Assessment of Temperature Measurements Using Thermocouples at NIS-Egypt

Thermocouples are increasingly used in industry and research. For many industrial heating processes, particularly those carried out at high temperatures, a thermocouple is the most convenient and simple instrument for temperature measurement. In some instances, it is the only feasible method. The aim of this study is to select and recommend the best thermocouples from both base and noble metals to users in industrial and scientific institutions. Different types of thermocouples and calibration methods are described. From this work, the Nicrosil–Nisil thermocouple has been proposed as the best base metal thermocouple and the Au/Pt thermocouple is the most recommended as a substandard up to 1,000 °C.     

Corrosion behavior of Cu–SiO<Subscript>2</Subscript> nanocomposite coatings obtained by electrodeposition in the presence of cetyl trimethyl ammonium bromide

Copper silica composite coatings are an attractive alternative to chromium and nickel coatings in order to avoid environmental problems and for application in electrical devices. However, co-deposition of SiO₂ particles with metals occurs to a rather limited extent, generally under 1%, due to the hydrophilicity of SiO₂, which makes the incorporation of particles in a metallic matrix difficult. To overcome this drawback, the influence of cetyl trimethyl ammonium bromide (CTAB) on the deposition and corrosion behavior of Cu–SiO₂ coatings on steel has been studied. It was established that CTAB plays a beneficial role in SiO₂ suspension stabilization, promotes the co-deposition of nanoparticles in the copper matrix and improves the deposit morphology and structure. Consequently, a higher corrosion resistance of Cu–SiO₂ deposits obtained in the presence of CTAB was noticed. The most important effect was observed in the case when CTAB was used in concentration of 10⁻³ M in the electroplating bath.     

Nucleation and growth mechanism of apatite on a bioactive and degradable ceramic/polymer composite with a thick polymer layer

Nucleation and growth mechanism of apatite on a bioactive and degradable PLLA/SiO₂–CaO composite with a thick PLLA surface layer were investigated compared to that on a bioactive but non-degradable polyurethane (PU)/SiO₂–CaO composite with a thick PU surface layer. The bioactive SiO₂–CaO particles were made by a sol–gel method from tetraethyl orthosilicate and calcium nitrate tetrahydrate under acidic condition followed by heat treatment at 600 °C for 2 h. The PLLA/SiO₂–CaO and PU/SiO₂–CaO composites were then prepared by a solvent casting method which resulted in thick PLLA and PU surface layers, respectively, due to precipitation of SiO₂–CaO particles during the casting process. Two composites were exposed to SBF for 1 week and this exposure led to form uniform and complete apatite coating layer on the PLLA/SiO₂–CaO composite but not on the PU/SiO₂-CaO composite. These results were interpreted in terms of the degradability of the polymers. A practical implication of the results is that a post-surface grinding or cutting processes to expose bioactive ceramics to the surface of a composite with a thick biodegradable polymer layer is not required for providing apatite forming ability, which has been considered as one of the pragmatic obstacles for the application as a bone grafting material.     

Synthesis of spherical Al2O3 and AlN powder from C@Al2O3 composite powder

A novel approach has been taken to produce (1) spherical Al₂O₃ particles by decarbonisation and (2) spherical AlN particles by nitridation and subsequent decarbonisation of C@Al₂O₃ composite particles. C@Al₂O₃ composite particles have been prepared by heterogeneous nucleation and crystallisation of Al(NO₃)₃ on surfactant encapsulated carbon nano particles followed by evaporative decomposition of the nitrate. Overpressure (0.4 MPa) of nitrogen and a temperature range (1723–1873 K) have been used for nitridation. Whiskers as well as spherical particles of AlN have been observed in the final product. The final product has been characterised by X-Ray Diffraction, Scanning Electron Microscope and Carbon–Hydrogen–Nitrogen content analysis by Elemental Analyser and the mechanism of the nitridation reaction has been analysed. The average size of the spherical AlN particles consisting of crystallites in nano-dimensions (30–50 nm) could be varied from 100 nm to 8 μm by changing the composition of the sol.     

