The purpose of this study was to evaluate the wear and surface damage mechanisms of polyethylene in retrieved CHARITÉ total disc replacements. The retrieved implants showed evidence of adhesive/abrasive wear mechanisms in the central domed region of the implants. In addition, there was also evidence of macroscopic rim damage, including radial cracking, plastic deformation, and third body damage. The retrieved total disc replacements (TDRs) displayed surface damage observed previously in both hip and knee replacements. The information from this study will be useful for engineers seeking to adequately replicate long-term, clinically relevant damage modes of TDRs using in vitro testing methods.
Proper aluminate control has a strong effect on the performance of most portland cement based mixtures. Insufficient aluminate control typically results in poor admixture dosage efficiency, loss of workability, and in extreme cases abnormal retardation of strength development. The amount of soluble sulfate needed for proper aluminate control depends on the reactivity of the aluminate phases, not the nominal amount given by chemical analysis. Many admixtures impact both the reactivity of the cement phases, the dispersion and wetting of cement grains, and sometimes also the rate of dissolution of the sulfates. Hence, it is imperative that cement and admixture must be tested together in performance tests. This paper reviews some basic cement-admixture chemical interactions and presents some examples of the application of isothermal calorimetry as a performance test of the hydration kinetics of portland cement in the presence of admixtures.
Interactions that take place between hydrating portland cement and chemical admixtures during the early hydration period affect the performance of concrete. Many of the early hydration reactions involve sulfate phases. Cement manufacturers intergrind calcium sulfate with clinker in the finish mill to provide control for the aluminate reactions during hydration. The calcium sulfate is typically added as gypsum, but some of this gypsum can dehydrate to calcium sulfate hemihydrate or soluble anhydrite, depending on the conditions in the finish mill. The final form of the calcium sulfate may affect the hydration characteristics of the cement in the presence of various chemical admixtures. This paper reports the results of studies of the performance of cement paste and mortar. Three cement samples were manufactured from a single clinker with the same amount of interground calcium sulfate but different relative ratios of gypsum and calcium sulfate hemihydrate. The clinker was manufactured to produce low-alkali Type V cement. The total calcium sulfate addition was approximately 3.7 %, and the amount remaining in the cement as gypsum was 47 %, 31 %, or 11 % of the total amount of gypsum and hemihydrate. Common chemical admixtures were studied, including lignosulfonate, naphthalene sulfonate, polycarboxylate, formulated Type A (non-lignosulfonate), and formulated non-chloride accelerator. Cement pastes that were prepared using the cements and admixtures were tested for workability, workability retention, and hydration profile with isothermal conduction calorimetry. Mortars that were prepared from the cements and admixtures were tested for workability, workability retention, air content, setting time, and early and late-age compressive strength. Initial indications are that the initial workability and workability retention of cement paste in the presence of admixtures are affected by the form of the calcium sulfate. The time of setting and strength development of mortar are affected by the form of the calcium sulfate as well.
A new method to in situ fabricate magnesium alloy reinforced with 8 wt % of TiB2 and TiC is described. The XRD result revealed the formation of TiB2 and TiC in master alloy magnesium matrix composites. Uniform distribution of fine reinforcement in the matrix material obtained through microstructural characterization. Mechanical characterization revealed that the presence of TiB2 and TiC leads to an increase on microhardness and tensile strength of magnesium matrix composites. Scanning electronic micrographs taken from the tensile fracture surface of magnesium matrix composites revealed typical brittle fracture.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.