CA1143925A

CA1143925A - Stabilization of aqueous silicates using alkali siliconates of silylalkyl phosphonates

Info

Publication number: CA1143925A
Application number: CA000321287A
Authority: CA
Inventors: Edwin P. Plueddemann
Original assignee: Dow Corning Corp
Current assignee: Dow Silicones Corp
Priority date: 1978-03-30
Filing date: 1979-02-12
Publication date: 1983-04-05
Also published as: BR7901923A; DE2912430A1; NL178972C; NL7902495A; JPS54133441A; SE7902801L; NL178972B; AU523148B2; SE448240B; IT7921277A0; FR2421205A1; IT1114218B; CH648325A5; JPS5942752B2; DE2954388C2; GB2018266A; GB2018266B; DE2912430C2; DE2954388A1; AU4557679A

Abstract

ABSTRACT OF THE DISCLOSURE

Noval alkali siliconate silylalkylphosphonates of the formula wherein M is a cation selected from the group consisting of sodium, potassium, lithium, rubidium and tetraorgano ammonium cations:
R is a divalent aliphatic hydrocarbon radical containing 1-3 carbon atoms or the benzul radical; and R' is a hydrocarbon radical or halohydrocarbon radical containing from 1-7 carbon atoms. These materials are capable of stabilizing water soluble silicates and capable of inhibiting corrosion of metal in aqueous systems.

Description

This invention relates to novel silylalkyl-phosphonates and their use in the stabilization of aqueous sllicates and as metal corrosion inhibi-tors. ~ ;
A~ueous silicates as a class of compounds have been known as metal corrosion inhibitors for aqueous systems. One of the ~ -~
disadvantages of the silicates, however, is the fact that they are ~`
unstable and after use at elevated temperatures tend to gel and precipitate out of solution. There have been many efforts therefore to stabilize silicates so that they could be more persistent in their corrosion inhibiting properties.
Arthur N. Pines et al. in U.S. Patents No. 3,312,622 and No. 3,198,820 describes combinations of silicone-silicate polymers as corrosion inhibitors. Although the patent does not specifically describe the stabilization of silicates, it is apparent from the specification that the so-called "novel ~;
organosilicon polymer" does in fact contribute to the persistency of the corrosion inhibition of the silicGne-silicate polymers of that invention. The novelty, as pointed out therein, is the use of silyl cationic carboxylates in conjunction with the silicates.
Such materials are discussed as enhancing the corrosion inhibition of common antifreeze compositions and overcome disadvantages of other prior art corrosion inhibitors such as handling and dispensing of the antifreezes; selective corrosion inhibition of ~ ~;
certain metalsr poor shelf life, tendency to attack rubber hoses, excessive foaming in use and the causing of alcohols to decompose.
In later issued U.S. Patents No. 3,341,469 and No.
3,337,496, Pines et al. describes another system that was found useful for inhibiting corrosion in aqueous alcohol compositions.
It consisted of a mixture of an alkyl sil~esquioxane, a siloxane modified with a cyanoalkyl or carbinol group and a silicate.
.~ .

.3~5 These materials are stated as being "remarkably soluble in aqueous liquids". Further, the compositions are alleged to overcome many ~ -of the above mentioned disadvantages.
Finally, U.S. Patent No. 3,948,964 issued April 6, 1976 describes the stabili~ation of partially hydrolyzed silicic acid esters using stabilizers selected from organic compounds such as cyclic ethers, ether alcohols, carboxylic acid esters and ketones.
Such stabilized materials are described as binders for zinc dust pigments and the like.
None of the above references, however, describe the compositions of the instant invention. The advantages of the prior art methods can be obtained with the instant invention and additional advantages over the prior art are obtained by this invention. Most notable are the advantages o low cost, enhanced effectiveness in stabili2ation of silicates and the persistency of corrosion inhibition.
This invention consists of several aspects of the same concept and one aspect is a composition of matter which is an alkali siliconate silylalkylphosphonate which has the general unit formula (I) MoSiRoPoOM
O R' wherein M is selected from a group consisting of alkaline metal cations selected from a group consisting of sodium, potassium, lithium and rubidium and, tetraorgano ammonium cations; R is a divalent alipha~ic hydrocarbon radical containing 1-3 carbon atoms ,3~ 5 or the benzyl radical; and R' is a hydrocarbon radical containing from 1-7 carbon atoms.
The phosphonate is derived from silylalkylesters of ~ -phosphorus by the reaction of an alkali metal hydroxide with the esters of phosphorus.
The precursor phosphorus compound, that is, the silylal~ylesters of phosphorus can be prepared by several methods but it is preferred to prepare them by the method shown in the U.S. Patent No~ 4,093,641 issued June 6, 1978, to Plueddemann.
Plueddemann's method is easy to carry out and gives high yields which gives the resulting product a low cost. The precursor phosphorus compounds are then treated with dilute sodium hydroxide and refluxed for several hours to saponify the phosphonate precursor. The resulting product, in the case of the use of sodium hydroxide, is O
~aOSiROPOONa o ~ ' .

