Soft mechanochemical synthesis of MgFe2O4 nanoparticles from the mixture of α-Fe2O3 with Mg(OH)2 and Fe(OH)3 with Mg(OH)2

Abstract

The influence of long term soft milling of a mixture of (1) Mg(OH)₂ and α-Fe₂O₃ and (2) Mg(OH)₂ and Fe(OH)₃ powders in a planetary ball mill on the reaction synthesis of nanosized MgFe₂O₄ ferrites was studied. Soft mechanochemical reaction leading to formation of the MgFe₂O₄ spinel phase was followed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and magnetisation measurements. The spinel phase formation was first observed after 5 h of milling and its formation was completed after 15 h in case (2). The synthesised MgFe₂O₄ ferrite had a nanocrystalline structure with a crystallite size of about 10 and 15 nm respectively for cases (1) and (2). Measurements after 15 h of milling show magnetisation values of 15·23 and 10·14 J T^–1 kg^–1 respectively for cases (1) and (2).     

Thermal properties of new copper matrix composite reinforced by β-eucryptite particulates

Abstract

Cu matrix composites with different volume fraction of Ag coated β-eucryptite particulates were successfully fabricated by powder metallurgy method. Low thermal expansion coefficient and high thermal conductivity were attained simultaneously in the new Cu matrix composite. The microstructure of β-eucryptite–Cu composite was studied by scanning electron microscope and transmission electron microscope. The thermophysical properties of β-eucryptite–Cu composites were analysed by means of thermal dilatometer and diathermometer. No interfacial reaction products between β-eucryptite and Cu were found in the composite. The research indicates that β-eucryptite, which has a negative coefficient of thermal expansion, is a useful reinforcement, which can remarkably reduce the coefficient of thermal expansion of Cu matrix composite. The effects of volume fraction of β-eucryptite particulates on the thermal expansion coefficient and thermal conductivity of the composite were investigated.     

Wear mechanisms of diamond coated dental burs

Abstract

Wear mechanisms of diamond burs consist of diamond wear-out, diamond pull-out, clogging by debris and degradation of the diamond binder material. These have been reported in the scientific literature and several discrepancies were found by the authors, which in itself, justifies an independent study. Diamond coated dental burs before and after use on human teeth were, therefore, compared in order to identify the predominant cause of wear. Fifteen new diamond coated burs were characterised using scanning electron microscopy before and after use on human teeth. The study focused on the condition of the same diamond particles before and after use. Clear evidence of diamond particle wear was detected rather than evidence of diamond pullout, clogging by debris or degradation of the diamond binder material.     

On deformation control of dental crowns prepared by titanium powder process

Abstract

This study describes the identification of the main cause of deformation of titanium dental copings prepared by a new powder metallurgy method. The deformation was observed during the process development and needed to be explained to achieve an approved fit. The coping fabrication process was divided into stages to find the main cause of deformation. Each individual stage was investigated to find the cause. Primarily the pressing, milling and sintering steps and the tooth preparation dies (mandrels) were studied. The main cause of the deformation was found to be a deformation of the tooth preparation die during the pressing phase. The other stages were all shown to contribute only slightly or not measurably to the deformation. When using tooth preparation dies of a stronger material (stainless steel) the dies did not deform measurably during cold isostatic pressing and copings of various individual forms with an approved fit could be prepared.     

The effect of hyper-branched polymers on the properties of dental composites and adhesives

With the emergence of commercial hyper-branched (HB) and dendritic polymers, having a three-dimensional (3D) morphology with high peripheral functionality, new opportunities have been created for formulating dental adhesives and composites with enhanced mechanical and physical properties. The objective of the present study was to investigate the properties obtained by incorporating HB and dendritic polymers into acrylate-based dental composite and adhesive systems. Four commercial HB polymers were evaluated: Polyamidoamine dendrimer, two dendripolyamides and HB polyesteramide. These were added to dental restorative glass filled prepolymers, based on BisGMA, HEMA and TEGDMA. The dendritic and HB polymers blended readily with the prepolymers. A significant effect of HB polyesteramide (HB1), addition (0.1–3.0 wt%) on the mechanical properties was shown. It was found that addition of 0.3 wt% (optimal value) of HB polyesteramide raised the compressive strength from 253±20 MPa to 386±20 MPa and lowered the linear shrinkage from 2.4±0.2% to 1.5±0.2 % (for a model dental composite formulation). It was shown that the HB polyesteramide added to the dental adhesive compositions increased the shear bond strength and enhanced the bond durability to a variety of dental surfaces.     

