Thermal Characterization and Microstructure Change of Cobalt Oxides

A series of cobalt oxides with different oxidation states have been prepared by using a precipitation-oxidation method and a controlled reduction method (in situ thermogravimetry-temperature programmed reduction, STG-TPR). The gradual change in microstructure with different oxides is studied by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that high-valence cobalt oxide is hexagonal with an elongated shape, Co₃O₄ is spinel with hollow spheroidal shape and CoO is a face-centered cubic structure, respectively.     

Low Cost Porous Alumina with Tailored Microstructure and Thermal Conductivity Prepared using Rice Husk and Sucrose

This study demonstrates a cost‐effective way to fabricate porous ceramics with tailored porosity and pore microstructure using 5–40 wt% rice husk (RH) in <75 μm, 75–180 μm, 180–355 μm, 355–420 μm, and 420–600 μm size, as pore former. Sucrose, used as binder, also acted as a pore former. Porous alumina compacts with 20%–66% volume fraction porosity and 50–516 μm pore size (length) were successfully fabricated. Microstructure of samples reveal randomly oriented elongated coarse pores and fine pores (avg. size 4 μm), created during burnout of RH and sucrose, respectively. Samples with isolated and/or interconnected pores were fabricated using this process. Thermal conductivity of the samples prepared was measured using Transient Plane Source (TPS) technique. Thermal conductivity ranges from 1.2 to 24 W/mK. Experimental results agree closely with predictions made based on Effective Medium Theory (EMT) for a two‐phase system.     

全丙乳液的合成及乳胶漆的制备

以甲基丙烯酸甲酯,丙烯酸丁酯为单体,用自制的乳化剂合成了全内乳液。配制了性能良好的乳胶漆,讨论了ＰＶＣ等因素对乳胶漆性能的影响。     

Synthesis,Characterization, Thermal Stability and Fluorescence of Hybrid Polymers Prepared from Amino-phenyl esters

Summary  This paper addresses paper the synthesis, characterization and properties of a new class of materials prepared from amino-phenyl esters. These materials are polymers prepared by self-condensation of the monomer at high temperature, using HCl as catalyst under different pressure conditions. The polymers were characterized by elemental analysis, FT-IR, ¹H-NMR, ¹³C-NMR, UV-visible and fluorescence spectroscopy. The composition, viscosities and thermal stability were also determined. The results showed that the polymers are hybrid materials because they contain simultaneously amide and imine groups in their backbones. When diminishing the pressure of the reaction medium, the polymers were obtained with higher viscosities, which were related with the composition and the thermal stability. Moreover, the polymers presented fluorescence which was associated to the polymers’ different functional groups.     

Crystalline Copper Phosphates: Synthesis and Thermal Stability

The syntheses of Cu(PO₃)₂, Cu₂P₂O₇, Cu₄P₂O₉, Cu₅P₂O₁₀, Cu₃(PO₄)₂, and Cu₂PO₄ were accomplished by several new solid-state routes. Attempts to synthesize CuPO₃ were unsuccessful, and it is suspected that this compound, which is reported in the literature, may not exist. The thermal stabilities of Cu(PO₃)₂, Cu₂P₂O₇ and Cu₃(PO₄)₂ were examined, and their decomposition was concluded to be strongly dependent on slow kinetics.     

Microstructure and Strength of Ceramics Prepared from Powders Synthesized Via Simultaneous and Sequential Deposition Routes

Sol-gel techniques for simultaneous and sequential deposition of precursor powders for preparation of ceramics in the ZrO₂ – Al₂O₃ – CeO₂ system are described. The phase composition of ceramics varies with the method of powder deposition. The intracrystallite arrangement pattern of the secondary phase in the system obtained via simultaneous deposition route provides the base for a ceramic that is superior in strength characteristics to ceramic prepared from ZrO₂ – Al₂O₃ powders deposited via sequential route.     

凝胶-滴注法制备的Al2O3多孔陶瓷球的显微结构与力学性能

以α-Al2O3为原料,环保无毒的海藻酸钠为凝胶体系,通过氯化钙溶液引入钙离子,利用凝胶-滴注及无压烧结的方法制备了Al2O3多孔陶瓷球,研究了固化时间及烧结温度对Al2O3多孔陶瓷球的气孔率、抗压强度及显微结构的影响规律.结果表明:固化时间延长,有利于钙离子迁移,与海藻酸钠发生反应,形成三维交联网状结构,使Al2O3...     