i e. the sodium salt of the sodium siliconate silylal~yl-phosphonate.
M in formula I can be independently an alkaline metal cation selected from sodium, potassium, lithium and rubidium and the tetraorgano ~onium cations. Typical tetraorgano ammonium cations are tetramethyl ammonium and tetraethyl ammonium.
R in the above formula is a divalent aliphatic hydrocarbon radical containing 1-3 carbon atoms or the benzyl 3~2S

radical. The material should be water soluble so there is a llmit to the size and type of R. ;
R' is a hydrocarbon radical or a halohydrocarbon radical~
of 1-7 carbon atoms and includes methyl, ethyl, phenyl, halobenzyl :~
or the like.
In actual practice, using a dichlorobenzyldimethyl~
phosphate as an example, the preparation is as follows: ; `
~:: '. :
Cl ~ CH2PO(OCH3)2 Cl benzyldimethylamine tCH3O)3SiCH2CH2CH2C1 135-200C./6 hours Cl ~ CH2POCH2CH2CH2si(OcH3)3 (I) Cl OCH3 ::

Aqueous ( I ) + NaOH -- - - >
re~lux/several hours < ~ CH2POCH2CH2CN25iONa Na The resulting product is used alone or in conjunction . ~
with a silicate as will be explained infra.

; ~ .

