A thermal protection system is subject to high forces, in particular compression, bending and wear, to aggressive environments of high temperatures, high velocity gases and particle shock. Typically, ceramic materials appear as a first barrier or outer shield over a metallic substrate responsible for the structure. When it comes to a coating due to the small thickness, the particles of the raw material are sub-micron scale, but when a shield with a few centimeters is built its structural and economic viability requires the use of wider particle size distributions. In this work, a ceramic fine-grained matrix of CaO-ZrO2-MgO was reinforced with commercial coarse Al2O3 particles. The results show that for larger size distributions, CZM-4A, replacing 63% of fine-grained matrix by coarse Al2O3 particles, the dimensional stability is obtained (ΔL = 5%) and the good mechanical properties such as flexural strength of 154 MPa, elastic modulus of 286 GPa, and hardness of 8.5 GPa, which allows to propose this ceramic composite for a structural application.
The aim of this work was to demonstrate a detailed study of the controlled release of the herbicide Tebuthiuron (TBH) encapsulated in microparticles of calcium alginate (Ca-ALG), to evaluate the phytotoxicity in different concentrations of herbicide (4, 6 and 8 g L-1), and their correlation with the depth of leaching using bioindicator plants. The Ca-ALG microparticles were prepared from the crosslinking of sodium alginate by Ca++ containing varied amounts of TBH supplied in calcium chloride (CaCl2) aqueous solution. The results showed that TBH herbicide, when encapsulated, leached to shallow depths relative to the conventional, non-encapsulated herbicide (which moved to a depth of 40-50 cm). The concentration of 4 g L-1 was the one that leached most in the PVC columns, but its mobility did not exceed 30 cm of depth. The results of the dry mass corroborated with the phytotoxicity results of the bioindicator plants, evidencing the mobility of the conventional herbicide in the soil at depths around 40 and 50 cm, while the herbicide encapsulated in the Ca-ALG microparticles did not show leaching beyond 20 -30 cm deep. The encapsulation of TBH in Ca-ALG microparticles can thus be considered as a more eco-friendly technology, reducing the leaching process and consequently soil contamination.
Calcium phosphate bioceramics such as hydroxyapatite (HA) and tricalcium phosphate (TCP) were successfully used in medical fields such as dentistry, orthopedics, and facial surgery due to their resorption and bioactivity characteristics. This work aims to obtain an osteoinductive ceramic matrix doped with metal ions. First, TCP doped with 10 mol.% of MgO was selected for the initial matrix due to the increased of HA content, microstructure densification (90%), and mechanical strength (27 MPa). Second, the addition of others metal ions (Zn, Mn, and Fe), at most 5 mol.%, to this initial matrix was evaluated by means of statistical analysis applying design of experiments (DOE). The presence of metal ions was studied by XRD and SEM-EDX analysis. The trace plots and equations were obtained for apparent and relative densities, apparent porosity, and diametral compression resistance, all for a 95% confidence interval and maximum error of p < 0,05. The results show a strong dependency between the addition of these metal ions and all studied properties.
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