Abstract: Hastelloy X is the trademark for a nickel-based, high-temperature superalloy that is increasingly applied in gas turbine engines because of its exceptional combination of oxidation resistance and high-temperature strength The superalloy suffers from hot cracking susceptibility, however, particularly when processed using additive manufacturing and laser powder bed fusion (LPBF) This paper systematically studies for the first time the effect of post-treatment hot isostatic processing (HIP) on the microstructure and mechanical properties of LPBF-fabricated Hastelloy X, with an emphasis on fatigue performance The experimental results demonstrate that despite the very small number of remaining gas-filled micropores due to pressure counteraction, the high temperature and high pressure during the HIP process promote recrystallisation and closing of the internal microcracks and gas-free pores The HIP-processed specimens are shown to be roughly 130 MPa and 60 MPa weaker than the non-processed specimens in yield strength and ultimate tensile strength, respectively The HIP-processed Hastelloy X exhibits significant improvements in fatigue life, however: the effect of the HIP processing is apparent once the applied stress decreases This improvement in fatigue performance is attributable to the reduction in stress concentration and residual stress release caused by the HIP process The paper also studies the hot cracking mechanism and finds that intergranular microcracks generally occur along high angle grain boundaries; the interdendritic liquid pressure drop between dendrite tip and root is found to be a significant factor in the hot crack mechanism The significance of this research is in developing a comprehensive understanding of HIP processing on the fatigue behaviour of the LPBF-fabricated Hastelloy X The insights on the cracking mechanism, which presents a significant step towards using additive manufacturing to produce complex crack-free parts from this superalloy

Abstract: Cracking is a common problem in concrete structures in real-life service conditions. In fact, crack-free concrete structures are very rare to find in real world. Concrete can undergo early-age cracking depending on the mix composition, exposure environment, hydration rate, and curing conditions. Understanding the causes and consequences of cracking thoroughly is essential for selecting proper measures to resolve the early-age cracking problem in concrete. This paper will help to identify the major causes and consequences of the early-age cracking in concrete. Also, this paper will be useful to adopt effective remedial measures for reducing or eliminating the early-age cracking problem in concrete. Different types of early-age crack, the factors affecting the initiation and growth of early-age cracks, the causes of early-age cracking, and the modeling of early-age cracking are discussed in this paper. A number of examples for various early-age cracking problems of concrete found in different structural elements are also shown. Above all, some recommendations are given for minimizing the early-age cracking in concrete. It is hoped that the information conveyed in this paper will be beneficial to improve the service life of concrete structures. Concrete researchers and practitioners may benefit from the contents of this paper.

Abstract: Liquid Zn-assisted embrittlement during resistance spot welding of Zn-coated high strength steels induces risks of surface cracking. This paper presents a state-of-the-art review on the surface cra...

Abstract: The oversupply of ethane, a major component of natural gas liquids, has stimulated the wide applications of ethylene since the shale gas revolution. However, ethylene production is energy-intensive and represents the most energy-consuming single process in the chemical industry. In this communication, we report, for the first time, a novel low-thermal-budget process for the co-production of ethylene and pure hydrogen using a proton-conducting electrochemical deprotonation cell. At a constant current density of 1 A cm−2, corresponding to a hydrogen production rate of 0.448 mol cm−2 per day, and 400 °C, a close to 100% ethylene selectivity was achieved under an electrochemical overpotential of 140 mV. Compared to an industrial ethane steam cracker, the electrochemical deprotonation process can achieve a 65% saving in process energy and reduce the carbon footprint by as much as 72% or even more if renewable electricity and heat are used. If the heating value of produced hydrogen is taken into account, the electrochemical deprotonation process actually has a net gain in processing energy. The electrochemical deprotonation process at reduced temperatures in the present study provides a disruptive approach for petrochemical manufacturing, shifting the paradigm from thermal chemical practice to a clean energy regime.

