Calcium Hydroxide

As an alternative, calcium hydroxide is often supplied as two-paste material that also includes zinc oxide in a suspension of calcium hydroxide in the organic liquid ethyl toluene sulphonamide, mixed with glycol salicylate containing inert fillers, pigments and radiopacifiers.

From: Materials for the Direct Restoration of Teeth , 2016

Materials for pulp capping

John Nicholson , Beata Czarnecka , in Materials for the Direct Restoration of Teeth, 2016

9.4.1 Composition

Calcium hydroxide, Ca(OH) 2, has a long history of use in dentistry for pulp capping and it is available in a number of forms. These include as a supersaturated solution, a hard setting cement and also a light-curable material. Its key feature is its high alkalinity (pH 11–12.5), and this can be achieved using calcium hydroxide powder mixed with pure water to the consistency of a light paste [34]. However, used in this way, calcium hydroxide does not set, has no mechanical strength and consequently there is the danger of it being displaced by the forces involved in placing a restorative material over it [35]. Also in this form it cannot be used directly under any resin-based restoration (composite resins, compomers and resin-modified glass-ionomers) because it is hydrophilic and would interfere with bonding systems. To overcome this problem, calcium hydroxide formulations that are capable of undergoing some sort of setting reaction, and thus building up a degree of mechanical strength, are generally used. However, they have slightly different properties and cannot replace supersaturated calcium hydroxide solutions in all clinical situations.

Setting calcium hydroxide cements are typically based on liquid alkyl salicylates, and they are supplied to the clinician as a two-paste pack [36]. Alkyl salicylates that have been used include methyl salicylate, isobutyl salicylate and 1-methyl trimethylene disalicylate [37]. These cements set because the alkyl salicylate contains a phenolic –OH group which has acid character, and this means it can react with the alkaline calcium hydroxide [38].

Calcium hydroxide formulations of this type do not contain water, as the composition shown in Table 9.1 makes clear. This formulation is that of Dycal®, a calcium hydroxide material that has been available for many years and is widely respected.

Table 9.1. Composition of Dycal®

Base paste Catalyst paste
1,3-Butylene glycol disalicylate Calcium hydroxide
Zinc oxide N-ethyl-o/p-toluene sulfonamide
Calcium phosphate Zinc oxide
Calcium tungstate Titanium dioxide
Iron oxide (pigment) Zinc stearate
Iron oxide (pigment) — dentine shades only

Despite the absence of water, such formulations are capable of absorbing a small amount of water to initiate their acid–base setting reaction. As reaction proceeds, so water is produced as one of the products, and this sustains the setting process. Studies using infrared spectroscopy have shown that a critical part of the setting reaction involves loss of the ester group. This is apparent from the reduction in the band in the region 1675–1695   cm−   1. At the same time, there is a corresponding formation of a carboxylate band in the region 1540–1560   cm−   1, showing that the product is a salt formed by chelation with the available calcium ions [38]. The typical product of such a reaction is shown in Fig. 9.1.

Fig. 9.1. Chelate structure of calcium ion and an alkylsalicylate.

Chelate materials of this type are products of reaction of a metal base, such as calcium hydroxide or metal oxide, with weakly acidic organic substances with at least two functional groups. The ones used clinically are typically hydrolytically unstable, and this is responsible for their therapeutic effects. Ions released have beneficial properties, reducing inflammation, being bacteriostatic and stimulating the odontoblasts to form secondary dentine. Ideally, calcium hydroxide chelates of this kind dissolve completely with time, and thus have the maximum possible therapeutic effect.

As well as chelate cements of this type, there are also curable calcium hydroxide cements available [39]. These materials have superior mechanical properties to the chelate-type calcium hydroxide cements [40] and also better chemical resistance [41], since they are not affected by treatment with phosphoric acid etchants. A typical example is Biocal®, which has the composition shown in Table 9.2.