二苯甲酮腙的合成及热稳定性研究

二苯甲酮与85%水合肼缩合得到二苯甲酮腙,反应优化条件为:水合肼与二苯甲酮的摩尔比为2.8∶1.0,反应时间为9 h,反应温度为80℃,冰乙酸为催化剂。产品结构经过红外、高效液相色谱表征,并在N2氛围中用热重及示差扫描量热分析法对其进行热分析研究。     

高热稳定性介孔ZrO2的制备及其结构稳定性研究

该文阐述了一种催化剂(载体)的制备方法,即在非水溶剂中,通过溶胶-凝胶技术将烷氧基锆和非离子型模板剂自组装,合成出具有蠕虫状结构的介孔氧化锆。发现对凝胶适当后处理,可大大提高介孔氧化锆的热稳定性。通过XRD、TEM、等温氮吸附技术表征,表明该法合成的介孔氧化锆在600～700℃仍能很好地保持介孔结构和形貌。考察了不同后处理方式对改善介孔氧化锆热稳定性的效果,发现随着处理溶液pH升高,产物的热稳定性提高,其中,NaOH等强碱性溶液,可以使介孔氧化锆的热稳定性提高至700℃。     

Hierarchical Structure of Porous Silicon Nitride Ceramics with Aligned Pore Channels Prepared by Ice‐Templating and Nitridation of Silicon Powder

A unique hierarchical porous structure of silicon nitride ceramic with 76.5% porosity is fabricated by combining an ice‐templating method and nitridation for a silicon powder. The porous silicon nitride ceramics were composed of a lamellar structure with aligned pore channels and ceramic walls filled with fibrous whiskers. This study is focused on the influences of freezing rate on the microstructures and properties of the silicon nitride ceramics. The properties were characterized by compressive strength and gas permeability, which were shown to vary with controlled microstructure. The compressive strength and the permeability reached up to 32.2 MPa and 0.035^?12 m², respectively.     

溴代丙二酸的合成及热稳定性分析

以丙二酸为原料,研究了无机和有机体系中溴代丙二酸的合成方法及影响因素。结果表明:有机体系中的合成要优于无机体系。在有机反应体系中,冰浴,乙醚和四氯化碳为反应溶剂,反应时间60 min,减压蒸馏,结晶得到产品,其收率为56.32%,熔点为114~116℃。用FTIR和MS对产品进行了表征,并用MS对产品的热稳定性进行了分析,发现溴代丙二酸的热稳定性较差,在加热过程中易发生进一步的溴化和脱羧反应。     

Porosity,Microstructure and Thermal Stability of Microwave-cured Polymeric Denture Molds

Abstract

The relevance of controlling the chemical structure, thermal stability, composition and the porosity, of microwave-cured polymeric denture-molds is a key parameter if some degree of control of the corresponding adhesion among components is to be achieved. Different microwave-cured only polymer blends (Epoxy resin + Hardener) for producing denture molds were characterized by different techniques and compared to microwave-cured composites, also used for producing denture molds (Epoxy resin + Hardener + Alumina). In both cases the porosity was characterized by SEM, and the best material (in terms of porosity) was then subjected also to thermal and structural characterization. The results show the lowest porosity for the 90% Epoxy resin + 10% Hardener blend. The morphology shows a homogeneous surface with irregular particles smaller than five microns and voids-free. Also, the optimum temperature 100.8[ddot]C for microwave-cured denture molds was achieved with only a 0.64% loss of the original mass.     

过氧化物预硫化与硫黄硫化制备的医用天然胶乳制品热氧稳定性的差异

用TG-DTG方法研究动态空气状态下过氧化物预硫化天然胶乳(PPVL)制品试样和硫黄硫化天然胶乳制品试样的热氧降解。结果表明，PPVL试样和硫黄硫化体系试样的热氧降解反应为二步反应，前者的热氧降解起始温度To，DTG主降解峰温度L，终止温度T1均明显低于后者，反应活化能也明显低于后者；在较低温度下，两者均出现增重过程，前者比后者较明显，是后者的4．7倍；DTA曲线显示，前者出现的放热效应初始温度比后者提前。     

Porosity and Thermal Stability of Montmorillonite Pillared with Mixed Oxides of Lanthanum, Calcium and Aluminium