Wear resistance of electrodeposited Ni–B and Ni–B–Si<Subscript>3</Subscript>N<Subscript>4</Subscript> composite coatings

The wear resistance of electrodeposited (ED) Ni–B and Ni–B–Si₃N₄ composite coatings is compared. The effect of incorporation of Si₃N₄ particles in the ED Ni–B matrix on the surface morphology, structural characteristics and microhardness has been evaluated to correlate the wear resistance. The wear mechanism of ED Ni–B and Ni–B–Si₃N₄ composite coatings appears to be similar; both involve intensive plastic deformation of the coating due to the ploughing action of the hard counter disc. However, the extent of wear damage is relatively small for ED Ni–B–Si₃N₄ composite coatings.     

Effect of mechanical milling on the corrosion behavior of Al–Zn/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite in NaCl solution

Ceramic particle reinforced aluminum metal matrix composites (MMCs) have resulted in potential use in aerospace and automobile industries. The composites have been processed by mechanical milling followed by traditional powder metallurgy route. The Al crystallite size is reduced to 27 nm after 60 h of milling. Results of the corrosion tests, evaluated using the potentiodynamic method in the NaCl solution, indicate that corrosion of the investigated composite materials depends on the weight fraction of the reinforcing particles. It has been found out, based on the determined anode polarization curves, that the investigated materials are susceptible to pitting corrosion. Moreover, experimental results suggest that the milled composite material Al–Zn/Al₂O_3p has higher corrosion resistance in the selected environment compared to unmilled composite Al–Zn/Al₂O_3p. Polarization curves show that the milling procedure improves the composite corrosion resistance in passive conditions. This is illustrated by the corrosion potential, which becomes nobler with milling.     

Correlation between the phase composition of composite YBa2Cu3O7−δ+xMeO superconductors and their strength characteristics

Experimental results on the doping of YBa₂Cu₃O_7−δ superconducting ceramic with various metals (Ti, Zr, Ag, Hf, Ta, and W) are summarized. Some conclusions are drawn on the degree of chemical interaction between the metals and the main phase of the composite responsible for the superconducting properties of the material as a whole. An assessment is also made if the influence of doping on the strength characteristics, which vary in the composite as a result of different effects examined in this study. Pis’ma Zh. Tekh. Fiz. 23, 32–37 (February 12, 1997)     

In vitro studies of novel CaO–SiO2–MgO system composite bioceramics

In this study, a series of CaO–SiO₂–MgO composites with different β-CaSiO₃ (CS)/Mg₂SiO₄ (M₂S) composite ratios were prepared to produce new bioactive and biodegradable biomaterials for potential bone repair. The mechanical properties of CS–M₂S composites increased steadily with the increase of M₂S ratios in composites. Dissolution tests in Tris–HCl buffer solution showed obvious differences with different CS initial composite ratio in composites. The dissolution rate increased with the increase of CS composite ratio, which suggested that the solubility of composites could be tailored by adjusting the initial CS/M₂S composite ratio. Formation of bone-like apatite on a range of CS–M₂S composites with CS weight percentage ranging from 0 to 100 has been investigated in simulated body fluid (SBF). The presence of bone-like apatite layer on the composite surface after soaking in SBF was demonstrated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM). The results showed that the apatite formation ability of the CS–M₂S composite with 70% CS was detected after 10 days immersion. In vitro cell experiments showed that the 50 and 70% CS composites supported greater osteoblast-like cell proliferation as compared with pure M₂S (p < 0.05). The results of this study suggested that the CS–M₂S composites with 50 and 70% initial CS composite amount might be more suitable for preparation of bone repair materials.     

Preparation of SiC–SiO<Subscript>2</Subscript>–CuO composites

SiC–SiO₂–CuO composite particles were prepared by double coating processes. SEM, DSC-TG, XRD techniques were carried out to characterize the coated composite particles and sintered compacts. It was found that a core-shell structure was constructed in the composite particles with the core of SiC and the shell of SiO₂–CuO. Cu–silicides were detected in hot-pressed compacts. SiO₂ might decompose at 1,300 °C. The decomposition product of Si would result in the transformation from Cu_6.69Si into Cu₃Si.     

