Argon Gas Protection Research Articles

Fabrication of superconducting magnesium diboride thin films by electron beamannealing

The technique of electron beam annealing for fabricatingMgB2 thin films hasbeen explored. MgB2 thin films were prepared by e-beam evaporation of M–B precursor films on 6H–SiC(0001) substrates followed by ex situ electron beam annealing without any extraMg vapor or argon gas protection. The very short annealing duration, about 1 s,effectively prevented volatilization and oxidation of Mg and decomposition ofMgB2. In comparisonwith the MgB2 thin films grown by other techniques, our films show mediumqualities including a superconducting transition temperature ofTconset ∼ 35.3 K, a transition widthΔTc ∼ 0.2 K, and a criticalcurrent density of Jc(5 K, 0 T) ∼ 3.2 × 106 A cm − 2. Such an electron beam annealing technique has potential for the fabrication of large-scaleMgB2 thin filmsas well as MgB2 wires and tapes.

Copper extraction from copper ore by electro-reduction in molten CaCl 2–NaCl

Sintered solid porous pellets of copper sulfide (Cu 2S) and Cu 2S/FeS were electrolysed at a cell voltage of 2.2–2.8 V to elemental Cu, S and Cu, Fe, S, respectively in molten CaCl 2–NaCl at 800 °C under the protection of argon gas. The process parameters for optimal electrolysis are presented. The electrolysis products are characterized by microscopic techniques and XRD. The product characteristics are linked to the process parameters. The direct electrolysis of the sulfide to copper with the emission of elemental sulphur offers an attractive green process route for the treatment of copper ore.

Brazing of diamond grits with Ag-Cu-Zn alloy activated by Cr or Ti powder under different environments

In this study, Ag-Cu-Zn brazing alloy together with Cr or Ti powder had been used to braze diamond grits under different environments, such as: air, vacuum, argon gas protection, salt covering and carbon powder covering. The microstructure on the interfaces of diamond grits, brazing alloy and steel substrate was examined by Scanning Electron Microscopy (SEM) and optical microscopy. The results showed that by adding Cr powder, the diamond grits could be brazed onto the steel substrate in air and owned enough bonding strength and wear resistance when grinding granite. By adding Ti powder, the diamonds could be well brazed in vacuum or in the air with the protection of carbon powder. In brazing, the migration of Cr or Ti element to the surface of diamond and the forming of Cr or Ti rich area had significantly improved the wettability of the brazing alloy to the diamond grits.

Study on Properties of Carbon Nanotube/Magnesium Matrix Composite

Under the protection of argon gas, carbon nanotube reinforced magnesium metal matrix composite was made by stirring carbon nanotube into magnesium melts and formed by die casting. TEM and EDS methods were introduced to analyze boundary structure and chemical composition between carbon nanotube and magnesium metal matrix. The mechanical carbon nanotube properties of the composite were tested. Nickel chemical plating surface of carbon nanotube is favorable to adhesion of carbon nanotube to magnesium. Tests show that carbon nanotube, especially chemical nickel-plated one, has excellent role in strengthening the magnesium. The structure of magnesium was fined .The tensile strength, elongation, hardness and elastic modulus of the composite are improved.

Microstructure and Fracture Surfaces of Carbon Nanotubes/Magnesium Matrix Composite

Using carbon nanotubes (CNTs) as reinforced phase, it was made to carbon nanotubes/Magnesium matrix composite by the foundry method in Argon gas protection. The experiment results show that CNTs can strengthen the mechanical properties of the CNTs/Magnesium matrix composite, and tensile strength and elongation ratio are greatly improved. Furthermore, the plating CNTs are better than un-plating CNTs in strengthening effects. Additionally the quantity of CNTs can not be too great, or the properties will be descended to a great extent without distraction of CNTs. Tensile strength has been higher by 150 % and the elongation ratio is higher by 30 % than matrix’s at best, and the fracture of the composite sample has a character of dimples.