Montmorillonite intercalated with mixed pillars of lantana and alumina was prepared using a refluxed solution of aluminium chlorohydrate and lanthanum chloride. It is found that there are two main groups of pores in the pillared clays so prepared, one of which is around 8 Å, being close to that in alumina pillared clay (Al-PILC) and the other is about 14 Å. In contrast to the alumina pillared clays, a significantly larger specific surface area and micropore volume remained in LaAl-PILC after heating at high temperatures (700°C and 800°C). It seems that lanthanum ions react with the clay sheets during heating at high temperatures, resulting in a new porous solid phase which is thermally stable but has poor crystallinity. Calcium cations were introduced into the clays during the pillaring process. The calcium, distributed in the micropores of the product, LaAlCa-PILCs, further enhances the resistance to heating at high temperatures. After heating at 800°C, the BET surface area and micropore volume of a LaAlCa-PILC sample remained at about 138 m²/g and 0.05 cc/g, respectively, with a narrow pore size distribution in the micropore region. The influence of lanthanum and calcium on the pore structure as well as the evolution of pore structure in the PILCs upon heating at high temperatures are discussed in detail.     

Synthesis and Thermal Stability of Aluminum Titanate Solid Solutions

Aluminum titanate solid solutions with empirical formulas of Al₂Ti_1-xZr_xO₅, Al_6(2-x)(6+x)Si_6x/(6+x)□_6x/(6+x)TiO₅, and Al_2(1-x)Mg_xTi_1+xO₅ were synthesized by reaction sintering and annealed at 900° to 1300°C in air to evaluate the thermal stability. Substitution of Al in Al₂TiO₅ by Si and 2Al by Mg and Ti ions to form solid solutions such as AI_{6(2-x)/(6+x)l-Si}6x/(6+x)□_6x/(6+x)TiO₅, and Al_2(1-x)Mg_xTi_1+xO₅ was effective in controlling the thermal decomposition, but substitution of Ti by Zr had little effect.     

Phase Formation and Microstructure of Titanium Oxides and Composites Produced by Thermal Plasma Oxidation of Titanium Carbide

The phase formation and microstructure of titanium oxides and composites produced by Ar–O₂ thermal plasma oxidation of titanium carbide powders were investigated in detail by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Relationships between the phase compositions and microstructures of the oxides were established by combined structural and phase analyses, in correlation with synthesis conditions and phase formation mechanisms. It is revealed that vapor condensation favored the formation of anatase, which existed as smaller particles, while liquid/solid oxidation favored the formation of rutile, which appeared as larger particles or composites. A higher oxygen input in the plasma gases (Ar + O₂) enhanced the formation of anatase due to impeded oxidation and evaporation. A small amount of Ti₄O₇ and Ti₃O₅ was detected in the larger particles coexisting with rutile or TiC. These suboxides were formed as intermediates in solid oxidation of TiC or precipitated from the Ti–C–O melt during cooling. Furthermore, extensive cracks, dislocations and stresses were observed in the monolithic rutile and composites, in association with the rapid quenching in this high-temperature in-flight oxidation process.     

Microstructural,Thermal, Crystallization,and Water Absorption Properties of Films Prepared from Never-Dried and Freeze-Dried Cellulose Nanocrystals

In this paper, the microstructural, optical, thermal, crystallization, and water absorption properties of films prepared from never-dried (ND) and freeze-dried (FD) cellulose nanocrystals (CNCs) are reported. Morphology of the ND CNCs reveals a needle-like structure, while after freeze-drying, they show a flake-like morphology. Microstructural analysis of ND and FD CNCs are further studied via small angle X-ray scattering to probe interactions. ND CNCs yield a transparent film with a low surface roughness (14 ± 4 nm), while the FD CNC film evidence a significant reduction of their transparency due to their higher surface roughness (134 ± 20 nm). Although Fourier transform infrared spectroscopy and energy-dispersive X-ray spectroscopy analyses reveal no chemical change occurs during the freeze-drying process, yet a more intense thermal degradation profile is observed for FD CNC film, probably due to the higher oxygen ingress within the gaps created between the stacked flakes. This, in turn, results in a greater loss of crystallinity at a higher temperature (300 °C) compared to the ND CNC film. A rapid decrease in water contact angle of the FD CNC film proves that the morphology of flakes and their orientation within the film has a strong influence in increasing water absorption capacity.