Structural transformations of the wurtzitic boron nitride-titanium nitride composition at high pressure and temperature

The results of the electron microscopy and XRD examination of structural transformations of the wurtzitic boron nitride-titanium nitride powder composite obtained by plasmachemical synthesis under a pressure of 8 GPa and temperature of 1100–1700°C have been considered. The interaction in this system has been shown to yield Ti-B-N solid solutions. It has been found that at 1300°C continuous BN-TiN interfaces form and at T ≥ 1500°C a monolithic layer, which is a nanodispersed TiN-TiB₂ composite, is formed between nitride boron grains.     

Current-activated pressure-assisted sintering (CAPAS) and nanoindentation mapping of dual matrix composites

Titanium boride (TiB_w) whiskers are currently recognized as one of the most compatible reinforcements for titanium (Ti) that have positively affected its wear resistance and stiffness. The fracture toughness and ductility have, however, been reported to deteriorate at increased TiB_w volume fractions, mainly due to the interlocking of these brittle TiB whiskers. This article investigates the processing of dual matrix Ti–TiB_w composites, where microstructures are generated consisting of TiB_w–Ti composite regions separated by a ductile, predominantly Ti, outer matrix. This microstructural design has the potential to prevent the continuous TiB_w interlocking over the scale of the composite (at high TiB_w volume fractions), and promote improved toughness of the material. The processing of these unique composites using current-activated pressure-assisted sintering (CAPAS) is discussed in this article. The effect of processing temperature on the microstructure and hardness of Ti–TiB_w dual matrix composites is also discussed, together with a simultaneous imaging and modulus-mapping nanoindentation technique used to characterize the composites     

Effect of thermal residual stresses on the strength for both alumina/Ni/alumina and alumina/Ni/nickel alloy bimaterials

This paper describes some technical limitations encountered in joining ceramics–ceramics or ceramics–metals, and how, to some extent, they have been practically overcome. The effect of the residual stresses on the strength of joints fabricated between alumina–alumina or alumina and the nickel base alloy HAYNES^? 214™ using a solid-state bonding technique with Ni interlayer was studied. Finite element analyses (FEA) for the elastic–plastic and elastic–plastic–creep behavior have also been used to better design the joints and to predict their performance. It was found that the residual stresses caused by the thermal expansion mismatch between alumina (Al₂O₃) and the Ni-based superalloy (HAYNES^? 214™) have severely deteriorated the joints compared to Al₂O₃–Al₂O₃ joint fabricated with the same solid-state bonding parameters. The high residual stresses zones obtained through the FEA simulation fitted well with the fractographic observations of the Al₂O₃/Ni/HAYNES^? 214™ joints. Also, in order to use the joint material as a structural material, the study about the effect of geometrical parameters has been performed. Optimal geometries have been determined.     

Production, bonding strength and electrochemical behaviour of commercially pure Ti/Al2O3 brazed joints

The brazing of commercially pure titanium to Al₂O₃ has been studied. Two different brazing alloys within the Ag–Cu–Ti system and pure silver were selected as bonding agents. Titanium hydride (TiH2) additions were also tested, with the aim of improving the wetting of the ceramic surface by the melted brazing alloy. The mechanical and electrochemical behaviour of the produced joints was assessed, and related to chemical and morphological features resulting from an analysis by scanning electron microscopy and energy dispersive spectroscopy. It was possible to produce joints presenting high integrity, good strength and high resistance to corrosion. The best results were obtained when using an Ag–26Cu–3Ti brazing alloy. The addition of TiH₂ increased the mechanical properties, leading to a maximum bonding strength of 80±8 MPa, as determined in three-point bending tests. In most of the cases, for a maximum deflection of 5 mm, there was only a partial detachment of the ceramic/metal joints. The lowest values for the corrosion rates (i_corr=1.38 μA cm−2) determined in potentiodynamic experiments also correspond to the use of the Ag–26Cu–3Ti brazing alloy. The bonding strength and electrochemical results could be explained in terms of the different chemical compositions of the interfaces. The use of TiH₂ additions proved to be quite effective, allowing for the replacement of the usual metallizing and plating pre-treatments needed for the brazing of ceramics to metals. This revised version was published online in November 2006 with corrections to the Cover Date.     