Table 9.2. Composition of Biocal®

Components
Calcium hydroxide
Ethylene urethane dimethacrylate
Barium sulphate
Inorganic filler
Titanium dioxide
Iron oxide (pigment)
Photo-initiator

The resin component is ethylene urethane dimethacrylate, UDMA [40], a substance of the type used in commercial composite resins. It contains two carbon–carbon double bonds and these are capable of undergoing addition polymerization. This particular reaction is triggered by the photo-initiators present when the material is exposed to light from a dental cure lamp. The calcium hydroxide component effectively serves as filler and is completely enclosed in the polymeric UDMA matrix after setting. Consequently, it cannot dissociate in water, and any release of Ca2   + and OH− ions must be minimal. This implies that its therapeutic properties are likely to be seriously compromised compared with other types of calcium hydroxide, a point on which further research is clearly needed.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B978008100491300009X

Fire Retardant Fillers for Polymers

R. Rothon , P. Hornsby , in Polymer Green Flame Retardants, 2014

7.1 Calcium hydroxide

Calcium hydroxide is the most available and lowest cost of the metal hydroxides and has a very significant endothermic decomposition at a temperature which, although a little on the high side, ought to be suitable for some polymers. As such, it has attracted some interest as a possible flame retardant additive.

Despite these apparently favorable properties, conventional calcium hydroxide does not appear to have a sufficient fire retardant effect. Ashley and Rothon [19] have reported testing at 125   phr in crosslinked EVA where it only achieved an oxygen index of 24.5% compared to that of aluminum hydroxide at 29.0%. Even less effect was found in polypropylene and polyamide. The polyamide result was especially disappointing as its decomposition temperature is similar to that of calcium hydroxide, so a good effect was expected. A strong ash was observed in the EVA case, but analysis showed this to be calcium carbonate not oxide. This is somewhat surprising in view of the same workers reporting that precipitated calcium carbonate formed an oxide ash in the same test and polymer. Nishimoto and coworkers also reported the lack of any significant effect in polypropylene [61].

There have been claims that calcium hydroxide can be made into an effective flame retardant by making it into a composite hydroxide with other metals in solid solution [62]. This does not seem to have been converted into any significant commercial production though.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444538086000093

Nanobiomaterials in endodontics

Maryam Khoroushi , ... Majid Abdolrahimi , in Nanobiomaterials in Dentistry, 2016

14.2.1 Calcium Hydroxide

For many years calcium hydroxide nanoparticles (CH NPs) have been investigated in different fields of science ( Roy and Bhattacharya, 2010; Salvadori and Dei, 2001) but studies on CH NPs are limited in dentistry. Comparison of cytotoxicity of CH and CH NPs on fibroblast cell lines showed that CH and CH NPs have comparable cytotoxic effects at 24, 48, and 72 h. Both types of CH had a significantly lower toxicity at 72 h compared to 24 and 48 h (Dianat et al., 2015a). In another study the antibacterial efficacy of CH and CH NPs was compared. Interestingly, the minimal inhibitory concentration of CH NPs was four times less than that of CH, indicating that CH NPs at lower concentrations have antibacterial efficacy similar to conventional CH at a higher concentration. In the agar diffusion test the combination of CH NPs and distilled water (DW) exhibited the highest efficacy, followed by chlorhexidine (CHX)/CH NPS, CHX/CH, and CH/DW. When the microbial content of dentinal tubules was assessed, no significant differences were observed in 200   μm of dentinal tubules between CH NPs and CH. However, at a depth of 400   μm, the CH NPs group exhibited a lower microbial content when compared to CH. It seems that CH NPs can penetrate into deeper depths of dentinal tubules (Dianat et al., 2015b).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B978032342867500014X

Role of nanomaterials in clinical dentistry

Shashikala Krishnamurthy , Sandhya Vijayasarathy , in Nanobiomaterials in Dentistry, 2016

9.3.1 Nanorestorative Materials: Pulp-Capping Agent

Calcium hydroxide cement (CHC), indicated as a direct and indirect pulp-capping material in deep caries management, has been widely used for several decades. In addition to their antibacterial, mineralization, and pH effect, CHCs have some disadvantages as well, such as high solubility and disintegration rate in oral fluids, without adhesive qualities, and low mechanical strength. Studies attempted to incorporate 3   wt% HA NPs to commercially available CHCs and showed improvement in the mechanical strength of the cement with an increase in the calcium release rate as a mineralization promoter without affecting the antibacterial behavior (Yasaei et al., 2013).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780323428675000096

Nanostructure/microstructure of metakaolin geopolymers

J.L. Provis , ... P. Duxson , in Geopolymers, 2009

5.6 Calcium in metakaolin geopolymers

The calcium hydroxide-metakaolin system is in itself of interest as a means of analysing the pozzolanic reaction in Portland cement concretes, entirely separate from any discussion of geopolymer chemistry. However, the introduction of an additional alkali source, as is the case in calcium-containing metakaolin geopolymers, introduces additional complexity into the range of phases that can form in this reaction system. In particular, the possibility of phase separation and metastable coexistence of calcium (alumino)silicate hydrate, C-(A)-S-H, and sodium aluminosilicate hydrate, N-A-S-H, gels is an issue of very significant interest ( Granizo et al. 2002, Yip and van Deventer 2003, Buchwald et al. 2007, García-Lodeiro et al. 2008, Yip et al. 2008, Yong 2009).

