Synthesis, structural and magnetic characterization of iron-zinc-borate glass ceramics containing nanocrystalline zinc ferrite

Two different glass ceramics with the composition of the (Fe₂O₃)_x·(B₂O₃)_(60−x)·(ZnO)₄₀, where x = 12.5 and 15 mol%, have been synthesized using the melt-quench method. The X-ray diffraction (XRD) patterns show the presence of nanometric zinc ferrite (ZnFe₂O₄) crystals, with spinel structure, in a glassy matrix after cooling from melting temperature. The estimated amount of crystallized zinc ferrite varies between 16 and 35%, as a function of the chemical composition. Glass transition (T_g), crystallization (T_p) and melting (T_m) temperatures were determined by differential thermal analysis (DTA) investigations. Fourier transform infrared (FTIR) data revealed that the BO₃ and BO₄ are the main structural units of these glass ceramics network. FTIR spectra of these samples show features at characteristic vibration frequencies of ZnFe₂O₄. Electron paramagnetic resonance (EPR) measurements show the presence of isolated Fe³⁺ ions predominantly situated in rhombic vicinities and as well as the Fe³⁺ species interacting by dipole–dipole interaction or to their superexchange coupled pairs in clustered formations. The magnetic properties of the studied glass ceramics were investigated by vibrating sample magnetometer (VSM). From the magnetization curves for glass ceramic containing 15 mol% Fe₂O₃ it was found that the nanoparticles exhibit ferromagnetic interactions combined with superparamagnetism with a blocking temperature, T_B. For studied samples the hysteresis is present. The coercive field is dependent on composition and magnetic field being around 0.05 μ_B/f.u for measurements performed in maximum 0.4 T.     

负载活性炭硅藻土多孔陶瓷的制备和过滤性能研究

采用注浆成型技术制备了负载活性炭的硅藻土多孔陶瓷,研究烧结温度对其孔径、孔隙率、强度和晶相的影响,并测定其细菌过滤性能。研究发现,经1000℃烧成的产品,硅藻土保持原有的微孔结构,孔隙率最高(67%),强度较好(5.81MPa),而且对大肠杆菌截留效果好,滤液中未检测出大肠杆菌,可满足国家饮用水标准的要求。     

Synthesis and characterization of Zn-B-Si-O nano-composites and their doped BaTiO3 ceramics

We synthesized Zn-B-Si-O (ZBSO) nano-composites via sol-gel process, and then used them to dope BaTiO₃ ceramics. The ZBSO nano-composites and their ceramics were characterized by means of thermogravimetric, Fourier-transform infrared, and X-ray diffraction methods, and using scanning and transmission electron microscopy. We also characterized the dielectric properties of the ceramics. The results indicated that the ZBSO nano-composites were nanometer-scale powders with an amorphous structure. The particle size of the powders increased with increasing pH value, but initially decreased and then increased with increasing calcining temperature. At pH about 2 and with calcining at 400 °C, the nano-composites attained minimum particle size (about 30 nm). The sintering temperature of the BaTiO₃ ceramics could be reduced to 1100 °C by adding 5 wt% of the ZBSO nano-composites. Uniform, fine-grained BaTiO₃ ceramics with a high permittivity (?_r = 2946 and ?_max = 5072) were obtained by adding nano-composites; these properties were superior to the ZBSO glass doped BaTiO₃ ceramics.     

Synthesis and characterization of Cr2AlC ceramics prepared by spark plasma sintering

The investigation of bulk Cr₂AlC ceramic fabricated by Spark Plasma Sintering (SPS) from coarse powders (CAC10) and fine powders (NCAC10) in the temperature range of 1100-1400 °C was carried out. The XRD results indicate that Cr₂AlC, as major phase, always appears with minor and trace amount of Cr₇C₃ and Cr₂Al respectively in both NCAC10 and CAC10 samples and the amounts of later two phases decrease with increase in temperature. However, the Cr₂AlC phase content in NCAC10 is higher than that of CAC10 sintered at the same temperature. The micrographs of back-scattered SEM show that grains with smaller size and pores with fewer amounts appear in SPSed NCAC10 in comparison to that of CAC10. As consequence, the higher hardness (5.6 GPa) of NCAC10 than that (3.9 GPa) of CAC10 was obtained. The patterns of XRD, microstructure and hardness of samples HPed at 1400 °C for the same composition were also presented for comparison.     

