晶核剂对玻璃纤维分相和析晶的影响

本文应用差热分析研究了ZrO_2、TiO_2和Cr_2O_3三种晶核剂对MgO 15(wt.%)、Al_2O_3 30(wt%)、SiO_2 55(wt.%)成份点玻璃纤维分相和析晶的影响,得出:不同晶核剂、不同预处理,分相机理不同、分相完善程度不同.1.ZrO_2含量从G(wt.%)的1~#棉增至12(wt.%)的2~#棉,能促进分相和析晶.2.ZrO_2和TiO_2的晶核剂作用相差不太大,都能促进分相和析晶,但混合晶核剂ZrO_29(wt.%)+TiO_2 3(wt.%)的3~#棉中TiO_2的作用在本实验中不显著.3.含Cr_2O_3 5(wt.%)的4~#棉能提高玻璃纤维的耐火度和抗粘结的性能.4.预处理能促进分相.5.770℃预处理时分相完善程度是:ZrO_2 12(wt.%)>ZrO_2 9(wt.%)+TiO_2 3(wt.%)>Cr_2O_3 5(wt.%).6.同一晶核剂在较低温度下分相较完善.     

TATMP对碳酸钙晶体生长动力学的影响

利用接种生长方法研究了TATMP 对过饱和溶液中碳酸钙晶体生长速度的影响。结果表明,TATMP 存在时,碳酸钙晶体生长服从不加阻垢剂时空白液中的速度方程,是二级界面控制过程。TATMP 显著降低了碳酸钙晶体的生长速度。     

晶体生长炉的压力控制系统设计

本文旨在设计一种排气系统,可对压力容器、压力烧结炉等,将设备中影响合成材料的杂质排除,可提高设备使用寿命,更可在提高产品品质等方面有很大的改善作用,如SiC单晶生长、LED荧光粉的合成.     

氟化钙晶核剂对废啤酒瓶微晶玻璃的影响

利用废旧啤酒瓶研制微晶玻璃,探讨不同含量的CaF2晶核剂对微晶玻璃的成核、晶化及性能的影响,确定适宜的添加量,从而研究解决废旧玻璃原料黏度大,难于成核和晶化的难题.用XRD和SEM表征样品的晶相及微观形貌;用Rietveld Quantification软件计算试样的晶相与玻璃相含量;按照微晶玻璃标准测试试样的抗折强度、吸水率、体积密度.实验结果表明,添加CaF2试样中析出的主晶相是Na2Ca(SiO4),Na2Ca3Si6O16和NaCa2Si4O10F,析出晶体含量随着CaF2添加量增加而增加.确定6%为最佳的CaF2添加量,此时微晶玻璃析出晶相的总量为42.91%,体积密度为2.283g·cm-3,吸水率为0.179%,抗折强度为149.3Mpa.     

氟化钙晶核剂对废啤酒瓶微晶玻璃的影响

利用废旧啤酒瓶研制微晶玻璃,探讨不同含量的CaF2晶核剂对微晶玻璃的成核、晶化及性能的影响,确定适宜的添加量,从而研究解决废旧玻璃原料黏度大,难于成核和晶化的难题.用XRD和SEM表征样品的晶相及微观形貌;用Rietveld Quantification软件计算试样的晶相与玻璃相含量;按照微晶玻璃标准测试试样的抗折强度、吸水率、体积密度.实验结果表明,添加CaF2试样中析出的主晶相是Na2Ca(SiO4),Na2Ca3Si6O16和NaCa2Si4O10F,析出晶体含量随着CaF2添加量增加而增加.确定6%为最佳的CaF2添加量,此时微晶玻璃析出晶相的总量为42.91%,体积密度为2.283g·cm-3,吸水率为0.179%,抗折强度为149.3Mpa.     

