Strengthening of a lithium disilicate glass-ceramic by rapid cooling

In order to improve the mechanical properties, a traditional physical strengthening process was applied to a lithium disilicate (LD) glass-ceramic with a dual-phase microstructure consisting of a glassy matrix and LD crystals. The strengthening process was based on the transformation behavior of the glass-ceramic. The process was conducted by heating the glass-ceramic to a temperature below the dynamic softening point, and then rapid cooling in silicon oil (quenching). Residual stresses and mechanical properties of the glass-ceramic were investigated after the quenching. It was found that residual compressive macro-stresses could be induced in the surface layer of the LD glass-ceramic by the quenching. The residual stresses remarkably increased with increasing the quenching temperature to near the dynamic softening temperature. Compared with the corresponding annealing state, the LD glass-ceramic could be effectively strengthened and toughened by the quenching at a suitable temperature. The results displayed the strengthening possibility and potential of the LD glass-ceramic by the traditional physical process.     

Evaluation of adhesion and mechanical properties of plasma sprayed NiCrAl/Al2O3-13wt.%TiO2 coatings

Plasma sprayed NiCrAl/Al₂O₃-13wt.%TiO₂ coating was fabricated and annealed at 300–900 °C in air atmosphere. The Elastic modulus (E), micro-hardness (H_V) and fracture toughness (K_ca) were evaluated by Vickers Indentation Fracture technique. The microstructure was studied by scanning electron microscopy. It can be concluded that with the increasing of annealing temperature, E and H_V at the interface of Substrate/Bond layer (S/B) are firstly increased and retain the highest value at 600 °C then decreased with higher annealing temperatures due to the phase transformation. E of the ceramic coating rised initially with annealing temperature increasing, reached the highest value at 400 °C, and then decreased with the further increasing of the temperature. The K_ca of the S/B interface firstly increased as the heating temperature increasing, confirming the crack initiation resistance increasing after annealing with the temperature below 700 °C. However, the K_ca decreased for further annealing temperature, even lower than that of the as-sprayed coating. Thereby, a proper annealing temperature can improve the mechanical properties of the coating since the coating becomes denser, ceramic lamellar structure becomes ambiguous and cracks are partially healed.     

Properties of magnesium-aluminate spinel derived from bauxite and magnesia

The synthesis of magnesium-aluminate spinel divided from bauxites and magnesias, the starting materials with different molar mass ratios (Al₂O₃: MgO) of 3, 1, and 0.6 were developed using solid-state reaction sintering at 1350-1500°C. The effects of different mass ratios and sintering temperatures on the phase composition, densification behavior, shrinkage, flexural strength, and microstructure of the synthetic materials were studied. It was found that as the relative content of bauxite decreased, the flexural strength first decreased before increasing. When n(Al₂O₃)/n(MgO) was 1, the spinel was the primary phase and the sample was dense. When the temperature became 1450°C, the flexural strength became maximized at 106.48 MPa.     

中子辐照6H-SiC晶体的退火特性及缺陷观测

利用X射线衍射（XRD）研究中子辐照6H-SiC晶体的退火特性,发现辐照后晶体的XRD峰的半高宽（full width atha lf maximum,FWHM）增大,之后又随退火温度的升高,在700～1230℃范围内呈线性规律的回复。以此规律为依据,可发展一种适合测量高温和复杂温度场温度的测温方法。采用添加了K2CO3的KOH为腐蚀剂,对辐照前、辐照后及辐照后退火的掺氮6H-SiC单晶进行位错腐蚀观察,发现经中子辐照的晶体中位错面积比随退火温度的变化趋势与FWHM随退火温度的变化趋势基本一致,由此认为经中子辐照所产生的位错可能是导致XRD峰的FWHM变化的一个重要因素。     

TEM Characterization of Nanostructured MgAl2O4 Synthesized by a Direct Conversion Process from γ-Al2O3

Nanostructured MgAl₂O₄ spinel was synthesized by a direct conversion process from cubic γ-Al₂O₃. The effect of post-annealing temperature (300°, 500°, and 800°C) on MgAl₂O₄ phase formation was investigated using transmission electron microscopy, selected area electron diffraction (SAED), electron energy loss spectroscopy (EELS), and energy-dispersive spectroscopy (EDS). Relative diffraction intensities as well as lattice parameter measurements from SAED revealed that MgAl₂O₄ spinel structure starts forming at temperatures as low as 300°C. EELS and EDS spectrum images also revealed an increase in elemental homogeneity with increasing annealing temperature. The degree of ordering of Mg and Al between octahedral and tetrahedral sites has been determined from relative diffraction intensities. Results show that annealing to 800°C leads to a spinel phase with an order parameter of 0.78.     