As mentioned carlier, the products of the invention, the alkali siliconate silylalkylphosphonates are able to stabilize ;
silicates that are useful as corrosion inhibitors for metals. ` :~
Thus, obvious uses for such materials is in antireeze compositions where metal corrosion is common due to high ~-:
temperatures which cause decomposition of the alcohols typically used as freezing point depressants. If the silicates protect the :~
internal metal parts of a cooling system, such as an automobile ~;
. engine, and if the silicates can be induced to have persistency in the aqueous system, then there is a distinct advantage. :~
This in~ention therefore also contemplates a composition of matter which is an improved corrosion inhibiting alcohol composition consisting essentially of an alcohol and, as a corrosion inhibitor, a corrosion inhibiting amount of a composition consisting essentially of a combination of (A) an alkali siliconate silylalkylphosphonate which has the general formula (II) MOSiROPOOM ~ :
O R' wherein M is independently an alkaline metal cation selected from the group consisting of sodium, potassium, lithium, rubidium and tetraorgano ammonium cations; R is a divalent aliphatic hydrocarbon radical containing 1-3 carbon atoms or the benzyl radical; and R' .is a hydrocarbon radical or a halohydrocarbon : ~-containing Erom 1-7 carbon atoms, with (B) a soluble silicate represented by the general unit formula (III) (MO)asio4-a wherein M has the meaning above and a has a value of 1~3.
It is contemplated that the alcohol composition can be anhydrous or contain, in addition to the alcohol and phosphonate-silicate, relatively small amounts of water and it is also contemplated that the alcohol composition can contain relatively large amounts of water, that is, the alcohol compositions may be "concentrates" or "coolants".
The alcohols that are useful in this invention include both monomeric alcohols such as methanol, ethanol, propanol and butanol and polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, glycerol and mixtures of the above. What is contemplated are the currently useful antifreeze alcohols, especially ethylene glycol.
The corrosion inhibitor of the above composition is a composition of matter which consists essentially o (A) 0.1 to 99.9 parts by weight of an alkali siliconate silylalkylphosphonate which has the general unit formula O ~' MOSiROPOOM
O R' wherein M is independently an alkaline metal cation selected from the group consisting o-f sodium, potassium, lithium, rubidium and ~;
tetraorgano ammonium cations; R is a divalent aliphatic hydrocarbon radical containing 1-3 carbon atoms or the benzyl radical; and R' ~s a hydrocarbon radical or halohydrocarbon radical containing from 1~7 carbon atoms, with (B~ 99.9 to 0.1 parts by weight o~ a soluble silicate represented by the general ~ 3 unit formula (Mo)asio4-a wherein M has the meaning above and a has a value of 1-3.
As indicated above, essentially all ratios of phosphonate (A) to silicate (B) are effective to produce a metal corrosion inhibiting material~ The ratio of ~A) to (B) depends on the particular system in which it is used. Therefore the ratio of (A) to ~B~ that is the most useful in this invention is dependent on the amount of water in the system, the amount and type of alcohol present, the temperature of the aqueous medium and other additives or chemicals in the system.
The phosphona-tes have been discussed above and therefore, turning to component (B) of this invention, it should be noted that ~he silicates intended herein are t:he water soluble silicates and are represented by formula III as shown above. M in that formula has the same meaning as set fort:h ahove for M and is a cation which would render the silicate water soluble.
Illustrative of these silicates are the alkali metal orthosilicates, alkali metal metasilicates, the alkali metal tetrasilicates, the alkali metal disilicates and the ~-tetraorganoa~nonium silicates.
Specific examples of these silicates are ~otassium metasilicate, sodium orthosilicate, potassium disilicate, lithium orthosilicate7 lithium metasilicate, lithium disilicate, rubidium disilicate, rubidium tetrasilicate, mixed silicates (e.g.
Na20 Li20 2SiO2 and K2o-Li2o~4sio2)~ tetra(methyl) ammonium silicate, te~ra(ethyl) ammonium silicate, phenyltrimethyl ammonium silicate, benzyltrimethyl ammonium silicate, ~uanidine silicate and tetra(hydroxy-ethyl) ammonium silicate. The preferred silicates are sodium and potassium silicates, especially sodium disilicate and potassium disilicate.
The silicate used in producing the phosphonate-silicate inhibitor can be added to the reaction mixture as such or it can be formed in-situ by adding the appropriate alkali hydroxide and silica to the reaction mixture.
It is contemplated within the scope of this invention that the combination of (A) and (B) can be mixtures of (A) and tB) or partial reaction products of (A) and (B) or mixtures of mixtures of (A) and (B) and partial reaction products of (A) and (B).
The phosphonate-silicate combination can be prepared by ~ ~ ;
simply mixing the components (A) and (B), in the proper ratios, and stirring to homogenize them.
The phosphonate-silicate combination is then added to the alcohol composition. The order in which the phosphonate, silicate and alcohol are added is not critical as long as the materials are ~;~
thoroughly mixed.
The alcoholic phosphonate-silicate combinations are found 20 to be useful in other areas besides automotive engine cooling. ~
For example r the materials can be used in refrigeration and air ~ ;
conditioning units, cooling cOilsr heat exchangers and the like.
It was indicated earlier that the phosphonate could be useful in this invention without actually combining it with a silicate before use, that is, the phosphonate could be added to aqueous systems without the silicate. This invention, therefore, contemplates the use of the phosphonate and the phosphonate-silicate compositions in aqueous systems other than anti-free~e systems, that is7 non-alcoholic aqueous systems which come in contact with metal surfaces, i.e. such uses as controlling scale in geothermal power plants, scale control in conventional heat exchange systems and the liXe.
The amount of the combination (A) and (B) required to protect metals from corrosion depends on the metals to be protected, the system in which the combination is used, the temperature of the system and the other components and additives used in the system. Generally, the combination (A) and (B) is used in an amount as low as 20 parts per million up to 2 parts per 100 parts based on the weight of the aqueous liquid used.
For automotive engine coolants, it has been found that 200 parts of the phosphonate-silicate, based on a million parts of the aqueous alcohol coolant is effective to prevent corrosion. In non-alcoholic aqueous mediums, larger quantities are sometimes necessary. The preferred range of use for all systems within the scope of this invention is 200 parts per million parts of aqueous medium to 2 parts per 100 of aqueous meclium.
It is within the scope of this invention to add various additives which impart special properties such as anti-foam agents, both organic and siloxane based, dyes, pH indicators, other inhibitorsr thickeners and the like.
The following examples are shown to illustrate the invention and are not intended to define the scope thereof.

