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.     

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。     

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 structural relaxation on crystal nucleation in a soda-lime-silica glass

The influence of structural relaxation on crystal nucleation has been underexplored and remains elusive. This article discusses its possible effect on the nucleation process using a stoichiometric soda-lime-silica (2Na₂O·CaO·3SiO₂) glass as a model system. We show that the relaxation effect is powerful at low temperatures, close and below the glass transition, , and leads to a continuous increase in the nucleation rate. At any given temperature, the nucleation rate eventually reaches its ultimate steady-state corresponding to the fully relaxed supercooled liquid (SCL). However, the time to reach the steady-state is two to three orders of magnitude longer than the average relaxation time estimated by the Maxwell relation (shear viscosity / shear modulus). The proposed nucleation mechanism and model, which take relaxation into account, and related experimental results also explain the alleged “breakdown” of CNT at low temperatures reported for various glasses. It confirms a few recent papers that this apparent flaw is merely because most researchers did not prolong nucleation treatments enough to complete the relaxation process to achieve a steady state. Another remarkable result is that the actual maximum nucleation temperature, , is significantly lower than the previously reported values. Finally, a comparative analysis of the kinetic coefficient using viscosity versus growth velocity favors the last. These results for this soda-lime-silica glass extend and validate recent findings for lithium disilicate on the significant (but often neglected) effect of relaxation on crystal nucleation.     

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.     

Anisotropic growth kinetics and electric properties of PZT-5H single crystal by solid-state crystal growth method

The PZT-5H single crystal growth on [111]c-, [110]c-, and [001]c-oriented seed crystal by solid-state crystal growth (SSCG) method was investigated. The growth rate of PZT-5H single crystal strongly depends on seed crystal orientation and annealing time. The mean growth distance is 682, 620, and 93 μm for [111]c-, [110]c-, and [001]c-oriented PZT-5H single crystal grown at 1150°C for 8 h, respectively. The growth kinetics of SSCG-grown PZT-5H single crystal was discussed. It is found that the growth of single crystal is driven by the solubility difference between the matrix grains and single crystal growth front interface, arising from the local curvature and the crystallographic directions dependent solubility. The growth of [001]c-oriented PZT-5H single crystal was mainly contributed from the difference solubility arising from the local curvature of growth front interface, while the growth of [111]c- and [110]c-oriented PZT-5H single crystal was mainly contributed from the difference solubility between {111} and {110} plane of single crystal and matrix grains. The piezoelectric coefficient d₃₃ of up to 1028pC/N (about 50% larger than that of the same component ceramic) was obtained in a [110]c-oriented PZT-5H single crystal with a Curie temperature of about 230°C. The large field piezoelectric constants d₃₃* of up to 1160 pm/V (about 50% larger than that of the same component ceramic) at 15 kV/cm was also obtained in [110]c-oriented PZT-5H single crystal with a large strain of 0.18%. This work deepens our understanding on the growth kinetics of SSCG and pushes the way of growth of soft PZT single crystal by SSCG.     

青霉素亚砜结晶生长与成核动力学

利用Mydlarz 和 Jones 模型（MJ2）,对乙酸丁酯中青霉素亚砜的成核与生长动力学进行研究。通过矩量法对MJ2模型进行处理后,利用晶体产品的粒度分布计算得到青霉素亚砜的生长速率与成核速率,然后利用最小二乘法拟合回归求解出成核与生长动力学方程参数。通过实验设计考察了过饱和度、温度与搅拌速度对青霉素亚砜晶体成核和生长过程的影响。研究表明青霉素亚砜晶体生长速率随过饱和度比的增加呈现指数型增长,确定青霉素亚砜晶体生长属于晶体表面生长控制过程。由于高速搅拌会增加青霉素亚砜晶体的破碎,促进了二次成核过程,随着搅拌速度的增加,晶体生长速率出现小幅下滑,而成核速率则明显升高。青霉素亚砜成核与生长动力学研究将有助于工业生产过程优化。     

Simulations of crystal aggregation and growth: Towards correct crystal area

Simulating crystal growth and aggregation can provide insight into factors that control the final product properties. Classical models involve formation of a volume-equivalent single crystal upon aggregation. This approach does not preserve particle area, resulting in an inadequate model of supersaturation depletion. Alternatively, crystal area can be computed accurately by a Monte Carlo method where each primary particle of an aggregate is described in its full geometric complexity. However, the drawback of this method is its computational cost. Thus, a third method is introduced as a compromise, describing particles by their volume and area and preserving both upon aggregation. The so-obtained two-dimensional model requires growth rate expressions in volume and area. We provide a method for parametrizing these expressions so that total volume and area closely match the values obtained with the method based on full geometric information. The parameters depend on primary particle geometry and the amount of growth. © 2019 American Institute of Chemical Engineers AIChE J, 65: e16525, 2019     

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。     

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.     

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。