Kinetic analysis of spinel formation from powder compaction of magnesia and alumina

A kinetic investigation into the formation of spinel from alumina (Al₂O₃) and magnesia (MgO) powder compaction with a stoichiometric mixing molar ratio of 1:1 was conducted in the temperature range of 1573 K to 1773 K over a certain time interval up to 25 h. The samples were pressed at pressures of 125, 375 and 750 MPa. The progress of the reaction was evaluated by monitoring the expansion ratio instead of the thickness of the spinel layer that was generated. The expansion ratio increases with increasing pressing pressure and holding time, and high temperature favored spinel formation. However, densification was observed at temperatures above 1673 K due to the occurrence of sintering between the powders. A kinetic model taking electrochemical potential as the driving force of the reaction was established, and the apparent activation energy was calculated to be 310.6 kJ/mol in the temperature range between 1573 K and 1673 K. The reaction was controlled by the inter-diffusion of Al³⁺ and Mg²⁺ ions in the spinel layer that was formed.     

Influence of annealing temperature on the lamellar and connecting bridge structure of stretched polypropylene microporous membrane

The influence of annealing temperature on the lamellar and connecting bridge structure of stretched polypropylene microporous membrane was investigated using small‐angle X‐ray scattering, temperature‐modulated differential scanning calorimetry and scanning electron microscopy. It is found that with increasing annealing temperature from 105 to 145 °C, the main lamella melting peak combines with that from connecting bridges and a uniform pore arrangement is obtained in the microporous membrane. The annealed lamella thickness is increased and lamellar structure is improved, due to the occurrence of melting and recrystallization during annealing. At the same time, more secondary crystals are formed. The melting and recrystallization and secondary crystals contribute to the appearance of an annealing peak in the differential scanning calorimetry curve of annealed film. During the following cold and hot stretching, the secondary crystals disappear and convert to initial connecting bridges. The improved lamellar structure can support the scaffold of pore structure, resulting in a uniform connecting bridge arrangement. But further increasing the temperature to 150 °C degrades the initial lamellar structure, leading to a decrease of pore arrangement in the stretched microporous membrane. Annealing leads to the difference of lamellar structure: the initial lamellar structure is improved and some weak secondary crystals are formed in the amorphous region. © 2014 Society of Chemical Industry     

Improvement of ageing issue in Zn0.4Fe2.1Co2Mn1.5O8 thermistor films

The Zn-Fe-Mn-Co-O spinel-structured thermistor films were synthesized by chemical solution deposition methods. The ageing performance of these films was investigated by co-doping Fe and Zn into the films and annealing at different temperatures. The surface morphology and microstructure of these films were improved with the increasing temperature. The contents of Mn³⁺ and Mn⁴⁺ were stable with the annealing temperature due to iron and zinc co-doping. Annealing at 700 °C was necessary for the iron cation to be fully activated in the spinel lattice. The optimal electrical properties and ageing performance of the films were obtained at 800 °C, with an optimal B value of ˜4472 K and the lowest rate of change for the film resistance.     

Relationship between orientation of amorphous chains and modulus in highly oriented polypropylene

By using oriented polypropylene prepared by forced quenching in a zone-drawing-type apparatus, the effect of taut tie molecules on the modulus is studied by measuring the changes of superstructure with an increasing draw ratio and the temperature at which the oriented polypropylene was annealed. Superstructure is analyzed by means of an x-ray method, differential scanning calorimetry, thermal shrinkage, birefringence, and infrared spectrum. Modulus increases with an increasing orientation function of amorphous chains, ?_a, and is decided only by the value of ?_a, so long as the higher value of orientation function of the crystal c axis does not change with the draw ratio or annealing. The taut tie molecules in ultrahigh-modulus polypropylene are loosened by annealing at temperatures below 420 K, but would be incorporated into folded lamellar crystals above the annealing temperature of 420 K. The taut tie molecules does not always have a 3₁ helix conformation.     

Tensile properties of random copolymers of propylene with ethylene and 1-butene: effect of crystallinity and crystal habit

The tensile modulus of elasticity and yield strength of semicrystalline random copolymers of propylene with different amount on ethylene or 1-butene co-units were analyzed as a function of the crystallinity and the crystal habit/shape. Samples were prepared by cooling the melt to ambient temperature, and subsequent annealing at elevated temperature. Variation of the cooling rate between 10⁻¹ and 10³ K s⁻¹ and of the temperature of annealing allowed preparation of semicrystalline specimens with either lamellar or non-lamellar crystals of different size, and with different crystallinity between about 30 and 70%. Young’s modulus and yield strength increase with increasing crystallinity and consistently are lower for samples containing nodular, that is, almost isometric, non-lamellar crystals of low aspect ratio. For samples of identical crystallinity and crystal habit, an only minor effect of presence of co-units in the crystalline and amorphous phases is observed.     

