用TEM研究非晶态Ni—P合金薄膜原位加热时的动态晶化过程

本文采用原位加热透射电子显微镜观察技术研究了非晶态Ni-P合金薄膜的动态晶化过程。实验结果表明,非晶态合金薄膜在等温退火时,首先在非晶态基体中产生微小的有序原子集团,并长大成取向无规的Ni_3P晶体微粒;然后是晶体的形成和长大。在晶体长大过程中这些晶体微粒通过切变(取向变化)直接沉积在晶体前沿上,而保持其结构形态不变。利用动态录像技术测量了晶化过程中的晶体长大过程,发现晶体在长大过程中有“台阶型”长大,这种“台阶型”长大过程对应于有序原子集团的切变沉积,不同温度下有序原子集团切变沉积使晶体长大速率的变化不同。     

Controlled crystallization of hydroxyapatite under hexadecylamine self-assembled monolayer

1　INTRODUCTIONCrystalnucleationandgrowthatorganicinter facesoftenhaveanimportantroleinbiologicalminer alizationandmayalsobeinvolvedinsomegeologicalcementation processes .Recently ,crystalgrowthatsyntheticorganicinterfaceshasbecomeanactiveareaofresearchbecauseoftherelevancetounderstandingbiomineralizationaswellastobringingnewideasandmoreimpetustothedesignofnovelmaterialswithoutresortingtohightemperaturetreatment (suchashy drothermaltreatmentandsintering) ,whichiscom monlyusedinceramicandgl…     

大块非晶合金淬态相等温长大过程

利用石英管水淬法制备了ZR41.2Ti13.8Cu12.5Ni10Be22.5大块非晶合金,在真空度不小于10-3Pa和原材料纯度99.9%的情况下,当制备样品直径大于10mm时,经常发现非晶基体中含有一定数量的淬态相,该相的数量不在X衍射仪检测范围内,同时DSC分析表明,这些淬态相对非晶合金的过冷液相区、晶化温度和玻璃转变温度影响也较小.非晶合金过冷液相区内的等温晶化过程表明,晶化初期淬态相具有优先长大的趋势,并有亚稳过渡相的生成.而在晶化的后期,形核和长大同步进行.利用经典形核和长大理论分析了非晶合金的形核和长大过程.     

多形性SrSO_4纳米粉体的制备与生长机制

采用化学沉淀法制备出具有不同形貌(片状、柱状和等轴状等)的纳米SrSO_4粉体.采用扫描电镜和X射线衍射仪等对粉体的结构、形貌及生长机制进行了研究.片状SrSO_4粉体厚度约100 nm,片长约200 nm;柱状粉体横向长度为80～150 nm,纵向长度为700～800 nm;等轴状粉体粒径约80 nm.衍射强度对比表明,低能面(002)与(210)晶面相对生长的快慢导致了片状和柱状SrSO_4晶体的形成;而反应物浓度的降低、EDTA的络合以及PEG的分散等环境因素的改变降低了晶体生长驱动力,导致球状SrSO_4晶体的形成.     

Crystallization of a Al–4Ni–6Ce glass and its influence on mechanical properties

The crystallization behaviour of a rapidly quenched, amorphous Al–4Ni–6Ce material has been examined during low temperature annealing, and shown to commence by the nucleation of nanoscale Al crystals, which stop growing once they reach a size of about 10 nm. In a subsequent, second phase of crystallization the dendritic Al crystals grow rapidly with the formation of a crystal–glass eutectic-like mixture. The nanoscale Al crystals lead to some hardening of the glass, but do not modify the good ductility of the material. Subsequent hardening and embrittlement of the glass–nanocrystal composite may depend on slight changes of the extent of crystallization or instead on changes occurring in the glass itself.     