Synthesis and characterization of antioxidants and detergent dispersant based on some polyisobutylene copolymers

Polyisobutylene succinic anhydride-urea/polyamines (PIBSA) copolymers were synthesized as potential antioxidants and detergent dispersant agents for lubricating oils samples (SAE-30). Homogeneity, thermal stability and dispersancy of the solutions were determined. Fully soluble oil compounds that are thermally stable up to 250 °C were achieved. The oxidation stability of lube oil samples in the presence of four designed PIBSA additives (varying in the number of amine groups) was determined for a time period of up to 72 hours. The dependence of the additive efficiency on its concentration was studied to achieve maximum stability. Some PIBSA additives at concentration 3.0 · 10⁴ ppm exhibit the best results. Dispersivity values were measured at predetermined oxidation times. The results proved reliable dispersion capability as the nitrogen content of the additive is increased, i.e. the increase in the basic character of the additive leads to the increase in the neutralization capability. Moreover, the designed PIBSA additives retain their efficiency after long oxidation times, confirming their role as multifunctional nitrogen containing polymeric additive. Electronic Publication     

Preparation and characterization of magnesium-aluminium-silicate glass ceramics

Synthesis of machinable quality magnesium aluminium silicate (MgO-Al₂O₃-SiO₂) for fabrication of insulators/spacers usable in high voltage applications under high vacuum conditions has been carried out following two different routes i.e. (i) sintering route, and (ii) glass route. A three-stage heating schedule involving calcination, nucleation and crystallization, has been evolved for the preparation of magnesium aluminium silicate (MAS) glass ceramic with MgF₂ as a nucleating agent. The effect of sintering temperature on the density of compacted material was studied. Microstructure and machinability of samples obtained from both routes were investigated. They were also characterized for microhardness. Initial studies on material obtained by glass route reveal that these samples are superior to those obtained from sintered route in respect of their high voltage breakdown strength and outgassing behaviour. Outgassing rate of 10⁻⁹ Torr l·s⁻¹ cm⁻² and breakdown strength of 160 kV/cm were obtained. Different types of spacers, lugs, nuts and bolts have been prepared by direct machining of the indigenously developed glass ceramic.     

Synthesis and characterization of some chalcogenides of AIB2IICIIID4VI composition

A number of quaternary diamond-like semiconducting phases of A^IB₂^IIC^IIID₄^VI composition (A^I = Cu,Ag; B^II = Zn, Cd; C^III = Ga, In; D^VI = Se,Te) were investigated. Microstructure, DTA and roentgenographic examinations, carried out on samples obtained by direct synthesis, show that the characteristics of homogeneity and single-phase seem to be restricted to copper (CuB₂^IIC^IIID₄^VI) and silver (AgCd₂InTe₄) based compositions, characterized by a generally incongruent metling and by cubic or hexagonal cells.     

Synthesis,structural characterization and some properties of a germanic analogue of phillipsite

Germanic phillipsite, with the chemical formula K₂O·Al₂O₃·2GeO₂·xH₂O, has been synthesized at 90°C from K⁺ containing gels. The parameters of its primitive (tetragonal) unit cell are : $\text{a}\text{=}\text{b}\text{= 14.515}\text{A}\text{?}$ and $\text{c}\text{= 9.733}\text{A}\text{?}$. IR spectroscopy shows that all the absorption bands are shifted towards longer wavelengths. The structural stability towards ion-exchange has been followed by X-ray diffraction. Adsorption isotherms of N₂ and H₂O have been measured. The pore opening of K-germanic phillipsite is approximately 3 Å.     