Combined Novel Bonding Method of Resin to Zirconia Ceramic in Dentistry: A Pilot Study

Zirconia is a promising metal-free framework material that can be used to construct all-ceramic resin-bonded restorations in modern minimally invasive dentistry. The lack of a durable bond to zirconia is the major limitation against its widespread use. A technique to promote adhesion to the zirconia surface has thus been actively sought in dental materials research. Selective infiltration etching (SIE) has emerged as a method of conditioning that creates a highly retentive zirconia surface. This in vitro pilot study tested a novel adhesion procedure in which two newly engineered silane-based zirconia primers were combined with the SIE method. Zirconia discs were SIE-surface-treated, coated with one of the 2 zirconia primers, and bonded to composite resin discs. Primer activation (hydrolysis) was monitored by Fourier transform infrared (FTIR) spectroscopy. The bilayered specimens were sectioned into microbars and subjected to the microtensile bond strength test. As-sintered zirconia discs served as controls. Surface analysis of zirconia specimens was carried out using photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Zirconia specimens that had been treated with both SIE and primers had a significantly higher (ANOVA) zirconia resin bond strength (40.6 MPa, SD 5.8 MPa) than control specimens (2.6 MPa, SD 3.0 MPa; p < 0.05, F = 13.8, ANOVA). Controls also exhibited spontaneous failure during sectioning. Additionally, the interfacial failure rate was lower for the specimens subjected to the new combined surface treatment than for controls. The novel combined method of surface treatment method might open new opportunities for enhanced adhesion of resin-bonded zirconia restorations.     

Characterisation of interfacial imperfections of TiAl and 40Cr diffusion bonding by ultrasonic amplitude and phase

Abstract

A characteristics extraction algorithm is proposed to characterise the interfacial imperfections in TiAl and 40Cr diffusion bonding. The algorithm is based on analysing the variation of the ultrasonic amplitude and phase after interacting with the bonding interface. Ultrasonic measurements were performed by an ultrasonic imaging testing system, and broadband transducers with central frequency of the 10 and 20 MHz were employed. Metallographic analyses and shear tests were also performed on the joints. It was found that the amplitude of the reflection coefficient is almost a constant, and the phase of the reflection coefficient is the same for the perfectly bonded interface; for the kissing bond interface, the amplitude increases with the ultrasonic frequency, and the phase is the same at the low frequencies and opposite at the high frequencies; the amplitude does not vary with the frequency, and the phase is opposite for the unbonded interface.     

Effect of temper rolling on tensile properties of C-Mn steels

Abstract

The tensile properties of two C-Mn steels TR1 (Fe-0.135C-0.66Mn) and TR2 (Fe-0.019C-0.18Mn) under different temper rolling conditions were investigated. It was found that the lower yield strength and ultimate tensile strength of steels TR1 and TR2 which were temper rolled at different reductions can be expressed by the following formula, σ(MPa)=σ⁰+K?_eq(%), where σ is the strength after temper rolling; σ⁰ is the strength without temper rolling; ?_eq is the equivalent strain of the temper rolling reduction; K is a constant. The uniform elongation and the total elongation of these two steels which have been temper rolled at different reductions (or equivalent plastic strains) are those of samples without temper rolling subtracted from their equivalent plastic strains. The work hardening exponents of temper rolled samples can be predicted using the tensile curves of the samples which have not been temper rolled. Very good agreement between the experimental results and the calculated data was obtained.     

IFHTSE Global 21: heat treatment and surface engineering in the twenty-first century: Part 9 – Influence of materials science on heat treatment and surface engineering

Abstract

Significant progresses have been made in the past decades in the discipline of materials science, which include, but not limit to, the synthesis of new materials, advancement in analytical and experimental techniques, sustainable and environmentally friendly processing technologies, computational material science and nanotechnology. These developments have major influences on the research and application of heat treatment and surface engineering, and provide new opportunities to engineer the surfaces of new and conventional materials using advanced technologies to meet the ever increasing demands in surface and subsurface related properties. This survey gives a brief review on some aspects of heat treatment and surface engineering which keep pace with new developments in materials science. The specific areas being examined include: (i) advanced analytical techniques; (ii) sustainable and environmentally friendly technologies; (iii) surface engineering of emerging new materials such as intermetallic compounds, shape memory alloys and biomaterials; (iv) the search for superhard coatings and surface nanostructured materials; (v) mathematical modelling of surface engineering systems.