Interface microstructure and shear strength in the diffusion brazing joint of TiC–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramic composite with W18Cr4V tool steel

The diffusion brazing of TiC–Al₂O₃ ceramic composite with W18Cr4V tool steel is realized by using Ti and Cu filler metals at 1500°K for 1 h under a pressure of 15 MPa in a vacuum of 10^–5 Pa. Thus, a brazed TiC–Al₂O₃/W18Cr4V joint was obtained with an interface shear strength of up to 105 MPa. The microstructural characteristics of the TiC–Al₂O₃/ W18Cr4V joint are studied by using a scanning electron microscope (SEM) with energy-dispersion spectroscopy (EDS) and X-ray diffractometer (XRD). The results indicated that the interface layer with a thickness of 90 μm was formed between TiC–Al₂O₃ and W18Cr4V steel. The Ti and Cu filler metals were completely fused and diffused to react with Al and C from the substrates, whereas Ti₃Al, Ti₃AlC₂, TiC, and CuTi₂ were produced in the TiC–Al₂O₃/W18Cr4V joint.     

Quantum-chemical calculation of the adhesion energy of contacting dissimilar metals in a medium

We have constructed a model of the contact interaction of dissimilar metals Al–Fe, Al–Cr, Cu–Al, and Cu–Fe in the presence of particles of a corrosive medium. We have used here the quantum-chemical method of density functionals with the exchange-correlation functional of generalized gradient approximation and LANL2DZ basic set in the cluster approximation. The adhesion energy for clusters of dissimilar metals has been calculated, and its dependence on the composition of corrosive medium has been evaluated. We have established that the adhesion energy of dissimilar metals is determined by the summary contribution of the surface energies of both contacting metals. It has a “quasichemical character,” i.e., its values are intermediate between the chemisorption energy and the energy of forces of physical nature. We have established a substantial change in the distribution of surface charges and spin electron densities of contacting metals in the course of their interaction with water molecules, chlorine ions, and glycerol molecules.     

Feasibility, tailoring and properties of polyurethane/bioactive glass composite scaffolds for tissue engineering

This research work aims to propose highly porous polymer/bioactive glass composites as potential scaffolds for hard-tissue and soft-tissue engineering. The scaffolds were prepared by impregnating an open-cells polyurethane sponge with melt-derived particles of a bioactive glass belonging to the SiO₂–P₂O₅–CaO–MgO–Na₂O–K₂O system (CEL2). Both the starting materials and the composite scaffolds were investigated from a morphological and structural viewpoint by X-ray diffraction analysis and scanning electron microscopy. Tensile mechanical tests, carried out according to international ISO and ASTM standards, were performed by using properly tailored specimens. In vitro tests by soaking the scaffolds in simulated body fluid (SBF) were also carried out to assess the bioactivity of the porous composites. It was found that the composite scaffolds were highly bioactive as after 7 days of soaking in SBF a HA layer grew on their surface. The obtained polyurethane/CEL2 composite scaffolds are promising candidates for tissue engineering applications.     

Effect of high energy ball milling on the displacement reaction in particulate reinforced Al–Si–Cu alloy matrix composite powders

The displacement reaction between Al and SiO₂ in an Al–3wt%Cu–3wt%Si–9wt%SiO₂ powder mixture has been studied when the mixture had been ball-milled, and compared with the reaction in the as-mixed powder. Diffusion couples consisting of Al/SiO₂ were formed during ball milling. The size of the composite powder particles and the diffusion couples was reduced by increasing the ball milling time. Differential thermal analysis and X-ray diffraction results showed that the displacement reaction between Al and SiO₂ did not occur in the as-mixed powder, but occurred in the as-milled powders in the temperature range of 640–680 °C. Furthermore, the onset temperature of the displacement reaction shifted to lower temperatures after increasing the ball milling time. On the basis of these results the milled powder was sintered at 640 °C in order to produce an Al–Cu–Si matrix composite reinforced with homogeneously distributed submicron-sized Al₂O₃ particles. This is much lower than the temperature required for the same reaction in other processes which are used to produce such composites, such as the melting infiltration process.     

