The effect of fluorine content on the mechanical properties of poly (?-caprolactone)/nano-fluoridated hydroxyapatite scaffold for bone-tissue engineering

In this study, the effect of fluorine content on the mechanical properties of the novel poly (?-caprolactone)/nano-fluoridated hydroxyapatite nanocomposite scaffolds was investigated. Poly (?-caprolactone)/nano-fluoridated hydroxyapatite (PCL-FHA) scaffolds were produced by solvent casting/particulate leaching method. The fluoridated hydroxyapatite nanopowders had a chemical composition of Ca₁₀(PO₄)₆OH_2−xF_x (where x values were selected equal to 0.5, 1, 1.5 and 2.0). Various weight percentages (10, 20, 30 and 40) of the FHA were added to the PCL. Sodium chloride (NaCl) particles having diameter of 300-500 μm were used as porogen. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) were used to identify the phase structure and functional groups of obtained scaffolds. Mechanical properties of the prepared scaffolds were also determined. Results showed that the compressive strength of scaffolds increases with decreasing the weight percent of fluorine in FHA.     

High-temperature elasticity of fibrous ceramics with a bird's nest structure

New fibrous ceramics with polycrystalline mullite fibers as the matrix and silica–boron sols as the high temperature binder, which was inspired by the bird's nest structure in nature, were synthesized. The most important structure characteristic of this fibrous material is that the silica–boron binder only fixed the fibers at the crossing points rather than filled the pores among the fibers. The elastic behavior was investigated, both at room temperature and elevated temperature. Compared to conventional ceramic matrix composites, the samples show a much higher degree of elasticity because of the bending of the fibers. The rebound resilience decreased slowly with the increase of the temperature, but it still remained 86% of that at ambient temperature at 1000 °C. The sample exhibits good elasticity performance, relatively high strength (2.25 MPa) and high porosity (83%) indicating it is a potential high-temperature seal material.     

Compressive and flexural properties of novel polylactic acid/hydroxyapatite/yttria-stabilized zirconia hybrid nanocomposite scaffold

The mechanical property is a crucial factor in the design of bone tissue engineering scaffolds. In the current study, novel PLLA (Poly-L-lactic acid)–Hydroxyapatite (HA)–yttria-stabilized zirconia (YSZ) nanocomposite scaffold with various compositions was prepared and characterized. The effect of HA and YSZ contents on the mechanical behavior of the resultant composites was investigated. TEM micrograph revealed that HA particles are needle-like in shape and nano in size. Scanning electron microscopy (SEM) micrograph also showed that YSZ powder is in granule form and submicron size. SEM disclosed that all scaffolds had a highly interconnected porous structure and X-ray diffractometry revealed that there were some molecular interactions between PLA (Polylactic acid), HA, and YSZ in the composites. The results depicted that introducing YSZ to the nanocomposite leads to a significant increase in compressive strength, modulus, and densification strain. In addition, flexural strength and modulus showed an upward trend by adding YSZ particles to scaffolds. It should be noted that PLA–20%HA–20%YSZ indicates the highest strength and modulus in both compression and bending tests, though, it did not demonstrate the proper strain compared to other scaffolds. Thus, PLA–15%HA–15%YSZ has been reported as the best candidate due to appropriate strength and strain. Also, energy absorption in nanocomposites showed an upward trend by increasing the amount of YSZ particles. It was found that the strength of samples was declined after being soaked in simulated body fluid. However, scaffolds with HA underwent more decrease in strength compared to samples containing YSZ.     

Synthesis and characterization of geopolymers containing blends of unprocessed steel slag and metakaolin: The role of slag particle size

The present research deals with the production and characterization of geopolymers prepared by mixing metakaolin with a steel slag from the production of chromium-manganese steel, a commercial sodium silicate solution and a sodium hydroxide solution. Different specimens were prepared by mixing metakaolin with different proportions of steel slag (20, 40, 60, 80 wt%) characterized by different maximum particle size. Specimens containing just metakaolin and steel slag alone were also prepared for comparison. All specimens have been characterized regarding their compressive strength, specific surface area, water absorption and microstructure. It has been observed that the use of fine steel slag powders leads to increases the performances and that the specimens containing 40 wt% steel slag and 60 wt% metakaolin revealed the best overall behaviour.     

