The Impact of Extended Heat Exposure on Rapid Sulphoaluminate Cement Concrete Up To 120°C

This study examined the stability of rapid sulphoaluminate cement concrete (R-SACC) when exposed to heat for extended periods of time. The physicochemical processes present in R-SACC as a function of temperature were determined through various tests. The general behavior of rapid sulphoaluminate cement (R-SAC) at a range of temperatures is summarized. The results show that observing color change could be a simple way to identify deterioration of R-SACC, along with the rebound hammer. The matrix formation of ettringite was broken and the mass of the hydrated product decreased with heat exposure; the major mineral composition of the paste consisted of CaSO4, CaCO3 and β-C2S; and the interface between aggregate and paste in the R-SACC become loosely structured with cracks. Between 50°C and 120°C, the rapid sulphoaluminate cement (R-SAC) paste first expanded and then shrank, and the shrinkage rate of R-SAC was much greater than that of R-SACC.

Properties and Reaction Mechanisms of Magnesium Phosphate Cement Mixed with Ferroaluminate Cement

A certain amount of ferroaluminate cement (FAC) was substituted for MgO during the magnesium phosphate cement (MPC) preparation to obtain the MPC–FAC composite cement. The influence of FAC on the strength, water resistance, pH, and setting time of MPC–FAC composite cement were examined. The microstructure and chemical composition were also analyzed by adopting scanning electron microscopic energy-dispersive spectrometer and X-ray diffraction, respectively. The study showed that setting time of MPC–FAC composite cement was dramatically prolonged when FAC substitution for MgO was between 30 and 40 wt %. The strength of MPC–FAC did not decrease during the early curing time (1 h and 1 d), whereas it increased during the late curing time (3, 7, and 28 days). Moreover, the existence of FAC decreased the hydrated product K-struvite during the early curing time and thus dramatically enhanced the water-resistance of MPC–FAC. With the addition of FAC, a large number of cementitious materials of AFt and AFm, as well as flocculent colloidal substances of AH3, C–S–H, and FH3, were generated during the hydration of MPC, which were filled in the internal pore of the hydrate. Thus, the internal compactness of the sample increased, while the compact protective covering layer was generated on the surface to enhance the water resistance and strength in the late curing time.

Seven membered chelate Pt(ii) complexes with 2,3-di(2-pyridyl)quinoxaline ligands: studies of substitution kinetics by sulfur donor nucleophiles, interactions with CT-DNA, BSA and in vitro cytotoxicity activities

Dichloro platinum(ii) complexes coordinated with 2,3-di(2-pyridyl)quinoxaline ligands form seven-membered chelates were synthesized, characterised and their respective hydrated product complexes were prepared by chloride metathesis.

Experimental Assessment of the Sealing Potential of Hydrated Solgel for the Remediation of Leaky Reservoirs

The full-scale deployment of underground storage of CO2 in permeable sedimentary reservoirs depends strongly on the sealing capacity of the caprocks and wellbore cement that may be degraded leading to hydraulic discontinuities. Remediation technologies consisting in rebuilding the sealing capacity of the degraded material, or adding a new sealing layer, is a critical issue as part of the risk mitigation procedure required for underground CO2 storage. Actually, engineered Portland cement injection is the foremost available industrial technique; however, alternative products offering, for instance, better injection properties, are currently investigated with variable success so far. In this study, a new technique aimed at using a low viscosity hydrated solgel as sealant product in case of leakage is presented. Its low cost, high injectivity capacity and low density of the hydrated product (hydrogel) makes this technique attractive. The solgel synthesis was optimized for (1) reducing energetic and material costs; (2) improving the chemical and mechanical properties of the emplaced product and (3) controlling the duration of the aging process in order to form a solid hydrogel after a few days. Permeability tests that consisted of injecting the synthesized solgel in different porous media confirmed the sealant capacity of the emplaced hydrogel to significantly reduce rock permeability.

Cement-Induced Coagulation of Aqueous Graphene Oxide with Ultrahigh Capacity and High Rate Behavior

Graphene oxide (GO) has excellent physicochemical properties and is used in multiple areas. However, the potential toxicity and environmental problems associated with GO increase its risk to the ecological system. In this study, cement was employed as a coagulant to eliminate GO from aqueous solutions. The effects of the cement dosage, the contact time, and the concentration and volume of the aqueous GO solution on the GO coagulation capacity were investigated in detail. The results showed that the dosage of cement had a significant effect on the coagulation process, and coagulation equilibrium was achieved in less than 1 h. Compared to coagulants used to remove GO from water in other reports, cement exhibited an ultrahigh coagulation capacity of approximately 5981.2 mg/g with 0.4 mg/mL GO solution. The kinetic analysis showed that the GO removal behavior could be described by a pseudo second-order model. The in-depth mechanism of GO coagulation using cement included Ca2+-induced coagulation of GO and adsorption by the hydrated product of cement paste. The present study revealed that cement could be a very cheap and promising material for the efficient elimination of GO from aqueous solutions.

