Citric acid cement

There are occasions where the mud pH must be lowered such as after drilling fresh cement or overtreatment by one of the alkaline materials discussed. Organic acids that have been used for this purpose include acetic acid [64-19-7], citric acid [77-92-9], and oxaHc acid [144-62-7]. These materials are used infrequently. Inorganic additives used to lower pH levels include sodium bicarbonate [144-55-8] and sodium acid pyrophosphate [7758-16-9] (SAPP). Of the two, sodium bicarbonate is used the most by far. 

Concrete, Mortar, and Plaster. Citric acid and citrate salts are used as admixtures in concrete, mortar, and plaster formulations to retard setting times and reduce the amount of water requited to make a workable mixture (172—180). The citrate ion slows the hydration of Portland cement and acts as a dispersant, reducing the viscosity of the system (181). At levels below 0.1%, citrates accelerate the setting rate while at 0.2—0.4% the set rate is retarded. High early strength and improved frost resistance have been reported when adding citrate to concrete, mortar, and plaster. 

Refractories and Molds. Citric acid is used as a binder for refractory cements, imparting volume stabiUty and strength in ceramic materials for electrical condensers, foundry and glassmaking molds, and sand molds for metal castings (219—223). 

Morrill Act of 1862, 24 353 Mortality studies, PCB-related, 13 141 Mortar cements, 5 500t Mortars, 5 467, 500t 21 482-483 citric acid application, 6 648 furan resins in, 12 274 slaked lime in, 15 64 Mortar substitute, sulfur coatings as, 23 593... 

Regulated-set cement and jet cement are modified Portland cements in which the normal aluminate phase is replaced by CuA CaF, through the use of a raw mix containing CaF,. Uchikawa and Tsukiyama (U2I) gave chemical (Table 10.4) and phase compositions of two jet cements. Botli contained approximately 60% of alite, 20% of C, i A CaF,. 1% of belite and 5% of ferrite. Admixtures are required to control the rate of reaction of the C, 1 A CaFj and the nature of the products. One of the cements included a proprietary retarder based on citric acid, togetlier with 2"/o of CaC O, . The other contained 2.5% of hemihydrale. In each case, Na,S04 (T o) and anhydrite were also present. The specific surface areas were around 550 m kg . 

Oysters and some other molluscs live their adult lives permanently cemented to a support on the sea floor. The local environment can occasionally become anaerobic. This means that these higher animals have to function as facultative anaerobes (text, p. 427). When oysters are deprived of oxygen, they accumulate succinate. Even though the citric acid cycle cannot be run as a cycle in the absence of oxygen, the reactions can be exploited in a way that maintains redox balance. The four-carbon reactions are run backwards, from oxaloacetate to succinate. This produces reduced NAD" and FAD. Simultaneously, the cycle runs forward from citrate to succinate. This... 

A. Yokoyama, S. Yamamoto, T. Kawasaki, T. Kdigo, M. Nakasu, Development of calcium [4ios[hate cement using chitosan and citric acid for bone substitute materials, Biomataials 23 (2002) 1091—1101. 

Fig. 4.39 Effect of citric acid addition on the potential of cement particles in the paste (according to [25])...

An interesting application concerns the chitosan- calcium phosphate cement. Chitosan or chitosan glycerophosphate mixed with calcium phosphate and citric acid forms an attractive injectable self-hardening system for bone repair or filling indications [134, 213, 214],... 

The setting time of the binder will depend on the amount of calcitmi chloroaluminate present, on the form of SO3 that is present, and on the SO3/AI2O3 ratio. Usually the cement sets faster than Portland cement. If required, a hydroxyc oxylic acid, such as citric acid, may be added to retard the setting process (Takuma et al, 1997). 

The setting time of these cements is typically between several minutes and half an horn, but may be conveniently extended by the addition of suitable retarders, such as citric acid. 

Injectable bone substitute material consisting of CTS, citric acid, and glucose solution as the liquid phase, and tricalcium phosphate powder as the solid phase, was developed by Liu and coworkers [141]. Four types of cements have been used to investigate the mechanical properties and in vitro biocompatibility of the material. In the presence of citric acid, tricalcium phosphate partially transformed into HAp and dicalcium phosphate. 

Citadur. Trade-name a high-alumina CEMENT (q.v.) made in Czechoslovakia. Citric Acid. An organic acid sometimes used for the treatment of steel prior to enamelling, or in some metal release tests. 

In order to accelerate or retard the setting of cement, water-soluble admixtures may be used (see Section 5.3.1). Whilst many inorganic salts, such as calcium chloride, can act as accelerators, lead and zinc salts, borates and phosphates, as well as hydrocarbonic acids (e.g., citric acid or tartaric acid) and, most importantly, sugar derivatives such as raffinose or sucrose, will tend to retard the setting process. As the rate of setting can be determined by recording the heat evolved during hydration, a plot of (in Wkg ) versus 1/t will yield a close to linear relationship. 

Sarda S, Fernandez E, Nilsson M, Balcells M, Planell JA (2002) Kinetic study of citric acid influence on calcium phosphate bone cements as water-reducing agent. J Biomed Mater Res 61 653-659... 

In general, retarders are effective in the very early hydration of cement. For a given percentage, Na gluconate, citric acid, or sucrose are better retarders of initial set of a normal low alkali cement than lignosul-fonate, salicylic acid, Na heptonate, or boroheptonate.1 1... 

Reg Set cement mortar with a citric acid retarder has greater strength than Reg Set cement regulated with calcium sulfate hemihydrate. The increased strength in Reg Set cement paste or mortar made with the addition of citric acid is usually a result of an increased degree of hydration, increased amount of ettringite, increased volume concentration of small pores, and lower total porosity. 

Seo, Mijung Lee, Ki Youn Jung, Sunnye Kim, Sung Soo, Preparation of a-Tricalcium Phospate Bone Cement Effect of Citric Acid Key Eng. Mater.imi, 342-343. 

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