Hydrothermal synthesis of zeolites from natural stellerite

Y and P zeolites were synthesized hydrothermaUy from natural stellerite under different conditions and were characterized via XRD and FT-IR. The results show that the higher crystaUinity of Y zeolite can be obtained in hydrothermal systesn with low alkalinity, low Ca^2 /Na^ ratio, and high SiO2/Al2O3 ratio. The lattice space of the samples decreases as crystallization time increases. P Zeolite is prompted under condition of higher alkalinity and higher Ca^2 /Na^ ratio. The intensity and number of bands in the range of 400 cm^-1～ 900cm^-1 increases with reaction time. Bands at 680cm^-1, 760cm^-1 and 860 cm^-1 corresponding to Y zeolite appear during the crystallization stage. Most of these bands shift to higher wavenumbers when SiO2/Al2O3 ratio increases generally. In the hydrothermal systesn with reverse condition above, bands at 600cm^-1, 420cm^-1～470cm^-1 hardly change as the crystallization time increases and the main crystal phase of P zeolite is obtained.     

ON THE CRYSTALLIZATION OF AMORPHOUS Ni-BASE ALLOY

本文研究了非晶态Ni_(83)Cr_7Fe_3Si_4B_3合金在动态加热及等温热处理条件下的晶化过程。结果表明,对于动态加热及等温热处理两种情况,镍基非晶态合金的晶化过程相同,结晶相没有发生变化。但是,在动态加热条件下,初始晶化主要是成核结晶,而在等温热处理晶化过程中晶粒长大起主要作用。     

SiO2-Al2O3-CaO-Fe2O3系微晶玻璃的晶化过程

利用差热分析（ＤＴＡ）、红外吸收光谱（ＩＲ）、Ｘ射线衍射（ＸＲＤ）和扫描电镜（ＳＥＭ）等手段研究了ＳｉＯ２－Ａｌ２Ｏ３－ＣａＯ－Ｆｅ２Ｏ３系微晶玻璃晶化过程及其结晶化过程及其结晶动力学。结果表明：ＳｉＯ２－Ａｌ２Ｏ３－ＣａＯ－Ｆｅ２Ｏ３系微晶玻璃晶化过程中,初晶相是钙铁透辉石,钙铝黄长石是中间过渡相且随晶化温度的提高而消失,最终晶相只有钙铁透辉石;晶体生长指数为２．９,属三维生长。玻璃网络中主要有     

Primary crystallization in Al-rich metallic glasses at unusually low temperatures

The initial stage of the primary crystallization reaction and the glass transition of the marginal metallic glass Al₈₉Y₆Fe₅ were investigated by conventional differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC), microcalorimetry, X-ray diffraction (XRD) and transmission electron microscopy. A sharp onset of the primary crystallization was found by microcalorimetry and XRD studies at temperatures which were 120 °C below the primary crystallization peak observed in conventional DSC. A systematic MDSC study of annealed samples revealed a wide spectrum of glass transition onsets, which show a strong dependence on the annealing conditions. In addition, the glass transition onsets can be linked to the initial stage of the primary crystallization. The spectrum of glass transition onsets observed is discussed with respect to the occurrence of phase separation preceding the nucleation and growth of dendritic aluminium nanocrystals.     

磁场对纳米MnZn铁氧体前驱体形貌的影响

采用SEM，XRD，TEM，TG等手段研究了磁场对共沉淀法制备纳米MnZn铁氧体前驱体形貌及晶态结构的影响。结果表明，随着磁感应强度增大并达到某一临界值时，纳米颗粒形貌由球状向链状转变，继续增加磁感应强度将获得针状、棒状或纤维状的颗粒，10T强磁场下获得棒状颗粒呈现单晶结构。热重分析表明10T磁场下获得的纳米颗粒由于单维尺寸增加而导致活性降低。根据晶体生长理论，讨论了磁场影响纳米颗粒形核和长大过程的机理。     