~ :
As indicated above, the materials of the art are subjected to very adverse conditions which affect their stabilizing properties. The materials of the instant invention were therefore subjected to adverse conditions in the following manner: -~

Nyacol~ 215, a commercial silica sol manufactured by Nyanza, Inc., Ashland, MA 01721 was used in this example. The sol, ~hich had a pH of 10.5 and which was Na+ stabilized, contained approximately 15~ silica which had a particle size of ~
approximately 2 m~m. The pH was reduced using 10% aqueous HCl ~ `
solution as shown in Table I. The freeze-thaw cycle consisted of placing 1 oz. glass vials of the solutions in a freezer and freezing for twelve (12) hours. The vials were then removed from the freezer and allowed to thaw. m e solutions were then checked for the appearance of precipitate indicating the solution was not stable.

:
To show the versatility of the materials, a second colloidal silica was treated and subjected to similar adverse conditions. See Table II. The silicate was Ludox~ as manufactured by E. I. DuPont De Nemours and Co., Wilmington, Delaware. The sol contains 30~ silica and i5 ammonia stabilized.
The pH of the sol was 9. 4 and it had an average particle size of 13-14 m~. The pH was reduced by the addition of 10% aqueous HCl solution as shown in Table II.
Example 3 ~ - -This example illustrates the stabilizing effect of the material in Nalcoag~ 1034A manufactured by the Nalco Chemical Co., Chicago, IL 60601. The sol is H+ stabilized and contains 34%
silica. It has an acid pH o~ 3.1 and the average particle size is 16-22 m~m.
The Nalcoag was made less acid by the addition of ammonia-be ore being tested as shown in Table III.

Example 4 This example illustrates the stahilizing effect of the~
material in Ludox~ SM 30 manufactured by E. I. DuPont De Nemours and Co., Wilmington, Delaware. The sol is Na+ stabiIized, has a pH of 9-10 and an average particle size of 7-8 m~m. The solutions~
were tested as shown in Table IV after being reduced in pH by the addition of 10% aqueous HCl. ;
Example 5 This example illustrates the effect of pH on stability.
Stability of silicate/siliconate mixtures has a minimum generally~
at pH 8.
A 7.5:1 mol ratio of sodium silicate "G" to product was used. The silicate "G" was a sodium silicate manufactured by Philadelphia Quartz Co. and has a weiyht ratio of SiO2/Na2O of 3.22 and a pH of 10.8. The product of this invention was a 1 ;~
molal aqueous siliconate, i.e. ~ ~
': ~ . ' .:
O
l, 5sicH2cH2cH2op-oNa ~ "~
CH3 ;
The mixture, after aging 1 day at room temperature, was acidifled with 10% aqueous HCl to various pH's and observed for gel time.
pH gel tlme 4 > 1 week 6 > 1 week 7 > 1 week 3 1 3/4 hrs.
9 9 hrs.
.
> 1 week :

;25 m e sample at the pH of 4 showed no gelling at 1 year.
Example 6 This example illustrates the effec-t of aging. A similar mixture as was prepared in Example 5 above was used for this example except the one (1) molal solution was 5:1 ratio of the silicate to the product.

Time Aged Stability at SampleAt Room Temp. pH 8 _ , A10 sec. 30 sec. -B 1 min. 70 sec. ;
C 5 min. 20 min. ~ ;
D15 min. > 1 week E45 min. > 1 week Samples D and E were still stable at this writing, some four weeks (4) from their preparation.
Example 7 This example shows the e~fect with sodium metasilicate, a low molecular weight silicate. A two molal sodi~m metasilicate solution was mixed with a two molal product~ i.e.

i.
Ol.5SiCH~CH2CH2OPONa in a mol ratio of 7:3. After aging at room temperature for 6 months, the equilibrated mixture was further diluted with sodium metasilicate as indicated and then the pH was adjusted to 8 with a ~ `
10% aqueous HCl solution and the solutions were then observed for stability.

