Influence Factors and Prediction Model of Bond Strength of Tunnel Fireproof Coating under Freeze–Thaw Cycles

The freeze–thaw resistant performance of a tunnel fireproof coating (TFC) has an important impact on bonding property and durability. The influence of redispersible emulsion powder, polypropylene fiber and air-entraining agent on TFCs was studied. Transverse fundamental frequency and ultrasonic sound velocity were used to evaluate the damage degree of TFC, and the mechanism was revealed by SEM and pore structure. The results show that the most beneficial effect on bond strength of TFC is redispersible emulsion powder, followed by air-entraining agent, and then polypropylene fiber. After freeze–thaw cycles, the cumulative pore volume of micropores in the TFC increases obviously, while the porosity of macropores does not change significantly. A prediction model was proposed, which can calculate the bond strength from the damage degree of TFC under freeze–thaw cycles. The achievement can promote the application of TFC in cold regions.     

In vitro modeling accurately predicts cardiac lead fracture at 10 years

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Neutron reflectivity study of the swollen structure of polyzwitterion and polyeletrolyte brushes in aqueous solution

The swollen brush structures of polycation and zwitterionic polymer brushes, such as poly(2-methacryloyloxyethyltrimethylammonium chloride) (PMTAC), poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), and poly[3-(N-2-methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfonate] (PMAPS), in aqueous solutions of various ionic strengths were characterized by neutron reflectivity (NR) measurements. A series of the polyelectrolyte brushes were prepared by surface-initiated controlled radical polymerization on silicon substrates. A high-graft-density PMTAC brush in salt-free water (D₂O) adopted a two-region step-like structure consisting of a shrunk region near the Si substrate surface and a diffuse brush region with a relatively stretched chain structure at the solution interface. The diffuse region of PMTAC was reduced with increase in salt (NaCl) concentration. The PMAPS brush in D₂O formed a collapsed structure due to the strong molecular interaction between betaine groups, while significant increase in the swollen thickness was observed in salt aqueous solution. In contrast, no change was observed in the depth profile of the swollen PMPC brush in D₂O with various salt concentrations. The unique solution behaviors of zwitterionic polymer brushes were described.     

Effect of Preparation Taper,Height and Marginal Design Under Varying Occlusal Loading Conditions on Cement Lute Stress: A Three Dimensional Finite Element Analysis

The functional surfaces of the porcelain fused to metal fixed partial dentures are often abraded to adjust occlusion, such restorations are often found to fail in service. This study was therefore conducted to study the effect of surface abrasion on flexural strength of glazed porcelain fused to metal samples. It was also the aim of this study to find the effect of re-glazing on flexural strength of abraded samples. A total of ninety glazed porcelain fused to metal bar samples of the dimension 15 mm × 2 mm × 1.5 mm were fabricated. These samples were then divided into three groups (30 samples each) according to the surface treatments: group A-glazed (control); group B-abraded and group C-abraded and then re-glazed (self-glazed). Flexural strength was measured by using three point bend test on universal testing machine (texture analyser) with a cross-head speed of 0.6 mm/min. Peak force at the time of failure for all the samples was recorded. Statistical analysis found that mean flexural strength was highest for group A-80.65 ± 12.81 MPa; as compared to group B-74.18 ± 10.74 MPa and group C-77.85 ± 9.39 MPa. Student’s t test indicated that the difference in the flexural strength between groups A and B was significant while it was non-significant between groups B and C and also between groups A and C. The ‘f’ test indicated that the difference between the groups was non-significant. This study therefore showed that there is a marked decrease in the flexural strength of the porcelain fused to metal restorations after occlusal abrasion. The study also found that reglazing of these restorations may not restore their flexural strength significantly.