The phase transformation temperature in 27% cold-worked materials remains virtually constant, despite the copper content, and increases with increasing heat-treatment temperature. The hysteresis in the B2-orthorhombic transformation stabilized via cold working is as low as 18 K.     

Study of the Thermal Properties of a Ni<Subscript>3</Subscript>Ta Shape Memory Alloy

Dilatation characteristics, thermal diffusivity, and thermal conductivity of a Ni₃Ta shape memory alloy were studied over the temperature range from room temperature up to 950 °C. The Ni₃Ta alloy was investigated in both polycrystalline and single crystal forms. The shape memory effect was positive for the polycrystalline samples and negative for the single crystal. While the transformation temperature of the M (martensite) → A (austenite) phase transformation was the same for both types of alloys and all measurements, the transformation temperature for the reverse phase transformation A → M was dependent on the maximum cycle temperature. Higher maximum temperatures of the thermal cycle yielded lower transformation temperatures for the A → M transformation. The thermal diffusivity and thermal conductivity of the austenite were higher than those of the martensite. No latent heat was found for the phase transformations.     

Martensitic transformation and shape memory properties of Ti-Ta-Sn high temperature shape memory alloys

The effects of Ta and Sn contents on the martensitic transformation temperature, crystal structure and thermal stability of Ti-Ta-Sn alloys are investigated in order to develop novel high temperature shape memory alloys. The martensitic transformation temperature significantly decreases by aging or thermal cycling due to the formation of ω phase in the Ti-Ta binary alloys. The addition of Sn is effective for suppressing the formation of ω phase and improves stability of shape memory effect during thermal cycling. The amount of Sn content necessary for suppressing aging effect increases with decreasing Ta content. High martensitic transformation temperature with good thermal stability can be achieved by adjustment of the Ta and Sn contents. Furthermore, the addition of Sn as a substitute of Ta with keeping the transformation temperature same increases the transformation strain in the Ti-Ta-Sn alloys. A Ti-20Ta-3.5Sn alloy reveals stable shape memory effect with a martensitic transformation start temperature about 440 K and a larger recovery strain when compared with a Ti-Ta binary alloy showing similar martensitic transformation temperature.     

Effect of cooling rate on phase transformation in the low-carbon boron-treated steel

In this research, phase transformation process under different thermal cycles corresponding to a low and a high heat input welding in the heat-affected zone of low-carbon boron-treated steel is systematically investigated by a high temperature laser scanning confocal microscopy. The effect of thermal cycles on the phase transformation process is quantified by measuring the transformation start temperature of each transformation product and the average number of nucleation sites of intragranular acicular ferrite.     

Study of incomplete transformations of near equiatomic TiNi shape memory alloys by DSC methods

The incomplete transformations of near equiatomic TiNi shape memory alloys were investigated by differential scanning calorimeter (DSC). The results showed that the incomplete transformation can induce multistage phase transformation in a sample showing R-phase transformation, when the turn back temperature located in a value between R_f and M_s, the heat flow detected upon following heating only shows one endothermic peak. With decreasing the turn back temperature to a temperature between M_s and M_f, two endothermic peaks (multistage phase transformation) can be observed upon the following heating. There were no incomplete transformation induced multistage phase transformations in a sample without R-phase transformation.