The addition of a sufficient quantity of calcium to geopolymers in the form of calcium hydroxide can lead to the formation of phase-separated C-(A)-S-H and geopolymer (N-A-S-H) gels. This is known to be more prevalent at relatively low alkalinity - low NaOH concentrations in hydroxide-activated systems (Alonso and Palomo 2001), or higher SiO2/Na2O ratios in silicate-activated systems (Yong 2009). It is likely that the common ion effect involving OH‒ in highly alkaline solutions means that the dissolution of Ca(OH)2 is hindered in such systems, and it is also possible that very highly alkaline conditions will lead to dissolution of any C-S-H type phases which are formed. Slag-metakaolin geopolymers show a significant extent of phase coexistence, as well as relatively high strength compared to many other metakaolin geopolymers (Yip and van Deventer 2003, Buchwald et al. 2007).

When adding calcium to geopolymers in the form of various calcium silicates (minerals, blast furnace slag and Portland cement), Yip et al. (2008) found that the replacement of 20% of the metakaolin in a geopolymer mix had varying effects depending on the specific nature of the calcium silicate source and also the alkalinity of the geopolymer-forming system. At low alkalinity, the compressive strength of geopolymer matrices prepared with predominantly amorphous calcium silicates (blast furnace slag) or containing crystalline phases specifically manufactured for reactivity (cement) was much higher than when the calcium was supplied as crystalline silicate minerals. The compressive strength of matrices containing natural calcium silicates improved with increasing alkalinity, however the opposite trend was observed in matrices synthesised with processed calcium silicate sources. The difference in compressive strength between matrices synthesised using different calcium silicate sources was significantly reduced at high alkalinity. At high alkalinity, calcium played a lesser role in determining the nature of the final binder, as it formed hydroxide precipitates rather than hydrated gels.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9781845694494500059

Development of Synthetic Hydroxyapatite-Based Household Defluoridation Unit

Ayushi Khare , ... Sanjeev Chaudhari , in Advances in Water Purification Techniques, 2019

11.3.1 Hydroxyapatite Synthesis and Characterization

HAP was synthesized by the precipitation method at room temperature by the following procedure:

The calcium hydroxide [Ca(OH) 2] suspension and di-ammonium hydrogen phosphate [DAP, (NH4)2HPO4] solution were prepared by adding analytical grade [Ca(OH)2] and (NH4)2HPO4 salts into 600 and 200   mL of distilled water, respectively. Final concentration of Ca2   + and PO 4 3 − in the mixture was 0.7775 and 0.4656   M, respectively for Ca/P molar ratio 1.67, which is theoretical molar ratio of HAP. The Ca(OH)2 and DAP solutions were stirred at room temperature for 20   min. DAP solution was added to the Ca(OH)2 suspension at a flow rate of 8   mL/min using peristaltic pump with continuous stirring. The mixture was kept under mixing for 2   h for maturation. The mixture was then centrifuged at 4000–5000   rpm to remove supernatant. Precipitate obtained was washed twice using distilled water, followed by centrifugation to remove un-reacted chemicals and by-products. The wet HAP paste was dried at 80°C. The dried HAP was ground to powder using porcelain mortar and pestle. The powder was sieved into different particle size fractions, stored in air tight resealable plastic poly-bags. Powder used for batch study had particles in size range of 25–355   μm.

The powder X-ray diffraction with Cu Kα (30   mA and 40   kV) was used with scanning rate of 0.017   degrees (2θ/20) and for the range of 10–80   degrees (2θ) to examine the formation of crystalline phases and purity of solids synthesized. The obtained XRD pattern of the HAP is presented in Fig. 11.1. The solid red line in Fig. 11.1 represents XRD pattern of standard synthetic HAP (Reference no.—00-003-0747, X'Pert software) and circular symbols represent experimental data. It can be seen from the figure that the crystalline peaks obtained are matching and agreed with that of synthetic HAP confirming the formation of HAP.