Abstract: Demand for propene as a petrochemical building block keeps growing, while its availability has been decreased by the adoption of shale gas resources, among others. Efforts to optimize its production by conventional means (including modified fluid catalytic cracking) and new on-purpose production technologies (including ethene to propene (ETP) and olefin cracking) are being pursued. This work reviews the progress made on olefin conversion processes, including the ETP reaction, which is still under development, and the cracking of butenes and higher olefins (C5–C8). The factors analyzed include the catalytic performance of different zeolite materials and their modifications to increase catalyst stability, yield, and selectivity to propene, as well as the effect of operating conditions, reaction thermodynamics, and mechanisms involved. The work is complemented by a survey of commercial technologies and developments on olefin conversion processes.

Abstract: In this paper, a number of artificial rock specimens with two parallel (stepped and coplanar) non-persistent joints were subjected to direct shearing. The effects of bridge length (L), bridge angle (γ), joint roughness coefficient (JRC) and normal stress (σ n) on shear strength and cracking process of non-persistent jointed rock were studied extensively. The experimental program was designed based on Taguchi method, and the validity of the resulting data was assessed using analysis of variance. The results revealed that σ n and γ have the maximum and minimum effects on shear strength, respectively. Also, increase in L from 10 to 60 mm led to decrease in shear strength where high level of JRC profile and σ n led to the initiation of tensile cracks due to asperity interlocking. Such tensile cracks are known as “interlocking cracks” which normally initiate from the asperity and then propagate toward the specimen boundaries. Finally, the cracking process of specimens was classified into three categories, namely tensile cracking, shear cracking and combination of tension and shear or mixed mode tensile–shear cracking.

Abstract: Concrete shrinkage and volume reduction happens due to the loss of moisture, which eventually results in cracks and more concrete deformation. In this study, the effect of polypropylene (PP), steel, glass, basalt, and polyolefin fibers on compressive and flexural strength, drying shrinkage, and cracking potential, using the ring test at early ages of high-strength concrete mixtures, was investigated. The restrained shrinkage test was performed on concrete ring specimens according to the ASTM C1581 standard. The crack width and age of restrained shrinkage cracking were the main parameters studied in this research. The results indicated that the addition of fiber increases the compressive strength by 16%, 20%, and 3% at the age of 3, 7, and 28 days, respectively, and increases the flexural toughness index up to 7.7 times. Steel and glass fibers had a better performance in flexural strength, but relatively poor action in the velocity reduction and cracking time of the restrained shrinkage. Additionally, cracks in all concrete ring specimens except for the polypropylene-containing mixture, was developed to a full depth crack. The mixture with polypropylene fiber indicated a reduction in crack width up to 62% and an increasing age cracking up to 84%.

Abstract: Waste high-density poly(ethylene) (HD-PE) plastic deformation into liquid hydrocarbon fuel using a pyrolysis-catalytic cracking process with a copper carbonate (CuCO3) catalyst, at a temperature range from 23 °C to 390 °C. The pyrolysis-catalytic deformation process will help in environmental purification. The liquid hydrocarbons collected for use as a fuel were analyzed using Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), two-dimensional gas chromatography/time of flight mass spectrometry (2D-GCxGC/TOFMS), inductively coupled plasma (ICP) analysis, and carbon, hydrogen, nitrogen, sulfur, and oxygen (CHNS/O) elemental analysis. The 2D-GCxGC/TOFMS results showed that various types of hydrocarbon compounds (aliphatics, aromatics, cyclics olefins, and phenanthrene) were available in the liquid hydrocarbon fuel. The conversion rates in four experiments which converted waste HD-PE plastic into liquid hydrocarbons for use as fuel were 85%, 90%, 94%, 92%, light gases 14.67%, 9.66%, 5.64%, 7.45% and residues 0.33%, 034%, 0.36%, 0.55%. Liquid hydrocarbons as fuel were found to be appropriate for use in petrol and diesel engines and they were found to be a good source of organic compounds/petrochemicals.