晶核剂含量对钨渣微晶玻璃性能的影响

钨渣微晶玻璃是以钨尾矿为主要原料,再加入长石、石英与熔剂等其他成分。晶核剂为萤石。用差热分析、X射线衍射、透射电镜、扫描电镜研究了萤石含量对钨渣微晶玻璃性能的影响。实验结果表明,添加5～7％的萤石为合适的晶核剂用量。     

TiO2和ZrO2复合晶核剂对玻璃陶瓷晶化行为的影响

通过差热分析、X射线衍射分析和扫描电镜观察等测试方法,研究了TiO2和ZrO2作复合晶核剂对玻璃陶瓷晶化行为的影响。研究表明:适量的TiO2和ZrO2复合晶核剂能使MAS系统玻璃陶瓷的形核和析晶的温度降低,并且能促进析晶,晶核剂含量的调整也会对玻璃陶瓷的结构和性能产生较大的影响。     

氯化镁浓度对氢氧化镁晶体生长的影响

高活性氧化镁通过水合反应制得氢氧化镁,通过添加不同浓度的MgCl_2,研究水化剂氯化镁浓度、水化温度对氢氧化镁晶体生长的影响。粒度仪、X-射线衍射仪(XRD)和扫描电子显微镜(SEM)的检测表明,氧化镁水合制备氢氧化镁的纯度较高;水化温度70℃,氯化镁浓度低于1.00 mol/L时,产品为片状氢氧化镁;当氯化镁浓度高于1.50 mol/L时,出现条状氢氧化镁;在160℃下高温水热,均能得到片状氢氧化镁;氯化镁浓度为1.00 mol/L时,产品形貌为形状规则的片状晶体。     

Effect of an electric field on the heterogeneous nucleation and crystal growth of potassium hydrogen tartrate in wines

Potassium hydrogen tartrate (KHT) is a naturally occurring salt in wines. To avoid the formation of KHT crystals in bottles, it is necessary to stabilize wines before bottling. However, none of the current techniques is fully satisfactory. A new process, called the trap process, has been developed that consists of cold-crystallizing KHT on a stainless steel packing. To accelerate the heterogeneous nucleation and/or crystal growth rate of the salt, the influence of an external electric field on these phenomena was studied. A potentiostatic circuit maintained a constant potential against a saturated calomel electrode. A preliminary cyclic voltammetry study led to the determination of the most suitable potential values (i.e., inducing no electrochemical reaction). A set of wine stabilization experiments was then performed using the trap process with and without potential. The results demonstrated that a potential of +200 mV vs SCE generates an increase in process efficiency, even in the case of wines containing a lot of inhibitors. It also significantly reduces the induction time of nucleation.     

硫酸锶晶体生长动力学研究

为了从控制晶体生长角度，说明制备纳米硫酸锶沉淀体系中存在的EDTA对产品粒径的影响作用，根据过程机理，用恒组成法研究硫酸锶晶体生长动力学。根据叠加模型和弱化模型，建立体系中有EDTA存在时，硫酸锶沉淀过程的晶体生长动力学模型。结果表明，硫酸锶沉淀过程中晶体生长属于表面反应控制机理。EDTA存在能降低晶体生长速率，有利于减小粉体粒径。     

原料纯度对Li2B4O7单晶生长的影响

Ｌｉ２Ｂ４Ｏ７单晶的宏观缺陷与原料纯度有关。     

Modeling layered crystal growth at increasing supersaturation by connecting growth regimes

Mechanistic modeling facilitates rational crystallization engineering and design space screening. For an accurate model, the dominant growth mechanism operating on each face must be determined, which is highly dependent on supersaturation. Considering the case of centrosymmetric growth units, we developed and connected existing mechanistic expressions for spiral and two‐dimensional‐nucleation growth regimes, through application of stationary nucleation rate theory. Our approach enables calculation of crossover supersaturations and forms a framework to model the specific mechanism operating on each face under given crystallization conditions. Increasing supersaturation can change the crystal morphology; as face families switch growth mechanisms, they may grow out of the steady‐state shape, or influence its aspect ratio. Application of the model to naphthalene, biphenyl, pentaerythritol and β‐HMX shows the ability to capture experimentally observed examples of such supersaturation‐dependent crystal habits. This methodology broadens the applicability of mechanistic crystal growth modeling to include higher‐supersaturation industrial processes. © 2017 American Institute of Chemical Engineers AIChE J, 63: 1338–1352, 2017     

流化床中硝酸钙晶体生长的实验研究

流态化结晶分离硝酸钙是改进硝酸磷肥工艺的关键技术。实验获得了流化床循环流动条件下的Ca(NO3)2-H2O二元体系溶液在6.5～24.5℃的第1过饱和曲线,其对应的拟介稳相区过饱和度Δw(Ca(NO3)2)=4.2%～4.5%。该条件下四水硝酸钙晶体在流化床中均匀生长,平均线性生长速率可达u=0.06mm/min。     