Fig. 11.1

Fig. 11.1. XRD pattern of synthesized noncalcined hydroxyapatite (HAP).

The quality of treated water varies in accordance with the Ca/P molar ratio of HAP. Actual Ca/P molar ratio in HAP was found by completely dissolving HAP precipitates into concentrated hydrochloric acid, Ca/P molar ratio was found to be 1.61, which is in close agreement with stoichiometric Ca/P molar ratio of 1.67.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128147900000119

Clean water unit operation design

Seán Moran , in An Applied Guide to Water and Effluent Treatment Plant Design, 2018

Lime/Soda softening

Adding lime (calcium hydroxide) or soda ash (sodium carbonate) precipitates out hardness as virtually insoluble calcium carbonate and magnesium hydroxide, readily removable by sedimentation and filtration. Temporary hardness is removed by the addition of lime and permanent hardness by the addition of soda ash.

The process produces large quantities of sludge, whose treatment and disposal should be considered during preliminary design.

Lime is usually supplied as a dry powder, and it can be added dry or as a slurry, made up on site from the powder. Soda ash is also usually supplied dry, and is made up on site into a solution for dosing.

The required lime dose if total hardness is equal to or less than total alkalinity can be estimated as follows:

Lime dosage = 1.2 × ( [ CO 2 ] + [ Total hardness ] + [ Mg ] )

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128113097000084

Dry-stack and compressed stabilised earth-block construction

H.C. Uzoegbo , in Nonconventional and Vernacular Construction Materials, 2016

8.2.5.2 Lime

Hydrated lime (calcium hydroxide) is also used as a stabiliser. There are two basic types of lime: high-calcium and high-magnesium lime. Their soil-stabilising efficiency is about the same. Lime will react readily with most plastic soils containing clay but lime does not improve sands or other noncohesive granular materials. Lime makes a good stabiliser for soil with clay content greater than 40%. It reacts with the clay to form strong bonds between soil particles. The recommended amount of lime for stabilisation ranges from 4% to 8% of the dry weight of soil. Soils ranging in plasticity index from 10 to 50 or higher are suitable for lime stabilisation. Lime stabilisation decreases the plastic index and volume change and increases the compressive strength of the soil material.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780081000380000081

Drugs of Abuse☆

Niamh NicDaéid , Craig McKenzie , in Encyclopedia of Analytical Science (Third Edition), 2019

Coca paste production

Coca leaves are mixed with calcium hydroxide (lime) and water. The mixture is crushed and stirred in a hydrocarbon solvent, usually kerosene. The extracted coca leaf residue is removed and the kerosene extracted with acidified water. The cocaine alkaloids are extracted into the aqueous layer and coca paste is precipitated by the addition of base. This paste contains crude cocaine as well as a mixture of inorganic salts. Alternatively, the leaves can be crushed in dilute sulfuric acid, extracted with kerosene and the aqueous layer basified with ammonia or similar to precipitate the alkaloids which are collected.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780124095472144592

Utilization of mining wastes to produce geopolymer binders

F. Pacheco-Torgal , ... J.P. Castro Gomes , in Geopolymers, 2009

13.3 Strength gain and mix design parameters

13.3.1 Influence of Ca(OH)2 and sodium hydroxide concentration

Previous investigations showed that mine waste mixtures without calcium hydroxide have a very low compressive strength performance. The mortar mixtures ( Table 13.4) with a 10% calcium hydroxide percentage present the maximum compressive strength, almost 30   MPa, for a sodium hydroxide concentration of 16M, (to which correspond a H2O/Na2O molar ratio of 13.4 (Fig. 13.3)). The total mass of water used to determine the water-binder ratio is the sum of water contained in the sodium hydroxide solution, the water contained in waterglass and the mass of extra water added to the mixture. These results are consistent with the ones obtained by Alonso and Palomo (2001a, 2001b). These authors, using metakaolin/calcium hydroxide mixtures, reported the influence of the sodium hydroxide concentration on the nature of the final reaction product formed. The results help to explain the importance of calcium in geopolymer binders and also why the composition of the geopolymer cement PZ-Geopoly® patent has a content of 11.1% of calcium oxide (Davidovits, 1999). Apart from the explanation that positive ions such as Ca2+ need to be present in the framework cavities to balance the negative charge of the aluminate group, it is still not clear why calcium hydroxide plays such a significant role in the strength of alkali-activated binders.