Characterization of an Aldolase Involved in Cholesterol Side Chain Degradation in Mycobacterium tuberculosis

ABSTRACT The heteromeric acyl coenzyme A (acyl-CoA) dehydrogenase FadE28-FadE29 and the enoyl-CoA hydratase ChsH1-ChsH2, encoded by genes within the intracellular growth (igr) operon of Mycobacterium tuberculosis, catalyze the dehydrogenation of the cholesterol metabolite 3-oxo-4-pregnene-20-carboxyl-CoA (3-OPC-CoA), with a 3-carbon side chain, and subsequent hydration of the product 3-oxo-4,17-pregnadiene-20-carboxyl-CoA (3-OPDC-CoA) to form 17-hydroxy-3-oxo-4-pregnene-20-carboxyl-CoA (17-HOPC-CoA). The gene downstream of chsH2, i.e., ltp2, was expressed in recombinant Rhodococcus jostii RHA1 in combination with other genes within the igr operon. His-tagged Ltp2 copurified with untagged ChsH1-ChsH2, ChsH2, or the C-terminal domain of ChsH2, which contains a domain of unknown function (DUF35). Ltp2 in association with ChsH1-ChsH2 or just the DUF35 domain of ChsH2 was shown to catalyze the retroaldol cleavage of 17-HOPC-CoA to form androst-4-ene-3,17-dione and propionyl-CoA. Steady-state kinetic analysis using the Ltp2-DUF35 complex showed that the aldolase had optimal activity at pH 7.5, with a Km of 6.54 ± 0.90 μM and a k cat of 159 ± 8.50 s−1. ChsH1-ChsH2 could hydrate only about 30% of 3-OPDC-CoA, but this unfavorable equilibrium could be overcome when the aldolase was present to remove the hydrated product, providing a rationale for the close association of the aldolase with the hydratase. Homologs of ChsH1, ChsH2, and Ltp2 are found in steroid-degrading Gram-positive and Gram-negative bacteria, suggesting that side chains of diverse steroids may be cleaved by aldolases in the bacteria. IMPORTANCE The C-C bond cleavage of the D-ring side chain of cholesterol was shown to be catalyzed by an aldolase. The aldolase associates with the hydratase that catalyzes the preceding reaction in the cholesterol side chain degradation pathway. These enzymes are encoded by genes within the intracellular growth (igr) operon of M. tuberculosis, and the operon was demonstrated previously to be linked to the pathogenicity and persistence of the bacteria in macrophages and in mice.

Influence of Slag on Water Resistance of Magnesia Phosphate Cement

Effect of different curing conditions on the mechanical properties of magnesium phosphate cement (MPC), and the water resistance of MPC was improved by adding slag, the influence of slag on component and microstructure of the hydrated product were studied in this paper. The additive amount of slag was 0% ,10% , 20%, 30% and 40% separately in the ratio of total amount of MPC. It indicates that the compressive strength and flexural strength increase by about 30%,40% when the amount of slag reaches 10% of phosphate cement, respectively , and the dissolution of some phosphate which has not reacted can be prevented when cured in water for days, it improves the pH value of the solution, so the main hydration product-MgKPO4·6H2O hard to be dissolved under alkaline environment resulting in the decreasing of porosity ,and the decrease of strength would be controlled.

Measuring acetic and formic acid by proton transfer reaction-mass spectrometry: sensitivity, humidity dependence, and quantifying interferences

We present a detailed investigation of the factors governing the quantification of formic acid (FA), acetic acid (AA) and their relevant mass analogues by proton transfer reaction-mass spectrometry (PTR-MS), assess the underlying fragmentation pathways and humidity dependencies, and present a new method for separating FA and AA from their main isobaric interferences. PTR-MS sensitivities towards glycolaldehyde, ethyl acetate and peroxyacetic acid at m/z 61 are comparable to that for AA; when present, these species will interfere with ambient AA measurements by PTR-MS. Likewise, when it is present, dimethyl ether can interfere with FA measurements. On the other hand, for E/N = 125 Townsend (Td), the PTR-MS sensitivity towards ethanol at m/z 47 is 5–20× lower than for FA; ethanol will then only be an important interference when present in much higher abundance than FA. Sensitivity towards 2-propanol is <1% of that for AA, so that propanols will not in general represent a significant interference for AA. Hydrated product ions of AA, glycoaldehyde, and propanols occur at m/z 79, which is also commonly used to measure benzene. However, the resulting interference for benzene is only significant when E/N is low (