Young's Modulus of Various Refractory Materials as a Function of Temperature

Young's modulus as a function of temperature was determined by a dynamic method for single-crystal sapphire and ruby and for polycrystalline aluminum oxide, magnesium oxide, thorium oxide, mullite, spinel, stabilized zirconium oxide, silicon carbide, and nickel-bonded titanium carbide. For the single crystals, Young's modulus was found to decrease linearly with increasing temperature from 100°C. to the highest temperature of measurement. For all the polycrystalline materials, except silicon carbide, stabilized zirconium oxide, and spinel, Young's modulus was found to decrease approximately linearly with increasing temperature until some temperature range characteristic of the material was reached in which Young's modulus decreased very rapidly and in a nonlinear manner with increasing temperature. This rapid decrease at high temperature is attributed to grain-boundary slip. Stabilized zirconium oxide and spinel were found to have the same rapid decrease in Young's modulus at high temperature, but they also had a decidedly nonlinear temperature dependence at low temperature.     

Low-pressure injection molding of magnesium aluminate nanoparticles: Rheological behavior and flexural properties of sintered component

This research aims to investigate the density and flexural strength of nanostructured spinel parts fabricated using the low-pressure injection molding (LPIM) method. For this purpose, firstly, the effect of the amount of binder was tested on the rheology behavior of the feedstocks containing spinel nanopowder for producing ceramic parts using the LPIM method. The rheometric analysis indicated that the feedstocks containing 80 wt% powder and 20 wt% binders showed shear-thinning fluid behavior and were chosen as the optimal low-viscosity feedstocks for the LPIM process. After binder removal from LPIMed part, secondly, the effect of sintering temperature was examined on the relative density and flexural strength of the spinel parts. The results indicated that by increasing sintering temperature from 1550 °C to 1700 °C, the size of pores was reduced and grain size was increased from 2 μm to 6 μm. Furthermore, the flexural strength of the parts sintered at 1700 °C was 10 MPa greater than that of the sample sintered at 1650 °C.     

Improvement of the photovoltaic properties for P3HT:PCBM system annealed at the temperature in liquid crystalline regions induced by liquid crystal molecules

The poly(3-hexylthiophene):[6, 6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction organic photovoltaics (BHJ OPVs) showed a maximum value of 3.5 % by incorporating of 6 wt% nematic liquid crystals (NLCs) of 4-octyloxy-4′-cyanobiphenyls (8OCB) after annealing at the temperature of 70 °C in liquid crystalline transitions. The 8OCB was immiscible with P3HT, and the melting temperature of P3HT was not influenced at 8OCB doping amount below 10 wt%. Based on the UV–vis analysis, the conjugation length and chain order of P3HT should be the highest at 8OCB content of 6 wt% after annealing at 70 °C. The reflection peak of P3HT shifted to lower positions as the annealing temperature increasing from 70 to 130 °C, indicating that PCBM and 8OCB molecules could be incorporated into the lamellar spacing of P3HT crystallites at high annealing temperatures. The improvement of the solar cell device after annealing at 70 °C is probably due to the optimized phase separation morphology and relatively higher hole mobility in P3HT:PCBM:8OCB system. The 8OCB molecules in the liquid crystalline state are supposed to be a good template for the crystallization of P3HT, as well as the phase separation between P3HT and PCBM.     

复合薄膜用交联型水性聚氨酯胶粘剂的研制

通过改变羧基(-COOH)含量、异氰酸酯基(-NCO)与羟基(-OH)的摩尔比(R值)、交联剂用量,考察了它们对聚氨酯乳液性能及复合薄膜T型剥离强度的影响。结果表明:粘度随-COOH含量的增大而增大; 随R值的增大先增大后减小,当R值=1．1时体系粘度最大。R值或-COOH含量发生变化,T型剥离强度也跟着发生改变。并且,交联剂能起到提高T型剥离强度的作用,且当交联剂含量为9％最佳。     

Annealing behavior of solution grown polyethylene single crystals

The morphology evolution of solution grown polyethylene single crystals has been studied upon annealing below their melting temperature by using atomic force microscopy (AFM). AFM investigations have been performed ex situ, which means AFM investigations at room temperature after the annealing treatment, and in situ at real temperature. Beside the well-known Swiss-cheese and picture frame appearance a novel morphological feature has been observed: the formation of saw-tooth-like patterns at the edges of the crystals, which become more and more pronounced with increasing annealing temperature. Controlled dissolution experiments have resulted in similar saw-tooth-like edge patterns of the single crystals, which indicate that the initial organization of the crystals influences the reorganization. This reorganization behavior upon annealing can be related to the presence of nano-sized fold defects, which have been monitored using the technique of n-alkane surface decoration.     