Abstract: The market share of different types of blended cements is increasing year by year. Generally, blended cements are ground to higher fineness and exhibit a slower development of mechanical properties compared to Ordinary Portland Cement (OPC), which might affect the concrete performance in terms of shrinkage cracking at early ages. In this paper, the performance of concretes made with different cement types is compared according to the ASTM C1579-13 standard for plastic shrinkage cracking. The cracking behavior was further correlated to the deformations of both unrestrained and restrained specimens measured by a 3D image correlation system. The main factors influencing the cracking behavior were discussed based on poromechanics. It is concluded that the bulk modulus evolution has a dominant effect on controlling the plastic shrinkage cracking. Concretes made of more reactive cements, in particular with higher clinker content, are less susceptible to plastic shrinkage cracking. For cements with the same clinker content, increasing the cement fineness reduces the risk of plastic shrinkage cracking.

Abstract: Alloy selection is critical for the performance of aerospace components repaired through laser cladding, as unsuitable combinations of clad and substrate materials can lead to defects during deposition. Different combinations of laser clad ultra-high strength steels have been studied to examine the effect of material composition on clad quality. Clad/substrate combinations of Aermet®100/300M, Aermet®100/4340, and 4340/300M were trialled using a range of processing parameters. While no defects occurred in the 4340/300M samples, solidification cracking was observed in the Aermet®100 multi-track clad samples, especially on 300M substrates. The cracking originates from macrosegregation trails caused by differences in melting temperature between clad and substrate. These trails interfere with liquid feeding beneath them when the substrate has a higher liquidus temperature, with entrapped liquid leading to short solidification cracks. A second larger form of solidification cracking was found in Aermet®100/300M due to Aermet®100 solidifying faster in the late stages of solidification, as this can entrap liquid in the inter-dendritic regions leading to cracking. Both forms of cracking can be avoided by increasing the laser interaction time during cladding, as this slows the solidification process to allow for more complete mixing and liquid feeding.

Abstract: The aim of this study is to convert polypropylene waste into usable liquid fuel via pyrolysis technique using kaolin as a low-cost catalyst. Waste polypropylene was thermally and catalytically degraded in a chemical vapour deposition (CVD) horizontal glass reactor at a temperature of 450 °C, residence time of 30 min, and heating rate of 30 °C/min. The kaolin clay was characterized by XRF analysis while the ultimate and proximate analysis of the polypropylene feed carried out gave combustible materials content of 93.77 wt%, fixed carbon of 1.62 wt%, calorific value of 45.20 MJ/kg and elemental composition with carbon (83.65%), hydrogen (14.27%), oxygen (0.15%), sulphur (0.1%), chlorine (1.16%), and nitrogen (0.67%). Thermal cracking was carried out in the absence of catalyst and the process gave a yield of liquid, gaseous, and solid products of 67.48, 8.85, and 23.67 wt%, respectively. Furthermore, kaolin clay was employed as a catalyst in catalytic pyrolysis of the same feedstock for catalyst-to-plastic ratio of 1:1, 1:2, 1:3, and 1:4 at the same operating parameters as in thermal cracking. Optimum yield was obtained at a catalyst-to-plastic ratio of 1:3 with a yield of 79.85, 1.48, and 18.67 wt% for liquid, gaseous, and solid products, respectively. The liquid products obtained for both thermal and catalytic cracking at optimum conditions were characterized for their suitability as fuel. The properties determined were density, viscosity, flash point, fire point, pour point, and calorific value. The results suggest that catalytic pyrolysis produced liquid products, whose properties are comparable to conventional fuels (gasoline and diesel oil) than that produced through thermal pyrolysis. FTIR analysis of the liquid product from catalytic pyrolysis also shows that it contains hydrocarbons with different functional groups such as aromatics, olefins, carbonyl, amines, sulphides, and hydroxyl.

Abstract: Although steam cracking is a mature technology, mitigation of coke formation remains one of the main challenges in the petrochemical industry. To increase the olefin output of existing plants, coil materials that can withstand higher temperatures are desired. This work reviews material technologies that were developed and tested in the past three decades to minimize the rate of coke deposition and extend the furnace run length. The material not only determines the mechanical properties of the coil but also affects the coking rate substantially. In some cases, differences in coking rates by more than a factor 10 have been observed. SiC materials could be operated at significantly higher temperatures, and this leads to higher olefin selectivity if one includes acetylene hydrogenation; however, the mechanical joints make it currently impossible to take advantage of their superior temperature resistance. On the industrial scale, operational improvements have been reported with advanced reactor surface technol...