PubMed · 772503
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N Ripp. 1976. Pulp capping. A review.. https://pubmed.ncbi.nlm.nih.gov/772503/
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Hydrochloride (HCl) is an acidic pollutant present in the flue gas of most municipal or hazardous waste incinerators. Hydrated lime (Ca(OH)2) is often used as a dry sorbent for injection in a spray reactor to remove HCI. However, due to the short residence time encountered, this control method has generally been found to have low conversion efficiencies which results in the high lime usage and generates large amount of fly ash as solid wastes. A fundamental study was carried outto investigate the kinetics of HCl-lime reaction under simulated flue gas conditions in order to better understand the process thereby providing a basis for an optimized lime usage and reduced fly ash production. The initial reaction rate and conversion of three limes were studied using a thermogravimetric analyzer by varying the gas flow rate, temperature (170-400 degrees C), and HCI concentrations (600-1200 mg/m3) as well as the associated particle size and surface area of the limes. The initial lime conversions were found to rely mostly on the residence time, while the ultimate lime conversions were strongly influenced by temperature and the reaction products. CaOHCI was found to be the primary product in most cases, while for one specific lime, CaCl2 was the ultimate conversion product after an extended time period. The true utilization of lime in flue gas cleanup is thus higher when CaOHCl is considered as the final product than those based on CaCl2 as the final product, which has been commonly used in previous studies. The initial reaction was controlled by diffusion of HCl in gas phase and the subsequent reaction by gaseous diffusion through the developing product layer. Increasing the HCI concentration raised the initial rate as well as conversion. However, overloading the lime with excessive HCI caused clogging at its surface and a drop in the ultimate conversion. Limes with smaller particle diameters and higher surface areas were found to be more reactive. The effect of gas-phase mass transfer was minimized when an optimum flow rate was chosen, and in the absence of internal diffusion the reaction was found to be first order with respect to HCI concentration.
- The pH values of the external aqueous medium, relative to the roots of 41 human premolar teeth filled with Ca(OH)2 in to several vehicles, were evaluated in the present study. After root canal biomechanical preparation and smear-layer removal, the teeth were stored individually, immersed in flasks containing 800 ml of ultra-pure deionized water for a period of 118 days. A pH meter was used to analyse the pH values as a function of time. The measurements were divided into phase 1: dissolution, in which all canals remained empty and open in the absence of medicament for 48 days, and phase 2: diffusion, in which the specimens were divided into 10 groups which consisted of three control groups: group 1, water control; group 2, sealing control; and group 3, opened canal dissolution control, and seven experimental groups, with five teeth each, whose canals were filled with Ca(OH)2 paste associated with the following vehicles: group 4, saline solution; group 5, polyethylene glycol (Calen); group 6, glycerin and parachlorophenol (PMCC); group 7, PMCC; group 8, glycerin; group 9, glycerin and formo cresol (FC); and group 10, anesthetic solution. This phase lasted for 70 days. A total of 1058 measurements of the pH values were made. Regression analysis was used for statistical evaluation. The results show that all groups containing polyol in the composition of the paste had a trend to acidification in the interval between filling and 14 days later (therapeutic period) and, at the end of the experiment (1687 h to 70 days after canal filling), the pH was slightly alkaline. We conclude that polyhydroxy alcohol (glycerin and polyethylene glycol, Calen) diffusion enhances acidification of the aqueous medium.
AIM: To investigate selected physical properties of five root-canal sealers. METHODOLOGY: The solubility, film thickness, flow, working and setting times of Roth 801, Tubli-Seal EWT, AH Plus, Apexit and Endion were evaluated. Solubility was measured by weight change of standard specimens in water over a 3-month period. Film thickness was measured as the distance between weighted glass slides containing a standard quantity of sealer. Flow was assessed by rate of sealer extrusion through a standard bore diameter, after unit time. Working time was taken as the point at which flow rate was reduced by 10%. The indentation test using a modified Gilmore needle was employed to investigate the setting times. RESULTS: AH Plus was the least soluble, whilst Apexit was the most unstable in water. The solubility values in increasing order were: AH Plus<Tubli-Seal EWT<Endion<Apexit. Also, AH Plus had the highest film thickness. All sealers showed comparable flow rates. The working time varied from 50 min for Endion to over 2 h for AH Plus and Tubli-Seal EWT. The range of setting times recorded was from 70 min for Tubli-Seal EWT to 8 days for Roth 801. CONCLUSIONS: 1. AH Plus showed the greatest stability in solution and Tubli-Seal EWT performed well, but Apexit and Endion had higher solubility values. 2. The film thickness values in increasing order were: Tubli-Seal EWT<Apexit<Endion=Roth 801<AH Plus. 3. The flow rates for all sealers were similar. 4. The working times for all sealers were greater than 50 min. 5. Roth 801 did not set when incubated in volumes sufficient to fill the test matrices.