Synthesis of aluminium matrix composites containing nanocrystalline oxide phases

Using nanocrystalline particles of mullite and zirconia respectively with diameters in the range 20–30 nm prepared by a sol-gel route, aluminium metal-matrix composites have been synthesized. A hot pressing technique has been used with temperatures varying from 450–610°C. The vickers hardness values for the composites are found to be substantially higher than that of pure aluminium. An order of magnitude increase in hardness is achieved when Al₅Mo phase is grown in the composite.     

Enhancement of the Seebeck coefficient in touching M/Bi–Te/M (M = Cu and Ni) composites

The resultant Seebeck coefficient α of the touching p- and n-type M/Bi–Te/M (M = Cu and Ni) composites was measured as a function of z at a scan step of 0.5 mm using thermocouples set at three different intervals of s = 4, 6.5 and 8 mm, where s is the interval between two probes and z is the distance from the center of Bi–Te compound to the middle of two thermocouples. Bi–Te compounds have a thickness of t _Bi–Te = 6 mm but the thickness t _M of both end metals sandwiching their compounds was varied from 0.5 mm to 6 mm. The composites were compacted tightly at a force of about 10 N by a ratchet. When two probes are placed on both end metals, the resultant α was significantly enhanced and exhibited a tendency to increase as s approaches t _Bi–Te, like the welded composites. The enhancement in α is attributed to the contribution from the barrier thermo-emf generated near the interface. When the thickness t ₀ of metal outside two probes set at s = 6.5 mm was increased from 0.25 mm to 5.75 mm, the averaged α for M = Cu and Ni was increased by 3.8% in the p-type composite, while reversely it was decreased by 4.8% in the n-type one. It was first observed that t ₀ also has a significant influence on the resultant α. The maximum α of the p- and n-type Ni/Bi–Te/Ni composites then reached great values of 264 μV/K at t _M = 6 mm (corresponding to t ₀ = 5.75 mm) and −280 μV/K at t _M = 1.2 mm (corresponding to t ₀ = 0.95 mm), respectively, which are 29% and 23% larger in absolute value than their intrinsic α values. These maximum α were barely changed with time. It was thus found that the barrier thermo-emf is generated steadily even in touching composites and the resultant α is highly sensitive to the position of leads connected to the metal electrode of a thermoelement.     

Metal–ceramic composite layers on stainless steel through the combination of electrophoretic deposition and galvanic processes

The use of metal–ceramic composite layers is of considerable technical interest for many areas of application. The use of electrochemical processes makes it possible to realize coatings on stainless steel which combine the properties of the metals with those of ceramics in an outstanding manner. The process presented here is based on a combination of electrophoretic and electrolytic deposition. At the same time, a very high ceramic ratio is attained in comparison to electrolytic dispersion depositions. It was therefore possible to achieve both nickel–zirconium oxide as well as a copper–zirconium oxide coatings with strong adhesive bonds on stainless steel. A preliminary nickel plating or preliminary copper plating of the stainless steel substrate was first realized. A nanoscale zirconium oxide powder (Tosoh TZ-8Y) from an ethanolic suspension was then applied electrophoretically onto this layer and sintered to an open-porous layer with a porosity of 40–50%. After this, the metal was galvanically infiltrated into the pores. An annealing process was then carried out to improve the layer bonding. Solid-state physical tests reveal that a good material bonding of the composite layer onto the substrate occurred as a result of diffusion processes. Metal–ceramic composite layers can be produced through a combination of electrophoretic and electroplating technology with strongly bond on the substrate by a final heat treatment.