Effect of sample radius on stability of electromagnetic levitation melting

Based on the power dissipating model of spherical sample in free convection gas medium and the expression of input power, the model of temperature calculation for electromagnetic levitation melting sample was established. Considering the limitation of levitation force and levitation sample temperature, the principle of stability levitation zone computation was determined. A spherical sample (ThDy)Fe2 under the protection of argon gas was examined, and the effect of radius of levitation sample and perturbation on the stable levitation zone was investigated. The results show that longitudinal perturbation and transverse perturbation can shorten the length of stable levitation zone and the range of levitation sample radius. By increasing the sample radius and weakening the perturbation the electromagnetic levitation melting stability of sample can be improved.

Properties and structure of magnesium matrix composite reinforced with CNTs

By using high pure Magnesium (99.9 wt%) as matrix and multi-walled bended carbon nanotubes (CNTs) as reinforced phase, carbon nanotubes/magnesium matrix composite was prepared by the foundry method under the argon gas protection, and its mechanical properties were tested. The interface structure and component of plating and un-plating carbon nanotubes were analyzed by TEM and EDS, and the action mechanism was discussed. The experiment results show that the CNTs can strengthen mechanical properties of the nanotube-reinforced Mg matrix composite, the tensile strength and elongation ratio are greatly improved. Furthermore, the plating CNTs are better than un-plating CNTs in strengthening effects. The tensile strength is inereased by 150% and the elongation ratio is increased by 30% than that of matrix when content of CNTs is 0.67 wt%.

Stable Levitation Zone of Sample in the Electromagnetic Levitation Melting

A model has been proposed for calculating the temperature of spherical samples levitated in the general levitation inducers under the protection of inert gas. Considering the limits of levitation force and sample temperature, a spherical (TbDy)Fe 2 sample under the protection of argon gas was examined, and the effect of structural parameters of levitation inducers, radius of levitation sample and frequency of power on the stable levitation zone was investigated. The present analysis enables us to improve the levitation stability by increase of the radius of samples, the turns and coning, the radius of down levitation-coil and decrease of the space length of down levitation-coil.

Physical and mechanical properties of cast under vacuum aluminum alloy 2024 containing lithium additions

Physical and mechanical properties of aluminum alloy 2024 containing lithium additions were investigated. Lithim (2, 3, and 4 wt%) was added to the alloy of 2024. Melting was carried out in an induction furnace under argon gas protection; casting was performed under vacuum. The cast material was hot extruded to produce tension test rods. To obtain the maximum strength and hardness, the specimens were solution heat treated at 495°C, then quenched in water at room temperature. They were then aged. For the purposes of comparison, some of the specimens were melted under argon gases, but casting was done without vacuum. All the specimens were subjected to tension and hardness tests. In this study, an increase of 6% in the modulus of elasticity and 3% decrease in the density were obtained for 1% lithium added to the alloy. The mechanical properties of the alloys cast under vacuum were found to be better than those cast without vacuum. Whatever the lithium percent in the alloys, all the mechanical properties reached their maximum level in 1 week of natural aging; for artificial aging, maximum levels were reached at 120°C in 24 h, at 160°C in 16 h, at 190°C in 12 h, and 200°C in 2 h. By increasing the lithium percent, the specific elastic modulus (E/ρ) of the alloy increased rapidly but the specific strength (σ/ρ) remained constant. Thus, aluminum lithium alloys that are difficult to manufacture by known methods can be manufactured safely by the vacuum metallurgy method.

An Investigation on the Elastic Modulus and Density of Vacuum Casted Aluminum Alloy 2024 Containing Lithium Additions

The elastic modulus and density of (2024+LiX) alloys are investigated. To the alloy of 2024, the weight percentages of lithium added are 2,3, and 4. Melting is carried out in an induction furnace under argon gas protection; casting is done under vacuum. To obtain the maximum strength and hardness, the specimens are solution heat treated under 495 C and quenched in water at room temperature. Then, they are aged naturally and artificially. For the purposes of comparing, some of the specimens are melted under argon gas, but casting is done without vacuum. All the specimens are subjected to tension tests.