Compressive properties of pristine and SiC-Te-added MgB2 powders,green compacts and spark-plasma-sintered bulks

Pristine and (SiC+Te)-added MgB₂ powders, green and spark plasma sintered (SPS) compacts were investigated from the viewpoint of quasi-static and dynamic (Split-Hopkinson Pressure Bar, SHPB) compressive mechanical properties The amount of the additive (SiC+Te) was selected to be the optimum one for maximization of the superconducting functional parameters. Pristine and added MgB₂ show very similar compressive parameters (tan δ, fracture strength, Vickers hardness, others) and fragment size in the SHPB test. However, for the bulk SPSed samples the ratio of intergranular to transgranular fracturing changes, the first one being stronger in the added sample. This is reflected in the quasi-static K_IC that is higher for the added sample. Despite this result, sintered samples are brittle and have roughly similar fragmentation behavior as for brittle engineering ceramics. In the fragmentation process, the composite nature of our samples should be considered with a special focus on MgB₂ blocks (colonies) that show the major contribution to fracturing. The Glenn-Chudnovsky model of fracturing under dynamic load provides the closest values to our experimental fragment size data.     

Transient liquid phase diffusion process for porous mullite ceramics with excellent mechanical properties

Porous mullite ceramics were fabricated by the transient liquid phase diffusion process, using quartz and fly-ash floating bead (FABA) particles and corundum fines as starting materials. The effects of sintering temperatures on the evolution of phase composition and microstructure, linear shrinkage, porosity and compressive strength of ceramics were investigated. It is found that a large amount of quartz and FABA particles can be transformed into SiO₂-rich liquid phase during the sintering process, and the liquid phase is transient in the Al₂O₃-SiO₂ system, which can accelerate the mullitization rate and promote the growth of mullite grains. A large number of closed pores in the mullite ceramics are formed due to the transient liquid phase diffusion at elevated temperatures. The porous mullite ceramics with high closed porosity (about 30%) and excellent compressive strength (maximum 105?MPa) have been obtained after fried at 1700?°C.     

快硬早强油井水泥在浅层高含水调整井中的应用

快硬早强油井水泥是针对常规油井水泥在低温条件下水泥浆候凝时间长、强度发展慢、稠化时间不易控制等现象开发的新型特种油井水泥,该水泥具有低温下凝结速度短、抗压强度高、微膨胀、综合性能优等特点,并具有优异的抗冷冻及抗水浸性能,在此基础上研制的低温快凝防窜水泥浆较好地解决了浅层高含水调整井的固井质量问题,为中原固井外闯市场提供了有力的技术保障。     

Investigation of the effects of fatty acids on the compressive strength of the concrete and the grindability of the cement

In cement industry, a great energy consumption has been observed during grinding of clinker. To reduce this consumption, some waste products have been used as grinding aids.In this investigation, the effects of sunflower oil (SO), oleic acid (OA), stearic acid (SA), myristic acid (MA) and lauric acid (LA) on the fineness and strength of the cement have been examined. These aids were added into clinker in certain ratios based on the cement clinker weight and the grinding has been done for a definite time at the same condition.All of the fatty acids used increased the fineness as compared with the cement without the grinding additives. SO and OA decreased the strength significantly, LA decreased it to a lesser extent and SA increased it definitely according to the common cement. But MA did not alter the strength of the cement as much as SA. In addition, the covering of the balls influences the grinding of cement clinker unfavourably.     

轻集料对高强次轻混凝土物理力学性能的影响

研究了轻集料种类及其在粗集料中所占比例、轻集料粒径与级配以及体积砂率对高强次轻混凝土的表观密度、抗压强度、抗拉强度和弹性模量的影响.试验结果表明,轻集料的种类及其在粗集料中所占比例对不同强度等级的高强次轻混凝土具有相似的影响规律,即当轻集料在粗集料中比例不超过50%时,混凝土的抗压、抗拉强度和弹性模量随轻集料掺量变化的变化并不明显,而超过50%时,则随着轻集料掺量增大而明显降低;高强次轻混凝土的力学性能随轻集料粒径减小而提高,间断级配对混凝土的力学性能影响不利;体积砂率存在最佳范围,约为40%左右.     

Characteristics of wood–polymer composite for journal bearing materials

Wood is widely used as a construction material, automotive parts, and equipment for leisure-time amusement; however, its application on the journal bearing was restricted, because of its low strength and poor tribological characteristics.In this work, paulownia wood which has low density and high porosity was impregnated with polyethylene glycol (PEG), lubricant oil (SAE 30), release agent and epoxy to improve the mechanical properties and tribological characteristics. The ultrasonic vibration was given to the wood immersed in the acetone tub to remove debris generated during the cutting process of wood and to dissolve the membrane of lignin in the wood. From the test results, it was found that the PEG was the promising material to improve the physical properties of wood for journal bearings.