几种新型高含磷含氮聚磷酰胺阻燃剂的合成与表征

以螺环季戊四醇双磷酸酯二酰氯（SPDPC）和苯基二氯磷酸酯（PDCP）为酰氯单体,分别与哌嗪及乙二胺通过溶液缩聚合成了4种聚磷酰胺阻燃剂——聚哌嗪季戊四醇双磷酸酯（PPS）、聚乙二胺季戊四醇双磷酸酯（PES）、聚哌嗪苯基磷酸酯（PPP）及聚乙二胺苯基磷酸酯（PEP）。以IR、1H NMR,31 P NMR、元素分析、TGA表征其结构及热性能,以乌氏粘度计测定PPS与PES特性黏度,结果发现反应18h聚合度最大,分别为0.19和0.21dL/g。以激光解吸电离-飞行时间质谱仪（MALDI-TOF MS）表征PPP与PEP分子量及组成。结果表明聚合度均在7～8之间。     

Characterization of some bioglass–ceramics

Controlled crystallization were carried out to convert some selected bioglasses to their corresponding bioglass–ceramics. Nucleation and crystallization regimes were carried out by parameters obtained from diloatometric measurement and differential thermal analysis (DTA). The formed crystalline phases were identified using X-ray diffraction investigation. Complete surface analyses were performed utilizing scanning electron microscopy.

Also, the infrared reflection spectroscopy of the bioglass–ceramics were measured before and after immersion for prolonged times in simulated body fluid and the results were compared with the same behavior for the parent bioglasses.

Experimental results indicate the formation of two main crystalline phases of sodium calcium silicate beside three other crystalline phases formed according to the change in the bioglass composition, namely, calcium sodium borate, calcium phosphate and calcium silicate. The bioactivity rate determined by the infrared reflection spectroscopy revealed slight retardation with the bioglass–ceramics except in the bioglasses containing high SiO₂ content.     

Dielectric properties of some hot-pressed nitrogen ceramics

The dielectric properties of some hot-pressed nitrogen ceramics have been measured at room temperature over the frequency range 200 Hz to 75 MHz and also at 9.3 GHz; low frequency measurements were also made at temperatures up to 500° C. The materials examined were Si₃N₄, 5.0 wt % MgO/Si₃N₄ and two sialons Si_(6–z)·Al _z ·O_z·N_(8–z) havingz = 4.0 and 3.2 respectively. At room temperature, the variation of the real part of the conductivity with frequency over the range 200 Hz to 9.3 GHz followed () ⁿ, withn = 0.9. The dielectric constant , and loss tan , both fell slightly over this frequency range, the average values at 10⁵ Hz being about 9.5 and 5.5 × 10^–3, respectively. The data fits well with the universal dielectric law, ^–1 (n < 1) and approximately fits the Kramers-Kronig relation ()/(() – = cot(n/2). This behaviour applies also at temperatures up to 500° C except that the value ofn decreases as the temperature increases. The effects may be caused by either dipolar or hopping charge phenomena.     

Fabrication and characterization of highly porous mullite ceramics

Highly porous mullite ceramics were fabricated by a reaction-bonding technique from a powder mixture of Al₂O₃ and SiC, with graphite particles as the pore-forming agent. The effects of sintering temperature on porosity and strength as well as pore size and surface area were investigated. It has been shown that the strength and pore size increase but the porosity and surface area decrease with the increase in sintering temperature. Due to the formation of a fine-grained microstructure with well-developed necks, an average strength up to 106 MPa was achieved at a porosity of 32.4%. On the other hand, a relatively high surface area of 12.4 m² g⁻¹ was obtained for a 61% porous mullite ceramic, which was observed to have a good thermal-shock resistance to crack propagation.     

Synthesis and characterization of new precursors to nearly stoichiometric SiC ceramics: Part 1 The copolymer route

Organosilicon polymers with a (C/Si (atomic ratio)<1.28) exhibiting Si–Si and Si–CH2–Si linkages in their backbone have been prepared and characterized by multinuclear magnetic resonance and infrared spectroscopies, size exclusion chromatography and thermogravimetric analysis. These precursors give SiC ceramics with a C/Si (atomic ratio)1.14 and a relatively low oxygen content (between 1.5–3 at %).     

Synthesis and characterization of new precursors to nearly stoichiometric SiC ceramics: Part II A homopolymer route

An original route to SiC ceramics possessing low free carbon(3.8 at%) and oxygen (1 at%) contents is reported. It consists of the polycondensation of 2,4-dichloro-2,4-disilapentane, prepared by Grignard reaction of dichloromethane on methyldichlorosilane. The undesired remaining chlorine was eliminated via a subsequent reduction using lithium aluminum hydride. The synthesis of the ceramic precursor was achieved by thermolysis under argon at atmospheric pressure, with the evolution of hydrogen and methane. The pyrolysis of the precursor provided SiC ceramics in an excellent yield (79%).     