High efficient extraction of M@C 2n (M = La, Ce) by a high pressure and high temperature method

A high pressure and high temperature method was used to efficiently extract on a large scale metallofullerenes M@C 2n (M=La,Ce) in a closed vessel under argon gas protection. With pyridine as the HPHT solvent, about 60–80% M@C 2n and 30–55% M@C 82 can be enriched, M@C 82 is dissolved selectively; With toluene as the HPHT solvent, M@C 2n can also be efficiently extracted, especially M@C 74, which is a new member of M@C 2n soluble species.

Sterilisation of canine anterior cruciate allografts by gamma irradiation in argon. Mechanical and neurohistological properties retained one year after transplantation

Bone-ACL-bone allograft transplantation is a potential solution to the problem of reconstruction of the anterior cruciate ligament (ACL), but sterilisation by gamma irradiation or ethylene oxide causes degradation of the graft. We have studied the biomechanical and histological properties of deep-frozen canine bone-ACL-bone allografts sterilised by gamma irradiation (2.5 Mrad) under argon gas protection. Particular attention was paid to their collagen structure and neuroanatomy compared with those of non-irradiated allografts. We used 60 skeletally mature foxhounds. In 30 animals one ACL was replaced by an irradiated allograft and in the other 30 a non-irradiated graft was used. In both groups the graft was augmented by a Kennedy Ligament Augmentation Device. Examination of the allografts at 3, 6 and 12 months after implantation included mechanical testing, histology, collagen morphometry, neuroanatomical morphology (silver and gold chloride stain) and studies of the microvasculature (modified Spalteholz technique). At 12 months the irradiated ACL allografts failed at a mean maximum load of 718.3 N, 63.8% of the strength of the normal canine ACL. The non-irradiated allografts failed at 780.1 N, 69.1% of normal. All the allografts showed a well-orientated collagen structure one year after transplantation and there was no difference between the irradiated grafts and the others. The silver staining technique demonstrated Golgi tendon organs and free nerve endings within both groups of allografts. As in the normal ACL these structures were most commonly found near the surface of the graft and at its bony attachments. At 12 months the irradiated allografts showed slight hypervascularity compared with the non-irradiated grafts.(ABSTRACT TRUNCATED AT 250 WORDS)

Anterior cruciate ligament reconstruction using cryopreserved irradiated bone-ACL-bone-allograft transplants.

Bone-ACL-bone allograft transplantation has been investigated as a potential solution to reconstruction of the anterior cruciate ligament (ACL). To minimize disease transmission (e.g. the acquired immuno deficiency syndrome), bony and collagenous tissues should be sterilized. Recent animal studies indicate that gamma irradiation and ethylene oxide sterilization result in diminished histological and biomechanical properties. The purpose of the present study was biomechanical and histological determination of the fate of deep-frozen gamma-irradiated (2.5 Mrad) canine bone-ACL-bone allografts with argon gas protection. Particular attention was paid to collagenous and neuroanatomical morphology 3, 6 and 12 months after implantation, by comparison to a non-irradiated control group. Sixty skeletally mature foxhounds were operated on in this study, divided up in two groups of 30 dogs each. In group A animals the ACL was replaced by a deep-frozen (-80 degrees C) bone-ACL-bone LAD-augmented allograft subjected to 2.5 Mrad gamma irradiation with argon gas protection. The animals in group B received an LAD-augmented ACL-allograft transplant without gamma irradiation. All knees from both groups were evaluated 3, 6 and 12 months after implantation in regard to biomechanical properties, collagen morphology and routine histology (haematoxylin and eosin stain, polarization microscopy), neuroanatomical morphology (silver and gold chloride stain) and microvasculature (modified Spalteholz technique). The irradiated ACL allografts withstood a maximum load that was 63.8% (718.3 N) of the maximum load of normal ACLs after 12 months. By contrast, the non-irradiated allografts failed at 69.1% (780.1 N) of the maximum load of normal control ACLs.(ABSTRACT TRUNCATED AT 250 WORDS)