Nucleation and growth mechanism of electrodeposited Ni−W alloy

The nucleation and growth mechanism of electrodeposited Ni?W alloy were investigated. Cyclic voltammetry (CV) and chronoamperometry (CA) were used to examine the electrochemical behavior and nucleation mechanism of the electrodeposited Ni?W alloy. The nucleation type and kinetic parameters of the electrodeposited Ni?W alloy were obtained from the CA analysis results. SEM, AFM, and TEM were also used to investigate the nucleation and growth process of the electrodeposition of Ni?W alloy. The results demonstrate that the nucleation and initial stages of the growth phase of the Ni?W alloy undergo the formation, movement, and aggregation of atoms, single crystals, and nanoclusters. When the size of single crystal increases up to approximately 10 nm and the average size of the crystal granules is approximately 68 nm, they no longer grow. Increasing the applied potential increases the number of nuclei but does not affect the size of the final crystal granules. Therefore, the electrodeposited Ni?W alloy shows a nanocrystalline structure.     

Electric-field-enhanced crystallization of amorphous Fe86Zr7B6Cu1 alloy

The effect of external electric field on the crystallization of amorphous Fe₈₆Zr₇B₆Cu₁ alloy was studied. It is shown that its crystallization process is markedly enhanced by external electric field. The crystallization time at 600 °C decreases from 1 to 0.5 h on application of a modest (10⁴ V/m) external electric field. The volume fraction of crystalline -Fe increases from 65.2 to 68.6%, while the grain size decreases from 13.2 to 11.9 nm. The electric-field-enhanced crystallization may result from the fact that the external electric field results in the increases of the crystal nucleation rate and the crystal growth rate. The complex permeability shows an apparent improvement in soft magnetic properties induced by electric field, thereby demonstrating the practical utility of electric-field-enhanced crystallization technique.     

A MATHEMATICAL EXPRESSION OF CRYSTAL GROWTH RATE DURING CRYSTALLIZATION OF AMORPHOUS ALLOYS

A mathematical expression of the crystal growth rate during crystallization of the amorphousalloys was derived from the micromechanism of crystallization newly developed by theauthors. Thus, the satisfactory explanation of the experimental results obtained by Nunogakiet al., Heimendahl et al. and the authors might be found. It seems also to be modelled with theexpression for the crystal growth and the crystal size influenced by time during thecrystallization of amorphous Ni-P alloy foil at in situ heating. Based on the expression, thefactors influencing the crystal growth rate, such as temperature, time and microstructure ofamorphous alloys have been discussed.     

一步晶化法制备微米级4A沸石的工业应用

用ICP、化学分析等技术研究了焙烧煤矸石与碱液一步晶化法制备微米级A型分子筛的反应过程,得到了一步晶化法制备A型分子筛的工业参数。工业实验证明一步晶化法制备4A型分子筛过程中凝胶化和晶化同时进行,合成过程中没有真正的纯胶体状态存在,凝胶化速度控制着整个晶化过程。一步晶化法制备A型沸石分子筛,不需成胶、老化阶段,工艺简单,生产周期短,节约能耗。一步晶化转化机理在沸石合成领域的实验佐证为大宗工业废渣的深层次开发利用提供了基础。     

冷却-加热对CaO-Al2O3-SiO2系玻璃析晶动力学的影响

以CaO-Al2O3-SiO2系玻璃为研究对象,采用Ozawa方程、Kissinger方程和JMA修正方程研究了冷却方式和加热温度对玻璃析晶动力学的影响。结果表明:化学组成相同的玻璃,冷却速度和加热温度对其析晶活化能E、Avrami指数n和析晶速率指前因子ν都有影响,但加热温度对析晶活化能E的影响更大,并在750℃出现极大值现象。通过玻璃析晶试验发现:冷却速度和加热温度对微晶玻璃主次晶相的析出没有影响,主、次晶相分别是钙长石和榍石。冷却速度和加热温度对析晶活化能E的影响主要来源于析出主、次晶相的比例不同。     