高剂量中子辐照6H-SiC晶体的退火特性

在温度为60～80℃的条件下用剂量为1.72×1019n/crm2的中子对6H-SiC晶体进行了辐照,利用X射线衍射等方法观测了中子辐照引起的缺陷及其恢复.重点追踪6H-SiC的(006)、(0012)晶面的衍射峰并进行实验观测.中子辐照对晶体造成了严重的损伤,使其内部产生了大量的缺陷,在某些被测晶面甚至出现非晶化.通过等时退火,缺陷逐渐消失,晶格开始恢复,其恢复特性由退火温度决定.通过X射线衍射峰的峰高和峰型发现,在温度低于600℃时,辐照损伤几乎不变,超过600℃后,温度越高,晶格恢复现象越明显.原来经辐照呈非晶化的晶面逐渐恢复有序,(006)面衍射峰的半高宽随退火温度的升高呈线性恢复.利用此种线性规律可以制作无线传感器,从而实现对某些复杂环境的温场测试.     

Study of Some of the Factors Affecting the Mechanical Properties of Zinc Polycarboxylate Cement

The variation of the tensile and compressive strength of a zinc polycarboxylate cement with annealing temperature was studied in the temperature range from room temperature up to 160°C. The effects of powder/liquid ratio and mixing temperature were also investigated. The results obtained showed that both tensile and compressive strengths increase with increasing powder/liquid ratio. Also the cement strength increases with annealing temperature to a certain limit. It was also found that the strength depends on the mixing temperature and shows its maximum value at room temperature. The reasons for the changes of both tensile and compressive strengths due to the previously mentioned factors are discussed.     

Strength of Synthetic Single Crystal Sapphire and Ruby as a Function of Temperature and Orientation

The modulus of rupture of sapphire single crystals was determined as a function of temperature for specimens with orientations favoring plastic deformation and for specimens with unfavorable orientations. From 600°C. to l000°C., the strength of both types increased with increasing temperature, but the increase was more pronounced for the former. Ruby specimens oriented favorably for plastic deformation also showed a large increase in strength. It is conjectured that the increase in strength results from stress relief by microscopic plastic deformation.     

Crystallization of double crystalline symmetric diblock copolymers

We report dynamic Monte Carlo simulation results on the crystallization of double crystalline symmetric A-B diblock copolymer, wherein the melting temperature of A-block is higher than B-block. Crystallization of A-block precedes the crystallization of B-block upon cooling from a homogeneous melt. The morphological development is controlled by the interplay between crystallization and microphase separation. With increasing segregation strength, we observe a gradual decrease in crystallinity accompanying with smaller and thinner crystals. During crystallization, A-block crystallizes first and creates confinement for the crystallization of B-block. Thus, crystallization of B-block slows down influencing the overall crystal morphology. At higher segregation strength, due to the repulsive interaction between blocks, block junction is stretched out, which is reflected in the increased value of mean square radius of gyration. As a result, a large number of smaller size crystals form with less crystallinity. The onset of microphase separation shifts towards higher temperature with increasing segregation strength. Isothermal crystallization reveals that the transition pathways strongly depend on segregation strength. The value of Avrami index shows the formation of two dimensional lamellar crystals of both the blocks. Two-step (sequential), compared to one-step (coincident) isothermal crystallization, produces higher crystallinity in A-block, however, the crystallinity of B-block is almost identical in both the cases.     

Characterization of two precursor polyblends: Polyhydroxyamide and poly(amic acid)

Blends of two precursor polymers, polyhydroxy amide (PHA) and poly(amic acid) (PAA), were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The presence of PHA enhanced thermal and mechanical properties of the polyblends. All of the polyblended films showed large endothermic peaks that decreased monotonically with increasing heat treatment temperature. The cyclization onset temperature (T₁), initial decomposition temperature (T₂), and weight residue at 900°C of the polyblends were shown to be in the ranges of 144–146°C, 532–540°C, and 44–45%, respectively. Also, the thermal stabilities were enhanced consistently with increasing annealing temperature from 25 to 250°C. The ultimate strength and initial modulus of the polyblends increased from 84 to 136 MPa and from 2.93 to 5.34 GPa, respectively, with increasing PHA content. Similar to the trend of thermal stability, increasing the annealing temperature of the polyblends increased the tensile properties of the films. The observed tensile properties are discussed in terms of the morphology of the fractured films as studied by scanning electron microscopy (SEM). The degree of crystallinity of the polyblends was characterized as a function of heat treatment temperatures by wide angle X‐ray diffractometry (WAXD).