Studies on the crystal growth of rice bran wax in a hexane medium

Rice bran oil (RBO) is well known for its high wax content (2–4%). A good separation of waxes must be ensured through the formation of crystals that can be removed with a minimal retention of oil to maintain high yields of refined oil. In the present study, the form and size distribution of RBO wax crystals were investigated using a laser diffraction technique. An attempt was made to study the effect of cooling on growth and size distribution of RBO wax crystals in hexane medium, and it showed that high cooling rate and low temperature induces the formation of a great number of small nuclei. In addition, experiments were performed to evaluate the effect on the growth of wax crystals of successive additions of gum and pure TG to the medium. The entire experiment was designed to optimize the temperature and incubation time of wax crystallization to facilitate the efficient separation of wax from crude RBO-hexane miscella using membrane technology.     

Electrocrystallisation of zinc from acidic sulphate baths; A nucleation and crystal growth process

The electrochemical nucleation and growth of zinc on low-carbon steel from acidic (pH 2.0-4.5) baths containing ZnSO₄, NaCl, and H₃BO₃, was studied by means of chronoamperometry at various cathodic potentials under a charge-transfer controlled regime. It is shown that at overpotentials in the range 0.30-0.55 V (negative to the Zn²⁺/Zn redox value) the electrodeposition proceeds by instantaneous three-dimensional nucleation, which turns to progressive at higher overpotentials and/or very acidic baths. At low cathodic overpotentials (<0.30 V), a two-dimensional contribution limited by the incorporation of Zn ad-atoms in the developing lattice becomes significant at the early stages of deposition, and is more progressive in type the more acidic is the bath pH. Nucleation rate constants were calculated and correlated analytically with the respective potentials, using the classical theory of heterogeneous nucleation, which though fails to lead to reasonable values for the critical nucleus size.     

晶体粒径对碰撞成核的影响

从单个晶体运动中与结晶器内其他晶体及固体壁面碰撞过程的能量损失角度,描述了碰撞成核过程,建立了晶体粒径与成核速率的理论关系模型。结果表明,晶体的粒度对碰撞成核速率有很大的影响。并利用氯化钠晶体进行了碰撞成核实验,使用理论模型对实验结果进行拟合,进而验证了理论模型所预期的规律。指出在分析二次成核时,应充分考虑晶体粒度对成核影响的重要作用。该理论模型为实现工业结晶过程的仿真模拟提供了依据。     

A single crystal of polyethylene crystallized under high pressure

A single crystal of polyethylene about 2 μm thick has for the first time been obtained through high pressure crystallization and studied by X-ray diffraction and scanning electron microscopy. A band of a few μm thickness observed on the fractured surface of high pressure crystallized polyethylene is identified as a single crystal at least several tens of μm wide. Furthermore, a bulk composed of several bands stacked approximately parallel gives hexagonal symmetry in an X-ray oscillation photograph, the oscillation axis being parallel to the end surface of the bands. On the basis of these observations, it is concluded that a thick single crystal in the hexagonal phase splits into several bands on the transition from the hexagonal to the orthorhombic phase; 〈110〉 or 〈010〉 of each band in the orthorhombic phase corresponds to one of three possible a-axes in the hexagonal phase.     

Effect of needle‐like crystal shape on measured particle size distributions

The effect crystal morphology has on measured particle size distributions (PSDs) is explored, with a focus on particles exhibiting a needle‐like habit. An idealized in silico study was performed, targeted at modeling the measurement principles of various particle sizing devices, namely laser diffraction, Coulter counter, focused beam reflectance measurement, a single and a dual projection imaging devices. The evolution of a crystal population is measured, allowing for an evaluation of the introduced biases. Further, the consequences of these biases are highlighted by demonstrating how the real growth mechanism may be incorrectly interpreted depending on the chosen particle sizing technique. It is found that techniques which utilize a one‐dimensional PSD are incapable of simultaneously describing the concentration profile and average length; in contrast, imaging techniques are able to reproduce both quantities. Finally, the dual projection imaging device is shown to be the only instrument to yield a nearly bias‐free measurement. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2974–2985, 2016