Table 13.4. Mortar composition (C105–C116)

Comp. Conc. hydróxide Waterglass: hydroxide Ms (silica modulus) H2O/Na2O Molar r. Calcium hydrox.(%)
C105 1.34 13.7 17.5
16M
C106 13.9 22.5
C107 1.41 14.3 17.5
14M
C108 14.6 22.5
C109 15.1 17.5
12M 1.49
C110 15.3 22.5
2.5:1
C111 16.0 17.5
10M 1.59
C112 16.3 22.5
C113 17.2 17.5
8M 1.72
C114 17.5 22.5
C115 1.90 18.7 17.5
6M
C116 19.1 22.5

13.3. Compressive strength versus sodium hydroxide concentration according to calcium hydroxide percentage (22.5; 17.5; 15 and 10%).

The mixtures in which calcium hydroxide percentage is higher than 10%, show strength decrease after 14   days curing. This strength loss related behaviour has been confirmed by others (Yip et al., 2005). The explanation for that is related to the formation of two different phases, geopolymeric gel and calcium silicate hydrates, being that the former acts as microaggregates. These authors believe that strength loss with curing time is maybe due to the fact that CSH reaction and the geopolymeric reaction will compete against each other for soluble silicates, giving rise to a binder composed of two porous phases that leads to strength loss. More recently Yip et al. (2008) studied the effect of calcium sources on the geopolymerization stating that lower strengths were due to the unreacted mineral particles that disrupt the geopolymeric gel network. An alternative explanation is related to the possibility of the occurrence of shrinkage cracking near the aggregates, originating a clear tensile strength reduction, that could only be confirmed when shrinkage and tensile strength were studied. Results show a compressive strength increase with the H2O/Na2O molar ratio decrease Fig. 13.4. It is clearer for mixtures with a 10% calcium hydroxide percentage a H2O/Na2O molar ratio lower than 15 and higher curing ages. The rest of the mixtures with higher calcium hydroxide percentages sometimes show a strength increase for H2O/Na2O molar ratio decreases that occurs from 14   days curing forward. However, sometimes they also present a strength decrease when H2O/Na2O molar ratio decreases. This behaviour has to do with calcium hydroxide solubility in high alkaline environment and with the formation of calcium hydroxide and CNSH precipitates (Stade, 1989; Macphee, 1989).

13.4. Compressive strength versus H2O/Na2O molar ratio according to calcium hydroxide concentration (10, 15, 17.5 and 20%).

13.3.2 Influence of H2O/Na2O molar ratio

A major strength increase, with 30MPa after just 1   day, reaching almost 70MPa after 28   days curing (Fig. 13.5) is noticed. This performance is mainly related to the use of less aggregates and thus less extra water (Table 13.5 ). The use of mixtures containing 5% calcium hydroxide leads to lower strength after long curing time than when 10% calcium hydroxide mixtures were used. The strength differences are much higher for the initial curing days, after just 1  day the mixtures with 5% calcium hydroxide have just half the strength of the 10% calcium hydroxide mixtures. The extraordinary strength increase is due to the use of a low H2O/Na2O molar ratio, which influences strength development. When the alkaline concentration rises, that implies a higher amount of dissolved aluminosilicate species, meaning more cementitious material available to react. Results show that compressive strength is influenced by the percentage of calcium hydroxide: the highest strength is achieved for 10% calcium hydroxide percentage. However the use of 5% calcium hydroxide percentage leads to similar strength results for long curing times. This means that for this mixing condition compressive strength is not so influenced by calcium hydroxide percentage. An explanation for such behaviour may rely in the fact that aluminosilicate (geopolymeric) compounds are being formed. The use of 16.7% and 25% calcium hydroxide percentages, although associated with a strength rise due to the use of a 24M concentration, achieved a far lower strength than the 10% calcium hydroxide percentage. This behaviour can be explained by the use of less aluminosilicate mine waste (replaced by calcium hydroxide) as well as from the increase of unreacted particles, due to less setting time, because calcium hydroxide shortens setting time.

13.5. Compressive strength according to curing time for several calcium hydroxide percentages and waterglass/sodium hydroxide mass ratios.

Table 13.5. Mortar composition (C126–C128)

Comp. Conc.hydróxide Waterglass:hydroxide Ms (sílica modulus) H2O/Na2O molar r. Calcium hydrox.(%)
C126 10.3 10
C127 24M 2.5:1 1.17 10.7 25
C128 10.2 5

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9781845694494500138