Synthesis and characterization of some binary chalcogen compounds by explosive laser irradiation and heat treatment

The thin film preparation of Se, Ge, Sn monolayers and also binary chalcogenide alloys with their various structures and morphologies have been thoroughly studied. A new phase of the composite materials was identified. The short range ordering structure of chalcogens when mixed up with four-fold-coordinated atoms like Ge and Sn produce alloys or compounds with a certain specific characteristic. Laser impulse on these materials caused rapid cooling allowing the materials to form alloys. The optical measurements of the chalcogen films are reported. The transmittance versus wavelength measurement in the UV-VIS-NIR was studied and the optical band gaps of the films were calculated to be 1.48 eV for Ge-Se and 1.65 eV for Sn-Se for the wavelength range 300-1100 nm.     

Microstructural characterization of reaction-formed silicon carbide ceramics

Microstructural characterization of two reaction-formed silicon carbide ceramics has been carried out by interference layering, plasma etching, and microscopy. These specimens contained free silicon and niobium disilicide as minor phases with silicon carbide as the major phase. In conventionally prepared samples, the niobium disilicide cannot be distinguished from silicon in light optical micrographs. After interference layering, all phases are clearly distinguishable. Backscattered electron imaging and energy-dispersive spectrometry in the scanning electron microscope confirmed the results obtained by interference layering. Plasma etching with CF₄ + 4% O₂ selectively attacks silicon in these specimens. It is demonstrated that interference layering and plasma etching are very useful techniques in the phase identification and microstructural characterization of multiphase ceramic materials.     

Synthesis and characterization of BaTiO<Subscript>3</Subscript>-based X9R ceramics

The effects of (Na_0.5Bi_0.5)TiO₃ (NBT) and MgO addition on the dielectric properties and microstructures of BaTiO₃ (BT) ceramics were investigated. NBT was first added to Nb₂O₅-doped BT system. As NBT content increases from 0 to 0.2 mol, the Curie temperature of the systems shifts to high temperatures and dielectric constant peak at T _c is suppressed evidently. The variation of capacity (ΔC/C _20 °C (%)) of the system at 200 °C decreases with increasing NBT content from 0.1 to 0.2 mol, but that of −55 and 125 °C increases monotonously. The stable temperature characteristics of the dielectric properties improved by NBT doping would be connected with the distortion and deformation of the structure induced by substitution of Na⁺ and Bi³⁺ into Ba sites. MgO was employed to further flatten the ΔC/C _20 °C–T curve. It is very helpful for this ceramic system to satisfy the requirement of EIA-X9R specification on ΔC/C _20 °C and still keep a satisfied dielectric constant. The addition of MgO improved effectively the temperature stability of the dielectric properties. Changes of the crystalline structure and microstructure induced by MgO doping might contribute to these improvements.     

Synthesis of oxygen-free aluminium nitride ceramics

The aluminum nitride raw material in the form of powder was synthesized using the Self propagating High temperature Synthesis (SHS) method which provides no oxygen impurities. Then AIN powder was sintered to the full density without sintering additives and under a high pressure in a belt apparatus. For the AIN ceramics obtained the temperature dependences of the thermal diffusivity were measured with the laser-flash method. Finally we produced oxygen-free aluminium nitride ceramics with parameters comparable with theoretical data.     

Sintering and characterization of fully dense aluminium nitride ceramics

Aluminium nitride ceramics with no sintering additives could be densified to close to theoretical density (99.6% theoretical) by pressureless sintering of tape-cast green sheets at 1900 °C for 8 h. The thermal conductivity and bending strength of the specimens were 114 Wm^–1 K^–1 and 240 MPa, respectively. The effect of Y₂O₃ additive on sinterability, thermal conductivity and microstructure of aluminium nitride ceramics was investigated. Thermal conductivity increased with increasing amount of Y₂O₃ additive, sintering temperature and holding time at the sintering temperature. Samples with a thermal conductivity up to 258 Wm^–1 K^–1 were fabricated by elimination of the grain-boundary phase.