mol ratio sodium ;
metasilicate/phosphonate 7:3 4:1 6 Stability at pH 8 ~ 1 week > 1 week 16 min ~ 3~325 Therefore, it can be observed that a mixture of sodium metasilicate and a phosphonate of this invention, at a ratio of 4:1 provide stable corrosion inhibitors that will not gel when neutralized. A fresh mixture at a ratio of 4:1 gelled in 6 minutes at pH 8, indicating that a period of equilibration is beneficial.
Example 8 - Stabilization of a potassium silicate (Kasil 5). :
A one (1) molal potassium silicate solution of weight ratio of SiO2/K2o of 2.10 (mol ratio 3.3:1) manufactured by Philadelphia Quartz, was mixed with two ratios of 1 molal siliconate solutions and after aging 15 minutes the pH was adjusted to 8 with aqueous 10~ HCl. -:

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composition of matter which is an alkali siliconate silylalkylphosphonate which has the general unit formula wherein M is a cation selected from a group consisting of sodium, potassium, lithium, rubidium and tetraorgano ammonium cations;
R is a divalent aliphatic hydrocarbon radical containing 1-3 carhon atoms or the benzyl radical; and R' is a hydrocarbon radical or halohydrocarbon radical containing from 1-7 carbon atoms.

2. An improved corrosion inhibiting alcohol composition consisting essentially of an alcohol and, as a corrosion inhibitor, a corrosion inhibiting amount of a composition consisting essentially of a mixture of (A) an alkali siliconate silylalkylphosphonate which has the general unit formula wherein M is a cation selected from the group consisting of sodium, potassium, lithium, rubidium and tetraorgano ammonium cations;
R is a divalent aliphatic hydrocarbon radical containing 1-3 carbon atoms or the benzyl-radical; and R' is a hydrocarbon radical or halohydrocarbon radical containing from 1-7 carbon atoms, and (B) a soluble silicate represented by the general unit formula wherein M has the meaning above and a has a value of 1-3.

3. A composition of matter which consists essentially of (A) 0.1 to 99.9 parts by weight of an alkali siliconate silylalkylphosphonate which has the general unit formula .
wherein M is a cation selected from the group consisting of sodium, potassium, lithium, rubidium and tetraorgano ammonium cations;
R is a divalent alipnatic hydrocarbon radical containing 1-3 carbon atoms or the benzyl radical; and R1 is a hydrocarbon radical or a halohydrocarbon radical containing from 1-7 carbon atoms, with (B) 99.9 to 0.1 parts by weight of a soluble silicate represented by the general unit formula wherein M has the meaning above and a has a value of 1-3.

4. A method of stabilizing soluble silicates comprising adding to the soluble silicates a composition consisting essentially of an alkali siliconate silylalkylphosphonate which has the general unit formula wherein M is a cation selected from a group consisting of sodium, potassium, lithium, rubidium and tetraorgano ammonium cations;
R is a divalent aliphatic hydrocarbon radical containing 1-3 carbon atoms or the benzyl radical; and R' is a hydrocarbon radical or halohydrocarbon radical containing from 1-7 carbon atoms.

5. A method of inhibiting metal corrosion in an aqueous medium by adding to the aqueous medium a composition consisting essentially of an alkali siliconate silylalkylphosphonate which has the general unit formula wherein M is a cation selected from a group consisting of sodium, potassium, lithium, rubidium and tetraorgano ammonium cations;
R is a divalent aliphatic hydrocarbon radical containing 1-3 carbon atoms or the benzyl radical; and R' is a hydrocarbon radical or halohydrocarbon radical containing from 1-7 carbon atoms.

6. A method of inhibiting metal corrosion in an aqueous medium by adding to the aqueous medium a composition consisting essentially of (A) 0.1 to 99.9 parts by weight of an alkali siliconate silylalkylphosphonate which has the general unit formula wherein M is a cation selected from the group consisting of sodium, potassium, lithium, rubidium and tetraorgano ammonium cations;
R is a divalent aliphatic hydrocarbon radical containing 1-3 carbon atoms or the benzyl radical; and is a hydrocarbon radical or halohydrocarbon radical containing from 1-7 carbon atoms, with (B) 99.9 to 0.1 parts by weight of a soluble silicate represented by the general unit formula wherein M has the meaning above and a has a value of 1-3.