单晶高温合金定向凝固过程中晶体竞争生长观察

本文选用镍基单晶高温合金，用籽晶法控制各晶粒的晶体取向，进行了多晶组合的竞争生长实验，模拟了定向凝固中不同晶体取向晶粒间的生长过程与竞争规律，结果表明：晶粒的竞争生长过程取决于晶粒的相对取向关系及其与热流方向的夹角，择优生长方向与热流方向最接近的晶粒将淘汰其它晶粒并逐渐占据整个试样截面，当两个晶粒的择优生长方向都与热流方向不平行且大发散角方式组合时，两晶粒间可出现第三个晶粒并最最终扩展至整个试样截     

白榴石增强的牙科饰面瓷研究现状

回顾了白榴石微晶玻璃在制备方法、热稳定性和力学性能3个方面的研究进展。与传统的玻璃析晶法相比,先制备白榴石晶体,然后将其与低软化点玻璃混合烧结,这种方法在控制白榴石晶体尺寸方面更具优势。烤瓷温度和时间会影响微晶玻璃中自榴石晶体的含量,进而影响微晶玻璃的热膨胀系数,因此需要严格控制。微晶玻璃中白榴石晶体的直径应该小于4μm,这样可以将微晶玻璃中微裂纹的影响减少到最小。作者制备的一种白榴石微晶玻璃在950℃保温60min后析晶完成,并且白榴石晶体的尺寸在1μm左右。     

Solvents for growing Al2(WO4)3 single crystals from high-temperature solutions

The crystallization conditions of Al₂(WO₄)₃ from Li₂O–WO₃ solvents (molar ratio 30.0:70.0, 32.5:67.5, 35.0:65.0, 45.0:55.0 and 55.0:45.0) as well as from Na₂O–WO₃ solvents (molar ratio 25.0:75.0, 27.5:72.5, 30.0:70.0 and 32.5:67.5) have been investigated. The concentration and temperature regions of crystallization of Al₂(WO₄)₃ and the density, viscosity as well as the solution losses due to evaporation have been established. On the basis of the data obtained it has been concluded that the most suitable solvent for growing Al₂(WO₄)₃ single crystals is Na₂O–WO₃ with a molar ratio of 27.5:72.5.     

等离子体循环刻蚀镀膜提高锆膜的水汽阻隔性

为了提高以锆金属镀层封闭聚氨酯泡沫塑料表面对水气的阻隔性,采用了等离子体循环刻蚀和中频磁控溅射镀膜相结合的方法改变锆膜晶粒的生长模式。结果表明,等离子体循环刻蚀以后,锆膜表面的晶粒呈现出非晶化趋势,无等离子体循环刻蚀时锆膜横截面晶粒的生长方式是法向柱状晶模式,而刻蚀后薄膜呈现的是一种柱状晶和细小球晶团的混合生长模式。水气阻隔实验表明,等离子体循环刻蚀的方法可明显提高锆膜的水气阻隔性。等离子体循环刻蚀抑制了锆膜的法向柱状晶生长,使晶粒更加细化,膜呈现非晶化趋势,这是膜致密性、水气阻隔性增加的根本原因。     

在Fe-Al-C系统中合成优质IIa型宝石级金刚石单晶

和优质Ib型宝石级金刚石单晶生长相比,作为当今高温高压晶体生长的一种高精尖技术,优质Ⅱa型宝石级金刚石单晶对合成技术提出了更高更苛刻的要求。本研究从晶体的生长速度出发,发现一开始阶段(大约几个小时)的晶体生长速度对优质宝石级金刚石单晶的后期生长至关重要。对Fe-A l-C系统(A l含量不大于2.5wt%)来说,采用多晶种法将晶体开始阶段的晶体生长速度由1.5mg/h降至0.5mg/h后,对生长过程中金属包裹体的进入有了明显的抑制作用,晶体的质量有了很大提高。从晶体中包裹体的存在形式来看,为了获得优质Ⅱa型宝石级金刚石单晶,在触媒中人为地添加除氮剂给晶体生长过程中的排杂过程带来了很大的难度。为了更好的实现排杂,必须很好的处理晶体表面的径向平铺生长速度和晶体轴向的堆积生长速度之间的关系。